The Design a TDCP-Smoothed GNSS/Odometer Integration Scheme with Vehicular-Motion Constraint and Robust Regression  
[PERSON]  
1 Department of Geomatics, National Cheng Kung University, Tainan 701, Taiwan; [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Geomatics, National Cheng Kung University, Tainan 701, Taiwan; [EMAIL_ADDRESS]  
[PERSON]  
2 Interdisciplinary Division of Aeronautical and Aviation Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China; [EMAIL_ADDRESS]  
[PERSON]  
3 Department of Land Economics, National Chengchi University, Taipei 116, Taiwan; [EMAIL_ADDRESS]  
November 5, 2021 November 5,  
positioning, code measurement is preferred for position estimation because it does not contain integer ambiguities, and meter-level accuracy can be expected from the single-point positioning (SPP) technique in open-sky environments [1]. However, unsatisfactory navigation could occur because of its low precision and the multipath effect [2]. Further, range errors due to the multipath effect could be introduced up to half a code chip (150 m for GPS C/A code) because of the code tracking error [3]. On the other hand, the maximum tracking error for carrier-phase measurements due to multipath interference from a reflected signal of the same amplitude as the direct signal is a quarter of a wavelength (e.g., 4.76 cm for GPS L1) [4]. The carrier-smoothed-code method is generally used for dynamic navigation applications, which combines a series of delta-phase and pseudorange into a single noise-reduced measurement. Here, a pseudorange provides absolute position information and an incremental carrier-phase measurement provides displacement information [5,6]. The advantage of using this method is the high spatial variation in multipath errors by averaging out most of the code multipath errors without significantly increasing the cost and computation load [4]. However, it is difficult to maintain pre-supposition of this phase-smoothing method in the range domain for continuous tracking of the same satellites in urban areas. Every time a signal outage occurs, all of the smoothed pseudo-range information is lost, and the accuracy of the combined measurements reverts to the nominal unsmoothed level [4,7]. On the other hand, the position-domain phase-smoothing method utilizes time-differenced carrier phase (TDCP) measurements as a constraint of the current position relative to the previous position. Theoretically, this epoch-to-epoch position change can be determined to the level of TDCP accuracy through the observables directly related to the position increment [7]. In addition to the enhancement of redundancy, the advantage of such information in the position domain over the range domain is that carrier-phase measurements from the same satellites are required, only since the immediately previous time epoch and not several previous epochs [5,7], which increases the availability of phase-smoothing. Nonetheless, a problem with the phase-smoothing methods including both domains is the frequent occurrence of cycle slip. Limited to the accuracy of cycle slip detection, especially for single-frequency GNSS receivers, the ambiguities emerging due to undetected loss of signals will be introduced into the incremental carrier-phase information and further influence the performance of estimation. Notably, phase-smoothing does not mitigate the effects of non-line-of-sight (NLOS) reception, in which the signal is received only via reflections. The range measurement error, caused by the NLOS reception, is equal to the additional path delay, which is the difference between the length of the path taken by the reflected signal, and the blocked-direct path, between the satellite and the receiver antenna [4,8]. In this situation, because the code and the carrier are affected in the same manner, the phase-smoothing techniques, including TDCP, cannot improve the position estimation. In these GNSS-degraded environments, the combination of multipath/NLOS contamination significantly challenges the reliability of GNSS positioning.