Research On The Beidou Clock Difference Observation And Strategy Of Autonomous Orbit Determination Under The Condition Of Inter-satellite Link

Inter-Satellite Link?ISL?technology is the leading edge of the development of GNSS in the world,and it will soon become an important support for the operation and control of the Beidou global system.The previous related studies are mostly based on simulation.In contrast,this paper uses the measured Inter-Satellite&Satellite-Earth Link data of Ka band provided by the five Beidou new generation experimental satellites.The clock offset observation and autonomous orbit determination strategy under the condition of the Beidou inter satellite link are studied systematically.The main work of the article includes:1.The mathematical model of the Ka band time-division dual one-way observation is derived in detail.The delay calibration method of inter satellite link equipment,which is consistent with the ground user algorithm,is studied.The calibration of equipment delay is carried out using the measured data from satellites and satellites,making the systematic deviation of clock deviation in Ka band and L band be reduced to less than 0.35ns.This soles the problem of the difference between equipment delay calibration and downlink navigation signal group delay.At the same time,the determinant condition of the visibility between satellites and between satellites-earth is derived,which provides a basis for judging the reasonableness of the measured data,and the efficiency of the MEO Inter-Satellite Link data simulation is raised by 30.4%.2.The performance of Beidou satellite clock offset observation based on ISL is analyzed systematically.Both the precision of inner and external coincidence of fitting results of measured Ka link clock offset are analyzed,so are the accuracy of clock offset prediction and the accuracy of indirect clock offset for overseas satellites.The experimental results show that:The external coincidence accuracy of Ka band 7d-long fitting clock speed is better than 10^-14?s/s2?,and that of the zero order term of fitting clock offset is better than 0.1ns;The inner coincidence accuracy of1d-long fitting clock offset is 70.3%higher than that in L band;The accuracy of 1d-long predicted clock offset is 28.1%higher than that in L band;The accuracy of indirect observation of clock offset in ISL is better than 1ns.The above results confirm the reliability of the Beidou ISL observation.3.The strategy of the centralized autonomous orbit determination of the Beidou is studied.A centralized batch autonomous orbit determination algorithm under the condition of inter satellite links is derived.The observability proves the observability of the satellite-earth observation to the right ascension of ascending node?RAAN?,and that it eliminates the problem of matrix rank loss for autonomous orbit determination.The test results of measured data for 3 days arc long orbit determination show that:With no anchor station,the orbit error of tangent?T?and normal?N?is more than 100m;When the observation of anchorage station time is shortened to 1/3,the reduction of orbit determination accuracy is not more than 1m.When the anchorage station is fully operational,reducing the inter satellite observation frequency has little influence on the orbit determination results.Which means that even when the ISL observation interval reaches 240minutes,the orbit determination accuracy of T and N is still better than 1m.4.The distributed autonomous orbit determination strategy of whole constellation is studied.A distributed autonomous orbit determination algorithm based on long term ephemeris constraints is derived,and the relationship between setting strategy of anchorage station and orbit determination accuracy is analyzed.The simulation results show that:Under the constraint of long term ephemeris,the average URE of 60d arc length is less than 4m,but URE still has accumulating trend;3 anchorage station is the best number plan,which can make the average URE rapidly converge to 0.5m within 0.54d;On the choice of anchorage station location,the high latitude anchorage station has no contribution to the improvement of autonomous orbit determination.However,low latitude single anchorage station can control URE to 1m.