Design of Underwater Mobile Sensor Networks for Real-time Aquatic Applications
Underwater sensor networking is generally regarded as an emerging technology to conduct oceanic exploration and research in an automated and effective manner. As underwater operations become more sophisticated, there is an increasing demand for real-time aquatic applications such as real-time video streaming. However, real-time video streaming requires high bandwidth as well as low latency. Amongst the resources, bandwidth is the most critical limitation. To help overcome this obstacle, we first propose an innovative MAC protocol called Multi-session FAMA (M-FAMA). M-FAMA leverages passively-acquired local information (i.e., neighboring nodes' propagation delay maps and expected transmission schedules) to launch multiple simultaneous sessions. M-FAMA's greedy behavior is controlled by a Bandwidth Balancing algorithm that guarantees max-min fairness across multiple contending sources. In addition to this, we propose a hybrid solution that combines acoustic and optical communications. Optics provides good quality real-time video. Acoustic maintains a "thin" channel for network topology and transmission control, and for still frame video delivery when the optical channel fails. In particular, we enable optical communications by acoustic-assisted alignment and use acoustic communications as a back up when the optical signal is interrupted. The main contribution is to enable reliable, real-time video streaming without underwater optical cables. Another important contribution is the smooth transition between the acoustic and optical video delivery mode, using popular image processing algorithms to compress the video before transmitting it on the acoustic channel.