GNSS Signal-in-space Performance Evaluation

Global navigation satellite system(GNSS)is the cornerstone of national defense and economic development,with a crucial role in navigation,positioning,and time synchronization.Currently,GNSS is planning next-generation navigation systems by adopting new technologies,developing new satellites,or constructing new systems to improve and enhance service performance for end-users in various applications.Therefore,evaluating the service performance of different navigation systems can provide a reference for the subsequent improvement and development of the system,to ensure the use of different users.In this paper,GNSS spatial signals are studied from three aspects: broadcast ephemeris accuracy,spaceborne atomic clock and positioning performance,and related preprocessing methods,evaluation procedures and mechanisms are discussed.The main research content and work are as follows:1.Provide a detailed introduction to the time and space reference frames of various GNSS and their corresponding conversion relationships,and describe the importance of the time and space reference frames for the assessment of GNSS signal-in-space.Then,explain a series of issues to be aware of when evaluating broadcast orbits,broadcast clock errors,and signal-inspace range error,and give evaluation indicators and methods for onboard atomic clocks.Finally,expound on the single-point positioning process and algorithms involved,which lay a theoretical foundation for subsequent work.2.Discuss the evaluation process and preprocessing methods for the signal-in-space accuracy of various GNSS systems,firstly,the statistics of broadcast ephemeris data completeness,spatial signal availability and continuity can provide reference for subsequent analysis,and then the precision ephemeris is regarded as the benchmark to evaluate GNSS broadcast orbit,broadcast clock difference and spatial signal ranging error and other indexes.Experimental results show that in terms of broadcast ephemeris completeness,BDS data completeness rate is greater than 99%,which is better than other navigation systems;in terms of signal-in-space availability,BDS-3 is better than BDS-2 and better than other navigation systems,with GPS and GLONASS being comparable after removing some satellites,and the Galileo system slightly worse;in terms of signal-in-space continuity,BDS-3 is better than BDS-2,with GPS and BDS-3 being comparable,followed by GLONASS and Galileo systems;in terms of broadcast orbit,the order of orbit accuracy of each system is Galileo,BDS-3,GPS,GLONASS,and BDS-2;in terms of broadcast clock error,Galileo has the best accuracy,BDS-3 and GPS have similar accuracy,both of which are better than BDS-2 and GLONASS;in terms of signal-in-space range error,the order of SISRE of each system from small to large is Galileo,BDS-3,GPS,BDS-2,and GLONASS.3.Evaluate the service performance of onboard atomic clocks in current GNSS systems,and assess the status and quality of onboard atomic clocks in various GNSS systems from the aspects of satellite clock error completeness rate,phase,frequency,frequency accuracy,frequency drift rate,frequency stability,and clock fitting accuracy.The experimental results show that in terms of precise clock error data completeness rate,the order of completeness rate from high to low is GPS,BDS-3,BDS-2,Galileo,and GLONASS;in terms of satellite phase and frequency,GPS,GLONASS,and Galileo have good continuity of phase and frequency data,but BDS-2 has frequent phase adjustment,and BDS-3 has more frequency adjustments.The frequency/phase adjustment frequency of hydrogen clocks is less than that of rubidium clocks,and there are significant differences in frequency/phase adjustment frequency among different orbit types.In terms of frequency accuracy,the order of frequency accuracy from high to low is GLONASS,GPS,Galileo,BDS-3,and BDS-2;in terms of the frequency drift rate,Galileo is the best,followed by GPS,GLONASS,and BDS is relatively poor;in terms of frequency stability,the corresponding indicator of Galileo is the best,BDS-3 is comparable to Galileo,better than GPS and GLONASS,while BDS-2 has the worst stability;in terms of atomic clock fitting accuracy,the order of accuracy from high to low is Galileo,BDS-3,GPS,BDS-2,and GLONASS,among which BDS-3 is 59% higher than BDS-2,and the fitting accuracy of different types of GPS satellites varies greatly,possibly due to differences in the length of service time of GPS satellites in orbit.4.Analyzing the positioning performance of GNSS systems under interference,this study evaluates the anti-jamming effects of various GNSS system frequencies from three aspects:signal-to-noise ratio,multipath,and terminal positioning performance.The experimental results show that in terms of signal-to-noise ratio and multipath,the anti-jamming effect of BDS B3 frequency is better than that of B1 frequency.The anti-jamming effects of GPS frequencies are ranked from smallest to largest as L1,L2,and L5.The GLONASS frequencies exhibit large and unstable multipath errors,with G2 frequency slightly better than G1 frequency.The antijamming effects of Galileo frequencies are ranked from smallest to largest as E1,E5 a,E5b,and E5,with E5 a and E5 b having similar multipath errors.In terms of terminal positioning,the Galileo system performs the best,with horizontal component accuracy of less than 1m and vertical component accuracy of less than 2m for each frequency,and the position accuracy is ranked from small to large as E1,E5 a,E5b,and E5.