Book Section records
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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenMon, 15 Apr 2024 23:51:14 +0000SMDS measurements and modeling to predict performance
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135509827
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Nichols-K-M', 'name': {'family': 'Nichols', 'given': 'K. M.'}}]}
Year: 1992
DOI: 10.1109/INFCOM.1992.263435
The authors describe a performance study of a trial switched multimegabit data service (SMDS) link (intended for inter-LAN connection) from the perspective of customers evaluating the feasibility of the link for some target applications. The goals were to take all measurements on the customer premises and to develop a methodology general enough to be used by customers to evaluate the link. The authors measured a lightly loaded system and developed a model of the SMDS connection suitable for evaluating applications via analysis or simulation. They document their methodology and present the SMDS connection delay values as well as a likely breakdown of the constituents of that delay. They used these data to create a simulation model and to simulate a simple application. In the trial configuration, where geographical distances were small, SMDS network delay was one of the notable components of end-to-end delay in the SMDS connection. However, for most packets, throughput is limited by the T1 capacity for transmitting SMDS cells, not by the SMDS network capacity.https://authors.library.caltech.edu/records/85ser-x0728Stability of a class of dynamic routing protocols (IGRP)
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135815455
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Varaiya-P-P', 'name': {'family': 'Varaiya', 'given': 'Pravin'}}]}
Year: 1993
DOI: 10.1109/INFCOM.1993.253311
An exact analysis of the dynamic behavior of IGRP, an adaptive shortest-path routing algorithm, is performed. The distance metric is a weighted sum of traffic-sensitive and traffic-insensitive delay components. The optimality and stability of the protocol is related to the ratio of the weights. In particular, it is shown that if the traffic-sensitive component is not given enough weight, then starting from any initial routing, the subsequent routings after finitely many update periods will oscillate between two worst cases. Otherwise, the successive routings will converge to the unique equilibrium routing. It is also shown that load sharing among routes whose distances are within a threshold of the minimum distance helps stabilize the dynamic behavior.https://authors.library.caltech.edu/records/dwzdz-93g12Probabilistic conformance testing of protocols with unobservable transitions
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135651335
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1993
DOI: 10.1109/ICNP.1993.340890
A probabilistic approach to conformance testing of protocols containing unobservable transitions is proposed. It is said that an implementation conforms to its specification if their observable behavior is probabilistically the same, when both are subject to the same random environment simulated by the tester. Under the randomized inputs, faults in unobservable transitions may manifest themselves in certain statistics measurable from the implementation, and hence can be detected by comparing these measurements against the desirable statistics computed from the specification. The sensitivity of the nonconformance criterion to the uncertainty in our knowledge of desirable statistics is also studied. The conventional testing of protocols without unobservable transitions uses mismatch in outputs to detect faults. Here, one relies, in addition, on mismatch in the dynamics of the protocol under input randomization.https://authors.library.caltech.edu/records/a0tmz-wca60Electronic marking and identification techniques to discourage document copying
https://resolver.caltech.edu/CaltechAUTHORS:BRAinfocom94
Authors: {'items': [{'id': 'Brassil-J', 'name': {'family': 'Brassil', 'given': 'J.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N', 'name': {'family': 'Maxemchuk', 'given': 'N.'}}, {'id': "O'Gorman-L", 'name': {'family': "O'Gorman", 'given': 'L.'}}]}
Year: 1994
DOI: 10.1109/INFCOM.1994.337544
Modern computer networks make it possible to distribute documents quickly and economically by electronic means rather than by conventional paper means. However, the widespread adoption of electronic distribution of copyrighted material is currently impeded by the ease of illicit copying and dissemination. In this paper we propose techniques that discourage illicit distribution by embedding each document with a unique codeword. Our encoding techniques are indiscernible by readers, yet enable us to identify the sanctioned recipient of a document by examination of a recovered document. We propose three coding methods, describe one in detail, and present experimental results showing that our identification techniques are highly reliable, even after documents have been photocopied.https://authors.library.caltech.edu/records/900jx-96a58The Use of Communications Networks to Increase Personal Privacy
https://resolver.caltech.edu/CaltechAUTHORS:20120215-152259404
Authors: {'items': [{'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemchuk', 'given': 'N. F.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1995
DOI: 10.1109/INFCOM.1995.515915
Communications networks can separate as well as join information. This ability can be used to increase personal privacy in an environment where advances in technology makes it possible to collect and correlate increasing amounts of information about individuals. The tools and principles necessary to increase personal privacy are demonstrated by creating an anonymous credit card, in which a person's identity and purchases are separated, and a national health insurance plan, in which treatment, payment and an individual's identity are separated. An analysis technique is developed to determine how well the information is separated.https://authors.library.caltech.edu/records/ks0dt-c0774Document Identification To Discourage Illicit Copying
https://resolver.caltech.edu/CaltechAUTHORS:20120223-090026500
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Lapone-A-M', 'name': {'family': 'Lapone', 'given': 'Aleta M.'}}, {'id': 'Maxemchuk-N', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas F.'}}]}
Year: 1995
DOI: 10.1109/GLOCOM.1995.502594
An important application of future communications networks will be electronic publishing and digital library, provided copyright can be protected. A way to discourage illicit copying and distribution of documents is to uniquely mark each document copy by shifting certain lines or words slightly so that the original registered recipient can be identified from an illicit copy by detecting its mark. In this paper we present two techniques for reliable document identification, the centroid and the correlation detection. By analyzing the noise characteristics, we obtain the maximum likelihood detectors for both methods and their probabilities of error. We have applied these results to implement a marking and identification strategy proposed earlier, which marks a line both vertically by line shift and horizontally by word shift to make the marking robust against distortions in either direction. Preliminary experimental results are presented.https://authors.library.caltech.edu/records/w21bw-gw259Collusion analysis of cryptographic protocols
https://resolver.caltech.edu/CaltechAUTHORS:20120131-134121360
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Maxemchuk-N-F', 'name': {'family': 'Maxemchuk', 'given': 'Nicholas F.'}}]}
Year: 1996
DOI: 10.1109/GLOCOM.1996.594324
As network applications such as electronic commerce proliferate, complex communications protocols that employ cryptographic building blocks, such as encryption and authentication, will become more common. We view a cryptographic protocol as a process by which information is transferred among some users and hidden from others. The collusion problem determines whether a subset of users can discover, through collusion, the information that is designed to be hidden from them after a protocol is executed. Earlier we introduced a model for cryptographic protocols and its collusion analysis, and solved a special case of the collusion problem. In this paper we present an algorithm that solves the general case.https://authors.library.caltech.edu/records/pwp2c-qf614An optimization approach to ABR control
https://resolver.caltech.edu/CaltechAUTHORS:20111215-103604063
Authors: {'items': [{'id': 'Lapsley-D-E', 'name': {'family': 'Lapsley', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1998
DOI: 10.1109/ICC.1998.683074
Available bit rate (ABR) sources react to network feedback by adjusting their transmission rates. Most schemes fall into one of two types depending on what is fed back and where the control decision is made. Explicit congestion notification schemes allow sources to make control decisions but only with incomplete information on congestion. Explicit rate schemes use more accurate congestion information but make the control decision inside the network without regard to the different desires of various sources. We propose an optimization approach that attempts to combine the advantage of both types of scheme. The objective is to maximize the total utility of all sources over their transmission rates. The dual problem suggests treating network links and ABR sources as processors in a distributed computation system to solve the dual problem using the gradient projection algorithm. In this system ABR sources select transmission rates that maximize their own benefits and network links adjust bandwidth prices to coordinate the sources' decisions. We show how to implement such a system using features defined in the ABR standard. We provide an asynchronous distributed algorithm for links and sources and illustrate their behavior with preliminary simulation results.https://authors.library.caltech.edu/records/99y7e-n8t43An IP implementation of optimization flow control
https://resolver.caltech.edu/CaltechAUTHORS:20111221-081205365
Authors: {'items': [{'id': 'Lapsley-D', 'name': {'family': 'Lapsley', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1998
DOI: 10.1109/GLOCOM.1998.776627
Flow control allows sources to adjust their bandwidth usage to the level of availability in a network, and hence reduces packet loss, increases network utilization, and prevents/reacts to network congestion. The Internet uses TCP flow control; asynchronous transfer mode networks will use rate based flow control. In this paper we present an optimization approach to rate based flow control. We describe an implementation of this flow control on an IP network, and we present some performance results of this implementation.https://authors.library.caltech.edu/records/fcfcw-2sv23Optimization flow control with Newton-like algorithm
https://resolver.caltech.edu/CaltechAUTHORS:ATHglobecom99
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1999
DOI: 10.1109/GLOCOM.1999.829974
We proposed earlier an optimization approach to reactive flow control where the objective of the control is to maximize the aggregate utility of all sources over their transmission rates. The control mechanism is derived as a gradient projection algorithm to solve the dual problem. In this paper we extend the algorithm to a scaled gradient projection. The diagonal scaling matrix approximates the diagonal terms of the Hessian and can be computed at individual links using the same information required by the unscaled algorithm. We prove the convergence of the scaled algorithm and present simulation results that illustrate its superiority to the unscaled algorithm.https://authors.library.caltech.edu/records/w49js-9wz86Resource allocation in a multicast tree
https://resolver.caltech.edu/CaltechAUTHORS:20170810-132912401
Authors: {'items': [{'id': 'Kodialam-M', 'name': {'family': 'Kodialam', 'given': 'Murali'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 1999
DOI: 10.1109/INFCOM.1999.749291
We consider how to allocate bandwidth in a multicast tree so as to optimize some global measure of performance. In our model each receiver has a budget to be used for bandwidth reservation on links along its path from the source, and each link has a cost function depending on the amount of total bandwidth reserved at the link by all receivers using that link. We formulate and solve a problem of allocating bandwidth in the multicast tree such that the sum of link costs is minimized.https://authors.library.caltech.edu/records/yhqzx-vt180An enhanced random early marking algorithm for Internet flow control
https://resolver.caltech.edu/CaltechAUTHORS:ATHinfocomm00
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Lapsley-D-E', 'name': {'family': 'Lapsley', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2000
DOI: 10.1109/INFCOM.2000.832540
We propose earlier an optimization based flow control for the Internet called Random Early Marking (REM). In this paper we propose and evaluate an enhancement that attempts to speed up the convergence of REM in the face of large feedback delays. REM can be regarded as an implementation of an optimization algorithm in a distributed network. The basic idea is to treat the optimization algorithm as a discrete time system and apply linear control techniques to stabilize its transient. We show that the modified algorithm is stable globally and converges exponentially locally. This algorithm translates into an enhanced REM scheme and we illustrate the performance improvement through simulation.https://authors.library.caltech.edu/records/egmab-2hb43Price computation in random early marking (REM)
https://resolver.caltech.edu/CaltechAUTHORS:ATHicon00
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2000
DOI: 10.1109/ICC.2000.853366
We proposed earlier a flow control algorithm derived from solving the dual of a welfare maximization problem. The algorithm however requires communication between network links and sources that is not achievable on the current Internet. We then extended the basic algorithm to a Random Early Marking (REM) scheme which can be implemented using only binary feedback. In this paper we proposed a new price computation algorithm for REM and present simulation results to illustrate its superior performance over the previous versions.https://authors.library.caltech.edu/records/v7san-q8p41Simulation comparison of RED and REM
https://resolver.caltech.edu/CaltechAUTHORS:ATHicon01a
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2000
DOI: 10.1109/ICON.2000.875770
We propose earlier an optimization based low control for the Internet called Random Exponential Marking (REM). REM consists of a link algorithm, that probabilistically marks packets inside the network, and a source algorithm, that adapts source rate to observed marking. The marking probability is exponential in a link congestion measure, so that the end-to-end marking probability is exponential in a path congestion measure. Because of the finer measure of congestion provided by REM, sources do not constantly probe the network for spare capacity, but settle around a globally optimal equilibrium, thus avoiding the perpetual cycle of sinking into and recovering from congestion. In this paper we compare the performance of REM with Reno over RED through simulation.https://authors.library.caltech.edu/records/3shtq-j5q80MATE: MPLS adaptive traffic engineering
https://resolver.caltech.edu/CaltechAUTHORS:20170810-111700737
Authors: {'items': [{'id': 'Elwalid-A', 'name': {'family': 'Elwalid', 'given': 'Anwar'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Widjaja-I', 'name': {'family': 'Widjaja', 'given': 'Indra'}}]}
Year: 2001
DOI: 10.1109/INFCOM.2001.916625
Destination-based forwarding in traditional IP routers has not been able to take full advantage of multiple paths that frequently exist in Internet service provider networks. As a result, the networks may not operate efficiently, especially when the traffic patterns are dynamic. This paper describes a multipath adaptive traffic engineering mechanism, called MATE, which is targeted for switched networks such as multiprotocol label switching (MPLS) networks. The main goal of MATE is to avoid network congestion by adaptively balancing the load among multiple paths based on measurement and analysis of path congestion. MATE adopts a minimalist approach in that intermediate nodes are not required to perform traffic engineering or measurements besides normal packet forwarding. Moreover MATE does not impose any particular scheduling, buffer management, or a priori traffic characterization on the nodes. This paper presents an analytical model, derives a class of MATE algorithms, and proves their convergence. Several practical design techniques to implement MATE are described. Simulation results are provided to illustrate the efficacy of MATE under various network scenarios.https://authors.library.caltech.edu/records/v7t5s-72a65Understanding TCP Vegas: a duality model
https://resolver.caltech.edu/CaltechAUTHORS:20161129-163917093
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Peterson-L-L', 'name': {'family': 'Peterson', 'given': 'Larry'}}, {'id': 'Wang-Limin', 'name': {'family': 'Wang', 'given': 'Limin'}}]}
Year: 2001
DOI: 10.1145/378420.378787
This paper presents a model of the TCP Vegas congestion control mechanism as a distributed optimization algorithm. Doing so has three important benefits. First, it helps us gain a fundamental understanding of why TCP Vegas works, and an appreciation of its limitations. Second, it allows us to prove that Vegas stabilizes at a weighted proportionally fair allocation of network capacity when there is sufficient buffering in the network. Third, it suggests how we might use explicit feedback to allow each Vegas source to determine the optimal sending rate when there is insufficient buffering in the network. We present simulation results that validate our conclusions.https://authors.library.caltech.edu/records/b3agn-2w871Flow control in networks with multiple paths
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112123164
Authors: {'items': [{'id': 'Wang-Wei-Hua', 'name': {'family': 'Wang', 'given': 'Wei-Hua'}}, {'id': 'Palaniswami-M', 'name': {'family': 'Palaniswami', 'given': 'Marimuthu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2001
DOI: 10.1117/12.434306
We propose two flow control algorithms for networks with multiple paths between each source-destination pair. Both are distributed algorithms over the network to maximize aggregate source utility. Algorithm 1 is a first order Lagrangian method applied to a modified objective function that has the same optimal solution as the original objective function but has a better convergence property. Algorithm 2 is based on the idea that, at optimality, only paths with the minimum price carry positive flows, and naturally decomposes the overall decision into flow control (determines total transmission rate based on minimum path price) and routing (determines how to split the flow among available paths). Both algorithms can be implemented as simply a source-based mechanism in which no link algorithm nor feedback is needed. We present numerical examples to illustrate their behavior.https://authors.library.caltech.edu/records/fhgq6-j4v94Scalable laws for stable network congestion control
https://resolver.caltech.edu/CaltechAUTHORS:PAGdcc01
Authors: {'items': [{'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2001
Discusses flow control in networks, in which sources control their rates based on feedback signals received from the network links, a feature present in current TCP protocols. We develop a congestion control system which is arbitrarily scalable, in the sense that its stability is maintained for arbitrary network topologies and arbitrary amounts of delay. Such a system can be implemented in a decentralized way with information currently available in networks plus a small amount of additional signaling.https://authors.library.caltech.edu/records/c16cq-var28An empirical validation of a duality model of TCP and queue management algorithms
https://resolver.caltech.edu/CaltechAUTHORS:ATHwsc01
Authors: {'items': [{'id': 'Athuraliya-S', 'name': {'family': 'Athuraliya', 'given': 'Sanjeewa'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2001
DOI: 10.1109/WSC.2001.977445
In this paper we validate through simulations a duality model of TCP and active queue management (AQM) proposed earlier. In this model, TCP and AQM are modeled as carrying out a distributed primal-dual algorithm over the Internet to maximize aggregate source utility. TCP congestion avoidance algorithms, such as Reno and Vegas, iterate on source rates, the primal variable. AQM algorithms, such as RED and REM, iterate on marking probability, the dual variable.https://authors.library.caltech.edu/records/b69hc-9pc52High-density model of content distribution network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-102351659
Authors: {'items': [{'id': 'Cameron-C-W', 'name': {'family': 'Cameron', 'given': 'Craig'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}]}
Year: 2002
DOI: 10.1109/IDC.2002.995378
It is well known that optimal server placement is NP-hard. We present an approximate model of a content distribution network for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view leads to a joint server allocation and placement algorithm that has a time-complexity that is linear in the number of users.https://authors.library.caltech.edu/records/hsfqx-tnq16High-density model for server allocation and placement
https://resolver.caltech.edu/CaltechAUTHORS:20160812-143246677
Authors: {'items': [{'id': 'Cameron-C-W', 'name': {'family': 'Cameron', 'given': 'Craig W.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}]}
Year: 2002
DOI: 10.1145/511334.511354
It is well known that optimal server placement is NP-hard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate vector quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that
location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view has led to a joint server allocation and placement algorithm that has a time-complexity that is linear in the number of clients.
Simulations are presented to illustrate its performance.https://authors.library.caltech.edu/records/7sxhk-sh147Enhancing TCP Performance over Wireless Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-133629598
Authors: {'items': [{'id': 'Li-Victor-H', 'name': {'family': 'Li', 'given': 'Victor H.'}}, {'id': 'Liu-Zhi-Qiang', 'name': {'family': 'Liu', 'given': 'Zhi-Qiang'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2002
TCP flow control algorithms have been designed for wireline networks where congestion is measured by packet loss due to buffer overflow. However, wireless networks also suffer from significant packet losses due to bit errors and handoffs. TCP responds to all the packet losses by invoking congestion control and avoidance algorithms and this results in degraded end-to-end performance in wireless networks. In this paper, we describe a Wireless Random Exponential Marking (WREM) scheme which effectively improves TCP performance over wireless networks by decoupling loss recovery from congestion control. Moreover, WREM is capable of handling the coexistence of both ECN-Capable and Non-ECN-Capable routers. We present simulation results to show its effectiveness and compatibility.https://authors.library.caltech.edu/records/8kjy3-0gt89Dynamics of TCP/RED and a scalable control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-135606639
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Adlakha-S', 'name': {'family': 'Adlakha', 'given': 'Sachin'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2002
DOI: 10.1109/INFCOM.2002.1019265
We demonstrate that the dynamic behavior of queue and average window is determined predominantly by the stability of TCP/RED, not by AIMD probing nor noise traffic. We develop a general multi-link multi-source model for TCP/RED and derive a local stability condition in the case of a single link with heterogeneous sources. We validate our model with simulations and illustrate the stability region of TCP/RED. These results suggest that TCP/RED becomes unstable when delay increases, or more strikingly, when link capacity increases. The analysis illustrates the difficulty of setting RED parameters to stabilize TCP: they can be tuned to improve stability, but only at the cost of large queues even when they are dynamically adjusted. Finally, we present a simple distributed congestion control algorithm that maintains stability for arbitrary network delay, capacity, load and topology.https://authors.library.caltech.edu/records/fgmq0-ewv80A server allocation and placement algorithm for content distribution
https://resolver.caltech.edu/CaltechAUTHORS:20170522-162939354
Authors: {'items': [{'id': 'Cameron-C-W', 'name': {'family': 'Cameron', 'given': 'Craig'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}]}
Year: 2002
DOI: 10.1109/ITW.2002.1115407
It is well known that optimal server placement is NP-hard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate vector quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view has led to a joint server allocation and placement algorithm that has a time-complexity that is linear in the number of clients. Simulations are presented to illustrate its performance.https://authors.library.caltech.edu/records/2w43f-hgg42Stabilized Vegas
https://resolver.caltech.edu/CaltechAUTHORS:20111026-082612870
Authors: {'items': [{'id': 'Choe-H', 'name': {'family': 'Choe', 'given': 'Hyojeong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/INFCOM.2003.1209249
We show that the current TCP Vegas algorithm can become unstable in the presence of network delay and propose a modification that stabilizes it. The stabilized Vegas remains completely source-based and can be implemented without any network support. We suggest an incremental deployment strategy for stabilized Vegas when the network contains a mix of links, some with active queue management and some without.https://authors.library.caltech.edu/records/48hq5-r4168An Empirical Study on the Connectivity of Ad Hoc Networks
https://resolver.caltech.edu/CaltechAUTHORS:20111028-093653374
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Florens-C', 'name': {'family': 'Florens', 'given': 'Cédric'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/AERO.2003.1235249
This paper discusses the probability of connectivity of ad hoc networks. An empirical formula is proposed to fit the simulation results. The parameters of the formula are determined for different cases and the asymptotic behavior is discussed. Finally, a new metric is proposed to quantify the connectivity of an ad hoc network.https://authors.library.caltech.edu/records/hj1xx-qdp28Can shortest-path routing and TCP maximize utility
https://resolver.caltech.edu/CaltechAUTHORS:20190306-132657017
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Li-Lun', 'name': {'family': 'Li', 'given': 'Lun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2003
DOI: 10.1109/INFCOM.2003.1209226
TCP-AQM protocol can be interpreted as distributed primal-dual algorithms over the Internet to maximize aggregate utility. In this paper, we study whether TCP-AQM together with shortest-path routing can maximize utility with appropriate choice of link cost, on a slower timescale, over both source rates and routes. We show that this is generally impossible because the addition of route maximization makes the problem NP-hard. We exhibit an inevitable tradeoff between routing instability and utility maximization. For the special case of ring network, we prove rigorously that shortest-path routing based purely on congestion prices is unstable. Adding a sufficiently large static component to link cost, stabilizes it, but the maximum utility achievable by shortest-path routing decreases with the weight on the static component. We present simulation results to illustrate that these conclusions generalize to general network topology, and that routing instability can reduce utility to less than that achievable by the necessarily stable static routing.https://authors.library.caltech.edu/records/pbv64-4wx74A new TCP/AQM for stable operation in fast networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131233358
Authors: {'items': [{'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Wang-Zhikui', 'name': {'family': 'Wang', 'given': 'Zhikui'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2003
DOI: 10.1109/INFCOM.2003.1208662
This paper is aimed at designing a congestion control system that scales gracefully with network capacity, providing high utilization, low queueing delay, dynamic stability, and fairness among users. In earlier work we had developed fluid-level control laws that achieve the first three objectives for arbitrary networks and delays, but were forced to constrain the resource allocation policy. In this paper we extend the theory to include dynamics at TCP sources, preserving the earlier features at fast time-scales, but permitting sources to match their steady-state preferences, provided a bound on round-trip-times is known. We develop two packet-level implementations of this protocol, using (i) ECN marking, and (ii) queueing delay, as means of communicating the congestion measure from links to sources. We discuss parameter choices and demonstrate using ns-2 simulations the stability of the protocol and its equilibrium features in terms of utilization, queueing and fairness. We also demonstrate the scalability of these features to increases in capacity, delay, and load, in comparison with other deployed and proposed protocols.https://authors.library.caltech.edu/records/jz4r0-bvs41Maximum and asymptotic UDP throughput under CHOKe
https://resolver.caltech.edu/CaltechAUTHORS:20170104-155944142
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1145/781027.781038
A recently proposed active queue management, CHOKe, aims to protect TCP from UDP flows. Simulations have shown that as UDP rate increases, its bandwidth share initially rises but eventually drops. We derive an approximate model of CHOKe and show that, provided the number of TCP flows is large, the UDP bandwidth share peaks at (e+1)^-1 = 0.269 when the UDP input rate is slightly larger than the link capacity, and drops to zero as UDP input rate tends to infinity, regardless of the TCP algorithm.https://authors.library.caltech.edu/records/qee23-c8k16Analysis and design of AQM based on state-space models for stabilizing TCP
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131823045
Authors: {'items': [{'id': 'Kim-Ki-Baek', 'name': {'family': 'Kim', 'given': 'Ki Baek'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/ACC.2003.1238948
In this paper, we formulate the AQM (active queue management) design problem for stabilizing a given TCP (Transmission Control Protocol) as state-space models. Thereby, we show that PD-type (proportional-derivative) AQM is a natural state-feedback control structure to stabilize the given TCP for the first time, to our knowledge, in the networking literature and by applying integral control action, a PID-control structure that is a unified framework for analysis and design of AQM. Next, we compensate for delays in congestion measure explicitly by using a memory control. Third, we obtain stabilizing optimal gains of the proposed feedback control structures for linearized systems of the given TCP. We interpret existing AQMs, including a simplified random early detection, random exponential marking, PI and a simplified adaptive virtual queue, as different approximations of the unified AQM structure. We discuss the impact of each structure on the performance from the results of the stabilizing optimal AQMs. Finally, we illustrate our results through simulations for TCP Reno.https://authors.library.caltech.edu/records/rr5ed-zw596A control theoretical look at internet congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131419777
Authors: {'items': [{'id': 'Paganini-F', 'name': {'family': 'Paganini', 'given': 'Fernando'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1007/3-540-36589-3_2
Congestion control mechanisms in today's Internet represent perhaps the largest artificial feedback system ever deployed, and yet one that has evolved mostly outside the scope of control theory. This can be explained by the tight constraints of decentralization and simplicity of implementation in this problem, which would appear to rule out most mathematically-based designs. Nevertheless, a recently developed framework based on fluid flow models has allowed for a belated injection of control theory into the area, with some pleasant surprises. As described in this chapter, there is enough special structure to allow us to "guess" designs with mathematically provable properties that hold in arbitrary networks, and which involve a modest complexity in implementation.https://authors.library.caltech.edu/records/vqwq3-03x96The case for delay-based congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131854762
Authors: {'items': [{'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/CCW.2003.1240796
We argue that, in the absence of explicit feedback, delay-based algorithms become the preferred approach for end-to-end congestion control as networks scale up in capacity. Their advantage is small at low speed but decisive at high speed. The distinction between packet-level and flow-level problems of the current TCP exposes the difficulty of loss-based algorithms at large congestion windows.https://authors.library.caltech.edu/records/hckkk-5zj18Optimizing 10-Gigabit Ethernet for Networks of Workstations, Clusters, and Grids: A Case Study
https://resolver.caltech.edu/CaltechAUTHORS:20161019-142754228
Authors: {'items': [{'id': 'Feng-Wu-chun', 'name': {'family': 'Feng', 'given': 'Wu-chun'}}, {'id': 'Hurwitz-J', 'name': {'family': 'Hurwitz', 'given': 'Justin (Gus)'}}, {'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Cottrell-R-L', 'name': {'family': 'Cottrell', 'given': 'R. Les'}}, {'id': 'Martin-Olivier', 'name': {'family': 'Martin', 'given': 'Olivier'}}, {'id': 'Coccetti-F', 'name': {'family': 'Coccetti', 'given': 'Fabrizio'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'Xiaoliang (David)'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1145/1048935.1050200
This paper presents a case study of the 10-Gigabit Ethernet (10GbE) adapter from Intel ®. Specifically, with appropriate optimizations to the configurations of the 10GbE adapter and TCP, we demonstrate that the 10GbE adapter can perform well in local-area, storage-area, system-area, and wide-area networks.
