Now showing items 1-60 of 134

  • Achievable Rates for Arbitrary Network Topologies with â Cheapâ Nodes 

    Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-05-01)
    In this paper, we derive achievable rates for arbitrary network topologies consisting of â cheapâ nodes. A node is labeled â cheapâ if its radio can only operate in TDD mode when transmitting and receiving in the ...
  • All-optical CDMA with bipolar codes 

    Nguyen, Lim; Aazhang, Behnaam; Young, James F. (1995-03-20)
    A method for the transmission and detection of bipolar sequences in a unipolar system is presented. It allows all-optical implementation, in noncoherent optical CDMA systems, of the bipolar codes that have been developed ...
  • Analysis of Decision-Feedback Based Broadband OFDM Systems 

    de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-11-01)
    In wireless communications, about 25% of the bandwidth is dedicated to training symbols for channel estimation. By using a semi-blind approach, the training sequence length can be reduced while improving performance. The ...
  • Antenna Packing in Low Power Systems: Communication Limits and Array Design 

    Muharemovic, Tarik; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-01-01)
    In this paper, we study design of transceiver antenna arrays and its impact on spectral efficiency of low-power systems. Our primary motivation is construction of practical and portable multi-antenna configurations with a ...
  • An Approach to Capacity Analysis of Coarsely Coordinated Low Power Multiple Access Systems 

    Muharemovic, Tarik; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-07-01)
    We consider multiaccess problem in low power systems, where we allow each user to select its own data rate and transmit power locally and independently from other users. Here, every user has a set of low power codebooks, ...
  • Bayesian Blind PARAFAC Recievers forDS-CDMA Systems 

    de Baynast, Alexandre; Declercq, David; De Lathauwer, Lieven; Aazhang, Behnaam (2003-10-01)
    In this paper an original Bayesian approach for blind detec-tion for Code Division Multiple Access (CDMA) Systems in presence of spatial diversity at the receiver is developed. In the noiseless context, the blind ...
  • Beamformer Design with Feedback Rate Constraints : Criteria and Constructions 

    Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Erkip, Elza; Aazhang, Behnaam (2003-07-20)
    In this work, we provide a geometrical framework for the analysis and design of beamformer codebooks with finite number of beamformer vectors. We present a design criterion for good beamfomer codebooks and show the equivalence ...
  • BER of optical communication system using fiber source 

    Nguyen, Lim; Aazhang, Behnaam; Young, James F. (1995-11-20)
    We analyze the bit-error rate (BER) of an optical communication system using the superfluorescent fiber source (SFS). The counting statistics of thermal light give improved performance relative to the Gaussian statistics ...
  • Blind PARAFAC Receivers for Multiple Access-Multiple Antenna Systems 

    de Baynast, Alexandre; De Lathauwer, Lieven; Aazhang, Behnaam (2003-10-01)
    In this paper, we present a new blind receiver for multiple access channel with multiple transmit antennas per user and multiple receive antennas (MIMO channel). After being multiplied by a spreading sequence, each user s ...
  • Bounds on Achievable Rates for General Multi-terminal Networks with Practical Constraints 

    Khojastepour, Mohammad; Aazhang, Behnaam; Sabharwal, Ashutosh (2003-04-20)
    We consider the problem of communication in a general multi-terminal network where each node of the network is a potential sender or receiver (or both) but it cannot do both functions together. The motivation for this ...
  • Broadcast Space-Time Coding 

    Memarzadeh, Mahsa; Sabharwal, Ashutosh; Aazhang, Behnaam (2001-08-20)
    In this paper, we study transmission techniques for broadcast channels with a single transmitter and multiple receivers. The transmitter is assumed to be equipped with multiple antennas. Further, each receiver is interested ...
  • The Capacity of Average and Peak Power Constrained Fading Channels with Channel Side Information 

    Khojastepour, Mohammad; Aazhang, Behnaam (2004-03-01)
    We derive the ergodic capacity of discrete-time fading channel with additive Gaussian noise subject to both peak and average power constraint. The average power can be interpreted as the cost that we incur to achieve a ...
  • A comparative study of multiple accessing schemes 

