Publications (39)47.51 Total impact

Conference Paper: Time difference of arrival based source localization within a sparse representation framework
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ABSTRACT: The problem addressed is source localization from time differences of arrival (TDOA). This problem is also referred to as hyperbolic localization and it is nonconvex in general. Traditional solutions proposed in the literature have generally poor robustness to errors in the TDOA estimates. More recent methods, which relax the nonconvex problem to a convex optimization by applying a semidefinite relaxation (SDR) method, were found to be more robust to TDOA errors than the traditional methods. However, the SDR methods are not optimal in general. In this paper, three convex optimization methods with different computational costs are proposed to improve the hyperbolic localization accuracy. The first method takes an SDR approach to relax the hyperbolic localization to a convex optimization. The second method follows a linearized formulation of the problem and seeks for a biased estimate of improved accuracy. The first two methods perform comparably when the source is inside the convex hull of the sensors. When the source is located outside, the second approach performs better, at the cost of higher computation. A third method is proposed by exploiting the source sparsity. With this, the hyperbolic localization is formulated as an ℓ<sub>1</sub>regularization problem, where the ℓ<sub>1</sub>norm is used as source sparsity constraint. Computer simulations show that the ℓ<sub>1</sub>regularization can offer further improved accuracy, but at the cost of additional computational effort. 
Conference Paper: Source localization using time difference of arrival within a sparse representation framework
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ABSTRACT: The problem addressed is source localization via timedifference ofarrival estimation in a multipath channel. Solving this localization problem typically implies crosscorrelating the noisy signals received at pairs of sensors deployed within reception range of the source. Correlationbased localization is severely degraded by the presence of multipath. The proposed method exploits the sparsity of the multipath channel for estimation of the lineofsight component. The timedelay estimation problem is formulated as an �∫ 1regularization problem, where the �∫ 1norm is used as a channel sparsity constraint. The proposed method requires knowledge of the pulse shape of the transmitted signal, but it is blind in the sense that information on the specific transmitted symbols is not required at the sensors. Simulation results show that the proposed method delivers higher accuracy and robustness to noise compared to conventional or even superresolution MUSIC timedifferenceof arrival source localization methods. 
Conference Paper: Performance bound for localization of a near field source
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ABSTRACT: The ZivZakai bound (ZZB) is developed for the estimation error of a radiating source located in a plane, and observed by sensors widely distributed over the same plane. The source is noncooperative in the sense that the transmitted waveform and its timing are unknown to the sensors. The sensors do have however, information on the power spectral density of the source. Moreover, sensors have ideal mutual time and phase synchronization. The source location is estimated by coherent processing exploiting the amplitude and phase information between pairs of sensors. An analytical expression is developed for the ZZB relating the estimation error to the carrier frequency, signal bandwidth, the number of sensors, and their location. Numerical examples demonstrate that the ZZB closely predicts the performance of the maximum likelihood estimate across the full range of signal to noise ratio (SNR) values. At low SNR, the ZZB bound demonstrates performance dominated by noise, at medium SNR, the performance is dictated by the presence of sidelobes in the localization metric, and at high SNR, it is shown that the ZZB converges to the CramerRao bound. 