For local-area, storage-area, and system-area networks in support of networks of workstations, network-attached storage, and clusters, respectively, we can achieve over 7-Gb/s end-to-end throughput and 12-µs end-to-end latency between applications running on Linux-based PCs. For the wide-area network in support of grids, we broke the recently-set Internet2 Land Speed Record by 2.5 times by sustaining an end-to-end TCP/IP throughput of 2.38 Gb/s between Sunnyvale, California and Geneva, Switzerland (i.e., 10,037 kilometers) to move over a terabyte of data in less than an hour. Thus, the above results indicate that 10GbE may be a cost-effective solution across a multitude of computing environments.https://authors.library.caltech.edu/records/bjpmj-p9j82A stabilizing AQM based on virtual queue dynamics in supporting TCP with arbitrary delays
https://resolver.caltech.edu/CaltechAUTHORS:20170810-132013399
Authors: {'items': [{'id': 'Kim-Ki-Baek', 'name': {'family': 'Kim', 'given': 'Ki Baek'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2003
DOI: 10.1109/CDC.2003.1271718
This paper studies how to design a stabilizing AQM in supporting TCP (Transmission Control Protocol) with arbitrary delays. For the well-known AIMD (Additive Increase Multiplicative Decrease) dynamic model of TCP, our study shows that we can compensate for arbitrary delays explicitly by applying a modified virtual queue dynamics that makes the equilibrium queuing delay zero. This study also verifies that a simplified AQM AVQ (Adaptive Virtual Queue) is the state-feedback control for the AIMD model based on the virtual queue dynamics.https://authors.library.caltech.edu/records/ssc23-hg079Optimization flow control with estimation error
https://resolver.caltech.edu/CaltechAUTHORS:20170810-134030592
Authors: {'items': [{'id': 'Mehyar-M', 'name': {'family': 'Mehyar', 'given': 'Mortada'}}, {'id': 'Spanos-D-P', 'name': {'family': 'Spanos', 'given': 'Demetri'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1109/INFCOM.2004.1356985
We analyze the effects of price estimation error in a dual-gradient optimization flow control scheme, and characterize the performance of the algorithm in this case. By treating estimation error as inexactness of the gradient, we utilize sufficient conditions for convergence subject to bounded error to characterize the long-term dynamics of the link utilization in terms of a region, which the trajectory enters in finite time. We explicitly find bounds for this region under a particular quantization error model, and provide simulation results to verify the predicted behavior of the system. Finally, we analyze the effects of the stepsize on the convergence of the algorithm, and provide analytical and numerical results, which suggest a particular choice for this parameter.https://authors.library.caltech.edu/records/0gqar-8xr78Global stability of Vegas-like TCP flow
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104523250
Authors: {'items': [{'id': 'Choe-Hyojeong', 'name': {'family': 'Choe', 'given': 'Hyojeong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Lee-Jin-S', 'name': {'family': 'Lee', 'given': 'Jin S.'}}]}
Year: 2004
A TCP Vegas flow adapts its sending rate to maintain a constant backlog in its path. The stability of nonlinear adaptation has been analyzed based on linearization and only accounted for a small signal. We extend the error model of TCP-like flow to a state-dependent coefficient form with nonlinear state feedback. The nonlinear feedback is here approximated by a saturation function. Using a quadratic Lyapunov function approach, we find a domain of attraction to show that the unique equilibrium point of the system is asymptotically stable in the domain.https://authors.library.caltech.edu/records/vn5bd-mkb70Stabilized Vegas
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105114024
Authors: {'items': [{'id': 'Choe-Hyojeong', 'name': {'family': 'Choe', 'given': 'Hyojeong'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1007/978-3-540-31597-1_2
TCP Vegas was introduced in 1994 [5] as an alternative to TCP Reno. Unlike Reno (or its variants such as NewReno and SACK), that uses packet loss as a measure of congestion, Vegas uses queueing delay as a measure of congestion [15, 18]. Vegas introduces a new congestion avoidance mechanism that corrects the oscillatory behavior of AIMD (Additive Increase Multiplicative Decrease). While the AIMD algorithm induces loss to learn the available network capacity, a Vegas source adjusts its sending rate to keep a small number of packets buffered in the routers along the path. Provided there is enough buffering, a network of Vegas sources will stabilize around a proportionally fair equilibrium and packet loss will be eliminated; see [15] for details. In this paper, we study the stability of this equilibrium in the presence of network delay, motivated by two lines of recent research.https://authors.library.caltech.edu/records/s9d3t-4jk94Analysis of nonlinear delay differential equation models of TCP/AQM protocols using sums of squares
https://resolver.caltech.edu/CaltechAUTHORS:20110831-081433118
Authors: {'items': [{'id': 'Papachristodoulou-A', 'name': {'family': 'Papachristodoulou', 'given': 'Antonis'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2004
DOI: 10.1109/CDC.2004.1429529
The simplest adequate models for congestion
control for the Internet are in the form of deterministic
nonlinear delay differential equations. However the absence
of efficient, algorithmic methodologies to analyze
them at this modelling level usually results in the investigation of their linearizations including delays; or in the analysis of nonlinear yet undelayed models. In this
paper we present an algorithmic methodology for efficient
stability analysis of network congestion control schemes at
the nonlinear delay-differential equation model level, using
the Sum of Squares decomposition and SOSTOOLS.https://authors.library.caltech.edu/records/fd6d7-z1f46Joint congestion control and media access control design for ad hoc wireless networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-103408504
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2005
DOI: 10.1109/INFCOM.2005.1498496
We present a model for the joint design of congestion control and media access control (MAC) for ad hoc wireless networks. Using contention graph and contention matrix, we formulate resource allocation in the network as a utility maximization problem with constraints that arise from contention for channel access. We present two algorithms that are not only distributed spatially, but more interestingly, they decompose vertically into two protocol layers where TCP and MAC jointly solve the system problem. The first is a primal algorithm where the MAC layer at the links generates congestion (contention) prices based on local aggregate source rates, and TCP sources adjust their rates based on the aggregate prices in their paths. The second is a dual subgradient algorithm where the MAC sub-algorithm is implemented through scheduling link-layer flows according to the congestion prices of the links. Global convergence properties of these algorithms are proved. This is a preliminary step towards a systematic approach to jointly design TCP congestion control algorithms and MAC algorithms, not only to improve performance, but more importantly, to make their interaction more transparent.https://authors.library.caltech.edu/records/xcehv-y5c92Optimization model of internet protocols
https://resolver.caltech.edu/CaltechAUTHORS:20161129-162643807
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Li-L', 'name': {'family': 'Li', 'given': 'L.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'A.'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jiantao', 'name': {'family': 'Wang', 'given': 'J.'}}]}
Year: 2005
DOI: 10.1145/1064212.1064245
Layered architecture is one of the most fundamental and influential structures of network design. Can we integrate the various protocol layers into a single coherent theory by regarding them as carrying out an asynchronous distributed primal-dual computation over the network to implicitly solve a global optimization problem? Different layers iterate on different subsets of the decision variables using local information to achieve individual optimalities, but taken together, these local algorithms attempt to achieve a global objective. Such a theory will expose the interconnection between protocol layers and can be used to study rigorously the performance tradeoff in protocol layering as different ways to distribute a centralized computation. In this talk, we describe some preliminary work towards this goal and discuss some of the difficulties of this approach.https://authors.library.caltech.edu/records/axcpq-9g913Optimization and Control of Communication Networks
https://resolver.caltech.edu/CaltechAUTHORS:20160831-160656108
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2005
DOI: 10.1145/1064212.1064244
Recently, there has been a surge in research activities that utilize the power of recent developments in nonlinear
optimization to tackle a wide scope of work in the analysis and design of communication systems, touching every
layer of the layered network architecture, and resulting in both intellectual and practical impacts significantly
beyond the earlier frameworks. These research activities are driven by both new demands in the areas of
communications and networking, and new tools emerging from optimization theory. Such tools include new
developments of powerful theories and highly efficient computational algorithms for nonlinear convex
optimization, as well as global solution methods and relaxation techniques for nonconvex optimization.
Optimization theory can be used to analyze, interpret, or design a communication system, for both forward-
engineering and reverse-engineering. Over the last few years, it has been successfully applied to a wide range of
communication systems, from the high speed Internet core to wireless networks, from coding and equalization to
broadband access, and from information theory to network topology models. Some of the theoretical advances
have also been put into practice and started making visible impacts, including new versions of TCP congestion
control, power control and scheduling algorithms in wireless networks, and spectrum management in DSL
broadband access networks.
Under the theme of optimization and control of communication networks, this Hot Topic Session consists of five
invited talks covering a wide range of issues, including protocols, pricing, resource allocation, cross layer design,
traffic engineering in the Internet, optical transport networks, and wireless networks.https://authors.library.caltech.edu/records/tx4gh-d6907Network equilibrium of heterogeneous congestion control protocols
https://resolver.caltech.edu/CaltechAUTHORS:TANinfocom05
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2005
DOI: 10.1109/INFCOM.2005.1498359
When heterogeneous congestion control protocols that react to different pricing signals share the same network, the resulting equilibrium may no longer be interpreted as a solution to the standard utility maximization problem. We prove the existence of equilibrium under mild assumptions. Then we show that multi-protocol networks whose equilibria are locally non-unique or infinite in number can only form a set of measure zero. Multiple locally unique equilibria can arise in two ways. First, unlike in the single-protocol case, the set of bottleneck links can be non-unique with heterogeneous protocols even when the routing matrix has full row rank. The equilibria associated with different sets of bottleneck links are necessarily distinct. Second, even when there is a unique set of bottleneck links, network equilibrium can still be non-unique, but is always finite and odd in number. They cannot all be locally stable unless it is globally unique. Finally, we provide various sufficient conditions for global uniqueness. Numerical examples are used throughout the paper to illustrate these results.https://authors.library.caltech.edu/records/e6mfd-9jh94Global Stability of FAST TCP in Single-Link Single-Source Network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105402423
Authors: {'items': [{'id': 'Choi-Joon-Young', 'name': {'family': 'Choi', 'given': 'Joon-Young'}}, {'id': 'Koo-Kyungmo', 'name': {'family': 'Koo', 'given': 'Kyungmo'}}, {'id': 'Lee-Jin-S', 'name': {'family': 'Lee', 'given': 'Jin S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2005
DOI: 10.1109/CDC.2005.1582427
We consider a single-link single-source network with FAST TCP source, and propose a static approximation of queuing delay dynamics at the link. The static approximation turns out to be a form with network feedback delay, which enables to analyze FAST TCP reflecting the effect of network feedback delay. Based on a continuous-time dynamic model of FAST TCP, we achieve the boundedness of window size and a sufficient condition for global asymptotic stability. The simulation results illustrate the validity of the sufficient condition for global asymptotic stability.https://authors.library.caltech.edu/records/nqwzw-h3b53Distributed Averaging on Asynchronous Communication Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170517-164222886
Authors: {'items': [{'id': 'Mehyar-M', 'name': {'family': 'Mehyar', 'given': 'Mortada'}}, {'id': 'Spanos-D-P', 'name': {'family': 'Spanos', 'given': 'Demetri'}}, {'id': 'Pongsajapan-J', 'name': {'family': 'Pongsajapan', 'given': 'John'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}]}
Year: 2005
DOI: 10.1109/CDC.2005.1583363
Distributed algorithms for averaging have attracted interest in the control and sensing literature. However, previous works have not addressed some practical concerns that will arise in actual implementations on packet-switched communication networks such as the Internet. In this paper, we present several implementable algorithms that are robust to asynchronism and dynamic topology changes. The algorithms do not require global coordination and can be proven to converge under very general asynchronous timing assumptions. Our results are verified by both simulation and experiments on a real-world TCP/IP network.https://authors.library.caltech.edu/records/4yh97-6b303The Design and Demonstration of the Ultralight Testbed
https://resolver.caltech.edu/CaltechAUTHORS:20110426-151150267
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bourilkov-D', 'name': {'family': 'Bourilkov', 'given': 'Dimitri'}}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-Xun', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Yang', 'name': {'family': 'Xia', 'given': 'Yang'}}]}
Year: 2006
DOI: 10.1109/BROADNETS.2006.4374312
In this paper we present the motivation, the design, and a recent demonstration of the UltraLight testbed at SC|05. The goal of the Ultralight testbed is to help meet the data-intensive computing challenges of the next generation of particle physics experiments with a comprehensive, network- focused approach. UltraLight adopts a new approach to networking: instead of treating it traditionally, as a static, unchanging and unmanaged set of inter-computer links, we are developing and using it as a dynamic, configurable, and closely monitored resource that is managed from end-to-end. To achieve its goal we are constructing a next-generation global system that is able to meet the data processing, distribution, access and analysis needs of the particle physics community. In this paper we will first present early results in the various working areas of the project. We then describe our experiences of the network architecture, kernel setup, application tuning and configuration used during the bandwidth challenge event at SC|05. During this Challenge, we achieved a record-breaking aggregate data rate in excess of 150 Gbps while moving physics datasets between many Grid computing sites.https://authors.library.caltech.edu/records/dxvkm-7sf21Equilibrium of heterogeneous congestion control protocols
https://resolver.caltech.edu/CaltechAUTHORS:20110811-093852596
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2006
DOI: 10.1109/CISS.2006.286548
When heterogeneous congestion control protocols that react to different pricing signals share the same network, the resulting equilibrium may no longer be interpreted as a solution to the standard utility maximization problem. We prove the existence of equilibrium in general multi-protocol networks under mild assumptions. For almost all networks, the equilibria are locally unique, and finite and odd in number. They cannot all be locally stable unless it is globally unique. Finally, we show that if the price mapping functions that map link prices to effective prices observed by the sources are similar, then global uniqueness is guaranteed.https://authors.library.caltech.edu/records/ygwfp-sgp79Cross-layer Congestion Control, Routing and Scheduling Design in Ad Hoc Wireless Networks
https://resolver.caltech.edu/CaltechAUTHORS:20110120-103630156
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/INFOCOM.2006.142
This paper considers jointly optimal design of crosslayer congestion control, routing and scheduling for ad hoc
wireless networks. We first formulate the rate constraint and scheduling constraint using multicommodity flow variables, and formulate resource allocation in networks with fixed wireless channels (or single-rate wireless devices that can mask channel variations) as a utility maximization problem with these constraints.
By dual decomposition, the resource allocation problem
naturally decomposes into three subproblems: congestion control,
routing and scheduling that interact through congestion price.
The global convergence property of this algorithm is proved. We
next extend the dual algorithm to handle networks with timevarying
channels and adaptive multi-rate devices. The stability
of the resulting system is established, and its performance is
characterized with respect to an ideal reference system which
has the best feasible rate region at link layer.
We then generalize the aforementioned results to a general
model of queueing network served by a set of interdependent
parallel servers with time-varying service capabilities, which
models many design problems in communication networks. We
show that for a general convex optimization problem where a
subset of variables lie in a polytope and the rest in a convex set,
the dual-based algorithm remains stable and optimal when the
constraint set is modulated by an irreducible finite-state Markov
chain. This paper thus presents a step toward a systematic way
to carry out cross-layer design in the framework of "layering as
optimization decomposition" for time-varying channel models.https://authors.library.caltech.edu/records/dznbh-6gn98The Motivation, Architecture and Demonstration of Ultralight
Network Testbed
https://resolver.caltech.edu/CaltechAUTHORS:20110728-121139631
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Bourilkov-D', 'name': {'family': 'Bourilkov', 'given': 'Dimitri'}}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-X', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Y', 'name': {'family': 'Xia', 'given': 'Yang'}}]}
Year: 2006
In this paper we describe progress in the NSF-funded Ultralight project and a recent demonstration of Ultralight technologies at SuperComputing 2005 (SC|05). The goal of the
Ultralight project is to help meet the data-intensive computing challenges of the next generation of particle physics experiments with a comprehensive, network-focused approach. Ultralight adopts a new approach to networking: instead of treating it traditionally, as a static, unchanging and unmanaged set of inter-computer links, we are developing and using it as a dynamic, configurable, and closely monitored resource that is managed from end-to-end. Thus we are constructing a next-generation global system that is able to meet the data processing, distribution, access and analysis needs of the particle physics community. In this paper we present the motivation for, and an overview of, the Ultralight project. We then cover early
results in the various working areas of the project. The remainder of the paper describes our experiences of the Ultralight network architecture, kernel setup, application tuning and configuration used during the bandwidth challenge event at SC|05. During this Challenge, we
achieved a record-breaking aggregate data rate in excess of 150 Gbps while moving physics datasets between many sites interconnected by the Ultralight backbone network. The exercise highlighted the benefits of Ultralight's research and development efforts that are enabling new and advanced methods of distributed scientific data analysis.https://authors.library.caltech.edu/records/eg3sr-1c078Layering As Optimization Decomposition: Framework and Examples
https://resolver.caltech.edu/CaltechAUTHORS:20190306-130031273
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Calderbank-A-R', 'name': {'family': 'Calderbank', 'given': 'A. Robert'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/ITW.2006.1633780
Network protocols in layered architectures have historically been obtained primarily on an ad-hoc basis. Recent research has shown that network protocols may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems in the form of Network Utility Maximization (NUM), providing insight into what they optimize and structures of the network protocol stack. This paper presents a short survey of the recent efforts towards a systematic understanding of 'layering' as 'optimization decomposition', where the overall communication network is modeled by a generalized NUM problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the sub-problems. Different decompositions lead to alternative layering architectures. We summarize several examples of horizontal decomposition into distributed computation and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and coding.https://authors.library.caltech.edu/records/y6b7y-8rk46Layering As Optimization Decomposition: Current Status and Open Issues
https://resolver.caltech.edu/CaltechAUTHORS:20170508-173109246
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Calderbank-A-R', 'name': {'family': 'Calderbank', 'given': 'A. Robert'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/CISS.2006.286492
Network protocols in layered architectures have historically been obtained on an ad-hoc basis, and much of the recent cross-layer designs are conducted through piecemeal approaches. Network protocols may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems in the form of generalized network utility maximization (NUM), providing insight on what they optimize and structures of the network protocol stack. This paper presents a short survey of the recent efforts towards a systematic understanding of "layering" as "optimization decomposition", where the overall communication network is modeled by a generalized NUM problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems. Furthermore, there are many alternative decompositions, each leading to a different layering architecture. Industry adoption of this unifying framework has also started. Here we summarize the current status of horizontal decomposition into distributed computation and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and coding. Key messages and methodologies arising out of many recent work are listed. Then we present a list of challenging open issues in this area and the initial progress made on some of them.https://authors.library.caltech.edu/records/e5hgh-e8n26On Asymptotic Optimality of Dual Scheduling Algorithm In A Generalized Switch
https://resolver.caltech.edu/CaltechAUTHORS:20110203-100201578
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/WIOPT.2006.1666500
Generalized switch is a model of a queueing system where parallel servers are interdependent and have time-varying service capabilities. This paper considers the dual scheduling algorithm that uses rate control and queue-length based scheduling to allocate resources for a generalized switch. We consider a saturated system in which each user has infinite amount of data to be served. We prove the asymptotic optimality of the dual scheduling algorithm for such a system, which says that the vector of average service rates of the scheduling algorithm maximizes some aggregate concave utility functions. As the fairness objectives can be achieved by appropriately choosing utility functions, the asymptotic optimality establishes the fairness properties of the dual scheduling algorithm.