    Erkip, Elza; Aazhang, Behnaam (1997-11-20)
    We compare the performance of different accessing schemes (frequency division, time division and code division) for the uplink in a wireless communication system. We assume an additive white Gaussian noise channel with ...
  • Computationally Efficient Iterative Multiuser Detection and Decoding 

    Das, Suman; Erkip, Elza; Aazhang, Behnaam (1998-11-20)
    We describe an iterative detection and decoding scheme for the uplink in a convolutionally coded direct sequence code division multiple access (DS-CDMA) system. We consider maximum-a-posteriori (MAP) decoding and reduce ...
  • Computationally Efficient Multiuser Detectors 

    Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam (1997-09-20)
    CDMA is becoming an increasingly popular multiplexing scheme in wireless communications and this has necessitated the development of efficient detection techniques. The exponential complexity of the optimal detector on ...
  • Constellations for Imperfect Channel State Information at the Receiver 

    Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam (2002-10-20)
    We consider the problem of digital communication in a Rayleigh flat fading environment using a multiple antenna system. We assume that the transmitter doesn't know the channel coefficients, and that the receiver has only ...
  • Contraction, Smoothness, and Low-Pass Filtering 

    Khojastepour, Mohammad; Aazhang, Behnaam; Baraniuk, Richard G. (2004-05-01)
    We introduce a generalized definition for "low-pass" filters that covers time-varying and nonlinear systems under the same umbrella. We show that the qualitative concept of signal smoothing can be made precise through the ...
  • Cooperative Communications in the Fading Channel 

    Ahmed, Nasir; Aazhang, Behnaam (2005-03-01)
    Cooperative coding is a communication paradigm that pools distributed resources of different nodes in a network, such that the nodes act like a collaborative system instead of greedy adversarial participants. Cooperation ...
  • COOPERATIVE COMMUNICATIONS: Fundamental Limits and Practical Implementation 

    Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-01-01)
    This chapter summarizes theoretically achievable gains and the construction of practical codes for user-cooperation. Most of these results relate to the relay channel, which is a three-terminal channel that captures the ...
  • Cut-set Theorems for Multi-state Networks 

    Khojastepour, Mohammad; Aazhang, Behnaam; Sabharwal, Ashutosh (2003-10-01)
    We derive new cut-set bounds on the achievable rates in a general multi-terminal network with finite number of states. Multiple states are common in communication networks in the form of multiple channel and nodes' states. ...
  • Cyclic spreading codes for CDMA systems 

    Lu, Jin; Aazhang, Behnaam (1997-10-20)
    In this paper, we propose a CDMA system using cyclic convolutional matched filter. The multiple access interference in this system is small under arbitrary relative delays
  • Data Collection by a Mobile Observer in a Single-hop Sensor Network 

    Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-01-15)
    In this paper, we demonstrate significant reduction in communication power by using a mobile observer to collect data from a wireless single-hop network of static sensors. The key challenge in using a mobile observer is ...
  • Delay and DOA estimation in CDMA communication systems via maximum likelihood techniques 

    Madyastha, Raghu; Aazhang, Behnaam (1997-10-20)
    We present a maximum likelihood method for delay estimation in a CDMA wireless communication system. An antenna array is used at the receiver, which facilitates the concomitant estimation of the direction of arrival (DOA) ...
  • Delay and Rate Constrained Transmission Policies over Wireless Channels 

    Rajan, Dinesh; Sabharwal, Ashutosh; Aazhang, Behnaam (2001-11-20)
    In this paper, we study delay and rate-constrained transmission of bursty traffic over wireless channels. We characterize the minimum power requirements via bounds for both single user and multiuser downlink problems, using ...
  • Delay bounded packet scheduling of bursty traffic over wireless channels 

    Rajan, Dinesh; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-01-01)
    In this paper, we study minimal power transmission of bursty sources over wireless channels with constraints on mean queuing delay. The power minimizing schedulers adapt power and rate of transmission based on the queue ...
  • Demonstration of all-optical CDMA with bipolar codes 

