Analysis of Extrinsic Information from Softbit-Source Decoding Applicable to Iterative Source-Channel Decoding

Authors:

Adrat, M. ,  Picard, J.-M. ,  Vary, P.

Book Title:

Proceedings of International ITG Conference on Source and Channel Coding (SCC)

Address:

Berlin, Germany

Date:

Jan. 2002

Language:

English

Abstract

This contribution deals with Softbit-Source Decoding applied to an iterative source-channel decoding approach. Iterative decoding approaches have been introduced to increase the robustness of digital mobile communication systems. Softbit-Source Decoding can be considered as an error concealment technique. In order to cope with transmission errors residual redundancy of source codec parameters is utilized. The impact of the source statistics on single data bits can be quantified in terms of so-called extrinsic information. As a novelty, we will carefully analyze the extrinsic information of Softbit-Source Decoding. We will show, that the extrinsic information due to the source statistics is much less sensitive to an update in the decoder's soft-input as usually known from iterative channel decoding techniques. This might explain why in iterative decoding processes the performance improvements due to Softbit-Source Decoding are already gained with a small number of iterations. In most applications of iterative source-channel decoding no significant gain will be obtainable by more than two iterations.

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