Dual-Hop TDA-MAC and Routing for Underwater Acoustic Sensor Networks

Abstract

This article investigates the application of underwater acoustic sensor networks (UASNs) for large scale monitoring of the ocean environment. The low propagation speed of acoustic waves presents a fundamental challenge for medium access control (MAC)—coordinating the access of multiple nodes to the shared acoustic communication medium. In this article, we propose sequential dual-hop transmit delay allocation MAC (SDH-TDA-MAC)—a centralized MAC and routing protocol that facilitates efficient dual-hop scheduling in UASNs without the need for clock synchronization among the sensor nodes. BELLHOP-based simulations of a 100 node network reveal that SDH-TDA-MAC can achieve full network connectivity with 16-dB lower transmit power, compared with the single-hop TDA-MAC protocol. This provides considerable energy savings, while still providing network goodput in excess of 50% of the channel capacity. We also present a method of incorporating routing redundancy into the SDH-TDA-MAC protocol that achieves a good tradeoff between the network throughput and reliability. For example, in a channel with 10% probability of link outage, incorporating double routing redundancy into SDH-TDA-MAC increases the packet delivery ratio from 81% to 95%, a significant improvement in network reliability, while still achieving the network goodput of 22% of the channel capacity, considerably higher than typical MAC protocols designed for UASNs. In summary, the high network goodput, low transmit power compared with the single-hop approach, no requirement for clock synchronization, and robust packet delivery via route diversity make SDH-TDA-MAC an efficient, reliable, and practical approach to data gathering in UASNs.