Underwater Acoustic Modems (S2CR Series) for Synchronization of Underwater Acoustic Network Clocks During Payload Data Exchange

Abstract

Modern underwater acoustic modems, in addition to receiving and transmitting data, can measure signal propagation time and evaluate the distance between the transmitter and the receiver. These capabilities can be exploited to support the synchronization of underwater acoustic sensor networks, where sensing and actuation must be coordinated across multiple nodes. However, the problem of accurate propagation time measurement, especially in highly reverberant environments, and the evaluation of clock skew on acoustically interacting modems have been investigated rather poorly. In this paper, therefore, we conduct an experimental evaluation of stability/precision of propagation time measurements considering underwater acoustic modems communicating in reverberant environments. We also show how modem built-in tools can provide opportunities for precise estimation of the modems clock skews. Additionally, we demonstrate that payload data exchange can be used as a “comfortable” way for clock synchronization of underwater acoustic networks nodes. At-sea experiments have been carried out considering several modem pairs and node positions in conditions of reverberant underwater acoustic channels. These experiments have been conducted in collaboration with the NATO Centre for Maritime Research and Experimentation (CMRE, La Spezia, Italy) that we gratefully acknowledge.