A triple-frequency cycle slip detection and correction method based on modified HMW combinations applied on GPS and BDS

By taking advantage of the additional combined signals introduced by triple-frequency GNSS, we propose a cycle slip detection and correction method based on the traditional extra-wide-lane Hatch–Melbourne–Wübbena (HMW) combination and also modified HMW combinations. Instead of using the combined code signals directly in the traditional HMW combination, the modified HMW combination adopts the original code signals and one combined phase signal with corrected cycle slips to eliminate the ionospheric bias and reduce the effect of the noise induced by the code measurement. To determine the optimally combined signals and the corresponding coefficients in the modified HMW combination, four constrained conditions are proposed based on the maximum acceptable ionospheric bias and measurement noise of the combination in the process of cycle slip detection. Two optimally combined signals are selected; however, the second best signal cannot maintain a 100% success rate when epoch intervals are increased, due to the effect of the remaining ionospheric bias. To solve this problem, a scale factor is introduced to balance the corrected percentage of the ionospheric bias and the amplification of the measurement noise. These selected signals are further tested with real triple-frequency GPS and BDS observations. Results show that the proposed method can provide a 100% success rate in detecting cycle slips in the observations with large epoch intervals (up to 30 s) from medium earth orbit satellites with elevation angles above 5°, as well as inclined geosynchronous orbit and geostationary orbit satellites with elevation angles above 20°.