## 4 Field Test Results and Discussions
Likewise, in the SPP mode, the results of the fusion method show upward trends of about 73% and 83% for the Xiaomi Mi8 and Samsung S21 Ultra, respectively. It is worth mentioning that the RMS values in the SPP mode are 4.484 m and 8.83 m, respectively (Figure 7). The results emphasize that the employed method is capable of overcoming various urban conditions. Both smartphones demonstrate precise positioning with the RTK mode, indicating that they can achieve high accuracy when RTK positioning is available. The SPP mode has the highest errors in both devices. This is expected, as the SPP mode typically does not use differential corrections and is thus more susceptible to errors due to atmospheric conditions, satellite geometry, and other factors. The fusion method consistently reduces the error compared to the SPP mode for both devices by effectively utilizing additional data sources or algorithms to enhance the accuracy. Finally, Khorramshahr Street is the widest street, with some high-rise buildings and occasional traffic congestion. The RMS value in the fusion method, compared to the RTK mode, was reduced by 84%, declining from 2.826 m to 0.446 m for the Xiaomi Mi8 smartphone. Similar to the Xiaomi Mi8 smartphone, there was a 76% decrease in the RMS values for the Samsung S21 Ultra, reducing from 2.955 m to 0.695 m. The RMS values for the SPP mode were 7.221 m and 21.382 m for the Xiaomi Mi8 and Samsung S21 Ultra, respectively. These values are higher than those of the fusion method by 94% and 97% (Figure 8). Figure 6: Easting and Northing errors regarding the reference trajectory for the Samsung Ultra S21 (**a**,**c**), and Xiaomi Mi8 (**b**,**d**), on Naderi Street, respectively. The dotted line is the zero-error axis. Figure 9 represents the sky plots of the GNSS receiver for the Samsung Galaxy S21 Ultra smartphone and the Xiaomi Mi 8 smartphone, respectively. The colors indicate the quality of the signal received from each satellite, with warmer colors like red or yellow indicating a stronger signal and cooler colors like blue indicating a weaker signal. Based on these figures, one can assess the coverage and quality of the satellite signals being used for navigation. In complex urban environments, buildings and other structures can cause signal reflection and blockage, affecting both the number of visible satellites and the quality of the received signals, which, in turn, affects the accuracy of the position fix. The sky plot from the Xiaomi Mi 8 shows a good distribution of satellites; the actual navigation performance would depend on several factors, namely, satellite visibility, signal quality, and the GPS receiver's capabilities. Without additional data, it is difficult to make a definitive statement on the comparative performance of the Xiaomi Mi 8 and the Samsung S21 Ultra solely based on the sky plots. The consistency of the data patterns across both  
Figure 8: Easting and Northing errors regarding the reference trajectory for the Samsung Ultra S21 (**a**,**c**), and Xiaomi Mi8 (**b**,**d**), on Khorramshahr Street, respectively. The dotted line is the zero-error axis. Figure 7: Easting and Northing errors regarding the reference trajectory for the Samsung Ultra S21 (**a**,**c**), and Xiaomi Mi8 (**b**,**d**), on Peyghambariyeh street, respectively. The dotted line is the zero-error axis. devices indicates that environmental factors had a similar impact on both. The numerical data show that both smartphones can maintain a low level of error when using the RTK mode, typically within \(\pm\)5 m and often within \(\pm\)2 m. This suggests that both devices have high-quality GNSS antennae capable of leveraging RTK signals for precise positioning. The SPP errors are considerably larger, peaking at \(\pm\)60 m for the S21 Ultra and \(\pm\)20 m for the Mi 8. While this is partly due to the lack of RTK corrections, it also reflects the antennas' ability to deal with urban challenges like multipath errors and signal obstructions.