Underwater Acoustic Sensor Networks (UASNs) are becoming increasingly promising to monitor aquatic environment. However, reliable data delivery remains challenging due to long propagation delay and high error-rate of underwater acoustic channel, limited energy and inherent mobility of sensor nodes. To address these issues, we propose a protocol called Path Reliability-Aware Data Delivery (PRADD) to improve data transfer reliability for delay tolerant underwater traffic. Data delivery reliability is significantly improved by selecting the next hop forwarder on-the-fly based on its link reliability, reachability to gateways and coverage probability through probabilistic estimation. Data forwarding solution is coupled with delay tolerant networking paradigm to improve delivery with reduced overhead. PRADD does not require active localization technique to estimate the updated location of a sensor node except its initial coarse location. The movement of an anchored node is exploited to estimate its coverage probability. Mobile message ferries are used to collect stored data from one or more nodes, called gateways. A strategy for gateway selection is devised to maximize their lifetime. Simulation results show that PRADD achieves significant performance improvement over competing protocols using low overhead and less energy.
Designing message forwarding protocols for underwater acoustic sensor networks (UASNs) is challenging mainly due to high propagation delay, limited bandwidth and high packet loss. Most such protocols operate on the assumption that precise location of sensor nodes is known, which is difficult as GPS waves cannot propagate through water. Moreover, due to the error-prone nature of the acoustic link, message forwarding over multiple hops degrades end-to-end reliability, consumes significant energy and incurs longer delay. In this paper, we propose a location unaware message forwarding technique. It employs opportunistic routing where nodes use accumulate-and-forward paradigm to route data. The technique also exploits nodes' ability to overhear one another's transmission to select reliable route. Our opportunistic model uses independent and local forwarding decisions to select next hop forwarder on-the-fly based on its link transmission reliability and reachability to the gateway. Message ferrying approach is utilized to collect sensor data from gateway nodes of multiple UASNs at high data rate. Our simulation results exhibit its effectiveness and superiority compared with two well established message forwarding algorithms in underwater in terms of packet delivery ratio, routing overhead and energy consumption.