Method of discriminating RFID tags in motion from static RFID tags

Patent metadata

Field	Value
Publication number	US-9886604-B2
Application number	US-201515516601-A
Country	US
Kind code	B2
Filing date	Oct 2, 2015
Priority date	Oct 3, 2014
Publication date	Feb 6, 2018
Grant date	Feb 6, 2018

Abstract

Some embodiments are directed to a method and a system allowing moving tags to be discriminated from stationary tags, which can be used in the field of tracking merchandise or objects provided with RFID tags.

First claim

The invention claimed is:

1. A method for processing a plurality of RFID tags, intended to discriminate between moving tags and stationary tags, the method comprising:
transmitting, from first and second remote reading stations placed along the path of the moving tags, a first and a second radiofrequency interrogation signal to said plurality of RFID tags,
determining whether said first and second reading stations receive response signals from tags in response to said first and second radiofrequency interrogation signals, respectively, in such a way that, for a current tag, if only one of said first and second reading stations receives a response signal from said current tag, said current tag is a stationary tag, and if said first and second reading stations each receive a response signal from said current tag, a k-nearest neighbors method, k being an integer greater than or equal to 1, is used to determine whether the current tag is stationary or moving,
which k-nearest ‘neighbors’ method includes:
learning on a population of N tags, called learning tags, the state of which, stationary or moving, is known, wherein a signal representative of the response signals received by said first and second reading stations for each of said N learning tags are recorded,
selecting the k learning tags having the recorded response signals that are the closest to the response signals received for a current tag according to a predetermined distance criterion, and
determining the stationary or moving state of the current tag on the basis of the state of the k learning tags selected.

2. The method according to claim 1 , wherein k is an odd number.

3. The method according to claim 1 , wherein, in order to select the k learning tags, said response signals of the current tag and the response signals of the N learning tags are compared over a time window having a predetermined length synchronized on a predetermined time reference.

4. The method according to claim 3 , wherein the length of the time window is determined on the basis of the speed of the moving tags and/or their minimum distance with said first and second reading stations.

5. The method according to claim 3 , wherein the time reference is the crest of a peak of the RSSI level of the response signals and the time window is centered on said crest.

6. The method according to claim 3 , wherein the time reference is provided by a device upstream of said first and second reading stations, said time reference marking the beginning of the time window.

7. The method according to claim 3 , wherein the time window is divided into M sub-windows, the learning step further comprises, for each of the learning tags, a step of calculating characteristic values representative of the response signals received during each of said M sub-windows by said first and second reading stations, and the step of comparing the response signals of a current tag and the response signals of the learning tags comprises:
calculating, for the current tag, characteristic values representative of the response signals received during each of said M sub-windows by said first and second reading stations, and
calculating distance between the characteristic values of the current tag and the stationary values of each of the N learning tags,
the k learning tags selected being the k learning tags having the smallest calculated distances.

8. The method according to claim 7 , wherein the characteristic value calculated for each of the sub-windows belongs to the following group:
the average of the RSSI level of the response signals of the tag over said sub-window;
the maximum value of the RSSI level of the response signals of the tag over said sub-window;
the standard deviation of the RSSI level of the response signals of the tag over said sub-window;
the difference between the maximum value and the minimum value of the RSSI level of the response signals of the tag over said sub-window;
the phase difference between the first and second interrogation signals and the response signals received over said sub-window.

9. The method according to claim 7 , wherein the sub-windows have distinct lengths.

Assignees

• Tagsys
• Univ Paris 6 Pierre Et Marie Curie
• Centre Nat Rech Scient
• Univ Amiens Picardie Jules Verne

Inventors

• Loussert Christophe
• Kervella Brigitte
• Zancanaro Mario Antonio
• Pereira Fonseca Mauro Sergio
• Akre Niamba Jean Michel
• Fladenmuller Anne
• Baey Sebastien

Classifications

• G06K7/10128

  the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device · CPC title

• G06K7/10435

  the interrogation device being positioned close to a conveyor belt or the like on which moving record carriers are passing (conveying in accordance with bodily destination marks, see B65G47/46, sorting of objects carrying identity markings, see B07C5/34) · CPC title

• G06K7/10138 Primary

  the step consisting of determining the type of record carrier, e.g. to determine if the record carrier is an RFID tag of the long or short range type, or to determine the preferred communication protocol of the RFID tag · CPC title

• G06K7/10108 Primary

  interrogating only those RFIDs that fulfill a predetermined requirement, e.g. selecting all RFIDs having the same speed and moving in a cloud like fashion, e.g. on the same train; interrogating only RFIDs having a certain predetermined temperature, e.g. in the same fridge, another possibility being the active ignoring of a group of tags that fulfill a predetermined requirement, equivalent to the Boolean NOT operation · CPC title

• G01S13/74

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