WO2001050408A1

WO2001050408A1 - Method for identifying electronic labels by amplitude discrimination of signals in a non-deterministic protocol

Info

Publication number: WO2001050408A1
Application number: PCT/FR2001/000040
Authority: WO
Inventors: Richard Kalinowski; Peter Cole; David Simplot
Original assignee: Gemplus
Priority date: 2000-01-07
Filing date: 2001-01-05
Publication date: 2001-07-12
Also published as: AU3184801A; FR2803673A1

Abstract

The invention concerns the field of electronic labels affixed on products. The identification method is used in a non-deterministic protocol and consists, in each label (10), in encoding the amplitude of the received signals and in transmitting a message containing said code (CA). The electronic querying-reading-recording device (40), which recognises the code (CA), re-transmits it to the labels (10) where it is compared to that of the labels which have transmitted in the transmission window. If there is conformity, the label ceases to transmit, otherwise, the label transmits at the next cycle.

Description

METHOD FOR IDENTIFYING ELECTRONIC LABELS

BY DISCRIMITATION OF SIGNAL AMPLITUDE

IN A NON-DETERMINIST PROTOCOL

The invention relates to the field of electronic labels which are affixed to products to identify them according to their attributes using an electronic interrogation-reading-recording device. It relates more particularly, in an electronic tag identification system, operating according to a statistical or non-deterministic protocol, a method for recognizing the electronic tags by amplitude discrimination of the signals received by the electronic tags.

It is known practice to use "bar" codes which are printed on the products to identify them and which are read by an optical device during their passage at the checkout of the sales store. The bar code which is read makes it possible to interrogate a computing device which provides, for example, the price of the product.

These bar codes have certain limitations which are mainly due to the fact that they are frozen when they are printed and therefore cannot be modified during the life of the product.

Also, it is now proposed to replace the bar codes by so-called electronic labels which contain electronic circuits such as a memory capable of recording a binary code with n bits. This binary code is representative of the bar code, in particular to indicate the type of product, but can also represent other information or attributes likely to be modified during the life of the product assuming, of course, that the memory is rewritable for at least some parts of the code binary with n digits. This can be the case for the date of sale, the identification of the store, the duration of the guarantee, the date of the end of the guarantee, etc. The interrogation-reading-recording device can operate in the same way as a barcode reading device, that is to say that it only dialogs with one electronic label at a time, the one which is presented in its radiation volume.

However, the interrogation-reading-recording device is capable of simultaneously interrogating all the electronic labels located in its radiation volume so that these also respond simultaneously and therefore cannot be identified one by one.

To solve this problem, it has been proposed to interrogate the electronic labels according to different so-called anti-collision methods which make it possible to "manage" the labels which respond simultaneously and which are therefore in "collision". These anti-collision processes are divided into two classes: deterministic and non-deterministic. In the first class, a first way of doing this is to interrogate the electronic labels on the basis, for example, of all or part of the product identification code until a single label responds to this code or part of code. This first way can lead to a high number of interrogations knowing that for a code with n = 64 bits

1 Q there are more than 10 possibilities.

A second way of doing this consists in making the interrogation-read-recording device repeat what it receives from the electronic labels and this bit by bit or block of bits by block of bits. The stickers electronics which recognize the repeated bit or block of bits know that they have been taken into account by the interrogation device and continue alone to transmit another bit or block of bits. These operations are repeated until a single electronic label is selected.

Deterministic processes assume that there are no two electronic labels with the same identification code, which constitutes a significant constraint in the case where there is a high number of products of the same type, for example in a supermarket, because each item must be labeled differently to be recognized. In addition, these deterministic methods only identify the electronic tags which are present at the start of the implementation of the method for a given set.

Any new label compared to this set cannot be taken into account and must wait for the next cycle of the identification process. As a result, these deterministic processes are not directly applicable to the continuous identification of products, for example those parading on a treadmill. In non-deterministic methods, the electronic tags are intended to send a message after a time interval of random duration counted from a starting point given by the interrogation-read-recording device. The electronic label will consider that its message has been recognized if it receives an acknowledgment of receipt from the interrogation-reading-recording device. In the absence of an acknowledgment, the unrecognized electronic label sends its message during the next cycle interrogation after the expiration of a new time interval of random duration.

