Transfer Beamforming via Beamforming for Transfer.

Although billions of battery-free backscatter devices (e.g., RFID tags) are intensively deployed nowadays, they are still unsatisfying in performance limitations (i.e., short reading range and high miss-reading rate) resulting from power harvesting inefficiency. However, applying classic beamforming technique to backscatter systems meets the deadlock start problem, i.e., without enough power, the backscatter cannot wake up to provide channel parameters; but, without channel parameters, the system cannot form beams to provide power. In this work, we propose a new beamforming paradigm called transfer beamforming (TBF), namely, beamforming strategies can be transferred from reference tags with known positions to power up unknown neighbor tags of interest. Transfer beamforming (is accomplished) via (launching) beamforming (to reference tags firstly) for (the purpose of) transfer. To do so, we adopt semi-active tags as reference tags, which can be easily powered up with a normal reader. Then beamforming is initiated and transferred to power up passive tags surrounded by reference tags. A prototype evaluation of TBF with 8 antennas presents a 99.9% inventory coverage rate in a crowded warehouse with 2,160 RFID tags. Our evaluation reveals that TBF improves the power transmission by 6.9 dB and boosts the inventory speed by 2 × compared with state-of-art methods.