Toronto Networking Seminar 2006

Wireless Network Information Theory

 Liang-Liang Xie
University of Waterloo

Date:  February  3,  3pm
Location: BA1210 (Bahen Center)


How much information can a wireless network with a multiplicity of nodes transport, and how should the nodes cooperate to transfer information? We are interested in the best throughput performance a wireless network can achieve. For this, one naturally turns to the field of information theory. However, network information theory for communication channels with multiple users is an area where even several simplest scenarios, such as the interference channel and the relay channel, have not been completely solved.

    We formulate a model of wireless networks that particularly takes into account the distances between nodes, and the resulting attenuation of radio signals, and study a performance measure, the transport capacity, that weights information by the distance over which it is transported.

    We show that there is a dichotomy between the regimes of high and low signal attenuations. In the high signal attenuation regime, the transport capacity is bounded by a constant multiple of the sum of the transmit powers of all the nodes in the network. If the nodes are individually power limited, the transport capacity consequently scales as O(n), where n is the number of nodes in the network. However, in the low signal attenuation regime, there exist networks that can provide unbounded transport capacity, even for fixed total power. Moreover, there are special networks that can even attain superlinear scaling. These examples show that nodes can profitably cooperate over large distances using coherence and multi-user estimation when the attenuation is low.

We conclude with some open issues.


Dr. Xie is currently an Associate Professor at the Department of Electrical and Computer Engineering, University of Waterloo.  He received the B.S. degree in mathematics from Shandong University, China and the Ph.D. degree in control theory from the Chinese Academy of Sciences in 1995 and 1999, respectively. He was a Guest Researcher in the Automatic Control Group, Linköping University, Sweden during 1999-2000 and a Postdoctoral Research Associate in the Coordinated Science Laboratory, University of Illinois at Urbana-Champaign, USA during 2000-2002.