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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenSat, 13 Apr 2024 01:05:10 +0000Bound-intersection detection for multiple-symbol differential unitary space-time modulation
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetc05
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chinthananda'}}]}
Year: 2005
DOI: 10.1109/TCOMM.2005.860056
This paper considers multiple-symbol differential detection (MSD) of differential unitary space-time modulation (DUSTM) over multiple-antenna systems. We derive a novel exact maximum-likelihood (ML) detector, called the bound-intersection detector (BID), using the extended Euclidean algorithm for single-symbol detection of diagonal constellations. While the ML search complexity is exponential in the number of transmit antennas and the data rate, our algorithm, particularly in high signal-to-noise ratio, achieves significant computational savings over the naive ML algorithm and the previous detector based on lattice reduction. We also develop four BID variants for MSD. The first two are ML and use branch-and-bound, the third one is suboptimal, which first uses BID to generate a candidate subset and then exhaustively searches over the reduced space, and the last one generalizes decision-feedback differential detection. Simulation results show that the BID and its MSD variants perform nearly ML, but do so with significantly reduced complexity.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pamwd-cgc31Polynomial Moment Relaxation for MIMO Detection
https://resolver.caltech.edu/CaltechAUTHORS:20110506-104232997
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chinthananda'}}]}
Year: 2006
DOI: 10.1109/ICC.2006.255286
We develop a polynomial-time detector for maximum
likelihood (ML) detection over multiple-input multiple-output (MIMO) channels. Our proposed polynomial moment relaxation (PMR) detection gives a unified framework for MIMO detection with relaxation including semi-definite relaxation as a special case. We give three approaches to replace a finite alphabet constraint with a polynomial constraint. Since both the objective function and the constraints are polynomials, we use a moment relaxation approach by applying the dual theories of moments and positive polynomials solvable by semi-definite programming.
With different relaxation orders, our PMR achieve a flexible
trade-off between complexity and performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/arsrc-pas27Multiple-Symbol Differential Detection for Single-Antenna and Multiple-Antenna Systems over Ricean-fading Channels
https://resolver.caltech.edu/CaltechAUTHORS:20110506-103423676
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2006
DOI: 10.1109/ICC.2006.254951
This paper considers multiple symbol differential detection (DD) for both single-antenna and multiple-antenna systems over flat Ricean-fading channels. We derive the optimal multiple symbol detection (MSD) decision rules for both Mary differential phase-shift keying (MDPSK) and differential unitary space-time modulation (DUSTM). The sphere decoder (SD) is adopted to solve the MSD for MDPSK. As well, an improved SD is proposed by using the Schnorr-Euchner strategy. A suboptimal MSD based decision feedback DD algorithm is proposed for the MSD of DUSTM. We also develop a sphere decoding bound intersection detector (SD-BID) to optimally solve the MSD problem for DUSTM, which still maintains low complexity. Simulation results show that our proposed MSD algorithms for both single-antenna and multiple-antenna systems reduce the error floor of conventional DD but with reasonably low computational complexity.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/a25x1-6p879Heuristic Tree Search for Detection and Decoding of Uncoded and Linear Block Coded Communication Systems
https://resolver.caltech.edu/CaltechAUTHORS:20110506-105351004
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chinthananda'}}]}
Year: 2006
DOI: 10.1109/ICC.2006.254759
A heuristic tree search algorithm is developed for
the maximum likelihood detection and decoding problem in
a general communication system. We propose several "cheap"
heuristic functions using constrained linear detectors and the minimum mean square errors (MMSE) detector. Even though
the MMSE heuristic function does not guarantee the optimal
solution, it has a negligible performance loss and provides a good complexity-performance tradeoff. For linear block coded systems, heuristic tree search is modified for soft decision decoding. High rate codes are decoded via the minimum state trellis, and low rate codes via the minimum complexity tree. Preprocessing is also discussed to further speed up the algorithms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qtzjs-my165Efficient blind decoding of orthogonal space-time block codes over time-selective fading channels
https://resolver.caltech.edu/CaltechAUTHORS:20110310-143335876
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2006
DOI: 10.1109/WCNC.2006.1696534
In this paper, we consider efficient blind decoder design
for orthogonal space-time block codes (OSTBCs). A general
decision rule for blind OSTBC decoding is derived assuming a
quasi-static flat multiple-input multiple-output (MIMO) Rayleigh
fading channel. We use the linear dispersion representation of
OSTBCs to derive a blind decoder that results in a quadratic
minimization problem, which can be solved efficiently by semidefinite
relaxation, sphere decoding or successive interference
cancellation. To resolve phase ambiguity problems inherent in
blind detectors, rather than using pilot symbols that results
in a bandwidth loss, we propose novel totally blind decoders
using dual constellations or a superimposed training scheme. To
alleviate the computational burden, a minimum mean-squareerror
(MMSE) channel estimator is also proposed to track the
time-varying channel without using the blind decoder.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5e9t8-cgy78Power delay profile and noise variance estimation for OFDM
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeecl06a
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2006
DOI: 10.1109/LCOMM.2006.1576558
In this letter, we present cyclic-prefix (CP) based noise-variance and power-delay-profile estimators for Orthogonal Frequency Division Multiplexing (OFDM) systems. Signal correlation due to the use of the CP is exploited without requiring additional pilot symbols. A heuristic estimator and a class of approximate maximum likelihood (ML) estimators are proposed. The proposed algorithms can be applied to both unitary and non-unitary constellations. These algorithms can be readily used for applications such as minimum mean-square error (MMSE) channel estimation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/akrh7-ad260Optimal low-complexity detection for space division multiple access wireless systems
https://resolver.caltech.edu/CaltechAUTHORS:WUYieeecl06
Authors: {'items': [{'id': 'Wu-Yue', 'name': {'family': 'Wu', 'given': 'Yue'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2006
DOI: 10.1109/LCOMM.2006.1603369
A symbol detector for wireless systems using space division multiple access (SDMA) and orthogonal frequency division multiplexing (OFDM) is derived. The detector uses a sphere decoder (SD) and has much less computational complexity than the naive maximum likelihood (ML) detector. We also show how to detect non-constant modulus signals with constrained least squares (CLS) receiver, which is designed for constant modulus (unitary) signals. The new detector outperforms existing suboptimal detectors for both uncoded and coded systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7qqba-tw556Joint data detection and channel estimation for OFDM systems
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetc06
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chinthananda'}}]}
Year: 2006
DOI: 10.1109/TCOMM.2006.873075
We develop new blind and semi-blind data detectors and channel estimators for orthogonal frequency-division multiplexing (OFDM) systems. Our data detectors require minimizing a complex, integer quadratic form in the data vector. The semi-blind detector uses both channel correlation and noise variance. The quadratic for the blind detector suffers from rank deficiency; for this, we give a low-complexity solution. Avoiding a computationally prohibitive exhaustive search, we solve our data detectors using sphere decoding (SD) and V-BLAST and provide simple adaptations of the SD algorithm. We consider how the blind detector performs under mismatch, generalize the basic data detectors to nonunitary constellations, and extend them to systems with pilots and virtual carriers. Simulations show that our data detectors perform well.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zmhp0-nxq61Linear Programming Detection and Decoding for MIMO Systems
https://resolver.caltech.edu/CaltechAUTHORS:20170515-163823021
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2006
DOI: 10.1109/ISIT.2006.261741
We develop an efficient linear programming detector (LPD) for multiple-input multiple-output (MIMO) systems. Instead of using the usual l2 norm, our proposed LPD uses the l1 norm as the detection metric, resulting in a mixed-integer linear program (MILP). Two branch-and-bound algorithms are proposed to solve the MILP. The solution of the MILP achieves the same full diversity order as the maximum likelihood detector. The MILP is further relaxed to a linear program (LP), which can be readily solved using the standard simplex method. We show that in some cases the solution of the LP is guaranteed to be that of the MILP. The LPD is also extended to the joint detection and decoding of linear block coded MIMO systems. Our LPD can be immediately implemented using mature circuits design for the simplex algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9dw5m-96851Analysis and optimization of pilot symbol-assisted Rake receivers for DS-CDMA systems
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetvt06
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2006
DOI: 10.1109/TVT.2006.877699
The effect of imperfect channel estimation (CE) on the performance of pilot-symbol-assisted modulation (PSAM) and MRC Rake reception over time- or frequency-selective fading channels with either a uniform power delay profile (UPDP) or a nonuniform power delay profile (NPDP) is investigated. For time-selective channels, a Wiener filter or linear minimum mean square error (LMMSE) filter for CE is considered, and a closed-form asymptotic expression for the mean square error (MSE) when the number of pilots used for CE approaches infinity is derived. In high signal-to-noise ratio (SNR), the MSE becomes independent of the channel Doppler spectrum. A characteristic function method is used to derive new closed-form expressions for the bit error rate (BER) of Rake receivers in UPDP and NPDP channels. The results are extended to two-dimensional (2-D) Rake receivers. The pilot-symbol spacing and pilot-to-data power ratio are optimized by minimizing the BER. For UPDP channels, elegant results are obtained in the asymptotic case. Furthermore, robust spacing design criteria are derived for the maximum Doppler frequency.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2kz6t-6mw87Efficient signal detection for space-time block coding over time-selective fading channels
https://resolver.caltech.edu/CaltechAUTHORS:20110310-142643346
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2006
DOI: 10.1109/WCNC.2006.1696556
In this paper, we consider the signal detection for
space-time block coding over time-selective fading channels.
