W.K. Leung
City University of Hong Kong
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Publication
Featured researches published by W.K. Leung.
international conference on communications | 2004
Li Ping; Lihai Liu; K.Y. Wu; W.K. Leung
This work provides a comprehensive study of IDMA systems. We first outline the basic IDMA principles in single-path and multi-path environments. We then describe a simple semi-analytical technique to assess the performance of IDMA systems, based on which we develop a power allocation scheme for performance optimization. We also discuss the use of low-rate codes to further enhance the power efficiency of IDMA systems. Simulation results demonstrate the advantages of the IDMA scheme in terms of both bandwidth and power efficiencies. For example, with simple convolutional/repetition codes an overall throughput of 8 bits/chip is achieved in single antenna systems. With turbo-Hadamard codes, performance at 1.4 dB away from the theoretical limit is demonstrated in a Gaussian MAC.
wireless communications and networking conference | 2003
Li Ping; Lihai Liu; W.K. Leung
This paper presents an asynchronous interleave-division multiple-access (IDMA) scheme, in which users are distinguished by different chip-level interleaving methods instead of by different signatures as in a conventional code-division multiple -access (CDMA) scheme. A very low-cost iterative detection algorithm is derived for the IDMA scheme based on a chip-by-chip detection principle. The proposed scheme can achieve nearly optimal performance for systems with a large number of users. Furthermore, receiver simplicity as well as high performance can be maintained in multipath environments.
IEEE Communications Letters | 2000
Li Ping; W.K. Leung
This letter is concerned with the implementation issue of the sum-product algorithm (SPA) for decoding the low density parity check codes. It is shown that the direct implementation of the original form of SPA is sensitive to the quantization effect. We propose a parity likelihood ratio technique to overcome the problem. It is shown that for comparable performance the new method can be implemented with much less quantization bits, which can lead to considerably lower decoding cost.
vehicular technology conference | 2003
Lihai Liu; W.K. Leung; Li Ping
This paper examines several low-cost iterative chip-by-chip multiuser detection algorithms for chip-interleaved code-division multiple-access (CDMA) systems in multipath and multiple antenna environments. The complexities (per user) of these algorithms are very low and increase either linearly or quadratically with path number. It is shown that a system employing a rate-1/2 16-state convolutional code and a length-8 spreading sequence can support more than 100 users with two receive antennas.
IEEE Communications Letters | 2004
Li Ping; Lihai Liu; K.Y. Wu; W.K. Leung
We show that the capacity of a Gaussian multiple access channel can be approached by interleaved low-rate codes together with a simple chip-by-chip iterative decoding strategy. Based on a rate /spl ap/ 1/69 code and with a total of 35 simultaneous users (the aggregate rate /spl ap/ 1/2), performance of BER=10/sup -5/ is observed at E/sub b//N/sub 0/ /spl ap/ 1.4 dB, which is close to the corresponding capacity limit (E/sub b//N/sub 0/ /spl ap/ 0 dB).
information theory workshop | 2002
Li Ping; K.Y. Wu; Lihai Liu; W.K. Leung
Techniques using interleaving as the basic means for signal separation are introduced for both multiple access systems and multiple transmit antenna systems. A very low-cost chip-by-chip iterative detection algorithm is presented. The proposed schemes can achieve nearly optimal performance for system with a large numbers of users or transmit antennas.
international conference on communications | 2003
K.Y. Wu; W.K. Leung; Li Ping
This paper presents a family of space-time codes employing interleavers to separate signals form different antennas. Noticeable performance improvement has been observed compared with existing schemes. An interactive detection algorithm is derived. The complexity involved is very low, and increases only linearly with the number of transmit antennas.
global communications conference | 2004
K.Y. Wu; Li Ping; W.K. Leung
We study a multi-layer space-time code, based on random interleaving and proper power allocation. We show that, theoretically, the proposed code can achieve capacity for any transmission rate by superimposing many ideal low-rate codes. We also show that, with practically available codes, the proposed scheme can achieve performance close to the theoretical limit.
international conference on communications | 2006
Guosen Yue; W.K. Leung; Li Ping; Xiaodong Wang
We introduce a new class of low-rate error correction codes called concatenated zigzag Hadamard (ZH) codes which are specified by a highly structured zigzag graph with each segment being a Hadamard codeword. The ZH codes enjoy extremely simple encoding and very-low-complexity soft-input soft-output (SISO) decoding. We present an asymptotic performance analysis of the proposed codes using the extrinsic mutual information transfer (EXIT) chart for infinite-length codes. We also provide a union bound analysis of the error performance for finite-length codes.
vehicular technology conference | 2004
Li Ping; K.Y. Wu; W.K. Leung
We propose a family of simple multi-layer space- time codes based on random interleaving and power allocation techniques. We show that the optimal space-time coding problem can be effectively resolved by superimposing several ideal low-rate codes for an AWGN channel. Simulation results demonstrate that the proposed high-rate space-time codes can achieve performance close to the theoretical limit. I. INTRODUCTIONS