Distributed on-demand MAC scheduling for 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 collision-free 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 independently generates on-demand and collision-free schedule for its cluster members using local information. Through pure scheduling and cooperation among neighboring clusters, DOS guarantees collision-free transmissions of both control and data packets. Compared with existing collision-free scheduling based MAC protocols, DOS is distributed and on-demand, i.e., it schedules according to nodes´ dynamic transmission requests. Further, DOS does not require CDMA or power adjustment for collision resolution. Extensive simulation results show that DOS far outperforms random access and handshake based MAC protocols. It also achieves a comparable throughput to a centralized scheduling algorithm, and this is a big accomplishment for DOS, a distributed solution.