360° carrier phase measurement for UHF RFID local positioning

Abstract

Carrier phase measurement in RFID and other wireless communication devices can be used in general for ranging, angle of arrival detection and localization. Modern ISO 18000-6C RFID readers perform fully coherent demodulation, detect the signal phase and deliver it to the user. However the presented phase is π-periodical and not 2π. This is caused by the symmetry of the received signal and the phase-recovery methodology used. In this paper we introduce a phase-recovery method retrieving a 2π-periodical phase. A larger ambiguity range for the phase measurement is beneficial for all phase-based localization methods: it allows, for example, increased array-element spacing in angle-of-arrival detection methods; and improves the resolution for imaging methods.