A multi-band Noise-aware MAC protocol for underwater acoustic sensor networks

We present a MAC protocol for underwater acoustic sensor networks (UASN) able to overcome the shortcomings induced by the temporary presence of noise sources within, or close-by, the region covered by the UASN. Our solution, named NAMAC for Noise-aware MAC protocol, exploits the ability of nodes equipped with multi-band modems to rapidly switch the frequency band used for communications upon detecting an increase of the in-band noise. Neighboring nodes may collectively decide to migrate to a different band and, as soon as the noise source is no longer impairing communications, to switch back to the default one. NAMAC also ensures connectivity across regions operating on different frequency bands induced by a different impact of noise at different locations. Additionally, if nodes are equipped with acoustic sensors able to monitor low frequencies, i.e., in the range from 0 to 5 kHz, NAMAC can exploit this capability to detect the approaching of a noisy vessel in advance, since noise at low frequencies is audible at larger distances. In this way, nodes can be pre-alerted for a band switch. We perform an extensive comparative performance evaluation of NAMAC based on ns-2 MIRACLE simulations. The noise frequency spectrum used in our simulations reproduces that of existing powerboats. Our performance evaluation shows that NAMAC is able to significantly outperform existing noise unaware MAC protocols that use a single band, increasing the network reliability in the presence of temporary noise sources like passing-by noisy vessels.