Concatenated error control codes and their applications in telecommunication systems

Abstract

This thesis is divided into two parts. Part I concerns the design issues of low-complexity concatenating codes and Part I1 discusses the application of the concatenating codes in mobile communication systems. In Part I, firstly, we present a semi-random encoding method of low-density parity-check (LDPC) code with encoding complexity linearly related to the information block sire. We also present an efficient implementation technique to the decoder of LDPC code. With this technique, the decoder can be implemented with addition only and it has considerably lower complexity compared with the original sum-product decoder of LDPC code. Secondly, we present a low-rate code constructed from Hadamard code arrays. A recursive encoding principle is employed to introduce an interleaving gain. Very simple trellis codes with only two or four states are sufficient for this purpose and the decoding cost involved in the trellis part is typically negligible. This code is of theoretical interest as it can achieve performance of BEK = 10 (-5) at E (b) / N (o) ≈ -1.2dB (only about 0.4 dB away from the ultimate Shannon limit) with an information block size of 65534. With regard to practical issues, the decoding complexity of the proposed code is considerably lower than that of existing low-rate turbo-type codes with comparable performance. Part 11 studies the coded communication systems and their iterative detection techniques. We first investigate a multiple-access scheme employing interleavers for user separation. We refer to this scheme as interleave-division multiple-access (IDMA), which is a special form of code-division multiple-access (CDMA) by viewing the interleaving index sequence as a code to distinguish users. Based on a rate 1116 low-rate code developed in Part I, IDMA can achieve performance of BER = 10 (-5) at E (b) / N (o) ≈ 1.4 dB with 8 simultaneous users (the aggregate rate = 1/2). It is close to the capacity of Gaussian multiple-access channel E (h) / N (o) ≈ 0 dB. Moreover, we study a family of interleave-based space-time codes using interleaver for signal separation. The basic principle is to transmit a randomly interleaved forward error control (FEC) codeword across multiple antennas in parallel. The rate of the FEC code can be much lower than that of the overall system, which allows a large amount of redundancy. Low-rate code can be used to exploit the expanded signaling dimension provided by multiple transmit antennas. The low-rate code developed in Part I can be employed to maximize coding gain. Performance reasonably close to the theoretical limit is demonstrated with arbitrary number of transmit antennas.

Date of Award	4 Oct 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Ping LI (Supervisor)