Location Of VHF Signals Propagated Via Tropospheric Duct Based On TDOA

In recent years,radio regulation agencies of some border areas in China have monitored numbers of unknown signals from outside.However,due to the limited number and functions of monitoring facilities,it is not possible to conduct further location analysis.With the development of radio monitoring technology,the diversification of monitoring scenarios,and the improvement of monitoring equipment,the RF sensor based on software radio idea can replace the traditional monitoring receiver and direction finder to intercept,measure and locate the signal.In this paper,through a work task of finding unknown FM signals in border area,a monitoring network composed of several RF sensors based on the TDOA(Time Diference of Arrival)location method is used to monitor and locate target signals,and the none-line-of-sight propagation via tropospheric duct is judged by the HTI index.Firstly,the basic theory of tropospheric duct is introduced,which contains its main types,judging conditions and influence on electromagnetic wave propagation.Then radio monitoring and location technology are studied and some performance evaluation indexes are analyzed.Secondly,according to the test requirements,the basic theory of TDOA location method and three typical algorithms are analyzed.The core process of TDOA is time delay estimation,which is analyzed in detail and corresponding solutions are provided.An improved hybrid correlation algorithm is proposed,which improvement of location performance is verified through simulation and practical test.Finally,based on the TDOA location method,the test work for the tropospheric duct is carried out.Through detailed data analysis,the statistical location pattern and some inferences of target signals propagated via tropospheric duct are obtained,which verifies the applicability of TDOA method to locate VHF signals propagated via tropospheric duct.