Listen to Others’ Failures: Cooperative ARQ Schemes for Low-Latency Communication Over Multi-Hop Networks
Jaya Goel, Harshan Jagadeesh · IEEE Transactions on Wireless Communications · 2021
Multi-hop networks comprising line-of-sight dominated wireless channels have found attractive applications in wireless networks involving unmanned aerial vehicles. It is well known that these applications require both high-reliability and low-latency features. While automatic-repeat-request (ARQs) based decode-and-forward (DF) relaying strategies provide the high-reliability feature, they are known to incur delay owing to multiple re-transmissions of packets. Towards addressing the above trade-off between reliability and low-latency of ARQ based DF strategies, we impose a sum constraint on the total number of ARQs across the nodes as it captures an upper bound on the time taken for packet re-transmissions. Subsequently, we propose various cooperative strategies among the nodes to minimize the packet-drop-probability (PDP). At the heart of our cooperative strategies lies the idea that unused ARQs of a node can be used by its neighbors to reduce the PDP without violating the sum constraint on the total number of ARQs. For each of the cooperative strategies, we formulate an optimization problem for distributing a given number of ARQs among the nodes. Then, we provide necessary and sufficient conditions on the optimal ARQ distribution in each of these strategies, and use these conditions to synthesize low-complexity algorithms to solve the problem. In addition to using PDP, we also present a thorough analysis on the delay profiles of the packets to incorporate the effect of cooperation on the latency performance of the cooperative strategies.