# Relative Positioning in Remote Areas Using a GNSS Dual Frequency Smartphone
## 5 Conclusions  
The differential results of the Galileo + GPS, Galileo-only and GPS-only combination show that it is possible to obtain good accuracy in the differential positioning mode with long baselines, using dual frequency smartphones (E1/L1, E5a/L5) that allow code and phase measurements. This work presents consistent results in the six tests, with an accumulated observation time of 16 h, based on the comparison with the reference coordinates of the pillars. A good performance was also observed in the evaluation with the results of the geodetic receiver. In general, errors are less than 25 cm in most cases for the long baselines, 277 km (CASC) and 645 km (CEUT), and as expected, the best results were obtained with the shorter baselines, with the GAIA (0.2 km) station showing results better than 15 cm. The accuracies obtained in the long-term surveys show the best results, with RMS values, in most cases below 5 cm, with the furthest station, CEUT, presenting values that in the worst cases reached 20 cm. In the case of the comparison between the two smartphone devices, we verified that the behavior is not strictly the same, showing some differences in the tracked satellites and in the signal strength, but the impact on the obtained solutions was similar. The analysis of the impact of the flight mode on (without Wi-Fi and GSM network) or off, on the performance of the GNSS signal, allowed us to conclude that the differences in signals and results are not significant. About the comparison of the signal strength between the Smartphone with the two geodetic receivers, the Trimble Alloy and the Sepentriro PolaRx5, we can see that the smartphone does not reach as high values in the two frequencies of the Galileo and GPS systems as the geodetic receivers, which is not a surprise, due to the lower quality of the smartphone antenna compared to the high performance of the geodetic antennas. However, a good standard of signal strength was obtained, with averages between 30-40 dBHz for E1, L1, E5a, and L5 signals, noting that the E1/L1 smartphone signals reached higher values than the E5a/L5 signals. It should be noted that at the moment we are still somewhat conditioned by the restricted number of satellites with the E5a and L5 signals on dual frequency smartphones, due to the Galileo constellation not being complete and the GPS not being fully modernized either. This forced us to make a plan to choose the best periods of the constellations, especially the Galileo constellation, with the objective of having the largest number of satellites in this constellation, because any satellite broadcasts E1/E5a allowing for always dual frequency terms, while in the case of GPS satellites, a satellite does not necessarily have L1/L5. It is hoped that soon, with the completion of the Galileo constellation and the ongoing modernization of the GPS, it will be easier to carry out any survey having a good number of dual frequency satellites. The performances we found in this work using a smartphone for differential georeferencing with long baseline remote reference stations, show us a low-cost GNSS equipment with the potential to be a quality tool in georeferencing in response to existing location needs, particularly in remote places of Africa, South America, and Antarctica, where access to dense CORS networks and also limited budgets make it difficult to purchase some expensive high-grade GNSS equipment. It has been shown in several works that different smartphones can provide different quality measures. However, this was not the focus of our work, the aim was to prove the concept that a smartphone can be used to obtain vertical and horizontal accuracies better than 30 cm, even when using reference stations with long baselines. Conceptualization, A.M., J.A.G. and L.B. ; methodology, A.M., J.A.G., L.B. and D.M. ; software, A.M.; validation, J.A.G., L.B. and D.M. ; formal analysis, A.M., J.A.G., L.B. and D.M. ; investigation, A.M., J.A.G., L.B. and D.M.