Communicating Delay-Sensitive and

Bursty Information Over an Outage Channel

Tara Javidi

Assistant Professor

Electrical and Computer Engineering

University of California, San Diego

Abstract: In this talk, we consider a basic cross-layer queue-channel optimization problem for bursty and delay-sensitive information sources. In particular, we are interested in communications over outage-limited channels (with no feedback) when the number of bits that arrive at the transmitter during any time slot is random but the delivery of bits at the receiver must adhere to a strict delay constraint. In this setting, the errors experienced by the source of information, concatenated with an infinite buffer and a constant-rate outage-limited channel, are caused by either erroneous decoding at the receiver or violation of the delivery deadline. It is intuitive, then, that there is a trade off between reliability over the channel and timely delivery of information. After briefly revisiting the difficulty in quantifying the above trade-off in its classical Shannon Theoretic context, we take advantage of the high SNR analysis of outage-limited channels to go around this difficulty. Hence, the focus of the talk becomes to characterize the error performance of the overall system in the high SNR regime.

This characterization motives novel queuing theoretic work on a many source large deviation analysis of queues with batch service and/or multi-queue systems with Max-Weight scheduling policies. In particular, we use a recent extension of contraction principle, due to Garcia, to arrive at the appropriate large-deviation of a queue concatenated by a channel. We show that the optimal decay behavior of the asymptotic error probability depends on how fast the burstiness of the source scales down with its mean, which itself scales with SNR. Furthermore, we identify a particular scaling of burstiness under which the optimal exponent of the total error probability reveals a tradeoff addressing the following fundamental question: How much of the delay budget and channel capacity should be utilized for gaining reliability over the channel versus accommodating the burstiness of the delay sensitive source?

Bio: Tara Javidi studied electrical engineering at Sharif University of Technology, Tehran, Iran from 1992 to 1996. She received the MS degrees in electrical engineering (systems), and in applied mathematics (stochastics) from the University of Michigan, Ann Arbor, in 1998 and 1999, respectively. She received her Ph.D. in electrical engineering and computer science from the University of Michigan, Ann Arbor, in 2002. From 2002 to 2004, she was an assistant professor at the Electrical Engineering Department, University of Washington, Seattle. She joined University of California, San Diego, in 2005, where she is currently an assistant professor of electrical and computer engineering.

Her research interests are in communication networks, stochastic resource allocation, stochastic control theory, and wireless communications.

Thursday, March 12, 2009

4:00 pm-5:00 pm, EECS 1500