## 5 Tracking Performance Verification
### Vehicle-Based Testing and Verification  
The objective of the field vehicle test is to validate the simulation results obtained in the previous section and to evaluate the real-time navigation performance of the deeply-coupled hardware prototype under realistic conditions.  
The vehicle dynamic testing was carried out in the suburbs of Wuhan under the open sky on 21 June 2013, to further verify the tracking performance. The test consists of a vehicle equipped with the self-built deeply-coupled prototype, medium-grade INS (FSAS), _etc._, and the open sky drive test, as shown in Figure 17. A GPS intermediate frequency (IF)/IMU raw data recording and playback unit is developed based on the hardware prototype, which cannot only replay GPS IF/IMU data to debug the deeply-coupled hardware prototype, but also can replace the onboard MEMS IMU data by other  
Figure 17: Setup of vehicle testing.  
IMU data, such as FSAS, to achieve medium-grade INS-aided PLLs testing. The acceleration and deceleration of the road vehicle tests were less than 5 m/s\({}^{2}\). Using PRN 13 as an example, the tracking error was analyzed with a CNR of 48 dB-Hz and an elevation of 45 degree.  
Figure 18 shows the tracking errors of normal PLLs and INS-aided PLLs. Figure 18a depicts the tracking error of a normal second-order PLL with an integration time of 20 ms and a bandwidth of 10 Hz. The tracking error almost has no change when the vehicle movement changes, similar to the simulator testing results in Figure 15a. Although the road vehicle dynamics are small (less than 5 m/s\({}^{2}\)), the dynamic tracking error increases significantly when the bandwidth of the normal PLL is compressed to 3 Hz, as shown in Figure 18b, similar to the simulator testing results in Figure 15b. Therefore, if the bandwidth of the normal PLL is compressed to enhance the tracking sensitivity of the carrier phase, its dynamic response error would increase, which is consistent with the normal PLL's error model, shown in Equation (8).  
Figure 18c,d respectively depict the tracking error of the MEMS INS-aided PLL and the medium-grade INS-aided PLL with an integration time of 20 ms and a bandwidth of 3 Hz. The carrier phase tracking error does not increase with the vehicle dynamics, which is consistent with the  
Figure 18: GNSS carrier phase tracking error testing based on the real vehicle test. **(a)** Normal PLL (20 ms, 10 Hz); **(b)** normal PLL (20 ms, 3 Hz); **(c)** MEMS INS-aided PLL (20 ms, 3 Hz); **(d)** medium-grade INS-aided PLL (20 ms, 3 Hz).  
theoretical analysis and the simulator test results. Furthermore, the assisting effect of MEMS IMU to the PLL is almost as good as the medium-grade IMU aiding effect. Therefore, the vehicle test results further validate the performance of INS-aided PLL designed based on the proposed steady-state error model on the deeply-coupled hardware prototype.  
INS-aided PLLs can reduce the tracking error, and the navigation precision should be improved accordingly. This is verified by comparing the velocity errors of integrated navigation using the Doppler measurement from the PLLs without and with MEMS INS aiding. Table 4 shows the performance differences of the integrated navigation results without and with INS aiding. The velocity errors are clearly smaller when the PLL is aided by INS, as expected. Therefore, the INS-aided loops in deeply-coupled systems can improve the navigation performance.