Research And Implementation Of Time Synchronization Technology Based On PTP+SyncE

With the increasing demand for high-precision positioning and the rapid development of 5G mobile network,base station positioning based on 5G mobile network,as an important means of indoor positioning,has considerable development potential.Compared with 4G applications,the high precision positioning based on 5G base station puts forward higher requirements for base station time synchronization.Base station positioning is mainly based on arrival time or arrival time difference.In order to achieve the meter level positioning accuracy,the synchronization deviation between base stations is required to be within 3ns.Precision Time Protocol(PTP)technology has been widely used in telecommunication networks.The precision of PTP is about 100 ns,and it is easy to realize interconnection.It is a good idea to optimize PTP based on the existing PTP and realize nanosecond level time synchronization.Existing PTP technology adopts hardware timestamp,and the synchronization accuracy can reach sub-microsecond level,but it cannot meet the requirements of high-precision time synchronization for 5G base stations.The limitation of PTP protocol lies in the poor frequency distribution effect,which can only guarantee the time synchronization of absolute time information.However,due to the different characteristics of frequency drift and aging rate of each clock in the network,the accumulation of clock difference becomes larger over a long time.Synchronous ethernet(SyncE)technology can realize the transmission and recovery of high precision clock information,but only the frequency information can be transmitted,not the time information.By combining PTP with synchronous ethernet technology,a time synchronization test platform based on PTP+ SyncE was developed.The main research contents of this paper are as follows:1.The precise time synchronization protocol,synchronous ethernet and White Rabbit(WR)clock synchronization protocol are analyzed and studied,and a time synchronization method based on PTP+SyncE is proposed.By analyzing and comparing the known methods,PTP was combined with SyncE.PTP is used to realize the delay measurement of the clock master and slave,and synchronous ethernet technology is used to realize the frequency synchronization,so as to improve the synchronization accuracy.2.The test platform of PTP+SyncE was designed.The physical layer chip DP83640 and microprocessor chip ARM Cortex-LPC1758 are used in the hardware design to realize the clock function and the main control function.The interconnection between the two chips is realized based on the RMII main mode,and the clock jitter problem is improved by power filtering technology.The software design adopts synchronous ethernet technology to realize frequency transmission,and realizes PTP message communication through message transceiver.Finally,the time synchronization test platform of PTP+ SyncE is realized.3.A test platform based on PTP+ SyncE and WR was built.By simulating the actual use environment,a variety of test methods were designed,and the time synchronization deviation and jitter were tested and evaluated respectively.Collect and process the data,compare and analyze the synchronization performance and the cause of performance difference.The synchronization effect of the clock frequency is analyzed.By analyzing the frequency stability of 10 MHz output from the slave clock before and after synchronization,as well as the frequency stability between the master and slave clock frequencies,it is found that the slave clock frequency can be improved and synchronized with the frequency source by using SyncE to transfer the frequency.To sum up,this paper designed and implemented a time synchronization test platform based on PTP+ SyncE,and built a synchronization performance test platform between PTP+ SyncE and WR for the purpose of high-precision time synchronization requirements between 5G base stations.The results show that the synchronization deviation is less than 3ns and the jitter is less than 200 ps based on PTP+ SyncE test platform.Based on the time synchronization technology of WR protocol,the synchronization deviation is on the sub-nanosecond scale,and the jitter is within 50 ps.