WO2007036967A1

WO2007036967A1 - Method for detecting increasing distances between a portable radio identification device and objects fitted with a transponder

Info

Publication number: WO2007036967A1
Application number: PCT/IT2005/000648
Authority: WO
Inventors: Lando Lancini
Original assignee: Lando Lancini
Priority date: 2005-09-27
Filing date: 2005-11-07
Publication date: 2007-04-05
Also published as: ITMI20051783A1

Abstract

A method of radio identification by means of transponders (RFID) in which a portable master device (MST) maintains control over objects of personal use (1-6) to which a transponder (T1-T6) is glued. Each transponder (T1-T6) stores its own individual identification code and the unequivocal code that identifies the master (MST) The transponders are then brought close up to the master (MST), and the user presses a control button (P1) on the master (MST) to store the configuration. The master, e.g. in the form of an armlet, is attached to the user. At this point the master (MST) begins to scan the set of transponders (T1-T6), including its own unequivocal code in the scanning signal. Replies come in from those transponders that have correctly received the scanning signal from a master whose unequivocal code corresponds to the one stored. The master, in turn, verifies that all the codes in the stored configuration have been emitted; in the event of at least one code not being received, a luminous signal (LD) lights up on the master accompanied by an acoustic warning.

Description

METHOD FOR DETECTING INCREASING DISTANCES BETWEEN A PORTABLE RADIO IDENTIFICATION DEVICE AND OBJECTS FOR PERSONAL USE FITTED WITH A TRANSPONDER

Range of application of the invention

The present invention relates to the field of Radio-Frequency Identification (RFID) and more particularly to a method for detecting how far a portable radio identification devices becomes separated from objects of personal use fitted with a transponder Present state of the art RFlD technique offers numerous examples of short-range radio identification of objects by means of miniaturized electric circuits to which they are associated, that respond to electro-magnetic stimulus given by a master; for instance, the widely used electronic systems operated at motorway tollbooths for automatic payment of the charge, or again, the checks kept on goods sold in supermarkets for preventing theft or for automatically calculating the cost when a shopper's trolley passes the cash desk (possible future developments). A characteristic feature of these systems is the presence of a centralized master and of one or more slaves that emit their individual identification codes. The slaves are also known as "transponders" or radiant "tags" (labels), and can be active or passive. A transponder is considered passive if it has no personal source of feed but acquires the power needed to operate internal circuits straight from the electro-magnetic field emitted by the scanner (master) and intercepted by the slave's antenna. The master scans the slaves at set intervals, infusing enough energy into their antennas for activating the programmed circuits so that a previously stored identifying code is returned possibly along with other data. The advantage of a passive transponder is that it has no battery, although this does limit the scanning range. Having no batteries, passive transponders are easy to make using planar technology (foil or inlay) obtaining devices that can operate at high frequencies and therefore be miniaturized and produced in various forms, for example that of flexible adhesive labels. The most common commercial devices operate in the Industrial Scientific Medical (ISM) bands not subject to licence, at 900 MHz and 2.4 GHz (UHF).

A transponder is considered as active if it contains its own source of feed (a battery). As a rule an active transponder periodically emits its own identification code without necessarily having to be stimulated by the master. This periodical recurrence must satisfy a criterion of compromise between the life of the internal battery and delay in detection by the master. The advantage of active transponders lies in their greater operative range whereby the objects to which they are connected are not obliged to pass close to the master in order to be detected. Compared with passive transponders, their disadvantages lie in greater size and higher costs due to the battery.

One problem relating to the presence of several transponders in the master's radio field is that of collision among the various codes emitted simultaneously by the transponders. The identifying code in binary format is emitted in serial mode as a sequence of noughts and ones. The string of bits is used for digital modulation (FSK, PSK, ASK) of the transmission carrier. Collision arises due to bits of different codes interfering one with another and, unless suitable counter-measures are taken, this makes it impossible for the master to discriminate correctly. RFDD technique offers various methods of dealing with collisions or for avoiding them: some well-known implementations exist in which the master can detect up to several hundred simultaneously active transponders. In the most common applications the master occupies a permanent or semi-permanent position and has a mobile transponder If the master is moved to another position, it does not usually happen that the transponders associated to the objects must necessarily follow the master to its new position This therefore seems to disclose a case in which the master and its controlled objects constitute a single entity that can be moved from one place to another with a possibility of independent movements within the space occupied by the whole system In this sense a conclusive example is provided by a person and his own set of personal objects wallet, bag, cash point card, mobile phone, briefcase, spectacles, bunch of keys, car keys, camera, pocket calculator etc It may happen that, when at home, the person sometimes forgets where he has put these things down and wastes time looking for them The same person may have to leave home taking with him all these belongings, such as going to another job or on a journey, in which case the same problem arises at his journey's end or even during the journey itself If it is desired to solve this problem by the RFID techniques it would appear, in view of the foregoing, that no valid suggestions could be offered The fact of being unable to maintain continuous and automatic control over one's own belongings increases the likelihood of losing them altogether, with all the trouble this involves, such as declaring their loss to the authorities, changing locks, blocking a bank account, asking for duplicates, finding lost data, and more besides Purpose and summary of the invention

