A simplified PPP-RTK atmospheric delay correction model and its positioning performance

Abstract The atmospheric delay corrections including tropospheric delay corrections and ionospheric delay corrections are critical information in positioning solutions of PPP-RTK (Precise Point Positioning-Real-Time Kinematic) rapid positioning service, in order to achieve rapid convergence of fixed ambiguity and high-precision positioning solutions in a short time. With rapid development of GNSS (Global Navigation Satellite Systems), the availability of multi-frequency and multi-GNSS observations has led to a significantly increase of number of atmospheric delay corrections, which will surely put more pressure on data transmission and reception to PPP-RTK service and potentially improve the cost of operational economy of users. Therefore, we propose a simplified method to process the atmospheric delay corrections, which sacrifices a certain degree of mathematical rigorousness in positioning equations, but significantly reduces the number of corrections while ensuring that the degradation in positioning performance remains in a controllable way. The traditionally used slant tropospheric delay corrections are simplified to zenith tropospheric delay corrections, and the usually used pseudo-range slant ionospheric delay corrections are no longer transmitted and are simply calculated as the opposite of phase slant ionospheric delay corrections at the user station. The experiments results show that the number of atmospheric delay corrections reduced about 60 %, and the differences between the atmospheric delay corrections processed by the proposed simplified method and the typically traditional method are acceptable to a certain extent for users located in networks with small/medium scale and under relatively stable atmospheric conditions. Although the employment of atmospheric corrections processed by the proposed method introduces the longer TTFF (Time To First Fix) and the lower success fixing rate of ambiguity, the positioning solutions with the proposed simplified method is still basically adequately to meet the positioning requirement of user stations. The proposed simplified model is beneficial to some users who prefer to put more emphasis on equipment portability and data transmission economy.