CFDAMA-SRR: A MAC Protocol for Underwater Acoustic Sensor Networks.

Underwater acoustic sensor networks are an enabling technology for many applications. Long propagation delays and limited bandwidth of the acoustic channel place constraints on the trade-off between achievable end-to-end delay, channel utilization, and fairness. This paper provides new insights into the use of the combined free/demand assignment multiple access (CFDAMA) schemes. The CFDAMA can be classified as adaptive TDMA, where capacity is usually assigned on demand. The CFDAMA with round robin requests (CFDAMA-RRs) are shown to minimize end-to-end delay and maximize channel utilization underwater. It sustains fairness between nodes with minimum overhead and adapts to changes in the underwater channel and time-varying traffic requirements. However, its performance is heavily dependent on the network size. The major contribution of this paper is a new scheme employing the round robin request strategy in a systematic manner (CFDAMA-SRR). Comprehensive event-driven Riverbed simulations of a network deployed on the sea bed show that the CFDAMA-SRR outperforms its underlying scheme, CFDAMA-RR, especially when sensor nodes are widely spread. Considering node locations, the novel scheme has a bias against long delay demand assigned slots to enhance the performance of the CFDAMA-RR. The illustrative examples show good agreement between the analytical and simulation results.