The purpose of the present invention, therefore, is to each htfw the RFID techniques can be used in the scenario described above To achieve this purpose the present invention proposes a method of radio identification by means of transponders, as described in the claims The method of the present invention comprises the following steps a) storage in each transponder of an unequivocal code that identifies the master, b) storage in the master of the configuration comprising all the individual transponder codes used, c) attaching the master to a person who intends to monitor the entities fitted with a transponder, d) emission by the master of a scanning signal directed to all the transponders at previously set intervals of time comprising at least the master's own unequivocal code of identification; e) emission of a reply signal by those transponders that have correctly received the scanning signal and have checked to see that the master's unequivocal code corresponds to the copy stored, f) checking by the master to see that the individual transponder codes contained in the replies as a whole correspond to all those in the configuration stored in step (b); g) activation of a luminous and/or acoustic signal in the master if at least one individual code has not been received.

The luminous and acoustic signals waπi the person carrying the master when he moves away from a monitored entity, or vice versa. The acoustic signal can be silenced by a push button, while the luminous signal is extinguished only when the configuration of the monitored entity is restored; this happens either because the entity that did not respond at first starts to do so again, or because a new configuration is stored in step (b) by pressing a specially provided storage button. The fact that two types of signalling are used together should not be considered as a limitation, but rather as proving more effective for attracting the user's attention

A distinctive feature of the method lies in the fact that the master is firmly attached to the person and not incorporated in some easily detachable object that might become included among those to be monitored. Preferably the master could be built into a special kind of armlet or into a pjendant to hang on the trous'er belt or on a belt loop; as a secondary choice, a hanging key holder could be used (excluding keys from the objects to be monitored). The choice of entities to monitor covers an extremely wide range, including: things, people, animals, plants or a combination of these, even if the objects most commonly used are "worn" by the person who also "wears" the master. In this case the luminous and acoustic warnings would mean that the person is moving away and has forgotten something, or else that someone is removing a monitored object. Use of an RFID system, according to the method described for the present invention, is also possible Compared with the normal use of RFID systems against theft in super-markets, where theft of an article on sale is detected by the transponder concealed in the object itself, the exact opposite occurs with the anti-theft method envisaged by the invention, namely that attention is drawn to the theft due to non-recognition of the transponder associated to the object to be monitored. This teaching may therefore be appreciated for its originality.

It follows that another subject of the invention is an anti-theft device based on the present invention's method of radio identification. Being so versatile, the invention can be applied in many fields, such as: security (e.g. children can wear an armlet fitted with a transponder making it easier to find them); automotive medical - electronic in general

- zoological-veterinary

- sport-fitness manufacturing chemical-botanical - means of transport (motor bicycles, bicycles, aeroplanes, ships...)

- financial banking

Taken as a whole, the invention confers peace of mind oh those who decide to use it, freeing them of the fear of losing the things they normally need and are accustomed to having with them, or of a feeling of panic if they lose a child in a crowded place

The method of the invention can be put into effect by using the commercial type of RFID components programmable by the user. The technology incorporated in the RFID devices today available on the market makes it possible to use passive transponders up to a distance of 10-11 m, though active transponders are needed for longer distances.