Article: EnergyEfficient Resource Allocation in Wireless Networks with QualityofService Constraints
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ABSTRACT: A gametheoretic model is proposed to study the crosslayer problem of joint power and rate control with quality of service (QoS) constraints in multipleaccess networks. In the proposed game, each user seeks to choose its transmit power and rate in a distributed manner in order to maximize its own utility while satisfying its QoS requirements. The user's QoS constraints are specified in terms of the average source rate and an upper bound on the average delay where the delay includes both transmission and queuing delays. The utility function considered here measures energy efficiency and is particularly suitable for wireless networks with energy constraints. The Nash equilibrium solution for the proposed noncooperative game is derived and a closedform expression for the utility achieved at equilibrium is obtained. It is shown that the QoS requirements of a user translate into a "size" for the user which is an indication of the amount of network resources consumed by the user. Using this competitive multiuser framework, the tradeoffs among throughput, delay, network capacity and energy efficiency are studied. In addition, analytical expressions are given for users' delay profiles and the delay performance of the users at Nash equilibrium is quantified.  [Show abstract] [Hide abstract]
ABSTRACT: A gametheoretic approach for studying energy efficiencydelay tradeoffs in multipleaccess networks is proposed. Focusing on the uplink of a codedivision multipleaccess (CDMA) network, a noncooperative game is considered in which each user seeks to choose a transmit power that maximizes its own utility while satisfying its (transmission) delay requirements. The utility function measures the number of reliable bits transmitted per joule of energy and the user's delay constraint is modeled as an upper bound on the delay outage probability. The Nash equilibrium for the proposed game is derived, and its existence and uniqueness are proved. Using a largesystem analysis, explicit expressions for the utilities achieved at equilibrium are obtained for the matched filter, decorrelating and (linear) minimummeansquareerror (MMSE) multiuser detectors. The effects of delay qualityofservice (QoS) constraints on the users' utilities (in bits per joule) and network capacity (i.e., the maximum number of users that can be supported) are quantified. Using the proposed framework, the tradeoffs between energy efficiency and delay are quantified in a competitive multiuser setting. 

Article: A GameTheoretic Approach to EnergyEfficient Modulation in CDMA Networks with Delay QoS Constraints
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ABSTRACT: A gametheoretic framework is used to study the effect of constellation size on the energy efficiency of wireless networks for MQAM modulation. A noncooperative game is proposed in which each user seeks to choose its transmit power (and possibly transmit symbol rate) as well as the constellation size in order to maximize its own utility while satisfying its delay qualityofservice (QoS) constraint. The utility function used here measures the number of reliable bits transmitted per joule of energy consumed, and is particularly suitable for energyconstrained networks. The bestresponse strategies and Nash equilibrium solution for the proposed game are derived. It is shown that in order to maximize its utility (in bits per joule), a user must choose the lowest constellation size that can accommodate the user's delay constraint. This strategy is different from one that would maximize spectral efficiency. Using this framework, the tradeoffs among energy efficiency, delay, throughput and constellation size are also studied and quantified. In addition, the effect of trelliscoded modulation on energy efficiency is discussed. 
Article: EnergyEfficient Resource Allocation in Wireless Networks: An Overview of GameTheoretic Approaches
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ABSTRACT: An overview of gametheoretic approaches to energyefficient resource allocation in wireless networks is presented. Focusing on multipleaccess networks, it is demonstrated that game theory can be used as an effective tool to study resource allocation in wireless networks with qualityofservice (QoS) constraints. A family of noncooperative (distributed) games is presented in which each user seeks to choose a strategy that maximizes its own utility while satisfying its QoS requirements. The utility function considered here measures the number of reliable bits that are transmitted per joule of energy consumed and, hence, is particulary suitable for energyconstrained networks. The actions available to each user in trying to maximize its own utility are at least the choice of the transmit power and, depending on the situation, the user may also be able to choose its transmission rate, modulation, packet size, multiuser receiver, multiantenna processing algorithm, or carrier allocation strategy. The bestresponse strategy and Nash equilibrium for each game is presented. Using this gametheoretic framework, the effects of power control, rate control, modulation, temporal and spatial signal processing, carrier allocation strategy and delay QoS constraints on energy efficiency and network capacity are quantified.  [Show abstract] [Hide abstract]
ABSTRACT: A unified approach to energyefficient power control is proposed for codedivision multiple access (CDMA) networks. The approach is applicable to a large family of multiuser receivers including the matched filter, the decorrelator, the linear minimum meansquare error (MMSE) receiver, and the (nonlinear) optimal detectors. It exploits the linear relationship that has been shown to exist between the transmit power and the output signaltointerferenceplusnoise ratio (SIR) in the largesystem limit. It is shown that, for this family of receivers, when users seek to selfishly maximize their own energy efficiency, the Nash equilibrium is SIRbalanced. In addition, a unified power control (UPC) algorithm for reaching the Nash equilibrium is proposed. The algorithm adjusts the user's transmit powers by iteratively computing the largesystem multiuser efficiency, which is independent of instantaneous spreading sequences. The convergence of the algorithm is proved for the matched filter, the decorrelator, and the MMSE receiver, and is demonstrated by means of simulation for an optimal detector. Moreover, the performance of the algorithm in finitesize systems is studied and compared with that of a conventional power control scheme, in which user powers depend on the instantaneous spreading sequences. 
