SYSTEM FOR AND METHOD OF ESTIMATING BEARINGS OF RADIO FREQUENCY IDENTIFICATION (RFID) TAGS THAT RETURN RFID RECEIVE SIGNALS WHOSE POWER IS BELOW A PREDETERMINED THRESHOLD

摘要

An RFID tag reading system and method estimate bearings of RFID tags. When the RSSI of a primary and/or secondary RFID receive signal is below a threshold, a primary receive beam is steered in a limited scan to an array of locations distributed around the location at which the RSSI of the primary receive signal is a maximum, and the RSSI of the primary receive signal is recorded at each location. The recorded RSSIs are processed to determine an effective weighted center of distribution of the recorded RSSIs, and the bearing for the tag based on the weighted center of distribution is thus estimated.

主权项

1. A radio frequency (RF) identification (RFID) tag reading system for estimating a bearing of an RFID tag associated with an item in a controlled area having sectors, comprising:
an RFID reader having a plurality of antenna elements, and a plurality of RF transceivers; and a controller operatively connected to the transceivers, and operative for controlling the transceivers by executing a tag processing module operative for steering a primary transmit beam in the controlled area by transmitting a primary transmit signal via the antenna elements to the tag, and for steering a primary receive beam in the controlled area at a primary steering angle by receiving a primary receive signal via the antenna elements from the tag, the controller being further operative for controlling the transceivers by executing a bearing processing module operative for steering a plurality of secondary receive beams in the controlled area at respective secondary steering angles that are offset from the primary steering angle by receiving a plurality of secondary receive signals via the antenna elements from the tag, the controller being further operative for steering the primary receive beam to a plurality of locations of a sector in the controlled area in a coarse scan to find the tag, for steering the secondary receive beams to the found tag, for comparing a receive signal strength indicator (RSSI) of at least one of the secondary receive signals against a threshold, and, when the RSSI is below the threshold, for determining the location at which the RSSI of the primary receive signal is a maximum, and for steering the primary receive beam in a limited scan to an array of locations distributed around the location at which the RSSI is a maximum, and for recording the RSSI of the primary receive signal at each location of the limited scan, and the controller being further operative for processing the recorded RSSIs at each location of the limited scan to determine an effective weighted center of distribution of the recorded RSSIs, and for estimating the bearing for the tag based on the weighted center of distribution.