基于FRFT的GOBS高精度水声时钟同步方法研究

High precision underwater acoustic clock synchronization for GOBS based on fractional Fourier transform

组合式海底地震采集站GOBS(Group Ocean Bottom Seismometer)为一种自容式海底地震采集站组网设备,为实现长期留海作业,其采集站的电路时钟源通常采用低功耗石英晶振.现有设备水下无法进行精确对钟,长时间留海作业将产生时钟时间漂移累积而导致多道GOBS数据难以处理.针对这一问题,本文提出了一种水声时钟同步方法,其基本原理是利用分数阶傅里叶变换对线性调频信号的能量聚集性精确估计信号到达时刻,通过水声时标与GOBS间多次的周期性单向消息传递得到GOBS本地时间与水声时标标准时间的映射关系,实现GOBS的时钟同步.本方法考虑到水下资源受限的现实条件,在控制同步消息开销和计算开销的前提下,采取水声时标向GOBS的单向消息广播模式,减少GOBS功耗,延长了GOBS的可持续工作时间.同时实现了时钟同步的目标,将所有GOBS的本地时间同步到一个全局时间上去,避免了节点时钟漂移的累积,提高了时钟精度.通过数值仿真和水池测试验证表明,本方法具有计算复杂度低、时钟同步精度高、能耗小的特点,具有较好的实用价值.

GOBS(Group Ocean Bottom Seismometer)is a kind of self-contained ocean seismic acquisition station that works in networking.In order to achieve long-term sea-holding operations,the clock source of GOBS usually uses a low-power quartz crystal resonator.Because existing equipments cannot perform accurate time under water,long-term sea-holding operations will result in an increase in time drift and cause multi-channel GOBS data difficult to process.Aiming at this problem,this paper proposes a hydroacoustic clock synchronization method.The basic principle is to use the fractional Fourier transform to accurately estimate the signal arrival time of the chirp signal,and obtain the mapping relationship between GOBS local time and the accurate time through the periodic one-way message transmission between the transmitter and the GOBSs and then realize the clock synchronization.Under the premise of controlling the synchronization message overhead and computational overhead,the method takes into account the real conditions of underwater resource limitation,and adopts the one-way message broadcasting mode from the transmitter to the GOBSs to reduce the power consumption of the GOBSs and prolong the GOBSs sustainable working time.At the same time,the goal of clock synchronization is achieved,and the local time of all GOBSs have been synchronized to a global time,which avoids the accumulation of nodes clock drift and improves the clock precision.The results of numerical simulation and pool experiment show that the method has the characteristics of low computational complexity,high clock synchronization accuracy and low energy consumption and has good practical value.