Conference Paper: A GameTheoretic Approach to EnergyEfficient Modulation in CDMA Networks with Delay Constraints
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ABSTRACT: A gametheoretic framework is used to study the effect of constellation size on the energy efficiency of wireless networks for MQAM modulation. A noncooperative game is proposed in which each user seeks to choose its transmit power (and possibly transmit symbol rate) as well as the constellation size in order to maximize its own utility while satisfying its delay qualityofservice (QoS) constraint. The utility function used here measures the number of reliable bits transmitted per joule of energy consumed, and is particularly suitable for energyconstrained networks. The bestresponse strategies and Nash equilibrium solution for the proposed game are derived. It is shown that in order to maximize its utility (in bits per joule), a user must choose the lowest constellation size that can accommodate the user's delay constraint. Using this framework, the tradeoffs among energy efficiency, delay, throughput and constellation size are also studied and quantified. The effect of trelliscoded modulation on energy efficiency is also discussed  [Show abstract] [Hide abstract]
ABSTRACT: The authors develop a centralized information fusion architecture from basic principles of information theory and Bayesian statistics. It is well known that any clustering, quantizing, or thresholding of data causes loss of information unless a sufficient statistic is computed in the processing. For the case of wideband active ranging systems, the coherent output of an optimum beamformer and a matched filter is a sufficient statistic that can be transmitted to the fusion center. For unknown target velocity, range, and bearing, the wideband spacetime matched filter output can be interpreted as a multidimensional wavelet transform or a delayscalebearing map. In this paper, a Bayesian, joint estimationdetection approach is used for computation of sufficient statistics and multisensor information fusion. An approach borrowed from sequential Bayesian processing is used to compute prior densities for joint Bayesian estimationdetection. In this approach, a posteriori densities become priors after a coordinate transformation that transforms the outputs of each sensor to a common reference frame for all sensors. Reproducing prior densities are used to simplify Bayesian computation 
Conference Paper: FullDiversity FiniteConstellation 4 x 4 Differential STBC Based on Finite Quaternion Groups
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ABSTRACT: This paper presents a novel way to construct unitary spacetime block codes suitable for differential modulation. The new codes rely on quaternionic algebra to achieve finite constellation. Among these, a particular code with a codebook of size 48 is studied and shown to be differentially decodable by means of two symbolbysymbol decoders (each symbol having 2 bits) and one larger decoder for a size 16 constellation. Simulations in a realistic WiMAX environment show the proposed code to outperform an optimized size 48 diagonal MPSK code by 1 dB. Ways to counter reduced performance in highly mobile environments are also suggested  [Show abstract] [Hide abstract]
ABSTRACT: A gametheoretic model for studying power control in multicarrier codedivision multipleaccess systems is proposed. Power control is modeled as a noncooperative game in which each user decides how much power to transmit over each carrier to maximize its own utility. The utility function considered here measures the number of reliable bits transmitted over all the carriers per joule of energy consumed and is particularly suitable for networks where energy efficiency is important. The multidimensional nature of users' strategies and the nonquasiconcavity of the utility function make the multicarrier problem much more challenging than the singlecarrier or throughputbasedutility case. It is shown that, for all linear receivers including the matched filter, the decorrelator, and the minimummeansquareerror detector, a user's utility is maximized when the user transmits only on its "best" carrier. This is the carrier that requires the least amount of power to achieve a particular target signaltointerferenceplusnoise ratio at the output of the receiver. The existence and uniqueness of Nash equilibrium for the proposed power control game are studied. In particular, conditions are given that must be satisfied by the channel gains for a Nash equilibrium to exist, and the distribution of the users among the carriers at equilibrium is characterized. In addition, an iterative and distributed algorithm for reaching the equilibrium (when it exists) is presented. It is shown that the proposed approach results in significant improvements in the total utility achieved at equilibrium compared with a singlecarrier system and also to a multicarrier system in which each user maximizes its utility over each carrier independently  [Show abstract] [Hide abstract]
