Abstract
Recently, some smartphone manufacturers have subsequently released dual-frequency GNSS smartphones. With dual-frequency observations, the positioning performance is expected to be significantly improved. Cycle-slip detection and correction play an important role in high-precision GNSS positioning, such as precise point positioning (PPP) and real-time kinematic (RTK) positioning. The TurboEdit method utilizes Melbourne–Wübbena (MW) and phase ionospheric residual (PIR) combinations to detect cycle-slips, and it is widely used in the data processing applications for geodetic GNSS receivers. The smartphone pseudorange observations are proved to be much noisier than those collected with geodetic GNSS receivers. Due to the poor pseudorange observation, the MW combination would be difficult to detect small cycle-slips. In addition, some specific cycle-slip combinations, where the ratio of cycle-slip values at different carrier frequencies is close to the frequency ratio, are also difficult to be detected by PIR combination. As a consequence, the traditional TurboEdit method may fail to detect specific small cycle-slip combinations. In this contribution, we develop a modified TurboEdit cycle-slip detection and correction method for dual-frequency smartphone GNSS observations. At first, MW and PIR combinations are adopted to detect cycle-slips by comparing these two combinations with moving-window average values. Then, the epoch-differenced wide-lane combinations are used to estimate the changes of smartphone position and clock bias, and the cycle-slip is identified by checking the largest normalized residual whether it exceeds a predefined threshold value. The process of estimation and cycle-slip identification is implemented in an iterative way until there is no over-limit residual or there is no redundant measurement. At last, the cycle-slip values at each frequency are estimated with the epoch-differenced wide-lane and ionosphere-free combinations, and the least-square ambiguity decorrelation adjustment (LAMBDA) method is adopted to further obtain an integer solution. The proposed method has been verified with 1 Hz dual-frequency smartphone GNSS data. The results show that the modified TurboEdit method can effectively detect and correct even for specific small cycle-slip combinations, e.g., (4, 3), which is difficult to be detected with the traditional TurboEdit method.
Highlights
In May 2016, Google released an application programming interface (API), which makes the developers access global navigation satellite system (GNSS) raw measurements, including pseudorange, phase, and doppler measurements, in Android 7.0 and up [1]
The epoch-differenced wide-lane combinations are used to estimate the changes of smartphone position and clock bias, and the cycle-slip is identified by checking the largest normalized residual whether it exceeds a predefined threshold value
The process of estimation and cycle-slip identification is implemented in an iterative way until there is no over-limit residual or there is no redundant measurement
Summary
In May 2016, Google released an application programming interface (API), which makes the developers access global navigation satellite system (GNSS) raw measurements, including pseudorange, phase, and doppler measurements, in Android 7.0 and up [1]. With a large noise level of smartphone single-frequency GNSS measurements, the positioning accuracy and reliability are unsatisfactory, especially under complex conditions [2,3]. In May 2018, the world’s first dual-frequency GNSS smartphone produced by Xiaomi was launched. It is equipped with a Broadcom BCM47755 chipset, which is a dual-frequency (L1/L5+E1/E5a) GNSS chipset [4,5,6]. Some smartphone manufacturers have recently released dual-frequency GNSS smartphones, e.g., P30/P30 Pro from Huawei, Galaxy Note 10/10+ from
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