United Estimation of Time Delay and Frequency Drift In XNAV

The original navigation information of XNAV is the arrival time series of X-ray photons received by spacecraft. The key issue is to estimate parameters, including time delay, frequency drift and change rate of the observed profile by comparing it with corresponding standard profile in "folding process". This paper illustrates the equation of equiphase point in time series of photons, and gets the initial approximate value of time delay and frequency drift by Larsson cycle folding and coherent function methods. Higher-order approximation is obtained by least square method, and more precise value is calculated by cyclic iteration. Simulation result indicates our method can achieve high precision even without noise eliminating and smoothing process. The proposed method, maybe kind of complicate, it proves the feasibility of XNAV.