# Relative Positioning in Remote Areas Using a GNSS Dual Frequency Smartphone
## 2 Materials and Methods
### Processing Options
The following processing settings were used to obtain the smartphone static solutions: dual frequency (E1/L1, E5a/L5); elevation mask 15 deg; broadcast ephemerides; [PERSON] [22] and Saastamoinen [23] models for ionosphere and tropospheric corrections; Antenna parameters from the ANTEX file ngs14.txt [24]. The same settings were used to compute the Septentrio PolaRx5 solutions, where, however, the triple frequency (E1/L1, E5a/L5, E5b/L2) measurements were used. Six research tests were performed with the objective of acquiring GNSS data to evaluate the positioning performance of a mobile device. To do this, different observation time  
Figure 2: CORS baselines lengths. intervals were carried out at different hours on different days using four reference stations with different baseline lengths to support the analysis of results. This variety of approaches performed aimed to support more reliability in the results, thus, tests were performed to analyze the comparison between smartphones and geodetic receivers. In each survey, smartphones were positioned using a platform mounted on a level base with forced centering (Figure 3), positioned with its GNSS antenna, located in the upper left corner, above the reference points (top of the pillars), to minimize horizontal errors due to displacements. The smartphone's duty cycle was turned off before starting data acquisition. Test 1 was done using two identical Mi8 smartphones, designated as smartphone A and smartphone B. The reason for using two devices of the same model was because the two smartphones had been acquired on different occasions and we wanted to assess a possible influence of the hardware and firmware versions on the measurements. Each survey had a duration of 10 min, with the two smartphones 28.5 cm above the pillar, Figure 3a. In order to assess possible disturbances on the GNSS signals, Wi-Fi, Bluetooth, and GSM were turned on and off (flight mode) during the signals' acquisitions. To perform these analyses, five points on pillars 2, 3, 5, 9, and 11 (see Figure 1) were surveyed in two rounds, simultaneously, with the two devices. In the first round the smartphone A was with flight mode ON and smartphone B with flight mode OFF, in the second round the roles were reversed. The survey started at 10:00 pm on 12 February and had a total duration of about two hours and a half, with a rapid-static survey, 10 min at each point. This test had a small time of survey to have the characteristics of a usual rapid-static survey. In Test 2, only smartphone A was used, placed vertically with an antenna offset by 42 cm in relation to the top of pillar 9 (Figure 3b). The survey lasted 2 h, starting at 3:27 pm on 25 February, with the aim of verifying the device's performance during a longer period of observation. To assess the quality of the signals acquired from the smartphone, measurements from a Trimble Alloy receiver (reference station), with a permanent Zephyr Geodetic II antenna, mounted on a nearby pillar, were used as a reference. The distance between the pillars is about 15 m.  
Figure 3: Test 1 with smartphones A and B (**a**); Tests 2 (**b**), 4 (**d**), 5 (**e**) and 6 (**f**) with smartphone A; Test 3 with smartphone A and PolaNt-MF antenna (**c**). Test 3 was carried out on 13 March, between 9:30 pm and 11:30 pm, surveying points on pillars 5, 9, and 11 for 30 min each with just one smartphone. The device was placed vertically with a displacement height of 30 cm to the pillar reference points. A Sepentrio PolaNt-MF antenna with a PolaRx5 receiver was also mounted in the same platform in eccentric mode, 18 cm North of the reference point and with a 20 cm offset height to the antenna reference point (ARP), Figure 3c. The PolaRx5 receiver was used to compare the positioning accuracy on the surveyed pillars between high-grade equipment and the smartphone. As the Alloy receiver is a permanent reference station, it cannot be used to survey other pillars. Tests 4, 5, and 6 were carried out with the aim of obtaining measurements during longer periods of observation.