『清华信息大讲堂』系列学术报告

Title:     Constructing very low rate optimal convolutional codes for CDMA

Speaker: Dr. Dawei Huang (Bell Labs Research China总监)

Time:    9:30-11:00am, 2006. 05. 11 (Thu)

Place：  Room 1-315, FIT Building

Contact Person：Prof. Zhisheng Niu (62781423)

Abstract:  Convolutional codes have been widely used for 50 years. However, “so far there has been little success in finding very good convolutional codes by algebraic methods” [1]. Most encoders used in practice with 2 or 3 generators were found by exhaustive search on computers. Such a search cannot be extended to very low rate convolutional codes, as low as 1/512, which can be used as spread code for CDMA as well. Efforts have been done in developing iterative search [2], but the resulted codes are not optimal in the sense of their distance spectrum.

In this talk, we try to solve this open problem by a fundamental property for binary codes, the Hadamard property based on GF(2) multiplications. Starting from a novel upper bound for arbitrary number of generators, we give a sufficient condition for arbitrary low rate optimal codes. Then we can calculate the optimal codes under different considerations by integer programming. The simulation result shows the new code really has better performance without extra cost for CDMA system.

[1]: Fundamentals of Convolutional Coding, R. Johannesson & K. Zigangirov, IEEE Press, 1999

[2] Code-spread CDMA using maximum free distance low-rate convolutional codes”, Frenger, Orten & Ottosson, IEEE COM48, pp135-144, 2000.

Biography : Dawei Huang received his Master of Science from the Dept of Mathematics, and Ph.D degrees from the Dept of Probability and Statistics, both in Peking University, in 1982 and 1987 respectively. Currently, he is the director of Bell Labs Research China (BLRC). He worked as a computer software engineer from 1973 to 1978; a Lecturer in Tsinghua University from 1982 to 1984; an Associate Professor in Peking University from 1987 to 1992; a Lecturer and a Senior Research Fellow in Queensland University of Technology from 1988 to 2000; a Contractor in Bell Labs, Murray Hill, Lucent Technologies in 1999 and 2000. He has joined Bell Lab Research China since August 2000, as a Member of Technical Staff, a Functional Manager and a Technical Manager. He was promoted to the director of BLRC in Feb 2004. He is an IEEE Senior Member. He published More than 60 papers on statistical and IEEE journals and conferences. He was granted many awards including the Third Class National Natural Sciences Award in China, 1995; the First Class Advanced Science and Technology Award by the State Education Committee (SEdC),China, 1995; the First Class Award in Science and Technology, Peking University,1993; the First Class Award in Science and Technology, Peking University, 1991; Time Series Analysis and Multivariate Analysis Award, China Academia in Science, 1989. His research interests include applications and theory in wireless system and multimedia communications, information theory, network modeling and transcoding and concealment, statistics and probability theory.