| With the continuous improvement of electronic countermeasures technology and the increasing complexity of the electromagnetic environment of air combat,the active positioning system observing stations are prone to expose their position to the enemy,facing a great survival threat under the targeted interference and attacks.This situation stimulates the generation of passive positioning systems that do not actively radiate electromagnetic signals.The passive positioning system can realize passive localization and tracking of radiation source only by receiving electromagnetic signals from the radiation source.It has strong survivability in the field of electronic countermeasures because of its strong anti-interference ability,long detection range and good concealment.Single-station passive positioning has poor real-time performance,low positioning accuracy and poor convergence,and its combat capability is not enough to effectively deal with the actual combat environment.In order to achieve high-precision estimation of radiation sources in a complex environment,a multi-station passive positioning system that combines multiple observing stations has become an inevitable trend of electronic countermeasures in the future.On the other hand,UAV has become an indispensable military force on the modern battlefield since it has the advantages of high efficiency,low cost,excellent maneuverability and reusability.Therefore,this paper uses UAV as the carrier of passive detection equipment,ultilizing multiple UAVs to locate and track stationary/mobile radiation sources passively.The main content of this thesis is as follows:1.The traditional methods of multi-UAV cooperative passive localization are introduced and analyzed.The methods include Angle of Arrival(AOA)positioning,Time Difference of Arrival(TDOA)positioning,Frequency Difference of Arrival(FDOA)positioning and Received Signal Strength Indicator(RSSI),etc.First,the basic principles of these positioning methods are introduced,and then the positioning accuracy of these methods is theoretically deduced,analyzed and simulated,which provides a basis for the joint positioning method.2.The positioning and tracking methods of multi-UAV for stationary/mobile radiation sources are studied.The TDOA/AOA and TDOA/FDOA joint positioning methods are respectively proposed for stationary radiation sources and mobile radiation sources.Then,the Cramer-Rao lower bound of the stationary/moving radiator state vector of the passive location algorithm is derived,which provides a quantitative standard for the analysis of the passive localization accuracy.Compared with the performance of a single positioning method,the proposed joint algorithm has achieved better stability and positioning accuracy.Furthermore,the simulation analyzes the influence of various measurement errors,multi-UAV station deployment methods and the selection of the main UAV on the accuracy of the passive positioning method.Finally,in order to reduce the influence of measurement error on positioning accuracy,a nonlinear filtering-based method to improve positioning performance is proposed.Simulations verify the effectiveness of the proposed method.3.The flight trajectory optimization algorithm of multi-UAV for passive positioning and tracking is studied.Since the UAV’s trajectory is critical to the positioning accuracy of the radiation source,the positioning accuracy and stability can be improved by optimizing the trajectory.First,comprehensively consider the flight constraints of the UAV and combined with the nonlinear filtering method,utilize the trace of the Cramer-Rao lower bound of the radiation source location as the optimization criterion,and convert the trajectory planning problem into solving the optimal control vector of the UAV.Then the penalty function method is ultilized to solve the control vector of the UAV at each time,plan its optimal flight trajectory,and then achieve the purpose of improving the positioning accuracy of the radiation source.Finally,simulation experiments verify the effectiveness of the algorithm. |
