QUO VADIS: QoS-aware underwater optimization framework for inter-vehicle communication using acoustic directional transducers

Underwater acoustic communications consume a significant amount of energy due to the high transmission power (10-50 W) and long data packet transmission times (0.1-1 s). Mobile Autonomous Underwater Vehicles (AUVs) can conserve energy by waiting for the `best´ network topology configuration, e.g., a favorable alignment, before starting to communicate. Due to the frequency-selective underwater acoustic ambient noise and high medium power absorption - which increases exponentially with distance - a shorter distance between AUVs translates into a lower transmission loss and a higher available bandwidth. By leveraging the predictability of AUV trajectories, a novel solution is proposed that optimizes communications by delaying packet transmissions in order to wait for a favorable network topology (thus trading end-to-end delay for energy and/or throughput). In addition, the solution proposed - which is implemented and compared with other solutions using an emulator that integrates underwater acoustic WHOI Micro-Modems - exploits the frequency-dependent radiation pattern of underwater acoustic transducers to reduce communication energy consumption by adjusting the transducer directivity on-the-fly.