The dual scheduling algorithm motivates a new architecture for scheduling, in which an additional queue is introduced to interface the user data queue and the time-varying server and to modulate the scheduling process, so as to achieve different performance objectives. Further research would include scheduling with Quality of Service guarantees with the dual scheduler, and its application and implementation in various versions of the generalized switch model.https://authors.library.caltech.edu/records/da85c-6j644Grid Networks and TCP Services, Protocols, and Technologies
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104241948
Authors: {'items': [{'id': 'Wydrowski-B-P', 'name': {'family': 'Wydrowski', 'given': 'Bartek'}}, {'id': 'Hegde-S', 'name': {'family': 'Hegde', 'given': 'Sanjay'}}, {'id': 'Suchara-M', 'name': {'family': 'Suchara', 'given': 'Martin'}}, {'id': 'Witt-R', 'name': {'family': 'Witt', 'given': 'Ryan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2006
DOI: 10.1002/0470028696.ch8
[No abstract]https://authors.library.caltech.edu/records/5zrtn-ns835Layering as Optimization Decomposition: Questions and Answers
https://resolver.caltech.edu/CaltechAUTHORS:20170508-172152981
Authors: {'items': [{'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Calderbank-A-R', 'name': {'family': 'Calderbank', 'given': 'A. Robert'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2006
DOI: 10.1109/MILCOM.2006.302293
Network protocols in layered architectures have historically been obtained on an ad-hoc basis, and much of the recent cross-layer designs are conducted through piecemeal approaches. Network protocols may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems in the form of generalized Network Utility Maximization (NUM), providing insight on what they optimize and on the structures of network protocol stacks. In the form of 10 Questions and Answers, this paper presents a short survey of the recent efforts towards a systematic understanding of "layering" as "optimization decomposition". The overall communication network is modeled by a generalized NUM problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems. Furthermore, there are many alternative decompositions, each leading to a different layering architecture. Industry adoption of this unifying framework has also started. Here we summarize the current status of horizontal decomposition into distributed computation and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and coding. We also discuss under-explored future research directions in this area. More importantly than proposing any particular crosslayer design, this framework is working towards a mathematical foundation of network architectures and the design process of modularization.https://authors.library.caltech.edu/records/j9v2d-wea54The Design and Implementation of the Transatlantic Mission-Oriented Production and Experimental Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170502-174109168
Authors: {'items': [{'id': 'Newman-H-B', 'name': {'family': 'Newman', 'given': 'Harvey'}, 'orcid': '0000-0003-0964-1480'}, {'id': 'Bourilkov-D', 'name': {'family': 'Bourilkov', 'given': 'Dimitri'}}, {'id': 'Bunn-Julian-J', 'name': {'family': 'Bunn', 'given': 'Julian'}, 'orcid': '0000-0002-3798-298X'}, {'id': 'Cavanaugh-R', 'name': {'family': 'Cavanaugh', 'given': 'Richard'}}, {'id': 'Legrand-I', 'name': {'family': 'Legrand', 'given': 'Iosif'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'McKee-S', 'name': {'family': 'McKee', 'given': 'Shawn'}}, {'id': 'Nae-D', 'name': {'family': 'Nae', 'given': 'Dan'}}, {'id': 'Ravot-S', 'name': {'family': 'Ravot', 'given': 'Sylvain'}}, {'id': 'Steenberg-C-D', 'name': {'family': 'Steenberg', 'given': 'Conrad'}}, {'id': 'Su-Xun', 'name': {'family': 'Su', 'given': 'Xun'}}, {'id': 'Thomas-Michael', 'name': {'family': 'Thomas', 'given': 'Michael'}}, {'id': 'van-Lingen-Frank', 'name': {'family': 'van Lingen', 'given': 'Frank'}}, {'id': 'Xia-Yang', 'name': {'family': 'Xia', 'given': 'Yang'}}]}
Year: 2006
DOI: 10.1109/E-SCIENCE.2006.261126
In this paper we present the design and implementation of the mission-oriented USLHCNet for HEP research community and the UltraLight network testbed. The design philosophy for these networks is to help meet the data-intensive computing challenges of the next generation of particle physics experiments with a comprehensive, network-focused approach. Instead of treating the network as a static, unchanging and unmanaged set of intercomputer links, we are developing and using it as a dynamic, configurable, and closely monitored resource that is managed from end-to-end. In this paper we will present our work in the various areas of the project including infrastructure construction, protocol research and application development. Our goal is to construct a next-generation global system that is able to meet the data processing, distribution, access and analysis needs of the particle physics community.https://authors.library.caltech.edu/records/kaa44-4z777Global Exponential Stability of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20170508-165210453
Authors: {'items': [{'id': 'Choi-Joon-Young', 'name': {'family': 'Choi', 'given': 'Joon-Young'}}, {'id': 'Koo-Kyungmo', 'name': {'family': 'Koo', 'given': 'Kyungmo'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Lee-Jin-S', 'name': {'family': 'Lee', 'given': 'Jin S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2006
DOI: 10.1109/CDC.2006.377711
We consider a single-link multi-source network with the FAST TCP sources. We propose a continuous-time dynamic model for the FAST TCP sources and a static model to describe the queuing delay behavior at the link. The proposed model turns out to be in a form revealing the network feedback delay, which allows us to analyze FAST TCP in due consideration of the network feedback delay. Based on the proposed model, we show the boundedness of both each source's congestion window and the queuing delay at the link; and the global exponential stability under a trivial condition that each source's congestion control parameter a is positive. The simulation results illustrate the validity of the proposed model and the global exponential stability of FAST TCP.https://authors.library.caltech.edu/records/deaz4-3qm82Reverse Engineering TCP/IP-like Networks using
Delay-Sensitive Utility Functions
https://resolver.caltech.edu/CaltechAUTHORS:20101005-121412518
Authors: {'items': [{'id': 'Pongsajapan-J', 'name': {'family': 'Pongsajapan', 'given': 'John'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/INFCOM.2007.56
TCP/IP can be interpreted as a distributed primal-dual algorithm to maximize aggregate utility over source rates. It has recently been shown that an equilibrium of TCP/IP, if it exists, maximizes the same delay-insensitive utility over both source rates and routes, provided pure congestion prices are used as link costs in the shortest-path calculation of IP. In practice, however, pure dynamic routing is never used and link costs are weighted sums of both static as well as dynamic components. In this paper, we introduce delay-sensitive utility functions and identify a class of utility functions that such a TCP/IP equilibrium optimizes. We exhibit some counter-intuitive properties that any class of delay-sensitive utility functions optimized by TCP/IP necessarily possess. We prove a sufficient condition for global stability of routing updates for general networks. We construct example networks that defy conventional wisdom on the effect of link cost parameters on network stability and utility.https://authors.library.caltech.edu/records/8w14h-arr72Optimization Based Rate Control for Multicast with Network Coding
https://resolver.caltech.edu/CaltechAUTHORS:20100826-092317616
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2007
DOI: 10.1109/INFCOM.2007.139
Recent advances in network coding have shown
great potential for efficient information multicasting in communication
networks, in terms of both network throughput and
network management. In this paper, we address the problem of
rate control at end-systems for network coding based multicast
flows. We develop two adaptive rate control algorithms for
the networks with given coding subgraphs and without given
coding subgraphs, respectively. With random network coding,
both algorithms can be implemented in a distributed manner, and
work at transport layer to adjust source rates and at network
layer to carry out network coding. We prove that the proposed
algorithms converge to the globally optimal solutions for intrasession
network coding. Some related issues are discussed, and
numerical examples are provided to complement our theoretical
analysis.https://authors.library.caltech.edu/records/w4e9r-dpk91Opportunistic Source Coding for Data Gathering in Wireless Sensor Networks
https://resolver.caltech.edu/CaltechAUTHORS:20100827-112133009
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2007
DOI: 10.1109/MOBHOC.2007.4428675
We propose a jointly opportunistic source coding and opportunistic routing (OSCOR) protocol for correlated data gathering in wireless sensor networks. OSCOR improves data gathering efficiency by exploiting opportunistic data compression and cooperative diversity associated with wireless broadcast advantage. The design of OSCOR involves several challenging issues across different network protocol layers. At the MAC layer, sensor nodes need to coordinate wireless transmission and packet forwarding to exploit multiuser diversity in packet reception. At the network layer, in order to achieve high diversity and compression gains, routing must be based on a metric that is dependent on not only link-quality but also compression opportunities. At the application layer, sensor nodes need a distributed source coding algorithm that has low coordination overhead and does not require the source distributions to be known. OSCOR provides practical solutions to these challenges incorporating a slightly modified 802.11 MAC, a distributed source coding scheme based on network coding and Lempel-Ziv coding, and a node compression ratio dependent metric combined with a modified Dijkstra's algorithm for path selection. We evaluate the performance of OSCOR through simulations, and show that OSCOR can potentially reduce power consumption by over 30% compared with an existing greedy scheme, routing driven compression, in a 4 x 4 grid network.https://authors.library.caltech.edu/records/v67bc-w4e96Modelling and stability of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20101029-153050412
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Choi-Joon-Young', 'name': {'family': 'Choi', 'given': 'Joon-Young'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1007/978-0-387-48945-2_14
We discuss the modelling of FAST TCP and prove four stability results. Using the traditional continuous-time flow model, we prove, for general networks, that FAST TCP is globally asymptotically stable when there is no feedback delay and that it is locally asymptotically stable in the presence of feedback delay provided a local stability condition is satisfied. We present an experiment on an emulated network in which the local stability condition is violated. While the theory predicts instability, the experiment shows otherwise. We believe this is because the continuous-time model ignores the stabilizing effect of self-clocking. Using a discrete-time model that captures this effect, we show that FAST TCP is locally asymptotically stable for general networks if all flows have the same feedback delay, no matter how large the delay is. We also prove global asymptotic stability for a single bottleneck link in the absence of feedback delay. The techniques developed here are new and applicable to other protocols.https://authors.library.caltech.edu/records/9gq55-tdf26Modelling and stability of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20101202-160829940
Authors: {'items': [{'id': 'Wang-Jintao', 'name': {'family': 'Wang', 'given': 'Jiantao'}}, {'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/INFCOM.2005.1498323
We introduce a discrete-time model of FAST TCP that fully captures the effect of self-clocking and compare it with the traditional continuous-time model. While the continuous-time model predicts instability for homogeneous sources sharing a single link when feedback delay is large, experiments suggest otherwise. Using the discrete-time model, we prove that FAST TCP is locally asymptotically stable in general networks when all sources have a common round-trip feedback delay, no matter how large the delay is. We also prove global stability for a single bottleneck link in the absence of feedback delay. The techniques developed here are new and applicable to other protocols.https://authors.library.caltech.edu/records/msnwd-y4x66Dual scheduling algorithm in a generalized switch: asymptotic optimality and throughput optimality
https://resolver.caltech.edu/CaltechAUTHORS:20170810-103710158
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2007
DOI: 10.1007/1-84628-274-8_7
In this article, we consider the dual scheduling algorithm for a generalized switch. For a saturated system, we prove the asymptotic optimality of the dual scheduling algorithm and thus establish its fairness properties. For a system with exogenous arrivals, we propose a modified dual scheduling algorithm, which is throughput-optimal while providing some weighted fairness among the users at the level of flows.
The dual scheduling algorithm motivates a new architecture for scheduling, in which an additional queue is introduced to interface the user data queue and the time-varying server and to modulate the scheduling process, so as to achieve different performance objectives. Further research stemming out of this article includes scheduling with Quality of Service guarantees with the dual scheduler, and its application and implementation in various versions of the generalized switch model.https://authors.library.caltech.edu/records/fnwed-6cv31An Accurate Link Model and Its Application to Stability Analysis of FAST TCP
https://resolver.caltech.edu/CaltechAUTHORS:20101008-113059058
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/INFCOM.2007.27
This paper presents a link model which captures the queue dynamics when congestion windows of TCP sources change. By considering both the self-clocking and the link integrator effects, the model is a generalization of existing models and is shown to be more accurate by both open loop and closed loop packet level simulations. It reduces to the known static link model when flows' round trip delays are similar, and approximates the standard integrator link model when the heterogeneity of round trip delays is significant. We then apply this model to the stability analysis of FAST TCP. It is shown that FAST TCP flows over a single link are always linearly stable regardless of delay distribution. This result resolves the notable discrepancy between empirical observations and previous theoretical predictions. The analysis highlights the critical role of self-clocking in TCP stability and the scalability of FAST TCP with respect to delay. The proof technique is new and less conservative than the existing ones.https://authors.library.caltech.edu/records/5h49v-2ws14Heterogeneous Congestion Control: Efficiency, Fairness and Design
https://resolver.caltech.edu/CaltechAUTHORS:TANicnp06
Authors: {'items': [{'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Wei-Xiaoliang-D', 'name': {'family': 'Wei', 'given': 'David'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chiang-Mung', 'name': {'family': 'Chiang', 'given': 'Mung'}}]}
Year: 2007
DOI: 10.1109/ICNP.2006.320206
When heterogeneous congestion control protocols that react to different pricing signals (e.g. packet loss, queueing delay, ECN marking etc.) share the same network, the current theory based on utility maximization fails to predict the network behavior. Unlike in a homogeneous network, the bandwidth allocation now depends on router parameters and flow arrival patterns. It can be non-unique, inefficient and unfair. This paper has two objectives. First, we demonstrate the intricate behaviors of a heterogeneous network through simulations and present a rigorous framework to help understand its equilibrium efficiency and fairness properties. By identifying an optimization problem associated with every equilibrium, we show that every equilibrium is Pareto efficient and provide an upper bound on efficiency loss due to pricing heterogeneity. On fairness, we show that intra-protocol fairness is still decided by a utility maximization problem while inter-protocol fairness is the part over which we don¿t have control. However it is shown that we can achieve any desirable inter-protocol fairness by properly choosing protocol parameters. Second, we propose a simple slow timescale source-based algorithm to decouple bandwidth allocation from router parameters and flow arrival patterns and prove its feasibility. The scheme needs only local information.https://authors.library.caltech.edu/records/78ve5-mts17Packet Loss Burstiness: Measurements and Implications for Distributed Applications
https://resolver.caltech.edu/CaltechAUTHORS:20170419-174638253
Authors: {'items': [{'id': 'Wei-Xiaoliang-David', 'name': {'family': 'Wei', 'given': 'David X.'}}, {'id': 'Cao-Pei', 'name': {'family': 'Cao', 'given': 'Pei'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2007
DOI: 10.1109/IPDPS.2007.370412
Many modern massively distributed systems deploy thousands of nodes to cooperate on a computation task. Network congestions occur in these systems. Most applications rely on congestion control protocols such as TCP to protect the systems from congestion collapse. Most TCP congestion control algorithms use packet loss as signal to detect congestion. In this paper, we study the packet loss process in sub-round-trip-time (sub-RTT) timescale and its impact on the loss-based congestion control algorithms. Our study suggests that the packet loss in sub-RTT timescale is very bursty. This burstiness leads to two effects. First, the sub-RTT burstiness in packet loss process leads to complicated interactions between different loss-based algorithms. Second, the sub-RTT burstiness in packet loss process makes the latency of data transfers under TCP hard to predict. Our results suggest that the design of a distributed system has to seriously consider the nature of packet loss process and carefully select the congestion control algorithms best suited for the distributed computation environments.https://authors.library.caltech.edu/records/mvqrw-jmx06Optimal Strategies for Efficient Peer-to-Peer File Sharing
https://resolver.caltech.edu/CaltechAUTHORS:MEHicassp07
Authors: {'items': [{'id': 'Mehyar-M', 'name': {'family': 'Mehyar', 'given': 'Mortada'}}, {'id': 'Gu-WeiHsin', 'name': {'family': 'Gu', 'given': 'WeiHsin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Effros-M', 'name': {'family': 'Effros', 'given': 'Michelle'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}]}
Year: 2007
DOI: 10.1109/ICASSP.2007.367325
We study a model for peer-to-peer file sharing. The goal is to distribute a file from a server to multiple peers. We assume the upload capacity of each peer is the only bottleneck. We examine the finish times of peers under different transmission strategies. Pareto optimality, min-max finish time, and optimal average finish time of the model are studied. We believe the results provide fundamental insights into practical peer-to-peer systems such as BitTorrent.https://authors.library.caltech.edu/records/manj6-p7b87Contention control: A game-theoretic approach
https://resolver.caltech.edu/CaltechAUTHORS:CHEcdc07
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2007
DOI: 10.1109/CDC.2007.4435015
We present a game-theoretic approach to contention control. We define a game-theoretic model, called random access game, to capture the contention/interaction among wireless nodes in wireless networks with contention-based medium access. We characterize Nash equilibria of random access games, study their dynamics and propose distributed algorithms (strategy evolutions) to achieve the Nash equilibria. This provides a general analytical framework that is capable of modelling a large class of systemwide quality of service models via the specification of per-node utility functions, in which systemwide fairness or service differentiation can be achieved in a distributed manner as long as each node executes a contention resolution algorithm that is designed to achieve the Nash equilibrium. We thus design medium access method according to distributed strategy update mechanism achieving the Nash equilibrium of random access game. In addition to guiding medium access control design, the random access game model also provides an analytical framework to understand equilibrium and dynamic properties of different medium access protocols and their interactions.https://authors.library.caltech.edu/records/y1aw1-ctj82ACK-Clocking Dynamics: Modelling the Interaction between Windows and the Network
https://resolver.caltech.edu/CaltechAUTHORS:20170810-130929589
Authors: {'items': [{'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Johansson-K-H', 'name': {'family': 'Johansson', 'given': 'Karl H.'}}, {'id': 'Hjalmarsson-H', 'name': {'family': 'Hjalmarsson', 'given': 'Håkan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2008
DOI: 10.1109/INFOCOM.2008.281
A novel continuous time fluid flow model of the dynamics of the interaction between ACK-clocking and the link buffer is presented. A fundamental integral equation relating the instantaneous flow rate and the window dynamics is derived. Properties of the model, such as well-posedness and stability, are investigated. Packet level experiments verify that this new model is more accurate than existing models, correctly predicting qualitatively different behaviors, for example when round trip delays are heterogeneous.https://authors.library.caltech.edu/records/y34pw-fjt23Progress on pricing with peering
https://resolver.caltech.edu/CaltechAUTHORS:20100721-152913560
Authors: {'items': [{'id': 'Lee-Eui-woong', 'name': {'family': 'Lee', 'given': 'Eui-woong'}}, {'id': 'Buchfuhrer-D', 'name': {'family': 'Buchfuhrer', 'given': 'David'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2008
DOI: 10.1109/CISS.2008.4558537
This paper examines a simple model of how a
provider ISP charges customer ISPs by assuming the provider
ISP wants to maximize its revenue when customer ISPs have
the possibility of setting up peering connections. It is shown that
finding the optimal pricing is NP-complete, and APX-complete.
Customers can respond to price in many ways, including throttling
traffic as well as peering. An algorithm is studied which
obtains a 1/4 approximation for a wide range of customer
responses.https://authors.library.caltech.edu/records/z56fc-7de71Implementation of Provably Stable MaxNet
https://resolver.caltech.edu/CaltechAUTHORS:20100802-104528960
Authors: {'items': [{'id': 'Suchara-M', 'name': {'family': 'Suchara', 'given': 'Martin'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Witt-R', 'name': {'family': 'Witt', 'given': 'Ryan'}}, {'id': 'Jacobsson-K', 'name': {'family': 'Jacobsson', 'given': 'Krister'}}, {'id': 'Wydrowski-B-P', 'name': {'family': 'Wydrowski', 'given': 'Bartek P.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1109/BROADNETS.2008.4769143
MaxNet TCP is a congestion control protocol that uses explicit multi-bit signalling from routers to achieve desirable properties such as high throughput and low latency. In this paper we present an implementation of an extended version of MaxNet. Our contributions are threefold. First, we extend the original algorithm to give both provable stability and rate fairness. Second, we introduce the MaxStart algorithm which allows new MaxNet connections to reach their fair rates quickly. Third, we provide a Linux kernel implementation of the protocol. With no overhead but 24-bit price signals, our implementation scales from 32 bit/s to 1 peta-bit/s with a 0.001% rate accuracy. We confirm the theoretically predicted properties by performing a range of experiments at speeds up to 1 Gbit/sec and delays up to 180 ms on the WAN-in-Lab facility.https://authors.library.caltech.edu/records/zka2f-32463How Bad is Single-Path Routing
https://resolver.caltech.edu/CaltechAUTHORS:20170327-172614113
Authors: {'items': [{'id': 'Wang-Meng', 'name': {'family': 'Wang', 'given': 'Meng'}}, {'id': 'Tan-Chee-Wei', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Tang-Ao', 'name': {'family': 'Tang', 'given': 'Ao'}, 'orcid': '0000-0001-6296-644X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1109/GLOCOM.2009.5425408
This paper investigates the network performance loss of using only single-path routing when multiple paths are available. The performance metric is the aggregate utility achieved by the joint optimization of congestion control and routing. As computing the exact loss for a general network topology is NP-hard, we develop analytical bounds on this "cost of not splitting". Our bound is independent of the number of source-destination pairs when the latter one is larger than the number of links in a network. We also propose a vertex projection method and combine it with branch-and-bound to provide progressively tighter bounds on the performance loss. Numerical examples are used to show the effectiveness of our approximation technique.https://authors.library.caltech.edu/records/vypy0-0bf02Congestion control algorithms from optimal control perspective
https://resolver.caltech.edu/CaltechAUTHORS:20170810-133936531
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2009
DOI: 10.1109/CDC.2009.5399554
This paper is concerned with understanding the connection between the existing Internet congestion control algorithms and the optimal control theory. The available resource allocation controllers are mainly devised to derive the state of the system to a desired equilibrium point and, therefore, they are oblivious to the transient behavior of the closed-loop system. This work aims to investigate what dynamical functions the existing algorithms maximize (minimize). In particular, it is shown that there exist meaningful cost functionals whose minimization leads to the celebrated primal and dual congestion algorithms. An implication of this result is that a real network problem may be solved by regarding it as an optimal control problem on which some practical constraints, such as a real-time link capacity constraint, are imposed.https://authors.library.caltech.edu/records/kt7kw-y0808File Fragmentation over an Unreliable Channel
https://resolver.caltech.edu/CaltechAUTHORS:20110401-160938362
Authors: {'items': [{'id': 'Nair-J', 'name': {'family': 'Nair', 'given': 'Jayakrishnan'}}, {'id': 'Andreasson-M', 'name': {'family': 'Andreasson', 'given': 'Martin'}}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2010
DOI: 10.1109/INFCOM.2010.5461953
It has been recently discovered that heavy-tailed
file completion time can result from protocol interaction even
when file sizes are light-tailed. A key to this phenomenon is
the RESTART feature where if a file transfer is interrupted
before it is completed, the transfer needs to restart from the
beginning. In this paper, we show that independent or bounded
fragmentation guarantees light-tailed file completion time as long
as the file size is light-tailed, i.e., in this case, heavy-tailed file
completion time can only originate from heavy-tailed file sizes.