ABSTRACT: A gametheoretic model is proposed to study the crosslayer problem of joint power and rate control with quality of service (QoS) constraints in multipleaccess networks. In the proposed game, each user seeks to choose its transmit power and rate in a distributed manner in order to maximize its own utility and at the same time satisfy its QoS requirements. The user's QoS constraints are specified in terms of the average source rate and average delay. The utility function considered here measures energy efficiency and the delay includes both transmission and queueing delays. The Nash equilibrium solution for the proposed noncooperative game is derived and a closedform expression for the utility achieved at equilibrium is obtained. It is shown that the QoS requirements of a user translate into a "size" for the user which is an indication of the amount of network resources consumed by the user. Using this framework, the tradeoffs among throughput, delay, network capacity and energy efficiency are also studied.  [Show abstract] [Hide abstract]
ABSTRACT: This paper examines the uplink user capacity in a twotier code division multiple access (CDMA) system with hotspot microcells when user terminal power is limited and the wireless channel is finitelydispersive. A finitelydispersive channel causes variable fading of the signal power at the output of the RAKE receiver. First, a twocell system composed. of one macrocell and one embedded microcell is studied and analytical methods are developed to estimate the user capacity as a function of a dimensionless parameter that depends on the transmit power constraint and cell radius. Next, novel analytical methods are developed to study the effect of variable fading, both with and without transmit power constraints. Finally, the analytical methods are extended to estimate uplink user capacity for multicell CDMA systems, composed of multiple macrocells and multiple embedded microcells. In all cases, the analysisbased estimates are compared with and confirmed by simulation results.  [Show abstract] [Hide abstract]
ABSTRACT: The energydelay tradeoffs in wireless networks are studied using a gametheoretic framework. A multiclass multipleaccess network is considered in which users choose their transmit powers, and possibly transmission rates, in a distributed manner to maximize their own utilities while satisfying their delay qualityofservice (QoS) requirements. The utility function considered here measures the number of reliable bits transmitted per Joule of energy consumed and is particularly useful for energyconstrained networks. The Nash equilibrium solution for the proposed noncooperative game is presented and closedform expressions for the users' utilities at equilibrium are obtained. Based on this, the losses in energy efficiency and network capacity due to presence of delaysensitive users are quantified. The analysis is extended to the scenario where the QoS requirements include both the average source rate and a bound on the average total delay (including queuing delay). It is shown that the incoming traffic rate and the delay constraint of a user translate into a "size" for the user, which is an indication of the amount of resources consumed by the user. Using this framework, the tradeoffs among throughput, delay, network capacity and energy efficiency are also quantified.  [Show abstract] [Hide abstract]
ABSTRACT: A gametheoretic model for studying power control in multicarrier codedivision multipleaccess systems is proposed. Power control is modeled as a noncooperative game in which each user decides how much power to transmit over each carrier to maximize its own utility. The utility function considered here measures the number of reliable bits transmitted over all the carriers per joule of energy consumed and is particularly suitable for networks where energy efficiency is important. The multidi mensional nature of users' strategies and the nonquasiconcavity of the utility function make the multicarrier problem much more challenging than the singlecarrier or throughputbasedutility case. It is shown that, for all linear receivers including the matched filter, the decorrelator, and the minimummeansquareerror detector, a user's utility is maximized when the user transmits only on its "best" carrier. This is the carrier that requires the least amount of power to achieve a particular target signaltoin terferenceplusnoise ratio at the output of the receiver. The existence and uniqueness of Nash equilibrium for the proposed power control game are studied. In particular, conditions are given that must be satisfied by the channel gains for a Nash equilibrium to exist, and the distribution of the users among the carriers at equilibrium is characterized. In addition, an iterative and distributed algorithm for reaching the equilibrium (when it exists) is presented. It is shown that the proposed approach results in significant improvements in the total utility achieved at equilibrium compared with a singlecarrier system and also to a multicarrier system in which each user maximizes its utility over each carrier independently. 