In such a non-deterministic process, it is probable that several electronic labels transmit simultaneously if their total number is significantly greater than the number of random durations planned in a cycle, which scrambles the message of the electronic label which issued in first. The performance of non-deterministic methods is determined by the maximum number NsMAX of windows of transmission duration during a cycle with respect to the number N of electronic tags, this number NsMAX also defining the number of possible random waits. Thus, in the case of N electronic labels, the method is optimal for an Nsl value of NsMAX but in the case of 2N electronic labels, the method is optimal for a 2Nsl value of NsMAX. This has the consequence that the method is not suitable for any number of electronic labels.

To overcome these drawbacks, it has been proposed to adapt the number of random waits or transmission windows to the number of electronic tags remaining to be identified. This adaptation is carried out by the interrogation-reading-recording device as a function of the identification results of the previous cycle.

In the French patent application N ° 99 08181 filed on June 25, 1999 by the plaintiff, there is described a method of identification of electronic labels affixed on products using an interrogation-reading-recording device. , characterized in that it comprises the following stages consisting in: (a) indicate on electronic labels the number Ns of consecutive emission windows of a first cycle or round,

(b) counting, during the cycle of Ns windows, the messages received from the electronic tags to determine the number ri _j of identifications, the number n _v of empty windows or boxes and the number n _c of collisions,

(c) stop the process if n _c = 0 or go to step (d) if n _c ≠ 0,

(d) calculate a number Nsl of transmission windows for the following cycle as a function of the values of Ns, n ^, n _v and n _c ,

(e) return to step (a) with Ns = Nsl calculated. In each electronic label, the method further comprises the following steps consisting in: (m) receiving the number Ns of windows in each cycle or round, (n) randomly choosing an emission window from Ns,

(o) send a message for the duration of the selected window,

(p) wait for a message from the interrogation-read-recording device, (q) receive the acknowledgment of receipt of the message sent from the interrogation-read-recording device in the absence of a collision,

(r) return to step (m) in the event of a failure to acknowledge receipt, that is to say in the event of a collision or of an empty window.

The method which has just been described succinctly will be called method of identification by adaptive rounds. This process makes it possible to adapt the number Nsl of transmission windows for the following cycle to the values of Ns, n ^, n _v and n _c of the cycle which has just ended. The process of identification by adaptive rounds considerably improves the average time of acquisition of a label and, for this purpose, simulations have shown that this average time is for example 8 to 9 milliseconds by the process of identification by rounds adaptive while it's 15 to

20 milliseconds for the other non-deterministic processes known to date. This average acquisition time can be further reduced to 5-6 milliseconds if the method plans to move to the next window as soon as an empty window or a collision is detected.

However, this adaptive round process does not allow for sure detection of two electronic tags which emit at exactly the same time. This can give rise to situations where an electronic label believes itself identified by the acknowledgment of receipt when the latter was intended for another electronic label. An object of the present invention is therefore, in a system for identifying electronic labels according to a non-deterministic protocol, in particular of the adaptive round type, to implement a method for selecting an electronic label from among several electronic labels emitting simultaneously .

This object is achieved by selecting according to the amplitude of the signals received by the electronic tags according to the steps of the process below. In a system for identifying electronic labels affixed to products using an electronic interrogation-reading-recording device, the electronic labels and the electronic device being each capable of transmitting and receiving messages according to a protocol of the type non-deterministic, the invention relates to a method for identifying electronic tags characterized in that it comprises the following steps consisting in: (a) measuring and coding, in each electronic tag, the amplitude of the signals of the messages received electronic device;

(b) transmit the amplitude code obtained by step (a) in the message sent by each electronic label during its transmission window;

(c) detecting, in the electronic device, a message sent by an electronic tag and recognizing the amplitude code therein;

(d) send, by the electronic device, a message containing at least the amplitude code recognized by the step (c);

(e) recognizing, in the electronic labels having emitted during the current emission window, the amplitude code emitted by the electronic device during step (d), and

(f) compare, in the electronic labels having emitted during the current emission window, the amplitude code recognized by step (e) with that obtained during 1 step (a), and - in case identity, stop the transmission of messages by the electronic tag concerned, or

- if not, continue sending messages by the electronic tag concerned during the next round. To implement the method, at least the electronic label must be modified to include, in addition to the known means:

means for measuring and coding the amplitude of the signals of the messages received from the electronic device so as to obtain an amplitude code CA; - means for transmitting the amplitude code CA;

- means for recognizing, in the messages received by the electronic tags, the amplitude code transmitted by the electronic device, and - means for comparing the code CA of the electronic tag concerned and the amplitude code received by the the label and to provide a signal for stopping the transmission of messages by the label in the event of identity or a signal for maintaining the transmission of messages by the label in the absence of identity.

