Bluetooth low-energy (BLE) beacon is a key enabler for smart interaction between the user device and the physical thing, in which the physical thing can actively engage users for interaction via its advertising packet. However, reliability is always an issue for the beacon-based interaction since the beacon employs an unreliable broadcasting approach which provides no way to check if the user device has received the correct packet. We define the sparse observation to describe the phenomenon where the number of packets received by the user device within an arbitrarily small time duration is less than the number of deployed beacons. This article studies the sparse observation causing by the following two factors: 1) the unpredictable environmental variations and 2) the uncontrollable operating conditions of a beacon. An analysis is provided to investigate the interaction reliability in connection with the above two factors. Motivated by the above challenges, a novel solution, which exploits the ambient RF fingerprinting to address the sparse-observation issues, is proposed to enhance the interaction reliability. Our proposed solution is validated with extensive experiments consisting of real data collected from both indoor and outdoor environments. Finally, the feasibility of our proposed solution is demonstrated with a proof-of-concept prototype implemented over multiple physical things.
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