School Seminars and Colloquia

Diffusion Approximation for a Heavily Loaded Multi-User Wireless Communication System with Cooperation


by Prof. Ruth Williams

Institution: University of California, San Diego
Date: Fri 1st August 2008
Time: 3:15 PM
Location: Theatre 1, ICT Bldg, Rm G06, 111 Barry Street, Carlton

Abstract: We consider a model for a cellular wireless communication system in which
data is transmitted to multiple users over a common channel. For
information theoretic reasons, the rate of transmission over this channel
can be enhanced by cooperation. Assuming a fixed channel and that the
average arrival rate of data for each user is known, we consider a simple
scheduling policy which exploits cooperation and which has been shown to
be throughput-optimal under Markovian assumptions. As a measure of
performance under this policy, we establish a heavy traffic diffusion
approximation for the workload process. This diffusion process is a
semimartingale reflecting Brownian motion (SRBM) living in the positive
orthant of N-dimensional space (where N is the number of users).
Nominally, this SRBM has one direction of reflection associated with each
of the 2 (N)-1 boundary faces. However, we show that in fact only those
directions associated with the (N-1)-dimensional boundary faces matter in
the heavy traffic limit. Based on joint work with Sumit Bhardwaj.

For More Information: Konstantin Borovkov