Irrespective of the type of transponder used, according to the method of the invention the master must be portable and therefore fed by a battery. In using a passive transponder, the maximum distance possible is established by standards for safeguarding a person's health that limit the irradiations from short-range devices with a built-in antenna (mobile phones, RFID masters, etc). These standards are applied in various national regulations that control emissions for the entire range of radio frequencies and therefore also those of the ISM bands not subject to licence In Europe, through the European Radio communications Office (ERO), the European Conference of Postal and Telecommunications Administrations (CEPT) has published its recommendations ERC REC 70-03, included in rules

ETSI EN 300-220 The following is an extract from this document for the UHF bands of greatest interest in the RFID field - band 868-870 MHz, maximum power of transmission 500 mW ERP (Effective Radiated Power); - band 2,400-2,483 5 MHz, maximum power of transmission 10 mW

EIRP (Effective Isotropic Radiated Power).

In the United States similar Federal Communications Commission (FCC) rules apply, published in the Code of Federal Regulations (CFR), Chapter 47, section 15 Where transmissions are subject to such controls, the power intercepted from passive transponders in their operative band is really very slight indeed (150-250 μW at 2 m), so that the limit on distance is set solely by the technology of integrated circuit's. Even with controls on maximum power values, the power that the master absorbs from the battery might be excessive if transmission lasted a long time. However, this does not happen with the present invention where idle

' time is much longer than transmitting time so that, practically speaking, the devices are left on stand-by

If active transponders are used, these can operate on signalling power lower than that needed for passive transponders so that, power emitted by the master being equal, there is an increase in maximum signalling capacity. Short description of the drawings

Further uses and advantages of the present invention will be made clear from the following detailed description of one example of a device actually produced, and from the attached drawings provided purely for explanatory purposes not limited to these, wherein:

- Fig.l shows an RFID system with a centralized master that communicates by radio with a number of objects each connected to a transponder;

- Figs 2a and 2b give flow diagrams showing how the RFID system in Figure 1 functions according to the method of the present invention;

- Fig.3 shows the functional block diagram of the master device in Figure 1;

Fig. 4 shows a functional block diagram of a transponder in Figure 1.

Detailed description of some preferred forms of realizing the invention

Referring to Figure 1, a group of objects 1 , ... ,6 are shown connected to their respective radio-identification slave devices T1,...,T6, called transponders, that communicate by radio with a master MST radio-identification device. Taken together, the master MST and the T1,...,T6 transponders form a system known in the art as RFID. The Tl,..., T6 transponders are made in the form of adhesive tags or labels to stick onto the respective objects 1,...,6 to be monitored. These latter may form part of a set of personal belongings Tl, T2, T3, T4 and T6, or can be separate from them like T5, to which a general type of symbol is assigned for this reason. Without thereby imposing any kind of limitation, the master MST is built into a pendant to be firmly attached to the person who intends to monitor the presence of the objects indicated within the master's range of action. This latter includes the detector's integrated circuit and a control panel comprising two press buttons Pl and P2, an LD LED and an acoustic device (buzzer) BZ. The way the RFID system in Figure 1 functions is described with the aid of Figures 2a and 2b. Referring to those figures, at step Sl, before the RFED system is put into operation, preferably the maker or, if not, the user stores in each transponder Tl,. .,T6 an unequivocal code of identification for the master MST and an individual code of identification for the transponder. In this way the transponders are programmed to recognise their own master which makes them immune from stimuli that may reach them from other masters in the vicinity. At step S2 the user moves all the transponders Tl,... ,T6 close up to the master MST. and then presses the storage button P 1 to induce the master to memorize the N individual codes of the N transponders that form the configuration to be kept constantly monitored At step S3 the master MST is attached to the user and the and the transponders Tl , ... ,T6 are fixed to their respective objects 1, .. ,6 that must be constantly monitored. At S4 the objects 1,...,6 provided with transponders, are placed where the user decides they are to go within the master's range of action. As already happens for the master, the objects provided with transponders, or even only a few of them, can also be attached directly to the user's person. At this point the master enters a cyclical stage of monitoring that comprises the next steps. At step S5 the master MST questions all the transponders emitting a scanning ^"signal in the form of a series of bursts comprising: a synchronizing word, its own unequivocal code of identification, and a request for connection At step S6 only those transponders that have correctly received the scanning signal first check to see if the master's unequivocal code in said signal coincides with the copy of the same code in store and only then, if the two coincide, will they emit their individual identification codes In S7 the master MST checks to see if all the individual transponder codes received correspond to the N copies _^ stored in the preceding step S2 and, if they do, introduces into the next step S8 a waiting cycle lasting for an established time Wl that can be programmed at the initial step Sl. A value of Wl equivalent to 2 seconds has been chosen for this present application. The Wl time must satisfy a criterion of compromise between the desired rapidity of detection and the interval for recharging the battery fitted to the master, and in the transponders if the active type are being used. At the end of time Wl, the master returns to the questioning step S5. If, at step S7, the master MST discovers that an individual code of one or more transponders has not been received, at step S9 it asks itself if the storage button Pl has again been pressed for storing a new configuration of transponders. A new configuration implies one of the following possibilities: a) the number of individual codes has changed (increased or reduced) compared with the N codes of the original configuration; b) the number has not changed but at least one code has acquired a new value, c) the number has changed and at least one code has acquired a new value. In the event of a negative reply being received at step S9, the master activates a luminous and / or acoustic signal on the square at step SlO. At step SIl the user can decide whether or not to press the reset button P2 to silence the buzzer BZ leaving the LD LED alight. In the event of an affirmative reply having been received at step S9, at step S12 the master turns off the luminous and acoustic signal (if still active) and, at the next step S 13, stores the new configuration of individual transponder codes in the part that differs from the preceding configuration.

