Code and phase multipath mitigation by using the observation-domain parameterization and its application in five-frequency GNSS ambiguity resolution

In multi-frequency and multi-constellation GNSS applications, the multi-frequency carrier ambiguity resolution (MCAR) is the prerequisite of high-precision positioning and navigation. Since the multipath is the main unmodeled error that cannot be easily mitigated, we first propose a new code and phase multipath mitigation method using a way of observation-domain parameterization, which can be applied to the GNSS like MCAR, including four-frequency and five-frequency carrier ambiguity resolution (FiCAR). First, take the five-frequency BDS-3 data as an example; the necessity of multipath mitigation in linear combinations is discussed. Second, for the proposed method, the between-receiver single-differenced (SD) multi-frequency multipath combinations are formed and preprocessed. Then the SD multipath can be estimated by the least squares. Finally, the multipath-reduced observations can be applied to the MCAR. Real five-frequency observations with multipath are tested. The proposed method is compared with the traditional method ignoring the multipath by using the single-epoch and multi-epoch modes, including the geometry-free and geometry-based models. The results indicate that the success rate and efficiency of ambiguity resolution can be improved significantly. Specifically, in the single-epoch mode, only the ambiguity resolution success rates of the proposed method are all 100% for the first to fourth signals. Besides, when fixing the fifth signal, the improvement of ambiguity resolution success rates can reach 19.4% on average. For the first four signals in the multi-epoch mode, the mean time-to-first-fix values of the traditional and improved methods are 18.25 and 1.00 s, respectively, and approximately 49 s can be shortened for the fifth signal. Undifferenced or double-differenced multipath can also be parameterized similarly, and then be used in other real-time or kinematic GNSS applications.

Automated summary

The paper introduces a new method for multipath mitigation in multi-frequency and multi-constellation GNSS applications, which can increase the success rate and efficiency of multi-frequency carrier ambiguity resolution.