Research And Implementation Of Time Synchronization Technology For Underwater Acoustic Navigation Node

In underwater acoustic navigation and positioning systems,there are various nodes such as surface vessels,buoys,submarines,and underwater targets.Time synchronization is often required between each node,and the accuracy of time synchronization directly affects the positioning accuracy.This article focuses on the working characteristics of each node in the underwater acoustic navigation system and conducts in-depth research on the time synchronization problem between nodes.Drawing on the existing NTP time synchronization protocol,a time synchronization scheme,corresponding hardware equipment and software for underwater acoustic navigation nodes are designed,which can achieve high-precision time synchronization between nodes.The paper first analyzes the NTP time synchronization protocol,and designs a time synchronization protocol that can be used in underwater acoustic channels based on the propagation characteristics of the channel.The focus is on designing the data structure,encoding format,and signal form of the time synchronization protocol,and analyzing the main factors that affect the accuracy of time synchronization.Then,based on the functions and main characteristics of the water surface node and the underwater target node,the hardware design and implementation of the time synchronization communication machine installed on the water surface node and the time synchronizer installed on the underwater target were carried out.We have focused on the detailed design and implementation of the ZYNQ core board module,clock module,interface module,power module,AD acquisition module,and GPS receiver module.Subsequently,targeted software design was carried out for the hardware structure and functions of the timing communication machine and time synchronizer.The design software module mainly includes GPS time information acquisition,PPS second pulse acquisition,second pulse synchronization and synchronization,as well as time information transmission and reception modules.Among them,the timing communication machine uses all software modules,while the time synchronizer only uses time information transmission and second pulse synchronization timing modules.Both simplify system design complexity through module reuse.Finally,functional and indicator testing and verification were conducted on the time service communication machine and time synchronizer.The functions of power supply,GPS time synchronization,transmission time information,and reception time information were tested in the laboratory,and the time synchronization accuracy of the timing communication machine and time synchronizer were tested separately.After the testing was completed,the system synchronization accuracy in the time synchronization scheme was tested in the pool.The test results show that this scheme can achieve high-precision time synchronization between surface nodes and underwater target nodes,with stable hardware modules and reliable software design functions.It can be applied in underwater acoustic navigation and positioning systems in the future to solve the problem of time synchronization between nodes.