Real-time precise point positioning with a low-cost dual-frequency GNSS device

In recent years, there is an increasing demand for precise positioning with low-cost GNSS devices in support of applications from self-driving cars to unmanned aerial vehicles. Although single-frequency GNSS devices are still dominant in the low-cost market to date, some GNSS manufacturers have released low-cost dual-frequency GNSS devices, which are able to track new civilian signals such as L2C or L5. With dual-frequency GNSS measurements, the ionospheric delays can be eliminated by forming ionospheric-free combinations to further improve the positioning accuracy and reliability with low-cost GNSS devices. Extensive work has been conducted in the past for precise point positioning using high-end dual-frequency GNSS receivers. For low-cost GNSS-based PPP, there are some issues that need to be addressed. One is that current low-cost dual-frequency receivers can track only civil signals but not all GPS satellites currently transmit L2C or L5 civil signals. This means that fewer dual-frequency GNSS measurements are available for position determination. Another is that the measurement quality of low-cost receivers is not as good as high-end receivers. The above will not only increase the convergence time but also affect the obtainable positioning accuracy. We propose a new method in which not only the conventional dual-frequency ionospheric-free code and phase measurements, but also the single-frequency ionosphere-corrected code measurements with precise ionospheric products, are adopted for position determination. To be more specific, ionospheric-free code and phase combinations are applied to satellites with the second civil signal, while the single-frequency ionosphere-corrected code measurement is applied to all observed satellites. Both stationary and automotive experiments have been conducted to assess the performance of the new method. The field test results show that it can quickly reach half-meter accuracy in horizontal at a much faster convergence speed than the conventional DF-PPP which would usually take several minutes to reach a similar accuracy. This indicates that the new method is more suitable for mass-market applications with low-cost GNSS devices.