We derive a general maximum likelihood (ML) decision rule
for space-time block coding (STBC). The resulting detector is
valid for any number of receive antennas and for all STBC
systems that have the linear dispersion property. The detector
results in a quadratic minimization problem, which can be solved
efficiently by sphere decoding or nulling-and-cancelling detection.
For orthogonal STBC systems, we also propose a suboptimal
detector using the principle of parallel interference cancellation
(PIC) that is valid for systems with an arbitrary number of
receive antennas.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0fa6c-vsj48Optimization based rate control for multicast with network coding: A multipath formulation
https://resolver.caltech.edu/CaltechAUTHORS:20100827-082408080
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'}}]}
Year: 2007
DOI: 10.1109/CDC.2007.4434960
Network coding offers new capabilities for efficient
information multicasting in communication networks. In this
paper, we study rate control for multicast with network coding.
We propose a path-based multicasting scheme, where each
source has multiple paths to each receiver in the multicast
group. One advantage of this approach over a tree-based
approach is that it is easier to find a minimum cost set of paths
as compared to trees. We present three end-to-end rate control
algorithms which operate over the set of paths supplied by the
network layer. With random network coding, all algorithms can
be implemented in a distributed manner. Our algorithms can
also be generalized to solve other optimization problems with
non-strictly concave objection function.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rsxxp-khw87Optimal Training Design for Channel Estimation in Amplify and Forward Relay Networks
https://resolver.caltech.edu/CaltechAUTHORS:20100827-092530965
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}]}
Year: 2007
DOI: 10.1109/GLOCOM.2007.763
In this paper, we study training based channel
estimation for relay networks using the amplify-and-forward
(AF) transmission scheme. We first point out that separately
estimating the channel from source to relay and the channel from
relay to destination incurs several problems. We then propose a
new estimation scheme that directly estimates the overall channel
from source to destination. The proposed channel estimation well
matches the AF based space time coding that was developed
recently. Both linear least-square estimator and minimum mean-square-error estimator are studied. The corresponding optimal
training sequences and the optimal precoding matrices are also
derived.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5mkwc-4rm88Opportunistic 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.eduhttps://authors.library.caltech.edu/records/v67bc-w4e96Maximum Likelihood Detection and Optimal Code Design for Differential Unitary Space-Time Modulation with Carrier Frequency Offset
https://resolver.caltech.edu/CaltechAUTHORS:20100827-105901767
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2007
DOI: 10.1109/GLOCOM.2007.532
In this paper, we answer the question that "Can conventional
differential unitary space time modulation (DUSTM)
be applied when there is an unknown carrier frequency offset
(CFO)?" and present a maximum likelihood (ML) detection rule
for this scenario. We analyze the asymptotical performance of our
ML detection and provide the code design criterion by using the
modified diversity product. The analysis also brings the insight
that our proposed decision rule is a new differential modulation
scheme in both temporal and spatial domains. Various simulations
are conducted, and the proposed algorithm is shown to
be more robust to the CFO drifting than the existing double
temporal differential modulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8ryhj-er565ML CFO and PO Estimation in DCT OFDM Systems under Non-Circular Transmissions
https://resolver.caltech.edu/CaltechAUTHORS:20100827-145242260
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'A.'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2007
DOI: 10.1109/ICC.2007.1039
Frequency synchronization is one of the most important
components in orthogonal frequency-division multiplexing
(OFDM) systems. Recently, the discrete cosine transform (DCT)
based OFDM system has received wide attentions due to several
advantages. Hence, the study of frequency synchronization issue
for this newly raised system is well on its time. To provide
a thorough study, we consider the non-circular transmissions,
and the results can be easily generated to circular transmissions
if the elliptic variance is set to zero. We present three joint
maximum likelihood (ML) carrier frequency offset (CFO) and
phase offset (PO) estimators. From both the theoretical analysis
and the numerical comparisons, we found new advantages of
the DCT-OFDM over the traditional discrete Fourier transform
(DFT) based OFDM. These advantages, as well as those already
studied in the early works on DCT-OFDM, support the belief that
the DCT-OFDM is a new promising multi-carrier modulation
(MCM) scheme.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8q8sp-v7f85Frequency Offset Tracking for OFDM Systems via Scattered Pilots and Virtual Carriers
https://resolver.caltech.edu/CaltechAUTHORS:20100827-141528018
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'A.'}}]}
Year: 2007
DOI: 10.1109/ICC.2007.846
In this paper, we propose a new carrier frequency
offset (CFO) tracking algorithm for orthogonal frequency division
multiplexing (OFDM) systems. Assuming that the channel
remains constant during two consecutive OFDM blocks, a CFO
estimation algorithm is proposed based on the limited number
of pilots in each OFDM block. Identifiability of this pilot based
algorithm is fully discussed under the noise free environment. A
weighted algorithm is then developed by considering both pilot
carriers and virtual carriers. The asymptotic mean square error
(MSE) of the proposed algorithm is provided, and simulation results
clearly show the performance improvement of the proposed
algorithm over the existing methods.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yc27e-p9867Distributed optimization in wireless networks using broadcast advantage
https://resolver.caltech.edu/CaltechAUTHORS:20100827-084745453
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'}}]}
Year: 2007
DOI: 10.1109/CDC.2007.4434958
In this paper, we consider cross layer optimization
in wireless networks with wireless broadcast advantage,
focusing on the problem of distributed scheduling of broadcast
links. The wireless broadcast advantage is most useful
in multicast scenarios. For a multicast scenario, we give a
subgradient algorithm for distributed joint congestion control,
network coding and session scheduling, which however requires
centralized link scheduling. Under the primary interference
model, link scheduling problem is equivalent to a maximum
weighted hypergraph matching problem that is NP-complete.
To solve the scheduling problem distributedly, locally greedy
and randomized approximation algorithms are proposed and
shown to have bounded worst-case performance. With random
network coding, we obtain a fully distributed cross-layer design.
