X-ray Ranging Under Extremely Low Signal-to-noise Ratio

X-rays have strong penetrating ability,low dispersion,and low attenuation in space propagation.Navigation and communication technologies based on X-rays have good application prospects in the field of deep space detection.This paper is based on the application requirements of distance measurement in the integrated project of space X-ray communication,navigation and ranging.Through X-ray ranging,it provides distance assistance information for pulsar navigation to support navigation applications based on range measurement enhancement.Aiming at the extremely low signal-to-noise ratio of longdistance transmission in deep space communication,this paper has carried out the research of X-ray ranging theory and method under extremely low signal-to-noise ratio,and proposed X-ray based on time coherent accumulation and short-time pulse gate technology.Singlephoton ranging method.The X-ray ranging system is built by using the integrated simulation device of space X-ray communication and measurement,and the X-ray ranging is verified.The main research work includes:1.Summarized the basic principles and application scenarios of existing ranging methods,expounded the current development of X-ray generators,established mathematical statistical models of X-ray photon signals,and studied the signal simulation methods.On this basis,combined with the transmission characteristics of X-rays,a one-way one-way ranging mode based on X-ray photons is proposed.2.Aiming at the extremely low signal-to-noise ratio during transmission,a ranging method based on time-coherent accumulation is designed.Multi-period ranging signals are repeatedly sent at the transmitting end,and epoch folding technology is adopted at the receiving end to achieve high-precision reconstruction of the signal,and the distance is calculated through the cyclic cross-correlation method.On this basis,through theoretical analysis and simulation experiments,the influence of the ranging signal type,signal period,accumulation time and other factors on the X-ray ranging accuracy is studied.The experimental results show that as the period of the ranging signal decreases and the contour accumulation time increases,the ranging accuracy gradually improves.When the period of the ranging signal is 340μs,the photon flow rate is 1000cnts/s,and the cumulative duration is 60 s,a rectangular pulse with a duty cycle of 5%,the ranging accuracy can reach 10 m.3.Aiming at the problem that the accumulation time is too long in the time-coherent cumulative ranging and the signal profile is difficult to recover when the received signal is weak to a single photon level,the principle of measuring the distance between the moon and the earth by laser is used for reference,and a high-precision X-ray ranging based on shorttime pulse gate is proposed.method.Using a priori information to screen X-ray photons,and using Bayesian estimation methods to achieve high-precision ranging within a few pulse periods.In this paper,a priori Bayesian time delay estimation model based on X-ray photons is established,and the theoretical value of Bayesian time delay estimation based on prior information and the lower bound of Cramereau theory are deduced and verified by simulation.Under the condition that the signal pulse width is ns level,the ranging accuracy can reach the meter level.This method shortens the measurement time while reducing the probability of false alarms,and greatly reduces the power consumption of the X-ray ranging system.4.Based on the integrated simulation device of space X-ray conduction and measurement,an X-ray ranging system was built,and a differential-based X-ray ranging verification method was designed to eliminate the system delay.By emitting different ranging signals,under different photon fluxes and different integration durations,the accuracy of the ranging method is verified.The experimental results show that the correlation coefficient between the ranging signal recovered by the actual system and the standard signal can reach over 0.99.When the anode high voltage of the analog device is 18 kV and the filament current is 1.8A,a rectangle with a period of 2ms and a duty cycle of 5% is used With pulse ranging signal,the ranging accuracy is better than 10 m under 50 s accumulation time.