| Global navigation satellite system (GNSS) plays an increasingly important role in people's lives,whether in tourism or national military security area,we can't leave the satellite navigation services. With the continuous development of GNSS system, L band(1164-1610MHz) of the navigation signal is becoming more and crowded. For this reason,ITU (International Telecommunication Union) has opened S (2483.5-2500MHz) and C band(5010-5030MHz) to navigation services successively, objectively, which makes multi-band joint navigation possible. It can be predicted, transband joint navigation will become a new generation of satellite navigation development trend.Compared with single band multi-frequency navigation technology, multi-band joint navigation is more favorable for correction of ionospheric delay, simplifies the calculation of integer ambiguity, shorten first positioning time, at the same time has a greater advantage in anti-jamming and anti-multipath. In addition, communication systems can be integrated and complementary to give full play to the effectiveness of satellite navigation system.Signal structure (or system) determines the performance limit of GNSS system, the modulation waveform is the key link in the design of signal structure, auto correlation function and power spectrum density of its decision and has a decisive impact on various performance mainly include the code tracking performance, anti-jamming, anti-multipath of the signal. Therefore, in multi-band joint navigation mode, how to design a universal modulation scheme which can satisfy the restriction and compatibility of the band becomes the focus of the paper, universal modulation scheme can share the baseband processing module, and relatively easily integrated to reduce the receiver volume, reduce the complexity and cost of the terminal of the multi-mode navigation system, speed up the practical process of multi-band joint navigation.Compared with traditional Phase Shift Keying (PSK), continue Phase Modulation (CPM)technology has higher frequency bandwidth utilization and power utilization, signal reserves abundantly, parameter modifies flexibly, can meet the requirements of the different bands'constraints, has the ability to deploy multi-frequency points, it is one of the more competitive alternative in multi-band navigation signal. The topic for the specific requirements of L, S and C band , discuss on the realization scheme of the CPM modulation in each wave band. Study on the evaluation method of GNSS signal quality, evaluate the proposed modulation scheme in ranging accuracy, anti-interference capability, anti-multipath capability and compatibility,To provide new ideas for the technical upgrading of the existing GNSS system and the design of the next generation satellite navigation signal system.Based on the above objectives, the main research content of this paper is :Firstly, To explore the feasibility of multi-band joint navigation based on multi-frequency combination observation in large band gap. Design carrier frequency points in L, S and C bands,and establish a mathematical model of the band frequency point combination.Secondly, for each band on the need for compatibility and compatibility, adjust CPM modulation waveform parameter, design different schemes in its different bands, meanwhile the performance of the proposed CPM scheme and the typical modulation schemes in each band are compared and analyzed. These typical modulation schemes mainly include: the Binary Phase Shift Keying (BPSK) modulation, Binary Offset Carrier (BOC) modulation,Gaussian Filtered Minimum Shift Keying (GMSK) modulation.Finally, analyze an evaluation method for the quality of satellite navigation signals,Based on the principle of code tracking, derive the mathematical model of code tracking accuracy, Gabor bandwidth, anti-multipath performance, anti-jamming performance and compatibility. According to the different requirements of civil signals and authorized signals,A method for evaluating the performance of the weighted navigation signal is studied. |
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