Numerical results show promising throughput gain using the
proposed algorithms, and surprisingly, in some cases even
with less complexity than cross-layer design without broadcast
advantage.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/b421s-jrv85Distributed minimum cost multicasting with lossless source coding and network coding
https://resolver.caltech.edu/CaltechAUTHORS:20100826-151540718
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}]}
Year: 2007
DOI: 10.1109/CDC.2007.4434962
In this paper, we consider minimum cost lossless
source coding for multiple multicast sessions. Each session
comprises a set of correlated sources whose information is
demanded by a set of sink nodes. We propose a distributed end-to-end algorithm which operates over given multicast trees, and
a back-pressure algorithm which optimizes routing and coding
over the whole network. Unlike other existing algorithms, the
source rates need not be centrally coordinated; the sinks control
transmission rates across the sources. With random network
coding, the proposed approach yields completely distributed
and optimal algorithms for intra-session network coding. We
prove the convergence of our proposed algorithms. Some
practical considerations are also discussed. Experimental results
are provided to complement our theoretical analysis.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qt1vn-1qr84Joint Frequency Offset and Channel Estimation for OFDM Systems Using Pilot Symbols and Virtual Carriers
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetwc07b
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2007
DOI: 10.1109/TWC.2007.348312
We consider joint estimation of carrier frequency offset and channel impulse response (CIR) for orthogonal frequency division multiplexing (OFDM) systems with pilot symbols and virtual subcarriers (VCs). We derive the receive-signal correlation structure due to the pilots and VCs, give the evidence of joint multivariate Gaussian distribution of the received samples, and derive an approximate maximum likelihood (ML) frequency offset estimator. We also derive the asymptotic mean-square error (MSE) and an approximate Cramer-Rao bound (CRB) and establish the asymptotic unbiasedness. Without pilots, in high signal-to-noise ratio, our estimator is equivalent to Liu and Tureli's estimator with Nv virtual carriers. When the pilot number (Np) is greater than the channel length L, our estimator acts as a subspace-based estimator with Nv + Np - L virtual carriers. A decision-directed joint ML estimator is derived to iteratively update the estimates of frequency offset, data symbols and CIR. The optimal pilot and virtual carrier placement strategies are also discussed. The resulting decision-directed joint estimator performs within 0.8 dB of the ideal case even when the frequency offset is as large as 20%.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/n6139-s3q11Semiblind Channel Estimation and Data Detection for OFDM Systems With Optimal Pilot Design
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetc07a
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2007
DOI: 10.1109/TCOMM.2007.895985
This paper considers semiblind channel estimation and data detection for orthogonal frequency-division multiplexing (OFDM) over frequency-selective fading channels. We show that the samples of an OFDM symbol are jointly complex Gaussian distributed, where the mean and covariance are determined by the locations and values of fixed pilot symbols. We exploit this distribution to derive a novel maximum-likelihood (ML) semiblind gradient-descent channel estimator. By exploiting the channel impulse response (CIR) statistics, we also derive a semiblind data detector for both Rayleigh and Ricean fading channels. Furthermore, we develop an enhanced data detector, which uses the estimator error statistics to mitigate the effect of channel estimation errors. Efficient implementation of both the semiblind and the improved data detectors is provided via sphere decoding and nulling-canceling detection. We also derive the Cramér-Rao bound (CRB) and design optimal pilots by minimizing the CRB. Our proposed channel estimator and data detector exhibit high bandwidth efficiency (requiring only a few pilot symbols), achieve the CRB, and also nearly reach the performance of an ideal reference receiver.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wtj0a-2d240Efficient Blind Receiver Design for Orthogonal Space-Time Block Codes
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetwc07a
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2007
DOI: 10.1109/TWC.2007.360390
We consider stochastic blind maximum-likelihood detection of orthogonal space-time block codes (OSTBCs) over a quasi-static flat multiple-input multiple-output (MIMO) Rayleigh fading channel. A general decision rule for stochastic blind maximum-likelihood OSTBC detection is derived. This rule is simplified using OSTBC linear dispersion matrices to realize a blind detector, which is implemented by semi-definite relaxation or sphere decoding. For the latter, the modifications necessary for both unitary and non-unitary constellations are developed. Two totally blind detectors using dual constellations or a superimposed training scheme are proposed. As a side product, two conditions for a rotatable OSTBC are also derived. A decision-directed, minimum mean-square-error (MMSE) channel estimator is developed. We also derive the Cramer-Rao bound (CRB) for channel estimation and discuss the optimal power allocation. Extensive simulation results are used to compare the different detectors in terms of complexity and performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/69pr8-f9608Blind Receiver Design for OFDM Systems Over Doubly Selective Channels
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetc07b
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2007
DOI: 10.1109/TCOMM.2007.894112
We develop blind data detectors for orthogonal frequency-division multiplexing (OFDM) systems over doubly selective channels by exploiting both frequency-domain and time-domain correlations of the received signal. We thus derive two blind data detectors: a time-domain data detector and a frequency-domain data detector. We also contribute a reduced complexity, suboptimal version of a time-domain data detector that performs robustly when the normalized Doppler rate is less than 3%. Our frequency-domain data detector and suboptimal time-domain data detector both result in integer least-squares (LS) problems. We propose the use of the V-BLAST detector and the sphere decoder. The time-domain data detector is not limited to the Doppler rates less than 3%, but cannot be posed as an integer LS problem. Our solution is to develop an iterative algorithm that starts from the suboptimal time-domain data detector output. We also propose channel estimation and prediction algorithms using a polynomial expansion model, and these estimators work with data detectors (decision-directed mode) to reduce the complexity. The estimators for the channel statistics and the noise variance are derived using the likelihood function for the data. Our blind data detectors are fairly robust against the parameter mismatch.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1qkp5-aam52On Distributed Distortion Optimization for Correlated Sources
https://resolver.caltech.edu/CaltechAUTHORS:20170425-162520744
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}]}
Year: 2007
DOI: 10.1109/ISIT.2007.4557631
We consider lossy data compression in capacity-constrained networks with correlated sources. We develop, using dual decomposition, a distributed algorithm that maximizes an aggregate utility measure defined in terms of the distortion levels of the sources. No coordination among sources is required; each source adjusts its distortion level according to distortion prices fed back by the sinks. The algorithm is developed for the case of squared error distortion and high resolution coding where the rate distortion region is known, and is easily extended to consider achievable regions that can be expressed in a related form. Our distributed optimization framework applies to unicast and multicast with and without network coding. Numerical example shows relatively fast convergence, allowing the algorithm to be used in time-varying networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hfexd-pz755Minimum Cost Integral Network Coding
https://resolver.caltech.edu/CaltechAUTHORS:20170425-161810594
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}]}
Year: 2007
DOI: 10.1109/ISIT.2007.4557632
In this paper, we consider finding a minimum cost multicast subgraph with network coding, where the rate to inject packets on each link is constrained to be integral. In the usual minimum cost network coding formulation, the optimal solution cannot always be integral. Fractional rates can be well approximated by choosing the time unit large enough, but this increases the encoding and decoding complexity as well as delay at the terminals. We formulate this problem as an integer program, which is NP-hard. A greedy algorithm and an algorithm based on linear programming rounding are proposed, which have approximation ratios k and 2k respectively, where k is the number of sinks. Moreover, both algorithms can be decentralized. We show by simulation that our algorithms' average performance substantially exceeds their bounds on random graphs.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2fnpk-17s78Opportunistic Source Coding for Data Gathering in Wireless Sensor Networks
https://resolver.caltech.edu/CaltechCSTR:2007.003
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'}]}
Year: 2007
DOI: 10.7907/Z9G73BP6
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 MAC layer, sensor nodes
need to coordinate wireless transmission and packet forwarding
to exploit multiuser diversity in packet reception.
At 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 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 Lempel-Ziv
code and network 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
reduces the number of transmissions by nearly 25%
compared with existing greedy scheme in small networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dd849-24158Distributed Optimization in Wireless Networks Using Broadcast Advantage
https://resolver.caltech.edu/CaltechCSTR:2007.002
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'}}]}
Year: 2007
DOI: 10.7907/Z9BK19BR
In this paper, we study cross-layer design for multicasting
in wireless networks by exploiting broadcast advantage.
