Joint Optimization of Iterative Source and Channel Decoding Using Over-Complete Source-Mapping

The intentionally imposed or inherent unintentional residual redundancy found in source encoded bitstreams can be exploited for supporting joint SoftBit-source decoding and channel decoding, which has the potential of improving both error correcting capability as well as the subjective audio or video quality of communication systems. As a potent error concealment technique, the softbit-based source decoding, proposed by Adrat Vary and Spittka exploits the residual redundancy or correlation inherent in the source codec parameters for mitigating the effects of transmission errors. However, when using efficient source encoders, limited source redundancy is left in the source- encoded bitstream. In this scenario the SoftBit-source decoder (SBSD) may have a limited extrinsic information contribution which results in no system performance improvements beyond two decoding iterations. In our novel approach, we partition the total available bit budget between the source and channel codecs in order to improve the attainable error correcting capability and hence to maximize the overall system´s performance. More explicitly, the inherent redundancy in the encoded bit- stream is intentionally increased with the aid of over-complete mapping, and extrinsic information transfer (EXIT) charts are used for designing a suitable mapping of the source-coded bits to the modulated symbols, leading to an approximately 2dB signal-to-noise gain.