Analysis of an Automatic Repeat Request Scheme Addressing Long Delay Channels

This paper proposes a variation to the classic implementation of Automatic Repeat reQuest (ARQ) which is particularly suitable for the long delay channels, as can be found, for example, in the underwater environment. The proposed technique, called Selective Repeat with a Second Replica ARQ, (SR)^2 ARQ, follows the same rationale as Selective Repeat ARQ, but, upon NACK reception, schedules two retransmissions, one taking place immediately, and the other put in a special queue to be released after further retransmissions, but before new packet transmissions. We propose an exact analysis of this technique, proving its ability of trading throughput for shorter delivery delay; thus, it is suitable for scenarios where the required data rate is not high, but a timely data delivery is very important, as is the case, for example, for underwater monitoring applications.