Research On Stratified Multi-signal Direction Finding Based On Short-wave Ionosphere

Short-wave direction finding and positioning technology is an important part of short-wave communication signal processing.Estimating the azimuth and elevation angle of short-wave signals accurately and efficiently is the main problem of shortwave communication signal spatial domain processing.However,in the actual environment,because of the multipath propagation caused by the ionosphere,there are coherent signal group in the received signal.When the signals are coherent,the traditional algorithms used in existing array direction finding systems will fail.This paper focuses on the direction finding problem of coherent signals generated by stratified reflection of ionosphere with different heights of the same signal source in short-wave propagation,including multisignal or multi-group signal direction finding problems.At the same time,the position issues of source is studied in short-wave scene.The main contents of this thesis are summarized as:Firstly,the two-dimensional Direction Of Arrival(DOA)estimation of coherent signals on the elevation plane in short-wave special coherent scenes is studied.A twodimensional DOA two-step estimation scheme for the multi-coherent signal of the elevation plane of the ionosphere is proposed.Under the array receiving model of shortwave ionospheric layered reflection,the independent azimuth estimation method based on the maximum value method is derived in the first step,and the effectiveness of the algorithm is verified by simulation.The second step derives the angular relationship between the one-dimensional DOA and the two-dimensional DOA,and applies the angle calculation method to estimate the elevation angle.Then the simulation experiment is used to compare the maximum likelihood method with the angle calculation method and the result confirmed they have the similar estimation performance when estimating the elevation angle.Finally,the applicable conditions of the angle calculation method are given by simulation analysis.Secondly,When the short-wave multi-source arrives at the same receiving station,the independent signal generated by the receiving station is mixed with the target coherent signal group,which makes the coherent signal DOA estimation difficult.In order to solve this problem.Firstly,the one-dimensional received signal model of the mixed signal arriving at the array is given.And the DOA estimation algorithm of the independent signal and the coherent signal in the mixed signal is analyzed in one dimension.Then,under the orthogonal L matrix,after deriving the spatial angle relationship,the dimension reduction and direction finding scheme of the two-dimensional DOA information of the coherent signal is estimated by using the estimated angle of the two-line array.And the simulation proves that the proposed scheme is effective.Thirdly,for the short-wave single-station positioning problem,the geometric relationship under the short-wave positioning scene is analyzed under circumstances of single-path and multi-path.The relationship among the direction-finding angle,the ionospheric reflection height and the distance from the direction-finding station to the source are derived.The F mode and E mode deviation introduced by the ionospheric tilt are analyzed.And the corresponding suggestions for reducing the error are given on the signal transmission model.Finally,the quantitative relationship between the direction finding error and the positioning error at different azimuth and elevation angles is analyzed and simulated.