SAH: Fine-grained RFID Localization with Antenna Calibration

Radio frequency identification (RFID) based localization has attracted increasing attentions due to competitive advantages of RFID tags: unique identification, low-cost, and battery-free. Although many advanced phase-based localization methods are proposed, few of them take fully the unknown phase center (PC) and the phase offset (PO) into account, which however are the key factors in fine-grained localization. In this paper, we propose a novel localization algorithm called Segment Aligned Hologram (SAH) that jointly calibrates the PC and the PO. SAH first builds a phase matrix and then designs a phase alignment algorithm based on the phase matrix for reducing the multi-path effect. Afterwards, SAH constructs a hologram for calibration and localization, which greatly reduces the system errors. We implement SAH through commercial RFID devices. Extensive experiments show that SAH can achieve a fine-grained localization accuracy in both the lateral and the radial directions with only a single antenna.