Approximate capacity of the Gaussian Multiple Access Channel with Two Cooperating Sources

Daniela Tuninetti, University of Illinois at Chicago
Wednesday, March 13, 2013 - 14:00 to 15:00
Council room of L2S (room B4.40), Supélec, campus of Gif-sur-Yvette, Supélec.

Abstract: We consider a multiple access channel with two sources and a single destination, i.e., the uplink of a  simple cellular system with two mobiles and one base station. The two sources have independent information streams for the destination and share the same wireless channel. Because of the broadcast nature of the wireless channel, each source can in principle receive the signal transmitted by the other source, which we shall call generalized feedback (GF). With GF, a source can learn what the other source is doing and cooperate with it with the aim to achieve higher rates compared to the classical non-cooperative case. For the multiple access channel with GF, inner and outer bounds to the capacity region are known; unfortunately they do not coincide in general, as opposed to the non-cooperative case. 

In this talk we focus on the Gaussian noise channel and we make progress towards determining its capacity by considering two approximations of the capacity: (1) the "generalized degrees of freedom", i.e., an exact characterization of the capacity region in the limit for very hight SNR, and (2) the "capacity to within a constant gap", i.e., for each rate point on the closure of cut-set outer bound we show a simple achievable scheme that at any finite SNR looses at most a constant number of bits per channel use. We study both the full- and half-duplex cases. In full-duplex, a source can send and receive at the same time and on the same frequency band; in half-duplex, a source can either send or receive but not both.

From this study, a number of important practical considerations emerged: (a) for both full- and half-duplex: unilateral cooperation suffices to achieve capacity to within a constant gap, where only the source with the strongest link to the destination needs to engage in cooperation, (b) for both full- and half-duplex: simple stripping decoding without memory across time suffices to achieve capacity to within a constant gap, and (c) for half-duplex: time sharing between the case where the two sources do not cooperate at all and the case where the source with the strongest link to the destination acts as pure relay for the other source suffices to achieve capacity to within a constant gap. These findings show that simple achievable strategies are approximately optimal for all channel parameters, with interesting implications for practical implementation of cooperative schemes in uplink of cellular systems, which is traditionally modeled as a multiple-access channel.

arXiv:1209.4238, The Capacity of the Gaussian Cooperative Two-user Multiple Access Channel to within a Constant Gap, Daniela Tuninetti, accepted at the 2013 IEEE International Conference on Communications (ICC 2013).

Biography: Daniela Tuninetti received the M.S. degree in telecommunication engineering from the Politecnico di Torino, Turin, Italy, in 1998 and the Ph.D. in electrical engineering from ENST/Telecom ParisTech, Paris, France (work done at the Eurecom Institute in Sophia Antipolis, France) in 2002. From 2002 to 2004, she was a postdoctoral research associate at the School of Communication and Computer Science, EPFL/Swiss Federal Institute of Technology, Lausanne. Since January 2005, she is with the Department of Electrical and Computer Engineering, University of Illinois at Chicago, where she currently is an Associate Professor.

Her research interests are in the ultimate performance limits of wireless interference networks, with special emphasis on cognition and user cooperation. She also collaborate with the UIC Medical School  on the application of engineering techniques and principles to the design of improved medical equipment.

Dr. Tuninetti is a senior member of IEEE. She was the editor-in-chief of the IEEE Information Theory Society Newsletter from 2006 to 2008 and an associate editor for the IEEE COMMUNICATION LETTERS from 2006 to 2009. She currently is an editor for the IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS. She received the best student paper award at the European Wireless Conference in 2002 and was the recipient of an NSF CAREER award in 2007.

The talk will also be broadcasted at the same time on XiMinds.