Article records
https://feeds.library.caltech.edu/people/Cui-Tao/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 12 Apr 2024 23:27:09 +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.edu/records/pamwd-cgc31Power 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.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.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.edu/records/zmhp0-nxq61Analysis 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.edu/records/2kz6t-6mw87Joint 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.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.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.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.edu/records/1qkp5-aam52Generalized 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.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.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.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.edu/records/ybc8a-5ae13Maximum 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.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.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.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.edu/records/g5jy3-71n23Distributed 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.edu/records/y84tx-hwq78Memoryless 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.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.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.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.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.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.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.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.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.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.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.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.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.edu/records/kmf57-95z02