Oriol Pallarés

TS-MUWSN: Time Synchronization for Mobile Underwater Sensor Networks

Time synchronization is an important, yet challenging, problem in underwater sensor networks (UWSNs). This challenge can be attributed to: 1) messaging timestamping; 2) node mobility; and 3) Doppler scale effect. To mitigate these problems, we present an acoustic-based time-synchronization algorithm for UWSN, where we compare several message time-stamping algorithms in addition to different Doppler scale estimators. A synchronization system is based on a bidirectional message exchange between a reference node and a slave one, which has to be synchronized. Therefore, we take as reference the DA-Sync-like protocol (Liu et al., 2014), which takes into account nodes movement by using first-order kinematic equations, which refine Doppler scale factor estimation accuracy, and result in better synchronization performance. In our study, we propose to modify both time-stamping and Doppler scale estimation procedures. Besides simulation, we also perform real tests in controlled underwater communication in a water test tank and a shallow-water test in the Mediterranean Sea.

Underwater acoustic communication messaging time stamp applied to global time synchronization

This paper presents a new approach to time stamp messages in underwater acoustic communication. Message time stamping is a widely used method for synchronizing two clocks over a cabled or wireless communication, by exchanging time information in pilot messages. In this work we use a National Instruments Field-Programmable Gate Array (FPGA) for performing deterministic hardware time stamp of windowed acquired data, and then we apply a software detection of frame information inside this acquisition window. Frame time stamp in conjunction with global time reference enclosed in the message, provide enough information for achieving synchronization accuracy between two clocks below few microseconds.

Time synchronization accuracy refinement for mobile shallow water acoustic sensor network

Time synchronization is an important factor to take into account when performing collaborative and distributed tasks along a sensor network. Message exchange based time synchronization algorithms ported to underwater acoustic sensor networks, have to deal with high latency communications, besides frame Doppler scaling and frame detection at the receiver side, which are key points for an accurate synchronization. Furthermore, mobile sensor networks lead to different propagation times in a bidirectional message exchange, such as the ones used to synchronize two sensors. In addition to time synchronization algorithm, a first order kinematic model in conjunction with Doppler estimation can be applied to precise frame time stamping and avoid drift between clocks. In this paper we present a complete time synchronization scheme optimized for mobile network, tested in simulation and experimented in real tests demonstrating high performance in time synchronization accuracy.