A New Approach for NRTK with Precise Ionosphere Model in Local Region

In order to improve of the accuracy of NRTK (Network Real Time Kinematic) and lighten the communication loads in RTK, a new approach for NRTK is proposed in this paper. Compared with the traditional NRTK, the corrections in the new approach are classified into two categories, one is dependent on the ionosphere; the other is independent on the ionosphere, including the satellite orbit, the clock biases and the tropospheric delay etc. The corrections are estimated using the code and phase observations from a network of reference stations with a double-differenced model, and broadcasted to users by a data severer center in (near) real-time mode. The performance of the proposed approach is validated using the real GPS data from eight reference stations in Tianjin, China. One of the eight stations is selected as a rover station and the others are considered as reference stations for estimating the corrections. The distance of inter-stations is about 40-100km. Numerical results show that (1) the fix-rate of ambiguity at the rover station is greater than 80% in single epoch with the corrections estimated from reference stations; (2) the RMS accuracy of instantaneous positioning is better than 5 cm and 6 cm in the horizontal and vertical components, respectively. The new approach is able to be used for achieving the instantaneous centimeter level positioning with local network of reference stations. Moreover, the performance of the proposed approach can be further improved with the multi-GNSS constellations.