Application of Code Combining to a Selective-Repeat ARQ Link

Various attempts have been made to devise ARQ schemes which maintain throughput at high channel bit error rates. Of these selective-repeat schemes, particularly hybrid verisons which employ error-correction coding, have proven most effective. However, even these schemes fail to provide useful throughput at very high bit error rates, despite a non-zero channel capacity. In this paper we demonstrate that a selective-repeat ARQ link employing code combining can maintain useful throughput at very high error rates (error rates approaching 50%). Moreover, with minor modifications this technique incurs no loss relative to previous schemes at low channel bit error rates. We substantiate these claims by comparing the throughput performance of code combining using a rate-½, constraint length 7 convolutional code on a selective-repeat ARQ link with other selective-repeat ARQ schemes.