Research On Multiband Navigation Signal Model Based On Continuous Phase Modulation

Along with the construction and development of global navigation satellite systems?GNSS?,the L band frequency allocations for satellite navigation are getting more overcrowded.A radical way for the evolution of navigation systems is to provide navigation services in new frequency bands.The S band?2483.5MHz-2500MHz?and C band?5010MHz-5030MHz?have been allocated by the International Telecommunication Union?ITU?to navigation service.Though the single S band or C band signal performance hardly surpasses that of L band,the couple of S band and C band with L band signal could improve positioning accuracy and promote the comprehensive performance of radio navigation services,thus multiband navigation would be a particularly crucial technique for future GNSS.The modulation scheme is the core part of the signal structure,completely determining the upper bound of the GNSS performance,and the modulation waveforms have very significant effects on the performance of navigation system,such as code tracking accuracy,multipath mitigation,and compatibility,etc.In views of increasingly severe radio spectrum compatibility issues in L and S bands,as well as strict out-of-band constraints of C band,together with quite high space loss of S and C bands,it is particularly essential to design a multiband universal signal model endowing strong out-of-band constraint and high navigation performance,contributing to accelerating the practical process of multiband navigation.Continuous phase modulation?CPM?is an envelope-constant and phase-continuous modulation technique,which also endows many other excellent characteristics,such as high power and bandwidth efficiency,large numbers of alternative waveforms and flexible parameter adjustment.These appealing properties make it very appropriate for power and band-limited GNSS system that employs nonlinear high power amplifiers.Thus,this thesis conducts a research on multiband navigation signal model based on CPM,aiming at improving the positioning accuracy and reliability of multiband navigation,enhancing the signal robustness as well as GNSS comprehensive performance.The prime research contents in the thesis are displayed below:Firstly,in multiband navigation mode,this thesis investigates the multifrequency measurement combination model for BeiDou system?BDS?in L,S and C bands,further proposes the multiband-multifrequency measurement combinations for extra wide-lane,?EWL?,wide-lane?WL?,medium-lane?ML?and narrow-lane?NL?.The frequency structures of S and C bands are designed to establish the BDS multifrequency measurement combination model based on L,S and C bands,and then the characteristics of multiband-multifrequency measurement combinations for EWL,WL,ML and NL are investigated by introducing the lane number,ionospheric factor and observation noise factor.After that,the multiband-multifrequency measurement combinations for both scenarios of long and short baselines are optimized.Secondly,the code tracking loop appropriate for CPM is designed and the anti-multipath analysis approach of GNSS signals is completed.By the investigation on CPM correlation property,this thesis designs a code tracking loop appropriate for CPM.Due to the fact that present multipath interference analysis only considers single reflected signal,and the implicit function approach is required to analyze the interference effects caused by more reflected signals,thus this thesis investigates multipath evaluation mechanism,and derives universal explicit function analysis approaches of multipath error envelope under coherent and noncoherent processing code tracking loops.Thirdly,since the relatively high sidelobes of modern GNSS modulations would deteriorate the radio spectrum compatibility issues in L,S and C bands,the CPM is proposed as modulation schemes for future multiband navigation.This thesis establishes CPM mathematical model,analyzes the effects of various modulation parameters on CPM power spectrum density and further proposes the parameter design approaches for CPM as GNSS signals with single mainlobe and double mainlobes.Also,some CPM subclasses are evaluated and optimized.Considering frequency distributions and compatibility of L,S and C bands,together with GNSS signal performance,this thesis uses parameter design approaches for CPM with applications to GNSS and optimized CPM subclasses to accomplish CPM signal design and evaluation for each band.Finally,the serially concatenated CPM with low density parity check?LDPC?code signal model?LDPC-CPM?with applications to multiband navigation system has positive feedback and real-time issues,thus a dynamic iterative stopping algorithm with extrinsic information weighted processing is proposed.To compensate severe space loss of S and C bands,the LDPC-CPM signal model with soft-input soft-output?SISO?algorithm is proposed for multiband navigation system.Then the extrinsic information weighted processing approaches are proposed to curb the systematic positive feedback issue in low E_b N₀ region,and improve the iterative convergence in medium-highE_b N₀ region.In views of systematic iterative real-time issue,this thesis uses extrinsic information transfer?EXIT?technique and dynamic iterative stopping algorithm based on mutual information to optimize the systematic iterative efficiency,achieving a perfect tradeoff between iterative decoding delay and bit error rate?BER?performance.