Graph-Based Turbo DeCodulation with LDPC Codes

Turbo DeCodulation is the combination of iterative demodulation and iterative source-channel decoding in a multiple Turbo process. The receiver structures of bit-interleaved coded modulation with iterative decoding (BICM-ID) and iterative source-channel decoding (ISCD) are merged to one joint Turbo system, which we further enhance in this paper by using a low- density parity check (LDPC) code for channel coding, resulting in a third iterative loop. We propose to use a special LDPC code structure with short sub-codes, which can be implemented very effectively in parallel. The quadripartite Tanner graph of the Turbo DeCodulation is presented, showing that the processing of all receiver nodes could be parallelized. Simulation results including an EXIT chart analysis demonstrate the excellent capabilities of Turbo DeCodulation with its performance gain exceeding the combined gain of BICM-ID and ISCD.