A joint power control and rate adaptation MAC protocol for underwater sensor networks

In this paper, we propose a new metric to measure the spatial reuse efficiency in networks: the spatial reuse index. We observed that the spatial reuse index in Underwater Sensor Networks (UWSNs) is significantly lower than in RF networks due to the relatively low spreading loss of acoustic signals. As a result, UWSNs generally have much lower network throughput. To address this problem, we propose an Underwater Power Control MAC protocol (UPC-MAC), which leverages dynamic transmission power adjustment and a novel rate adaptation algorithm to enhance the spatial reuse efficiency. UPC-MAC is a reservation based channel access scheme. It makes use of control packet's exchanges to collect neighboring nodes' data transmission requests and channel condition between senders and receivers. With such information, UPC-MAC allows for concurrent data transmissions by applying Nash Equilibrium to transmission power adjustment, which can be done independently on each sender in a distributed way. Furthermore, with the channel information, senders can adjust their data transmission rates by running a rate adaptation algorithm which considers the features of a real Orthogonal Frequency Division Multiplexing (OFDM) acoustic communication system. Simulation results show that UPC-MAC outperforms Slotted FAMA in terms of network goodput and lowers the energy consumption in two representative network scenarios. The simulation results also justify that our rate adaptation algorithm does improve the performance of UPC-MAC. UWSNs (Underwater Sensor Networks) have gained tremendous attention in recent years because of their wide civilian and military applications such as scientific/com-mercial exploitation, disaster prediction and coastline protection [1–3]. This motivates more research on a reliable and efficient UWSN designs. Due to the severe attenuation of radio waves caused by the conductivity of water, acoustic communication has proved to be the only practical method for long range wireless communication in underwater so far [4]. However, underwater acoustic communication also faces grand challenges , such as (a) limited bandwidth: current acoustic communication system is up to 40 km kbps for the range-rate product, (b) long propagation delay: the speed of sound underwater is approximately 1500 m/s, which is 2 Â 10 5 times slower than the speed of radio, (c) high energy consumption: most existing commercial acoustic modems are battery powered and have to be recharged after working continuously for several days.