Successive Interference Cancellation for Uplink CDMA

Prof. Jeff Andrews

Electrical and Computer Engineering
The University of Texas at Austin

Friday, November 1st, 3:00 PM, ENS 637

jandrews@ece.utexas.edu

Abstract

Successive interference cancellation (SIC) is a promising technique for increasing the capacity of uplink CDMA systems due to its low complexity, allowance of strong error-correcting codes, and robustness in an asynchronous environment. Despite these attractive qualities and a decade of research, SIC has been plagued by several crucial problems that have prevented its adoption by industry. This talk presents effective solutions to these problems.

First, an optimum power control distribution is derived, that is specifically designed to accommodate estimation error. This power control formula is a general result for CDMA; previous results are special cases. It is shown that by using this distribution, even estimation error of up to 50% can be tolerated in using SIC to more than double the overall system capacity.

Second, a non-uniform received power distribution apparently implies greater power control complexity, as all users must be kept at or near their optimum power levels, which differ based on their decoding order. Nevertheless, a simple iterative technique for achieving the optimum distribution is shown to exist and converge.

Finally, a multipath channel seriously hinders previous SIC systems, suggesting the need for an integrated OFDM-front end. Analytical BER expressions for a novel Multicarrier-SIC (MC-SIC) system are derived in a frequency-selective fading channel, and simulation results confirmed the effectiveness of using narrowband carriers to combat multipath. There is virtually no degradation relative to an AWGN channel, and it is shown that the proposed MC-SIC system design with optimal power control increases capacity by an order of magnitude over current industry systems.

Finally, we summarize areas of current and future research for successive interference cancellation.

Biography

Jeffrey G. Andrews is an Assistant Professor in the Department of Electrical and Computer Engineering at the University of Texas at Austin, in the Wireless Networking and Communications Group (WNCG). He received the B.S. in Engineering with high distinction from Harvey Mudd College in Claremont, California in 1995, and the M.S. and Ph.D. in Electrical Engineering from Stanford University in 1999 and 2002, respectively.

From 1995 to 1997, he was an engineer at Qualcomm in San Diego, California, developing the Globalstar satellite communication system. He has served as a frequent consultant on wireless communications and signal processing to industry and the government, in particular to Microsoft, Ricoh, and NASA.

His research interests focus on advanced CDMA systems, particularly system level design of multiuser receivers. He also has research interests in OFDM, MC-CDMA, multiple antenna CDMA, and wireless ad hoc 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