Other characteristics and advantages of the present invention will appear on reading the following description of a particular embodiment, said description being made in relation to the accompanying drawings in which:

FIG. 1 is a functional diagram of a contactless electronic label and of an interrogation-reading-recording device of such an electronic label to which the method according to the invention applies,

FIG. 2 is a diagram showing the different stages of the identification process by adaptive rounds,

FIG. 3 is a diagram showing the progress of the identification process by adaptive rounds in the case of one hundred electronic labels, and

- Figure 4 is a diagram illustrating the different steps of the method according to the invention. The invention will be described in its application to an identification system of electronic labels by adaptive rounds, but it applies to any non-deterministic identification system.

A contactless electronic label 10 comprises for example (FIG. 1), an antenna 12 constituted by a tuned circuit which comprises an induction winding 14 and a capacitor 16. The tuning frequency F _Q of the antenna 12 is, for example, 13.56 Megahertz.

This tuned circuit of the antenna is connected to different circuits which each perform a particular function. Thus, a circuit 24 performs the function of full-wave rectification of the signal across the terminals of the tuned circuit, for example, by a diode bridge.

8. This rectifying circuit 24 is followed by a filtering capacitor 26 of the rectified signal which supplies the supply voltage V _dd of all the other circuits of the electronic label, in particular those represented in rectangle 10 in FIG. 1 A circuit 18 performs the so-called Clock function and the synchronization of the latter from the frequency FQ • The signals at different frequencies supplied by this Clock circuit 18 are applied to the other circuits of the label represented or not except the antenna 12 and to the rectification circuit 24. The circuit 20 performs the function of demodulation and decoding of the signals which modulate the signal at the carrier frequency F ₀ , signals which constitute the information received by the label.

The information relating to the product with which the label is associated is recorded in a memory 22 which is addressable by a recording-reading circuit 30.

This recording-reading circuit 30 is under the control of the signals detected and decoded by the circuit 20 and supplies signals which are applied to a message synthesis circuit 32.

The messages provided by the synthesis circuit 32 are applied to an antenna load modulation circuit which has been shown diagrammatically by a circuit 28 and by a switch 38 controlled by the circuit 28. A load resistor 36 has been shown in series with the switch 38.

The tag interrogation-read-recording device 10 comprises for example in known manner an antenna 42 consisting of a tuned circuit which comprises an induction winding 44 and a capacitor 66, the tuning frequency being FQ - The two antennas 12 and 42 are magnetically coupled as shown by the arrow 46. The antenna 42 is supplied by electrical signals at the carrier frequency F ₀ which are modulated by low frequency digital signals conveying the information to be transmitted to the label 10. These modulated electrical signals are produced by a modulator 50 which receives, on the one hand, a signal at the frequency F ₀ from an oscillator 48 and the modulation signals from a message generator 52. The signals of the modulator 50 are applied to a power amplifier 54, the output terminal of which is directly connected to the antenna 42.

The signals received by the antenna 42 are applied to a reception circuit 56 which performs their detection, demodulation and decoding. The decoded signals are applied to a microprocessor 58 which interprets them and provides the control signals for the message generator 52.

The method of identifying electronic tags according to a non-deterministic protocol of the adaptive round type will be described in relation to a set comprising electronic tags of the type described with the aid of FIG. 1 and an interrogation device also described. using FIG. 1. After a start (rectangle 60), the method comprises the following steps consisting in: (a) indicate on electronic labels the number Ns of consecutive emission windows or slots of a first cycle or round (rectangle 62),

(b) counting, during the cycle of Ns windows, the messages received from the electronic tags to determine the number n-j_ of identifications, the number n _v of empty windows or boxes and the number n _c of collisions (rectangle 64),

(c) stop the process if n _c = 0 (rectangle 68) or go to step (d) if n _c ≠ 0,

(d) calculate a number Nsl of transmission windows for the following cycle as a function of the values of Ns, n ^, n _v and n _c (rectangle 70),

(e) return to step (a) with Ns = Nsl calculated (rectangle 62).

FIG. 3 illustrates the steps of the method according to the invention in the case where N = 100 and Ns = 32. The first cycle or the first round includes thirty-two windows (step (a)) and having regard to the fact that N = 100 is much greater than Ns = 32, the number of collisions will be for example n _c = 27, with n ^ = 4 identifications and an empty window (n _v = l), which is counted by step (b).

As n _c ≠ 0, there is passage to step (d) which consists in calculating a value of Nsl as a function of Ns = 32, n _c = 27, n ^ = 4 and n _v = l, which gives Ns = 101 for Nr = 96 electronic labels remaining to be identified.

