Now showing items 1-17 of 17

  • Distributed Cooperative Communications in Wireless Networks 

    Khojastepour, Mohammad (2005-01-01)
    The primary challenge in communication over wireless networks, unlike wireline networks, is the existence of interference and channel variations (fading). Having more users at higher data rates means that current ...
  • 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 ...
  • How Quickly Can We Approach Channel Capacity? 

    Baron, Dror; Khojastepour, Mohammad; Baraniuk, Richard G. (2004-11-01)
    Recent progress in code design has made it crucial to understand how quickly communication systems can approach their limits. To address this issue for the channel capacity C, we define the nonasymptotic capacity C/sub ...
  • 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 ...
  • 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 ...
  • Delay-constrained Scheduling: Power Efficiency, Filter Design, and Bounds 

    Khojastepour, Mohammad; Sabharwal, Ashutosh (2004-03-01)
    In this paper, packet scheduling with maximum delay constraints is considered with the objective to minimize average transmit power over Gaussian channels. The main emphasis is on deriving robust schedulers which do ...
  • 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 ...
  • 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 ...
  • 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 ...
  • Power Optimal Scheduling with Maximum Delay Constraints 

    Khojastepour, Mohammad; Sabharwal, Ashutosh (2003-10-01)
    Most multimedia sources are bursty in nature, a property which can be used to trade queuing delay with the resulting average transmission power [2, 3, 4]. In this paper, we study the relation between average transmission ...
  • 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. ...
  • 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 ...
  • 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 ...