Abstract
Time synchronization is the basis of many applications. Aiming at the limitations of the existing clock synchronization algorithms in underwater wireless sensor networks, we propose a pairwise synchronization algorithm called K-Sync, which is based on the Kalman filter. The algorithm does not need the assistance of the position sensor or the speed sensor, and the high time synchronization accuracy can be realized only by utilizing the time-stamps information in the process of message exchange. The K-Sync uses the general constraints of the motion characteristics of the sensor nodes to establish the recursive equations of the clock skew, clock offset, relative mobility velocity, and relative distance. At the same time, the time-stamps are viewed as the observation variables and the system observation equation is obtained. The K-Sync estimates the normalized clock skew and offset of the node via the Kalman filter to achieve high-precision clock synchronization between the two nodes. The simulation shows that the K-Sync has obvious advantages in the key indicators such as the estimated accuracy of clock skew and clock offset, convergence speed, etc. In addition, the K-Sync is more robust to a variety of underwater motion scenes.
Highlights
Underwater Wireless Sensor Networks (UWSNs) typically consists of power-limited terminals capable of computing and communications
Most of the applications that employ WSNs demand all of the sensor nodes to run on a common time scale, which highlights the importance of clock synchronization
It is hard for UWSNs to ensure the accuracy of clock by implementing frequent synchronization process
Summary
Underwater Wireless Sensor Networks (UWSNs) typically consists of power-limited terminals capable of computing and communications. The authors of [5] comprehensively study the time synchronization algorithm of terrestrial wireless sensor networks, including some widely used time synchronization protocols. The clock synchronization protocol for terrestrial wireless networks is not applicable to the underwater domain. Underwater sensor networks relying on acoustic signals to communicate have great differences compared to radio communication, due to their high speed of electromagnetic waves [6]. Challenges brought by acoustic-based communication such as a large propagation delay, sensor node mobility, ray bending, multipath effects, limited bandwidth, and so on, add difficulties to UWSNs [7]. 0.83–1.67 m/s [8], and the time-varying propagation delay caused by the slow propagation speed of the acoustic wave and nodes inherent mobility is the keys to the underwater. The time synchronization of the entire network, can be realized through the clock synchronization of pair nodes
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