The Simulation Of Galileo Signal And The Verification Of Its Acquisition And Tracking Algorithm

Galileo system, independently developed by the European Union, is a multi-mode civilian-oriented Global Navigation Satellite System. It is designed to provide location-based services of high precision and high reliability all over world at any time. Galileo system has drawn experience from the latest techniques available in the navigation realm, and has carried about an extensive cooperation with the United States, Russia and other countries. It claims to achieve a high compatibility with the existing GPS system of United States and GLONASS system of Russia. Galileo system has adopted a series of new modulation schemes based on the innovative Binary Offset Carrier (BOC) modulation. Theoretically, BOC signals should achieve better tracking performance and anti-jamming capability than its BPSK counterpart adopted by GPS civilian signal. So far, the BOC signal and its receiving technology have gained an increasing research from the academia.In this dissertation, the Galileo system is first introduced from the viewpoint of a'system'. It includes an introduction to the architecture of the Galileo System, the key services provided, the in-orbit validation satellites and the basic principles underlying the system. Then the Galileo signals are introduced from the viewpoint of the'Signals'. It includes a summary of the frequency plan, signal parameters and modulation techniques, with a special focus on the analysis of the BOC modulation. The BOC(1,1) signal has been selected and simulated as the prototype signal suitable for the research of the signal receiving technology, with the correctness of the simulated signal being verified from the perspective of its power spectral density and autocorrelation function. The signal receiving has been characterized as a fine estimation process of two parameters, i.e. the Doppler frequency and code delay of the pseudo random noise (PRN) code of the satellite signals. Drawn from the viewpoint of the software receiver, this dissertation focuses on the signal acquisition and signal tracking, which are key parts of the signal receiving process. Signal acquisition can be considered as a coarse estimation of the corresponding parameters, while the signal tracking a fine estimation of the parameters. During the study of the signal acquisition, the basic principles of signal acquisition are analyzed. Drawn from the analysis, the signal acquisition is characterized as a two-dimensional search problem in the domain expanded by the Doppler frequency and code delay of PRN code, based on the cross-correlation of the receiving signal and local reference signal. Followed is the discussion of four common implementations of the signal acquisition: the serial approach, the time-domain parallel approach, the parallel Doppler frequency approach and the parallel code delay approach, together with a simulation of signal acquisition based on the parallel code delay approach. After pointing out the problem of multiple peaks within the cross-correlation plane in the acquisition, a BPSK-like solution is given and simulated to verify its validity. The study of signal tracking includes two parts, i.e. the carrier tracking loop and the code tracking loop. The former is used to achieve the fine estimation of the carrier frequency while the later is used to achieve the fine estimation of the code delay of the PRN code. During the discussion on the former, the principle of the phase lock loop is analyzed and the S-curves of four common discriminators are simulated and compared, while during the discussion on the later, the classic early-late gate structure is analyzed, and the problem of multiple zero-crossing points in the S-curve is discovered. A method based on the extended early-late gate structure has been proposed to solve this problem and the validation of this method is verified based on the theoretical analysis and simulation experiments on its S-curve.