A hybrid ARQ scheme for DS-CDMA mobile data communications

This paper proposes a selective repeat hybrid-ARQ scheme for mobile data communications. An simplified Chase decoding and Viterbi decoding with code combining and diversity combining are concatenated as forward error correction (FEC). The Chase (1972) decoding algorithm is simplified in such a way that the algorithm searches for error bits according to their reliability information, and the try order for correct errors is controlled in order to reduce the number of calculations. The frames used for code combining and diversity combining are selected according to the reliability of the received frames. The extremely bad frames are discarded and only the good frames are combined for decoding, thus enhancing the decoding ability. The simplified Chase decoding increases the throughput in higher Eb/N0 ranges and the Viterbi decoding with code combining and diversity combining improves the throughput in the lower Eb/N0 ranges. Computer simulation results show that the proposed scheme used in a wideband coherent DS-CDMA system improves the throughput within a very wide Eb/N0 ranges