With network coding, a distributed subgradient algorithm for joint congestion control, session scheduling, and network coding is proposed, which requires a centralized scheduling algorithm in general. Under the primary interference model, we find that
any valid link schedule corresponds to a hypergraph matching. To solve the scheduling problem distributedly, local greedy, randomized, and hybrid algorithms are proposed. We also modify the randomized algorithm into a constant-time algorithm. With random network coding, we obtain a fully distributed cross-layer design. Our experimental results show promising
throughput gain by using our proposed framework, in some cases with less complexity than cross-layer
design without broadcast advantage. Lastly, we also extend
our framework to the case without network coding.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3r82h-7hj05Statistical Pruning for Near Maximum Likelihood Detection of MIMO Systems
https://resolver.caltech.edu/CaltechAUTHORS:20100909-133322426
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2007
DOI: 10.1109/ICC.2007.905
We show a statistical pruning approach for maximum
likelihood (ML) detection of multiple-input multiple-output
(MIMO) systems. We present a general pruning strategy for
sphere decoder (SD), which can also be applied to any tree search
algorithms. Our pruning rules are effective especially for the case
when SD has high complexity. Three specific pruning rules are
given and discussed. From analyzing the union bound on the
symbol error probability, we show that the diversity order of the
deterministic pruning is only one by fixing the pruning probability.
By choosing different pruning probability distribution
functions, the statistical pruning can achieve arbitrary diversity
orders and SNR gains. Our statistical pruning strategy thus
achieves a flexible trade-off between complexity and performance.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5bypp-dg578Opportunistic source coding for data gathering in wireless sensor networks
https://resolver.caltech.edu/CaltechAUTHORS:20161005-155121935
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}]}
Year: 2007
DOI: 10.1145/1347787.1347801
We propose a jointly opportunistic source coding and oppor
tunistic routing (OSCOR) protocol for correlated
data gathering in wireless sensor networks. OSCOR
improves data gathering efficiency by exploiting
opportunistic data compression and multi-user diversity on wireless broadcast. OSCOR attacks challenges
across network protocol layers by incorporating a slightly modified 802.11 MAC, a distributed source coding
scheme based on Lempel-Ziv code
and network coding, and a node compression ratio dependent metric combined with a modified Dijkstra's algorithm for
path selection. We simulate OSCOR's performance and
show it reduces the number of transmissions by nearly
25% compared with other schemes in small networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0zj2w-r1158Space-Time Communication Protocols for N-way Relay Networks
https://resolver.caltech.edu/CaltechAUTHORS:20110407-113333118
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Kliewer-J', 'name': {'family': 'Kliewer', 'given': 'Jörg'}}]}
Year: 2008
DOI: 10.1109/GLOCOM.2008.ECP.205
We address communication protocols for N-way relay networks with M antennas at the relay and a single antenna at the N source terminals. In particular, amplify-and-forward
(AF), decode-and-forward (DF), and compress-and-forward (CF)
strategies are extended to these networks, and in addition, two new relaying protocols, denoise-and-forward and estimate-andforward, are proposed. In the first part of the paper, the performance of these schemes is analyzed in terms of the achievable rate region. Also, the optimal diversity-multiplexing tradeoff is derived for both AF and DF. The second part of the paper is devoted to practical space-time transmission strategies. Linear dispersion codes are used, which are optimized by maximizing the sum rate. For AF a diversity order of close to M can be achieved by using a specific space-time code construction.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xe8yx-5dz47Physical Layer Differential Network Coding for Two-way Relay Channels
https://resolver.caltech.edu/CaltechAUTHORS:20110407-113423361
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2008
DOI: 10.1109/GLOCOM.2008.ECP.884
In this work, we consider differential modulation in
two-way relay channels (TWRC). In single antenna systems,
we propose non-coherent schemes for both amplify-and forward (AF) and decode-and-forward (DF) where the channel state information is not required. These new schemes are counterparts of the traditional non-coherent detection in point to point communications. The difficulty with differential modulation design in TWRC is that the received signal is a mixture of the signals from both source terminals. We derive maximum likelihood (ML) detectors
for both AF and DF. The DF protocol can be considered as
performing differential network coding at the physical layer. In addition, we propose several suboptimal alternatives including decision feedback and prediction based detectors. All these strategies work well as evidenced by simulation results. We also extend the schemes to the multiple-antenna case and provide design criterion of differential unitary space time modulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/f6w93-f7z76Memoryless Relay Strategies for Two-Way Relay Channels: Performance Analysis and Optimization
https://resolver.caltech.edu/CaltechAUTHORS:20100629-080753182
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Kliewer-J', 'name': {'family': 'Kliewer', 'given': 'Jörg'}}]}
Year: 2008
DOI: 10.1109/ICC.2008.222
We consider relaying strategies for two-way relay channels, where two terminals transmits simultaneously to each other with the help of relays. A memoryless system is considered, where the signal transmitted by a relay depends only on its last received signal. For binary antipodal signaling, we analyze and optimize the performance of existing amplify and forward (AF) and absolute (abs) decode and forward (ADF) for two- way AWGN relay channels. A new abs-based AF (AAF) scheme is proposed, which has better performance than AF. In low SNR, AAF performs even better than ADF. Furthermore, a novel estimate and forward (EF) strategy is proposed which performs better than ADF. More importantly, we optimize the relay strategy within the class of abs-based strategies via functional analysis, which minimizes the average probability of error over all possible relay functions. The optimized function is shown to be a Lambert's W function parameterized on the noise power and the transmission energy. The optimized function behaves like AAF in low SNR and like ADF in high SNR, resp., where EF behaves like the optimized function over the whole SNR range.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/er5yr-v4323Some results on relay strategies for memoryless two-way relay channels
https://resolver.caltech.edu/CaltechAUTHORS:20170418-174812677
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Kliewer-J', 'name': {'family': 'Kliewer', 'given': 'Jörg'}}]}
Year: 2008
DOI: 10.1109/ITA.2008.4601042
We consider relaying strategies for memoryless two-way relay channels, where the signal transmitted by a relay depends only on its previously received signal. For binary antipodal signaling under the general case of different SNRs on the terminal-relay channels, we consider two classes of relay strategies: abs-based strategies in which the processing at the relay is solely based on the absolute value of the received signal, and non-abs-based strategies. We analyze and optimize the performance of existing and new schemes for two-way relay channels under an average power constraint, including abs-based and non-abs-based versions of amplify and forward (AF), decode and forward (DF), and estimate and forward (EF). Additionally, we optimize the relay function via functional analysis such that the average probability of error is minimized in the high signal-to-noise ratio (SNR) regime. Finally, we show that all these results can also be generalized to higher order constellations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5vkxt-9t355Generalized feedback detection for spatial multiplexing multi-antenna systems
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetwc08
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2008
DOI: 10.1109/TWC.2008.060513
We present a unified detection framework for spatial multiplexing multiple-input multiple-output (MIMO) systems by generalizing Heller's classical feedback decoding algorithm for convolutional codes. The resulting generalized feedback detector (GFD) is characterized by three parameters: window size, step size and branch factor. Many existing MIMO detectors are turned out to be special cases of the GFD. Moreover, different parameter choices can provide various performance-complexity tradeoffs. The connection between MIMO detectors and tree search algorithms is also established. To reduce redundant computations in the GFD, a shared computation technique is proposed by using a tree data structure. Using a union bound based analysis of the symbol error rates, the diversity order and signal-to-noise ratio (SNR) gain are derived analytically as functions of the three parameters; for example, the diversity order of the GFD varies between 1 and N. The complexity of the GFD varies between those of the maximum-likelihood (ML) detector and the zero-forcing decision feedback detector (ZFDFD). Extensive computer simulation results are also provided.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0xfb6-7qj61Scattered Pilots and Virtual Carriers Based Frequency Offset Tracking for OFDM Systems: Algorithms, Identifiability, and Performance Analysis
