Turbo codes for image transmission - A joint channel and source decoding approach

This paper studies an application of Turbo codes to compressed image/video transmission and presents an approach to improving error control performanc e through joint channel and source decoding (JCSD). The proposed approach t o JCSD includes error-free source information feedback, error-detected sour ce information feedback, and the use of channel soft values (CSV) for sourc e signal postprocessing. These feedback schemes are based on a modification of the extrinsic information passed between the constituent maximum a post eriori probability (MAP) decoders in a Turbo decoder, The modification is m ade according to the source information obtained from the source signal pro cessor. The CSV's ape considered as reliability information on the hard dec isions and are further used for error recovery in the reconstructed signals . Applications of this joint decoding technique to different visual source coding schemes, such as spatial vector quantization, JPEG coding, and MPEG coding, are examined. Experimental results show that up to 0.6 dB of channe l SNR reduction can be achieved by the joint decoder without increasing com putational cost for various channel coding rates.