Research And Implementation On The Key Algorithm Of Satellite Navigation Signals Tracking In Complex Environments

Nowadays,the Global Navigation Satellite System has been applied to various fields and penetrated into people's daily life.Not only has it been gradually penetrated into military fields such as aerospace,emergency telecommunications,and missile guidance,but it has also been widely applied to civil aspects such as car navigation,tourism,field trips,and mobile phone terminals.With the increasing demand for applications in forests,urban canyons,and indoor complex environments,how to improve the user experience of GNSS receivers in complex environments has become a research hotspot in the field of navigation.Since the stability and reliability of satellite signal tracking play a decisive role in the real-time location of the receiver,this paper focuses on the bit synchronization algorithm and carrier-to-noise ratio estimation algorithm of satellite navigation signal tracking to improve the performance of the receiver in complex environments,which based on ctual engineering application.The main work of this article is as follows:1.The GNSS system simulation platform was built with MATLAB.The basic theory of the GNSS system,the characteristics of the complex environment and the challenges it brings to satellite navigation signal tracking were analyzed.The current research status of bit synchronization algorithm and carrier-to-noise ratio estimation algorithm in signal tracking were analyzed,which lays a foundation for further research in this paper.2.In order to solve the problem of the traditional bit synchronization algorithms usually use a large number of fixed non-coherent accumulation times in complex environments,resulting in prolonged first positioning time.To overcome this issue,a novel adaptive bit synchronization algorithm was proposed.The number of non-coherent accumulation times of the threshold constraint was set by using the maximum bit energy in this method,so that the bit synchronization algorithm could adjust the non-coherent accumulation times for different signal strengths.And considering the error of the input signal,the upper limit of the number of non-coherent accumulations was set.The simulation analyses show that the correct synchronization probability of the proposed adaptive algorithm is only 5%lower than that of traditional fixed non-coherent accumulative bit synchronization algorithm when the preset threshold is1.5?10~8.However,its average estimated time is reduced by 85%,which makes the first fixed time of the receiver be largely reduced.3.In order to solve the problem that the high complexity of implementation and poor adaptability to GEO satellites of China Beidou system in existing carrier-to-noise ratio estimation algorithm.Firstly,an improved narrow to wideband carrier-to-noise ratio estimation method was proposed,based on the Narrow to Wideband Power Ratio Method.The signal energy is mainly distributed in the I branch when the signal is tracked well.Based on this feature,this method only takes the I-branch signal simplifies the broadband in the traditional Narrow to Wide Power Ratio Method and holds the narrow band constant to estimate the carrier-to-noise ratio.The simulation analyses show that the improved algorithm is basically equivalent to the traditional algorithm.The estimated bias is maintained within 1dB and the estimated standard deviation is maintained within 0.3dB.However,compared with the traditional Narrow to Wide Power Ratio Method,the improved algorithm can reduce about 1000 times in the add and multiply amount of the algorithm complexity,about 60%of the traditional algorithm,which makes the complexity is effectively reduced.Based on the research of the improved algorithm,a low complexity and strong adaptability carrier-to-noise ratio algorithm was proposed.The accurate expression of the carrier noise ratio estimation was derived from the detailed analysis of the I branch two moment distributions and I,Q four moment distributions in this method.The simulation analyses show that the estimated bias is maintained within 1dB and the estimated standard deviation is maintained within 0.3dB.Under the premise of ensuring higher estimation accuracy,the implementation complexity of this method is moderate.The problems that Narrow Band Power Ratio Method cannot being directly applied to BeiDou system and Variance Summing Method is more complicated in its practical application are solved.It can be widely used in the GNSS system,especially in BeiDou system.4.Finally,the algorithm in this paper is transplanted to the C platform for simulation test,and the overall test is performed by the actual receiver board to verify the excellent performance of the proposed algorithm.