Grouped Packet Coding: A Method for Reliable Communication Over Fading Channels With Long Delays

In this paper, we investigate an automatic repeat request (ARQ) for reliable transmission over half-duplex links. We design a method based on grouped packet coding (GPC) that combines a stop-and-wait (S&W) ARQ procedure with random linear packet coding and selective acknowledgments applied to groups of coded packets. Our goal in doing so is to boost the throughput efficiency on poor-quality links with long delay. Such links are notably encountered in underwater acoustic channels, where the bit error rate may be as high as $10^{-3}$ and round-trip delays can be measured in thousands of bits. To quantify the benefits of the proposed S&W-GPC method, we evaluate its throughput efficiency analytically and compare it with the throughput efficiency of standard S&W methods, as well as the benchmark efficiency of full-duplex methods. Our results show that S&W-GPC outperforms all other techniques on half-duplex links with long delay, as well as rateless packet coding on full-duplex links with long delay. We present results for a point-to-point link, as well as for a multicast network. In addition to the performance analysis, we offer guidelines for an optimal system design, which involves a judicious choice of the packet size, packet coding, and grouping parameters.