# Localization of a BLE Device Based on Single-Device RSSI and DOA Measurements
## 2 Related Works  
BLE devices are intended for applications that require low data rates and low power. A BLE device broadcasts its presence over advertising channels before establishing a connection to another compatible BLE device (described in more detail in Section 4). This ability to broadcast continuous has made them ideal for use as beacons in proximity sensing applications. These applications include providing users with information on a point of interest when they are in the region, indoor positioning, and item or asset tracking. Existing implementations of Bluetooth-based tags by manufacturers like Tile(C) [4] and Chipolo(C) [5] use the merits of BLE beacons to locate the position of items with the help of a smartphone application. A beeper on these tags allows users track lost or misplaced items to which they are attached. Although these devices have been successful in the consumer market, they rely on the user to track and locate the beep generated by the tag. Monitoring the Bluetooth signal as opposed to following the beep can be a good alternative for finding a lost item, and achieving this has been a challenge in the field of signal localization. Substantial research has been carried out on Bluetooth signal localization for indoor positioning and asset tracking with the idea of primarily estimating the proximity between two BLE devices or between two smartphones by monitoring their RSSI [6; 7; 8]. The three widely used techniques for indoor positioning are trilateration, fingerprinting, and centroid methods. Effective trilateration and filtering techniques for Bluetooth localization using multiple beacons are discussed in [9; 10]. Studies on using the trilateration method in indoor positioning and its accuracy can be seen in [11; 12]. The authors of [13; 8; 14; 15; 16] proposed the use of various fingerprinting techniques for localization of BLE beacons with [8] focusing on detecting the proximity between smartphones and BLE beacons. In the papers [17; 18; 19],estimation of the location of a beacon by monitoring RSS with the help of an antenna array for deriving the DOA and direction of departure (DOD) is discussed. In [18, 19], research is focused on using the antenna array method for localization of BLE signal in warehouse asset management. These techniques require multiple BLE beacons for a single measurement or require an antenna array for estimating the DOA of the BLE signal. These requirements result in limitations to some applications, such as finding lost items in a home environment where it can be impractical to have additional hardware pre-installed in the BLE device. In our research, we present a novel method of finding a BLE beacon using a single scanner device, which can be a smartphone or a tablet/iPad commonly available in home environments. In recent years, ultra-wideband (UWB) technology has been used in indoor positioning and localization applications. Apple and Samsung have advanced this technology into their flagship smartphones [20, 21] and created new devices (Apple air tag and Galaxy smart tag) that can assist in finding lost items. UWB is a short-range wireless communication technology similar to Bluetooth or WiFi but operating at a higher frequency. Because of its operation at a higher frequency band, UWB avoids the congested 2.4 GHz band where other communication technologies like Bluetooth, WiFi, and NFC exist. The larger bandwidth of UWB and shorter pulses of about once every 2 nanoseconds allow for real-time positioning of devices at a higher accuracy. Utilizing this technology requires a UWB-enabled transmitter and scanner devices. At the time of writing this paper, only a few scanner devices (smartphones) support UWB, including Apple iPhone (iPhone 11 Pro/Pro Max, and all models from 12 to 15i) and Samsung Galaxy (Note 20 Ultra, S21 Plus/Ultra, and all models from S22 to S23).