Research On Cooperative Acquisition Algorithms For Modernized GNSS Data/Pilot Signals

The increasing demand for navigation and positioning services promotes Global Navigation Satellite Systems (GNSSs) to be modernized and reconstructed. Compared with the traditional GPS, modernized GNSS can provide more signals as well as better accuracy, integrity and anti-jamming capacity. Such improvement in system performance should mainly attribute to the adoption of new structures, spreading code patterns and modulations in GNSS signals. Thus, it is important to understand the characters of new GNSS signals, and then make use of their traits to design the high performance receiver. This paper has a deep research on the cooperative acquisition for the data/pilot signals, which have been widely used in modernized GNSS, and introduces some new algorithms.First of all, the paper analyzes the basic structure of date/pilot signal, to point out that there are two creative technologies adopted here, tiered code and BOC modulation. Then, the generator principle and correlation characteristics of tiered code are investigated in representatives of that of GPS L5C signal and GALILEO E1 signal. The simulation results illustrate the advantage of this code pattern in the anti-jamming capacity and compatibility between different signals. After that, BOC modulation has been analyzed with its principles, power spectrum diversity and auto-correlation characteristics, which manifest the superiority of such design. Based on the above discussion, the in-phase D/P signal model and orthogonal D/P signal model are built as the objective of research on acquisition algorithms.Secondly, this paper divides the acquisition process into four parts--correlative receiving and optimization, post-processing, decision and search--and presents the classical methods and the relevant traits for every part. Moreover, the probability formulas in cell domain and decision domain are systematically discussed with the example of single channel coherent acquisition. In view of the incomplete prior information of desired signal, a method to set the threshold with the false alarm probability in absence of signal is proposed, and proved feasible by simulation.Finally, referring to the concept of non-coherent cooperation and coherent cooperation, FFT-based non-coherent cooperative acquisition and FFT-based coherent cooperative acquisition algorithms are proposed ; Referring to the correlation between the two channels, the idea of space-differential coherent cooperation is introduced and developed into three concrete schemes. Found on peak detection strategy, the statistical expressions of one-cell probabilities for the three proposed algorithms are strictly deduced. Besides that, with the threshold set by the new method, the performances of new algorithms aiming at two different signal models are test and analyzed. According to the test result, three proposed algorithms can successfully realize signal acquisition and provide better performance. What is more, the paper compares the three cooperative algorithms in the aspect of probability characteristic, accuracy and average acquisition time, and then draws the conclusion.