GNSS time offset monitoring based on the single difference among systems

Time offset monitoring of multiple Global Navigation Satellite Systems is important for compatibility and interoperability. Unlike conventional signal space approaches, such as single-point positioning (SPP) and precise point positioning, an approach based on the principle of single difference among systems, single-difference point positioning (SDPP), is proposed to omit the receiver clock parameter and reduce the influence of the common model errors during estimation. The proposed approach was validated on different datasets, and results shown that the estimated time offset among systems using SDPP has no significant difference with that using SPP. Moreover, SDPP retrieves the best time offset estimation when considering it as a random walk process, as it provides smooth estimation with low noise. Furthermore, considering constraints from station coordinates and tropospheric delay further improves time offset estimation. The time offset estimation over time remains within a reasonable range, exhibits some periodicity, and estimation from different stations is consistent if disregarding system biases. In addition, the estimated time offset can be used to improve the SPP accuracy.