If the file size is heavy-tailed, then the file completion time is
necessarily heavy-tailed. For this case, we show that when the
file size distribution is regularly varying, then under independent
or bounded fragmentation, the completion time tail distribution
function is asymptotically upper bounded by that of the original
file size stretched by a constant factor. We then prove that if the
failure distribution has non-decreasing failure rate, the expected
completion time is minimized by dividing the file into equal sized
fragments; this optimal fragment size is unique but depends on
the file size. We also present a simple blind fragmentation policy
where the fragment sizes are constant and independent of the
file size and prove that it is asymptotically optimal. Finally, we
bound the error in expected completion time due to error in
modeling of the failure process.https://authors.library.caltech.edu/records/hw8ym-bf685Utility Functionals Associated With Available Congestion Control Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20110406-104430537
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2010
DOI: 10.1109/INFCOM.2010.5462103
This paper is concerned with understanding the connection between the existing Internet congestion control algorithms and the optimal control theory. The available resource allocation controllers are mainly devised to derive the state of the system to a desired equilibrium point and, therefore, they are oblivious to the transient behavior of the closed-loop system. To take into account the real-time performance of the system, rather than merely its steady-state performance, the congestion control problem should be solved by maximizing a proper utility functional as opposed to a utility function. For this reason, this work aims to investigate what utility functionals the existing congestion control algorithms maximize. In particular, it is shown that there exist meaningful utility
functionals whose maximization leads to the celebrated primal, dual and primal/dual algorithms. An implication of this result is that a real network problem may be solved by regarding it as an optimal control problem on which some practical constraints, such as a real-time link capacity constraint, are imposed.https://authors.library.caltech.edu/records/nhkrb-ceq04Load-shedding probabilities with hybrid renewable power generation and energy storage
https://resolver.caltech.edu/CaltechAUTHORS:20170314-151537459
Authors: {'items': [{'id': 'Xu-Huan', 'name': {'family': 'Xu', 'given': 'Huan'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Clarke-C-R', 'name': {'family': 'Clarke', 'given': 'Christopher R.'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2010
DOI: 10.1109/ALLERTON.2010.5706912
The integration of renewable energy resources, such as solar and wind power, into the electric grid presents challengs partly due to the intermittency in the power output. These difficulties can be alleviated by effectively utilizing energy storage. We consider, as a case study, the integration of renewable resources into the electric power generation portfolio of an island off the coast of Southern California, Santa Catalina Island, and investigate the feasibility of replacing diesel generation entirely with solar photovoltaics (PV) and wind turbines, supplemented with energy storage. We use a simple storage model alongside a combination of renewables and varying load-shedding characterizations to determine the appropriate area of PV cells, number of wind turbines, and energy storage capacity needed to stay below a certain threshold probability for load-shedding over a pre-specified period of time and long-term expected fraction of time at load-shedding.https://authors.library.caltech.edu/records/hr890-8f768Two Market Models for Demand Response in Power Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104228265
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2010
DOI: 10.1109/SMARTGRID.2010.5622076
In this paper, we consider two abstract market models for designing demand response to match power supply and shape power demand, respectively. We characterize the resulting equilibria in competitive as well as oligopolistic markets, and propose distributed demand response algorithms to achieve the equilibria. The models serve as a starting point to include the appliance-level details and constraints for designing practical demand response schemes for smart power grids.https://authors.library.caltech.edu/records/wscs9-cx135Relationship between power loss and network topology in power systems
https://resolver.caltech.edu/CaltechAUTHORS:20170810-134325354
Authors: {'items': [{'id': 'Lavaei-J', 'name': {'family': 'Lavaei', 'given': 'Javad'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2010
DOI: 10.1109/CDC.2010.5717352
This paper is concerned with studying how the minimum power loss in a power system is related to its network topology. The existing algorithms in the literature all exploit nonlinear, heuristic, or local search algorithms to find the minimum power loss, which make them blind to the network topology. Given certain constraints on power level, bus voltages, etc., a linear-matrix-inequality (LMI) optimization problem is derived, which provides a lower bound on the minimum active loss in the network. The proposed LMI problem has the property that its objective function depends on the loads and its matrix inequality constraint is related to the topology of the power system. This property makes it possible to address many important power problems, such as the optimal network reconfiguration and the optimal placement/sizing of distributed generation units in power systems. Moreover, a condition is provided under which the solution of the given LMI problem is guaranteed to be exactly equal to the minimum power loss. As justified mathematically and verified on IEEE test systems, this condition is expected to hold widely in practice, implying that a practical power loss minimization problem is likely to be solvable using a convex algorithm.https://authors.library.caltech.edu/records/62mbz-5w718A simple optimal power flow model with energy storage
https://resolver.caltech.edu/CaltechAUTHORS:20170810-102952651
Authors: {'items': [{'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Xu-Huan', 'name': {'family': 'Xu', 'given': 'Huan'}}]}
Year: 2010
DOI: 10.1109/CDC.2010.5718193
The integration of renewable energy generation, such as wind power, into the electric grid is difficult because of the source intermittency and the large distance between generation sites and users. This difficulty can be overcome through a transmission network with large-scale storage that not only transports power, but also mitigates against fluctuations in generation and supply. We formulate an optimal power flow problem with storage as a finite-horizon optimal control problem. We prove, for the special case with a single generator and a single load, that the optimal generation schedule will cross the time-varying demand profile at most once, from above. This means that the optimal policy will generate more than demand initially in order to charge up the battery, and then generate less than the demand and use the battery to supplement generation in final stages. This is a consequence of the fact that the marginal storage cost-to-go decreases in time.https://authors.library.caltech.edu/records/cd7d5-pat18Effect of buffers on stability of Internet congestion controllers
https://resolver.caltech.edu/CaltechAUTHORS:20120403-131857340
Authors: {'items': [{'id': 'Sojoudi-S', 'name': {'family': 'Sojoudi', 'given': 'Somayeh'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}]}
Year: 2011
Almost all existing fluid models of congestion control assume that the fluid flow at the output of a link is the same as the fluid flow at the input of the link. This means that all links in the path of a flow see the original source rate. In reality, a fluid flow is modified by the queueing processes on its path, so that an intermediate link will generally not see the original source rate. In this paper, we propose a simple model that explicitly takes into account of the effect of buffering on output flows. We study the dual and primal-dual algorithms that use implicit feedback and show that, while they are always asymptotically stable if feedback delay is ignored, they can be unstable in the new model.https://authors.library.caltech.edu/records/7pfse-91y07Max-min weighted SINR in coordinated multicell MIMO downlink
https://resolver.caltech.edu/CaltechAUTHORS:20170810-095519100
Authors: {'items': [{'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Quek-Tony-Q-S', 'name': {'family': 'Quek', 'given': 'Tony Q. S.'}}, {'id': 'Tan-Chee-Wei', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/WIOPT.2011.5930029
This paper studies the optimization of a multicell multiple-input-single-output (MISO) downlink system in which each base station serves multiple users, and each user is served by only one base station. First, we consider the problem of maximizing the minimum weighted signal-to-interference-plus-noise ratio (SINR) of all users subject to a single weighted-sum power constraint, where the weights can represent relative power costs of serving different users in each cell. We apply concave Perron-Frobenius theory to propose a joint power control and linear beamforming algorithm which converges geometrically fast to the optimal solution. As a by-product, we resolve an open problem of convergence of a previously proposed algorithm by Wiesel, Eldar, and Shamai in 2006. Next, we study the max-min weighted SINR problem subject to multiple weighted-sum power constraints and we show that it can be decoupled into its associated single-constrained subproblems.https://authors.library.caltech.edu/records/j9w21-fez97Greening geographical load balancing
https://resolver.caltech.edu/CaltechAUTHORS:20120522-080032032
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Lin-Minghong', 'name': {'family': 'Lin', 'given': 'Minghong'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Andrew-L-L-H', 'name': {'family': 'Andrew', 'given': 'Lachlan L. H.'}}]}
Year: 2011
DOI: 10.1145/1993744.1993767
Energy expenditure has become a significant fraction of data center operating costs. Recently, "geographical load balancing" has been suggested to reduce energy cost by exploiting the electricity price differences across regions. However, this reduction of cost can paradoxically increase total energy use.
This paper explores whether the geographical diversity of Internet-scale systems can additionally be used to provide environmental gains. Specifically, we explore whether geographical load balancing can encourage use of "green" renewable energy and reduce use of "brown" fossil fuel energy. We make two contributions. First, we derive two distributed algorithms for achieving optimal geographical load balancing. Second, we show that if electricity is dynamically priced in proportion to the instantaneous fraction of the total energy that is brown, then geographical load balancing provides significant reductions in brown energy use. However, the benefits depend strongly on the degree to which systems accept dynamic energy pricing and the form of pricing used.https://authors.library.caltech.edu/records/14c3j-8my38Optimal demand response based on utility maximization in power networks
https://resolver.caltech.edu/CaltechAUTHORS:20120330-135152938
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/PES.2011.6039082
Demand side management will be a key component of future smart grid that can help reduce peak load and adapt elastic demand to fluctuating generations. In this paper, we consider households that operate different appliances including PHEVs and batteries and propose a demand response approach based on utility maximization. Each appliance provides a certain benefit depending on the pattern or volume of power it consumes. Each household wishes to optimally schedule its power consumption so as to maximize its individual net benefit subject to various consumption and power flow constraints. We show that there exist time-varying prices that can align individual optimality with social optimality, i.e., under such prices, when the households selfishly optimize their own benefits, they automatically also maximize the social welfare. The utility company can thus use dynamic pricing to coordinate demand responses to the benefit of the overall system. We propose a distributed algorithm for the utility company and the customers to jointly compute this optimal prices and demand schedules. Finally, we present simulation results that illustrate several interesting properties of the proposed scheme.https://authors.library.caltech.edu/records/nkymn-pk975Optimal Charging of Plug-in Hybrid Electric Vehicles in Smart Grids
https://resolver.caltech.edu/CaltechAUTHORS:20120406-131234298
Authors: {'items': [{'id': 'Sojoudi-S', 'name': {'family': 'Sojoudi', 'given': 'Somayeh'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/PES.2011.6039236
Plug-in hybrid electric vehicles (PHEVs) play an important role in making a greener future. Given a group of PHEVs distributed across a power network equipped with the smart grid technology (e.g. wireless communication devices), the objective of this paper is to study how to schedule the charging of the PHEV batteries. To this end, we assume that each battery must be fully charged by a pre-specified time, and that the charging rate can be time-varying at discrete-time instants. The scheduling problem for the PHEV charging can be augmented into the optimal power flow (OPF) problem to obtain a joint OPF-charging (dynamic) optimization. A solution to this highly nonconvex problem optimizes the network performance by minimizing the generation and charging costs while satisfying the network, physical and inelastic-load constraints. A global optimum to the joint OPF-charging optimization can be found efficiently in polynomial time by solving its convex dual problem whenever the duality gap is zero for the joint OPF-charging problem. It is shown in a recent work that the duality gap is expected to be zero for the classical OPF problem. We build on this result and prove that the duality gap is zero for the joint OPF-charging optimization if it is zero for the classical OPF problem. The results of this work are applied to the IEEE 14 bus system.https://authors.library.caltech.edu/records/31kqm-vmp47Real-time demand response with uncertain renewable energy in smart grid
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131626157
Authors: {'items': [{'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/Allerton.2011.6120322
We consider a set of users served by a single load serving entity (LSE) in the electricity grid. The LSE procures capacity a day ahead. When random renewable energy is realized at delivery time, it actively manages user load through real-time demand response and purchases balancing power on the spot market to meet the aggregate demand. Hence, to maximize the social welfare, decisions must be coordinated over two timescales (a day ahead and in real time), in the presence of supply uncertainty, and computed jointly by the LSE and the users since the necessary information is distributed among them. We formulate the problem as a dynamic program. We propose a distributed heuristic algorithm and prove its optimality when the welfare function is quadratic and the LSE's decisions are strictly positive. Otherwise, we bound the gap between the welfare achieved by the heuristic algorithm and the maximum in certain cases. Simulation results suggest that the performance gap is small. As we scale up the size of a renewable generation plant, both its mean production and its variance will likely increase. We characterize the impact of the mean and variance of renewable energy on the maximum welfare. This paper is a continuation of [2], focusing on time-correlated demand.https://authors.library.caltech.edu/records/agqe2-xdb37Optimal power flow over tree networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-095656194
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice F.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2011
DOI: 10.1109/Allerton.2011.6120323
The optimal power flow (OPF) problem is critical to power system operation but it is generally non-convex and therefore hard to solve. Recently, a sufficient condition has been found under which OPF has zero duality gap, which means that its solution can be computed efficiently by solving the convex dual problem. In this paper we simplify this sufficient condition through a reformulation of the problem and prove that the condition is always satisfied for a tree network provided we allow over-satisfaction of load. The proof, cast as a complex semi-definite program, makes use of the fact that if the underlying graph of an n × n Hermitian positive semi-definite matrix is a tree, then the matrix has rank at least n-1.https://authors.library.caltech.edu/records/6xz0p-emq71Optimal design of hybrid energy system with PV/wind turbine/storage: A case study
https://resolver.caltech.edu/CaltechAUTHORS:20170810-125833627
Authors: {'items': [{'id': 'Huang-Rui', 'name': {'family': 'Huang', 'given': 'Rui'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}, {'id': 'Clarke-C-R', 'name': {'family': 'Clarke', 'given': 'Christopher R.'}}]}
Year: 2011
DOI: 10.1109/SmartGridComm.2011.6102376
Hybrid energy systems with renewable generation are built in many remote areas where the renewable resources are abundant and the environment is clean. We present a case study of the Catalina Island in California for which a system with photovoltaic (PV) arrays, wind turbines, and battery storage is designed based on empirical weather and load data. To determine the system size, we formulate an optimization problem that minimizes the total construction and operation cost subject to maximum tolerable risk. Simulations using the Hybrid Optimization Model for Electric Renewable (HOMER) is used to determine the feasible set of the optimization problem.https://authors.library.caltech.edu/records/y43yg-pnk53Inverter VAR control for distribution systems with renewables
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112707612
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Clarke-C-R', 'name': {'family': 'Clarke', 'given': 'Christopher R.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2011
DOI: 10.1109/SmartGridComm.2011.6102366
Motivated by the need to cope with rapid and random fluctuations of renewable generation, we presents a model that augments the traditional Volt/VAR control through switched controllers on a slow timescale with inverter control on a fast timescale. The optimization problem is generally nonconvex and therefore hard to solve. We propose a simple convex relaxation and prove that it is exact provided over-satisfaction of load is allowed. Hence Volt/VAR control over radial networks is efficiently solvable. Simulations of a real-world distribution circuit illustrates that the proposed inverter control achieves significant improvement over the IEEE 1547 standard in terms of power quality and power savings.https://authors.library.caltech.edu/records/56qs2-jnm02GRIP - Grids with intelligent periphery: Control architectures for Grid2050^π
https://resolver.caltech.edu/CaltechAUTHORS:20170215-173725326
Authors: {'items': [{'id': 'Bakken-D', 'name': {'family': 'Bakken', 'given': 'D.'}}, {'id': 'Bose-A', 'name': {'family': 'Bose', 'given': 'A.'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. M.'}}, {'id': 'Khargonekar-P-P', 'name': {'family': 'Khargonekar', 'given': 'P. P.'}}, {'id': 'Kuh-A', 'name': {'family': 'Kuh', 'given': 'A.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'von-Meier-A', 'name': {'family': 'von Meier', 'given': 'A.'}, 'orcid': '0000-0003-4675-752X'}, {'id': 'Poolla-K', 'name': {'family': 'Poolla', 'given': 'K.'}}, {'id': 'Varaiya-P-P', 'name': {'family': 'Varaiya', 'given': 'P. P.'}}, {'id': 'Wu-F', 'name': {'family': 'Wu', 'given': 'F.'}}]}
Year: 2011
DOI: 10.1109/SmartGridComm.2011.6102397
A distributed control and coordination architecture for integrating inherently variable and uncertain generation is presented. The key idea is to distribute the intelligence into the periphery of the grid. This will allow coordination of generation, storage, and adjustable demand on the distribution side of the system and thus reduce the need to build new transmission facilities to accommodate large amounts of renewable generation.https://authors.library.caltech.edu/records/0kg75-e8b44Optimal demand response: Problem formulation and deterministic case
https://resolver.caltech.edu/CaltechAUTHORS:20170810-104829103
Authors: {'items': [{'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1007/978-1-4614-1605-0_3
We consider a set of users served by a single load-serving entity (LSE). The LSE procures capacity a day ahead. When random renewable energy is realized at delivery time, it manages user load through real-time demand response and purchases balancing power on the spot market to meet the aggregate demand. Hence, optimal supply procurement by the LSE and the consumption decisions by the users must be coordinated over two timescales, a day ahead and in real time, in the presence of supply uncertainty. Moreover, they must be computed jointly by the LSE and the users since the necessary information is distributed among them. In this chapter, we present a simple yet versatile user model and formulate the problem as a dynamic program that maximizes expected social welfare. When random renewable generation is absent, optimal demand response reduces to joint scheduling of the procurement and consumption decisions. In this case, we show that optimal prices exist that coordinate individual user decisions to maximize social welfare, and present a decentralized algorithm to optimally schedule a day in advance the LSE's procurement and the users' consumptions. The case with uncertain supply is reported in a companion paper.https://authors.library.caltech.edu/records/vhfv5-bc902Optimal decentralized protocol for electric vehicle charging
https://resolver.caltech.edu/CaltechAUTHORS:20131003-100205684
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/CDC.2011.6161220
Motivated by the power-grid-side challenges in the integration of electric vehicles, we propose a decentralized protocol for negotiating day-ahead charging schedules for electric vehicles. The overall goal is to shift the load due to electric vehicles to fill the overnight electricity demand valley. In each iteration of the proposed protocol, electric vehicles choose their own charging profiles for the following day according to the price profile broadcast by the utility, and the utility updates the price profile to guide their behavior. This protocol is guaranteed to converge, irrespective of the specifications (e.g., maximum charging rate and deadline) of electric vehicles. At convergence, the l2 norm of the aggregated demand is minimized, and the aggregated demand profile is as "flat" as it can possibly be. The proposed protocol needs no coordination among the electric vehicles, hence requires low communication and computation capability. Simulation results demonstrate convergence to optimal collections of charging profiles within few iterations.https://authors.library.caltech.edu/records/cjrzr-pn804Multi-period optimal energy procurement and demand response in smart grid with uncertain supply
https://resolver.caltech.edu/CaltechAUTHORS:20170306-162127856
Authors: {'items': [{'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2011
DOI: 10.1109/CDC.2011.6161320
We propose a simple model that integrates two-period electricity markets, uncertainty in renewable generation, and real-time dynamic demand response. A load-serving entity decides its day-ahead procurement to optimize expected social welfare a day before energy delivery. At delivery time when renewable generation is realized, it sets prices to manage demand and purchase additional power on the real-time market, if necessary, to balance supply and demand. We derive the optimal day-ahead decision, propose real-time demand response algorithm, and study the effect of volume and variability of renewable generation on the social welfare.https://authors.library.caltech.edu/records/s78cv-h5711Optimal Max-min Fairness Rate Control in Wireless Networks: Perron-Frobenius Characterization and Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20121127-111501274
Authors: {'items': [{'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Tan-Chee-Wei', 'name': {'family': 'Tan', 'given': 'Chee Wei'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/INFCOM.2012.6195808
Rate adaptation and power control are two key resource allocation mechanisms in multiuser wireless networks. In the presence of interference, how do we jointly optimize end-to-end source rates and link powers to achieve weighted max-min rate fairness for all sources in the network? This optimization problem is hard to solve as physical layer link rate functions are nonlinear, nonconvex, and coupled in the transmit powers. We show that the weighted max-min rate fairness problem can, in fact, be decoupled into separate fairness problems for flow rate and power control. For a large class of physical layer link rate functions, we characterize the optimal solution analytically by a nonlinear Perron-Frobenius theory (through solving a conditional eigenvalue problem) that captures the interaction of multiuser interference. We give an iterative algorithm to compute the optimal flow rate that converges geometrically fast without any parameter configuration. Numerical results show that our iterative algorithm is computationally fast for both the Shannon capacity, CDMA, and piecewise linear link rate functions.https://authors.library.caltech.edu/records/c4x65-fnb29Frequency-Based Load Control in Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20121003-154738717
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/ACC.2012.6315283
Maintaining demand-supply balance and regulating frequency are key issues in power system control. Conventional approaches focus on adjusting the generation so that it follows the load. However, relying on solely regulating generation is inefficient, especially for power systems where contingencies like a sudden loss in generation or a sudden change in load frequently occur. We present a frequency-based load control scheme for demand-supply balancing and frequency regulation. We formulate a load control optimization problem which aims to balance the change in load with the change in supply while minimizing the overall end-use disutility. By studying the power system model that characterizes the frequency response to real power imbalance between demand and supply, we design decentralized synchronous and asynchronous algorithms which take advantage of local frequency measurements to solve the load control problem. Case studies show that the proposed load control scheme is capable of relatively quickly balancing the power and restoring the frequency under generation-loss like contingencies, even when users only have the knowledge of a simplified system model instead of an accurate one.https://authors.library.caltech.edu/records/f5xnd-c8z22Energy-efficient congestion control
https://resolver.caltech.edu/CaltechAUTHORS:20161025-154452155
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Walid-A', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1145/2254756.2254770
Various link bandwidth adjustment mechanisms are being developed to save network energy. However, their interaction with congestion control can significantly reduce network throughput, and is not well understood. We firstly put forward a framework to study this interaction, and then propose an easily implementable dynamic bandwidth adjustment (DBA) mechanism for the links. In DBA, each link updates its bandwidth according to an integral control law to match its average buffer size with a target buffer size. We prove that DBA reduces link bandwidth without sacrificing throughput---DBA only turns off excess bandwidth---in the presence of congestion control. Preliminary ns2 simulations confirm this result.https://authors.library.caltech.edu/records/dnr2g-fc688Stochastic distributed protocol for electric vehicle charging with discrete charging rate
https://resolver.caltech.edu/CaltechAUTHORS:20170810-112506562
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/PESGM.2012.6344847
To address the grid-side challenges associated with the anticipated high electric vehicle (EV) penetration level, various charging protocols have been proposed in the literature. Most if not all of these protocols assume continuous charging rates and allow intermittent charging. However, due to charging technology limitations, EVs can only be charged at a fixed rate, and the intermittency in charging shortens the battery lifespan. We consider these charging requirements, and formulate EV charging scheduling as a discrete optimization problem. We propose a stochastic distributed algorithm to approximately solve the optimal EV charging scheduling problem in an iterative procedure. In each iteration, the transformer receives charging profiles computed by the EVs in the previous iteration, and broadcasts the corresponding normalized total demand to the EVs; each EV generates a probability distribution over its potential charging profiles accordingly, and samples from the distribution to obtain a new charging profile. We prove that this stochastic algorithm almost surely converges to one of its equilibrium charging profiles, and each of its equilibrium charging profiles has a negligible sub-optimality ratio. Case studies corroborate our theoretical results.https://authors.library.caltech.edu/records/1n3dg-b2s46Optimal inverter VAR control in distribution systems with high PV penetration
https://resolver.caltech.edu/CaltechAUTHORS:20170206-172908857
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Neal-R', 'name': {'family': 'Neal', 'given': 'Russell'}}, {'id': 'Clarke-C', 'name': {'family': 'Clarke', 'given': 'Christopher'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/PESGM.2012.6345736
The intent of the study detailed in this paper is to demonstrate the benefits of inverter var control on a fast timescale to mitigate rapid and large voltage fluctuations due to the high penetration of photovoltaic generation and the resulting reverse power flow. Our approach is to formulate the volt/var control as a radial optimal power flow (OPF) problem to minimize line losses and energy consumption, subject to constraints on voltage magnitudes. An efficient solution to the radial OPF problem is presented and used to study the structure of optimal inverter var injection and the net benefits, taking into account the additional cost of inverter losses when operating at non-unity power factor. This paper will illustrate how, depending on the circuit topology and its loading condition, the inverter's optimal reactive power injection is not necessarily monotone with respect to their real power output. The results are demonstrated on a distribution feeder on the Southern California Edison system that has a very light load and a 5 MW photovoltaic (PV) system installed away from the substation.https://authors.library.caltech.edu/records/q23mz-x9q46Equivalence of Branch Flow and Bus Injection Models
https://resolver.caltech.edu/CaltechAUTHORS:20130731-091844876
Authors: {'items': [{'id': 'Subhonmesh-B', 'name': {'family': 'Subhonmesh', 'given': 'Bose'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}]}
Year: 2012
DOI: 10.1109/Allerton.2012.6483453
A branch flow model has recently been proposed for the analysis and optimization of power flows. In this paper we show that the model is equivalent to the more popular bus injection model. Moreover, we prove the equivalence of various relaxations of these two models.https://authors.library.caltech.edu/records/rk6zp-gad61Swing dynamics as primal-dual algorithm for optimal load control
https://resolver.caltech.edu/CaltechAUTHORS:20130828-101518387
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/SmartGridComm.2012.6486046
In electricity transmission networks, loads can provide flexible, fast responsive, and decentralized sources for frequency regulation and generation-demand balancing, complementary to generation control. We consider an optimal load control (OLC) problem in a transmission network, when a disturbance in generation occurs on an arbitrary subset of the buses. In OLC, the frequency-insensitive loads are reduced (or increased) in real-time in a way that balances the generation shortfall (or surplus), resynchronizes the bus frequencies, and minimizes the aggregate disutility of load control. We propose a frequency-based load control mechanism and show that the swing dynamics of the network, together with the proposed mechanism, act as a decentralized primal-dual algorithm to solve OLC. Simulation shows that the proposed mechanism can resynchronize the bus frequencies, balance demand with generation and achieve the optimum of OLC within several seconds after a disturbance in generation. Through simulation, we also compare the performance of the proposed mechanism with automatic generation control (AGC), and discuss the effect of their incorporation.https://authors.library.caltech.edu/records/w6w9y-cfd86Exact Convex Relaxation of OPF for Radial Networks using Branch Flow Model
https://resolver.caltech.edu/CaltechAUTHORS:20130826-134301716
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/SmartGridComm.2012.6485951
The optimal power flow (OPF) problem is generally nonconvex. Recently a second-order cone relaxation for OPF has been proposed using the branch flow model. In this paper, we provide sufficient conditions under which the relaxation is exact, and demonstrate that these conditions hold for a wide class of practical power distribution systems.https://authors.library.caltech.edu/records/e6qj1-29t23Demand response in radial distribution networks: Distributed algorithm
https://resolver.caltech.edu/CaltechAUTHORS:20130802-082120272
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/ACSSC.2012.6489288
Demand response has recently become a topic of active research. Most of work however considers only the balance between aggregate load and supply, and abstracts away the underlying power network. In this paper, we study demand response in a radial distribution network, by formulating it as an optimal power flow problem that maximizes the aggregate user utilities and minimizes the supply cost and the power line losses, subject to the power flow constraints and operating constraints. We propose a fully distributed algorithm for the users to coordinate their demand response decisions through local communication with their neighbors so as to achieve the optimum. Numerical examples with the real-world distribution circuits are provided to complement our theoretical analysis.https://authors.library.caltech.edu/records/8v9tq-x2v45Some Problems in Demand Side Management
https://resolver.caltech.edu/CaltechAUTHORS:20130815-100621563
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Jiang-Libin', 'name': {'family': 'Jiang', 'given': 'Libin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}]}
Year: 2012
We present a sample of problems in demand side
management in future power systems and illustrate how they
can be solved in a distributed manner using local information.
