A data link layer in support of swarming of autonomous underwater vehicles

Swarms of underwater autonomous vehicles (UAVs) are being increasingly used in civilian and military applications. Formations of UAVs are being utilized to detect mine-like objects and oilfields, collect water quality information, detect intruders, and in navigation assistance applications, among others. This paper introduces a new data link layer for underwater communications suitable for non-synchronized ad-hoc networks using multiple frequency channels that supports linear and polygon formations of UAVs. At the MAC layer, the 2MAC protocol is introduced. 2MAC is a contention-based and collision avoidance scheme designed to work on top of an OFDMA-based acoustic channel at the physical layer and coordinate the simultaneous transmissions of multiple OFDMA sub-channels simultaneously with only one transceiver. This 2MAC-OFDAM multichannel transmission solves the hidden, exposed terminal, capture, and deafness problems commonly found in ad-hoc networks and also increases the network throughput and packet delivery rate considerably. In addition, since the nodes are only equipped with one transceiver, the design preserves the low cost advantage of current single-channel single-transceiver CSMA-based nodes. In addition, 2MAC includes an improvement of the Binary Exponential Backoff algorithm (BEB), more adequate for underwater channels. At the logical link layer, we present SW-MER, a new protocol based on Stop and Wait and Sliding Window approaches that includes an exponential retransmission strategy to achieve better channel utilization and high reliability. A performance evaluation is carried out using the well-known Bernoulli error model and also a more realistic underwater channel simulated using synthetic traces that correspond to a shallow water channel. Simulation results in terms of reliability and throughput efficiency demonstrate the superior performance of the new data link protocol when compared with the current CSMA/CA protocol at the mac sublayer or tradit- ional Stop and Wait protocols at the logical link control sublayer.