Research Of Theory And Method On GPS/BDS Measurement Software Receiver

Receiver is an important part of GPS.The software receiver draws on the idea of software radio and realizes the baseband signal processing part of the traditional hardware receiver through software.The software receiver has the advantages of flexibility and scalable.It can correspondingly changes with the development of GNSS,especially the BDS,which is in the rapid development iteration stage.At present,most of the software receivers use pseudorange to get positions,and the positioning accuracy is quite limited.There is less research on the high precision positioning using the Carrier-phase Observation.BDS and GPS are the two most widely used satellite navigation systems in China.This paper aims to build a measuring GPS/BDS software receiver.First,the key technology of the acquisition and tracking of the software receiver is studied.After that,the Carrier-phase Observation and the pseudorange are theoretically derived.Finally,the single frequency PPP experiment based on software receiver is carried out.The main contents and achievements are as follows:(1)Three classical signal coarse acquisition algorithms are studied in the coarse acquisition stage.Aiming at problems of large computation and low efficiency in the current coarse acquisition algorithm,the circumference shift property of FFT and the zero-padding pseudo code algorithm are studied.After that,an improved method is proposed to solve the leakage detection problem caused by the low Doppler resolution in the coarse acquisition stage based on the circumference shift acquisition algorithm.In addition,an improved zero-padding pseudo code algorithm is proposed,which combines the pseudo code zero algorithm and the circumference shift property.Experiment results show that the algorithm greatly shortens the coarse acquisition time and ensures the efficiency of the coarse acquisition for the BDS signal.(2)In the fine acquisition stage,the traditional fine acquisition based on FFT or CZT are studied.These two fine acquisition algorithms have a good effect on the fine capture of GPS signals,but the effect is not good for BDS signal.They are easily affected by the navigation data bits,and the Doppler frequency estimation error may be too large,and “secondary encode” need to be stripped in advance.In order to solve this problem,a new algorithm for fine acquisition using submillisecond signal is proposed.The experiment shows that the algorithm has excellent performance of fine acquisition in normal observation environment.(3)The traditional carrier tracking loop and pseudo code tracking loop based on PLL are studied.The tracking precision of the traditional tracking loop is low.In order to achieve high precision tracking performance,the three order Kalman filter phase locked loop is deeply studied.However,the phase locked loop has the divergence problem.In view of the problem,the Kalman filtering frequency unbiased correction algorithm based on the adaptive under regulated gain model is proposed.The experiment proves that the algorithm solves the divergence problem of the traditional Kalman filtering algorithm,and can achieve the stable and high precision tracking of the satellite signal and keep not divergent.(4)In the software receiver,the method of extracting pseudorange in the software receiver is studied,and the method of extracting the Carrier-phase Observation is deduced.Compared with the traditional extracting Carrier-phase Observation method,the initial phase of the input signal is added to the Carrier-phase Observation.Through the comparison of the positioning test,it is found that the positioning result of the single frequency PPP with the Carrier-phase Observation added to the initial phase of the input signal is better than the other one,which slightly improved 2%~3%,but the improvement is not large;the Carrier-phase Observation obtained by the software receiver is the observed value.The Carrier-phase Observation obtained by the software receiver can be used to carry out single frequency PPP,but there is a gap in the data quality compared with the hardware receiver.Compared with the single frequency PPP positioning results of the hardware receiver,the positioning results obtained by the Carrier-phase Observation value of the software receiver for single frequency PPP reach the level of the hardware receiver.