First, we consider a set of users served by a single load-serving
entity (LSE). The LSE procures capacity a day ahead. When
random renewable energy is realized at delivery time, it manages
user load through real-time demand response and purchases
balancing power on the spot market to meet the aggregate
demand. Hence optimal supply procurement by the LSE and the
consumption decisions by the users must be coordinated over two
timescales, a day ahead and in real time, in the presence of supply
uncertainty. Moreover, they must be computed jointly by the
LSE and the users since the necessary information is distributed
among them. We present distributed algorithms to maximize
expected social welfare. Instead of social welfare, the second
problem is to coordinate electric vehicle charging to fill the valleys
in aggregate electric demand profile, or track a given desired
profile. We present synchronous and asynchronous algorithms
and prove their convergence. Finally, we show how loads can
use locally measured frequency deviations to adapt in real time
their demand in response to a shortfall in supply. We design
decentralized demand response mechanism that, together with
the swing equation of the generators, jointly maximize disutility
of demand rationing, in a decentralized manner.https://authors.library.caltech.edu/records/a5yj9-kj319On the exactness of convex relaxation for optimal power flow in tree networks
https://resolver.caltech.edu/CaltechAUTHORS:20131220-094526108
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/CDC.2012.6426045
The optimal power flow problem is nonconvex, and a convex relaxation has been proposed to solve it. We prove that the relaxation is exact, if there are no upper bounds on the voltage, and any one of some conditions holds. One of these conditions requires that there is no reverse real power flow, and that the resistance to reactance ratio is non-decreasing as transmission lines spread out from the substation to the branch buses. This condition is likely to hold if there are no distributed generators. Besides, avoiding reverse real power flow can be used as rule of thumb for placing distributed generators.https://authors.library.caltech.edu/records/xqngg-p9h45Deadline differentiated pricing of deferrable electric power service
https://resolver.caltech.edu/CaltechAUTHORS:20170201-153706452
Authors: {'items': [{'id': 'Bitar-E', 'name': {'family': 'Bitar', 'given': 'Eilyan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/CDC.2012.6425944
As the penetration of wind and solar energy into the electric grid continues to grow, there will be an increasing need to evolve demand-side solutions capable of compensating the inherent variability in power supply from such renewable resources. Today, demand is largely treated as inelastic. However, the power requirements of many commercial and residential loads are such that a fraction of power demand at any given moment is inherently deferrable in time subject to a deadline constraint on the total energy supplied. Examples include thermal systems such as refrigerators, water heaters, HVAC systems, data centers, and, assuming mass adoption of plug-in electric vehicles, batteries. In this paper, we discuss some limitations of dynamic pricing mechanisms (e.g., real-time pricing) as a means of inducing demand response and suggest a novel forward contracting mechanism for deadline-differentiated deferrable energy contracts to alleviate some of these difficulties. Essentially, consumers who consent to deferral of their consumption in time - subject to a pre-specified deadline - will receive a discounted per-unit price for said energy. In this way, the supplier is capable of extracting flexibility in the delivery of energy to participating deferrable loads, while consumers receive a discount on energy with an associated deadline guarantee on delivery. The supply side is modeled as random to capture variability in renewable power supply. Using a general model for consumer preferences to capture the effect of consumption deferral on utility, we prove the existence of a competitive equilibrium and provide a characterization of deadline-differentiated prices yielding such an equilibrium. We also discuss provably optimal online scheduling policies to dynamically allocate the variable supply to a bundle of deadline-differentiated energy tasks.https://authors.library.caltech.edu/records/d112d-rtb18Branch flow model: Relaxations and convexification
https://resolver.caltech.edu/CaltechAUTHORS:20131220-084709018
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/CDC.2012.6425870
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) problems that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact and we characterize when the angle relaxation may fail. We propose a simple method to convexify a mesh network using phase shifters so that both relaxation steps are always exact and OPF for the convexified network can always be solved efficiently for a globally optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network graph and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints. Since power networks are sparse, the number of required phase shifters may be relatively small.https://authors.library.caltech.edu/records/f03t1-zt633Branch flow model for radial networks: convex relaxation
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114313789
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
Power flow optimization is generally nonlinear and non-convex, and a second-order cone relaxation has been proposed recently for convexification. We prove several sufficient conditions under which the relaxation is exact. One of these conditions seems particularly realistic and suggests guidelines on integrating distributed generations.https://authors.library.caltech.edu/records/0vwxf-41144An optimization-based demand response in radial distribution networks
https://resolver.caltech.edu/CaltechAUTHORS:20130730-133244823
Authors: {'items': [{'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2012
DOI: 10.1109/GLOCOMW.2012.6477803
Demand response has recently become a topic of active research. Most of work however considers only the balance between aggregate load and supply, and abstracts away the underlying power network and the associated power flow constraints and operating constraints. In this paper, we study demand response in a radial distribution network, by formulating it as an optimal power flow problem that maximizes the aggregate user utilities and minimizes the power line losses, subject to the power flow constraints and operating constraints. As the resulting problem is non-convex and difficult to solve, we propose a convex relaxation that is usually exact for the real-world distribution circuits. We then propose a distributed algorithm for the load-serving entity to set the price signal to coordinate the users' demand response so as to achieve the optimum. Numerical examples show that the proposed algorithm converges fast for real-world distribution systems.https://authors.library.caltech.edu/records/qtmgt-jpt39Real-time deferrable load control: handling the uncertainties of renewable generation
https://resolver.caltech.edu/CaltechAUTHORS:20161025-161438752
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1145/2487166.2487179
Real-time demand response is essential for handling the uncertainties of renewable generation. Traditionally, demand response has been focused on large industrial and commercial loads, however it is expected that a large number of small residential loads such as air conditioners, dish washers, and electric vehicles will also participate in the coming years. The electricity consumption of these smaller loads, which we call deferrable loads, can be shifted over time, and thus be used (in aggregate) to compensate for the random fluctuations in renewable generation. In this paper, we propose a real-time distributed deferrable load control algorithm to reduce the variance of aggregate load (load minus renewable generation) by shifting the power consumption of deferrable loads to periods with high renewable generation. At every time step, the algorithm minimizes the expected variance to go with updated predictions. We prove that suboptimality of the algorithm vanishes as time horizon expands. Further, we evaluate the algorithm via trace-based simulations.https://authors.library.caltech.edu/records/m4gqe-7j072Towards smart, flexible and efficient power systems: Vision and research challenges
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114148121
Authors: {'items': [{'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Khargonekar-P-P', 'name': {'family': 'Khargonekar', 'given': 'Pramod'}}]}
Year: 2013
DOI: 10.1109/ACC.2013.6580653
The electric power infrastructure is transforming into a smarter, increasingly flexible, and more efficient system with the potential to play an integral role in the changing energy landscape. This paper and the accompanying tutorial session at the 2013 American Control Conference provide an overview of this transformation. It then highlights three emerging optimization and controls techniques that can help facilitate the necessary changes to power grid design, operation and management.https://authors.library.caltech.edu/records/5xpw8-e5b06Multipath TCP Algorithms: Theory and Design
https://resolver.caltech.edu/CaltechAUTHORS:20130828-103050742
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Walid-A', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1145/2494232.2466585
Multi-path TCP (MP-TCP) has the potential to greatly improve
application performance by using multiple paths transparently.
We propose a fluid model for a large class of MP-TCP
algorithms and identify design criteria that guarantee
the existence, uniqueness, and stability of system equilibrium.
We characterize algorithm parameters for TCP-friendliness
and prove an inevitable tradeoff between responsiveness
and friendliness. We discuss the implications of
these properties on the behavior of existing algorithms and
motivate a new design that generalizes existing algorithms.
We use ns2 simulations to evaluate the proposed algorithm
and illustrate its superior overall performance.https://authors.library.caltech.edu/records/e5xj7-b8y78Exact Convex Relaxation for Optimal Power Flow in Distribution Networks
https://resolver.caltech.edu/CaltechAUTHORS:20131008-160444682
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}]}
Year: 2013
DOI: 10.1145/2494232.2465535
The optimal power flow (OPF) problem seeks to control the
power generation/consumption to minimize the generation
cost, and is becoming important for distribution networks.
OPF is nonconvex and a second-order cone programming
(SOCP) relaxation has been proposed to solve it. We prove
that after a "small" modification to OPF, the SOCP relaxation is exact under a "mild" condition. Empirical studies
demonstrate that the modification to OPF is "small" and
that the "mild" condition holds for all test networks, including the IEEE 13-bus test network and practical networks
with high penetration of distributed generation.https://authors.library.caltech.edu/records/2d15y-8ry21Convexifying Optimal Power Flow: Recent Advances in OPF Solution Methods
https://resolver.caltech.edu/CaltechAUTHORS:20131219-091842168
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}]}
Year: 2013
The optimal power flow (OPF) problem is nonconvex and generally hard to solve, see e.g. [1], [2]. In this tutorial, we will provide an overview of two different solution approaches. The first uses the bus injection model, which is the standard model for power flow analysis and optimization. It focuses on nodal variables such as voltages, current and power injections and does not directly deal with power flows on individual branches. A key advantage is the simple linear relationship I = Y V between the nodal current injections I and the bus voltages V through the admittance matrix Y. Recently, it has been observed that this form of OPF can be reformulated as a nonconvex QCQP (quadratic constrained quadratic program), which leads to a standard convex relaxation through semidefinite programming [3]-[5]. For radial networks, different sufficient conditions have been derived under which the semidefinite relaxation turns out to be exact [6]-[8]. The second solution technique employs the branch flow model, which focuses on currents and powers on the branches rather than the nodal variables. The branch flow model has been historically used primarily for modeling distribution circuits, which tend to be radial. It has therefore received far less attention. A branch flow model has recently been proposed for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving OPF that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, both relaxation steps are always exact, provided there are no upper bounds on loads [9]. For mesh networks, the conic relaxation is always exact and we provide a simple way to determine if a relaxed solution is globally optimal. We describe a simple method to convexify a mesh network using phase shifters so that both relaxation steps are alw- ys exact and OPF for the convexified network can always be solved efficiently for a globally optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network graph and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints [10]. The tutorial will describe precisely the bus injection model and the semidefinite relaxation of OPF as well as the branch flow model and its associated relaxations. We prove sufficient conditions for exact relaxations and verify our results on simulations of various IEEE test systems. Finally we explain the equivalence between the bus injection model and branch flow model.https://authors.library.caltech.edu/records/q9rrm-sds41Convex relaxation of optimal power flow: A tutorial
https://resolver.caltech.edu/CaltechAUTHORS:20170130-172039929
Authors: {'items': [{'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/IREP.2013.6629391
This is a short survey of recent advances in the convex relaxation of the optimal power flow problem. Our focus is on understanding structural properties, especially the underlying convexity structure, of optimal power flow problems rather than different computational algorithms.https://authors.library.caltech.edu/records/96ne9-50515The redistribution of power flow in cascading failures
https://resolver.caltech.edu/CaltechAUTHORS:20170810-133558423
Authors: {'items': [{'id': 'Lai-Chengdi', 'name': {'family': 'Lai', 'given': 'Chengdi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/Allerton.2013.6736639
Understanding the redistribution of power flow is crucial to understanding the dynamics of cascading failures. Such redistribution is complicated, with monotonicity being the exception rather than the norm. We study the monotonicity of a quadratic function of branch power flow with respect to link failure and load shedding, respectively. The quadratic function can be considered as a measure of the aggregate network loading. We show that the value of this measure increases when (more) link failure occurs. On the other hand, while arbitrary load shedding can increase the measure value, we establish the existence of load shedding that can guarantee its reduction. Utilizing these monotonicity properties, we show that the failure of a link will cause the power flow over its adjacent link to have a change in the same direction (away or towards their commonly incident bus) as the original flow over the failed link.https://authors.library.caltech.edu/records/we34e-nw941Demand Response Optimization for Smart Home Scheduling Using Genetic Algorithm
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105100899
Authors: {'items': [{'id': 'Chen-Chao-Rong', 'name': {'family': 'Chen', 'given': 'Chao-Rong'}}, {'id': 'Lan-Ming-Jen', 'name': {'family': 'Lan', 'given': 'Ming-Jen'}}, {'id': 'Huang-Chi-Chen', 'name': {'family': 'Huang', 'given': 'Chi-Chen'}}, {'id': 'Hong-Ying-Yi', 'name': {'family': 'Hong', 'given': 'Ying-Yi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/SMC.2013.252
For mitigating the urgency of constructing power plant, alleviating supply pressure of power company, electricity scheduling of customers is a very important issue, wherein to promote demand response is a key factor. The demand response is mainly through electricity price publicized by utility company to guide customers in electricity scheduling, and by use of price negotiating mechanism, to reach mutual benefits for both sides of demand and supply. The paper proposes a method of minimizing tariff for customers through changing elastic load use time intervals where customers' electricity use time is divided into inelastic and elastic intervals by electricity use characteristics. In the paper, customer's one day electricity used is assumed to conduct simulation, by genetic algorithm, comparing variations among scheduling and tariff under different electricity use limitation situations. As shown in the results, it is found that through elastic load use time interval changes, minimum tariff objective can be reached, and feasibility of the proposed method is verified.https://authors.library.caltech.edu/records/2pj21-3mz75Optimal power flow in tree networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-113418095
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Topcu-U', 'name': {'family': 'Topcu', 'given': 'Ufuk'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760226
The optimal power flow (OPF) problem seeks to control power generation/demand to optimize certain objectives such as minimizing the generation cost or power loss. It is becoming increasingly important for tree distribution networks due to the emerging distributed generation and controllable loads. The OPF problem is nonconvex. We prove that after modifying the OPF problem, its global optimum can be recovered via a second-order cone programming (SOCP) relaxation for tree networks, under a condition that can be checked in advance. Empirical studies justify that the modification is "small", and that the condition holds, for the IEEE 13-bus network and two real-world networks.https://authors.library.caltech.edu/records/16qrb-p1t76Optimal branch exchange for feeder reconfiguration in distribution networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-131659189
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760333
The feeder reconfiguration problem chooses the on/off status of the switches in a distribution network in order to minimize a certain cost such as power loss. It is a mixed integer nonlinear program and hence hard to solve. A popular heuristic search consists of repeated application of branch exchange, where some loads are transferred from one feeder to another feeder while maintaining the radial structure of the network, until no load transfer can further reduce the cost. Optimizing each branch exchange step is itself a mixed integer nonlinear program. In this paper we propose an efficient algorithm for optimizing a branch exchange step. It uses an AC power flow model and is based on the recently developed convex relaxation of optimal power flow. We provide a bound on the gap between the optimal cost and that of our solution. We prove that our algorithm is optimal when the voltage magnitudes are the same at all buses. We illustrate the effectiveness of our algorithm through the simulation of real-world distribution feeders.https://authors.library.caltech.edu/records/cqytx-nhs12Optimal Power Flow in Direct Current Networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-113122736
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760774
The optimal power flow (OPF) problem seeks to control power generation/demand to optimize certain objectives such as minimizing the generation cost or power loss. Direct current (DC) networks (e.g., DC-microgrids) are promising to incorporate distributed generation. This paper focuses on the OPF problem in DC networks. The OPF problem is nonconvex, and we study solving it via a second-order cone programming (SOCP) relaxation. In particular, we prove that the SOCP relaxation is exact if there are no voltage upper bounds, and that the SOCP relaxation has at most one solution if it is exact.https://authors.library.caltech.edu/records/1dyvw-6kd28Equilibrium and dynamics of local voltage control in distribution systems
https://resolver.caltech.edu/CaltechAUTHORS:20170810-113209963
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2013
DOI: 10.1109/CDC.2013.6760555
We consider a class of local volt/var control schemes where the control decision on the reactive power at a bus depends only on the local bus voltage. These local algorithms form a feedback dynamical system and collectively determine the bus voltages of a power network. We show that the dynamical system has a unique equilibrium by interpreting the dynamics as a distributed algorithm for solving a certain convex optimization problem whose unique optimal point is the system equilibrium. Moreover, the objective function serves as a Lyapunov function implying global asymptotic stability of the equilibrium. The optimization based model does not only provide a way to characterize the equilibrium, but also suggests a principled way to engineer the control. We apply the results to study the parameter setting for the inverter-based volt/var control in the proposed IEEE 1547.8 standard.https://authors.library.caltech.edu/records/dps39-gck77Pricing Link by Time
https://resolver.caltech.edu/CaltechAUTHORS:20140804-112817922
Authors: {'items': [{'id': 'Lai-Chengdi', 'name': {'family': 'Lai', 'given': 'Chengdi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Stephen H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Leung-Ka-Cheong', 'name': {'family': 'Leung', 'given': 'Ka-Cheong'}, 'orcid': '0000-0001-7999-2572'}, {'id': 'Li-Victor-O-K', 'name': {'family': 'Li', 'given': 'Victor O. K.'}}]}
Year: 2014
DOI: 10.1145/2591971.2591974
The combination of loss-based TCP and drop-tail routers
often results in full buffers, creating large queueing delays. The challenge with parameter tuning and the drastic consequence of improper tuning have discouraged network administrators from enabling AQM even when routers support
it. To address this problem, we propose a novel design principle for AQM, called the pricing-link-by-time (PLT) principle. PLT increases the link price as the backlog stays above a threshold β, and resets the price once the backlog goes below β. We prove that such a system exhibits cyclic behavior that is robust against changes in network environment and protocol parameters. While β approximately controls the level of backlog, the backlog dynamics are invariant for β across a wide range of values. Therefore, β can be chosen to reduce delay without undermining system performance. We validate these analytical results using packet-level simulation.https://authors.library.caltech.edu/records/33gaz-zr760Energy Efficient Multipath TCP for Mobile Devices
https://resolver.caltech.edu/CaltechAUTHORS:20140820-114017534
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}, {'id': 'Walid-Anwar', 'name': {'family': 'Walid', 'given': 'Anwar'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1145/2632951.2632971
Most mobile devices today come with multiple access interfaces, e.g., 4G and WiFi. Multipath TCP (MP-TCP) can greatly improve network performance by exploiting the connection diversity of multiple access interfaces, at the expense of higher energy consumption. In this paper, we design MP-TCP algorithms for mobile devices by jointly considering the performance and energy consumption. We consider two main types of mobile applications: realtime applications that have a fixed duration and file transfer applications that have a fixed data size. For each type of applications, we propose a two-timescale algorithm with theoretical guarantee on the performance. We present simulation results that show that our algorithms can reduce energy consumption by up to 22% without sacrificing throughput compared to a baseline MP-TCP algorithm.https://authors.library.caltech.edu/records/gk9g2-93559Solving quadratically constrained quadratic programs on acyclic graphs with application to optimal power flow
https://resolver.caltech.edu/CaltechAUTHORS:20150501-091249022
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Gayme-D-F', 'name': {'family': 'Gayme', 'given': 'Dennice F.'}}, {'id': 'Chandy-K-M', 'name': {'family': 'Chandy', 'given': 'K. Mani'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/CISS.2014.6814135
This paper presents a class of non-convex quadratically constrained quadratic programs that can be solved in polynomial time when their underlying graph is acyclic, provided the constraints satisfy a technical condition. We demonstrate its use on optimal power flow problems over radial networks.https://authors.library.caltech.edu/records/zxwv3-g7g20Branch flow model: Relaxations and convexification
https://resolver.caltech.edu/CaltechAUTHORS:20170124-173857414
Authors: {'items': [{'id': 'Farivar-M', 'name': {'family': 'Farivar', 'given': 'Masoud'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/TDC.2014.6863260
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact but the angle relaxation may not be exact, and we provide a simple way to determine if a relaxed solution is globally optimal. We propose convexification of mesh networks using phase shifters so that OPF for the convexified network can always be solved efficiently for an optimal solution. We prove that convexification requires phase shifters only outside a spanning tree of the network and their placement depends only on network topology, not on power flows, generation, loads, or operating constraints. Part I introduces our branch flow model, explains the two relaxation steps, and proves the conditions for exact relaxation. Part II describes convexification of mesh networks, and presents simulation results.https://authors.library.caltech.edu/records/ge52c-d6z17Pricing data center demand response
https://resolver.caltech.edu/CaltechAUTHORS:20161128-163510694
Authors: {'items': [{'id': 'Liu-Zhenhua', 'name': {'family': 'Liu', 'given': 'Zhenhua'}}, {'id': 'Liu-Iris', 'name': {'family': 'Liu', 'given': 'Iris'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2014
DOI: 10.1145/2591971.2592004
Demand response is crucial for the incorporation of renewable energy into the grid. In this paper, we focus on a particularly promising industry for demand response: data centers. We use simulations to show that, not only are data centers large loads, but they can provide as much (or possibly more) flexibility as large-scale storage if given the proper incentives. However, due to the market power most data centers maintain, it is difficult to design programs that are efficient for data center demand response. To that end, we propose that prediction-based pricing is an appealing market design, and show that it outperforms more traditional supply function bidding mechanisms in situations where market power is an issue. However, prediction-based pricing may be inefficient when predictions are inaccurate, and so we provide analytic, worst-case bounds on the impact of prediction error on the efficiency of prediction-based pricing. These bounds hold even when network constraints are considered, and highlight that prediction-based pricing is surprisingly robust to prediction error.https://authors.library.caltech.edu/records/8s4tj-11n34Chordal relaxation of OPF for multiphase radial networks
