# Study of Global Navigation Satellite System Receivers' Accuracy for Unmanned Vehicles
## 4 Discussion  
The experimental results show that both antennas may receive GNSS signals in the L1 and L5 frequency bands. Due to the narrow radiation pattern, the reception of the rising and setting satellites is labored and their signal levels are lower compared with the ceramic patch antenna. However, the higher gain of the helix antenna may increase the satellite signal Carrier-to-Noise (C/No) levels over 50 dB/Hz. Figure 16 represents the results of the tracked satellites of the MinewSemi ME32 GR01 receiver. The number of visible satellites using patch and helix antennas are approximately equal (18 vs. 19 satellites for patch and helix antennas, respectively), and the best obtained values for PDOP and HDOP parameters are 1.0 and 0.6, respectively, as multiple GNSS systems are used for localization (GPS, GLONASS and Galileo). It also shows the satellite signal levels for the L1 and L5 bands, which allow the position errors to be reduced to 0.5 m. The study results may be summarized as follows:  
* NEO-F10T (from U-blox AG company)--determination of PDOP and HDOP coefficients. Best results obtained: PDOP = 1.0; HDOP = 0.7. * ME32 GR01 (from MinewSemi Co., Ltd.)--determination of PDOP and HDOP coefficients. Best results obtained: PDOP = 1.0; HDOP = 0.6. * ATGM332D (from Zhongkewei Group)--determination of PDOP and HDOP coefficients. Best results obtained: PDOP = 1.6; HDOP = 1.4. Similar results were obtained for the latest generation GNSS receiver, U-blox NEO F10T (Figure 17). The number of tracked satellites increased to 24 \(\div\) 28, but the PDOP and HDOP parameters were not improved compared to the ME32 GR01 (MinewSemi, Shenzhen, China) receiver, because L5 satellites are not an appropriate choice for the constellation (the only visible L5 satellite, E25, is not tracked). The reception of L5 signals enhanced the GPS system's penetration due to its higher power and unique wavelength properties, which offer slightly better penetration capabilities through obstacles like foliage and building materials. Figure 16: _Cont._Figure 16: MinewSemi ME32 GR01 receiver (patch and helix antenna, respectively). Figure 17: _Cont._  
The experimental study of the position accuracy of the latest generation L1 receivers, such as the U-blox MAX-M10S, MinewSemi MS32 SN1 and ATGM336H (Zhongkewei Group, Shenzhen, China) modules, which are shown in Figures 12-14, respectively, shows the improved position accuracy when the number of constellations used is increased from one (MinewSemi MS32 SN1) to four (U-blox MAX-M10S), because the number of tracking satellites could not exceed ten. The best obtained HDOP and PDOP values are [0.9, 1.0] and [1.3, 1.4], respectively. The next study was a comparison of DOP parameters for GNSS receivers from one manufacturer but from a different production generation. The study covers the PDOP and HDOP measurements of 8 th- and 10 th-generation MAX-series GNSS receivers from U-blox AG company. The results are presented in Figures 12 and 15, respectively. The significant improvement of DOP parameters of the 10 th-generation GNSS receiver (HDOP decreases from 1.10 to 0.68) is explained by the increased number of tracked satellites and the choice of a better satellite constellation. The experimental study of L1/L5 GNSS receivers shows that the tracking of more than 16-20 satellites leads to excellent position accuracy in the sub-meter range. The receiver deviation maps show accuracy down to 0.5 m when HDOP values are down to 0.6 \(\div\) 0.7. The comparison of the obtained data shows some conclusions:  
* The number of processing satellites is approximately equal for GNSS modules with active patch and passive helix antenna. The wider radiation pattern of the patch antenna is compensated for by the higher gain of the helix antenna. In the multi-constellation cases, where the number of tracked satellites exceeded 16, it is well observed that lots of satellites are not used in navigation or are not tracked.