| The B1 frequency of the Beidou-3 satellite navigation system adopts complex constant envelope modulation.As a new civil navigation signal of B1 frequency,B1 C signal adopts data and pilot separation to realize message transmission and ranging function.The data component is modulated by BOC(1,1)and the pilot component is modulated by QMBOC(6,1,4/33).The new signal system brings a series of performance enhancements to the system,and also puts forward higher requirements on the receiver algorithm and signal quality evaluation algorithm.Combining with the design scheme of B1 C signal,this paper studies the improvement of signal tracking accuracy and the establishment of signal quality evaluation methods.The main results are as follows:1.For the signal structure characteristics of the pilot component QMBOC(6,1,4/33),the TM61 tracking algorithm and the modified code tracking algorithm are used to improve the loop tracking accuracy.The pseudo-code tracking accuracy is theoretically analyzed and the range of carrier-to-noise ratios applicable to the TM61 algorithm is given.The optimal correction coefficient of the modified code tracking under different receiver parameters is derived and given,which breaks the limitation of the selection range of the traditional receiver correlation interval.This provides a reference for the high-precision civilian receiver design of the B1 C pilot channel of Beidou-3.2.In order to improve the tracking accuracy of data components,a tracking strategy combining data and pilot is adopted.Three joint modes with different complexity are used respectively: correlator output amplitude superposition,discriminator output linear combination,and loop filter output linear combination.The tracking accuracy and applicability of the DLL and PLL under each combination mode are theoretically analyzed,combined with the satellite data verification results show that the higher the degree of consistency between the pilot component and the data component code,the more obvious the effect of the joint tracking accuracy improvement;Under the condition of high SNR,the method of using 'correlator output amplitude superposition' in carrier tracking loop and code tracking loop not only has best tracking accuracy,but also has the simplest structure.Under the condition of low SNR,the combination of "code loop filter output linear joint + carrier loop phase detector output linear combination" has the best tracking accuracy and the simplest structure.3.Based on the code phase and carrier phase of high-precision tracking output,the method for estimating the zero-crossing deviation of S curve of B1 C signal is improved.Firstly,the standard correlation function estimation method is used to compensate the correlation peak phase deviation caused by external interference or finite sampling,so that the obtained correlation curve is more accurate.Secondly,an improved S-curve zero-crossing deviation analysis method is proposed to solve the mis-lock phenomenon caused by the speciality of QMBOC signal platform,and this method is tested by satellite data.Finally,the natural pseudo-range deviation of the simplest system of Beidou-3 is given,which has certain engineering significance.4.Based on the observation information provided by the high-precision tracking of the software receiver,a more complete and accurate evaluation method is proposed for the consistency between the pilot component and the data component of the B1 C signal,including: code-carrier deviation,code phase deviation and carrier phase quadrature deviation.The signal consistency analysis of the software receiver under any measurement period is realized.When the code-carrier deviation meets the requirements of the ICD index,the smoothed code pseudo-range is used to evaluate the code phase deviation,and the stability of the measurement result is two orders of magnitude higher than the traditional method. |
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