## 1 Introduction  
### Background  
Bluetooth is a wireless communication technology under the standard of Wireless Personal Area Networks (WPAN), which is managed by the Bluetooth Special Interest Group (Bluetooth SIG) [1]. It aims at providing short-range communication and data exchange in 2.4 GHz channel as a replacement of the connection between devices with wires [2]. This technology has been commonly used in our daily life, such as in hands-free headsets, wireless mouse and keyboards, and data transfers between smart mobile devices, as well as the wireless control applications in smart homes. Bluetooth Low Energy (BLE, which started from Bluetooth version 4.0) is a low-cost, low-power protocol that is an extension of the general Bluetooth standard used for wireless communication. It allows short-range wireless communication and significantly reduces power consumption when compared to regular Bluetooth transmission [3]. The latest development of Bluetooth version 5 allows communication within a few hundred meters distance, increases transmission speed, enhances direction-finding and it is optimized for Internet of Things (IoT) applications [4; 5]. iBeacon is a framework proposed by Apple [6] based on BLE. The iBeacon device operates in the 2.4 GHz unlicensed band, which is the same as the Bluetooth standard channel, and emits Bluetooth signals in advertising mode with general information using major and minor identifiers, media access control (MAC) address and universally unique identifier (UUID) [6]. These identifiers allow a BLE-enabled device to identify which specific area is the user, and they are useful in the development of mobile applications which interact with users. For example, when a user gets close to an item on exhibit in a museum, an app will pop up with information about the exhibition based on the distance and identification information broadcasted from iBeacon installed near the exhibit. iBeacon devices using BLE can now operate for a period of several months to a couple of years on a single coin battery, which support sustainable practices in broadcasting signals. Bluetooth-equipped mobile devices are able to detect their proximity to an iBeacon transmitter based on the Bluetooth signals. Although iBeacon was originally specified by Apple, the BLE proximity features are compatible with Android and other BLE-equipped devices. With the development of smart devices, location-based services can be used in many areas, for example, positioning and navigation, range monitoring and trackers, entertainment, business advertisement and information dissemination. Nowadays, real-time positioning is available for most smart devices with an embedded Global Positioning System (GPS) receiver, and outdoor positioning is no longer a complicated task. However, there are some limitations in GPS positioning, as this method relies on satellite visibility and receiver-satellite geometry. Due to the inaccessible GPS signals in indoor environments, indoor positioning becomes difficult, and researchers have attempted to use radio networks to tackle this issue. To provide location-based services in indoor environments, Wi-Fi fingerprinting has been used for indoor positioning [7; 8] down to a few meters of accuracy, given a highly surveyed environment and Wi-Fi coverage. However, Wi-Fi is power-demanding compared to BLE. As well, Wi-Fi-based indoor positioning systems generally lack ideal density and geometry of access points for positioning purposes, as the Wi-Fi capabilities were not originally designed for this purpose. iBeacon, therefore, offers the potential of unrestricted indoor positioning, as it is available in almost every possible location via the placement of iBeacons [9]. The original goal of BLE iBeacons was to provide proximity-based application services, such as targeted advertising and checkpoint services. By detecting the range to an iBeacon from the mobile devices, location-based notification and information can be disseminated to the user devices.