Publications (26)25.15 Total impact
 [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.IEEE Transactions on Information Theory 08/2009; 55(755):3220  3228. DOI:10.1109/TIT.2009.2021374 · 2.33 Impact Factor  IEEE Transactions on Wireless Communications 01/2008; 7:12081216. · 2.50 Impact Factor

Article: EnergyEfficient Resource Allocation in Wireless Networks: An Overview of GameTheoretic Approaches
[Show abstract] [Hide abstract]
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: FullDiversity FiniteConstellation 4 x 4 Differential STBC Based on Finite Quaternion Groups
[Show abstract] [Hide abstract]
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 suggested2006 IEEE Information Theory Workshop  ITW '06 Chengdu; 10/2006  [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 independentlyIEEE Journal on Selected Areas in Communications 07/2006; 24(624):1115  1129. DOI:10.1109/JSAC.2005.864028 · 3.45 Impact Factor  [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: 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.
[Show abstract] [Hide abstract]
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.Proceedings of the 2006 IEEE International Conference on Multimedia and Expo, ICME 2006, July 912 2006, Toronto, Ontario, Canada; 01/2006  [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
[Show abstract] [Hide abstract]
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.IEEE Transactions on Communications 12/2005; 53(1153):1885  1894. DOI:10.1109/TCOMM.2005.858695 · 1.99 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A unified approach to energyefficient power control, applicable to a large family of receivers including the matched filter, the decorrelator, the (linear) minimummeansquareerror detector (MMSE), and the individually and jointly optimal multiuser detectors, has recently been proposed for codedivisionmultipleaccess (CDMA) networks. This unified power control (UPC) algorithm exploits the linear relationship that has been shown to exist between the transmit power and the output signaltointerferenceplusnoise ratio (SIR) in large systems. Based on this principle and by computing the multiuser efficiency, the UPC algorithm updates the users' transmit powers in an iterative way to achieve the desired target SIR. In this paper, the convergence of the UPC algorithm is proved for the matched filter, the decorrelator, and the MMSE detector. In addition, the performance of the algorithm in finitesize systems is studied and compared with that of existing power control schemes. The UPC algorithm is particularly suitable for systems with randomly generated long spreading sequences (i.e., sequences whose period is longer than one symbol duration).  [Show abstract] [Hide abstract]
ABSTRACT: In this work, the crosslayer design problem of joint multiuser detection and power control is studied using a gametheoretic approach. The uplink of a directsequence code division multiple access (DSCDMA) 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 SIRbalanced with the minimum mean square error (MMSE) detector as the receiver. In addition, this framework is used to study power control 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 admission control scheme based on maximizing the total utility in the network is proposed.  [Show abstract] [Hide abstract]
ABSTRACT: This paper studies a twotier codedivision multipleaccess (CDMA) system in which the microcell base is converted into a data access point (DAP), i.e., is a limitedrange base station that provides highspeed access to one user at a time. The microcell (or DAP) user operates on the same frequency as the macrocell users and has the same chip rate. However, it adapts its spreading factor, and thus its data rate, in accordance with interference conditions. By contrast, the macrocell serves multiple simultaneous data users, each with the same fixed rate. The achievable throughput for individual microcell users is examined and a simple accurate approximation for its probability distribution is presented. Computations for average throughputs, both peruser and total, are also presented. The numerical results highlight the impact of a desensitivity parameter used in the baseselection process.IEEE Transactions on Wireless Communications 08/2005; 4(44):1302  1306. DOI:10.1109/TWC.2005.852144 · 2.50 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Energy efficiency, low latency, high estimation accuracy, and fast convergence are important goals in distributed incremental estimation algorithms for sensor networks. One approach that adds flexibility in achieving these goals is clustering. In this paper, the framework of distributed incremental estimation is extended by allowing clustering amongst the nodes. Among the observations made is that a scaling law exists where the estimation accuracy increases proportionally with the number of clusters. The distributed parameter estimation problem is posed as a convex optimization problem involving a social cost function and data from the sensor nodes. An incluster algorithm is then derived using the incremental subgradient method. Sensors in each cluster successively update a cluster parameter estimate based on local data, which is then passed on to a fusion center for further processing. We prove convergence results for the distributed incluster algorithm, and provide simulations that demonstrate the benefits clustering for least squares and robust estimation in sensor networks.  [Show abstract] [Hide abstract]
ABSTRACT: A gametheoretic approach for studying power control in multipleaccess networks with transmission delay constraints is proposed. A noncooperative power control game is considered in which each user seeks to choose a transmit power that maximizes its own utility while satisfying the user's 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 minimum mean square error multiuser detectors. The effects of delay constraints on the users' utilities (in bits/Joule) and network capacity (i.e., the maximum number of users that can be supported) are quantified. Comment: To apprear in the proceedings of the 2005 IEEE International Symposium on Information Theory, Adelaide, Australia, September 49, 2005 
Article: An energyefficient approach to power control and receiver design in wireless data networks.
 [Show abstract] [Hide abstract]
ABSTRACT: Accurate foreground segmentation is a difficult task due to such factors as illumination variation, occlusion, background movements, and noise. In this paper we present a novel adaptive transform domain approach for foreground segmentation in video sequences. A set of DCTbased features is employed to exploit the spatial and temporal correlation in the video sequences. We maintain an adaptive background model and make a decision based on the distance between the features of the current frame and that of the background model. Additional higher level processing is employed to deal with the variation of the environment and to improve the accuracy of segmentation. The approach is shown to be insensitive to illumination change and to noise. It also overcomes many common difficulties of segmentation such as foreground aperture, and moved background objects. The algorithm can perform in realtime.Acoustics, Speech, and Signal Processing, 1988. ICASSP88., 1988 International Conference on 01/2005; 2:685688. DOI:10.1109/ICASSP.2005.1415497 · 4.63 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Estimating a channel that is subject to frequencyselective Rayleigh fading is a challenging problem in an orthogonal frequency division multiplexing (OFDM) system. We propose three EMbased algorithms to efficiently estimate the channel impulse response (CIR) or channel frequency response of such a system operating on a channel with multipath fading and additive white Gaussian noise (AWGN). These algorithms are capable of improving the channel estimate by making use of a modest number of pilot tones or using the channel estimate of the previous frame to obtain the initial estimate for the iterative procedure. Simulation results show that the bit error rate (BER) as well as the mean square error (MSE) of the channel can be significantly reduced by these algorithms. We present simulation results to compare these algorithms on the basis of their performance and rate of convergence. We also derive CramerRaolike lower bounds for the unbiased channel estimate, which can be achieved via these EMbased algorithms. It is shown that the convergence rate of two of the algorithms is independent of the length of the multipath spread. One of them also converges most rapidly and has the smallest overall computational burden.EURASIP journal on advances in signal processing 08/2004; 2004(10). DOI:10.1155/S1110865704311121 · 0.78 Impact Factor
Publication Stats
819  Citations  
25.15  Total Impact Points  
Top Journals
Institutions

20042009

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


2003

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