https://resolver.caltech.edu/CaltechAUTHORS:GAOieeetc08
Authors: {'items': [{'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}]}
Year: 2008
DOI: 10.1109/TCOMM.2008.060050
In this paper, we propose a novel carrier frequency offset (CFO) tracking algorithm for orthogonal frequency division multiplexing (OFDM) systems by exploiting scattered pilot carriers and virtual carriers embedded in the existing OFDM standards. Assuming that the channel remains constant during two consecutive OFDM blocks and perfect timing, a CFO tracking algorithm is proposed using the limited number of pilot carriers in each OFDM block. Identifiability of this pilot based algorithm is fully discussed under the noise free environment, and a constellation rotation strategy is proposed to eliminate the c-ambiguity for arbitrary constellations. A weighted algorithm is then proposed by considering both scattered pilots and virtual carriers. We find that, the pilots increase the performance accuracy of the algorithm, while the virtual carriers reduce the chance of CFO outlier. Therefore, the proposed tracking algorithm is able to achieve full range CFO estimation, can be used before channel estimation, and could provide improved performance compared to existing algorithms. The asymptotic mean square error (MSE) of the proposed algorithm is derived and simulation results agree with the theoretical analysis.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wvy8d-t0q44On Multiple Symbol Detection for Diagonal DUSTM Over Ricean Channels
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetwc08b
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2008
DOI: 10.1109/TWC.2008.060872
This letter considers multiple symbol differential detection for multiple-antenna systems over flat Ricean-fading channels when partial channel state information (CSI) is available at the transmitter. Using the maximum likelihood (ML) principle, and assuming perfect knowledge of the channel mean, we derive the optimal multiple symbol detection (MSD) rule for diagonal differential unitary space-time modulation (DUSTM). This rule is used to develop a sphere decoding bound intersection detector (SD-BID) with low complexity. A suboptimal MSD based decision feedback DD (DF-DD) algorithm is also derived. The simulation results show that our proposed MSD algorithms reduce the error floor of conventional differential detection and that the computational complexity of these new algorithms is reasonably low.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/mg68s-zvg29Constrained Detection for Spatial-Multiplexing Multiple-Input–Multiple-Output Systems
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeetvt08
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}, {'id': 'Wu-Yue', 'name': {'family': 'Wu', 'given': 'Yue'}}]}
Year: 2008
DOI: 10.1109/TVT.2007.907291
A family of detectors that exploit signal constraints is developed for maximum-likelihood detection for multiple-input–multiple-output (MIMO) systems. Real constrained detectors and decision-feedback detectors are proposed for real constellations by forcing the relaxed solution to be real. A generalized minimum mean square error (GMMSE) and constrained least squares MIMO detectors are also developed for unitary and nonunitary signal constellations. Using these constrained detectors, we propose a new ordering scheme to achieve a tradeoff between interference suppression and noise enhancement. Moreover, to mitigate the inherent error propagation, the decision-feedback MIMO detectors are integrated with signal constraints. The simulation results show that our combined detector achieves a significant performance gain over vertical Bell Laboratories layered space-time (V-BLAST) detection.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ybc8a-5ae13Energy Efficient Opportunistic Network Coding for Wireless Networks
https://resolver.caltech.edu/CaltechAUTHORS:20100707-141558183
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'}}]}
Year: 2008
DOI: 10.1109/INFOCOM.2008.81
We consider energy efficient network coding design in wireless networks with multiple unicast sessions. Our approach decomposes multiple unicast sessions into a superposition of multicast and unicast sessions, with coding occurring only within each session. We give an optimization approach that is more general than the existing poison-remedy optimization formulation. For the case of wireless, we consider XOR coding and give an achievable rate region for a primary interference model. To simplify network operation, we give an oblivious backpressure algorithm which does not optimize overhearing of transmissions, and a practical protocol called COPR based on the oblivious backpressure algorithm. Simulation experiments show that COPR largely reduces network power consumption over existing algorithms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/m50vk-hrr38Maximum likelihood channel estimation in decode-and-forward relay networks
https://resolver.caltech.edu/CaltechAUTHORS:20170404-174823799
Authors: {'items': [{'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}]}
Year: 2008
DOI: 10.1109/ISIT.2008.4595184
In this paper, we provide a complete study on the training based channel estimation for relay networks that employ the decode-and-forward (DF) scheme. Since multiple relay nodes are geographically distributed over the service region, channel estimation is different from the traditional way in that each relay has its own individual power constraint. We consider the maximum likelihood (ML) channel estimation and derive closed form solutions for the optimal training as well as for the optimal power allocation. It is seen that the optimal power allocation follows a multi-level waterfilling structure.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9as92-1rz46Maximum likelihood based estimation of frequency and phase offset in DCT OFDM systems under non-circular transmissions: algorithms, analysis and comparisons
https://resolver.caltech.edu/CaltechAUTHORS:GAOieeetc08b
Authors: {'items': [{'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'A.'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'C.'}}]}
Year: 2008
DOI: 10.1109/TCOMM.2008.060411
Recently, the advantages of the discrete cosine transform (DCT) based orthogonal frequency-division multiplexing (OFDM) have come to the light. We thus consider DCT- OFDM with non-circular transmission (our results cover circular transmission as well) and present two blind joint maximum- likelihood frequency offset and phase offset estimators. Both our theoretical analysis and numerical comparisons reveal new advantages of DCT-OFDM over the traditional discrete Fourier transform (DFT) based OFDM. These advantages, as well as those already uncovered in the early works on DCT-OFDM, support the belief that DCT-OFDM is a promising multi-carrier modulation scheme.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/84d5w-4aj95A Game-Theoretic Framework for Medium Access Control
https://resolver.caltech.edu/CaltechAUTHORS:CUIieeejsac08
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Chen-Lijun', 'name': {'family': 'Chen', 'given': 'Lijun'}}, {'id': 'Low-S-H', 'name': {'family': 'Low', 'given': 'Steven H.'}, 'orcid': '0000-0001-6476-3048'}]}
Year: 2008
DOI: 10.1109/JSAC.2008.080909
In this paper, we generalize the random access game model, and show that it provides a general game-theoretic framework for designing contention based medium access control. We extend the random access game model to the network with multiple contention measure signals, study the design of random access games, and analyze different distributed algorithms achieving their equilibria. As examples, a series of utility functions is proposed for games achieving the maximum throughput in a network of homogeneous nodes. In a network with n traffic classes, an N-signal game model is proposed which achieves the maximum throughput under the fairness constraint among different traffic classes. In addition, the convergence of different dynamic algorithms such as best response, gradient play and Jacobi play under propagation delay and estimation error is established. Simulation results show that game model based protocols can achieve superior performance over the standard IEEE 802.11 DCF, and comparable performance as existing protocols with the best performance in literature.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gv77s-5zg41Maximum likelihood detection for differential unitary space-time modulation with carrier frequency offset
https://resolver.caltech.edu/CaltechAUTHORS:GAOieeetc08c
Authors: {'items': [{'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chinthananda'}}]}
Year: 2008
DOI: 10.1109/TCOMM.2008.060672
Can conventional differential unitary space time modulation (DUSTM) be applied when there is an unknown carrier frequency offset (CFO)? This paper answers this question affirmatively and derives the necessary maximum likelihood (ML) detection rule. The asymptotic performance of the proposed ML rule is analyzed, leading to a code design criterion for DUSTM by using the modified diversity product. The resulting proposed decision rule is a new differential modulation scheme in both the temporal and spatial domains. Two sub-optimal multiple-symbol decision rules with improved performance are also proposed. For the efficient implementation of these, we derive a modified bound intersection detector (BID), a generalization of the previously derived optimal BID for the conventional DUSTM. The simulation results show that the proposed differential modulation scheme is more robust against CFO drifting than the existing double temporal differential modulation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/765p9-xa890Optimal Training Design for Channel Estimation in Decode-and-Forward Relay Networks With Individual and Total Power Constraints