    Dennis, Tasshi; Aazhang, Behnaam; Young, James F. (1996-10-20)
    Using a fiber-based testbed, we experimentally verify that the advantageous correlation properties of bipolar spread-spectrum codes can be preserved in an optical channel using direct detection and all-optical encoder/decoders. ...
  • Design of Coded Modulation Schemes for Orthogonal Transmit Diversity 

    Borran, Mohammad Jaber; Memarzadeh, Mahsa; Aazhang, Behnaam (2001-06-20)
    In this paper, we propose a technique to decouple the problems of spatial and temporal diversity gain maximization involved in the design of space-time codes in fast Rayleigh fading channels by using orthogonal transmit ...
  • Design of Coded Modulation Schemes for Orthogonal Transmit Diversity 

    Borran, Mohammad Jaber; Memarzadeh, Mahsa; Aazhang, Behnaam (2001-05-20)
    In this paper, we propose a technique to decouple the problems of maximizing spatial diversity gain, temporal diversity gain, and coding gain, involved in the design of space-time codes in Rayleigh fading channels. For ...
  • Design of Multiple Antenna Coding Schemes with Channel Feedback 

    Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Aazhang, Behnaam (2001-11-20)
    In this paper, we derive multiple antenna transmission strategies in the presence of limited channel information at the transmitter and the receiver. In particular, we look at the cases of complete channel information, ...
  • Design of Space Time Codes With Optimal Coding Gain 

    Mukkavilli, Krishna Kiran; Aazhang, Behnaam; Ionescu, Michael D. (2000-09-20)
    Space time codes have been proposed in the literature as an efficient means for improving the data rates over fading channels with multiple transmit antennas. In particular, the rank and the determinant of code difference ...
  • Design of space-time codes with optimal coding gain 

    Mukkavilli, Krishna Kiran; Ionescu, Michael D.; Aazhang, Behnaam (2000-10-20)
    Space time codes have been proposed in the literature as an efficient means for improving the data rates over fading channels with multiple transmit antennas. In particular, the rank and the determinant of code difference ...
  • Design of the Transit Access Point Hardware Platform 

    Murphy, Patrick; Frantz, Patrick; Aazhang, Behnaam (2005-09-01)
    Our objective is to design, analyze, prototype and experimentally study the theoretical underpinnings for a wireless internet that simultaneously achieves deployability, scalability, high performance and a cost-effective ...
  • Design of WARP: A Wireless Open-Access Research Platform 

    Murphy, Patrick; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-09-01)
    This paper presents the design of WARP, a custom platform for research in advanced wireless algorithms and applications. The platform consists of both custom hardware and FPGA implementations of key communications blocks. ...
  • Distorted Channel Capacity: A Geometrical Approach 

    Das, Suman; Cavallaro, Joseph R.; Erkip, Elza; Aazhang, Behnaam (2000-06-20)
    Shannon's capacity result has often been used as a benchmark to compare the performance of practical codes. Shannon's theorem helps us to calculate the maximum rate at which data can be transferred without making any errors. ...
  • DSP architectural considerations for optimal baseband processing 

    Rajagopal, Sridhar; Rixner, Scott; Cavallaro, Joseph R.; Aazhang, Behnaam (2002-08-20)
    The data rate requirements for future wireless systems has increased by orders-of-magnitude (from Kbps to several Mbps), requiring more sophisticated algorithms for their implementation. This tutorial will explore different ...
  • Dual Problems in Power Control 

    Sabharwal, Ashutosh; Rajan, Dinesh; Aazhang, Behnaam (2001-10-20)
    In this paper, we study power control to minimize packet loss for delay-bounded transmission of bursty sources over Gaussian channels and transmission of constant rate sources over time-varying block fading channels. In ...
  • Efficient Multiuser Receivers for CDMA Systems 

    Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam (1999-09-20)
    We focus on the design of multiuser receiver structures for Code Division Multiple Access (CDMA) communication systems, in the presence of multipath elects and multiple sensors at the base station receiver. We present a ...
  • Efficient VLSI Architectures for Baseband Signal Processing for Wireless Base-Station Receivers 