This number Ns = 101 is indicated on the electronic labels remaining to be identified (step (a)), the latter randomly choosing to transmit in one of 101 windows.

This leads to a second step (b) in which one counts n ^ = 38 identifications, n _c = 22 collisions and n _v = ll empty windows. The calculation of the second step (d) leads to Ns = 52, a number which is indicated on the electronic tags remaining to be identified (3 ^rd step (a)), the latter randomly choosing to send in one of 52 windows.

The accounting of the third step (b) determines the values of

n _c = n _v = 15 and 20 which calculate a new Ns = 35 ^(3rd step (d)) for a fourth cycle or round. This fourth cycle identifies

labels and count n _c = 12 collisions and n _v = ll empty windows, which gives a new Ns = 30 for the fifth cycle.

This fifth cycle leads to

n _c = 8 and n _v = ll, i.e. a new Ns = 19 for the sixth cycle.

This sixth cycle leads to n ^ = 7, n _c = 5 and n _v = 7, i.e. a new Ns = 12 for the seventh cycle.

This seventh cycle leads to n _i = 3, n _c = 3 and n _v = 6, i.e. a new Ns = 8 for the eighth cycle. This eighth cycle leads to

, or a new Ns = 8 for the ninth cycle.

This ninth cycle leads to n ^ _ = 7, n _c = 0 and n _v = l.

As there is no collision, the method proceeds to step (c) at the end of the process (rectangle 68). The steps of the process which have just been described correspond to a particular operation of electronic labels, the following steps of which consist in:

(m) receive the number Ns of windows in each cycle or round,

(n) randomly choose a transmission window from

Ns,

(o) send a message for the duration of the selected window, (p) wait for a message from the interrogation-read-recording device,

(q) receive the acknowledgment of the message sent from the interrogation / reading / recording device in the absence of a collision,

(r) return to step (m) in the event of a failure to acknowledge receipt, that is to say in the event of a collision. The number Ns has been defined as determining the number of transmission windows in a cycle or round, each start of window corresponding to a random duration counted from the start of the cycle.

In the example described in relation to FIG. 3, it has been assumed that this random duration was counted in number of windows, which means that the electronic labels emit at the start of the window chosen randomly. This operation leads to an identification procedure of duration equal to at least Ns. d if d is the fixed duration of a window. This total duration can be reduced if it is taken into account that the duration of the empty windows or with collisions can be shortened by going to the next window as soon as they are detected.

To this end, the interrogation device can be provided to emit a signal to pass to the next window as soon as an identification of a label has ended or as soon as it has detected a collision or empty window.

However, it may be that, when a label has been identified in a window, there are other labels which emitted during this window but which were not taken into account because their signal was too weak to be detected. Besides, if their signal had been detected, the window would have been classified with collisions. These undetected tags receive an identification message from the electronic device as if they had been identified, so that they will not issue during the next round and will never be identified.

To overcome this problem, the invention proposes that all the messages sent by the labels contain a code representative of the amplitude of the signal received from the electronic device, this code allowing the label taken into account to recognize itself when it receives it. in return for the electronic device and thus to no longer participate in the following rounds. On the other hand, the other labels which have not been taken into account receive an amplitude code which is not theirs and continue to participate in the next round.

To obtain this operation, the method according to the invention comprises the following steps consisting in: (a) measuring in each electronic label the amplitude of the signals of the messages received and then coding this amplitude in a binary code CA with several digits, for example four. This CA code is representative of the magnetic or electromagnetic field created by the antenna of the electronic device at the antenna of each electronic label. This field may be weak due to the distance from the electronic label but also from the fact that the electronic label is close but that its coupling with the antenna of the device is poor; (b) transmit the amplitude code CA obtained in step (a) in the message sent by each electronic label during its transmission window; (c) detecting, in the electronic device, a message sent by an electronic label and recognizing therein the amplitude code CA; this code CA will correspond to the largest amplitude among all the labels of the transmission window, the codes of the other undetected labels corresponding to very low amplitudes since they have not been detected in collision;

(d) send, by the electronic device, a message containing at least the amplitude code CA recognized during step (c) in the message sent by the detected label;

(e) recognizing, in the electronic tags having sent during the current sending window, the amplitude code CA contained in the message sent by the electronic device during step (d);

(d) compare the amplitude code CA contained in the message sent by the electronic device to that obtained during step (a), and - in case of identity, stop the transmission of messages by the electronic tag that has been detected or, if not, maintain the sending of messages by the electronic tag during the next round. The steps which have just been described have the effect:

- to stop the emission of the electronic label whose message was detected during a transmission window, - to maintain, for the next round, the emission of messages by the other labels which were not detected colliding during this transmission window, - to be certain that the electronic tag from which the transmission of messages has been stopped is indeed that which has been detected by the electronic device,

- to be certain to detect all the electronic tags present because the tags having weak signals will be detected during the following round (s).

