Phase-based ranging for backscatter RFID tags

摘要

A RF tag reader may use spatial averaging to compensate for the limitations of performing multi-frequency continuous-wave ranging (MFCW) in a bandwidth-limited environment. Although MFCW provides an estimate of the separation distance between a RF tag and the tag reader with errors that vary widely, the error values form a pattern based on the separation distance. That is, as the separation distance increases or decreases, the error values oscillate between maximum and minimum values centered on the correct separation distance. Accordingly, in one embodiment, the receiver uses spatial averaging to average out this oscillating error (e.g., the maximum errors are counter-balanced by the minimum errors). The more accurate, spatially-averaged MFCW estimate may then be used to resolve the cycle ambiguity in continuous-wave ranging to identify the separation distance between the RF tag and the tag reader.

主权项

1. A method of performing phase-based ranging techniques, comprising:
outputting at least a first signal for transmission to a radio frequency (RF) tag; obtaining at least a second signal from the RF tag; estimating a plurality of first distances between the RF tag and an RF tag reader using a continuous-wave (CW) ranging technique based, at least in part, on the first signal and the second signal; estimating a plurality of second distances between the RF tag and the RF tag reader using a multi-frequency continuous-wave (MFCW) ranging technique based, at least in part, on the first signal and the second signal; and performing spatial averaging based on the pluralities of first and second distances to mitigate the effects of an error associated with the plurality of second distances.