https://resolver.caltech.edu/CaltechAUTHORS:20150203-145330203
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/ISCAS.2014.6865509
We formulate optimal power flow problem for unbalanced multiphase radial networks. We show that there is an equivalent single-phase mesh network that has a radial structure at the macro-level and a clique structure corresponding to each line in the radial network. Existing sufficient conditions for exact semidefinite relaxation are therefore applicable to unbalanced multiphase networks. In particular, they imply that if a semidefinite relaxation is exact over each of the cliques in the mesh equivalent network, then it is exact for the entire network.https://authors.library.caltech.edu/records/szyhw-g8827Convexification of AC optimal power flow
https://resolver.caltech.edu/CaltechAUTHORS:20170123-174612725
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/PSCC.2014.7038373
This overview paper summarizes the key elements of semidefinite relaxations of the optimal power flow problem, and discusses several open challenges.https://authors.library.caltech.edu/records/qy345-88r41Convex relaxations and linear approximation for optimal power flow in multiphase radial networks
https://resolver.caltech.edu/CaltechAUTHORS:20170810-114020714
Authors: {'items': [{'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/PSCC.2014.7038399
Distribution networks are usually multiphase and radial. To facilitate power flow computation and optimization, two semidefinite programming (SDP) relaxations of the optimal power flow problem and a linear approximation of the power flow are proposed. We prove that the first SDP relaxation is exact if and only if the second one is exact. Case studies show that the second SDP relaxation is numerically exact and that the linear approximation obtains voltages within 0.0016 per unit of their true values for the IEEE 13, 34, 37, 123-bus networks and a real-world 2065-bus network.https://authors.library.caltech.edu/records/1fcqw-beg37Advanced optimization methods for power systems
https://resolver.caltech.edu/CaltechAUTHORS:20170810-130952392
Authors: {'items': [{'id': 'Panciatici-P', 'name': {'family': 'Panciatici', 'given': 'P.'}}, {'id': 'Campi-M-C', 'name': {'family': 'Campi', 'given': 'M. C.'}}, {'id': 'Garatti-S', 'name': {'family': 'Garatti', 'given': 'S.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'S. H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Molzahn-D-K', 'name': {'family': 'Molzahn', 'given': 'D. K.'}}, {'id': 'Sun-A-X', 'name': {'family': 'Sun', 'given': 'A. X.'}}, {'id': 'Wehenkel-L', 'name': {'family': 'Wehenkel', 'given': 'L.'}}]}
Year: 2014
DOI: 10.1109/PSCC.2014.7038504
Power system planning and operation offers multitudinous opportunities for optimization methods. In practice, these problems are generally large-scale, non-linear, subject to uncertainties, and combine both continuous and discrete variables. In the recent years, a number of complementary theoretical advances in addressing such problems have been obtained in the field of applied mathematics. The paper introduces a selection of these advances in the fields of non-convex optimization, in mixed-integer programming, and in optimization under uncertainty. The practical relevance of these developments for power systems planning and operation are discussed, and the opportunities for combining them, together with high-performance computing and big data infrastructures, as well as novel machine learning and randomized algorithms, are highlighted.https://authors.library.caltech.edu/records/t0qvx-ca337Optimal load-side control for frequency regulation in smart grids
https://resolver.caltech.edu/CaltechAUTHORS:20150203-091127023
Authors: {'items': [{'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/ALLERTON.2014.7028527
Frequency control rebalances supply and demand while maintaining the network state within operational margins. It is implemented using fast ramping reserves that are expensive and wasteful, and which are expected to grow with the increasing penetration of renewables. The most promising solution to this problem is the use of demand response, i.e. load participation in frequency control. Yet it is still unclear how to efficiently integrate load participation without introducing instabilities and violating operational constraints. In this paper we present a comprehensive load-side frequency control mechanism that can maintain the grid within operational constraints. Our controllers can rebalance supply and demand after disturbances, restore the frequency to its nominal value and preserve inter-area power flows. Furthermore, our controllers are distributed (unlike generation-side), can allocate load updates optimally, and can maintain line flows within thermal limits. We prove that such a distributed load-side control is globally asymptotically stable and illustrate its convergence with simulation.https://authors.library.caltech.edu/records/k2vxs-4nb81The role of a market maker in networked Cournot competition
https://resolver.caltech.edu/CaltechAUTHORS:20170810-101313051
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Cai-Desmond-W-H', 'name': {'family': 'Cai', 'given': 'Desmond W. H.'}, 'orcid': '0000-0001-9207-1890'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2014
DOI: 10.1109/CDC.2014.7040088
We study the role of a market maker (or market operator) in a transmission constrained electricity market. We model the market as a one-shot networked Cournot competition where generators supply quantity bids and load serving entities provide downward sloping inverse demand functions. This mimics the operation of a spot market in a deregulated market structure. In this paper, we focus on possible mechanisms employed by the market maker to balance demand and supply. In particular, we consider three candidate objective functions that the market maker optimizes - social welfare, residual social welfare, and consumer surplus. We characterize the existence of Generalized Nash Equilibrium (GNE) in this setting and demonstrate that market outcomes at equilibrium can be very different under the candidate objective functions.https://authors.library.caltech.edu/records/7ak7c-qp636Optimal decentralized primary frequency control in power networks
https://resolver.caltech.edu/CaltechAUTHORS:20170123-165356940
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2014
DOI: 10.1109/CDC.2014.7039765
We augment existing generator-side primary frequency control with load-side control that are local, ubiquitous, and continuous. The mechanisms on both the generator and the load sides are decentralized in that their control decisions are functions of locally measurable frequency deviations. These local algorithms interact over the network through nonlinear power flows. We design the local frequency feedback control so that any equilibrium point of the closed-loop system is the solution to an optimization problem that minimizes the total generation cost and user disutility subject to power balance across entire network. With Lyapunov method we derive a sufficient condition for any equilibrium point of the closed-loop system to be asymptotically stable. A simulation demonstrates improvement in both the transient and steady-state performance over the traditional control only on generators, even when the total control capacity remains the same.https://authors.library.caltech.edu/records/5szw4-8t878Distributional analysis for model predictive deferrable load control
https://resolver.caltech.edu/CaltechAUTHORS:20170810-105540217
Authors: {'items': [{'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Gan-Lingwen', 'name': {'family': 'Gan', 'given': 'Lingwen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2014
DOI: 10.1109/CDC.2014.7040398
Deferrable load control is essential for handling the uncertainties associated with the increasing penetration of renewable generation. Model predictive control has emerged as an effective approach for deferrable load control, and has received considerable attention. Though the average-case performance of model predictive deferrable load control has been analyzed in prior works, the distribution of the performance has been elusive. In this paper, we prove strong concentration results on the load variation obtained by model predictive deferrable load control. These results highlight that the typical performance of model predictive deferrable load control is tightly concentrated around the average-case performance.https://authors.library.caltech.edu/records/10c4g-rc417Distributed Generator and Load-Side Secondary Frequency Control in Power Networks
https://resolver.caltech.edu/CaltechAUTHORS:20150429-072859434
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/CISS.2015.7086825
We design a distributed secondary frequency control scheme for both generators and controllable loads. The proposed scheme operates via local sensing and computation, and neighborhood communication. Equilibrium and stability
analysis of the closed-loop system is performed with a power
network model including turbines and governors of generators
and nonlinear AC power flows. After a change in power supply
or demand, the proposed scheme is able to stabilize the system, restore bus frequencies and net inter-area power exchanges, and minimize total generation cost minus user utility at equilibrium.https://authors.library.caltech.edu/records/kpymp-a2s93Distributed Algorithm for Optimal Power Flow on an Unbalanced Radial Network
https://resolver.caltech.edu/CaltechAUTHORS:20160217-095123759
Authors: {'items': [{'id': 'Peng-Qiuyu', 'name': {'family': 'Peng', 'given': 'Qiuyu'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/CDC.2015.7403309
The optimal power flow (OPF) problem is fundamental in power systems operation and planning. Large-scale renewable penetration calls for real-time feedback control, and hence the need for distributed solutions for the OPF problem. In this paper we propose a solution for an unbalanced radial distribution network. Our distributed algorithm is based on alternating direction method of multiplier (ADMM). The main idea is to exploit the tree topology of distribution networks and decompose the OPF problem in such a way that the subproblems in each ADMM macro-iteration either have closed-form solutions or reduce to eigenvalue problems whose size remains constant as the network size scales up. We present simulations on IEEE 13, 34, 37 and 123 bus unbalanced distribution network to illustrate the scalability and optimality of the proposed algorithm.https://authors.library.caltech.edu/records/bjnkn-68v07A differential analysis of the power flow equations
https://resolver.caltech.edu/CaltechAUTHORS:20160217-080729960
Authors: {'items': [{'id': 'Dvijotham-K', 'name': {'family': 'Dvijotham', 'given': 'Krishnamurthy'}, 'orcid': '0000-0002-1328-4677'}, {'id': 'Chertkov-M', 'name': {'family': 'Chertkov', 'given': 'Michael'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2015
DOI: 10.1109/CDC.2015.7402082
The AC power flow equations are fundamental in all aspects of power systems planning and operations. They are routinely solved using Newton-Raphson like methods. However, there is little theoretical understanding of when these algorithms are guaranteed to find a solution of the power flow equations or how long they may take to converge. Further, it is known that in general these equations have multiple solutions and can exhibit chaotic behavior. In this paper, we show that the power flow equations can be solved efficiently provided that the solution lies in a certain set. We introduce a family of convex domains, characterized by Linear Matrix Inequalities, in the space of voltages such that there is at most one power flow solution in each of these domains. Further, if a solution exists in one of these domains, it can be found efficiently, and if one does not exist, a certificate of non-existence can also be obtained efficiently. The approach is based on the theory of monotone operators and related algorithms for solving variational inequalities involving monotone operators. We validate our approach on IEEE test networks and show that practical power flow solutions lie within an appropriately chosen convex domain.https://authors.library.caltech.edu/records/f16pb-7ff49A unified framework for frequency control and congestion management
https://resolver.caltech.edu/CaltechAUTHORS:20160823-102449874
Authors: {'items': [{'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Bialek-J', 'name': {'family': 'Bialek', 'given': 'Janusz'}}]}
Year: 2016
DOI: 10.1109/PSCC.2016.7541028
The existing frequency control framework in power systems is challenged by lower inertia and more volatile power injections. We propose a new framework for frequency control and congestion management. We formulate an optimization problem that rebalances power, restores the nominal frequency, restores inter-area flows and maintains line flows below their limits in a way that minimizes the control cost. The cost can be squared deviations from the reference generations, minimizing the disruption from the last optimal dispatch. Our control thus maintains system security without interfering with the market operation. By deriving a primal-dual algorithm to solve this optimization, we design a completely decentralized primary frequency control without the need for explicit communication among the participating agents, and a distributed unified control which integrates primary and secondary frequency control and congestion management. Simulations show that the unified control not only achieves all the desired control goals in system equilibrium, but also improves the transient compared to traditional control schemes.https://authors.library.caltech.edu/records/9qbcj-wfm82Real-Time Recommendation Algorithm of Battery Swapping Stations for Electric Taxis
https://resolver.caltech.edu/CaltechAUTHORS:20161117-095916202
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Yang-Zaiyue', 'name': {'family': 'Yang', 'given': 'Zaiyue'}, 'orcid': '0000-0002-8288-3833'}, {'id': 'Zhang-Yongmin', 'name': {'family': 'Zhang', 'given': 'Yongmin'}}, {'id': 'Fu-Lingkun', 'name': {'family': 'Fu', 'given': 'Lingkun'}}]}
Year: 2016
DOI: 10.1109/PESGM.2016.7741620
This paper proposes a real-time algorithm that recommends battery swapping stations (BSSs) to electric taxis (ETs) that need their batteries swapped. The algorithm takes into consideration available batteries at BSSs, driving ranges of ETs and the current traffic conditions, etc, in order to avoid long queues at BSSs. We consider a basic model that assumes past decisions are perfectly executed, and formulate an optimal ET-to-BSS assignment problem. This problem is an integer program and therefore hard to scale. For real-time implementation, we approximate the optimal assignment problem by a repeated potential game and propose an iterative best response algorithm to compute ET-to-BSS assignments. Preliminary numerical results suggest that our heuristic algorithm solves the optimal assignment problem approximately.https://authors.library.caltech.edu/records/a12q9-51s14Optimal charging schedule for a battery switching station serving electric buses
https://resolver.caltech.edu/CaltechAUTHORS:20170616-102356802
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Yang-Zaiyue', 'name': {'family': 'Yang', 'given': 'Zaiyue'}, 'orcid': '0000-0002-8288-3833'}, {'id': 'Zhang-Yongmin', 'name': {'family': 'Zhang', 'given': 'Yongmin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}]}
Year: 2016
DOI: 10.1109/PESGM.2016.7741397
We propose a model of a battery switching station (BSS) for electric buses (EBs) that captures the predictability of bus operation. We schedule battery charging in the BSS so that every EB arrives to find a battery ready for switching. We develop an efficient algorithm to compute an optimal schedule. It uses dual decomposition to decouple the charging decisions at different charging boxes so that independent subproblems can be solved in parallel at individual charging boxes, making the algorithm inherently scalable as the size of the BSS grows. We propose a direct projection method that solves these subproblems rapidly. Numerical results illustrate that the proposed approach is far more efficient and scalable than generic algorithms and existing solvers.https://authors.library.caltech.edu/records/qck3j-rv138Monotone operator approach to power flow solutions
https://resolver.caltech.edu/CaltechAUTHORS:20170810-111302484
Authors: {'items': [{'id': 'Dvijotham-K', 'name': {'family': 'Dvijotham', 'given': 'Krishnamurthy'}, 'orcid': '0000-0002-1328-4677'}, {'id': 'Chertkov-M', 'name': {'family': 'Chertkov', 'given': 'Michael'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/ACC.2016.7525174
The AC power flow equations underlie all operational aspects of power systems. In this paper, Here we solve this problem using the theory of monotone operators. We show that it is possible to characterize a "contractivity domain" in the power flow variables (voltage magnitudes and phases). The construction of these domains depends on the specific representation chosen for the power flow equations, so that different representations lead to different domains. Given this domain, there is a simple efficient algorithm that will either find a solution in the domain, or certify that no solutions exist in it. We validate the approach on several IEEE test cases.https://authors.library.caltech.edu/records/vk8eg-25q59Demand response with capacity constrained supply function bidding
https://resolver.caltech.edu/CaltechAUTHORS:20170615-105827991
Authors: {'items': [{'id': 'Xu-Yunjian', 'name': {'family': 'Xu', 'given': 'Yunjian'}}, {'id': 'Li-Na', 'name': {'family': 'Li', 'given': 'Na'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/PESGM.2016.7741247
We study the problem faced by an operator who aims to allocate a certain amount of load adjustment (either load reduction or increment) to multiple consumers so as to minimize the aggregate consumer disutility. We propose and analyze a simple uniform-price market mechanism where every consumer submits a single bid to choose a supply function from a group of parameterized ones. These parameterized supply functions are designed to ensure that every consumer's load adjustment is within an exogenous capacity limit that is determined by the current power system operating condition. We show that the proposed mechanism yields bounded efficiency loss at a Nash equilibrium. In particular, the proposed mechanism is shown to achieve approximate social optimality at a Nash equilibrium, if the total capacity of all consumers (excluding the consumer with the largest capacity) is much larger than the total amount of load to be adjusted. We complement our analysis through numerical case studies.https://authors.library.caltech.edu/records/a1pm0-4gv67The role of strong convexity-concavity in the convergence and robustness of the saddle-point dynamics
https://resolver.caltech.edu/CaltechAUTHORS:20170217-154230896
Authors: {'items': [{'id': 'Cherukuri-A', 'name': {'family': 'Cherukuri', 'given': 'Ashish'}, 'orcid': '0000-0002-7609-5080'}, {'id': 'Mallada-E', 'name': {'family': 'Mallada', 'given': 'Enrique'}, 'orcid': '0000-0003-1568-1833'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Cortés-J', 'name': {'family': 'Cortés', 'given': 'Jorge'}}]}
Year: 2016
DOI: 10.1109/ALLERTON.2016.7852273
This paper studies the projected saddle-point dynamics for a twice differentiable convex-concave function, which we term saddle function. The dynamics consists of gradient descent of the saddle function in variables corresponding to convexity and (projected) gradient ascent in variables corresponding to concavity. We provide a novel characterization of the omega-limit set of the trajectories of these dynamics in terms of the diagonal Hessian blocks of the saddle function. Using this characterization, we establish global asymptotic convergence of the dynamics under local strong convexity-concavity of the saddle function. If this property is global, and for the case when the saddle function takes the form of the Lagrangian of an equality constrained optimization problem, we establish the input-to-state stability of the saddle-point dynamics by providing an ISS Lyapunov function. Various examples illustrate our results.https://authors.library.caltech.edu/records/mebm6-zf506Optimal placement of energy storage in distribution networks
https://resolver.caltech.edu/CaltechAUTHORS:20170111-145514472
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2016
DOI: 10.1109/CDC.2016.7798759
We study the problem of optimally placing energy storage devices in distribution networks to minimize total energy loss, focusing on structural results. We use a continuous linearized branch-flow model to model the distribution network. For the special case of a linear network, modeling a main feeder, we explicitly derive the optimal solution when all loads have the same shape and prove several useful monotonicity properties of the optimal solution. We illustrate through simulations that these structural properties hold approximately also on radial networks modeled by standard discrete nonlinear power flow models and even when loads have different shapes. We discuss how these structural results provide insight for the planning of energy storage devices.https://authors.library.caltech.edu/records/1etyk-65845Decentralized Optimal Frequency Control of Interconnected Power Systems with Transient Constraints
https://resolver.caltech.edu/CaltechAUTHORS:20170111-135813725
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2016
DOI: 10.1109/CDC.2016.7798345
We design decentralized frequency control of multi-area power systems that will re-balance power and drive frequencies to their nominal values after a disturbance. Both generators and controllable loads are utilized to achieve frequency stability while minimizing regulation cost. In contrast to recent results, the design is completely decentralized and does not require communication between areas. Our control enforces operational constraints not only in equilibrium but also during transient. Moreover, our control is capable of adapting to unknown load disturbance. We show that the closed-loop system is asymptotically stable and converges to an equilibrium that minimizes the regulation cost. We present simulation results to demonstrate the effectiveness of our design.https://authors.library.caltech.edu/records/0h1k9-nza14Adaptive charging network for electric vehicles
https://resolver.caltech.edu/CaltechAUTHORS:20170811-093351619
Authors: {'items': [{'id': 'Lee-George', 'name': {'family': 'Lee', 'given': 'George'}}, {'id': 'Lee-Ted', 'name': {'family': 'Lee', 'given': 'Ted'}}, {'id': 'Low-Zhi-H', 'name': {'family': 'Low', 'given': 'Zhi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Ortega-C', 'name': {'family': 'Ortega', 'given': 'Christine'}}]}
Year: 2016
DOI: 10.1109/GlobalSIP.2016.7905971
We describe a snapshot of an adaptive charging network (ACN) for electric vehicles at Caltech. We overview the system design, from the power distribution system to advanced charger design to control and communication system and the software system that integrates the overall network. We present a simple mathematical formulation of the charging problem. We have collected three months' of baseline charging data from the Caltech ACN. We demonstrate, by simulating a charging algorithm on the baseline data, the large potential benefit of ACN in saving infrastructure costs.https://authors.library.caltech.edu/records/6qqbz-5vk54Real-time OPF based on quasi-Newton methods
https://resolver.caltech.edu/CaltechAUTHORS:20170517-151532951
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Dvijotham-K', 'name': {'family': 'Dvijotham', 'given': 'Krishnamurthy'}, 'orcid': '0000-0002-1328-4677'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CISS.2017.7926163
Optimal power flow is a central problem in the operation of power systems. So far the majority of the literature deals with offline algorithms for traditional applications, but the proliferation of distributed energy resources and smart appliances in power networks motivates real-time and scalable algorithms. We introduce a real-time OPF algorithm based on quasi-Newton methods that can track the optimal operation when the state of the network is changing. Theory and simulations show that the proposed algorithm has guaranteed tracking performance and is computationally efficient.https://authors.library.caltech.edu/records/yq9ka-f2127Smoothed Least-laxity-first Algorithm for EV Charging
https://resolver.caltech.edu/CaltechAUTHORS:20170515-140123828
Authors: {'items': [{'id': 'Nakahira-Yorie', 'name': {'family': 'Nakahira', 'given': 'Yorie'}, 'orcid': '0000-0003-3324-4602'}, {'id': 'Chen-Niangjun', 'name': {'family': 'Chen', 'given': 'Niangjun'}, 'orcid': '0000-0002-2289-9737'}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1145/3077839.3077864
We formulate EV charging as a feasibility problem that meets all EVs' energy demands before departure under charging rate constraints and total power constraint. We propose an online algorithm, the smoothed least-laxity-first (sLLF) algorithm, that decides on the current charging rates based on only the information up to the current time. We characterize the performance of the sLLF algorithm analytically and numerically. Numerical experiments with real-world data show that it has significantly higher rate of generating feasible EV charging than several other common EV charging algorithms.https://authors.library.caltech.edu/records/1gjze-jr229Event detection and localization in distribution grids with phasor measurement units
https://resolver.caltech.edu/CaltechAUTHORS:20180208-150455146
Authors: {'items': [{'id': 'Ardakanian-O', 'name': {'family': 'Ardakanian', 'given': 'Omid'}, 'orcid': '0000-0002-6711-5502'}, {'id': 'Yuan-Ye', 'name': {'family': 'Yuan', 'given': 'Ye'}, 'orcid': '0000-0001-7858-0437'}, {'id': 'Dobbe-R', 'name': {'family': 'Dobbe', 'given': 'Roel'}, 'orcid': '0000-0003-4633-7023'}, {'id': 'von-Meier-A', 'name': {'family': 'von Meier', 'given': 'Alexandra'}, 'orcid': '0000-0003-4675-752X'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Tomlin-C', 'name': {'family': 'Tomlin', 'given': 'Claire'}}]}
Year: 2017
DOI: 10.1109/PESGM.2017.8273895
