“…Request permissions from Permissions@acm.org. Infrastructure-free approaches have focused on leveraging already existing WiFi [5,15,49,40,41,45,6,22,47,50], FM and TV [8,9,34,28,29,27,12,33,19,48], GSM [31,44], geo-magnetic [10], and sound signals [43] to enable indoor localization through detailed fingerprinting. Infrastructure-based approaches rely on the deployment of customized RF-beacons [37], such as RFID [30], infrared [46], ultrasound [36,20], Bluetooth [7], short-range FM transmitters [26], lights [23], and magnetic signal modulators [32,2] to enable accurate indoor position estimation.…”