Several independent RFID systems can be present in the same ambient; thanks to the master's unequivocal code and to the presence of adequate anti- collision measures, these systems do not interfere with each other although they share the same transmission channel and possibly the same individual transponder code. For this purpose the diagram in Figure 2a must be altered as follows:

- the reply from each transponder at step S6 also includes 'the master's unequivocal code;

- a new step S7' (not shown in the figure) is introduced immediately before S7 in which the master analyses replies received from the transponders and rejects those that do not carry its unequivocal code of identification.

Figure 3 shows the block configuration of the master MST in its most general form. Referring to this figure, the master MST includes a non- volatile memory 7 (EEPROM) connected to the bus of a microprocessor 8 (MMP) where it is also connected to a RAM memory 9, to a clock 10 (CLK) signal generator and band base logic 11. A rechargeable battery 12 feeds the circuits of the master MST The band base logic 11 sends the serial signal to be modulated to a modulator 13 (MOD) connected to a radio frequency amplifier 14 (PTX). This latter converts a radio frequency, amplifies the modulated signal and sends it on to an entry port of a duplexer filter 15 (DUP). A two-way port of the duplex filter 15 is connected to an antenna 16 used both for emitting the signal from PTX and for receiving the signals from various transponders. The signal received from the antenna 16 reaches the two-way port of the duplex filter 15 and from there is transferred to an exit port of its own to which is connected the entrance to a low-noise amplifier 17 (LNA). After being converted to an intermediate frequency, the outgoing signal from the receiving amplifier 17 reaches a demodulator 18 (DEM) that supplies the demodulated signal to the band base logic 11 for detection.

Figure 4 shows the block configuration of each active transponder in its most general form. It will be seen that the internal architecture is similar to that of the master MST since both devices include a transmitter and receiver, a modulator and demodulator, the related band base logic and a microprocessor system including a non-volatile memory and a RAM. The main difference lies in the operating program The following equivalents may be recognised among similar elements in Figures 3 and

4. 7→29, 8→27, 9-→28, 10→25, 11→24, 12-→26, 13→30, 14→31, 15-→21. 16→20, 17→22, and 18-*23. The only difference between the configuration of the passive transponder and that shown in Figure 4 is that the battery 26 is replaced by a circuit able to convert a part of the radio frequency energy intercepted by the antenna into energy stored in the electrostatic field of a condenser. A conversion circuit operating in the pre-established ISM band consists of a particular configuration of Schottky diodes and condensers known as -a "charging pump" that enables the VDC to be raised to the voltage required for reading and writing data in the EEPROM 29. The devices in the preceding Figures 3 and 4 can be made using components available on the market. In the prototype stage use was made of devices by Cypress, in the catalogue CYWUSB6934 (master) and CYWUSB6935 (active transponders). The prototypes of both master and slave cards are made using two separate components: a) the corresponding transceiver device, b) an external microprocessor for purposes of control. The microprocessor is programmed using 'C language so that, in its final form, it does not have to depend on the type of microprocessor used. Final dimensions of the printed circuit card, with the antenna placed right on the substrate and with space for the battery, can be estimated at mm 25 x 25 for both master and slave, without changing the technology and therefore in full logico-functional correspondence with the prototypes. The prototypes can be further improved by having the two components (a) and (b) (microprocessor and radio) combined in a single device. This change too can be made without altering the logico-functional structure of the system and using, for this purpose, ^"a new device made by the same manufacturer, one that combines the radio with the microprocessor (as shown in Figures 3 and 4).

