Study of Reduced Complexity Syndrome Based TTCM Decoder

Turbo codes were a major milestone in the forward error correction codes which can even achieve an excellent bit error rates at low SNR. The original proposal was for the BPSK scheme but were soon successful with multilevel coded as well. The “Turbo Trellis Coded Modulation” (TTCM) employing two TCM codes as parallel concatenation of two recursive TCM encoder, and adapted puncturing mechanism to avoid the obvious disadvantage of the rate loss The iterative decoder of Turbo Trellis Coded Modulation (TTCM) exchanges extrinsic information between the constituent TCM decoders, which imposes a high computational complexity at the receiver. Therefore we conceive the syndrome-based block decoding of TTCM, which is capable of reducing the decoding complexity by disabling the decoder, when syndrome becomes zero. Quantitatively, we demonstrate that a decoding complexity reduction of at least 17% is attained at high SNRs, with at least 20% and 45% reduction in the 5 and 6th iterations, respectively. KeywordsBlock syndrome decoding, TTCM, iterative decoding, BSD BICM.