Clock Synchronization Through Time-Variant Underwater Acoustic Channels
Rice, Joseph A.
Clark, Grace A.
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The goal of this work is to develop methodologies for synchronizing the clocks of neighboring nodes of an underwater acoustic network. Clock synchronization requires an estimate of the signaling time delay between the nodes, which is particularly challenging in the presence of multipath propagation through the acoustic communication channel. This thesis focuses on modeling the underwater acoustic communication channel, accounting for the multipath arrivals, and creating a set of signal processing algorithms for estimating the required delay times that enable clock synchronization protocols for the underwater acoustic network. The proposed method involves correlating the responses of the bidirectional channels to exploit the underlying reciprocity. Performed in two stages, a sequence of probe signals is first transmitted to create an ensemble, which contains information about the time-variability of the acoustic communication channel with multipath. From this ensemble, we determine its dominant time-invariant characteristic and use it as a reference datum for the time delay measurements. The second stage consists in performing time-delay estimation of two probe signals exchanged between nodes. The two stages are tested using simulated signal measurements, and actual signal measurements were performed in a fresh-water lake for the first phase only. Both computer simulations and experimental results show the effectiveness of the proposed techniques.
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