The Underwater Selective Repeat Error Control Protocol for Multiuser Acoustic Networks: Design and Parameter Optimization

In this paper, we introduce Underwater Selective Repeat (USR), a Selective Repeat Automatic Repeat reQuest (SR-ARQ) mechanism for multiuser underwater acoustic networks. Our scheme exploits the typically large round-trip time (RTT) of underwater acoustic links to interlace the transmission of data and acknowledgment (ACK) packets, such that the transmitter never starts sending data packets when it should receive ACKs. No specific synchronization mechanism is required to do so. It is shown that the timing of point-to-point communications can be adjusted to optimize the performance of multiuser networks of a given size. Moreover, it is shown that the proposed strategy can be made robust to mobility, hence to time-varying RTTs. We provide detailed simulation results that assess the performance of USR as a function of the protocol parameters, both in static and in mobile networks. Based on these results, we propose an adaptive version of USR, whereby a node can modify its behavior (e.g., it can pack data transmissions more tightly or more loosely within one RTT) by reacting to packet errors induced by multiple-access interference.