# Real-Time Kinematic Positioning Using Multi-Frequency Smartphone Measurements +
## 2 Methodology and Experimental Set-Up  
The tests presented in this paper were carried out using the Huawei P40 Mate smartphone. This smartphone was selected because can track three frequencies, specifically, GPS L1/L5, Galileo E1/E5a/E5b, Glonass L1, and Beidou B1/B2a. However, from preliminary tests, it has been observed that the number of Galileo E5b tracked signals is very limited and has very low signal power. Therefore, it was not possible to use the above frequency for positioning. A first analysis has been performed to characterise the antenna's impact on the quality of smartphone measurements. For this purpose, a survey-grade antenna (PG-F1 [5], Topcon, Livermore, CA, USA) and a patch antenna (ADFGP60A [6], Taoglas, Dublin, Ireland) have been connected to the smartphone, which was placed in a portable shielded box as shown in the scheme in Figure 1a. Inside the shielded box, a re-radiator was placed to broadcast the signal to the phone. The antennas were placed in the middle of a field under open-sky conditions. At the same time, a high-grade receiver was connected to the same antenna in order to act as a reference. Moreover, a test was performed using the smartphone without any external antenna. As shown in Figure 1b, the smartphone was placed on a tripod in the middle of a field under open-sky conditions. The back of the phone was pointing up, since, after some preliminary tests, it was observed that this position maximised the received signal power. The Google GNSS logger application was used to record files including GNSS measurements that were then processed to obtain a Receiver Independent Exchange Format (Rinex) file using UofC CSV2 RINEX; available at [[https://github.com/FarzanehZangeneh/csv2](https://github.com/FarzanehZangeneh/csv2) rinex]([https://github.com/FarzanehZangeneh/csv2](https://github.com/FarzanehZangeneh/csv2) rinex) (accessed on 3 March 2024). The RINEX files were sent as input to the Topcon RTK engine and the binary files were recorded by different base stations. Then, a post-processing kinematic solution was obtained for the different cases. A routine was prepared to test different combinations of settings in the RTK engine and select the best combination, that is, the one leading to the higher percentage of fix solutions, higher accuracy, and lower TTFF. The tests' set-up description, along with the results, are reported in the following sections. The tests were performed using three bases placed at different distances (CN09: 1 km, CGU2: 5 km, and GUAS: 25 km). The following key performance indicators were evaluated in the signal quality and positioning domains:  
1. TTFF: number of epochs needed to achieve the first fix position solution in RTK mode. 2. Percentage of fixed solutions. 3. Horizontal/vertical accuracy (computed with respect to the position surveyed exploiting the NET-G5 receiver used as a reference). In addition, two kinematic tests were performed using a car in a rural/semi-urban environment. As shown in Figure 2, some sections of the path were characterised by the presence of tall trees with rich foliage rendering the signal reception very challenging. Moreover, in other sections of the path, buildings and houses also made the environment difficult in terms of signal reception. For the automotive test, the Topcon survey-grade PG-F1 antenna was mounted on the roof of a car and connected to a survey-grade HyperVR receiver (Topcon, Livermore, CA, USA) [7] that was used as a reference. During the first test, the smartphone was placed inside the car, specifically, attached to the front car's glass with the back of the phone pointing outside. The setup is shown in Figure 3a. For a second test, the smartphone was mounted on the car's roof so as to have better visibility. Finally, a further kinematic test was conducted by fixing the smartphone on the windshield of a tractor, as shown in Figure 3b. Also, in this case, the above survey-grade antenna/receivers were used for reference purposes.