Research On The Accurate Effective Carrier Power-to-noise Density Ratio Calculation Model In GNSS Radio Frequency Compatibility Assessment

Only under the condition that the system is compatible with each other,it is meaningful to improve the performance of the single navigtion system.While the compatible criterion of multiple navigation system has not been unified yet,so far the systematic research of compatible criterion has been an key and basic problem to be solved urgently both at home and abroad.In the traditional compatibility assessment model,in order to simplify the analysis process and computational complexity,some impacted factors are ignored when calculating.For instance,the code length,data rate and multipath effect on the power spectrum density of the receiving end baseband signal.When calculating the 'effective power spectral density',using the ideal continuous spectrum envelope instead of the real power spectrum of the signal.The influence of multipath effect and the high dynamic motion mode of receiver on the effective carrier power-to-noise density ratio is ignored.It is assumed that the interference signals are independent of each other and are not correlated to the required signals and are not correlated to the desired signals,the combined effects of multiple interfering signals are statistically equivalent to 'white noise'.In order to further enhance the accuracy of radio frequency compatibility(RFC)assessment among multi-GNSS,those factors should be considered more.The main contents and results of this paper are as follows:1.By deriving the calculation expression of the real power spectrum of the navigation signal,the real power spectrum of the civil signal C/A code,B1 code and E1B code is drawn,and the similarities and differences of the real power spectrum and the power spectrum envelope are analyzed and compared.The simulation results show that the power spectrum envelope and the real power spectrum are identical in shape.However,from the numerical point of view,the power spectrum envelope is about 20?30dB larger than the real power spectrum.2.The signal model considering the cross-correlation items is established,the signal power of the cross-correlation items is derived.The methodologies borrow concepts of spectral separation coefficient(SSC).Cross spectral separation coefficient(CSSC)is defined to the inner product of the power spectral densities between the desired and cross-correlation items signal and provides a measure of the overlap of PSD between the desired and cross-correlation items signal.Using the signal's real power spectrum and power spectrum envelope simulation to analyze its SSC and CSSC,and comparing similarities and differences.The formula of the effective carrier power-to-noise density ratio under the influence of the cross-correlation items is derived.STK and MATLAB are used to simulate the maximum carrier power-to-noise density ratio and their global distribution.3.The multipath signal model of the navigation signal is set up.From the processing of GNSS receiver,the processing of multipath desired signal,multipath interference signal and noise are analyzed.The expression of power spectral density of multipath signal is deduced.Considering the extreme case,that is,the multipath interference signal and the direct-to-desired signal are in phase or in reverse phase.4.Considering the influence of cross-correlation items and multipath interference,the effective carrier power-to-noise density ratio model is corrected,and a more accurate formula is obtained.STK and MATLAB are used to simulate the maximum effective carrier power-to-noise density ratio's attenuation in GNSS intrasystem and intersystem interference,and compared with the traditional calculation methods.The simulation results show that the attenuation values of the effective carrier power-to-noise density ratio in GPS,BDS and Galileo are larger than those only considering the cross-correlation items in the same phase,and the values in the reverse phase are almost all smaller than those only considering the cross-correlation items.Compared with the traditional simplified analysis,the modified effective carrier power-to-noise density ratio model can more accurately reflect the GNSS interference.