Research On Radiation Source Location Algorithm Based On The UAV Platform With Antenna Array

In recent years,Unmanned Aerial Vehicles(UAVs)have been widely used in various fields due to their flexible mobility.Radiation source location has been widely used in wireless communication,radar,sonar and other fields.This thesis combines two important research areas and focus on the estimation of the spatial position of the radiation source based on the UAV airborne array antenna.Airborne array antennas can achieve the multi-target Angle of Arrival(AOA)estimation at the same time,compared to the time of arrival(TOA),time difference of arrival(TDOA),and frequency difference of arrival(FDOA).The method based on AOA does not require time or frequency synchronization between observation stations.This thesis mainly researches the AOA estimation technology based on airborne array antenna,the spatial position estimation technology of the radiation source based on AOAs,the direct position determination(DPD)methods based on array antennas and the location performance optimization scheme based on UAV path planning.The topic has theoretical significance and application value.The main work of this thesis is organized as follows:1)A two-dimensional approach angle estimation method for rotating airborne linear array is proposed.The rotation method of the airborne line array has to be considered first.Utilizing the flexible rotation characteristics of the UAV,it sequentially rotates 45 ° to sample in three directions.The virtual array direction vector can be obtained by virtualizing the array direction vector and removing the duplicates,and the received signal can be obtained similarly by the virtual array.A rough search of the AOA is performed by the DFT method,and then the refined estimate is solved by the compressed sensing method.The proposed algorithm uses the DFT method to obtain the rough AOA estimate of the radiation source,and then constructs a complete dictionary set near the rough estimate.The spectral range of the complete dictionary set is compressed to achieve low computational complexity.Then,the compressed sensing method is used to obtain precise estimates.2)An asymptotically unbiased estimation method of the radiation source position based on AOA is proposed.The pseudo-linear equation constructed by AOA will have a large bias when estimating the spatial position of the radiation source.This algorithm is effective to reduce the bias.A pseudo-linear equation is established based on the measured values of the azimuth and elevation angles.The cost function of the spatial position estimate of the radiation source is constructed by optimizing the weighted least squares.The cost function is divided into two parts,one is the real value,and the other is the term that causes the deviation.The term that causes the deviation is constrained by a constant to reduce its biased effect on the spatial position estimation of the radiation source.However,because the bias term contains measurement errors,it cannot be accurately known,and this term can only be calculated by statistical methods.In this way,the original problem is transformed into a constraint weighted least squares problem.For this constraint problem,Lagrange multiplier method is used to solve the problem.The final result of this algorithm is a closed-form solution,which has very low computational complexity and can reduce bias to obtain good location performance.3)The direct position determination methods of the radiation source are studied.This algorithm mainly solves the problems of poor positioning accuracy and instability of the two-step positioning method based on AOA at low signal-to-noise ratio.Compared with the two-step positioning methods(the indirect positioning methods),the direct position determination methods avoid the secondary transmission of measurement errors in indirect positioning methods based on signal parameters(such as TDOA,AOA,FDOA,etc.).Therefore,the two-step positioning methods have better positioning accuracy and stability at a low signal-to-noise ratio.In this thesis,the direct position determination methods based on the MUSIC algorithm and ESPRIT algorithm are mainly studied.The performance comparison of the two methods is performed in this article.The DPD method based on MUSIC algorithm has better positioning accuracy than the ESPRIT algorithm.4)A path planning method is proposed when the position of the observation station is in error.This method makes full use of the UAV's mobility to improve positioning accuracy.This method uses the Fisher information matrix determinant maximization as the optimization criterion.In this scenario,because the position of the UAV observation station is only the measurement,it is not completely known.Therefore,the variables to be estimated are the spatial position of the radiation source and the position of the observation station,and then the Fisher information matrix of the variables will be calculated.By using the Fisher information matrix equal to the inverse matrix relationship of Cramer's lower bound(CRLB),the Fisher information matrix with the spatial position of the radiation source as a variable will be calculated from the Fisher information matrix just calculated.Finally,the optimization criterion of Fisher information matrix determinant maximization is used for UAV path planning.The method proposed in this thesis reduces the impact of the position errors and AOA measurement errors on the location performance at the same time,so it can obtain better location performance than the path planning scheme that does not consider the position error of the observation station.