Research And Verification Of Node Time Service Technology In Underwater Sensor Networks

Underwater wireless sensor networks play a vital role in monitoring the marine environment,marine resource exploration,underwater target detection,tracking and positioning and other fields,and have attracted extensive attention.Time synchronization is the basis for achieving work coordination among underwater wireless sensor networks nodes and jointly completing distributed tasks,but huge underwater propagation delay,node movement Severe Doppler frequency shift and limited energy supply seriously affect the synchronization accuracy of underwater nodes.The existing time synchronization algorithms cannot fully solve the above problems.Some algorithms consider Doppler frequency shift while also increasing energy consumption,while others effectively reduce energy consumption but reduce time synchronization accuracy.Based on this,this article proposes an effective underwater time synchronization algorithm based on Doppler shift(DS-Sync:Underwater time synchronization algorithm based on Doppler shift)in response to the current situation of time synchronization problems.The aim is to effectively solve the Doppler frequency shift problem,reduce the energy cost of the algorithm,and further improve the work efficiency of nodes on the basis of existing time synchronization algorithms.The DS-Sync algorithm is divided into two stages: data collection stage and parameter estimation stage.In the data collection stage,a mixed interaction method,namely multiple one-way interactions and one two-way interaction,is used to collect data information,reducing the amount of data required for the synchronization process,thereby reducing the computational difficulty and greatly saving the algorithm’s message overhead;In the parameter estimation stage,the clock frequency deviation is calculated using the minimum square error estimation criterion,which minimizes the sum of the squares of the estimated and observed values,using data information from multiple one-way interactions.The clock phase offset is calculated using data information from one two-way interaction and the estimated clock frequency deviation.In order to reduce the impact of Doppler frequency shift on time synchronization accuracy,the relative movement speed between nodes and clock frequency deviation were jointly considered when estimating the Doppler scale factor,which improved the estimation accuracy of the Doppler scale factor to a certain extent.In the face of the problem that the signal strength in large-scale underwater acoustic networks gradually decreases with the increase of communication distance,this paper proposes the concept of clustering nodes in the underwater acoustic network and designs a clustering model,which divides the entire network into several clusters.First,the standard time nodes are synchronized with the cluster head,and then the cluster head is synchronized with the member nodes within the cluster,The global time synchronization is achieved in a hierarchical and phased manner,avoiding excessive attenuation of signal strength and improving the time synchronization accuracy of remote nodes.In addition,in order to evaluate the performance of existing underwater time synchronization algorithms,this article has developed a set of algorithm performance evaluation system,which evaluates from three aspects: timing accuracy,taming accuracy,and message cost,providing reference basis for experimenters in different application scenarios and synchronization needs.Finally,this article further verifies the effectiveness of the algorithm through lake experiments.Compared with existing time synchronization algorithms CD-Sync and MU-Sync,DS-Sync algorithm has more obvious advantages and efficiency in time synchronization accuracy and message overhead.