## 3 Methodology
### Device Selection  
Research in Android GNSS measurements have shown that the measurement's quality is not equal among all devices, even under identical measurement scenarios, as the manufacturers can embed different GNSS receivers in each new model [12]. Even access to specific GNSS observables (e.g., carrier phase, navigation message) cannot be ensured for each device. While the impact of these discrepancies can be minimal or unseen by the general user, it can prevent some of the research potential. Therefore, we performedthe surveys over multiple Android devices for better assessment of their capacities in this study.  
As the number of existing Android smartphones is enormous, the selection of the best devices can prove challenging. Thanks to the research community, a comprehensive list of Android devices with their GNSS capacities has been created through crowdsourcing and it is available online [32]. While it may contain multiple entries and some contradictory information, it still offers a first filter to select the devices with the required GNSS capacities. We note, however, that no smartwatch has been reported in this list so far.  
To maximize the potential of each evaluated device and the quality of the dataset, we have decided to select devices under four constraints: (1) support of dual-frequency reception; (2) available carrier-phase measurements; (3) available navigation message; (4) GNSS chipset diversity. Point (3) was the most constraining, as many devices do not retrieve the satellite's ephemeris from the navigation message anymore. Using the aforementioned list, we came down to only 22 devices checking all four requirements. More than half of them used a Broadcom BCM4775 or BCM4776 chip. The BCM4775 has been extensively reviewed in research before given that it was implemented in the Xiaomi Mi8 [10; 14; 17]; we have decided to focus on evaluating only the new generation BCM4776 instead. The rest of the receivers were chosen based on prices and in order to maximize GNSS chipset and manufacturer diversity. As one smartphone (Samsung A52) was already present in our lab for previous research purposes, we decided to also include it in these surveys for comparison purposes, even though it did not fit the requirements mentioned before. In total, four smartphones were selected and are summarized in Table 1. Note that while the Xiaomi 11T was said to have the navigation message enabled in the online list, we did not receive any during our experiments, and reported it accordingly in the table.  
As no previous studies have looked into GNSS measurements in smartwatches, we decided to review the recently released Google Pixel Watch (October 2022) [33]. The watch also embeds a BCM4776 GNSS chip, similar to the one in the Pixel 7, enabling the measurement comparisons between both platforms. For example, while the BCM4776 is supposed to be dual-frequency-enabled, only L1 frequencies were received during the survey. The most logical hypothesis is that the dual-frequency reception was disabled in order to save energy, as it was proven to have a large impact on the energy budget of Android devices [34]. This shows that even when the GNSS chipset model is similar in two devices, large differences in the measurements can still be present.  
In the following sections, devices will be referred to by the acronym listed in Table 1 for simplicity.