The Method Of Time Delay Measurement Based On Fast Maximum Likelihood For Pulsar Pulse Profile

Pulsars are highly magnetized rotating neutron stars which emit extremely strong stable periodic signals, known as the most stable natural clocks in the nature. According to the feature, X-ray pulsars can offer position, velocity, time and attitude high-precision navigation information for the spacecrafts in the near-earth orbit, deep space exploration and interplanetary, as well as cruise devices on the planetary surface without dense atmosphere. Thus, X-ray pulsar-based navigation has wide application value in the autonomous navigation system, and has become a hot research field both at home and abroad.In the X-ray pulsar-based navigation system (XPNAVS), the time difference of the pulse photon arrival (TDOA) is one of the key technologies, the accuracy of TDOA directly determines the accuracy of speeding, timing and positioning for the spacecrafts. The accuracy of TDOA mainly depends on the measurement accuracy of the time delay of the measured pulse profile relative to the standard pulse profile. Hence, we study the measurement method of the time delay of the measured pulse profile relative to the standard pulse profile, and study the method based on the fast maximum likelihood estimation (FML) to calculate the time delay of the X-ray pulsar pulse profile. This method extracts the pulse profile by epoch folding firstly, and then creates likelihood function, finally the time delay of the X-ray pulsar pulse profile is calculated by calculating the maximum of likelihood function. This paper also proposes a fast maximum likelihood time delay estimation based on narrowing the phase interval of the standard pulse profile. In this method, the standard pulse profile can include more phase information by narrowing the phase interval of the standard pulse profile, than uses the fast maximum likelihood criteria to calculate the time delay by the algorithm combing rough estimation with accurate estimation.This paper uses the pulsar data observed by Rossi X-ray Timing Explorer (RXTE) from the aspects of the observed time, the phase interval, Shapiro delay term, Doppler Effect and computation to experiment. Compared with the measurement accuracy of the Taylor FFT algorithm, the experimental result shows that, the measurement accuracy of the FML algorithm is significantly higher than the Taylor FFT algorithm. When the Shapiro delay correction is removed, the FML algorithm can still maintain the high measurement accuracy. The FML algorithm is less affected by the Doppler Effect. The measurement accuracy of the FML algorithm which narrows the phase interval of the standard pulse profile is higher than the FML algorithm which not narrows the phase interval of the standard pulse profile, the computation of the FML algorithm which narrows the phase interval of the standard pulse profile also increases a little, but compared with the improving magnitude of the measurement accuracy, the increased computation can be acceptable.