# Low-Cost Dual-Frequency GNSS Receivers and Antennas for Surveying in Urban Areas
## 4 Conclusions  
Low-cost GNSS receivers with calibrated low-cost and geodetic antennas were compared to geodetic GNSS devices in urban areas where various obstacles can affect the quality of the received signals. Therefore, the C/N\({}_{0}\), multipath effect, and ambiguity fix ratio were analyzed under both conditions, open-sky and urban, highlighting the differences between the devices/antennas used. The positioning performance of low-cost devices was also tested in urban areas at different locations with and without buildings/obstacles nearby. The results from this study lead us to the following conclusions:  
* Low-cost GNSS devices have lower C/N\({}_{0}\) than high-quality geodetic GNSS devices in both open-sky and urban areas. In the first case, C/N\({}_{0}\) is below 25 dBHz at elevation  
Figure 11: Horizontal, vertical, and spatial positioning accuracy in the open-sky (ST 1) and urban areas (ST 2, ST 3, ST 4) for 24 sessions: (**a**) LC\(-\)1 at ST 1; (**b**) LC\(-\)1 at ST 2; (**c**) LC\(-\)1 at ST 3; and (**d**) LC\(-\)1 at ST 4.  
angles lower than 15\({}^{\circ}\), whereas the C/N\({}_{0}\) remains above 25 dBHz for low elevations in the case of geodetic devices. In urban areas, the C/N\({}_{0}\) is greater than 25 dBHz at elevation angles below 20\({}^{\circ}\) for geodetic instruments, whereas C/N\({}_{0}\) is always below 25 dBHz for low-cost GNSS equipment. The urban conditions affect low-cost GNSS devices more than geodetic devices;
* Low-cost GNSS instruments exhibit a multipath RMSE two times higher than geodetic devices in the open sky, while this difference is up to four times higher in urban areas. Geodetic GNSS devices show almost the same results under both conditions, where the multipath worsens significantly for low-cost devices and urban areas, even when a geodetic antenna is used;
* The ambiguity fix ratio is more than 95% for low-cost devices in the open sky in combination with a low-cost and geodetic antenna;
* In urban areas, the low-cost GNSS antenna performs worse than the geodetic antenna, and the ambiguity fix ratio is 18.4% lower for the low-cost GNSS antenna used;
* In the open sky, low-cost GNSS receivers with calibrated low-cost antennas achieve a horizontal and spatial positioning accuracy of 5 mm over short baselines even if short sessions (15 min) are considered;
* In urban areas with surrounding obstacles, horizontal accuracy is better than 10 mm in 85% of sessions, while spatial accuracy is better than 15 mm in 77.5% of sessions. For the vertical component, the accuracy is smaller than 15 mm in 82.5 % of sessions;
* Low-cost GNSS sensors are more sensitive to multipath and other error sources that degrade the quality of position determination in urban areas. Consequently, fix solutions were not obtained in some sessions. However, considering their price and the demonstrated positioning performance, those GNSS sensors can be an alternative option to geodetic GNSS devices for surveying in static relative mode (e.g., establishing geodetic networks) in urban areas, especially in projects with a limited budget;
* Low-cost GNSS instruments can achieve 1-3 cm positioning accuracy in RTK mode in urban areas and are suitable to be used in many surveying projects. In this study, all tests were performed over short baselines because the goal was to only evaluate the performance of double-frequency low-cost GNSS receivers in urban areas, as these devices are more sensitive to different error sources that can degrade the positioning quality. The results presented in this paper should be considered as preliminary. A more detailed analysis will be performed in the future when we will test these devices in RTK mode over longer baselines. Conceptualization, V.H. and B.S. ; methodology, V.H. ; software, V.H. ; formal analysis, V.H. ; investigation, V.H. ; data curation, V.H. ; writing--original draft preparation, V.H. ; writing--review and editing, V.H., P.-P., B.S. and O.S. ; visualization, V.H. ; supervision, P.-P., B.S. and O.S.