Research On Compatibility And Anti-Jamming Of Bei Dou Regional Short Message Signal

Regional Short Message Communication(RSMC)service is a featured service provided by Bei Dou Satellite Navigation System(BDS)with extremely low downlink signal power,and its frequency band is close to the 4G and 5G mobile communication signal of high transmission power,which makes RSMC signal extremely easy to be interfered,thus the compatibility between Bei Dou RSMC and adjacent signals is worth of discussing.In the meanwhile,the problem of improving the compatibility of Bei Dou receiver is also solved in this thesis.Taking Globalstar downlink signal,which operates in the same frequency band as the Bei Dou RSMC,and 4G/5G signals as examples,simulations and measurements of the compatibility between Bei Dou RSMC and the signals of the three adjacent systems are made,and a system to improve the compatibility of Bei Dou receiver is designed.The main content and achievement is as follows:1.Based on the principle of Bei Dou receiver,the thesis derived the equations to calculate signal-to-interference-plus-noise ratio(SINR).Then the equivalent carrier-to-noise ratio(CNR)of the receiver is derived from the SINR expression,and the calculation shows the equivalent carrier-to-noise ratio of 50 d BHz is used as the threshold.This threshold is used to judge whether the interference can be ignored and will be useful in the compatibility analyzing.2.Five factors,which are bandwidth,subcarrier-spacing,out-of-band power limitation,frequency gap of Bei Dou RSMC and the power of the interference,are simulated when analyzing 4G/5G signals.The interference effect of these five factors on Bei Dou RSMC signal and the critical point where the interference can be ignored when the interference signal power reaches the Bei Dou receiver port are obtained.3.Based on the fact that 4G and 5G signals present at the same time,the thesis simulated the equivalent CNR taking the both two signals into consideration.In the simulation two factors,the amount of 4G and 5G users and the distance between the base-station and receiver,are also calculated.The simulation gives the relation between equivalent CNR and the two factors,and determines the safety distance,where the 4G and 5G signals has no influence on the receiver.4.After testing the receiver in actual scenario with 4G and 5G signals,the receiver has severe compatibility problems without anti-interference methods.When the receiver is near to the base station and the interference is only suppressed by band-pass filtering,the receiver’s communicate succession rate is still below 95%.5.The thesis proposes an anti-interference system that combined spatial filtering and adaptive beamforming to solve the compatibility problems with the adjacent frequency signals.The system uses spatial filtering to decrease the interference signals in the first place,then despread the signal to make the wanted signal power greater than other satellites’ signal power,and finally use adaptive beamforming to increase the power of the wanted signal.The anti-interference system is simulated to validate its ability to decrease the interference and increase the wanted signal.The system uses an improved power inversion algorithm,which can inhibit both the powerful and wake interference signals,the adaptive beamforming algorithm based on maximum SNR can get array gain without prior information and can be used in any beam forming system.