Research On Code Tracking Accuracy For Satellite Navigation Signals

Global Navigation Satellite System has become one of the most important infrastructures and ofvital significance for a country. Major space powers of the world have not hesitated to developtheir own satellite navigation system. Currently, Global Navigation Satellite Systems have beenbuilt and are being built include GPS, GLONASS, GALILEO and COMPASS. BOC (includingALTBOC and MBOC signals) modulated signals have been widely adopted, while thetraditional PSK-R modulation signal is still preserved via the four GNSS signal systemparameters. Therefore, the coexistence situation for PSK-R and BOC modulation signal isinevitable. Pseudo-range is a basic observed quantity of satellite navigation system. Theextraction of pseudo-range observed quantity is achieved through the code and carrier tracking,therefore, the code and carrier tracking accuracy directly determines the accuracy of thepseudo-range observations. Code tracking accuracy is a key indicator which must be consideredduring the design of navigation signal system. The study on impact factors for code trackingaccuracy is of great significance, which can provide theoretical guidance for research anddevelopment of satellite navigation system receiver.Pseudo-code tracking accuracy and external factors and internal factors on tracking accuracyare studied in depth combined with relevant theory including classic power spectral density,auto-correlation function, pseudo-code tracking and others in this paper. External factorsanalyzed include white noise, Gaussian interference, multipath interference and the receivingsystem; while the influence of internal factors including arbitrary sub-carrier phase and constantenvelope composite technology which both belonging to signal system on code trackingaccuracy is analyzed. The main research contents will be shown as followings.(1) General theory for solving signal power spectral density and correlation function iselaborated systematically. According to the characteristics of the navigation signals, the powerspectral density and autocorrelation function for PSK-R, BOC, ALTBOC and MBOCmodulation signals are analyzed in detail and their characteristics are summarized.(2) Pseudo-code tracking accuracy is analyzed from two aspects of qualitative andquantitative.S curve which stems from autocorrelation function can be used for qualitativejudging the performance of code tracking loop. It is not enough for us to make a qualitativeanalysis on code tracking loop error via S curve, next, under canonical model framework ofTOA error estimation, using no-coherent delay lock loop, through modeling and derivation canget a quantitative formula between code tracking error and SNIR calculated theoretically and the RF front-end bandwidth, early code and late code space, carrier to noise ratio, integrationtime and code loop bandwidth, which leading to a quantitative analysis of the non-coherentdelay lock loop for code tracking error. SNIR and root mean square error of code tracking canreflect the effect on code tracking accuracy of noise, interference. Based on theoretical resultsof the pseudo-code tracking accuracy, the code tracking under white noise, narrowbandinterference, bandlimited white interference with fixed centre frequency and differentbandwidths, and matched spectrum interference are studied in detail.(3) Explicit analytical expression for pseudo-code and carrier phase multipath error is deducedbased on standard correlator, which to make up for the deficiencies of the traditional implicitfunction numerical analysis method, and the error introduced by the explicit analyticalexpression is negligible. A more practical and reliable way for multipath error analysis based onexplicit analytical expression of statistical channel model is advanced considering the effect ofmultipath scenario and elevation of satellite. This includes three kinds of evaluation methodscontaining running average multipath error envelope, weighted multipath error envelope andrunning weighted multipath error envelope, which make a more realistic analysis of themultipath error.(4) The calculation model about the GNSS receiving system is proposed, and the antenna noisetemperature, the cable insertion loss, the noise figure and the equivalent noise temperature areanalyzed, the linear simplified calculation method is proposed; In the condition of the powergain coefficient of the component and the modules is known, according to the definition ofnoise coefficient and equivalent noise temperature, the calculation method of carrier to noiseratio for whole receiving system is proposed. This paper mainly detailed analyze the effect ofcarrier to noise ratio loss on tracking accuracy and bit error rate from the ADC quantization,CIC decimation filter, code delay and doppler residual error.(5) Common explicit expression for BOC signal power spectral density of arbitrary phasesub-carrier is derived through rigorous modeling and derivation which based on a commonapproach for solving the navigation signal power spectral density and representation for spreadspectrum symbols of segmental waveform by selection of arbitrary phase subcarrier. Formula isverified correct by analyzing two kinds of typical BOC signals, and some important conclusionsare drawn. Gabor bandwidth and code tracking lower bound error for modulation signals ofarbitrary phase sub-carrier are studied in depth based on the analytical expression of any phasesub-carrier power spectral density.(6) The principle about the Interplex and CASM constant envelope and mutual multiplexingmethods is systematically elaborated, and the combining loss is defined. The power spectraldensity of constant envelope synthesis and realization is discussed, and the examples about the multiplexing of three and four signals are given. The efficiency of constant envelope andmutual multiplexing are analyzed, and the power distribution parameters are chosen accordingto the best constant envelope multiplexing. The tracking error code in relative signal to noiseratio variation method are put forward, which can realize constant envelope and mutualmultiplexing power spectrum and combining loss count to the code tracking RMS error.