Methods and system for enhanced RFID direction finding

Patent metadata

Field	Value
Publication number	US-10976408-B2
Application number	US-201816235835-A
Country	US
Kind code	B2
Filing date	Dec 28, 2018
Priority date	Dec 28, 2018
Publication date	Apr 13, 2021
Grant date	Apr 13, 2021

Abstract

At least some embodiments of the present invention are directed to RFID reader systems configured to estimate a directional bearing of an RFID tag. In an embodiment, the present invention is an RFID system configured in a way that upon a detection of a variance in the direction of a maximum RSSI value for a given RFID tag in response to a plurality of interrogation signals transmitted by an RFID reader over a respective plurality of different directions, the RFID reader retransmits the plurality of interrogation signals over the respective plurality of different directions with successively lower power levels until the only response(s) being received no longer exhibit the previously detected variance.

First claim

We claim:

1. A method of estimating a direction of a radio frequency (RF) identification (RFID) tag, comprising:
transmitting, by an RFID reader, a first transmit signal in a first transmit direction;
receiving, at the RFID reader, a first plurality of receive signals generated in response to the first transmit signal, each of the first plurality of receive signals having a respective first-receive-signal strength and being received from one of a plurality of receive directions;
transmitting, by the RFID reader, a second transmit signal in a second transmit direction that is different from the first transmit direction;
receiving, at the RFID reader, a second plurality of receive signals generated in response to the second transmit signal, each of the second plurality of receive signals having a respective second-receive-signal strength and being received from one of the plurality of receive directions;
determining a first receive direction, the first receive direction being associated with one of the first plurality of receive signals having a maximum first-receive-signal strength;
determining a second receive direction, the second receive direction being associated with one of the second plurality of receive signals having a maximum second-receive-signal strength;
comparing the first receive direction and the second receive direction;
responsive to a difference between the first receive direction and the second receive direction being within a predetermined threshold, determining an estimated direction of the RFID tag based on at least one of the first receive direction and the second receive direction; and
responsive to the difference between the first receive direction and the second receive direction exceeding the predetermined threshold:
(a) transmitting, by the RFID reader, another first transmit signal in the first transmit direction, the another first transmit signal being transmitted at a lower power level than an immediately precedingly transmitted first transmit signal;
(b) transmitting, by the RFID reader, another second transmit signal in the second transmit direction, the another second transmit signal being transmitted at a lower power level than an immediately precedingly transmitted second transmit signal;
(c) determining one of a presence and a lack of another first plurality of receive signals received at the RFID reader in response to the another first transmit signal;
(d) determining one of a presence and a lack of another second plurality of receive signals received at the RFID reader in response to the another second transmit signal;
(e) responsive to the presence of the another first plurality of receive signals and the lack of the another second plurality of receive signals,
determining the estimated direction of the RFID tag based on the first receive direction;
(f) responsive to the lack of the another first plurality of receive signals and the presence of the another second plurality of receive signals, determining the estimated direction of the RFID tag based on the second receive direction; and
(g) responsive to the presence of the another first plurality of receive signals and the presence of the another second plurality of receive signals, repeating (a)-(g).

2. The method of claim 1 , wherein the operation of determining the estimated direction of the RFID tag based on the first receive direction includes equating the estimated direction of the RFID tag with the first receive direction, and wherein the operation of determining the estimated direction of the RFID tag based on the second receive direction includes equating the estimated direction of the RFID tag with the second receive direction.

3. The method of claim 1 , wherein the predetermined threshold is between 5 degrees and 15 degrees.

4. The method of claim 1 , wherein, responsive to the difference between the first receive direction and the second receive direction exceeding the predetermined threshold, the method further includes:
(f.1) responsive to the lack of the another first plurality of receive signals and the lack of the another second plurality of receive signals:
transmitting, by the RFID reader, still another first transmit signal in the first transmit direction, the still another first transmit signal being transmitted at a power level that is higher than a power level of the immediately precedingly transmitted first transmit signal and lower than a power level of a most-recent first transmit signal that cause a receipt of a first RFID tag response by the RFID reader;
transmitting, by the RFID reader, still another second transmit signal in the second transmit direction, the still another second transmit signal being transmitted at a power level that is higher than a power level of the immediately precedingly transmitted second transmit signal and lower than a power level of a most-recent second transmit signal that cause a receipt of a second RFID tag response by the RFID reader; and
repeating (c)-(g).

5. The method of claim 4 , wherein the power level of the still another first transmit signal and the power level of the still another second transmit signal are approximately equal.

6. The method of claim 1 , wherein a power level of the another first transmit signal and a power level of the another second transmit signal are approximately equal.

7. The method of claim 1 , wherein, responsive to the difference between the first receive direction and the second receive direction being within the predetermined threshold, the operation of determining the estimated direction of the RFID tag based on at least one of the first receive direction and the second receive direction includes equating the estimated direction of the RFID tag with one of (i) the first receive direction, (ii) the second receive direction, and (iii) an average receive direction based on the first receive direction and the second receive direction.

8. The method of claim 1 ,
wherein the another first transmit signal being transmitted at the lower power level than the immediately precedingly transmitted first transmit signal includes the another first transmit signal being transmitted at a 1 dB to 3 dB lower power level than the immediately precedingly transmitted first transmit signal, and
wherein the another second transmit signal being transmitted at the lower power level than the immediately precedingly transmitted second transmit signal includes the another second transmit signal being transmitted at a 1 dB to 3 dB lower power level than the immediately precedingly transmitted second transmit signal.

9. A method of estimating a direction of a radio frequency (RF) identification (RFID) tag, comprising:
transmitting, by an RFID reader, a first transmit signal in a first transmit direction;
receiving, by the RFID reader, a first RFID tag response constituting a plurality of first response signals being received from a plurality of receive directions, wherein one of the plurality of first response signals that has a highest signal strength constitutes a maximum first response signal;
transmitting, by an RFID reader, a second transmit signal in a second transmit direction different from the first transmit direction;
receiving, by the RFID reader, a second RFID tag response constituting a plurality of second response signals being received from the plurality of receive directions, wherein one of the plurality of second response signals that has a highest signal strength constitutes a maximum second response signal;
responsive to a difference between a respective direction of the maximum first response signal and a respective direction of the maximum second response signal being within a predetermined threshold, determining an estimated direction

Assignees

• Zebra Tech Corp

Inventors

• Koch Michael J
• Bekritsky Benjamin J
• Swope Charles Burton

Classifications

• G01S13/75 Primary

  using transponders powered from received waves, e.g. using passive transponders {, or using passive reflectors} · CPC title

• G06K19/07

  with integrated circuit chips · CPC title

• G01S13/74

  Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems · CPC title

• G01S3/16 Primary

  using amplitude comparison of signals derived sequentially from receiving antennas or antenna systems having differently-oriented directivity characteristics or from an antenna system having periodically-varied orientation of directivity characteristic · CPC title

• G01S13/878

  Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector (G01S13/874 takes precedence) · CPC title