The elements of the system, with codes prefigured, can be sold in kit form. Each kit should comprise a master with a stored unequivocal identification code, and up to eight slaves programmed to recognise the master's unequivocal identification code and each having stored its own particular identification code. The possibility of increasing the overall number of transponders (and of systems) is further ensured by being able to use up to ten different transmission channels.

• Transceiver operating in the ISM band without licence comprised

between 2,400 and 2,483 MHz

• Speed of transmission 62 Kbits/second. • Reception sensitivity of -90 dBm.

• Two values of maximum programmable operative distance: m 0-50 or m 0-10, both by controlling transmission power and by measuring the quality of reception

When operating, the master and slave devices are usually on stand-by so that consumption is very low The master emits 6 bytes (48 bits) while the slave replies with 2 bytes (16 bits) only; transmission times are therefore less than a millisecond during which time peak current absorbed for transmission is high (20-50 mA). However, considering that actual transmission time is extremely short (1 ms every 2 s), mean current required by the battery is very low (5-15 μA) From this it may be assumed that battery life is long, or that there is a very long interval between one recharge and the next. If passive transponders are used, peak current for the battery (600-700 Ma) is decidedly higher than the above, but mean current still remains sufficiently low (60 μA) to ensure a satisfactorily long life for the battery.

Claims

1. Method of radio identification of entities (1,...,6) fitted with transmitting devices (T1,...,T6), called transponders, appropriate for transmitting an individual code of identification towards a master (MST) device that monitors the presence of said entities by detection of said individual codes, characterized by the fact that it includes the following steps: a) storage within each transponder (T1,...,T6) of an unequivocal code that identifies the master (MST); b) storage in the master (MST) of the configuration comprising all the individual codes of the transponders used; c) attachment of said master (MST) to a person who intends to monitor said entities (1, ... ,6) fitted with transponders (Tl, ...,T6); d) transmission by the master (MST) of a scanning signal directed to all the transponders (T1,...,T6) at time intervals of a previously set duration comprising at least the unequivocal identification code of the master; e) transmission of a reply signal from those transponders (T1,...,T6) that have correctly received said scanning signal and have checked to ensure that said unequivocal code of the master (MST) corresponds to the stored copy of the code; f) check made by the master (MST) to ensure that the individual transponder codes contained in the set of replies correspond to all those in the configuration stored in step (b); g) activation of a luminous LD and/or acoustic BZ signal in the master (MST) if at least one individual code has not been received.

2. The method in claim 1, characterized by the fact that said initial configuration stored by the master in step (b) can later be changed and the new configuration stored in the master in place of the preceding one.

3. The method in claim 2, characterized by the fact that the unequivocal code of identification of the master (MST) is stored in each new transponder introduced into said new configuration.

4. The method of any one of the preceding claims, characterized by the fact that several master devices are simultaneously present on the same channel of communication, each with its own unequivocal identification code stored in the associated transponders.

5. The method in claim 4, characterized by the fact that the reply from the transponders to step (e) includes the master's unequivocal identification code.

6. The method in claim 5, characterized by the fact that, before carrying out step (f), the master checks to ensure that its own unequivocal identification code corresponds to that contained in each reply signal and ignores said reply signals for which correspondence is not verified.

7. The method of any one of the preceding claims, characterized by the fact that said storage step (b) is operated by the user who presses a storage button (Pl) on the master (MST) after said entities (1,...,6) fitted with transponders (Tl,...,T6) have been placed close to the master (MST).

8. The method of any one of the preceding claims, characterized by the fact that said acoustic signal is silenced at the user's discretion by pressing a reset button (P2) on the master (MST).

9. The method of any one of the preceding claims, characterized by the fact that said entities (1,...,6) fitted with transponders (Tl,..., T6) are: things, or people, or animals, or plants or a combination of these.

10. The method of claim 1, characterized by the fact that said entities (1,...,6) fitted with transponders (T1,...,T6) are objects of personal use carried by the person to whom the master (MST) is attached.

11. Anti-theft device functioning according to the method in claim 1, characterized by the fact that the theft is signalled by an ^"acoustic and/or luminous warning that becomes activated in a portable master (MST) when, within a previously set scanning time, reception is lacking of an identification code of a transponder applied to an object included among the objects to be monitored fitted with transponders, said code belonging to a configuration stored in the master (MST).