Study On Synchronization Method Of Ambiguity Inhibition In TDDM Signal

As a key source of time and location information of great commercial and military value for global users,Global Navigation Satellite System(GNSS)has become a research hotspot in various countries in the world.At the same time,GNSS's crucial confidentiality demand havs prompted the system to introduce new forms of modulation technology,one of which is Time Division Data Modulation(TDDM).TDDM modulated signal has the characteristic of time-division transmission of data,which improves the confidentiality of signal transmission and improves the signal tracking accuracy.And its ambiguity problem caused by the information flip feature poses a challenge for effective pseudo-code synchronization.To this end,the synchronization method with ambiguity inhibition for the TDDM signal characteristic is researched.In this thesis,based on the research of a new generation of satellite navigation signals,the signal generation mechanism and characteristics are analyzed in which the main content are the structure,auto-correlation and spectrum characteristics of TDDM signals.Aiming at the limitation of existing synchronization technology and its application in TDDM signal synchronization,the problem of synchronization ambiguity in TDDM signal is studied in two aspects from time and frequency domain,and the improved methods are proposed.In view of the time-domain ambiguity problem of TDDM signals,a time-domain ambiguity suppression synchronization method is proposed.In this method,Doppler frequency offset is achieved through two-channel superposition decision,and Doppler compensation is implemented.Meanwhile,synchronization channel selection is used to realize secondary synchronization and estimate data inversion bit to improve synchronization accuracy.Through this method,the ambiguity problems of the pseudo-code phase shift,the correlation of local spread spectrum pseudo-code and signal and the certainty of data inversion bits are effectively improved.Further,aiming at the ambiguity problem of frequency-domain Doppler frequency offset synchronization of TDDM signals,a frequency-domain ambiguity inhibition synchronization method is proposed.This method achieves Doppler compensation through double channel superposition decision,and combines with DBZP algorithm to achieve the purpose of suppressing the Doppler frequency ambiguity.Further more,on the basis of theoretical research,the simulations are completed,and the results show that the proposed methods effectively solve the problems of time and frequency domain ambiguity in TDDM signal synchronization and has good environmental adaptability.