Precise Point Positioning Ambiguity Resolution with Multi-frequency Ionosphere-Reduced Combination

Precise point positioning (PPP) with ambiguity resolution can improve positioning accuracy and reliability. In conventional dual-frequency ionosphere-free (IF) PPP (IFPPP), the IF ambiguity loses its integer property, so the fixing process needs to be decomposed into a two-step way of fixing wide-lane (WL) and narrow-lane (NL) ambiguity separately. Only when both are fixed at the same time, can a reliable positioning solution be obtained. In order to take full advantages of multi-frequency signals and simplify the ambiguity resolution process, by proper selecting the combination coefficients, a PPP ambiguity resolution method based on ionosphere-reduced (IR) combination is proposed in this paper. The proposed IRPPP model hardly needs to consider the effect of ionosphere, while has the equivalent wavelength and observation noise compared with conventional IFPPP. In addition, the combined IR ambiguity maintains its integer solvability, thus only one-step of directly fixing the IR ambiguity is need to achieve positioning performance comparable to conventional IFPPP. The model is further evaluated globally, and the results show that the IRPPP is superior to the conventional IFPPP in terms of the number of available NL ambiguity and the time to first fix (TTFF), and the average TTFF can be shortened by 22.6%. As for positioning accuracy, both models are basically the same with centimeter-level accuracy.