Research On Key Technologies Of Passive Location For LEO Satellites

With the development of electronic information technology,electronic warfare has been widely used in the military field.Electronic reconnaissance technology analyzes the important information in enemy communications by capturing and observing radiation source signals,which is a prerequisite for electronic warfare.In recent years,the development trend of low-earth orbit satellite Internet has been rapid,and satellite location,as the main means of electronic reconnaissance,has become a research hotspot in various countries.According to different signal sources,satellite location is used in two scenarios: active location and passive location.Active location requires satellites to be loaded with high-power transmitters,the satellites has high load pressure and are easy to be counterdetected by the enemy.Passive location has become the mainstream location method,thanks to its high concealment,small size and light weight of satellites.Realtime performance and location accuracy are the main indicators of satellite location.Single-satellite location needs to accumulate Doppler information,the real-time performance is poor,and there are ambiguous points in the location process.Threesatellite location network is convenient,the transmission delay between satellites is short,and the real-time performance is good,but there are initial value problems and local convergence problems in nonlinear equation solving.This thesis focuses on the singlesatellite location model and the three-satellite location model,aiming to eliminate the location ambiguity and improve the location accuracy.In this thesis,single-satellite and three-satellite location models are established,and the Cramer-Rao lower bound of location error of the two models is deduced in detail.Based on the single-satellite location model,the single-satellite location algorithm based on Doppler frequency and the single-satellite location algorithm based on Doppler frequency shift rate are studied.Due to the symmetry of the Doppler effect in the subsatellite point trajectory,it is easy to miss the real location point,and it is impossible to obtain the unique location point.In this thesis,the sub-satellite point trajectory is firstly represented as a function,leaving only a real location point and a fuzzy location point.Secondly,two methods of time-sharing revisiting and coordinating fuzzy location are proposed to eliminate the fuzzy location points.In the three-satellite location model,the coordinate transformation of the positive spherical model brings a large error to the three-satellite time difference positioning Chan algorithm.In this thesis,the location result of the Chan algorithm is used as the initial point of the Newton iterative time difference location method,and the location error is close to the Cramer-Rao lower bound of time difference location model.The timefrequency difference location equation of three-satellite has the characteristics of nonlinearity and overdetermination,in this thesis,the nonlinear problem is transformed into an optimization problem,and the frequency difference equation is used as a constraint to improve the location accuracy.Under the condition of low TDOA measurement error,the FDOA measurement error has a great influence on the location.The weight curve is designed,and the optimization model algorithm and the Newton iterative algorithm are integrated to weaken the influence of the FDOA measurement error.The frequency change rate difference is introduced,and the satellite acceleration information is added to establish a new three-satellite location model,and the CramerRao theoretical error is further reduced.In addition to optimizing the satellite location algorithm,this thesis discusses the factors that affect the positioning accuracy in the location model,establishes a theoretical error model for the above factors,and conducts simulation comparisons.In singlesatellite location,the larger the signal carrier frequency,the longer the observation time.The lower the orbital height,the higher the positioning accuracy.In the three-satellite location,the measurement noise correlation coefficient is negatively correlated with the positioning error,and the optimal three-star configuration is obtained.