Determining movement of a radio frequency identification tag using a phase difference/frequency model

摘要

Determining movement of a Radio Frequency Identification (RFID) tag first establishes a phase difference/frequency model comprising a set of phase-wrapped local rates-of-change and an intercept point. RFID tag readings are then made to measure phase differences between the interrogation signal and the tag response at different frequencies. A correlation is determined between the measured phase differences versus frequency and the phase-wrapped local phase rates-of-change of the phase difference/frequency model. If the correlation is better than or equal to a predetermined limit, the tag is stationary, or if the correlation is worse than the predetermined limit, the tag is moving.

主权项

1. A system for determining movement of a Radio Frequency Identification (RFID) tag, the system comprising:
a processor operable to establish a wrapped phase difference/frequency model comprising a set of local rates-of-change and an intercept point; and an RFID reader operable to periodically transmit at least one interrogation signal to an RFID tag using at least one respective frequency and receive at least one respective backscattered modulated response from the RFID tag at the at least one respective frequency, wherein the processor is further operable to: measure a phase difference between the at least one signal and the at least one respective response at the at least one respective frequency to determine a measured phase rates-of-change after the wrapped phase difference/frequency model is established, determine a correlation of (1) the measured phase rates-of-change at the at least one respective frequency after the wrapped phase difference/frequency model is established to (2) a derived phase rates-of-change at least said one respective frequency as determined from the wrapped phase difference/frequency model, said correlation is proportional to the covariance of said measured phase rates-of-change and said derived phase rates-of-change sampled over a group of neighboring frequencies, wherein if the correlation is greater than or equal to a predetermined limit, the processor sends an indication to a server that the tag is stationary, and if the correlation is less than the predetermined limit, the processor sends an indication to a server that the tag is moving.