In other words, these are electronic tags which determine themselves whether or not they have been detected according to the result of the comparison carried out in each tag. Thus, the electronic label which has been detected will stop transmitting during the following rounds while the undetected electronic labels will continue to transmit during the following round.

To implement the method of the invention, the electronic label must be modified to measure the amplitude of the received signal, to code its amplitude CA, to transmit the CA code, to recognize a CA code retransmitted by the electronic device and to compare it with CA code coded in the label.

The diagram of FIG. 1 can, for example, be modified, as regards the label 10, in the following manner. The amplitude of the signal received from the electronic device 40 is measured and coded in a circuit 80 and the CA code which is obtained is transmitted by means of circuits 32, 28 and 38. The amplitude code received from the electronic device is recognized by circuit 20 and compared, in a comparator 82, to the code CA. The signal resulting from the comparison is used to block or not the circuit 28.

The method has been described using an electronic label according to a modified diagram to measure the electronic amplitude of a received signal, amplitude reflecting the intensity of the magnetic or electromagnetic field at the antenna of the electronic label or reflecting the coefficient of magnetic coupling between the antenna of the electronic label and that of the electronic device. However, the method of the invention can be implemented using any device for measuring the intensity of the magnetic field or the magnetic coupling at the label. It is also possible to measure a particular signal emitted by the electronic device. This signal can consist of a particular modulation (amplitude, frequency) or a code or a combination of the two, particularly suitable for measuring the coupling coefficient or the distance between the electronic device and the electronic label, or any other physical quantity making it possible to distinguish the label concerned.

Claims

1. Method for identifying electronic labels (10) affixed to products using an interrogation-reading-recording device (40), the electronic labels and the electronic device being each capable of transmitting and to receive messages according to a non-deterministic type protocol, said method being characterized in that it comprises the following steps consisting in:

(a) measuring and coding (80), in each electronic label (10), the amplitude of the signals of the messages received from the electronic device so as to obtain an amplitude code (CA);

(b) transmit (32, 28, 38) the amplitude code (CA) obtained by step (a) in the message sent by each electronic label during its transmission window;

(c) detecting (56), in the electronic device, a message sent by an electronic label (10) and recognizing therein the amplitude code (CA); (d) transmitting (50, 54), by the electronic device (40), a message containing at least the amplitude code (CA) recognized by step (c);

(e) recognizing (20), in the electronic labels having emitted during the current emission window, the amplitude code (CA) emitted by the electronic device during step (d), and

(f) compare (82), in the electronic labels having emitted during the current emission window, the amplitude code recognized by step (e) with that obtained (CA) during step (a ), and

- in the event of identity, stop the transmission of messages by the electronic tag concerned, or if not, continue sending messages by the electronic tag concerned during the next round.

2. System for identifying electronic labels (10) affixed to products using a interrogation-reading-recording device (40), the electronic labels and the electronic device being each capable of transmitting and to receive messages according to a non-deterministic type protocol, characterized in that each electronic label comprises:

- means (80) for measuring and coding the amplitude of the signals of the messages received from the electronic device so as to obtain an amplitude code (CA);

- means (32, 28, 38, 12) for transmitting the amplitude code (CA);

- means (20) for recognizing, in the messages received by the electronic tags, the amplitude code transmitted by the electronic device, and means (82) for comparing the code (CA) of the relevant electronic tag and the amplitude code received by the tag and to provide a signal to stop sending messages by the tag in the event of identity or a signal to keep sending messages by the tag in the event of lack of identity.

3. System according to claim 2, characterized in that the amplitude codes (CA) are representative of the intensity of the magnetic or electromagnetic field at the electronic label.

4. System according to claim 2, characterized in that the amplitude codes (CA) are representative of magnetic coupling between the antenna (42) of the electronic device and the antenna (12) of the electronic tag.

5. System according to claim 2, characterized in that the amplitude codes (CA) correspond to a particular signal emitted by the electronic device 40.

6. System according to claim 5, characterized in that the particular signal is obtained by modulating the signal emitted by the electronic device (40).

7. System according to claim 5 or 6, characterized in that the particular signal is obtained by a code transmitted by the electronic device (40).