# Relative Positioning in Remote Areas Using a GNSS Dual Frequency Smartphone
## 3 Satellite Visibility and Observed Signals
### Signal Quality
Figure 9: Test 3 SNR: E1 smartphone (**a**) and receiver (**b**); L1 smartphone (**c**) and receiver (**d**); E5a smartphone (**e**) and receiver (**f**); L5 smartphone (**g**) and receiver (**h**). The SNR analysis of Test 1, Figures 6 and 7, and Table 3 shows the results obtained for the two smartphones A and B, with flight mode on or off. In Test 2, the SNR analysis shown in Figure 8 and Table 4 was performed between the signals from smartphone A (flight mode activated) and the Trimble Alloy receiver with the Zephyr Geodetic II antenna mounted on a pillar 15 m away from the mobile device located in pillar 9. In Figure 9 and Table 5, we see the Test 3 analysis made between smartphone A and the signals provided by the multi-constellation geodetic receiver, Septentrio PolaRx5 combined with a PolaNt-MF antenna mounted on the same platform as the smartphone (see Figure 3c). Looking at the signal strength of the two smartphones during Test 1, we see some small discrepancies between the two devices at both frequencies, with the statistical average varying between 0.5 and 2 dBHz. As mentioned before, data acquisition was performed in different modes: flight mode ON or OFF. This does not significantly affect the signal's strength in the different frequencies. We see that the SNR values for GPS are a little higher than for Galileo, with maximum values in L1 exceeding 40 dBHz and the L5 above 37 dBHz, while the E1 and E5a are below these values. However, we note that Galileo E1 and E5a standard deviations are better in both devices. The averages of the two systems show differences in the order of 3 dBHz for the E5a/L5 bands and 2 dBHz for the E1/L1 band. By analyzing the signals acquired with the smartphone in Test 2, we found that the SNR on all signals is lower than that of the Alloy receiver. The averages of the E1/L1 bands on the smartphone are around 38 dBHz, while on the geodetic receiver they are 46 dBHz for the E1 signal and 44 dBHz for the L1 signal. In E5a/L5 signals the differences found are greater with the smartphone presenting values in the order of 34 dBHz, while the Alloy presents values above 46 dBHz. Normally, the difference between a smartphone and a geodetic receiver in terms of SNR is around 10 dBHz, according to several studies presented by some authors (see [PERSON] [10], [PERSON] et al. [25] and [PERSON] et al. [26]), the values of 8 and 12 dBHz in the E1/L1 and E5a/L5 bands, respectively, obtained by us are in agreement with a reference value. We also see that the smartphone's minimum values are below 20 dBHz, while the receiver values are above this value. At maximum, the smartphone does not exceed 50 dBHz, while the receiver has managed to reach values of 54 dBHz in the L5 band. In general, smartphone signals have more fluctuations, especially for low satellites. Just like in Test 2, in this experiment signals from the smartphone show lower SNR, with average values below 40 dBHz, while for the geodetic receiver, the values reach 47 dBHz. The differences are bigger in the E5a/L5 signals, 12-13 dBHz, while in the E1/L1 signals, the differences are around 5 dBHz. In this test, the minimums between the two devices are much closer than in the previous Test 2, with most values are below 20 dBHz, even for the geodetic receiver PolaRx5. The lower values with this geodetic receiver can be explained mainly by the lower performance of the PolaNt-MF used by the Septentrio receiver when compared with the Zephyr II antenna from the Alloy. This rover antenna does not have such high performance as in the case of the Trimble antenna, a piece of very suitable equipment to work as a reference station. We noticed that STD values from the smartphone are better than the PolaRx5. The SNR values obtained in tests 4, 5, and 6 were identical to those obtained in the other tests performed and, in order not to become too repetitive, we chose not to present them. The analysis of the signals in the different tests shows that for the smartphones the SNR values for E1 /L1 are higher than for E5a/L5 bands.