The recent introduction of synchrophasor technology into power distribution systems has given impetus to various monitoring, diagnostic, and control applications, such as system identification and event detection, which are crucial for restoring service, preventing outages, and managing equipment health. Drawing on the existing framework for inferring topology and admittances of a power network from voltage and current phasor measurements, this paper proposes an online algorithm for event detection and localization in unbalanced three-phase distribution systems. Using a convex relaxation and a matrix partitioning technique, the proposed algorithm is capable of identifying topology changes and attributing them to specific categories of events. The performance of this algorithm is evaluated on a standard test distribution feeder with synthesized loads, and it is shown that a tripped line can be detected and localized in an accurate and timely fashion, highlighting its potential for real-world applications.https://authors.library.caltech.edu/records/py6df-w6k87Optimal Online Adaptive Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20180209-075953281
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Erliksson-K-F', 'name': {'family': 'Erliksson', 'given': 'Karl F.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/PESGM.2017.8274166
We propose an online linear program (OLP) based algorithm for scheduling electric vehicle (EV) charging. To determine the charging rates in each control period, OLP solves a linear program based only on EVs currently in the charging facility, assuming no future EV arrivals. We prove that OLP achieves the offline optimal where all future EV arrivals are assumed to be known in advance, provided the cost coefficients are uniformly monotone. For general cost functions, we prove that the competitive ratio is upper bounded by the variability in the cost coefficients. We demonstrate the performance of OLP using real charging data from Google and Caltech's Adaptive Charging Network.https://authors.library.caltech.edu/records/15bpb-0ct28Monotonicity Properties and Spectral Characterization of Power Redistribution in Cascading Failures
https://resolver.caltech.edu/CaltechAUTHORS:20180125-135003175
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/ALLERTON.2017.8262836
In this work, we apply spectral graph theory methods to study the monotonicity and structural properties of power redistribution in a cascading failure process. We demonstrate that in contrast to the lack of monotonicity in physical domain, there is a rich collection of monotonicity one can explore in the spectral domain, leading to a systematic way to define topological metrics that are monotonic. It is further shown that many useful quantities in cascading failure analysis can be unified into a spectral inner product, which itself is related to graphical properties of the transmission network. Such graphical interpretations precisely capture the Kirchhoff's law expressed in terms of graph structural properties and gauge the impact of a line when it is tripped. We illustrate that our characterization leads to a tree-partition of the network so that failure cascading can be localized.https://authors.library.caltech.edu/records/hwwv8-eb206System Level Synthesis: A Tutorial
https://resolver.caltech.edu/CaltechAUTHORS:20180126-080200870
Authors: {'items': [{'id': 'Doyle-J-C', 'name': {'family': 'Doyle', 'given': 'John C.'}, 'orcid': '0000-0002-1828-2486'}, {'id': 'Matni-N', 'name': {'family': 'Matni', 'given': 'Nikolai'}, 'orcid': '0000-0003-4936-3921'}, {'id': 'Wang-Yuh-Shyang', 'name': {'family': 'Wang', 'given': 'Yuh-Shyang'}, 'orcid': '0000-0001-7357-7247'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CDC.2017.8264074
This tutorial paper provides an overview of the System Level Approach to control synthesis; a scalable framework for large-scale distributed control. The system level approach is composed of three central components: System Level Parameterizations (SLPs), System Level Constraints (SLCs) and System Level Synthesis (SLP) problems. We describe how the combination of these elements parameterize the largest known class of constrained controllers that admit a convex formulation.https://authors.library.caltech.edu/records/c5bs6-ncw54Spectral Characterization of Controllability and Observability for Frequency Regulation Dynamics
https://resolver.caltech.edu/CaltechAUTHORS:20180126-083110449
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CDC.2017.8264611
We give a full characterization using spectral graph theory of the controllability and observability of the swing and power flow dynamics in frequency regulation. In particular, we show that the controllability/observability of the system depends on two orthogonal conditions: 1) intrinsic structure of the system graph 2) algebraic coverage of buses with controllable loads/sensors. Condition 1) encodes information on graph symmetry and is shown to hold for almost all practical systems. Condition 2) captures how buses interact with each other through the network and can be verified using the eigenvectors of the graph Laplacian matrix. Based on this framework, the optimal placement of controllable loads and sensors in the network can be formulated as a set cover problem. We demonstrate how our results identify the critical buses in real systems by performing simulation in the IEEE 39-bus New England interconnection test system. We show that for this testbed, a single well chosen bus is capable of providing full controllability/observability.https://authors.library.caltech.edu/records/3kkv8-ayb51Distributed Algorithm for Time-varying Optimal Power Flow
https://resolver.caltech.edu/CaltechAUTHORS:20180126-083431585
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2017
DOI: 10.1109/CDC.2017.8264138
Future power system applications may require real-time optimization of a large network of distributed energy resources. This has motivated recent development of online algorithms for solving time-varying optimal power flow problems. We have proposed a centralized quasi-Newton algorithm and have derived theoretical guarantees for its tracking performance. In this paper we show how this algorithm can be implemented in a distributed manner by a network of controllable energy resources coordinated by an operator. The proposed distributed implementation now can handle general convex quadratic constraints on power injections, and only requires minimal communication between the operator and local controllers. Simulation shows that the proposed distributed implementation has good performance.https://authors.library.caltech.edu/records/cv55z-8d480Battery Swapping Assignment for Electric Vehicles: A Bipartite Matching Approach
https://resolver.caltech.edu/CaltechAUTHORS:20180126-075222317
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Sun-Youxian', 'name': {'family': 'Sun', 'given': 'Youxian'}}]}
Year: 2017
DOI: 10.1109/CDC.2017.8263853
This paper formulates an optimal station assignment problem for electric vehicle (EV) battery swapping that takes into account both temporal and spatial couplings. The goal is to reduce the total EV cost and station congestion due to temporary shortage in supply of available batteries. We show that the problem is reducible to the minimum weight perfect bipartite matching problem. This leads to an efficient solution based on the Hungarian algorithm. Numerical results suggest that the proposed solution provides a significant improvement over a greedy heuristic that assigns nearest stations to EVs.https://authors.library.caltech.edu/records/h2fy8-vbr82Combating Bufferbloat in Multi-Bottleneck Networks: Equilibrium, Stability, and Algorithms
https://resolver.caltech.edu/CaltechAUTHORS:20181023-103508493
Authors: {'items': [{'id': 'Ye-Jiancheng', 'name': {'family': 'Ye', 'given': 'Jiancheng'}, 'orcid': '0000-0002-1296-171X'}, {'id': 'Leung-Ka-Cheong', 'name': {'family': 'Leung', 'given': 'Ka-Cheong'}, 'orcid': '0000-0001-7999-2572'}, {'id': 'Li-Victor-O-K', 'name': {'family': 'Li', 'given': 'Victor O. K.'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/INFOCOM.2018.8486251
Bufferbloat is a phenomenon where router buffers are constantly being filled, resulting in high queueing delay and delay variation. Larger buffer size and more delay-sensitive applications on the Internet have made this phenomenon a pressing issue. Active queue management (AQM) algorithms, which play an important role in combating bufferbloat, have not been widely deployed due to complicated manual parameter tuning. Moreover, AQM algorithms are often designed and analyzed based on models with a single bottleneck link, rendering their performance and stability unclear in multi-bottleneck networks. In this paper, we propose a general framework to combat bufferbloat in multi-bottleneck networks. We first conduct an equilibrium analysis for a general multi-bottleneck TCP/ AQM system and develop an algorithm to compute the equilibrium point. We then decompose the system into single-bottleneck subsystems and derive sufficient conditions for the local asymptotic stability of the subsystems. Using the proposed framework, we present a case study to analyze the stability of the recently proposed Controlled Delay (CoDel) in multi-bottleneck networks and devise Self-tuning CoDel to improve the system stability and performance. Extensive simulation results show that Self-tuning CoDel effectively stabilizes queueing delay in multi-bottleneck scenarios, and thus contributes to combating bufferbloat.https://authors.library.caltech.edu/records/zad0y-v8j28Efficient Online Station Assignment for EV Battery Swapping
https://resolver.caltech.edu/CaltechAUTHORS:20180529-104115111
Authors: {'items': [{'id': 'You-Pengcheng', 'name': {'family': 'You', 'given': 'Pengcheng'}, 'orcid': '0000-0003-1532-8773'}, {'id': 'Cheng-Peng', 'name': {'family': 'Cheng', 'given': 'Peng'}}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John Z. F.'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1145/3208903.3212032
This paper investigates the online station assignment for (commercial) electric vehicles (EVs) that make battery swapping requests to a central operator, with the aim of minimizing cost to EVs and congestion at service stations. Inspired by a polynomial-time solvable offline solution via a bipartite matching approach, we develop an efficient online station assignment algorithm that provably achieves a tight (optimal) competitive ratio under mild conditions.https://authors.library.caltech.edu/records/8w8sn-pxw38Disaggregation for Networked Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20181102-085439162
Authors: {'items': [{'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.23919/PSCC.2018.8442521
Electricity data such as supply, demand, prices, and line flows, are sensitive. Utility companies, understandably do not want to, in fact often cannot, make this data publicly available. However, such data is critical in many fundamental areas in power systems research. As a compromise, aggregated data sets are sometimes made available. In such a setting it may be the case that data is aggregated over a geographical region and time. This forces researchers to try and "invert" the data to obtain dis aggregated data sets. In this paper we rigorously formulate the disaggregation problem for networked power systems and present two algorithms that provide solutions to the DC version of the problem. We show that it is possible to invert the data, but that does not imply that ground truth solutions are obtained, thus the utility companies maintain a notion of privacy. The aim of this paper is to highlight the potential benefits to both the research community and utility companies of releasing aggregated data.https://authors.library.caltech.edu/records/r7dvm-95871Cyber Network Design for Secondary Frequency Regulation: A Spectral Approach
https://resolver.caltech.edu/CaltechAUTHORS:20180906-143422101
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.23919/PSCC.2018.8442814
We present a preliminary theoretical framework based on spectral graph theory that captures how the cyber topology of a distributed secondary frequency control scheme impacts the stability, optimality, and transient performance of our power system as a cyber-physical network. We show that a collection of polynomials defined in terms of the cyber and physical Laplacian eigenvalues encode information on the interplay between cyber and physical networks. It is demonstrated that to understand the impact of adding cyber connectivity, one should separate the low-damping and high-damping regimes. Although adding cyber connectivity always improves the performance for high-damping systems, it is not the case for low-damping scenarios. Based on the theoretical study, we discuss how a good cyber network should be designed. Our empirical study shows that for practical systems, the number of communication channels that is needed to achieve near-optimal performance is usually less than twice the number of buses.https://authors.library.caltech.edu/records/7cwt2-6p715Profit-Maximizing Planning and Control of Battery Energy Storage Systems for Primary Frequency Control
https://resolver.caltech.edu/CaltechAUTHORS:20190104-140522282
Authors: {'items': [{'id': 'Zhang-Angela-Yingjun', 'name': {'family': 'Zhang', 'given': 'Angela Yingjun'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Tang-Wanrong', 'name': {'family': 'Tang', 'given': 'Wanrong'}}]}
Year: 2018
DOI: 10.1109/pesgm.2018.8586290
We consider a two-level profit-maximizing strategy, including planning and control, for battery energy storage system (BESS) owners that participate in the primary frequency control (PFC) market. Specifically, the optimal BESS control minimizes the operating cost by keeping the state of charge (SoC) in an optimal range. Through rigorous analysis, we prove that the optimal BESS control is a "state-invariant" strategy in the sense that the optimal SoC range does not vary with the state of the system. As such, the optimal control strategy can be computed offline once and for all with very low complexity. Regarding the BESS planning, we prove that the the minimum operating cost is a decreasing convex function of the BESS energy capacity. This leads to the optimal BESS sizing that strikes a balance between the capital investment and operating cost. Our work here provides a useful theoretical framework for understanding the planning and control strategies that maximize the economic benefits of BESSs in ancillary service markets.https://authors.library.caltech.edu/records/8fsct-8gh48Distributed Frequency Control with Operational Constraints, Part II: Network Power Balance
https://resolver.caltech.edu/CaltechAUTHORS:20190104-142158857
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2018
DOI: 10.1109/pesgm.2018.8586037
In Part I of this paper we propose a decentralized optimal frequency control of multi-area power system with operational constraints, where the tie-line powers remain unchanged in the steady state and the power mismatch is balanced within individual control areas. In Part II of the paper, we propose a distributed controller for optimal frequency control in the network power balance case, where the power mismatch is balanced over the whole system. With the proposed controller, the tie-line powers remain within the acceptable range at equilibrium, while the regulation capacity constraints are satisfied both at equilibrium and during transient. It is revealed that the closed-loop system with the proposed controller carries out primal-dual updates with saturation for solving an associated optimization problem. To cope with discontinuous dynamics of the closed-loop system, we deploy the invariance principle for nonpathological Lyapunov function to prove its asymptotic stability. Simulation results are provided to show the effectiveness of our controller.https://authors.library.caltech.edu/records/2r1bj-9d227Some Emerging Challenges in Electricity Markets
https://resolver.caltech.edu/CaltechAUTHORS:20180925-152901176
Authors: {'items': [{'id': 'Bose-Subhonmesh', 'name': {'family': 'Bose', 'given': 'Subhonmesh'}, 'orcid': '0000-0002-3445-4479'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1007/978-3-319-98310-3_2
Energy deregulation in the 90s led to the development of power markets in the United States. The Public Utilities Regulatory Policies Act (PURPA) in 1978 laid down the early foundations of deregulation. Subsequent legislations included the Energy Policy Act of 1992 (EPAct92) and FERC Order No. 888 in 1996. They established the rules to "remove impediments to competition in the wholesale bulk power marketplace" by promoting "non-discriminatory transmission services" [1]. These legislations led to the development of two different market architectures in different parts of the US. In one, utility companies established a bilateral market to transact with independent power producers and/or other utilities. In others, a third-party nonprofit facilitator—an Independent System Operator (ISO) or a Regional Transmission Organization (RTO)—was established to mediate between the buyers and the sellers of power at the wholesale level. Our discussion in this article will primarily revolve around the latter.https://authors.library.caltech.edu/records/x1rhb-bz413Large-Scale Adaptive Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20190104-154430902
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Chang-Daniel', 'name': {'family': 'Chang', 'given': 'Daniel'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Lee-George-S', 'name': {'family': 'Lee', 'given': 'George S.'}}, {'id': 'Lee-Rand', 'name': {'family': 'Lee', 'given': 'Rand'}}, {'id': 'Lee-Ted', 'name': {'family': 'Lee', 'given': 'Ted'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/smartgridcomm.2018.8587550
Large-scale charging infrastructure will play an important role in supporting the adoption of electric vehicles. In this paper, we address the prohibitively high capital cost of installing large numbers of charging stations within a parking facility by oversubscribing key pieces of electrical infrastructure. We describe a unique physical testbed for large-scale, high- density EV charging research which we call the Adaptive Charging Network (ACN). We describe the architecture of the ACN including its hardware and software components. We also present a practical framework for online scheduling, which is based on model predictive control and convex optimization. Based on our experience with practical EV charging systems, we introduce constraints to the EV charging problem which have not been considered in the literature, such as those imposed by unbalanced three-phase infrastructure. We use simulations based on real data collected from the ACN to illustrate the trade-offs involved in selecting models for infrastructure constraints and accounting for non-ideal charging behavior.https://authors.library.caltech.edu/records/yvb0d-sqe61Large-Scale Adaptive Electric Vehicle Charging
https://resolver.caltech.edu/CaltechAUTHORS:20190228-160214269
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Chang-Daniel', 'name': {'family': 'Chang', 'given': 'Daniel'}}, {'id': 'Jin-Cheng', 'name': {'family': 'Jin', 'given': 'Cheng'}}, {'id': 'Lee-George-S', 'name': {'family': 'Lee', 'given': 'George S.'}}, {'id': 'Lee-Rand', 'name': {'family': 'Lee', 'given': 'Rand'}}, {'id': 'Lee-Ted', 'name': {'family': 'Lee', 'given': 'Ted'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/GlobalSIP.2018.8646472
Large-scale charging infrastructure will play an important role in supporting the adoption of electric vehicles. In this extended abstract, we describe a unique physical testbed for large-scale, high-density EV charging research which we call the Adaptive Charging Network (ACN). We describe the architecture of the ACN including its hardware and software components. We also present a practical framework for online scheduling, which is based on model predictive control and convex optimization. We use simulations based on real data collected from the ACN to illustrate the trade-offs involved in accounting for non-ideal charging behavior.https://authors.library.caltech.edu/records/4y0cd-7e894Graph Laplacian Spectrum and Primary Frequency Regulation
https://resolver.caltech.edu/CaltechAUTHORS:20190204-110323666
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/CDC.2018.8619252
We present a framework based on spectral graph theory that captures the interplay among network topology, system inertia, and generator and load damping in determining the overall grid behavior and performance. Specifically, we show that the impact of network topology on a power system can be quantified through the network Laplacian eigenvalues, and such eigenvalues determine the grid robustness against low frequency disturbances. Moreover, we can explicitly decompose the frequency signal along scaled Laplacian eigenvectors when damping-inertia ratios are uniform across buses. The insight revealed by this framework partially explains why load-side participation in frequency regulation not only makes the system respond faster, but also helps lower the system nadir after a disturbance. Finally, by presenting a new controller specifically tailored to suppress high frequency disturbances, we demonstrate that our results can provide useful guidelines in the controller design for load-side primary frequency regulation. This improved controller is simulated on the IEEE 39-bus New England interconnection system to illustrate its robustness against high frequency oscillations compared to both the conventional droop control and a recent controller design.https://authors.library.caltech.edu/records/ezh7h-8fd72Failure Localization in Power Systems via Tree Partitions
https://resolver.caltech.edu/CaltechAUTHORS:20190201-135634765
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zocca-A', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2018
DOI: 10.1109/cdc.2018.8619562
Cascading failures in power systems propagate non-locally, making the control and mitigation of outages extremely hard. In this work, we use the emerging concept of the tree partition of transmission networks to provide an analytical characterization of line failure localizability in transmission systems. Our results rigorously establish the well perceived intuition in power community that failures cannot cross bridges, and reveal a finer-grained concept that encodes more precise information on failure propagations within tree-partition regions. Specifically, when a non-bridge line is tripped, the impact of this failure only propagates within well-defined components, which we refer to as cells, of the tree partition defined by the bridges. In contrast, when a bridge line is tripped, the impact of this failure propagates globally across the network, affecting the power flow on all remaining transmission lines. This characterization suggests that it is possible to improve the system robustness by temporarily switching off certain transmission lines, so as to create more, smaller components in the tree partition; thus spatially localizing line failures and making the grid less vulnerable to large-scale outages. We illustrate this approach using the IEEE 118-bus test system and demonstrate that switching off a negligible portion of transmission lines allows the impact of line failures to be significantly more localized without substantial changes in line congestion.https://authors.library.caltech.edu/records/76deq-fe812A Feedback-Based Regularized Primal-Dual Gradient Method for Time-Varying Nonconvex Optimization
https://resolver.caltech.edu/CaltechAUTHORS:20190204-111158128
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': "Dall'Anese-E", 'name': {'family': "Dall'Anese", 'given': 'Emiliano'}}, {'id': 'Bernstein-A', 'name': {'family': 'Bernstein', 'given': 'Andrey'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2018
DOI: 10.1109/CDC.2018.8619225
This paper considers time-varying nonconvex optimization problems, utilized to model optimal operational trajectories of systems governed by possibly nonlinear physical or logical models. Algorithms for tracking a Karush-Kuhn-Tucker point are synthesized, based on a regularized primal-dual gradient method. In particular, the paper proposes a feedback-based primal-dual gradient algorithm, where analytical models for system state or constraints are replaced with actual measurements. When cost and constraint functions are twice continuously differentiable, conditions for the proposed algorithms to have bounded tracking error are derived, and a discussion of their practical implications is provided. Illustrative numerical simulations are presented for an application in power systems.https://authors.library.caltech.edu/records/za34x-x0j92ACN-Sim: An Open-Source Simulator for Data-Driven Electric Vehicle Charging Research
https://resolver.caltech.edu/CaltechAUTHORS:20190614-091204247
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary'}}, {'id': 'Johansson-D', 'name': {'family': 'Johansson', 'given': 'Daniel'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1145/3307772.3330170
Electric vehicles have recently garnered significant attention in the research community due to their potential has a large, highly controllable load which can be used in demand response, load shaping, and renewable energy integration. However, research into practical charging algorithms has been hampered by the lack of a widely available, realistic simulation environment. To meet this need in the community, we are releasing ACN-Sim, a data-driven, open-source simulator based on our experience building and operating real-world charging systems. This simulator provides researchers who may lack access to real EV charging systems with a realistic environment to evaluate their algorithms and test their assumptions. It also provides a common platform on which algorithms can be evaluated head-to-head, allowing researchers to better understand and articulate how their work fits into the existing literature.https://authors.library.caltech.edu/records/ycfa4-mw888ACN-Data: Analysis and Applications of an Open EV Charging Dataset
https://resolver.caltech.edu/CaltechAUTHORS:20190614-091205559
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1145/3307772.3328313
We are releasing ACN-Data, a dynamic dataset of workplace EV charging which currently includes over 30,000 sessions with more added daily. In this paper we describe the dataset, as well as some interesting user behavior it exhibits. To demonstrate the usefulness of the dataset, we present three examples, learning and predicting user behavior using Gaussian mixture models, optimally sizing on-site solar generation for adaptive electric vehicle charging, and using workplace charging to smooth the net demand Duck Curve.https://authors.library.caltech.edu/records/yvh76-f6d35Differential Privacy of Aggregated DC Optimal Power Flow Data
https://resolver.caltech.edu/CaltechAUTHORS:20190626-153106599
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.48550/arXiv.1903.11237
