Research On Time Delay Estimation For X-ray Pulsar Navigation

As a special celestial body,the X-ray pulsar has the physical characteristics with high quality,density and energy,it also has high accuracy and stable cycle than the atomic clock so that it is widely used as a reference time in the celestial navigation.As a basis of the positioning in the X-ray navigation,the TOA estimation is significant,and its accuracy is directly affected by the accuracy of the time delay between the standard pulsar integrated pulse profile and the observed one,so the time delay become a very important measured data.Therefore,it is an important way to improve the performance of X-ray pulsar navigation by studying the high precision,real time and fast time delay estimation method.In the X-ray pulsar navigation,as a method to estimate the time delay of the integrated pulse profie,the bispectrum algorithm can suppress the Gaussian noise completely,but the two-dimensional Fourier transform and iterative process will increase the complexity of the navigation algorithm and the run time.In this paper,the time delay measurement for the X-ray pulsar integrated pulse profile based on the bispectrum algorithm is studied,then we improved the algorithm according to the characteristics of the X-ray pulsar's signal from two side,optimization of bispectrum estimation process and the extraction of spectral feature points.(1)We proposed a new method of fast time delay measurement for pulsar integrated pulse profile.The proposed method sets the one-dimensional slice spectrum of the third-order auto-cumulants of standard pulse profile,the one-dimensional slice spectrum of the third-order cross-cumulants of the standard and the observed pulse profile as basic variables,and employs the general cross correlation function instead of the spectrum transform of these two variables to speed the calculation,and then estimate the time delay of pulsar integrated pulse profiles by finding the maxium value of the general cross correlation.(2)We presented a new method to estimate the time delay of the X-ray pulsar integrated profile by combining the spectrum algorithm and the swarm intelligence algorithm.The proposed method is used to extract the bispectral feature points of the standard pulsar integrated pulse profile by the Swarm Optimization Algorithm on the ground control center,and store these feature points into the spacecraft's database.Then to estimate the time delay faster,it is only necessary to calculate the self-bispectrum and the cross-bispectrum of the standard pulsar integrated pulse profile and the observed one at the extracted bispectral feature points during flying.In this paper,we got the information of the X-ray pulsar form the Europe Pulsar Network database,and then generated the standard pulsar integrated pulse profile and the observed one.We did some experiments to get the running time and accuracy by using those methods we proposed,and then compared them with the traditional bispectrum algorithm.The results shows that the proposed methods in this paper not only retains the advantages with high accuracy of the traditional bispectrum algorithm,but also reduce the calculation time greatly.