Iterative source decoding, channel decoding and channel equalisation

Abstract

In this thesis, we apply EXtrinsic Information Transfer (EXIT) charts for analysing iterative decoding and detection schemes.  We first consider a two-stage iterative source/channel decoding scheme, which is then extended to a three-stage serially concatenated turbo equalisation scheme.  As a result, useful design guidelines are obtained for optimising the system’s performance.

More explicitly, in Chapter 2 various source codes such as Huffman codes, Reversible Variable-Length Codes (RVLCs) and Variable-Length Error-Correcting (VLEC) codes are introduced and a novel algorithm is proposed for the construction of efficient RVLCs and VLEC codes.  In Chapter 3, various iterative source decoding, channel decoding and channel equalisation schemes are investigated and their convergence behaviour is analysed by using EXIT charts.  The effects of different source codes and channel precoders are also considered. In Chapter 4, a three-stage serially concatenated turbo equalisation scheme consisting of an inner channel equaliser, an intermediate channel code and an outer channel code separated by interleavers is proposed.  With the aid of the novel concept of EXIT modules, conventional 3D EXIT chart analysis may be simplified to 2D EXIT chart analysis.  Interestingly, it is observed that for the three-stage scheme relatively weak convolutional codes having short memories result in lower convergence thresholds than strong codes having long memories.  Additionally, it is found that by invoking the outer and the intermediate decoder more frequently the total number of decoder activations is reduced, resulting in a relatively lower decoding complexity.  Furthermore, the three-stage turbo equalisation schemes employing non-unity rate intermediate codes or IRregular Convolutional Codes (IRCCs) as the outer constituent codes are investigated.  The performance of the resultant schemes is found to become gradually closer to the channel’s capacity at the expense of the increase of decoding complexity.

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