The performance of type-I trellis coded hybrid-ARQ protocols over AWGN and slowly fading channels

A method is described for modifying trellis coded modulation systems for use in type-1 hybrid-ARQ protocols. The difference between the partial path metric of the survivor and that of the best nonsurvivor at each node in the trellis is used to determine the desirability of a retransmission request for a given received packet. Bounds on the reliability and throughput performance of the resulting error control scheme are derived for AWGN channels and slowly fading Rician channels. Examples are included to illustrate the achievable gain of the proposed system relative to ordinary forward-error-correcting trellis coded systems. Hybrid-ARQ protocols based on ordinary trellis coded modulation and multiple trellis coded modulation are also compared over slowly fading Rician channels. The dependence of performance on packet length is examined and illustrated by examples. All analytical results are supported by data from a series of simulations