More Accurate Model for GNSS Radio Frequency Compatibility Assessment

摘要

The past and more simplistic assessment of intersystem interference among GPS， Galileo and BDS resulted in pessimistic results, and in some cases, erroneous results. This paper presents more refined methodologies under more realistic conditions, considering the multipath propagation effect of the interesting signal and interference. The superimposed multipath signals not only lead to the distortion of the correlation function between the received signal and the local reference signal, but also reducing or increasing the power of received signal. Thereby multipath effect would cause estimation errors of the C/N_0 and code tracking accuracy, causing the assessment deviation of radio frequency compatibility (RFC). Therefore, in order to further enhance the accuracy of assessment, multipath effect would not be ignored. This study is to estimate the contribution of multipath effect to RFC assessment, aims to provide more realistic and exact interference calculation and assessment results. Firstly, the equation of effective carrier power of multipath interesting signal and the equation of equivalent noise PSD under multipath effects after correlation are derived by introducing matched filtering receiving. Therefore, the more accurate analytic expression of effective carrier power-to-noise density ratio ((C/N_0)_(eff)) is presented Then, the intersystem and intrasystem interference is computed for signals where GPS, Galileo and BDS systems are sharing in L1 band, considering the geometry-dependent and time-varying terms such as space constellation, signal modulation, emission power level, space loss, satellite antenna gain and user receiver characteristic. Comparing with the traditional expression of (C/N_0)_(eff), our new method considers the Cross-Power Spectra Density, the Doppler frequency effect, and the power variations which caused by multipath effect. And the analysis results show that multipath interference has a great influence on intrasystem interference, and has a small influence on intersystem interference.