Implementation of frequency and phase synchronization of fiber-optic hydroacoustic sensors array

Abstract

Subject of Research.The problem of synchronization in arrays of distributed fiber-optic hydroacoustic sensors is considered. It is shown that noise floor level is one of the most important factors affecting the operation of the sensors. The maximum allowable level of phase noise arising from the operation of the synchronization system is determined. The main existing methods of synchronization are considered, and their influence on phase noise level is estimated. Method. The signal resampling method was used as the approach for signal synchronization task. Mathematical modeling of that method in the MATLAB environment was performed. It was shown that the addition of samples to the studied signal leads to a significant increase in phase distortion. Main Results. The impact of the clock frequency instability at the signal skew in the absence of synchronization system is numerically estimated. In case of ± 20 ppm generator clock frequency deviation, the skew reaches one second after 7 hours of work. It is shown that when 8 samples per second are added to the synchronized signal, spectral distortions reach the order of 100 µrad/Hz1/2. A hardware synchronization method is proposed that provides the possibility to increase the synchronization accuracy without distortion of the spectral and phase characteristics of the signal. The method is realized by adjusting local clock frequency generator involving feedback signal. Practical Relevance. The paper proposes two synchronization methods that allow for application of the Ethernet interface according to the IEEE 802.3 standard aimed at the implementation of the distributed sensor system synchronization. The paper presents an analytical and experimental evaluation of phase jitter value between different channels of the measuring system. These methods can be used in other distributed systems, where there is an urgent task of synchronization of its nodes while maintaining scalability and flexibility of the entire system.