Research On Relevant Theory For GNSS Signal Design And Evaluation

Global Navigation Satellite System(GNSS) is one of the most important infrastructures for nations. Following the GPS and GLONASS, European and china started building their own global navigation satellite system named Galileo and COMPASS. At the same time, in order to consolidate the GPS navigation as the global leader in the field, the United States also gradually upgrades the traditional GPS, that is, the modernization of GPS. GNSS signal determines the inherent performance of the system. It has a decisive impact on both the single system performance and the compatibility and interoperability between multiple systems. Therefore, whether in the construction of new systems, or in the GPS modernization process, signal designing are the focus of global concern.The thesis is divided into two parts. The first part analyzes in detail two key problems in navigation signal performance evaluation, code tracking accuracy and code multipath error evaluation, in which the theoretical direction will be extracted. The second part discusses the signal design theory and methods, including what factors should be considered during signal design process and how to take these factors into account. After that, the signal structures of GPS and Galileo are compared, and their design ideas are analyzed. Main contents are as follows:1) Research on the PN (Pseudo Noise) code tracking performance evaluation theory is completed. Up to now, the most widely used code tracking performance evaluation theory is presented by Betz. However. Betz's original paper which contains the detail proof of the theory hasn't been published. In order to applies the theory in the navigation signal process, it is necessary to recovery this important work. This thesis sets up a code tracking accuracy analysis model in the 2nd chapter, derives the code tracking accuracy expressions for coherent EML (Early Minus Late) and non-coherent EMLP (Early Minus Late Power) tracking loops. Based on the theory, the effects of GNSS signal characters and receiver parameters on code tracking performance in white noise environment are discussed in detail. Next, the theoretical analysis method of code tracking performance in non-white interference environment is presented, which is followed by the discussion on the effects of interference frequency, bandwidth and receiver correlator spacing on code tracking accuracy. These analysis methods and conclusions are instructive for signal design.2) The code tracking Error caused by multipath effect is studied theoretically, and the methods to improve multipath rejection ability in signal design phase are given out. After presents a novel theoretical code tracking multipath error model under band limited conditions, the theoretical expression for multipath error envelope is derived, Using this theoretical expression, we get the theoretical lower bound, which indicates the relationship between signal bandwidth, power spectrum density (PSD) and multipath error envelope. Theoretical analysis and simulation results prove that increase signal bandwidth and the high frequence component of PSD will lead to superior multipath rejection.3) This thesis presents three kinds of GNSS signal PSD expression, which are respectively fit for the conditions of PN code period is bigger, equal or smaller than the data bit width. What different from the traditional navigation signal PSD analysis is it considered the effect of second code and effect of data bit transition during one code period. After that, the effects of code shape, PN code and data rate on GNSS signal PSD is detailed discussed.4) After discussing the code effects on code tracking performance, the quantitative relation between signal mutual interference, PSD, PN code autocorrelation character and PN code crosscorrelation character is analyzed in detail. Analysis results shows, GNSS signal performance is main decided by PSD envelope. Furthermore, as the influence of data bits, linear correlation characters of PN code are more suited to characterize the code effects on GNSS signal performance than circle correlation characters. Therefore, two new indexes which are called linear autocorrelation merit factor and linear crosscorrelation merit factor are defined to evaluate the correlation performance of PN codes, and they could be used in the code selection process.5) GNSS signal design method is given out systematically. We divided the signal performance into independent performance and adaptability of it. Independent performance includes the performance of acquisition, code tracking, carrier tracking performance and demodulation. Adaptability of signal includes multipath rejection ability, anti-jamming ability, compatibility and interoperability. After discussing the relation between these signal performance and signal parameters including chip rate, chip waveform, code length, code type, data rate, FEC coding and carrier frequency, we present the advices on how to select these parameters.6) GPS and Galileo signal structures are discussed in detail. We compared the signal structures of GPS and Galileo, discussed their design ideas with the evolution process, analyzed their consideration in signal design, which would be instructive for future signal design works.