Research On Synchronization Of GNSS Baseband Signal Based On BOC Modulation

As early as the late 1950s,the U.S.military started research on the meridian satellite positioning system for military purposes.In order to obtain higher positioning accuracy and meet the pressing needs of the U.S.military and civilians,the United States NRL began to conduct GPS precise positioning studies in the late 1960s.GLONASS,an abbreviation of the Russian "global satellite navigation system",was a military project of the former Soviet Union in 1960.Influenced by the disintegration of the former Soviet Union,its development was more tortuous until Russia released GLONASS's interface control file twice in the end of the 20th century,which had provided GLONASS with support in a wide range of applications around the world,and also broke the monopoly of the United States on satellite navigation and positioning systems.As navigation technology went further,the GPS navigation and positioning system was proposed to be modernized by USA firstly.With the progress of information technology,China and the EU started to construct global navigation and positioning system,and some countries also started to establish regional systems or enhanced systems.In order to meet the needs of positioning accuracy,and interferences between navigation systems are also inevitable with more and more satellites launched.The BOC modulation technology allows designers to focus their energy on a bilaterally symmetrical frequency band according to their requirements,which makes the newly-broadcast navigation signal adopt the BOC modulation method to share the limited bandwidth resources without causing interferences to the existing signals.The main peak of the autocorrelation function of the BOC code is sharper than that of the BPSK code,which can improve positioning accuracy and has better anti-multipath and anti-jamming.But,BOC modulation also causes ambiguity in the synchronization process while it brings many advantages.In order to solve the problem of missed acquisition of BOC signal,this thesis proposes an energy compensation correlation reconstruction algorithm,and uses the acquisition probability as the main index to measure the capture performances of the three algorithms:traditional method,improved GRASS and the energy compensation correlation reconstruction algorithm.For the false lock phenomenon in the tracking loop,this thesis constructs a new type of loop and focuses on the analysis of the phase-functions and multipath suppression performances of two algorithms related to narrow correlation and the correlation reconstruction algorithm.The main work and achievements of this thesis are as follows:1)This paper describes the basic principle of BOC modulation and the characteristics of sine and cosine phases modulation signals,then analyzes the mechanism of derivative signals such as CBOC,TMBOC,AltBOC and QMBOC and the ambiguity of BOC signal synchronization process.2)In view of the shortcomings of the existing unambiguous acquisition methods which are low accuracy or not suitable for high-order BOC modulation signal acquisition.This paper proposes an unambiguous acquisition algorithm of compensated correlation function reconstruction and gives the implementation of the framework and performance analysis,which show that there is a higher probability of acquisition without ambiguity.3)This paper presents a new unambiguous tracking structure which is based on the proposed correlation function reconstruction principle.The simulations show that the DLL discriminator function of the proposed algorithm does not have false lock point,and multipath mitigation performance is greatly improved.4)Based on the analysis above,we establish the signal generation module,multi-channel module and receiver module which are implemented on Simulink software platform,and verify the acquisition and tracking of a modern GNSS signal finally.5)We summarize the work of this paper,and look forward to the research focus related to BOC modulation.