Research On UAV Positioning Based On LTE Illuminators

The wide application of unmanned aerial vehicles(UAVs)poses a serious threat to the low-altitude safety of cities.The monitoring and positioning requirements of illegal UAVs are increasingly urgent for managers.The passive radar systems with illuminators of opportunity can locate by the target reflected signal from the non-cooperative illuminators,which has been paid much attention by many researchers because of its strong invisibility and anti-jamming ability.There are still some difficult problems,such as how to use more stable illuminators and how to improve the target positioning accuracy.The main works of this thesis are as follows:1.This thesis proposes a UAV positioning system based on LTE(Long Term Evolution)illuminators.Based on the unique frame structure of LTE signal,the observation station is constructed by installing a positioning module on the working base station in the telecommunication network.In the observation station,the local reference signal is generated by the system prior information,which is used to suppress the interference of the received signal and obtain the target location information.In this thesis,the detailed design of the UAV positioning system based on LTE illuminators includes:the interference suppression of the received signal,the time-frequency two-dimensional correlation,constant false alarm prediction,and target positioning,etc.By analyzing the geometric distribution of positioning accuracy,the ambiguity function of LTE signal and the Cramer-Rao Lower Bound,this thesis evaluates and verifies the good performance of the system comprehensively.2.This thesis studies the interference suppression method of the received signals under the UAV positioning system based on multiple LTE illuminators.The signal from the LTE illuminator is reflected by the UAV and received by the observation-station,which is called target echo signal.As an effective signal,it is inevitably affected by the interference of the direct signal and multipath signal from the same illuminator,and the signals between different illuminators will interfere with each other.In this thesis,the interference between illuminators is analyzed and controlled in the tolerable range by reasonable base station parameter configuration and antenna setting.In this thesis,the rigid requirement of reference channel for conventional passive radar is avoided.Local reference signal is generated by prior information at the observation station,and the clutter subspace matrix is formed by expanding local reference signal to effectively suppress the interference.3.This thesis studies the target positioning method under the mentioned system.Through power analysis,the two possible scenarios in the system are studied with different positioning methods.In the case of single observation station with multiple illuminators,this thesis studies the indirect location method based on the TOA(Time of Arrival)principle.In the case of multiple observation stations and multiple illuminators,this thesis presents a nonlinear equation solution method based on the TOA principle under synchronous error.The statistical characteristics of synchronization error are considered into the positioning method.The Chan algorithm and multi-step Weighted Least Square method are combined to improve the positioning accuracy by using the redundant information.And this method is compared with other nonlinear problem solving methods such as Least Square,Weighted Least Square,etc.In the case of synchronization error,the positioning accuracy of the proposed method is higher.