## 3 Experiment  
In the experiment, the reference system uses a high tactical-grade INS (NovAtel SPAN(r) LCI, Canada) with a multi-band reception antenna (NovAtel GPS-GGG-703-HV), and the evaluated system is an automotive-grade Allystar EVK-2024 module with a single-band active patch antenna (Alllystar AGR 6301, China); these sensors are mounted on the same vehicle platform (Figure 4). Table 1 lists the specifications of the reference system. Table 2 shows the performance of the OBD II odometer applied in this study, which is evaluated from the other individual tests in an urban area. To evaluate the performance with the proposed methods, an experimental route (red trajectory) is designed under a GNSS-challenging environment (Tainan city), as shown in Figure 5. The referenced position solution from tactical-grade INS is based on post-smoothing processing with full constellations and frequencies receiving, whereas the evaluated EVK-2024 module uses two satellite constellations (GPS, Beidou) with single-frequency (L1 band) reception in the SPP mode. All of the results are synchronized with GPS time, and the relationship between the reference system and the EVK-2024 antenna (as shown in Figure 4) are measured by the surveying tapes. The performance analysis can be implemented after the referenced results are projected to the evaluated antenna. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Accelerometer** & **Gyroscope** \\ \hline Bias instability & \(\leq\) 0.1 mg & 0.05 \({}^{\circ}\)/hr \\ Random walk noise & 0.0588 m/s/\(\sqrt{\mathrm{Hz}}\) & \(\leq\) 0.012 \({}^{\circ}\)/\(\sqrt{\mathrm{hr}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of NovAtel SPAN® LCI. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Unit: m/s** & **Overall 1** & **Straight 2** & **Turning 3** \\ \hline
**Mean** & 0.053 & 0.068 & 0.116 \\
**Max** & 1.282 & 0.929 & 1.043 \\
**STD** & 0.141 & 0.132 & 0.205 \\
**RMSE** & 0.151 & 0.148 & 0.235 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Performance of OBD II Odometer. Figure 3: Process flow of the designed scheme with the proposed methods. Figure 4: **(a)** NovAtel SPAN(r) LCLI and GPS-GGG-703-HV antenna; **(b)** Allystar EVK-2040 and AGR 6301 antenna; **(c)** Experimental platform. The total experiment duration is approximately 40 min. The tested results are based on forward-filter estimation with the proposed EKF design and without any post-smoothing processing. The scenarios A-E are selected to discuss the contribution of the proposed methods, where are multipath/NLOS-contaminated environments, and their locations are represented by white blocks in Figure 5. The corresponding street-view images of these areas are shown in Figure 6a-f. Moreover, as shown in Figure 7a,b, respectively, the position dilution of precision (PDOP) increases, and the number of visible satellites significantly decreases after the vehicle approaches urbanized areas, although two constellations are used. The observability of healthy satellite signals is frequently unsatisfactory during the operation. For analysis, the implemented methods are classified into proposed odometer-aided constraints and robust regression, i.e., method A, and method B, respectively. The tested results include code-based measurements only (conventional GNSS), code/TDCP measurements (TDCP-aided GNSS), code/TDCP measurements with odometer-aided constraints (TDCP-aided GNSS with method A), code/TDCP measurements with robust regression (TDCP-aided GNSS with method B), and code/TDCP measurements with both methods (TDCP-aided GNSS with both methods). The evaluated solutions are colored in cyan, orange, blue, green, and black, in order for the following analysis for the trajectory and the line chart of errors. Moreover, to evaluate the performance of these solutions during a GNSS outage (area I of scenario E, Figure 6e), the solutions without method A will use assumptions, such as constant velocity from the last epoch to bridge the gap during GNSS positioning.