Now showing items 1-60 of 134

  • 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. ...
  • 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 ...
  • LDPC Code-Design for the Relay Channel 

    Chakrabarti, Arnab; de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-06-01)
    We propose LDPC code designs for the half-duplex relay channel. Our designs are derived from the information theoretic random coding scheme for decode-and-forward relaying. An important advantage of our scheme is that it ...
  • LDPC Code Design for Relay Channel in Time-Division mode 

    de Baynast, Alexandre; Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-06-01)
    We address the problem of LDPC code design for relay channel in time-division mode based on a distributed strategy: In the first time slot, the source transmits part of the codeword. The relay and the destination receive ...
  • LDPC Code-Design for the Relay Channel 

    Chakrabarti, Arnab; de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2006-02-01)
    We propose LDPC code designs for the half-duplex relay channel. Our designs are derived from the information theoretic random coding scheme for decode-and-forward relaying. An important advantage of our scheme is that it ...
  • 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 ...
  • 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 ...
  • 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 ...
  • LDPC Code Design for Half-Duplex Decode-and-Forward Relaying 

    Chakrabarti, Arnab; de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-09-01)
    We propose LDPC code designs for the half-duplex relay channel. Our designs mimic the information theoretic random coding scheme for decode-and-forward relaying. An important advantage of our scheme is that it is built ...
  • 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 ...
  • Low Complexity Iterative Multiuser Detection and Decoding for Real-Time Applications 

    Das, Suman; Erkip, Elza; Cavallaro, Joseph R.; Aazhang, Behnaam (IEEE, 2005-07-01)
    This paper presents a low-complexity multiuser decoding technique that can be implemented in real time for a convolutionally coded direct sequence code division multiple access (DS-CDMA) system. The main contribution, ...
  • LDPC Code Design for OFDM Channel: Graph Connectivity and Information Bits Positioning 

    de Baynast, Alexandre; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-07-01)
    We present an optimized channel coding scheme for OFDM transmission. In the future wireless standards such IEEE 802.11n, frame error rates (FER) as low as 0.0001 are targeting. Irregular LDPC codes have excellent performance ...
  • Sensitivity of Achievable Rates for Half-Duplex Relay Channel 

    Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2005-06-01)
    This paper investigates the sensitivity of achievable rates for the half-duplex AWGN relay channel to the choice of modulation, receiving time fraction, and source-relay correlation. Our study is motivated by practical ...
  • Throughput Gains with Limited Feedback in Cooperative Relay Networks 

    Ahmed, Nasir; Aazhang, Behnaam (2005-06-01)
    In this work, we consider delay-constrained systems in cooperative relay networks, and derive methods to maximize the throughput when a limited feedback link to the transmitter nodes exist. We derive the optimal rate control ...
  • 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 ...
  • 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 ...
  • 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 ...
  • Outage Minimization with Limited Feedback for the Fading Relay Channel 

    Ahmed, Nasir; Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-12-01)
    In this work, we consider practical methods to approach the theoretical performance limits in the fading relay channel under different assumptions of transmitter channel knowledge. Specifically, we consider two degrees of ...
  • Power efficient broadcast scheduling with delay deadlines 

    Rajan, Dinesh; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-10-01)
    In this paper, we present a framework for the design of minimal power schedulers that satisfy average packet delay bounds for multiple users in a Gaussian wireless broadcast channel. We completely characterize the achievable ...
  • On Limits of Antenna Packing in Low Power Systems 

    Muharemovic, Tarik; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-09-01)
    We evaluate spectral efficiency limits of low power portable communication devices which are only constrained by fixed transceiver aperture G "subset&equal" real<sup>3</sup> for mounting antennas. A new notion of ...
  • 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, ...
  • Outage behaviour with delay and CSIT 

    Rajan, Dinesh; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-06-01)
    In this paper, we demonstrate that the packet outage probability for fading channels can be significantly reduced by exploiting queuing delay and transmitter channel information. Queuing delay gain is conceptually similar ...
  • 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 ...
  • 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 ...
  • Outage Minimization and Optimal Power Control for the Fading Relay Channel 

    Ahmed, Nasir; Khojastepour, Mohammad; Aazhang, Behnaam (2004-05-01)
    In this work, we show that in the wireless relay network, a tremendous savings in energy can be achieved by having side information at the transmitters and by employing power control. We present efficient protocols and the ...
  • MultiHop Communication is Order Optimal for Homogeneous Sensor Networks 

    Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-04-01)
    The main goal of this paper is to show that multi-hop single-user communication achieves the per node transport capacity of O(lnN/N) in homogeneous sensor networks, making it order-optimal. Our contributions in this paper ...
  • A Recursive Construction for Low-Complexity Non-coherent Constellations 

    Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-04-01)
    It is known that at high signal to noise ratio (SNR), or for large coherence interval (T), a constellations of unitary matrices can achieve the capacity of the non-coherent multiple-antenna system in block Rayleigh flat-fading ...
  • On Power Control with Finite Rate Feedback for Cooperative Relay Networks 

    Ahmed, Nasir; Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-03-01)
    Power control strategies with finite rate feedback are studied for the cooperative channel. The main contribution of this paper is to show that quantized feedback information can lead to significant reduction in outage ...
  • 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 ...
  • Lower Bounds on the Capacity of Gaussian Relay Channel 

    Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-03-01)
    It has been shown recently that the overall throughput of dense wireless networks can increase significantly when wireless nodes collaborate in transmission of different packets. In this paper, we focus on a simple network ...
  • Partially Coherent Multiple Antenna Systems: Design Criterion and Construction Methods for Constellations and Coded Modulation 

    Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam (2004-01-15)
    We consider multiple-antenna communication systems in Rayleigh fading channel, where the transmitter does not know the channel coefficients and the receiver has only an estimate of them. We further assume that the transmitter ...
  • 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 ...
  • On Capacity of Gaussian â Cheapâ Relay Channel 

    Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-12-01)
    In this paper, we derive the capacity of the Gaussian degraded â cheapâ relay channel, consisting of nodes using â cheapâ radios operating in TDD mode when transmitting and sending in the same frequency band. The TDD ...
  • Partially Coherent Constellations for Multiple-Antenna Systems 

    Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam; Varshney, Prabodh (2003-11-20)
    We consider the problem of digital communication in a Rayleigh flat fading environment using a multiple antenna system. We assume that the transmitter doesnâ t know the channel coefficients, and that the receiver has only ...
  • 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 ...
  • 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 ...
  • User Cooperation Diversity--Part II: Implementation Aspects and Performance Analysis 

    Sendonaris, Andrew; Erkip, Elza; Aazhang, Behnaam (2003-11-20)
    This is the second in a two-part series of papers on a new form of spatial diversity, where diversity gains are achieved through the cooperation of mobile users. Part I described the user cooperation concept and proposed ...
  • User Cooperation Diversity--Part I: System Description 

    Sendonaris, Andrew; Erkip, Elza; Aazhang, Behnaam (2003-11-20)
    Mobile users' data rate and quality of service are 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 ...
  • On Design Criteria and Construction of Non-coherent Space-Time Constellations 

    Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-10-20)
    We consider the problem of digital communication in a Rayleigh flat fading environment using a multiple-antenna system, when the channel state information is available neither at the transmitter nor at the receiver. It ...
  • On Beamforming with Finite Rate Feedback in Multiple Antenna Systems 

    Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Erkip, Elza; Aazhang, Behnaam (2003-10-20)
    In this paper, we study a multiple antenna system where the transmitter is equipped with quantized information about instantaneous channel realizations. Assuming that the transmitter uses the quantized information for ...
  • 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 ...
  • 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 ...
  • 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. ...
  • Power-Efficient Non-coherent Space-Time Constellations 

    Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-07-20)
    We consider the problem of digital communication in a Rayleigh flat-fading environment using a multiple-antenna system, when the channel state information is available neither at the transmitter nor at the receiver. It ...
  • 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 ...
  • Spreading and Power Allocation for Multiple Antenna Transmission using Decorrelating receivers 

    Rajan, Dinesh; Erkip, Elza; Aazhang, Behnaam (2003-05-20)
    We propose a new scheme for multiple antenna transmission in the context of spread spectrum signaling. The new scheme consists of using shifted Gold sequences to modulate independent information on the multiple antennas. ...
  • 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 ...
  • Using Predictable Observer Mobility for Power Efficient Design of Sensor Networks 

    Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-04-20)
    In this paper, we explore a novel avenue of saving power in sensor networks based on predictable mobility of the observer (or data sink). Predictable mobility is a good model for public transportation ve- hicles (buses, ...
  • 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 ...
  • On the Capacity of `Cheap' Relay Networks 

    Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam (2003-04-20)
    We consider the communication problem in a multi-hop relay network where the intermediate relay nodes cannot transmit and receive at the same time. The motivation for this assumption comes from the fact that current radios ...
  • Robust Slope Region for Wideband CDMA With Multiple Antennas 

    Muharemovic, Tarik; Aazhang, Behnaam (2003-04-01)
    We analyze a low power, wideband CDMA system with multiple antennas. The joint "slope region" - of transmission rates at minimum energy per bit - is derived as a function of proportion between vanishing rates for multiple ...
  • Performance limits on beamforming with finite rate feedback for multiple antenna systems 

    Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Erkip, Elza; Aazhang, Behnaam (2002-11-20)
    In this work, we address the problem of evaluating the outage performance of beamformers designed for multiple transmit and single receive antenna systems when quantized channel state information is available at the ...
  • Maximum Weight Basis Decoding of Convolutional Codes 

    Das, Suman; Erkip, Elza; Cavallaro, Joseph R.; Aazhang, Behnaam (IEEE, 2002-11-01)
    In this paper we describe a new suboptimal decoding technique for linear codes based on the calculation of maximum weight basis of the code. The idea is based on estimating the maximum number locations in a codeword which ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • On Design Criteria and Construction of Non-coherent Space-Time Constellations 

    Borran, Mohammad Jaber; Sabharwal, Ashutosh; Aazhang, Behnaam; Johnson, Don (2002-07-20)
    We consider the problem of digital communication in a Rayleigh flat fading environment using a multiple antenna system, when both the transmitter and the receiver are unaware of the channel coefficients. Using Stein's lemma ...
  • Real-Time Algorithms and Architectures for Multiuser Channel Estimation and Detection in Wireless Base-Station Receivers 

    Rajagopal, Sridhar; Bhashyam, Srikrishna; Cavallaro, Joseph R.; Aazhang, Behnaam (IEEE, 2002-07-20)
    This paper presents alogrithms and architecture designs that can meet real-time requirements of multiuser channel estimation and detection in future wireless base-station receivers. Sophisticated algorithms proposed to ...
  • On the outage proabability of a class of signaling schemes for multiple antennas 

    Mukkavilli, Krishna Kiran; Muharemovic, Tarik; Sabharwal, Ashutosh; Aazhang, Behnaam (2002-07-20)
    In this work, we investigate large SNR behavior of the outage probability for a class of signaling schemes designed for flat fading Rayleigh multiple antennas systems. Outage probability is important in a practical system ...