“…To address this, several techniques including Wireless Fidelity (WiFi), Radio Frequency Identification(RFID), Bluetooth Low Energy (BLE) and ZigBee, where the localization is performed based on the received signal strength have been explored [ 18 , 19 , 20 , 21 , 22 ]. However, these techniques have drawbacks such as low accuracy, low data-rate and/or short range communication [ 18 , 19 , 20 , 21 , 22 ]. Furthermore, when using narrow-band device-free indoor communication, multipath fading and a cluttered environment make it difficult to design a low-cost and low-complexity receiver [ 23 , 24 , 25 ].…”