“…Location-based services rely on location sensing systems that use various technologies either individually or in combination. These technologies include, GNSS, mobile networks [ 36 ], WiFi [ 1 , 37 ], inertial sensors [ 38 , 39 , 40 ], infrared (IR) light [ 41 ], visible light communication (VLC) [ 42 , 43 ], ultrasound [ 44 , 45 ], audible sound [ 46 ], radio frequency identification (RFID) [ 47 ], bluetooth (BT) [ 48 ], ultra wideband (UWB) [ 16 , 49 ], Zigbee [ 50 ], vision (image/video) based techniques [ 51 , 52 , 53 , 54 ] and frequency modulation (FM) [ 55 ]. Frequently, several technologies are combined.…”