https://resolver.caltech.edu/CaltechAUTHORS:AOieeetsp08
Authors: {'items': [{'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}]}
Year: 2008
DOI: 10.1109/TSP.2008.2005084
In this paper, we study the channel estimation and the optimal training design for relay networks that operate under the decode-and-forward (DF) strategy with the knowledge of the interference covariance. In addition to the total power constraint on all the relays, we introduce individual power constraint for each relay, which reflects the practical scenario where all relays are separated from one another. Considering the individual power constraint for the relay networks is the major difference from that in the traditional point-to-point communication systems where only a total power constraint exists for all colocated antennas. Two types of channel estimation are involved: maximum likelihood (ML) and minimum mean square error (MMSE). For ML channel estimation, the channels are assumed as deterministic and the optimal training results from an efficient multilevel waterfilling type solution that is derived from the majorization theory. For MMSE channel estimation, however, the second-order statistics of the channels are assumed known and the general optimization problem turns out to be nonconvex. We instead consider three special yet reasonable scenarios. The problem in the first scenario is convex and could be efficiently solved by state-of-the-art optimization tools. Closed-form waterfilling type solutions are found in the remaining two scenarios, of which the first one has an interesting physical interpretation as pouring water into caves.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/g5jy3-71n23On multiple access random medium access control
https://resolver.caltech.edu/CaltechAUTHORS:20100816-095201318
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}]}
Year: 2009
DOI: 10.1109/ISIT.2009.5205457
In this paper, we develop a new class of medium access control protocol, which allows each user to transmit at different data rates chosen randomly from an appropriately determined set of rates. By using successive interference cancellation, multiple packets can be received simultaneously. In slotted Aloha type Gaussian networks, we show that the achievable total throughput of the proposed protocol is at least a constant fraction of the mac sum rate when the number of transmission rates at each node is equal to the number of users in the network. We also study the case when only a limited number of transmission rates is available at each node. Extension to rate splitting is discussed. Simulation results show that the proposed protocol can achieve a significant throughput gain over the conventional Aloha.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ccp5e-02z13Achievable rate and optimal physical layer rate allocation in interference-free wireless networks
https://resolver.caltech.edu/CaltechAUTHORS:20100816-100837500
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Kliewer-J', 'name': {'family': 'Kliewer', 'given': 'Jörg'}}]}
Year: 2009
DOI: 10.1109/ISIT.2009.5205903
We analyze the achievable rate in interference-free
wireless networks with physical layer fading channels and
orthogonal multiple access. As a starting point, the point-to-point
channel is considered. We find the optimal physical and network
layer rate trade-off which maximizes the achievable overall rate
for both a fixed rate transmission scheme and an improved
scheme based on multiple virtual users and superposition coding.
These initial results are extended to the network setting, where,
based on a cut-set formulation, the achievable rate at each node
and its upper bound are derived. We propose a distributed
optimization algorithm which allows to jointly determine the
maxim um achievable rate, the optimal physical layer rates on
each network link, and an opportunistic back-pressure-type
routing strategy on the network layer. This inherently justifies
the layered architecture in existing wireless networks. Finally,
we show that the proposed layered optimization approach can
achieve almost all of the ergodic network capacity in high SNR.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jh766-y0w46Distributed space-time coding for two-way wireless relay networks
https://resolver.caltech.edu/CaltechAUTHORS:20090514-153538553
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}]}
Year: 2009
DOI: 10.1109/TSP.2008.2009025
In this paper, we consider distributed space-time coding for two-way wireless relay networks, where communication between two terminals is assisted by relay nodes. Relaying protocols using two, three, and four time slots are proposed. The protocols using four time slots are the traditional amplify-and-forward (AF) and decode-and-forward (DF) protocols, which do not consider the property of the two-way traffic. A new class of relaying protocols, termed as partial decode-and-forward (PDF), is developed for the two time slots transmission, where each relay first removes part of the noise before sending the signal to the two terminals. Protocols using three time slots are proposed to compensate the fact that the two time slots protocols cannot make use of direct transmission between the two terminals. For all protocols, after processing their received signals, the relays encode the resulting signals using a distributed linear dispersion (LD) code. The proposed AF protocols are shown to achieve the diversity order of min{N,K}(1- (log log P/log P)), where N is the number of relays, P is the total power of the network, and K is the number of symbols transmitted during each time slot. When random unitary matrix is used for LD code, the proposed PDF protocols resemble random linear network coding, where the former operates on the unitary group and the latter works on the finite field. Moreover, PDF achieves the diversity order of min{N,K} but the conventional DF can only achieve the diversity order of 1. Finally, we find that two time slots protocols also have advantages over four-time-slot protocols in media access control (MAC) layer.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y84tx-hwq78Optimal Quantization in Energy-Constrained Sensor
Networks under Imperfect Transmission
https://resolver.caltech.edu/CaltechAUTHORS:20100511-151403304
Authors: {'items': [{'id': 'Zhang-Li', 'name': {'family': 'Zhang', 'given': 'Li'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Zhang-Xian-Da', 'name': {'family': 'Zhang', 'given': 'Xian-Da'}}]}
Year: 2009
DOI: 10.1109/CISS.2009.5054792
This paper addresses the optimization of quantization at local sensors under strict energy constraint and imperfect transmission to improve the reconstruction performance at the fusion center in the wireless sensor networks (WSNs). We present optimized quantization scheme including the optimal quantization bit rate and the optimal transmission power allocation among quantization bits for BPSK signal and binary orthogonal signal with envelope detection, respectively. The optimization of the quantization is formulated as a convex problem and the optimal solution is derived analytically in both cases. Simulation results demonstrate the effectiveness of our proposed quantization schemes.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1ehj9-an320Throughput Optimization in High Speed Downlink Packet Access (HSDPA)
https://resolver.caltech.edu/CaltechAUTHORS:20100907-094109886
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Lu-Feng', 'name': {'family': 'Lu', 'given': 'Feng'}}, {'id': 'Goteti-A', 'name': {'family': 'Goteti', 'given': 'Anil'}}, {'id': 'Sethuraman-V', 'name': {'family': 'Sethuraman', 'given': 'V.'}}, {'id': 'Rao-S-P', 'name': {'family': 'Rao', 'given': 'S. P.'}}, {'id': 'Subrahmanya-P', 'name': {'family': 'Subrahmanya', 'given': 'P.'}}]}
Year: 2009
DOI: 10.1109/ICC.2009.5199527
In this paper, we investigate throughput optimization
in High Speed Downlink Packet Access (HSDPA). Specifically,
we propose offline and online algorithms for adjusting
the Channel Quality Indicator (CQI) used by the network to
schedule data transmission. In the offline algorithm, a given
target BLER is achieved by adjusting CQI based on ACK/NAK
history. By sweeping through different target BLERs, we can
find the throughput optimal BLER offline. This algorithm could
be used not only to optimize throughput but also to enable fair
resource allocation among mobile users in HSDPA. In the online
algorithm, the CQI offset is adapted using an estimated short
term throughput gradient without specifying a target BLER. An
adaptive stepsize mechanism is proposed to track temporal variation
of the environment. We investigate convergence behavior
of both algorithms. Simulation results show that the proposed
offline algorithm can achieve the given target BLER with good
accuracy. Both algorithms yield up to 30% HSDPA throughput
improvement over that with 10% target BLER.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hhmpy-ndw48Memoryless relay strategies for two-way relay channels
https://resolver.caltech.edu/CaltechAUTHORS:20091104-153456802
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Kliewer-J', 'name': {'family': 'Kliewer', 'given': 'Jörg'}}]}
Year: 2009
DOI: 10.1109/TCOMM.2009.10.080222
