High Precision Time Synchronization System Based On FPGA

High precision time synchronization technology is the foundation and key technology in the fields of global navigation and positioning,aerospace technology,and missile precise guidance.In these fields,there is a very high requirement for time accuracy.It is vital for these fields to have a high-precision time synchronization system.At present,the time synchronization technology with high precision and wide application range is satellite time synchronization technology.The precision of satellite time synchronization technology can meet the needs of various time synclhronization precision applications below nanosecond level,but it can not meet the needs of higher precision levels such as deep space exploration.In addition,satellite time synchronization is vulnerable to various environmental conditions outside,and the construction environment is complex,and there are security risks.But Optical fiber time synchronization can achieve higher precision and optical fiber has the characteristics of strong anti-interference ability and high security.So in recent years,optical fiber time synchronization technology has attracked more and more attention.However,optical fiber time synchronization needs to consider the impact of fiber loss and fiber dispersion,and the cumulative noise of optical amplifier will also affect signal transmission.In order to study the influence of various factors in optical fiber time synchronization system and further optimize the optical fiber time synchronization system,it is very important to build a prototype of high-precision time synchronization system.In this paper,a high-precision time synchronization system based on FPGA is studied,and it uses the FPGA as the transceiver of the system.It uses the FPGA to convert the pulse per second signal into a pseudo-random sequence for transmission at the transmitter,and then recovers from the autocorrelation property of the pseudo-random sequence at the receiver.It can make the time deviation between the local end and the far-end as small as possible after 1000km long-distance fiber transmission.Also use the precise time measurement method to measure the time within one FPGA clock period that can not be determined and achieve more precision time synchronization.This paper has mainly completed the work in the following aspects:1.Design the scheme of high-precision time synchronization system based on FPGA that is based on optical fiber bidirectional comparison method.Use the FPGA to receive the pulse per second and generate pseudo-random code,then convert the digital signal to analog signal in order to send the signal to the fiber link.Convert the analog signal to digital signal at receiving end and receive the corresponding pseudo-random code at the receiving end and use the autocorrelation property of the pseudo-random code to recover the pulse per second.The characteristic of pseudo-random codes is that the autocorrelation value is 1 after receiving a complete sequence of pseudo-random codes,and the rest of the time is 1/2.The autocorrelation characteristic is consistent with the pulse per second signal and can be used to recover the pulse per second signal.Moreover,by using pseudo-random sequence,the original single pulse per second signal can be transformed into a sequence.Even if some bits in the sequence are misjudged,it will not affect its self-correlation value,which reduces the deteriorating effect of waveform after long-distance optical fiber transmission and increases the time synchronization accuracy of the system.2.Complete the logic programming of receiving pulse per second and generating pseudo-random sequence on the FPGA,and complete the autocorrelation logic algorithm of pseudo-random sequence,also use the FPGA to drive the sub-card AD/DA to convert analog signal to digital signal and digital signal to analog signal.In order to solve the limitation that the FPGA can not determine when the signal arrives in one clock cycle,we analyze the traditional precise time measurement method and the requirements of the system.In addition,we propose a scheme of precise time measurement using logic units in the FPGA and complete the related theoretical research and program implementation of the scheme.In addition,we complete the serial communication in FGPA and transmit data to computer.3.Simulate the relevant code and build the corresponding system to test.Test whether the time point of signal meets the expectation and whether the data transmitted is correct.We have built the corresponding system to test.And the final result is that the time synchronization accuracy is 5ns,the system stability is 160ps and the minimum measurement accuracy is 60ps in 1000km fiber time synchronization system.