Iterative decoding for joint source-channel coding using combined TCQ/CPM

An iterative soft decoding approach to joint source and channel coding using combined trellis coded quantization (TCQ) and continuous phase modulation (CPM) is proposed. The channel is assumed to be AWGN. The performance in terms of the signal-to-distortion ratio (SDR) is compared with that for a combined TCQ with trellis coded modulation (TCM) system. It is observed that the combined TCQ/CPM systems are both power and bandwidth efficient compared with the combined TCQ/TCM system. A convergence analysis, based on the uniform error property of geometrically uniform codes, has been generalized to codes with a nonuniform error property. For source encoding rate R=1 and R=2 bits/sample, the combined systems working at symbol level converge faster than those working at bit level. This can be explained by examining the error events of the combined system. The novelty of this work is the use of a soft decoder and an iterative decoding algorithm for TCQ based joint source channel coding systems. Also, combined TCQ/CPM systems operating at symbol level are considered for the first time.