We propose relaying strategies for uncoded two-way relay channels, where two terminals transmit simultaneously to each other with the help of a relay. In particular, we consider a memoryless system, where the signal transmitted by the relay is obtained by applying an instantaneous relay function to the previously received signal. For binary antipodal signaling, a class of so called absolute (abs)-based schemes is proposed in which the processing at the relay is solely based on the absolute value of the received signal. We analyze and optimize the symbol-error performance of existing and new abs-based and non-abs-based strategies under an average power constraint, including abs-based and non-abs-based versions of amplify and forward (AF), detect and forward (DF), and estimate and forward (EF). Additionally, we optimize the relay function via functional analysis such that the average probability of error is minimized at the high signal-to-noise ratio (SNR) regime. The optimized relay function is shown to be a Lambert W function parameterized on the noise power and the transmission energy. The optimized function behaves like abs-AF at low SNR and like abs-DF at high SNR, respectively; EF behaves similarly to the optimized function over the whole SNR range. We find the conditions under which each class of strategies is preferred. Finally, we show that all these results can also be generalized to higher order constellations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7d8nm-83q79Differential modulation for two-way wireless communications: a perspective of differential network coding at the physical layer
https://resolver.caltech.edu/CaltechAUTHORS:20091106-113105073
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2009
DOI: 10.1109/TCOMM.2009.10.080254
This work considers two-way relay channels (TWRC), where two terminals transmit simultaneously to each other with the help of a relay node. For single antenna systems, we propose several new transmission schemes for both amplify-and-forward (AF) protocol and decode-and-forward (DF) protocol where the channel state information is not required. These new schemes are the counterpart of the traditional noncoherent detection or differential detection in point-to-point communications. Differential modulation design for TWRC is challenging because the received signal is a mixture of the signals from both source terminals. We derive maximum likelihood (ML) detectors for both AF and DF protocols, where the latter can be considered as performing differential network coding at the physical layer. As the exact ML detector is prohibitively complex, we propose several suboptimal alternatives including decision feedback detectors and prediction-based detectors. All these strategies work well as evidenced by the simulation results. The proposed protocols are especially useful when the required average data rate is high. In addition, we extend the protocols to the multiple-antenna case and provide the design criterion of the differential unitary space time modulation (DUSTM) for TWRC.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qc7wf-c7p51Power scheduling of distributed estimation in sensor networks with repetition coding
https://resolver.caltech.edu/CaltechAUTHORS:20091224-092459953
Authors: {'items': [{'id': 'Zhang-Li', 'name': {'family': 'Zhang', 'given': 'Li'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Zhang-Xian-Da', 'name': {'family': 'Zhang', 'given': 'Xian-Da'}}]}
Year: 2010
DOI: 10.1016/j.sigpro.2009.07.032
This paper considers the optimal power scheduling for the distributed estimation of a source parameter using quantized samples of noisy sensor observations in a wireless sensor network (WSN). Repetition codes are used to transmit quantization bits of sensor observations to achieve unequal error protection, and a quasi-best linear unbiased estimate is constructed to estimate the source parameter at the fusion center (FC). Based on the adopted distributed estimation scheme (DES), we optimize the power scheduling among sensors to minimize the L^1-norm of the power vector subject to the desired tolerance, which implies minimizing the total transmission power. Since the optimization problem is not convex, we propose a low-complexity alternative, which minimizes the L^2-norm of the power vector while insuring the desired tolerance. We derive the closed form solution of the L^2-norm power scheduling scheme. Simulation results show that the total power consumption of the L^2-norm power scheduling scheme is close to that of the L^1-norm power scheduling scheme, while complexity analysis demonstrates that the L^2-norm power scheduling scheme has very low complexity.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0p2jc-wxk94On distributed scheduling in wireless networks exploiting broadcast and network coding
https://resolver.caltech.edu/CaltechAUTHORS:20100520-142930645
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'}}]}
Year: 2010
DOI: 10.1109/TCOMM.2010.04.080564
In this paper, we consider cross-layer optimization in wireless networks with wireless broadcast advantage, focusing on the problem of distributed scheduling of broadcast links. The wireless broadcast advantage is most useful in multicast scenarios. As such, we include network coding in our design to exploit the throughput gain brought in by network coding for multicasting. We derive a subgradient algorithm for joint rate control, network coding and scheduling, which however requires centralized link scheduling. Under the primary interference model, link scheduling problem is equivalent to a maximum weighted hypergraph matching problem that is NP-complete. To solve the scheduling problem distributedly, locally greedy and randomized approximation algorithms are proposed and shown to have bounded worst-case performance. With random network coding, we obtain a fully distributed cross-layer design. Numerical results show promising throughput gain using the proposed algorithms, and surprisingly, in some cases even with less complexity than cross-layer design without broadcast advantage.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rja53-k9m88Moment-Based Parameter Estimation and Blind Spectrum Sensing for Quadrature Amplitude Modulation
https://resolver.caltech.edu/CaltechAUTHORS:20110322-134058782
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tang-Jia', 'name': {'family': 'Tang', 'given': 'Jia'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2011
DOI: 10.1109/TCOMM.2010.120710.090667
Knowing accurate noise variance and signal power is crucial to most spectrum-sensing algorithms such as energy detection, matched filter detection, and cyclostationary detection. In this paper, we consider a practical scenario when these two parameters are unknown and are needed to be estimated before the spectrum sensing. This task is non-trivial without knowing the status of the primary user, and we categorize the related spectrum sensing as a blind one. We develop the estimation algorithms for unknown parameters by exploiting the signal constellation of the primary user. Three different parameter estimators that do not require any training are then proposed based on the moments of the received signals. Since the secondary user may not know the primary user's signal constellation, we develop a robust approach that approximates a finite quadrature amplitude modulation (QAM) constellation by a continuous uniform distribution. We also derive the modified Cramér-Rao bound (CRB) for noise variance estimation. Then the optimal moment pair is found from minimizing the mean squared error (MSE) of the signal-to-noise ratio (SNR). The method of choosing the spectrum sensing threshold by taking into consideration the estimation error is also discussed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ybg2b-tp440OFDM channel estimation and data detection with superimposed pilots
https://resolver.caltech.edu/CaltechAUTHORS:20110505-081943895
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2011
DOI: 10.1002/ett.1461
We propose three iterative superimposed-pilot based channel estimators for Orthogonal Frequency Division Multiplexing (OFDM) systems. Two are approximate maximum-likelihood, derived by using a Taylor expansion of the conditional probability density function of the received signal or by approximating the OFDM time signal as Gaussian, and one is minimum-mean square error. The complexity per iteration of these estimators is given by approximately O(NL^2), O(N^3) and O(NL), where N is the number of OFDM subcarriers and L is the channel length (time). Two direct (non-iterative) data detectors are also derived by averaging the log likelihood function over the channel statistics. These detectors require minimising the cost metric in an integer space, and we suggest the use of the sphere decoder for them. The Cramér–Rao bound for superimposed pilot based channel estimation is derived, and this bound is achieved by the proposed estimators. The optimal pilot placement is shown to be the equally spaced distribution of pilots. The bit error rate of the proposed estimators is simulated for N = 32 OFDM system. Our estimators perform fairly close to a separated training scheme, but without any loss of spectral efficiency.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9vmhj-sfx12Optimization of Cooperative Spectrum Sensing in Cognitive Radio
https://resolver.caltech.edu/CaltechAUTHORS:20110606-110530431
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Gao-Feifei', 'name': {'family': 'Gao', 'given': 'Feifei'}}, {'id': 'Nallanathan-A', 'name': {'family': 'Nallanathan', 'given': 'Arumugam'}}]}
Year: 2011
DOI: 10.1109/TVT.2011.2116815
