Research On Acquisition Techniques Of GNSS Signals Based On BOC Modulation

Global Navigation Satellite System(GNSS) has been widely used in military and civil field. With the development of GNSS, there are many increasingly serious problems, such as frequency band crowded and mutual interference between signals. The proposing of Binary Offset Carrier(BOC) modulation can effectively solve the problem and possess higher code tracking accuracy and better multi-path discrimination capability.The signal acquisition is an indispensable part of the GNSS signal processing, at present, the existing PSK modulated signals acquisition technology is not applicable for the BOC modulated signals. Therefore, based on the characteristics of BOC modulation signals, three problems in the acquisition process of GNSS signals based on BOC modulation, which include two-dimensional acquisition, weak signal acquisition and unambiguous acquisition have been analyzed in this paper. The main research contents and wok are as follows:Firstly, developing research on the BOC modulation signals, and elaborating the principle of the BOC modulation, the structure and the generation process of the BOC modulation signals, analyzing the spectrum and autocorrelation characteristics of BOC modulation signals by the comparison with the traditional GPS signal, and the related Matlab simulation was studied. The simulation results show that the BOC modulation signal has a characteristic of spectrum splitting, and the autocorrelation function has multiple side-peaks,which may bring about ambiguity in signal acquisition and tracking. In addition, the generation of the MBOC and Alt BOC modulation signals has also been studied.Secondly,the principles and realization technology of the main two-dimensional acquisition algorithms of GNSS signals several acquisition methods are introduced,which includes some traditional acquisition algorithms such as serial acquisition, FFT-based parallel acquisition and delay and multiply approach, and the new proposed extended replica folding acquisition search technique. Besides, based on the traditional SNR accumulation algorithm, this paper starts to research the technology to improve SNR, and analyze the advantages and limitations of the various accumulation algorithms. On this basis, alternative acquisition algorithms of weak navigation signal have been studied, including half-bits method, full-bits method and double block zero padding method.Thirdly, since the ambiguity issue is the biggest difference between BOC signals and traditional navigation signals, this paper has put more efforts into the study of unambiguous acquisition techniques. Further researches on traditional BPSK-like techniques and side-peaks eliminating technique have been made, and the simulation results shows side-peaks eliminating techniques have a better performance on ambiguity mitigating. By the analysis and research on the shortcomings of existing side-peaks eliminating techniques, an unambiguous deterministic compressed acquisition technique for BOC signal has been proposed combining with the compressed sensing technique.Finally, detailed theoretical analyses on the acquisition performance and the implementation steps of the proposed technique have been given. In addition, this paper also accomplishes the simulation analysis by using Matlab, the simulation results shows that at the cost of some degradation of detection probability in acquisition the proposed technique can eliminate the ambiguity threat in the acquisition process with lower computation complexity.