Research On Direction Finding Of Short-wave Based On Distributed Sources Model

For a long time,Short-wave communication has always been a hot and difficult point in the field of communication.Short-wave communication has the advantages of costeffective performance,strong resistance to damage,and global transmission.At the same time,short-wave direction-finding technology has also made great achievements with the development of short-wave communication,and it has been widely used in many fields.However,considering the complexity of the ionosphere,the performance of the short-wave direction-finding isn't ideal,which puts forward higher requirements for the short-wave direction-finding technology.Therefore,based on the distributed source models,thesis focuses on the problem of direction-finding in the ionospheric scenario.Firstly,the time-varying characteristics of the ionosphere bring about signal fading,and there may be coexistence of strong and weak signals at the receiving array.At this time,the weak signal is suppressed by the strong signal,which seriously affects the Direction Of Arrival(DOA)estimation.Thesis firstly summarizes several important characteristics of ionospheric channel,such as doppler shift and spread,signal fading,multipath.Secondly,in view of the signal fading,thesis proposes and simulates a standard to measure fluctuations of the received signal power in the short-wave ionospheric scenario.Finally,the parameter reference range to avoid the phenomenon of strong and weak signals is given.Secondly,due to the multipath,there are multiple signals at the array after shortwave is reflected by the ionosphere.When multiple signals have a strong cross-correlation,the performance of DOA estimation will be seriously degraded.Thesis analyzes the correlation of the transmitted signal and the channel respectively.The thesis analyzes the influence of parameters such as baseband code,code period and modulation method under the condition of insufficient statistics,and simulates how the different ionospheric channel parameters have an influence on the cross-correlation.The characteristics of cross-correlation between multiple signals are summarized,which lays a foundation for the establishment of distributed source model.Finally,assuming that channel fading occurs independently with a certain probability and that the sum of the power of multiple stations is equal to the power of a single station,thesis compare the advantages of multistation compared with single station.Thirdly,using the conclusions of the previous chapters,thesis summarizes the characteristics of the angle distribution in view of the azimuth and elevation angles of the signals at the receiving array.Then thesis revises the traditional distributed source model under the orthogonal L array,and proposes a two-dimensional distributed source model under the ionospheric scenario.Thesis theoretically derives the generalized steering matrix,and uses the generalized MUSIC direction-finding algorithm to estimate the twodimensional DOA.Then thesis analyzes the relationship between the performance of direction-finding and signal-to-noise ratio and the number of array elements.Finally,thesis compares the distributed source direction-finding algorithm and the traditional point source direction-finding algorithm,and gives suggestions for shortwave direction finding.