Hybrid ARQ system employing soft decoding algorithm

It is known that by applying a soft decoding algorithm to the error-detecting code in the ARQ system, a hybrid ARQ system can be realized in which error detection and correction are possible. This paper discusses the application of the soft decoding algorithm to the ARQ system, where the multivalued digital modulation is employed. A scheme for a practical system is proposed, including the detection of channel measurement information in the multivalued digital modulation system and estimation of error patterns. By the proposed method, the hybrid ARQ system can easily be realized by adding some peripheral circuits to the conventional ARQ receiver. Theoretical study is made on the number of error patterns that can be estimated for a long block length as well as the probability of miss and the probability of retransmission request. The proposed scheme was applied experimentally to the ARQ system employing SG VIII V.29 modem based on CCITT recommendation, and the usefulness of the proposed scheme was verified by experiment.