Concatenated Space-time Codes for Quasi-static Fading Channels
Mr. Vivek Gulati
Ph.D. Thesis Advisor: Prof. Krishna Narayanan
Electrical and Computer Engineering
Texas A&M University
Friday, October 11th, 3:00 PM, ENS 637
vivekgu@ee.tamu.edu
Abstract
Capacity results for multiple-input multiple-output (MIMO) quasi-static fading
channels (QSFC) indicate significant gains over single-input single-output
channels.
However, these results assume infinitely long Gaussian i.i.d. inputs, leaving
open the question of practical coding schemes. We address some of these issues
in this talk by considering a concatenation of an outer code with an inner
space-time code. This perspective encompasses three different coding schemes
obtained by changing the inner code to a serial-to-parallel converter (viz.
direct transmission), an orthogonal space-time block code (o-STBC) or a
space-time trellis code (STTC). For each of these schemes, we compute the
constrained modulation outage information rate. The capacity results show that
for very low rates, the space-time block codes are ideally suited. For higher
rates, the trellis codes have an information rate higher than both the block
codes and the direct transmission scheme. Finally, there is a range of rates
unachievable by both the block codes and the trellis codes so that direct
transmission is the only available option among these three choices. We then
look at the design of appropriate outer codes that enable us to approach these
information rates. For the direct transmission scheme, low-density parity check
(LDPC) codes can be designed to give a good performance. The orthogonal
space-time block codes convert the channel into an instantaneous AWGN channel
and so codes that achieve capacity on AWGN channels are capacity approaching
for the MIMO system as well. The use of recursive space-time trellis codes with
outer convolutional or product codes results in a serial concatenation system
that performs close to capacity over a range of rates.
Biography
Vivek Gulati received his B.Tech.(H) degree in Electronics and
Electrical Communications from Indian Institute of Technology, Kharagpur
in 1999. He is currently pursuing a doctoral degree in Electrical
Engineering at Texas A&M University.
Vivek's research interests include space-time codes, iteratively
decodable codes and wireless networks.
A list of Wireless Networking and Communications Seminars is available at
from the ECE department Web pages under "Seminars".
The Web address for the Wireless Networking and Communications Seminars is
http://signal.ece.utexas.edu/seminars