一种应用于卫星通信的间接时间同步方法
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摘要
针对卫星扩频通信系统的时间同步需求,提出一种基于GNSS授时的卫星通信前向链路间接时间同步方法。通过由星地自发自收链路与锁相环构成的钟差间接修正环路,对发送端码时钟进行闭环修正。这将使前向链路信号起始扩频码相位在到达接收端的时刻与卫星导航授时模块输出的1 PPS保持精确稳定的同步。实现了不需要位同步的扩频信号定时接收。分析并得到间接时间同步误差表达式及其与环路带宽的变化关系,给出使同步误差最小的最优环路带宽值。星地链路试验结果表明时间同步误差随环路带宽的变化关系与理论分析一致,最佳环路带宽对应的钟差间接修正环路秒脉冲1σ同步误差约为20 ns,验证了本方法的有效性。在此同步误差条件下,接收端成功地进行扩频伪码的同步和电文解调,实现了卫星导航授时对通信的辅助。
An indirect time synchronization method is proposed to be applied in forward link for time synchronization requirements of satellite spread spectrum communication system.Based on GNSS timing,an indirect clock correction loop consisting of ground-satellite round-trip link and phase lock loop is designed to correct the transmitter clock.The initial code phase of forward link spread spectrum signal is synchronized with GNSS 1 PPS at the receiving end.The spread spectrum signal timing receiving without bit synchronization is realized.A formula for time synchronization error and relationship of the error with loop bandwidth of the indirect clock correction loop are derived.The optimal loop bandwidth to minimize the synchronization error is also proposed.The satellite-ground link experiments show that variation of the synchronization error with the loop bandwidth is in agreemeent with theoretical analysis,and the minimum 1σ error of 20 ns is reached.
An indirect time synchronization method is proposed to be applied in forward link for time synchronization requirements of satellite spread spectrum communication system.Based on GNSS timing,an indirect clock correction loop consisting of ground-satellite round-trip link and phase lock loop is designed to correct the transmitter clock.The initial code phase of forward link spread spectrum signal is synchronized with GNSS 1 PPS at the receiving end.The spread spectrum signal timing receiving without bit synchronization is realized.A formula for time synchronization error and relationship of the error with loop bandwidth of the indirect clock correction loop are derived.The optimal loop bandwidth to minimize the synchronization error is also proposed.The satellite-ground link experiments show that variation of the synchronization error with the loop bandwidth is in agreemeent with theoretical analysis,and the minimum 1σ error of 20 ns is reached.
引文
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[2]王磊.消除相位翻转影响的扩频信号捕获方法[J].中国科学院大学学报,2015,32(1):110-115.
[3]Parkinson B W,Spilker J J.Global positioning system:theory and applications Vol.I[M].Washington:American Institute of Aeronautics and Astronautics,Inc,1996:395-396.
[4]Ziedan N I,Garrison J L.Bit synchronization and doppler frequency removal at very low carrier to noise ratio using a combination of the Viterbi algorithm with an extended Kalman filter[C]∥Proceedings of the 16th International Technical Meeting of the Satellite Division of the Institute of Navigation.Portland,USA,2003:616-627.
[5]Kokkonen M,Pietil S.A new bit synchronization method for a GPS receiver[C]∥2002 IEEE Position Location and Navigation Symposium.Palm Springs,CA,USA,2002:85-90.
[6]Li X,Guo W.Efficient differential coherent accumulation algorithm for weak GPS signal bit synchronization[J].IEEE Communications Letters,2013,17(5):936-939.
[7]Kim Y.Holdover clock errors in GPS-disciplined chip-scale atomic clock[C]∥Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting,Bellevue,Washington,December 2013:101-106.
[8]Mcclelland T,Shtaerman I,Zarjetski E,et al.Disciplined rubidium oscillator for harsh environments[C]∥Frequency Control and the European Frequency and Time Forum(FCS),2011 Joint Conference of the IEEE International,2011:1-5.
[9]向为,徐博,牟卫华,等.基于锁相环的GNSS授时接收机钟差校准算法[J].国防科技大学学报,2013,35(2):115-119.
[10]李志刚,杨旭海,施浒立,等.转发器式卫星轨道测定新方法[J].中国科学:物理力学天文学,2008,38(12):1 711-1 722.
[11]杨旭海,李志刚,冯初刚,等.GEO卫星机动后的星历快速恢复方法[J].中国科学:物理力学天文学,2008,38(12):1 759-1 765.
[12]崔小准,米红,李懿,等.一种全球定位系统卫星C/A信号通道绝对时延标定算法[J].上海交通大学学报,2012,46(11):1 843-1 847.
[13]Rovera D,Abgrall M,Uhrich P,et al.Techniques of antenna cable delay measurement for GPS time transfer[C]∥Frequency Control Symposium&the European Frequency and Time Forum(FCS),2015 Joint Conference of the IEEE International,2015:239-244.
[14]Kaplan E D,Hegarty C J.GPS原理与应用[M].寇艳红,译.2版.北京:电子工业出版社,2007.
[15]Knight M F.Ionospherie seintillation effects on global positioning system receivers[D].Adelaide:The University of Adelaide,2000:277-281.
[16]Aguirre S,Hurd W J.Design and performance of sampled data loops for subcarrier and carrier tracking[J].Telecommunications&Data Acquisition Progress Report,1984,79:81-95.