# BLE RSS Measurements Dataset for Research on Accurate Indoor Positioning
## 2 Setup and Collection Procedure  
The beacons used in this work are off-the-shelf Accent Systems' IBKS 105 [37] with a Nordic nRF51822 core [38]. Those beacons are capable of concurrent broadcasting iBeacon(tm) and Eddystone(tm) advertisements across several emission slots. The deployed beacons were configured to use only one iBeacon slot and an advertising period of 200 ms (5 Hz), which is a setup that provides a battery duration of 8 to 10 months. The collection was organized in campaigns, and performed by trained individuals (hereinafter, the subjects), that stood at predefined positions, holding their smartphones with the right hand in front of their chests in a way that resembled people following directions for an indoor environment. The radio signals in indoor environments are known to be affected by factors like multi-path, fast fading [39], and in the case of 2.4 GHz frequencies, strong human body absorption, which may account for up to \(\approx\)10 dBm [40], being even more notable for devices like smartwatches [41]. In addition, the BLE advertisements are broadcast on three narrow (2 MHz width) advertising channels in quick succession, which made the reported signal instability a higher challenge than in Wi-Fi positioning [11]. The BLE data collection was performed using Android smartphones, due to their abundance and availability. We adapted a previous Wi-Fi RSS collection application [24] to perform campaign-directed BLE RSS collections. Android provides two ways of notifying BLE advertisement detections: anytime an advertisement is received, or when a batch of advertisements is collected. According to our tests, the batch approach leads to fewer advertisement detections, and thus, we decided to use the former approach. Giving that the advertisement collection was not batch-driven, a fingerprint abstraction was created, so that all measurements received in a window of 1s were placed into a fingerprint. If a beacon was detected more than once in a fingerprint window time, only its mean RSS value, (and the first detection time in nanoseconds since device boot), was stored. The smartphones that the subjects used for RSS collection had the previously mentioned application, which helped the subjects (Figure 1) in following a collection campaign and avoiding errors like wrong position tagging. A collection campaign is an ordered list of positions. The subjects had to follow that order and collect a number of consecutive samples (fingerprints) at each point facing a specific direction. The collection orientations, i.e., the facing directions, were those corresponding to the usual walking directions. The RSS measurement collection was performed in two environments (zones) from the UJI, in Castellon, Spain: an area among bookshelves in the Library building (hereinafter, Library) and an area of the office space of the Geotec Research Group (hereinafter, Geotec). Table 1 presents data describing the collection, the beacon deployment and the environment of each zone. In Table 1, MDMS represents the maximum distance from the position of a collection point to another collection point that is the closest to it in the space. MDMB is described as MDMS, but considering beacon positions instead of collection points positions. The deployment in the Library (Figure 2a) had the goal of supporting a positioning service for users trying to find a book. The 22 beacons were placed inside the enclosed top of the (wooden) shelves for security concerns (Figure 2b). Therefore, there were no line-of-sight situations to beacons in this environment. The dense deployment was designed so that the area covered by the beacons included all shelves and the deployed beacons were as far apart from each other as possible. The shelves height is 2.35 m, which is almost as high as the altitude of the ceiling (about 2.60 m). The collection was divided into two campaigns, one with the subjects facing the up or down directions and another one with them facing the left or right directions (blue squares and orange circles in Figure 2b, respectively).