Research On Analysis And Design Technique For Radio Frequency Compatibility Of GNSS Signals

Global Navigation Satellite Systems (GNSS) is one of the critical infrastructuresin this era of information. Therefore the world major countries are competitivelydeveloping their own GNSS. By the year2020, there will be four major GNSS built,which are, American Global Positioning System (GPS), Russian Global NavigationSatellite System (GLONASS), European Galileo system and Chinese Compasssystem. With the co-existence of multiple GNSS and having them operating inoverlapped frequency domain, GNSS compatibility issues has drawn major attentionfrom system providers and users. It has also become a focus of research in the field ofsatellite navigation. This thesis is the conclusion of few researches supported andfinanced by the National High Technology Research and Development Program (alsoknown as the “863” Program) under the project topic “Interoperability of multipleGNSS constellations–the key technologies and simulation platform”, and by theCompass special project under the research topic “Compatibility technology specialresearch”. The researches include1) Providing a GNSS compatibility assessmenttheory that covers the assessment mathematic model, methodology and criteria;2)Improving the compatibility assessment model;3) Developing a compatibilityassessment simulation system; and4) Providing a series of new signal design throughthe study results of signal design technology based on compatibility.This thesis makes an intensive study of the basic theory of GNSS compatibility,compatibility assessment calculation model, GNSS signals modulation techniques andsignal multiplex techniques. The primary research contributions and technicalapproaches are presented in the following four aspects:(1) Based on the theory of GNSS receiver, the effects of interference signal ontoa receiver at its signal capture, carrier tracking, code tracking and data demodulationprocessing phases are studied. Then the equations to calculate Signal to Noise plusInterference Power Ratio (SNIR) of correlator output is derived, and the computationmodel to calculate the effective signal to noise ratio ((C N0)eff) based on the SNIR ofcorrelator output and code tracking error are built. This thesis also analyzes thecompatibility assessment methods, standard, input and output parameters, andintegrates compatibility assessment theories to establish a GNSS compatibilitysimulation system. Using this model, the compatibility simulation results betweenGPS and Compass Phase III (CP III) system are provided. (2) This thesis gives an in-depth study of the Power Spectrum Density (PSD) ofbaseband signal, the influences of pseudo random code length, navigation data rateand code-chip rate to compatibility calculation. Then it proposes simplifiedmathematic models to calculate the Spectral Separation Coefficient (SSC) and CodeTracking Spectral Sensitivity Coefficient (CT_SSC). Combining the receiver’sBandlimiting, Sampling and Quantizing (BSQ) losses model and power spectrumanalysis result, it derives a simplified model to assess the compatibility with bettercomputational efficiency and accuracy. Using this simplified model, it runs thecompatibility simulation test to all signal channels between Compass Phase II (CP II)and other GNSS.(3) The theory of modulation signal is studied, then the application for a series ofrectangular wave modulation, sine wave modulation and Multilevel Coded Symbols(MCS) modulation to GNSS is also discussed. It further improves the modulationsignal wave design theory by proposing Generalized Multilevel Coded Symbols(GMCS) modulation that would allows varied signals been expressed and analyzed bya unified method. Based on these researches of signal modulation theory, it designsCP III modulation scheme and provides performance analysis results for CP III.(4) The theories and characteristic of common used multiplexing techniques,such as linear modulation, Hard Limiting, Coherent Adaptive Sub-Carrier Modulation(CASM), Interplex and Majority Voting (MV) are analyzed. Then multiplexingscheme of GPS and Galileo are given. Through the analysis and study of differentmultiplexing technique, the multiplexing scheme for CP III on B1band are designedwith maximized power efficiency.The key technologies and innovations in the research focus on the followingpoints:(1) This thesis realizes the overall integration of compatibility assessment theory.Based on it, a simulation system is designed, and simulation results of compatibilityanalysis between different GNSS are provided. Simulation results can supportinternational GNSS compatibility negotiation and contribute to the signal design ofCompass system.(2) Based on PSD analysis and BSQ losses, an improved compatibilityassessment model with better computational efficiency and accuracy comparing withtraditional assessment model is proposed. Full frequency bands simulation testbetween CP II and other GNSS is conducted and more accurate assessmentconclusions are given.(3) MCS and GMCS are derived for navigation signal wave modulation.Meanwhile, an applicable modulation scheme is proposed for CP III.(4) Key technology for signal multiplexing is analyzed. Multiplexing schemesfor GPS, Galileo and Compass are realized with maximized power efficiency and optimized constant-envelop modulation.The conclusive results from the research presented in this thesis are:(1) When the navigation signal complies with the criteria L≥f c/fd,where L isPseudorandom Noise (PRN) code length,f cis code-chip rate andf dis data rate,SSC and CT_SSC of the signal is converged to a constant value and does not showperiodic changes along with Dopple offset. With this condition, the signal PSD can bereplaced by code-chip PSD in SSC, CT_SSC and (C N0)effcalculations.(2) The BSQ losses of receiver will be increasing along with the decreasing ofquantiser level N. When quantizer level N≤4, BSQ losses of will be greater than0.5dB which is a unignorable factor to the final compatibility result, therefore, shallbe included in the compatibility assessment model.(3) With the co-existence of multiple GNSS GNSS Signal design shall considerboth the signal’s basic performance and its compatibility performance. The CP IIIsignal modulation scheme using AltBOC(15,10) with center frequncy at1191.795MHz and1176.4MHz designed by this thesis not only delivers best codetracking performance and higher Gaber bandwidth but also provides excellentcompatibility performance.(4) When number of signal components is greater than4, the Majority voting andits derivatives are the preferential constant-envelop multiplexing technique. Themultiplexing scheme for CP III signal on B1band designed by this thesis is usingMajority voting with weighting for4signal components with maximum power, thenusing Interplex multiplexing to further multiplex to produce a final multiplexed signalthat is the constant-envelop multiplexing scheme with minimum power losses.