Research On The Position Solution And Integrity Improvement Of GNSS Using The System Time Offset

With the process of GPS and GLONASS modernization,the development of Galileo and the formal operation of BDS,multi-GNSS is the development trend of future satellite navigation system.The advantages of multiple system satellite navigation include increased numbers of available satellites and better the accuracy and reliability of positioning result,etc.However,when using ranging signals from multiple systems,the challenge is not only to maximize the benefits of additional pseudorange measurements,but also to deal with GNSS time offset.Multi-GNSS navigations are also expected to achieve better positioning performance in the degraded environment especially.There exist several problems in degraded environments: the number of visible satellites decreases and user-satellite geometry deteriorates extremely,which result in poor the accuracy and reliability of positioning result.In this thesis,GNSS time offset is applied to multi-GNSS positioning and integrity algorithms.Based on GNSS system time offset monitoring data and four-constellation combined positioning test platform,the improvement of multi-GNSS positioning and integrity is evaluated when using GNSS time offset.The main research results of this thesis are as follows:1.The method of GNSS system time offset monitoring and performance evaluation is studied.The error distribution of GNSS system time offset monitoring based on signal-in-space reception method is discussed,then the characteristic and calibration method of key parameter are researched in this thesis.Taking the monitoring data from BIPM Circular T as reference value,the performance of GNSS time offset is evaluated by means of mutual contrast.2.Four-constellation combined positioning algorithm is investigated.On the basis of single system positioning,four-constellation combined positioning algorithm is studied in this thesis.Meanwhile,different four-constellation combined positioning equations based on two processing strategies of GNSS time offset are implemented,which are utilized to prove the improvement of GNSS time offset on multi-GNSS combined positioning.3.The integrity algorithms for four-constellation combined positioning are researched which are autonomous integrity monitoring algorithms based on receiver.The specifications of availability and reliability are analyzed using the algorithms.The integrity improvement of GNSS time offset-assisted multi-GNSS combined positioning is proved based on two processing methods of GNSS time offset.4.According to the theoretical analysis mentioned above,the experiments which verify GNSS time offset-assisted positioning and integrity are designed and implemented.The measurement data of four-constellation receiver and the GNSS time offset monitoring data of National Time Service Center is used according to experiment scheme.The improvement effect of multi-GNSS combined positioning performance and integrity is assessed when using GNSS time offset.The results indicate that positioning performance and integrity of four-constellation combined shows the best performance in 30 degrees elevation angle when using GNSS time offset.The positioning error RMS,PDOP,GDOP,HPL and MDB values are 3.92 meters,2.34,2.88,93.84 meters and 9.29 meters respectively.While the corresponding improvement percentages are 46.76%,55%,55.5%,83% and 70% respectively in comparison with GPS stand-alone navigation system.