Multi-frequency and multi-GNSS PPP-RTK for vehicle navigation in urban environments

PPP-RTK which combines the advantages of real-time kinematic (RTK) and precise point positioning (PPP), is able to provide centimeter-level positioning accuracy with rapid integer ambiguity resolution. In recent years, with the development of BDS and Galileo as well as the modernization of GPS and GLONASS, more than 130 GNSS satellites are available and new-generation GNSS satellites are capable of transmitting signals at three or more frequencies. Multi-GNSS and multi-frequency observations bring more possibilities for enhancing the performance of PPP-RTK. In this contribution, we develop a multi-frequency and multi-GNSS PPP-RTK model aiming to achieve rapid centimeter-level positioning for vehicle navigation in urban environments. The precise undifferenced atmospheric corrections are derived from multi-frequency and multi-GNSS observations of regional networks. Then the corrections are distributed to users to achieve PPP rapid ambiguity resolution. Vehicle experiments in different scenarios such as suburbs, overpasses, tunnels are conducted to validate the proposed method. Our results indicate that the multi-frequency and multi-GNSS PPP-RTK can achieve 2~3 cm positioning accuracy in the horizontal direction, 5~6 cm positioning accuracy in the vertical direction with the time to first fix of 5~7 s. In the urban environments where signals are interrupted frequently, a fast ambiguity recovery can be achieved within 5 s. Moreover, the PPP-RTK performance is significantly improved with multi-GNSS and multi-frequency observations. Compared to GPS-only solution, the positioning accuracy can be improved by 75%, and the fixing percentage can be up to 90% with this new method.