In this paper, we consider cooperative spectrum sensing when two secondary users (SUs) collaborate via the relaying scheme. We investigate two cooperative sensing strategies, i.e., SUs exchange data information locally, and SUs relay information to a central controller. The relaying scheme at each SU is optimized via functional analysis with either the average or peak power constraints. For the local cooperative sensing strategy, the optimal relaying schemes look like amplify-and-forward (AF) in the low-signal-to-noise-ratio (SNR) region and behave like decode-and-forward (DF) in the high-SNR region. The fundamental performance limit using local cooperative sensing is discussed. For the global cooperative sensing strategy, we propose both coherent and noncoherent sensing, depending on whether SUs are synchronized. In the coherent case, a decentralized approach is designed, and each SU optimizes its relaying function locally. In the noncoherent case, we use linear energy combination detector to decouple the relaying function from weight coefficient optimization. Simulation results demonstrate that the proposed protocols achieve much better performance over the existing protocols.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/tkqp4-t1k03Local Zones of Endoplasmic Reticulum Complexity Confine
Cargo in Neuronal Dendrites
https://resolver.caltech.edu/CaltechAUTHORS:20120227-100338887
Authors: {'items': [{'id': 'Cui-Wang-Tingting', 'name': {'family': 'Cui-Wang', 'given': 'Tingting'}}, {'id': 'Hanus-C', 'name': {'family': 'Hanus', 'given': 'Cyril'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Helton-T', 'name': {'family': 'Helton', 'given': 'Thomas'}}, {'id': 'Bourne-J', 'name': {'family': 'Bourne', 'given': 'Jennifer'}}, {'id': 'Watson-D', 'name': {'family': 'Watson', 'given': 'Deborah'}}, {'id': 'Harris-K-M', 'name': {'family': 'Harris', 'given': 'Kristen M.'}}, {'id': 'Ehlers-M-D', 'name': {'family': 'Ehlers', 'given': 'Michael D.'}}]}
Year: 2012
DOI: 10.1016/j.cell.2011.11.056
Following synthesis, integral membrane proteins dwell in the endoplasmic reticulum (ER) for variable periods that are typically rate limiting for plasma membrane delivery. In neurons, the ER extends for hundreds of microns as an anastomosing network throughout highly branched dendrites. However, little is known about the mobility, spatial scales, or dynamic regulation of cargo in the dendritic ER. Here, we show that membrane proteins, including AMPA-type glutamate receptors, rapidly diffuse within the continuous network of dendritic ER but are confined by increased ER complexity at dendritic branch points and near dendritic spines. The spatial range of receptor mobility is rapidly restricted by type I mGluR signaling through a mechanism involving protein kinase C (PKC) and the ER protein CLIMP63. Moreover, local zones of ER complexity compartmentalize ER export and correspond to sites of new dendritic branches. Thus, local control of ER complexity spatially scales secretory trafficking within elaborate dendritic arbors.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ret29-qym40Distributed Distortion Optimization for Correlated Sources with Network Coding
https://resolver.caltech.edu/CaltechAUTHORS:20120619-082839926
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'}}]}
Year: 2012
DOI: 10.1109/TCOMM.2012.032012.100791
We consider lossy data compression in capacity-constrained networks with correlated sources. We derive, using dual decomposition, a distributed algorithm that maximizes an aggregate utility measure defined in terms of the distortion levels of the sources. No coordination among sources is required; each source adjusts its distortion level according to distortion prices fed back by the sinks. The algorithm is developed for the case of squared error distortion and high resolution coding where the rate-distortion region is known, and can be easily extended to consider achievable regions that can be expressed in a related form. Our distributed optimization framework applies to unicast and multicast with and without network coding. Numerical examples show relatively fast convergence, allowing the algorithm to be used in time-varying networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fxj7v-jd624Communication Protocols for N-way All-Cast Relay Networks
https://resolver.caltech.edu/CaltechAUTHORS:20130116-102514916
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Kliewer-J', 'name': {'family': 'Kliewer', 'given': 'Jörg'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}]}
Year: 2012
DOI: 10.1109/TCOMM.2012.080212.110395
We consider communication protocols for N-way all-cast relay networks, which comprise N source terminals such that each source terminal demands messages from all other source terminals with the help of a relay. The derived protocols are characterized by the fact that physical layer network coding is employed at the relay, where each source has side information about the signals it has sent. Amplify-and-forward (AF) and decode-and-forward (DF) protocols are applied to the N-way relay network setting, where the achievable rate regions for those protocols are derived and compared with outer capacity bounds. We propose several practical space-time coding schemes for AF and DF, and introduce two new protocols denoted as denoise-and-forward (DNF) and estimate-and-forward (EF). Further, for AF and DF the fundamental diversity-multiplexing trade-off is characterized.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/n9hrg-88407On Secure Network Coding With Nonuniform or Restricted Wiretap Sets
https://resolver.caltech.edu/CaltechAUTHORS:20130207-073335417
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Ho-Tracey', 'name': {'family': 'Ho', 'given': 'Tracey'}}, {'id': 'Kliewer-J', 'name': {'family': 'Kliewer', 'given': 'Jörg'}}]}
Year: 2013
DOI: 10.1109/TIT.2012.2216936
The secrecy capacity of a network, for a given collection of permissible wiretap sets, is the maximum rate of communication such that observing links in any permissible wiretap set reveal no information about the message. This paper considers secure network coding with nonuniform or restricted wiretap sets, for example, networks with unequal link capacities where a wiretapper can wiretap any subset of k links, or networks where only a subset of links can be wiretapped. Existing results show that for the case of uniform wiretap sets (networks with equal capacity links/packets where any k can be wiretapped), the secrecy capacity is given by a cut-set bound if random keys are injected at the source (and decoded at the sink), whether or not the communicating users have information about the choice of wiretap set. In contrast, we show that for the nonuniform case, this secrecy rate is achievable for the case of known but not unknown wiretap set. We give achievable linear optimization-based strategies where random keys are canceled at intermediate nonsink nodes or injected at intermediate nonsource nodes. Finally, we show that determining the secrecy capacity is an NP-hard problem.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ek2q6-g6962Probability-Distribution-Based Node Pruning for Sphere Decoding
https://resolver.caltech.edu/CaltechAUTHORS:20130620-105921302
Authors: {'items': [{'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}, {'id': 'Han-Shuangshuang', 'name': {'family': 'Han', 'given': 'Shuangshuang'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}]}
Year: 2013
DOI: 10.1109/TVT.2012.2233226
Node pruning strategies based on probability distributions are developed for maximum-likelihood (ML) detection for spatial-multiplexing multiple-input-multiple-output (MIMO) systems. Uniform pruning, geometric pruning, threshold pruning, hybrid pruning, and depth-dependent pruning are thus developed in detail. By considering the symbol error probability in the high signal-to-noise ratio (SNR) region, the desirable diversity order of uniform pruning and the threshold level for threshold pruning are derived. Simulation results show that threshold pruning saves complexity compared with popular sphere decoder (SD) algorithms, such as the K-best SD, the fixed-complexity SD (FSD), and the probabilistic tree pruning SD (PTP-SD), particularly for high SNRs and large-antenna MIMO systems. Furthermore, our proposed node pruning strategies may also be applied to other systems, including coded MIMO systems and relay networks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/g7vnr-j8y52SNR-dependent radius control sphere detection for MIMO systems and relay networks
https://resolver.caltech.edu/CaltechAUTHORS:20150420-081903174
Authors: {'items': [{'id': 'Han-Shuangshuang', 'name': {'family': 'Han', 'given': 'Shuangshuang'}}, {'id': 'Tellambura-Chinthananda', 'name': {'family': 'Tellambura', 'given': 'Chintha'}}, {'id': 'Cui-Tao', 'name': {'family': 'Cui', 'given': 'Tao'}}]}
Year: 2015
DOI: 10.1002/ett.2620
A new sphere decoder algorithm for uncoded spatial multiplexing multiple-input multiple-output (MIMO) systems is proposed. It overcomes the drawbacks of traditional sphere decoders: variable complexity and high complexity in low signal-to-noise ratios (SNRs). Its main novelty lies in scaling the search radius by a heuristic SNR-dependent factor. This new SNR-dependent radius control sphere decoder offers near maximum likelihood performance over the entire range of SNRs, while keeping its complexity roughly constant. This algorithm also incorporates channel ordering to save complexity. To quantify the variability of complexity, the normalised variance of the complexity is evaluated. This algorithm is also extended for joint iterative detection and decoding in coded MIMO systems and for MIMO-relay networks. Simulation results and theoretical analysis demonstrate the benefits of the proposed algorithm.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kmf57-95z02