DOS: Distributed On-demand Scheduling for High Performance MAC in Underwater Acoustic Networks

In underwater acoustic networks (UANs), due to the unique characteristics of acoustic modems such as long preambles and extremely low transmission rates, contentions are usually costly. As a result, both random access and handshake based MAC protocols do not perform as well as expected. A collisionfree approach is therefore considered to more likely achieve a better performance. Following this principle, we propose a collision-free scheduling-based MAC protocol, called DOS, for UANs. DOS is a cluster-based protocol, where each cluster head generates on-demand and collision-free schedule for its cluster members independently using local information. Through scheduling, DOS can guarantee collision-free transmissions of both control and data packets. Compared with existing collisionfree scheduling MAC protocols, DOS is distributed and ondemand, i.e., it schedules according to nodes’ dynamic transmission requests. Further, DOS does not require CDMA or power adjustment for collision resolution. Extensive simulation shows that DOS far outperforms random access and handshake based MAC protocols, and achieves a comparable throughput to a centralized scheduling algorithm.