    Rajagopal, Sridhar; Bhashyam, Srikrishna; Cavallaro, Joseph R.; Aazhang, Behnaam (2000-07-20)
    A real-time VLSI architecture is designed for multiuser channel estimation, one of the core base-band processing operations in wireless base-station receivers. Future wireless basestation receivers will need to use ...
  • Efficient VLSI architectures for multiuser channel estimation in wireless base-station receivers 

    Rajagopal, Sridhar; Bhashyam, Srikrishna; Cavallaro, Joseph R.; Aazhang, Behnaam (Kluwer Academic Pubishers, 2002-06-20)
    This paper presents a reduced-complexity, fixed-point algorithm and efficient real-time VLSI architectures for multiuser channel estimation, one of the core baseband processing operations in wireless base-station receivers ...
  • EM-Based Multiuser Detection in Fast Fading Multipath Environments 

    Borran, Mohammad Jaber; Aazhang, Behnaam (2002-08-01)
    We address the problem of multiuser detection in fast fading multipath environments for DS-CDMA systems. In fast fading scenarios, temporal variations of the channel cause significant performance degradation even with the ...
  • Experimental demonstration of bipolar codes for direct detection multi-user optical communication 

    Dennis, Tasshi; Nguyen, Lim; Aazhang, Behnaam; Young, James F. (1996-10-20)
    We report the first experimental demonstration of a broadband spectral encoding and decoding technique using bipolar codes for optical code-division multiple access. The codeword correlations are verified and rejection of ...
  • Fast Multi-user Detector for a Time-varying CDMA System 

    Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam (SPIE, 1997-07-01)
    This paper investigates methods to reduce the amount of computation needed to detect information bits using a linear detector for a CDMA system. We show windowing technique coupled with pipelining can reduce the amount of ...
  • Feedback gain in Multiple Antenna Systems 

    Bhashyam, Srikrishna; Sabharwal, Ashutosh; Aazhang, Behnaam (2002-05-20)
    Multiple antenna transmission and reception have been shown to significantly increase the achievable data rates of wireless systems. However, most of the existing analysis assumes perfect or no channel information at the ...
  • Finite Backlog Effects on Downlink Scheduling 

    Ahmed, Nasir; Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-11-20)
    In a multi-user downlink system, the use of channel estimates in the scheduling process can significantly improve the spectral efficiency. Recent work has shown that from a sum rate capacity standpoint, and assuming infinite ...
  • Finite Memory-length Linear Multiuser detection for Asyncchronous Communications 

    Juntti, Markku J.; Aazhang, Behnaam (1997-05-20)
    Decorrelating, linear, minimum mean-squared error (LMMSE), and noise-whitening multiuser detectors for code-division multiple-access systems (CDMA) are ideally infinite memory-length (referred to as IIR) detectors. To ...
  • Finite memory-length linear multiuser detection for asynchronous CDMA communications 

    Juntti, Markku J.; Aazhang, Behnaam (1997-10-20)
    Decorrelating, linear, minimum mean-squared error (LMMSE), and noise-whitening multiuser detectors for code-division multiple-access systems (CDMA) are ideally infinite memory-length (referred to as IIR) detectors. To ...
  • Finite Rate Feedback Design for Multiple Transmit Antennas 

    Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Aazhang, Behnaam (2002-10-20)
    Many practical systems employ a feedback channel to convey the channel state information to the transmitter.The capacity of the feedback channels is usually limited to a few bits per frame. We design feedback based ...
  • Fixed Point Error Analysis Of Multiuser Detection and Synchronization Algorithms For CDMA Communication Systems 

    Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam (1998-04-20)
    Conventional correlation based single-user techniques for Direct Sequence Code Division Multiple Access (DS-CDMA) wireless communication systems are susceptible to performance degradation due to interference from other ...
  • Generalized Beamforming for MIMO Systems with Limited Transmitter Information 

    Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-11-20)
    In this work, we investigate the outage performance of beamforming schemes in wireless systems equipped with multiple transmit and receive antennas. In particular, we analyze the outage performance of unit rank beamforming ...
  • Gradient Estimation for Sensitivity Analysis and Adaptive Multiuse Interface Rejection in Code-division Multiple-access Systems 

    Mandayam, Narayan B.; Aazhang, Behnaam (1997-07-20)
    In this paper, we consider a direct-sequence code-division multiple-access (DS-CDMA) system in the framework of a discrete-event dynamic system (DEDS) in order to optimize the system performance. Based on this formulation, ...
  • Gradient estimation for stochastic optimization of optical code-division multiple-access systems. II. Adaptive detection 

    Mandayam, Narayan B.; Aazhang, Behnaam (IEEE, 1997-05-20)
    For pt.I see ibid., vol.15, no.4, p.731-41 (1997). We develop infinitesimal perturbation analysis (IPA)-based stochastic gradient algorithms for deriving optimum detectors with the average probability of bit error being ...
  • Gradient Estimation for Stochastic Optimization of Optical Code-Division Multiple-Access Systems: Part I -- Generalized Sensitivity Analysis 

    Mandayam, Narayan B.; Aazhang, Behnaam (1997-05-20)
    For optimizing the performance of optical code-division multiple-access (CDMA) systems, there is a need for determining the sensitivity of the bit-error rate (BER) of the system to various system parameters. Asymptotic ...
  • Half-Duplex Estimate-and-Forward Relaying: Bounds and Code Design 

    Chakrabarti, Arnab; de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-07-01)
    We propose a coding scheme for half-duplex estimate-and-forward relaying. Our first contribution is to present an achievable rate for the estimate-and-forward protocol. We also derive the achievable rate for the special ...
  • Half-Duplex Estimate-and-Forward Relaying:Bounds and Code Design 

    Chakrabarti, Arnab; de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-01-01)
    We propose a coding scheme for half-duplex estimate-and-forward relaying. Our first contribution is to present an achievable rate for the estimate-and-forward protocol. We also derive the achievable rate for the special ...
  • Hybrid Linear-Iterative Detection Algorithms for MIMO CDMA 

    Muharemovic, Tarik; Onggosanusi, Eko; Dabak, Anand; Aazhang, Behnaam (2002-05-20)
    We assume a CDMA downlink multiuser scenario, where the base station is equipped with multiple transmit antennas, and each user has multiple receive antennas. For this setup we propose a new, computationally effective MIMO ...
  • Impact of Multiple Access on Uplink scheduling 

    Rajan, Dinesh; Sabharwal, Ashutosh; Aazhang, Behnaam (2001-09-20)
    In this paper, we consider uplink scheduling for bursty traffic. We characterize the achievable rate region for Gaussian multiple access in terms of minimum required powers, with a constraint on average transmission delay ...
  • Importance sampling for analysis of direct detection optical communication systems 

    Mandayam, Narayan B.; Aazhang, Behnaam (1995-02-20)
    Analytical solutions of the performance of optical communication systems are difficult to obtain and often, Monte Carlo simulations are used to achieve realistic estimates of the performance of such systems. However, for ...
  • Improved Achievable Rates for User Cooperation and Relay Channels 

    Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-06-01)
    In this paper, we derive a new achievable rate region for the user cooperation channel, which exceeds the best known result for this channel [Wil83]. Since the user cooperation channel includes many other known channels ...
  • Increasing uplink capacity via user cooperation diversity 

    Sendonaris, Andrew; Erkip, Elza; Aazhang, Behnaam (IEEE, 1998-08-20)
    Mobile users' capacity is limited by the fact that within the duration of any given call, they experience severe variations in signal attenuation, thereby necessitating the use of some type of diversity. We are proposing ...
  • Information Theoretic Optimality of Orthogonal Space-Time Codes and Concatenated Code Construction 

    Muharemovic, Tarik; Aazhang, Behnaam (2000-06-20)
    We demonstrate that the information theoretic capacity of multiple-transmit antenna systems is not reduced by using space-time orthogonal transmit schemes as means of exploiting the transmit diversity. Then, we consider ...