| Satellite navigation technology has always been the crystallization of human wisdom,with the popularity of global satellite navigation technology,navigation and human life is closely related.Beidou satellite navigation is the independent research and development of the global satellite navigation system in our country,not only can it provide navigation services,but also other aspects,at present,it is mainly used in military.GPS blocked the navigation of high-end technology,so it is necessary to research and develop China’s own navigation system! Tracking is an important part of the navigation baseband signal processing,only the accurate tracking can demodulate the navigation message,so as to achieve the final positioning.Research the tracking module is to promote the development of the Beidou navigation.In this thesis,taking the Beidou navigation system architecture and receiver theory as the beginning,we can understand the link of the tracking module in the navigation system from the overall point of view.Secondly,it mainly analyzes the composition of Beidou satellite signal,and then describes the software receiver,Finally,the principle of the whole signal tracking and the noise characteristics of the loop are analyzed in detail.On the basis of theoretical analysis,combined with the traditional phase-locked loop,an improved tracking algorithm that can work in a high dynamic environment is put forward.The improved algorithm use wavelet to denoise the phase difference signal,and estimate the dynamic characteristics of the input signal with the pure phase difference signal,so can solve the optimal bandwidth according to the total error threshold formula.The loop bandwidth can be adjusted in real time with the dynamic characteristics of the signal.Because of the incorporation of wavelet denoising,the noise bandwidth can be extended without increasing the noise,and the dynamic performance of the tracking loop can be increased,and the problem of noise bandwidth setting can be solved.At the same time,makes the optimal bandwidth more accurate.In order to test the effectiveness of the improved algorithm,through the modeling to generate the high dynamic IF signal,and then use the traditional carrier tracking loop and improved carrier tracking loop to track it,do MATLAB simulation test.The experimental results show that the proposed algorithm improves the tolerance of high dynamic signals and improves the tracking performance compared with the traditional tracking algorithm.In high dynamic environment of simulation,the signal-to-noise ratio of the loop input signal is-14 d B,use the scheme that newly proposed,the RMS error is reduced to 6.0069 Hz and the mean error is reduced to 3.8085 Hz when the PLL is in the second order;the RMS error is reduced to 2.1951 Hz and the mean error is reduced to 1.7190 Hz when the PLL is in the third order.Finally,this thesis uses MATLAB GUI to build a beidou signal tracking verification platform.The platform includes low dynamic signal tracking and high dynamic tracking.The low dynamic tracking is based on the real Beidou satellite signal,by capturing the results and some main parameters setting,can get the tracking results,and demodulate out the real navigation message which is used to deal with the positioning process.For high dynamic tracking,to obtain the input source by modeling and simulation.The algorithm uses the proposed improved carrier tracking plan.Through this platform,we can get the results of the integral I branch and Q branch,phase difference signal,doppler shift tracking result and its error.The entire platform is simple and convenient,and can be used for navigation signal tracking processing. |
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