Abstract
The detection and repair of cycle slips are key steps in high-accuracy GNSS (Global Navigation Satellite System) data processing using carrier phase observations. BDS (BeiDou Navigation Satellite System) triple-frequency observations provide better combinations for cycle slip detections and repairs compared to dual-frequency observations. Although a number of algorithms have been developed and may correctly detect cycle slips most of the time, the reliability of empirical thresholds methods cannot be guaranteed. In this study, an adaptive threshold is proposed for three sets of triple-frequency Geometry-Free (GF) pseudorange minus phase combinations to improve the cycle slip detection performance and reduce the false alarm rate of the cycle slip detection by combining the predicted epoch-differenced ionospheric delays under active ionospheric conditions. Moreover, in the cycle slip repair, the integral combined cycle slips are determined by directly rounding the estimated float-combined cycle slips, which will lead to a repair error if the between-epoch ionospheric variation is large. In this study, a new rounding method considering the predicted epoch-differenced ionospheric delays is proposed, and it is proven that the new method has a higher success rate for estimating the integer value of a cycle slip than the traditional method. The performance of the newly proposed method is validated by using static BDS triple-frequency observations that contain simulated cycle slips. BDS triple-frequency observations were collected at 30-s sampling intervals under active ionospheric conditions. The results show that this method can successfully detect and repair all slips of more than one cycle. In addition, dynamic BDS data collected with a vehicle-based receiver at a 1-s sampling intervals are processed, and the results show that the proposed method is also effective in the detection and repair of cycle slips in dynamic data.
Highlights
To meet the needs of high-precision applications, the highquality carrier phase measurements of GNSS must be utilized in data processing
Inevitable cycle slips caused by a low signal-to-noise ratio, a failure of the receiver software or a strong ionospheric scintillation will greatly reduce the accuracy of the positioning results if the cycle slips are not correctly detected and repaired
These methods consider high ionospheric activity, but studies on triplefrequency cycle slips under high noise levels are relatively few, especially regarding detection combinations that are based on pseudorange observations
Summary
To meet the needs of high-precision applications, the highquality carrier phase measurements of GNSS must be utilized in data processing. To repair triple-frequency cycle slips, Chang et al [22] proposed an adaptive Kalman filter based on variance component estimations to predict ionospheric delays These methods consider high ionospheric activity, but studies on triplefrequency cycle slips under high noise levels are relatively few, especially regarding detection combinations that are based on pseudorange observations. According to the above discussion, a real-time cycle slip detection and repair method has been proposed for BDS triple-frequency between-epoch differenced observations that have low sampling rates, large noise and are collected. An adaptive threshold determination method developed by considering an active ionospheric condition is proposed, and three linearly independent GF pseudorange minus phase combinations are used jointly to reduce the false rate and miss rate of the cycle slip detections.
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