We consider the problem of privately releasing aggregated network statistics obtained from solving a DC optimal power flow (OPF) problem. It is shown that the mechanism that determines the noise distribution parameters are linked to the topology of the power system and the monotonicity of the network. We derive a measure of "almost" monotonicity and show how it can be used in conjunction with a linear program in order to release aggregated OPF data using the differential privacy framework.https://authors.library.caltech.edu/records/cwcrk-zzr18Compositional Set Invariance in Network Systems with Assume-Guarantee Contracts
https://resolver.caltech.edu/CaltechAUTHORS:20190201-135605069
Authors: {'items': [{'id': 'Chen-Yuxiao', 'name': {'family': 'Chen', 'given': 'Yuxiao'}, 'orcid': '0000-0001-5276-7156'}, {'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Kalsi-Karan', 'name': {'family': 'Kalsi', 'given': 'Karan'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Ames-A-D', 'name': {'family': 'Ames', 'given': 'Aaron D.'}, 'orcid': '0000-0003-0848-3177'}]}
Year: 2019
DOI: 10.23919/ACC.2019.8814437
This paper presents an assume-guarantee reasoning approach to the computation of robust invariant sets for network systems. Parameterized signal temporal logic (pSTL) is used to formally describe the behaviors of the subsystems, which we use as the template for the contract. We show that set invariance can be proved with a valid assume-guarantee contract by reasoning about individual subsystems. If a valid assume-guarantee contract with monotonic pSTL template is known, it can be further refined by value iteration. When such a contract is not known, an epigraph method is proposed to solve for a contract that is valid, -an approach that has linear complexity for a sparse network. A microgrid example is used to demonstrate the proposed method. The simulation result shows that together with control barrier functions, the states of all the subsystems can be bounded inside the individual robust invariant sets.https://authors.library.caltech.edu/records/875b0-fjn33Distributed Optimal Frequency Control Considering a Nonlinear Network-Preserving Model
https://resolver.caltech.edu/CaltechAUTHORS:20200210-125626205
Authors: {'items': [{'id': 'Wang-Zhaojian', 'name': {'family': 'Wang', 'given': 'Zhaojian'}, 'orcid': '0000-0002-4998-6339'}, {'id': 'Liu-Feng', 'name': {'family': 'Liu', 'given': 'Feng'}, 'orcid': '0000-0003-2279-2558'}, {'id': 'Pang-John-Z-F', 'name': {'family': 'Pang', 'given': 'John'}, 'orcid': '0000-0002-6485-7922'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2019
DOI: 10.1109/pesgm40551.2019.8974065
This paper addresses the distributed optimal frequency control of power systems considering a network-preserving model with nonlinear power flows and excitation voltage dynamics. Salient features of the proposed distributed control strategy are fourfold: i) nonlinearity is considered to cope with large disturbances; ii) only a part of generators are controllable; iii) no load measurement is required; iv) communication connectivity is required only for the controllable generators. To this end, benefiting from the concept of "virtual load demand", we first design the distributed controller for the controllable generators by leveraging the primal-dual decomposition technique. We then propose a method to estimate the virtual load demand of each controllable generator based on local frequencies. We derive incremental passivity conditions for the uncontrollable generators. Finally, we prove that the closed-loop system is asymptotically stable and its equilibrium attains the optimal solution to the associated economic dispatch problem. Simulations, including small and large-disturbance scenarios, are carried on the New England system, demonstrating the effectiveness of our design.https://authors.library.caltech.edu/records/45z9q-1wc55ACN-Sim: An Open-Source Simulator for Data-Driven Electric Vehicle Charging Research
https://resolver.caltech.edu/CaltechAUTHORS:20191204-131602950
Authors: {'items': [{'id': 'Lee-Zachary-J', 'name': {'family': 'Lee', 'given': 'Zachary J.'}}, {'id': 'Johansson-D', 'name': {'family': 'Johansson', 'given': 'Daniel'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/smartgridcomm.2019.8909765
Smart electric vehicle charging has recently garnered significant attention in the research community due to need to charge vast numbers of electric vehicles (EVs) economically, as well as the potential of providing grid services using EVs. However, research into practical online charging algorithms has been hampered by the lack of a widely available, realistic simulation environment in which to evaluate algorithms and test assumptions. To meet this need, we have developed ACN-Sim, a data-driven, open-source simulator based on our experience building and operating real-world charging systems. ACN-Sim provides a modular, extensible architecture which models the complexity of real charging systems, including battery charging behavior and unbalanced three-phase infrastructure. In addition, ACN-Sim integrates with a broader ecosystem of research tools for EV charging, including ACN-Data, an open dataset of EV charging sessions to provide realistic simulation scenarios, and ACN-Live, a framework for field-testing charging algorithms.https://authors.library.caltech.edu/records/p40d5-h5819Sufficient Conditions for Exact Semi-definite Relaxation of Optimal Power Flow in Unbalanced Multiphase Radial Networks
https://resolver.caltech.edu/CaltechAUTHORS:20200911-103127164
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/cdc40024.2019.9029827
This paper proves that in an unbalanced multi-phase network with a tree topology, the semi-definite programming relaxation of optimal power flow problems is exact when critical buses are not adjacent to each other. Here a critical bus either contributes directly to the cost function or is where an injection constraint is tight at optimality. Our result generalizes a sufficient condition for exact relaxation in single-phase tree networks to tree networks with arbitrary number of phases.https://authors.library.caltech.edu/records/6ny6f-f9r98Less is More: Real-time Failure Localization in Power Systems
https://resolver.caltech.edu/CaltechAUTHORS:20190626-143544929
Authors: {'items': [{'id': 'Guo-Linqi', 'name': {'family': 'Guo', 'given': 'Linqi'}}, {'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zocca-A', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2019
DOI: 10.1109/CDC40024.2019.9029393
Cascading failures in power systems exhibit nonlocal propagation patterns, which make the analysis and mitigation of failures difficult. In this work, we propose a distributed control framework inspired by the recently proposed concepts of unified controller and network tree-partition that offers strong guarantees in both the mitigation and localization of cascading failures in power systems. In this framework, the transmission network is partitioned into several control areas which are connected in a tree structure, and the unified controller is adopted by generators or controllable loads for fast timescale disturbance response. After an initial failure, the proposed strategy always prevents successive failures from happening, and regulates the system to the desired steady state where the impact of initial failures are localized as much as possible. For extreme failures that cannot be localized, the proposed framework has a configurable design, that progressively involves and coordinates more control areas for failure mitigation and, as a last resort, imposes minimal load shedding. We compare the proposed control framework with Automatic Generation Control (AGC) on the IEEE 118-bus test system. Simulation results show that our novel framework greatly improves the system robustness in terms of the N - 1 security standard, and localizes the impact of initial failures in majority of the load profiles that are examined. Moreover, the proposed framework incurs significantly less load loss, if any, compared to AGC.https://authors.library.caltech.edu/records/pqhxh-6sk78Learning Graph Parameters from Linear Measurements: Fundamental Trade-offs and Application to Electric Grids
https://resolver.caltech.edu/CaltechAUTHORS:20200915-153320598
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Werner-Lucien', 'name': {'family': 'Werner', 'given': 'Lucien'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/cdc40024.2019.9029949
We consider a specific graph learning task: reconstructing a symmetric matrix that represents an underlying graph using linear measurements. We study fundamental trade-offs between the number of measurements (sample complexity), the complexity of the graph class, and the probability of error by first deriving a necessary condition (fundamental limit) on the number of measurements. Then, by considering a two-stage recovery scheme, we give a sufficient condition for recovery. In the special cases of the uniform distribution on trees with n nodes and the Erdös-Rényi (n, p) class, the sample complexity derived from the fundamental trade-offs is tight up to multiplicative factors. In addition, we design and implement a polynomial-time (in n) algorithm based on the two-stage recovery scheme. Simulations for several canonical graph classes and IEEE power system test cases demonstrate the effectiveness of the proposed algorithm for accurate topology and parameter recovery.https://authors.library.caltech.edu/records/fmwp0-rn435A Second-Order Saddle Point Method for Time-Varying Optimization
https://resolver.caltech.edu/CaltechAUTHORS:20200911-133139018
Authors: {'items': [{'id': 'Tang-Yujie', 'name': {'family': 'Tang', 'given': 'Yujie'}, 'orcid': '0000-0002-4921-8372'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2019
DOI: 10.1109/cdc40024.2019.9028955
Time-varying optimization studies algorithms that can track solutions of optimization problems that evolve with time. A typical time-varying optimization algorithm is implemented in a running fashion in the sense that the underlying optimization problem is updated during the iterations of the algorithm, and is especially suitable for optimizing large-scale fast varying systems. In this paper, we propose and analyze a second-order method for time-varying optimization. Each iteration of the proposed method can be formulated as solving a quadratic-like saddle point problem that incorporates curvature information. Theoretical results on the tracking performance of the proposed method are presented, and discussions on their implications and comparison with existing second-order and first-order methods are also provided.https://authors.library.caltech.edu/records/kq858-70711Worst-Case Sensitivity of DC Optimal Power Flow Problems
https://resolver.caltech.edu/CaltechAUTHORS:20200707-112527402
Authors: {'items': [{'id': 'Anderson-James-D', 'name': {'family': 'Anderson', 'given': 'James'}, 'orcid': '0000-0002-2832-8396'}, {'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.23919/ACC45564.2020.9147770
In this paper we consider the problem of analyzing the effect a change in the load vector can have on the optimal power generation in a DC power flow model. The methodology is based upon the recently introduced concept of the OPF operator. It is shown that for general network topologies computing the worst-case sensitivities is computationally intractable. However, we show that certain problems involving the OPF operator can be equivalently converted to a graphical discrete optimization problem. Using the discrete formulation, we provide a decomposition algorithm that reduces the computational cost of computing the worst-case sensitivity. A 27-bus numerical example is used to illustrate our results.https://authors.library.caltech.edu/records/pz4tz-smj42Mitigating Cascading Failures via Local Responses
https://resolver.caltech.edu/CaltechAUTHORS:20210113-163505900
Authors: {'items': [{'id': 'Liang-Chen', 'name': {'family': 'Liang', 'given': 'Chen'}}, {'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Zocca-Alessandro', 'name': {'family': 'Zocca', 'given': 'Alessandro'}, 'orcid': '0000-0001-6585-4785'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}]}
Year: 2020
DOI: 10.1109/smartgridcomm47815.2020.9302934
This work proposes an approach for failure mitigation in power systems via corrective control named Optimal Injection Adjustment (OIA). In contrast to classical approaches, which focus on minimizing load loss, OIA aims to minimize the post-contingency flow deviations by adjusting node power injections in response to failures. We prove that the optimal control actions obtained from OIA are localized around the original failure and use numerical simulations to highlight that OIA achieves near-optimal control costs despite using localized control actions.https://authors.library.caltech.edu/records/gjbhs-0b062Learning Optimal Power Flow: Worst-Case Guarantees for Neural Networks
https://resolver.caltech.edu/CaltechAUTHORS:20210113-163505813
Authors: {'items': [{'id': 'Venzke-Andreas', 'name': {'family': 'Venzke', 'given': 'Andreas'}, 'orcid': '0000-0002-6101-6001'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Chatzivasileiadis-Spyros', 'name': {'family': 'Chatzivasileiadis', 'given': 'Spyros'}}]}
Year: 2020
DOI: 10.1109/smartgridcomm47815.2020.9302963
This paper introduces for the first time a framework to obtain provable worst-case guarantees for neural network performance, using learning for optimal power flow (OPF) problems as a guiding example. Neural networks have the potential to substantially reduce the computing time of OPF solutions. However, the lack of guarantees for their worst-case performance remains a major barrier for their adoption in practice. This work aims to remove this barrier. We formulate mixed-integer linear programs to obtain worst-case guarantees for neural network predictions related to (i) maximum constraint violations, (ii) maximum distances between predicted and optimal decision variables, and (iii) maximum sub-optimality. We demonstrate our methods on a range of PGLib-OPF networks up to 300 buses. We show that the worst-case guarantees can be up to one order of magnitude larger than the empirical lower bounds calculated with conventional methods. More importantly, we show that the worst-case predictions appear at the boundaries of the training input domain, and we demonstrate how we can systematically reduce the worst-case guarantees by training on a larger input domain than the domain they are evaluated on.https://authors.library.caltech.edu/records/xw1d2-9sz32DeepOPF+: A Deep Neural Network Approach for DC Optimal Power Flow for Ensuring Feasibility
https://resolver.caltech.edu/CaltechAUTHORS:20210113-163505726
Authors: {'items': [{'id': 'Zhao-Tianyu', 'name': {'family': 'Zhao', 'given': 'Tianyu'}}, {'id': 'Pan-Xiang', 'name': {'family': 'Pan', 'given': 'Xiang'}, 'orcid': '0000-0002-6565-2339'}, {'id': 'Chen-Minghua', 'name': {'family': 'Chen', 'given': 'Minghua'}}, {'id': 'Venke-Andreas', 'name': {'family': 'Venzke', 'given': 'Andreas'}, 'orcid': '0000-0002-6101-6001'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.1109/smartgridcomm47815.2020.9303017
Deep Neural Networks approaches for the Optimal Power Flow (OPF) problem received considerable attention recently. A key challenge of these approaches lies in ensuring the feasibility of the predicted solutions to physical system constraints. Due to the inherent approximation errors, the solutions predicted by Deep Neural Networks (DNNs) may violate the operating constraints, e.g., the transmission line capacities, limiting their applicability in practice. To address this challenge, we develop DeepOPF+ as a DNN approach based on the so-called "preventive" framework. Specifically, we calibrate the generation and transmission line limits used in the DNN training, thereby anticipating approximation errors and ensuring that the resulting predicted solutions remain feasible. We theoretically characterize the calibration magnitude necessary for ensuring universal feasibility. Our DeepOPF+ approach improves over existing DNN-based schemes in that it ensures feasibility and achieves a consistent speed up performance in both light-load and heavy-load regimes. Detailed simulation results on a range of test instances show that the proposed DeepOPF+ generates 100% feasible solutions with minor optimality loss. Meanwhile, it achieves a computational speedup of two orders of magnitude compared to state-of-the-art solvers.https://authors.library.caltech.edu/records/rgw7s-71x60A Sufficient Condition for Local Optima to be Globally Optimal
https://resolver.caltech.edu/CaltechAUTHORS:20210121-152558409
Authors: {'items': [{'id': 'Zhou-Fengyu', 'name': {'family': 'Zhou', 'given': 'Fengyu'}, 'orcid': '0000-0002-2639-6491'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2020
DOI: 10.1109/cdc42340.2020.9303868
Consider an optimization problem with a convex cost function but a non-convex compact feasible set X, and its relaxation with a compact and convex feasible set X̂ ⊃ X. We prove that if from any point x ∈ X̂∖X there is a path connecting x to X along which both the cost function and a Lyapunov-like function are improvable, then any local optimum in X for the original non-convex problem is a global optimum. We use this result to show that, for AC optimal power flow problems, a wellknown sufficient condition for exact relaxation also guarantees that all its local optima are globally optimal. This helps explain the widespread empirical experience that local algorithms for optimal power flow problems often work extremely well.https://authors.library.caltech.edu/records/c481g-2ep34Approaching Prosumer Social Optimum via Energy Sharing with Proof of Convergence
https://resolver.caltech.edu/CaltechAUTHORS:20210503-115704998
Authors: {'items': [{'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Zhao-Changhong', 'name': {'family': 'Zhao', 'given': 'Changhong'}, 'orcid': '0000-0003-0539-8591'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Mei-Shengwei', 'name': {'family': 'Mei', 'given': 'Shengwei'}, 'orcid': '0000-0002-2757-5977'}]}
Year: 2021
DOI: 10.1109/ciss50987.2021.9400276
The conventional power system operation approach has been proven to be effective and reliable for decades. Specially, at the demand side, customers are managed centrally by aggregators and usually not price-responsive. With the prevalence of distributed energy resources (DERs), traditional consumers are now endowed with the ability to produce energy, turning into so-called prosumers. Prosumers can tradeoff between supply and demand and participate in energy management proactively. At the same time, the intermittent and uncertain nature of DERs call for a stronger capability of dealing with real-time energy fluctuation. In this context, exploiting demand-side flexibility to support real-time energy balancing, which can reduce required generation reserves and save costs, is a promising direction for energy system modernization. However, the traditional centralized scheme fails to allow a prosumer to act upon its profit-maximizing philosophy, which reduces prosumer incentives and restricts demand-side flexibility. Therefore, a new prosumer-oriented approach is desired.https://authors.library.caltech.edu/records/wb0wr-p3f29Information Aggregation for Constrained Online Control
https://resolver.caltech.edu/CaltechAUTHORS:20210607-115053999
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Chen-Yue', 'name': {'family': 'Chen', 'given': 'Yue'}, 'orcid': '0000-0002-7594-7587'}, {'id': 'Sun-Bo', 'name': {'family': 'Sun', 'given': 'Bo'}, 'orcid': '0000-0003-3172-7811'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1145/3410220.3461737
We consider a two-controller online control problem where a central controller chooses an action from a feasible set that is determined by time-varying and coupling constraints, which depend on all past actions and states. The central controller's goal is to minimize the cumulative cost; however, the controller has access to neither the feasible set nor the dynamics directly, which are determined by a remote local controller. Instead, the central controller receives only an aggregate summary of the feasibility information from the local controller, which does not know the system costs. We show that it is possible for an online algorithm using feasibility information to nearly match the dynamic regret of an online algorithm using perfect information whenever the feasible sets satisfy a causal invariance criterion and there is a sufficiently large prediction window size. To do so, we use a form of feasibility aggregation based on entropic maximization in combination with a novel online algorithm, named Penalized Predictive Control (PPC).https://authors.library.caltech.edu/records/ah7r7-edq95Pricing flexibility of shiftable demand in electricity markets
https://resolver.caltech.edu/CaltechAUTHORS:20210629-211519470
Authors: {'items': [{'id': 'Werner-Lucien', 'name': {'family': 'Werner', 'given': 'Lucien'}}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2021
DOI: 10.1145/3447555.3464847
Enabling participation of demand-side flexibility in electricity markets is key to improving power system resilience and increasing the penetration of renewable generation. In this work we are motivated by the curtailment of near-zero-marginal-cost renewable resources during periods of oversupply, a particularly important cause of inefficient generation dispatch. Focusing on shiftable load in a multi-interval economic dispatch setting, we show that incompatible incentives arise for loads in the standard market formulation. While the system's overall efficiency increases from dispatching flexible demand, the overall welfare of loads can decrease as a result of higher spot prices. We propose a market design to address this incentive issue. Specifically, by imposing a small number of additional constraints on the economic dispatch problem, we obtain a mechanism that guarantees individual rationality for all market participants while simultaneously obtaining a more efficient dispatch. Our formulation leads to a natural definition of a uniform, time-varying flexibility price that is paid to loads to incentivize flexible bidding. We provide theoretical guarantees and empirically validate our model with simulations on real-world generation data from California Independent System Operator (CAISO).https://authors.library.caltech.edu/records/1fzny-bps82Exploiting Linear Models for Model-Free Nonlinear Control: A Provably Convergent Policy Gradient Approach
https://resolver.caltech.edu/CaltechAUTHORS:20220628-677879700
Authors: {'items': [{'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Yu-Chenkai', 'name': {'family': 'Yu', 'given': 'Chenkai'}, 'orcid': '0000-0001-8683-7773'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}]}
Year: 2021
DOI: 10.1109/cdc45484.2021.9683735
Model-free learning-based control methods have seen great success recently. However, such methods typically suffer from poor sample complexity and limited convergence guarantees. This is in sharp contrast to classical model-based control, which has a rich theory but typically requires strong modeling assumptions. In this paper, we combine the two approaches. We consider a dynamical system with both linear and non-linear components and use the linear model to define a warm start for a model-free, policy gradient method. We show this hybrid approach outperforms the model-based controller while avoiding the convergence issues associated with model-free approaches via both numerical experiments and theoretical analyses, in which we derive sufficient conditions on the non-linear component such that our approach is guaranteed to converge to the (nearly) global optimal controller.https://authors.library.caltech.edu/records/p99an-mjp78Stability Constrained Reinforcement Learning for Real-Time Voltage Control
https://resolver.caltech.edu/CaltechAUTHORS:20230315-336401000.3
Authors: {'items': [{'id': 'Shi-Yuanyuan', 'name': {'family': 'Shi', 'given': 'Yuanyuan'}, 'orcid': '0000-0002-6182-7664'}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}, {'id': 'Anandkumar-A', 'name': {'family': 'Anandkumar', 'given': 'Anima'}, 'orcid': '0000-0002-6974-6797'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}]}
Year: 2022
DOI: 10.23919/acc53348.2022.9867476
Deep reinforcement learning (RL) has been recognized as a promising tool to address the challenges in real-time control of power systems. However, its deployment in real-world power systems has been hindered by a lack of formal stability and safety guarantees. In this paper, we propose a stability constrained reinforcement learning method for real-time voltage control in distribution grids and we prove that the proposed approach provides a formal voltage stability guarantee. The key idea underlying our approach is an explicitly constructed Lyapunov function that certifies stability. We demonstrate the effectiveness of the approach in case studies, where the proposed method can reduce the transient control cost by more than 30% and shorten the response time by a third compared to a widely used linear policy, while always achieving voltage stability. In contrast, standard RL methods often fail to achieve voltage stability.https://authors.library.caltech.edu/records/rqwbe-dd932Robustness and Consistency in Linear Quadratic Control with Untrusted Predictions
https://resolver.caltech.edu/CaltechAUTHORS:20220802-839213000
Authors: {'items': [{'id': 'Li-Tongxin', 'name': {'family': 'Li', 'given': 'Tongxin'}, 'orcid': '0000-0002-9806-8964'}, {'id': 'Yang-Ruixiao', 'name': {'family': 'Yang', 'given': 'Ruixiao'}}, {'id': 'Qu-Guannan', 'name': {'family': 'Qu', 'given': 'Guannan'}, 'orcid': '0000-0002-5466-3550'}, {'id': 'Shi-Guanya', 'name': {'family': 'Shi', 'given': 'Guanya'}, 'orcid': '0000-0002-9075-3705'}, {'id': 'Yu-Chenkai', 'name': {'family': 'Yu', 'given': 'Chenkai'}, 'orcid': '0000-0001-8683-7773'}, {'id': 'Wierman-A', 'name': {'family': 'Wierman', 'given': 'Adam'}, 'orcid': '0000-0002-5923-0199'}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2022
DOI: 10.1145/3489048.3522658
We study the problem of learning-augmented predictive linear quadratic control. Our goal is to design a controller that balances "consistency", which measures the competitive ratio when predictions are accurate, and "robustness", which bounds the competitive ratio when predictions are inaccurate. We propose a novel λ-confident controller and prove that it maintains a competitive ratio upper bound of 1 + min {O(λ²ε)+ O(1-λ)²,O(1)+O(λ²)} where λ∈ [0,1] is a trust parameter set based on the confidence in the predictions, and ε is the prediction error. Further, motivated by online learning methods, we design a self-tuning policy that adaptively learns the trust parameter λ with a competitive ratio that depends on ε and the variation of system perturbations and predictions. We show that its competitive ratio is bounded from above by 1+O(ε) /(Θ)(1)+Θ(ε))+O(μVar) where μVar measures the variation of perturbations and predictions. It implies that by automatically adjusting the trust parameter online, the self-tuning scheme ensures a competitive ratio that does not scale up with the prediction error ε.https://authors.library.caltech.edu/records/qb28c-gj814