A dynamic NAV determination protocol in 802.11 based underwater networks

In underwater networks, when designing contention-based MAC protocols such as CSMA/CA, a long propagation delay should be considered. Particularly, most protocols like 802.11, the most typical CSMA/CA protocol, which utilize the RTS/CTS handshaking technique with network allocation vector (NAV), determine the NAV using a value of duration field in RTS/CTS. The duration value is determined with a fixed inter-frame space such as SIFS and message lengths of CTS/DATA/ACK. Hence, they might be revised to employ the maximum propagation delay when determining the duration value. Nevertheless, in the cases where two closely-located nodes communicate, an unnecessarily long NAV duration according to the maximum propagation delay defers their neighbor nodes¿ transmission for a long duration time, which results in degrading network throughput. This paper therefore proposes a novel MAC protocol which determines the NAV dynamically by considering the propagation delay between nodes in order to avoid such an unnecessary long deferring. Through ns-2 based simulations, we verify that our MAC protocol achieved the performance improvements in terms of MAC transfer delay and throughput, as compared to a modified version of 802.11 which determines the NAV with the maximum propagation delay.