Inter-glider underwater communication and coordination for ocean monitoring and coastal tactical surveillance
Creators: name: Chen, Baozhi
Publisher: name: No Publisher Supplied
Year: 2012

description: In order to achieve efficient and cost-effective sensing of the vast under-sampled 3D aquatic volume, intelligent adaptive sampling strategies involving teams of Autonomous Underwater Vehicles (AUVs)  endowed with underwater wireless communication capabilities become essential. These autonomous  vehicles should coordinate and steer through the region of interest, and cooperatively sense and transmit multimedia data to onshore stations for real-time data processing and analysis. Because of  the propagation limitations of Radio Frequency (RF) and optical waves, the typical wireless physical-layer communication technology in underwater networks, for distances above a hundred of meters, relies on acoustic waves.    Due to the stringent constraints of the underwater acoustic channels, as of today existing works on underwater acoustic communications are mostly focused on enabling delay-tolerant low-bandwidth applications tailored for measuring only scalar physical phenomena. Hence, it is necessary to design solutions for reliable, high data-rate multimedia underwater acoustic communications and to seamlessly integrate the control and communication of AUVs. In this dissertation, I propose solutions to improve the performance of inter-vehicle acoustic communication and coordination among AUVs. In particular, these solutions are based on underwater gliders and can be extended to other classes of AUVs following predictable trajectories.    Due to the inaccessibility of Global Positioning System (GPS) signal underwater, location estimates of a node may be inaccurate. Inaccuracies in models for deriving position estimates, self-localization errors, and drifting due to ocean currents, however, cause uncertainty when estimating an AUV's position. In this dissertation, I first propose a statistical model to estimate an AUV's position and its associated position uncertainty. Then, the position uncertainty under the influence of ocean currents is further predicted using the Unscented Kalman Filter. Based on this model, in order to optimize the inter-vehicle communications, I propose a delay-tolerant networking solution exploiting the predictability of AUV trajectories and the directional radiation pattern of transducers, a reliable geocasting solution for AUVs with high position uncertainty, and an under-ice localization solution that can minimize localization uncertainty and communication overhead.    Based on these underwater communication techniques, I also propose efficient team-formation and -steering algorithms for underwater gliders in order to take measurements in space and time from the under-sampled vast ocean. Team formation and steering algorithms relying on underwater acoustic communications are proposed to enable glider swarming that is robust against ocean currents and acoustic channel impairments. These algorithms use real underwater acoustic modems and are combined with realistic underwater communication models. Additionally, novel bio-inspired underwater acoustic communication techniques are also proposed to improve the coordination performance.    I also designed and implemented an underwater network emulator using WHOI Micro-Modems, and the performance of the proposed solutions is evaluated using this emulator as well as software simulations. Communication protocols were also implemented on acoustic modems and tested in ocean experiments.