[CPCC] SEMINAR: Beamforming in Relay-Interference Networks 4/20 10 AM

[Ender Ayanoglu]

                               SEMINAR

         Beamforming in Wireless Relay-Interference Networks
                      with Quantized Feedback

                                 by
                            Erdem Koyuncu
                              UC Irvine

                           April 20, 2009
                               Monday
                                10 AM
                       Engineering Gateway 3161

                              ABSTRACT

We study quantized beamforming in wireless amplify-and-forward (AF)
relay networks. In the first part of the talk, we focus on a network
with a single-transmitter receiver pair. We use the Generalized Lloyd
Algorithm to design the quantizer of the feedback information and
specifically to optimize the bit error rate (BER) performance of the
system. Achievable bounds for different performance measures are
derived. First, we analytically show that a simple feedback scheme
based on relay selection can achieve full diversity. Then, for
high-rate feedback, we find an upper bound on the average
signal-to-noise ratio (SNR) loss. Using this result, we demonstrate
that both the average SNR loss and the capacity loss decay at least
exponentially with the number of feedback bits. In addition, we
provide approximate upper and lower bounds on the BER, which can be
calculated numerically. We observe that our designs can achieve both
full diversity as well as high array gain with only a moderate number
of feedback bits. Simulations also show that our approximate BER is a
reliable estimation on the actual BER. We also generalize our
analytical results to asynchronous networks, where perfect carrier
level synchronization is not available among the relays.

In the second part of the talk, we study quantized beamforming in
wireless AF relay interference networks with multiple
transmitter-receiver pairs. Two different quantization schemes are
considered. First, using a global quantizer structure, we analytically
show that a simple feedback scheme based on relay selection can
achieve full diversity. Then, we design a local quantization scheme
with distributed quantizer encoders at each receiver. We show that,
with only a few feedback bits from each receiver, high diversity gains
can be obtained with the local quantizer structure as well. We observe
that our designs guarantee an equal diversity gain for each
transmitter-receiver pair.

                        SPEAKER'S BIOGRAPHY

Erdem Koyuncu received the B.S. degree from the Department of
Electrical and Electronics Engineering of Bilkent University, Ankara,
Turkey in 2005, and the M.S. degree in 2006 from the Department of
Electrical Engineering and Computer Science of the University of
California, Irvine, Irvine, CA, USA, where he is currently a
Ph.D. candidate. His research interests include wireless
communications and signal processing.