CFDAMA-IS: MAC Protocol for Underwater Acoustic Sensor Networks

This paper is concerned with coordinating underwater transmissions of acoustic sensor nodes. The use of acoustic waves to communicate underwater poses challenges to the functionality of Medium Access Control protocols. Long propagation delay and limited channel bandwidth are some of these challenges, which place severe constraints on the trade-off between end-to-end delay and achievable channel utilisation. The Combined Free and Demand Assignment Multiple Access (CFDAMA) protocol is known to significantly enhance the delay/utilisation performance. However, CFDAMA will suffer from long round trip delays and inefficient utilisation of its frames if it is implemented in medium and deep water. The major contribution of this paper is a new approach, namely CFDAMA with Intermediate Scheduler (CFDAMA-IS), to efficiently use CFDAMA in underwater environments. The paper compares these two protocols in typical underwater scenarios. It is shown that the proposed approach significantly reduces mean end-to-end delay and enhances channel utilisation.