[CPCC] TALK: Bidirectional Relay Network Capacity (4/13/2009)

[Ender Ayanoglu]

                                    TALK

         Capacity Region of the Bidirectional Wireless Relay Network

                                 Aydin Sezgin
                                April 13, 2009
                                     10 AM
                            Engineering Gateway 3161

                                  ABSTRACT

In this talk we study the capacity region of the multi-pair
bidirectional (or two-way) wireless relay network, in which a relay
node facilitates the communication between multiple pairs of users. We
first examine this problem in the context of the deterministic channel
interaction model, which eliminates the channel noise and allows us to
focus on the interaction between signals.  For clarity of presentation
we first discuss the one pair of users case and later on generalize
the result to the multi-pair-case.  We characterize the capacity
region of this network. We show that the cut-set upper bound is tight
and, quite interestingly, the capacity region is achieved by a
divide-and-conquer strategy, in which the relay applies a simple
equation-forwarding scheme.  We then use the insights gained from the
deterministic network for the Gaussian bidirectional (or two-way)
relay network.  Also in the Gaussian case, we first discuss the
one-pair case and later on generalize it to the two-pair case later
on.  For the single-pair case, one interpretation of the strategy of
the deterministic channel is to use superposition encoding with two
random Gaussian codes at the source nodes. The relay quantizes the
received signal and forwards it to the destinations. We analyze the
achievable rate of this scheme and show that for all channel gains it
achieves to within 3 bit/sec/Hz per user of the cut-set upper bound on
the capacity region of the one-pair bidirectional relay channel. For
the multi-pair case, the strategy in the deterministic channel
translates to a specific superposition of lattice codes and random
Gaussian codes at the source nodes for the Gaussian network. The relay
attempts to decode the Gaussian codewords and the superposition of the
lattice codewords of each pair. Then it forwards this information to
all users. We analyze the achievable rate of this scheme and show that
for all channel gains it achieves to within 2 bits/sec/Hz per user of
the cut-set upper bound on the capacity region of the two-pair
bidirectional relay network.

                                BIOGRAPHY

Aydin Sezgin received the Dipl.-Ing. (M.S.) degree in communications
engineering and the Dr.-Ing. (Ph.D.) degree in electrical engineering
(both with distinction) from the University of Applied Sciences,
Berlin, Germany, in 2000 and the University of Technology Berlin, in
2005, respectively. From 2001 to 2006, he was with the Department of
Broadband Mobile Communication Networks, Fraunhofer Institute for
Telecommunications, Heinrich-Hertz-Institut (HHI), Berlin. From 2006
to 2007, he was lecturer at the Department of Mobile Communications,
University of Technology Berlin. From 2006 to 2008, he was with the
Information Systems Laboratory, Department of Electrical Engineering,
Stanford University, Stanford, CA as a postdoctoral research
associate. From 2007 to 2008, he was co-lecturer at the Stanford
University. Since 2008, he has been a postdoctoral research scholar
with the Department of Electrical Engineering and Computer Science,
University of California Irvine, CA. His current research interests
are in the area of information theory, signal processing and multiple
antenna systems (e.g., MIMO transceiver design and interference
channels).