DTMAC: A Delay Tolerant MAC Protocol for Underwater Wireless Sensor Networks

Unlike radio communication in terrestrial wireless sensor networks, acoustic channel in underwater wireless sensor network (UWSN) is challenged by long propagation delay and swarm mobility. The long propagation delay causes the deterioration of network throughput and unfairness. Moreover, the swarm mobility causes unreliable access and the failure of channel reservation. In this paper, we propose a novel delay tolerant MAC protocol (DTMAC) inspired by the coupon collector's problem. It proposes a distributed coupon collection algorithm in UWSNs. If a node needs to send a packet, the packet will be repeatedly transmitted m times, with a transmission probability to be p. Under the traditional protocol interference model, we first set up a probability model for throughput of DTMAC, and then give the throughput-optimal value for m and p with the successful transmission probability as tuning parameter. Because no any acknowledge or channel reservation is used, the throughput of DTMAC is not influenced by propagation delay. In addition, space unfairness problem also no longer exists since DTMAC is not concerned with transmission distance. The simulation results show that the throughput of DTMAC greatly outperforms that of MAC protocol with RTS/CTS scheme in most underwater scenarios.