Abstract:
Underwater acoustic sensor network (UASN) is composed of different number of sensors and moving vehicles which are distributed over a long range area to perform collective monitoring. Underwater acoustic channel, characterized by long propagation delay and low data rate, suffers from space time uncertainty causing spatial unfairness in UASN. A sender node which sends its request to send (RTS) at earlier time may not always be allowed to send its data packets earlier due to its long propagation delay. In UASN, usually a receiver node allows a sender node to transmit based on the earliest reception of its RTS packet which eventually deprives the terminal nodes with earlier transmission time, thereby creating spatial unfairness problem. In order to solve the problem, existing Medium Access Control (MAC) protocols allow the sender node which initiates its RTS packet at the earliest time. However, by allowing earliest RTS transmitter, existing MAC protocols create another kind of unfairness among the closer neighbor nodes. In this research work, a spatially fair MAC protocol is proposed in which a receiving node divides all its neighbor nodes into two groups based on average propagation delay of all of its neighbor nodes. The receiver then permits one prospective sender node from each group based on the earliest transmission time within a group. Receiver node, by employing a collision avoidance algorithm which exploits the benefit of propagation delay mapping of all its neighbor nodes, ensures that the two transmitted data packet will not collide at receiver's end. Otherwise, only a single sender node with the earliest transmission time within two groups is allowed to transmit. A simulation model based on OMNeT++ is developed to compare the performance of the proposed MAC protocol. Simulation results show that the proposed scheme achieves better performance in terms of latency, handshaking, fairness, network throughput, average RTS collision and clear to send (CTS) success rate compared to the contemporary SF-MAC and RET-MAC protocol.
