Spectral Efficient Navigation Signal Modulation And PN Code Design

With the rapid development of location-based services(LBS)and the increase in user demand for performance,the Global Navigation Satellite System(GNSS)continues to evolve,and the number of signals and occupied bandwidth are gradually increasing.At present,the L-band spectrum resources are basically exhausted by the four major GNSS,and the new signals gradually extend to the S-band and C-band.However,these newly allocated bandwidths for navigation services are narrower than the L-band,the propagation loss is larger than the L-band,and the constraints of out-of-band radiation are more stringent,which are not conducive to improving navigation signal performance.Therefore,improving spectral efficiency is a key issue that must be solved in the future navigation signal design.This thesis studies the design method of spectral efficient navigation signals from two aspects of modulation method and PN code design.Among them,the main goal of modulation mode design is to reduce out-of-band radiation and improve in-band performance,the main goal of PN code design is to reduce the performance degradation caused by multiple access interference in the system.Together,they improve the system's spectral efficiency in the actual scene.In terms of modulation design,considering the new frequency band's restriction of the out-of-band radiation and the performance evaluation model of the band-limited signal,a high spectral efficiency constant envelope modulation method is proposed.By joint optimizing the relative delay and chip waveform of the I and Q branches,the out-of-band radiation is reduced by 7.6-35.2dB without significantly degrading the in-band signal performance,and the spectral efficiency increases by 7.3-34.3dB.For the PN code design,four-step PN code optimization and pairing algorithm are designed based on the key criteria such as balance,odd and even correlation,linear correlation quality factor and spectral line characteristics,which was applied to Beidou B1 C PN code sequence design.The results show that the performance of PN code based on this method is slightly better than GPSL1 C.Furthermore,a design method of navigation signal PN code based on chaotic sequence is proposed.Based on this method,a code sequence set which shows better performance than GPS L1 C is obtained.Different from PN code based on the Weil sequence such as GPS L1 C code and the Beidou B1 C code,the PN code based on chaotic sequence can not only obtain good even and odd correlation performance,but also has the characteristics of large initial value space and can be generated by iterative method,which is convenient for code family expansion and reducing the requirement for storage resources.The research work of this thesis can provide a useful reference for the design of high spectral efficiency navigation signal system.