On ARQ strategies over random access protocols in underwater acoustic networks

In this paper, we introduce a mechanism to improve the performance of ARQ over underwater links. Our scheme aims at reproducing a Selective Repeat ARQ strategy: to do this, it sets up a form of time-division duplex link between the transmitter and its receiver, by leveraging on the propagation delay incurred by underwater sound. In fact, such delay typically allows to interlace the transmission of data and ACK packets in such a way that the two operations do not interfere or cause nodes to be deaf to the transmissions of each other. We consider two different versions of our protocol (in terms of channel access persistence) and compare them against ALOHA and CSMA with and without ARQ, in both static and mobile scenarios. We conclude that in multiuser networks our form of Selective Repeat ARQ outperforms other ACK-based protocols at low and intermediate traffic.