DLink: Introducing a Framework for Link Adaptation in Flooding-Based Underwater Networks

The underwater acoustic environment is known for its unpredictability, making it challenging to establish configuration parameters for acoustic modems before network deployment. When the modems are configured for robustness, potential throughput is often sacrificed; meanwhile, opting for high-rate links can result in communication failures in highly dynamic acoustic conditions. Given these challenges, this article presents an adaptation framework for networked underwater acoustic modems. Its primary objective is to let modems adaptively select communication links that balance information rate and reliability. It is assumed that the modems provide a set of preconfigured links with monotonically increasing information rate and decreasing reliability. The framework is developed specifically for flooding-based routing protocols, which efficiently handle sudden changes in network topology. By leveraging existing network traffic and implicit acknowledgments, the framework achieves link adaptation with minimal network overhead, necessitating only the addition of a “previous node” address field in the packet headers. Field experiments were conducted by deploying six acoustic modems in a time-varying acoustic environment. A well-known flooding-based protocol, DFlood, was used for routing in the experiments. The network's throughput with the adaptation framework was compared to that when only robust links were permitted. Results of the framework, using modems configured with four different links, show an increase in the average information per packet by a factor of up to 12, and a reduction in network transmission times of 25%–50%, demonstrating DLink's ability to enhance channel utilization, outperforming configurations that rely solely on robust links.