Conference Paper: Object Tracking in Compressed Video with Confidence Measures.
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ABSTRACT: In this paper, a novel robust tracking algorithm in compressed video is proposed. Within the framework of video compression standards, we consider how to accurately estimate motion of an object by utilizing motion vectors available in compressed video together with derived confidence measures. These confidence measures are based on DCT coefficients, spatial continuity of motion and texture measure of the object. We perform tracking directly on the compressed data and also consider tracking of an object with image scale change. In order to achieve robust tracking, we develop a system which enables us to detect object appearance change such as illumination change and occlusion by exploring the confidence measures derived above. Preliminary results indicate that our tracking algorithm works well with a variety of video sequences.  [Show abstract] [Hide abstract]
ABSTRACT: A wireless sensor network with a fusion center is considered to study the effects of dependent observations on the parameter estimation problem. The sensor observations are corrupted by Gaussian noise with geometric spatial correlation. From an energy point of view, sending all the local data to the fusion center is the most costly, but leads to optimum performance results since all the dependencies are taken into account. From an estimation accuracy point of view, sending only parameter estimates is the least accurate, but is the most parsimonious in terms of communication costs. Hence, this tradeoff between the energy efficiency and the estimation accuracy is explored by comparing the performance of maximum likelihood estimator (MLE) and the sample average estimator (SAE) under various topologies and communication protocols. We start by reviewing the results from the onedimensional case and continue by extending those results to various twodimensional topologies. Surprisingly, we discover a class of regular polygon topologies where the MLE under spatial correlation reduces to the SAE. 
Article: An EnergyEfficient Approach to Power Control and Receiver Design in Wireless Data Networks
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ABSTRACT: In this paper, the crosslayer design problem of joint multiuser detection and power control is studied, using a gametheoretic approach that focuses on energy efficiency. The uplink of a directsequence codedivision multipleaccess data network is considered, and a noncooperative game is proposed in which users in the network are allowed to choose their uplink receivers as well as their transmit powers to maximize their own utilities. The utility function measures the number of reliable bits transmitted by the user per joule of energy consumed. Focusing on linear receivers, the Nash equilibrium for the proposed game is derived. It is shown that the equilibrium is one where the powers are signaltointerferenceplusnoise ratiobalanced with the minimum meansquare error (MMSE) detector as the receiver. In addition, this framework is used to study powercontrol games for the matched filter, the decorrelator, and the MMSE detector; and the receivers' performance is compared in terms of the utilities achieved at equilibrium (in bits/joule). The optimal cooperative solution is also discussed and compared with the noncooperative approach. Extensions of the results to the case of multiple receive antennas are also presented. In addition, an admissioncontrol scheme based on maximizing the total utility in the network is proposed.
Publication Stats
1k  Citations  
47.51  Total Impact Points  
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Institutions

20012011

Princeton University
 Department of Electrical Engineering
Princeton, New Jersey, United States


2007

Qualcomm
San Diego, California, United States


2006

Lehigh University
 Department of Electrical and Computer Engineering
Bethlehem, PA, United States
