Zero-Energy Devices for 6G: First Real-Time Indoor Localization Thanks to Ambient Backscattering of Commercial 4G UEs

Traditional approaches for indoor localization of smartphones, such as Wi-Fi signal strength, and Bluetooth low energy (BLE) localization techniques, face limitations like energy consumption and costly infrastructure deployment. This paper presents a novel indoor localization system, based on zero-energy devices (ZED) which are energy-autonomous (powered by light), and based on ambient backscatter communication (AmBC) technique which re-uses ambient mobile networks infrastructures and waves. Uplink pilot signals broadcasted by user equipment (UEs) are backscattered by ZEDs close by, and base stations (BS) detect the ZED message in the received UL pilot signal. We implement two scenarios of our localization system. In the first scenario, ZEDs are fixed with known locations in rooms and the location of the UE (a smartphone) carried by a moving user is tracked. In the second variant, the UEs (4G modems) are fixed and in known locations, and the location of the flexible ZED worn by a moving user is tracked. We demonstrate the two scenarios, in real-time, in a real indoor environment, with 4^th Generation (4G) commercial UEs (4G smartphone and 4G modem) and a 4G software defined radio base station. We achieve room-based detection accuracy.