Research On Method Of Satellite-ground Time Synchronization Base On Ka Band ISL System Of BDS

Navigation satellite's inter-satellite link(ISL)is an important part for GNSS' modernization.All clock errors between each satellite can be obtained by highprecision two-way measurement technology,and then the time of the whole satellite clocks are unified.Relying on the satellite-ground link of ISL system,satellite-ground time synchronization technology can be used to achieve clock error between satellite and ground,and then satellite time and ground time can be unified,making the unity of satellite clock and ground time.The Ka band ISL of BDS has two forms: dual-frequency continuous-time system and single frequency time division system.Focusing on single frequency time division system,this paper carries out research of satellite-ground time synchronization.The main research results are as follows:(1)According to the characteristics of single-frequency time-division ISL,the method of calculating the epoch conversion in satellite-ground measurement of different time-length is studied.And the method is verified by both simulation and experimental data,results show that by using the polynomial interpolation method of epoch conversion,the accuracy can be better than 1mm.(2)To detect clock jump and gross error in data of satellite clock,a two-step method for the error detection of satellite clock data is proposed by combining the single difference algorithm of epochs and Quasi-Accurate Detection method(QUAD).The detecting process is set forth,the performance is analyzed by using emulating data,and the algorithm is verified by experimental data,both examples show that using the twostep method can effectively avoid clock jump influence,and can accurately detect small gross errors,which close to 2 times the background noise's standard deviation.(3)By analyzing characteristics of single-frequency time-division ISL,a method of applying two-way satellite-ground time synchronization technology to satelliteground link in time-division inter-satellite links mode is proposed,which firstly calculate the epoch conversion for dual one way psudo-range and secondly do the twoway time synchronization.And the method is verified in both initial boot mode and normal mode of ISL system,respectively.The results show that: in normal mode under the fitting time 1h,the accuracy is up to 0.15 ns.(4)Methods of ground-ground time synchronization and indirect ground-satellite time synchronization with a satellite as an intermediary node are proposed,which can achieve the time synchronization between two stations and achieve the satellite-ground time synchronization for invisible satellite under Ka band ISL.Methods are verified by experimental data,and the results show that: time synchronization accuracy between short baseline of ground-ground is better than 0.19 nanoseconds;the time synchronization accuracy of the indirect ground-satellite is the same as direct groundsatellite,and the problem of invisible satellite's satellite-ground time synchronization is solved,greatly increasing the time-length of satellite-ground time synchronization.