# Study of Global Navigation Satellite System Receivers' Accuracy for Unmanned Vehicles
## 3 Results  
The position-accuracy navigation receivers from different producers were studied using two types of antennas. The first type was a commercial L1/L5 active patch antenna (Figure 11) with the following characteristics:  
* Ceramic size: upper patch--20 \(\times\) 20 mm, bottom patch--35 \(\times\) 35 mm.
* Frequencies: GPS (L1/L5), Galileo (E1), GLONASS (L1), Beidou (B1).
* Gain: L1: 5 \(\pm\) 1 dBi, L5: 3 \(\pm\) 1 dBi.
* Bandwidth: min 10 MHz.
* Voltage Standing Wave Ratio (VSWR): \(\leq\)2.0.
* Low-noise amplifier (LNA): Gain (L1: 32 \(\pm\) 3 dB, L5: 28 \(\pm\) 3 dB); Noise Figure NF \(<\) 1.0 dB; VSWR \(<\) 2.0.  
The second antenna type was a passive helix wideband antenna, described in Section 2.2. Both antennas were tested simultaneously in outdoor situations. The helix antenna was directed at 45\({}^{\circ}\) in azimuth.  
The experiments were accomplished using a GNSS software application U-center 2, ver. 24.07.111267 from U-blox AG company (Thalwil, Switzerland). The dilution-of-precision (DOP) parameter was used for measuring the precision of the GNSS receiver position. The horizontal dilution of precision (HDOP) and Position (3D) dilution of precision (PDOP) were calculated for each receiver with ceramic and helix antennas. This parameter was chosen to achieve an improved navigation performance in urban areas. A new GNSS update strategy is proposed in a loosely coupled GNSS/IMU fusion scheme based on the average of the predicted pseudo-range errors and the value of Position Dilution of Precision (PDOP) [33].  
For the calculation of the DOP parameters, the almanac data may be used and thus determined before the actual measurement. This parameter is a function of visible satellites and time. The smaller its value, the better the placement of the visible satellites. It is considered to have good geometry if the PDOP has a value of less than three and HDOP has a value of less than two. The best results are obtained when the HDOP value varies from 0.5 to 1.0. With this parameter, a preliminary choice can be made about which satellites will be used when solving the navigation task. It should be noted that this is the parameter that transforms measurement errors into positioning errors.  
Here, random errors have been separated from those due to other influences. The total error from the various influences is a sum of the errors of the individual influences, while the random errors (assuming they are all root mean square) combine as the square root of the sum of their squares. To determine the total error, it is suggested in the literature to add the triple total random error to the total influence error. With this tripling, the root mean square error becomes absolute with a confidence probability of 99.7% (corresponds to 3\(\sigma\)).  
The experimental study of a high-accuracy GNSS module covers the determination of positioning accuracy in outdoor situations using abovementioned U-center 2 software on the following modules:  
* NEO-F10T (from U-blox AG company)--L1/L5 bands GNSS receiver.
* ME32 GR01 (from Minew Semi Co., Ltd.)--L1/L5 bands GNSS receiver.
* ATGM332D (from Zhongkewei Group)--L1 band GNSS receiver.  
Figure 11: Ceramic patch GNSS L1/L5 antenna.  
The results obtained from the experimental study of L1/L5 GNSS receivers were compared with the latest generation L1 band receivers, such as the U-blox MAX-M10S, MinewSemi MS32 SN1 and Zhongkewei Group ATGM336H modules. The measurement results for each GNSS receiver are shown in Figures 12-14, respectively.  
Figure 13: MinewSemi MS32 SN1 receiver (patch and helix antenna, respectively).  
The experimental study of GNSS receivers was also extended with a comparison of the receivers from one manufacturer but from a different generation. To achieve this goal, the results obtained from the MAX M10S receiver were compared with the performance of the MAX M8Q receiver, which is shown in Figure 15.  
Figure 14: ATGM336H receiver (patch and helix antenna, respectively).  
Figure 15: U-blox MAX M8Q (patch and helix antenna, respectively).