Comparative analysis of two realizations for hybrid-ARQ error control

This paper addresses the implementation and performance of hybrid-ARQ error control on a coherent slowly fading Ricean channel. Using a convolutional code with soft-decision Viterbi decoding for error correction, there are two methods for realizing the simultaneous error detection capability which characterizes hybrid-ARQ error control: (1) a two code approach which pre-encodes the information based on a high rate CRC code and performs error detection on the output of the Viterbi decoder, (2) a single code approach which modifies the Viterbi decoder to reject packets with low reliability during the Viterbi decoding process. The resulting analysis shows that the two code method is more robust than single code method with the most significant performance advantages realized for Rayleigh fading. The two code approach provides acceptable error rate performance and offers a throughput characteristic which is not as sensitive to changes in the average SNR as the single code approach. Since the implementational complexity of the two methods is comparable, the two code method is the preferred implementation for hybrid-ARQ on flat fading channels.