A Novel Cycle Slips Detection and Repair Method with AR Model of BDS-3 Dual-Frequency Signal in Severe Multipath Environments  
[PERSON]  
1 College of Surveying and Geo-Informatics, Shandong Jianzhu University, Jinan 250101, China 1 [PERSON]
when the BDS high-precision positioning is performed, the cycle slips in the original observation value must be detected and repaired. For the dual-frequency cycle slips detection method, the high-order difference method between epochs [10], the Doppler integration method [11], and the TurboEdit method, they utilize Melbourne-Wubbena (MW) [12] and geometry-free (GF) combinations [11; 12; 13; 14; 15]. The TurboEdit algorithm improves the reliability of the detection of cycle slips by combining the MW and GF method, becoming the most commonly used method for dual-frequency cycle slips processing [16]. However, dual-frequency signals have longer wavelengths, but are also subject to more multipath effects [17]. Especially for the MW combination, false detection occurs frequently in a severe multipath environment and it is difficult to detect 1-2 cycle slips, and sometimes the MW combination even fails. In order to reduce the influence of pseudorange errors and improve the cycle slips detection capability in a severe multipath environment, many scholars have put forward different ideas. The first category is to improve the TurboEdit algorithm, for instance, [PERSON] (2011) improved the TurboEdit method [18] by introducing a satellite altitude angle weighting factor into the MW combination, but this method does not change the issue that the MW combination noise is too large to detect the small cycle slips of the GNSS measurements. [PERSON] (2020) proposed an improved TurboEdit cycle slip detection and repair method, which uses the ultra-wide lane combination with a difference between epochs to estimate the changes in the smartphone position and clock skew and identifies the cycle slip by checking the maximum normalized residual [19], but it is not satisfactory in complex environments. [PERSON] (2021) used the method of dividing the cycle slips' arc segment based on the multipath RMS size to repair the multipath value hopping to 0m, and then used the TurboEdit method for a joint detection, which improved the cycle slips' detection efficiency and further improved the dual-frequency positioning accuracy [20]. The second category is to weaken the pseudorange errors, e.g., [PERSON] (2013) combined the forward and backward moving window (FBMWA) algorithm with the second-order time-difference phase ionospheric residual (STPIR) algorithm to reduce the influence of large pseudorange errors to improve the cycle slips' detection accuracy [21], but its moving window cannot contain the cycle slips data, which is difficult to satisfy in real life. [PERSON] (2021) proposed a BDS dual-frequency signal cycle slips detection and repair method (BDCSR) to construct a discriminant function to repair cycle slips, which overcomes the interference of large pseudorange errors, and not only eliminates the influence of pseudorange errors, but also has a good recognition misjudgment capability [12]. [PERSON] (2021) adopts the phase-Doppler combination and the geometry-free combination to detect cycle slips and uses the simple rounding method with the dual-frequency least-square ambiguity decorrelation adjustment (LAMBDA) method to repair the cycle slips. This method reduces the influence of the multipath effect, but it requires a high sampling rate and a stable ionospheric environment to be effective [22]. [PERSON] (2019) proposed a novel method relying on the satellite orbit and smoothed pseudorange. This method solves the error of the cycle slips' detection results caused by the gross error on the pseudorange, but is only suitable for a single GNSS system due to the limitation of computation [23]. [PERSON] (2018) used BDS tri-frequency data and considered the multipath effect when setting the threshold in a fixed single epoch ambiguity.