Study On Signal Identification And Cycle Ambiguity Resolution Technology For X-ray Pulsar

The existing space navigation methods are highly dependent on the ground station,X-ray Pulsar-based Navigation(XPNAV)can provide time,position,and attitude for the spacecrafts.Compared with existing navigation method,The XPNAV has lower cost,higher reliability and wider range of application.This dissertation focus on the problems of signal identification,phase measurement and ambiguity resolution,The author’s major contributions are outlined as follows:1.In order to improve the identification efficiency for X-ray pulsar signal,a new algorithm which using the time difference of photon arrival(TDOPA)as data object is proposed.First,based on the Poisson model of X-ray pulsar signal,the effect of signal phase and radiation intensity on TDOPA is analyzed,and the distribution probability of TDOPA is derived.Then the probability characteristic of TDOPA sequence is presented,the identification method based on the probability characteristic is put forward.At last,the Doppler Effect on mean profile and TDOPA is discussed,and the influence of it on different signal identification methods is analyzed.The simulation results verify the effectiveness of the suggested method,theoretical analysis and contrast experiment shows that:the method has faster identification speed,do not need phase searching and is not affected by Doppler Effect.2.In order to reduce the observation time of X-ray pulsar signal identification,a new identification algorithm based on the photons distribution statistics is proposed.The influence of cumulation period variation on photons distribution is analyzed,according to the cumulation period correct or not,two kinds Poisson model are developed to characterize the cumulation profiles.The photons distribution statistics is constructed,and the difference of photons distribution statistics between two kind profiles is presented.RXTE observation data is used for simulation,and the simulation result verifies the effectiveness of the suggested method.3.The distortion of cumulaiton profile which caused by detector movement can be used for pulsar signal Doppler estimation.In this paper,a Doppler estimation method based on profile feature is proposed.At first,a nonhomogeneous Poisson model is developed to characterize the cumulation profile,and the influence of Doppler Effect on cumulation profile is presented.Second,a profile feature function is defined to measure cumulation profile distortion.Then according to the relationship between function value and period error,signal period is recognized by searching method.In the search process,restriction on cumulation period is eliminated through transforming observation data into energy density.At last,Doppler estimation is realized by comparing period search result with signal standard period.The simulation result verifies the effectiveness of the suggested method,compared with frequency domain method,the suggested method has high accuracy in Doppler estimation.4.The accuracy of timing and location based on X-ray pulsar signal is determined by the signal phase measurement error,in order to estimate measurement error and improve measurement accuracy,a new phase measurement algorithm is proposed in this paper.The measurement error is considered as a random variable,based on the Poisson model of X-ray signal,the measurement error probability density of a given measurement result is derived by using observation data.The mean-square error is employed as discrimination standard for signal phase searching,and a measurement result whit minimum mean-square error for given observation data is obtained.The mean-square errors of different measurement methods whit same observation time are analyzed,the analysis shows that the suggested method is asymptotic efficient and has minimum mean-square error.The simulation result verifies the effectiveness of error estimation,in contrast experiments,the suggested method has a higher phase measurement accuracy.5.In order to reduce the test number of cycle ambiguity space searching algorithm,a novel method based on matching search for ambiguity resolution is proposed.At first,three pulsars are used to determine the position of aircraft,and a set of planes are established by bringing in an additional pulsar.Then the ambiguity vectors are evaluated by calculating the minimum distances between aircraft and the above planes.Secondly,the relationships between the minimum distances,cycle sets and phase differences are exhibited and the influences on the minimum distances due to the variation of integer cycles are analyzed.After that,a searching template is built to refrain from testing each candidate cycle set and obtain the cycle ambiguity resolution.Therefore,the test number is cut down.At last,simulation results show that,in the same experimental environment,the test number of matching search algorithm is reduced by 4 orders of magnitude compared to the existing algorithms.