Now showing items 21-40 of 68

  • 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 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 ...
  • An FPGA Based Rapid Prototyping Platform for MIMO Systems 

    Murphy, Patrick; Lou, Feifei; Sabharwal, Ashutosh; Frantz, Patrick (2003-11-20)
    There exists a seemingly limitless demand for wireless communications systems capable of higher datarates with lower power consumption. While the demand for improvement in these systems seems limitless, the spectrum ...
  • FPGA in Wireless Communications Applications 

    Amiri, Kiarash; Duarte, Melissa; Cavallaro, Joseph R.; Dick, Chris; Rao, Raghu; Sabharwal, Ashutosh (2012-07-12)
    In the past decade we have witnessed explosive growth in the wireless communications industry with over 4 billion subscribers worldwide. While first and second generation systems focused on voice communications, third ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • 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 ...
  • Network Channel Estimation in Cooperative Wireless Networks 

    Khoshnevis, Ahmad; Sabharwal, Ashutosh (2003-05-20)
    In distributed wireless networks, where nodes actively participate in helping communication for other nodes, they are typically unaware of their neighourhood and hence have to "estimate" it before sending any useful data. ...
  • 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 ...
  • 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 ...