An improved ARQ scheme in underwater acoustic sensor networks

In underwater acoustic communications, using the property of long propagation delay, a concurrent packet transmission between two nodes could be made feasible without any collision. In this paper, utilizing the channel-sharing property, an efficient ARQ scheme is proposed. By controlling packet size such a way that transmission time becomes smaller than propagation delay, and by scheduling such packets properly, the collision-free transmission between multiple nodes is achieved. In addition, during a packet-relay through multiple hops, the typical acknowledgement (ACK) signal is replaced with overhearing data packet returned back from the next hop. The usage of overhearing as an ACK not only save power consumption but also significantly reduces overhead and transmission latency. Through the mathematical analysis and simulations, we evaluate proposed scheme in terms of the latency by comparing with an existing Stop & Wait ARQ.