Practical distributed turbo coding through soft information relaying

In this paper, we propose a novel distributed turbo coding (DTC) scheme which can be used in a system where imperfect decoding occurs at a relay. For the proposed scheme, rather than making a decision on the transmitted information symbols at the relay as in the conventional DTC, we calculate and forward the corresponding soft information at the relay. For the proposed scheme, we derive the parity symbols soft estimates for the interleaved source information when only the a posteriori probabilities (APP) of the information symbols are known. Analytical results show that the performance of the proposed scheme, at high SNR, is limited by the ratio of the received SNR at the relay and that at the destination. In order to make the performance loss of the proposed scheme, compared to the perfect DTC as small as possible, the relay should be placed closer to the source than to the destination and/or make the transmit power from the source larger than that from the relay