| Beidou satellite navigation system,as the most complicated aerospace system in China Aerospace,is also the first one that competes internationally with other navigation systems.Its system design must focus on the application needs and technological development in the next 20 to 30 years.As the operational control section of BeiDou system can only distribute domestic stations,it greatly limits the measurement,control and maintenance of navigation satellites.The key way to solve the navigation constellation from ground stations is to build inter-satellite links(ISLs).The global navigation satellite system performance can be significantly enhanced by introducing ISLs in navigation constellation.The improvement in position,velocity,and time accuracy as well as the realization of autonomous functions requires ISL distance measurement data as the original input.In order to achieve the accuracy of the orbit determination and time synchronization at the meter level,the precision and accuracy of the inter-satellite measurement should reach the decimeter or even centimeter level,while the in-orbit revision of inter-satellite measurement is the essential premise of ensuring precision and accuracy.In order to seize the highest technical point in the future global satellite navigation system and build a high-quality ISLs,the precision measurement of in-orbit revision technology has become a key issue to be solved.The paper focuses on the following key technical issues.1.For the ranging offset caused by the phase change of navigation constellation satellite clock,a zero-phase distortion time-delay revision method based on frequency division is proposed.The method according to the satellite clock frequency and phase adjustment,phase change of power switch model,based on the phase conversion characteristics of frequency division factor and phase tracking characteristics of DPLL,not only realizes a phase revision for the problem of ranging offset,but also overcomes the problem of compensating the ambiguous phase in skip area compared with traditional methods,to ensure a consistent revision of ISLs ranging offset.2.For the problem of ranging offset caused by satellite temperature change in navigation system,a zero-phase shift time-delay revision method based on temperature-sensed is proposed.Based on the time-delay temperature characteristics of ISL payload equipment,this method constructs a temperature-dependent delay distribution model and adopts a combination of ground pre-processing and on-board real-time correction.Compared with the traditional method,the system revision error,resource occupation and design complexity are all improved.The system power consumption is reduced from more than 2W to 90 mW,the revision circuit occupies an area of only 15 mm × 12 mm,and it does not take up the link time slot and not introduce systematic error.Under the condition of temperature change of 90 ?,the root mean square of the revised transmit delay and receive delay residual are 0.0084 ns and 0.0399 ns respectively,which are both less than the random error of the ISL pseudo-code measurement.3.In view of the problem that any link in the navigation system time-chain leads to the failure of the inter-satellite link building,a principle and system design for autonomous time synchronization of the ISL is proposed.And for the ranging offset under autonomous time synchronization,a time-delay revision method based on synthesized frequency adaptive decomposition of clock error is proposed.Based on TWRTT pseudo-range and clock error model and DDFS frequency synthesis principle,the method decomposes the clock delay into integer and fractional phases of the synthesized frequency,and then implements frequency counting and phase control,which effectively solves the residual adjustment clock error and the on-board atomic clock accumulating deviation.The corrected time synchronization accuracy is less than 0.2ns and the accuracy of one-way measurement is less than 0.15 ns.4.For the in-orbit testing and verification of the first ISL payload's precision ranging in Beidou satellite,considering the system requirements and the construction cost,an experimental system architecture of "one fixed station + two mobile stations" was put forward,which constructed a space-ground integrated test environment for ISL.Through the analysis and evaluation of the the two-way measured pseudo-range data,the satellite laser ranging data and the satellite-ground joint orbit determination data,it is proved that the method proposed in this paper is technically feasible and effective.Finally,the paper summarizes the research results and forecasts the work to be done in the next step.The research results in this paper have been realized in BeiDou new generation navigation satellite and ground integrated test system,and have been fully verified by in-orbit test.It is of great practical significance for our independently developed Beidou global navigation satellite ISL system and future PNT system. |
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