An analysis of multi-sensor navigation system based on PPP-GNSS, wheel speed sensor and inertial navigation system

Precise point positioning ( PPP) is increasingly being used in many precise positioning applications, which can provide centimeter-to-decimeter-level accuracy with using a single receiver and not be dependent on differential correction. As the railways in China's western region have the characteristics of long mileage, low traffic volume and inadequate infrastructure, PPP results not only further improve the positioning accuracy without the limitation of the operation range, but lower set-up and maintenance cost at the same time. In order to obtain more information of train location, one widely used solution to deliver a more consistent position, speed and attitude is the integration of GNSS and Inertial Navigation System ( INS). However, GNSS signals cannot be always maintained in difficult areas such as bridges, tunnels and valleys, the performance of the GNSS/INS integrated navigation system therefore degrades greatly because of the gyroscope and accelerometer errors. Fusing the wheel speed sensor and the Inertial Measurement Unit ( IMU) data is one of the most efficient way to provide train position in GNSS signal outage area. In this research, we focus on the PPP performance for train kinematic positioning computed by the different International GNSS Service ( IGS) products, and propose a feasible PPP-GNSS/INS/wheel speed sensor integrated navigation system. In order to evaluate the performance of the proposed train positioning system, a real experiment was conducted on the Qinghai-Tibet railway in western China. Compared with the measurements of Differential Global Positioning System ( DGPS), the RMS value of PPP-GNSS/INS/wheel speed sensor integrated navigation positioning results computed by IGS final products are 0.7549m, 0.6053m and 1.7454m in north, east, and vertical direction, respectively. It is interesting to note that the accuracy of integrated navigation positioning results computed by the IGS Rapid products is compared with that computed by the IGS Final products, while the performance of positioning results computed by IGS Ultra-rapid products is unsatisfied owing to the errors of predicted satellite clocks and orbits. Also, the experimental results indicate that the PPP-GNSS/INS/wheel speed sensor integrated navigation system could provide accurate and continuous positioning results in both open-sky and GNSS signal-obstructed environments.