Title of Invention

SYSTEM FOR ACCESS CONTROL FROM A DATA STATION TO MOBILE DATA CARRIERS

Abstract

The present invention provides a system for access control from a data station to mobile data carriers. A check is carried out to determine whether two different bit values are received at one bit position in the identification numbers which are transmitted synchronously by the data carriers. In order to continue the arbitration, those data carriers are selected which have a bit value, which is predetermined by the data station, in the identification number at that bit position. FSK modulations is expediently used for transmission of the bit values in the identification numbers. Filter means are provided in the receiving equipment in order to split the received signal between the frequencies assigned to the bit values, in order to identify the simultaneous reception of different bit values at one bit position.

Full Text

-1A- The invention relates to a system for access control from a data station to at least two mobile data carriers. The invention furthermore relates to a mobile data carrier and a data station as well as to a system comprising mobile data carriers and a data station for carrying out the method. In the case of mobile data carriers, in particular those which communicate with a data station without direct contact, a plurality of data carriers may be located in the reception area of the data station. Measures therefore have to be provided in order that, during data traffic from the data station to one of the mobile data carriers, a collision is avoided with other data carriers which are located in the reception area. In principle, arbitration methods have been used until now in wire-based bus systems. These arbitration methods, in particular the arbitration method which is known from the so-called CAN bus, are predicated on the connected bus subscribers also being able to receive and evaluate messages transmitted between one another. Since, in contrast to a wire-based bus subscriber, a mobile data carrier has a quite low transmission power, which is not sufficient for reception of the message by other mobile data carriers, these arbitration methods which are known from wire-based bus systems cannot be applied directly to mobile data carriers. In addition, these arbitration methods require complex control measures in each bus subscriber. The literature reference IBM Technical Disclosure Bulletin, Volume 37, No, 04B, April 1994, pages 235 - 237 discloses a data transmission system for the automatic identification of vehicles. A base station transmits a signal at a predetermined frequency, as a result of which the vehicles are caused to register, with a multiple 95 P 1726 - 2 - access protocol being processed. The mobile stations have a transmission channel in order to transmit their identification designations to the base station. The multiple access protocol takes account of the case when more than one vehicle accesses the same transmission channel. After registration has been carried out, a confirmation is given to the vehicles by the base station. The literature reference "Identifikationssysteme und kontaktlose Chipkarten" [Identification systems and smart cards without direct contact], GME Specialist Report 13, VDE Press Berlin and Offenbach, 1994 discloses various implementation options for data carriers and base stations for data transmission without direct contact. A data carrier operating on the principle of frequency-shift keying (FSK) is described on page 11. FSK being modulated onto a carrier by means of switches is described on page 16. Pages 25 and 29 disclose the data carrier containing an LC tuned circuit. A complete transmission system is illustrated on page 34, the data carrier module comprising two coil circuits whose output signal is supplied to a phase demodulation device for data reception. The object of the invention is to specify a method for access control from a data station to at least two mobile data carriers, which system reliably prevents collisions and can be implemented easily. 2A This object is achieved by a system comprising at least two mobile data carriers and one data station, each mobile data carrier having - a tuned circuit for inductively coupled signal transmission to the data station, the oscillation of which tuned circuit can be modulated either with a signal at a first frequency or with a signal at a second frequency as a function of a bit, which is to be transmitted, of an identification tag, the data station having - a tuned circuit for inductive reception of signals which are transmitted from the data carriers, - filter means, which are coupled to the tuned circuit, for separating the received signal into a frequency range con taining the first frequency and a frequency range contai ning the second frequency, each frequency being assigned to one bit value in the identification tag, and - a control device which is coupled to the filter means and by means of which the reception of two different bit values located at the same bit position in the identifica tion tag can be confirmed, wherein - the data carriers transmit an identification tag synchro nously on request of the data station and, - if two different bit values have been confirmed by the con trol device as having been received at at least one bit po sition in the identification tag, only a data carrier, who se identification tag has a bit value defined by the data station at the bit position, transmits at least a part of the identification tag once again on request by the data station. - 95 P 1726 - 3 - invention, "monitoring" of the data traffic between mobile data carriers and the data station by another data carrier is unnecessary. The control measures for the arbitration are essentially arranged in the data station. If two different bit values are detected by the data station at one bit position in the identification tag transmitted by the data carriers, the further sequence of the arbitration method is continued using a bit value defined by the data station. If one bit value is always given priority, a priority rule results between the data carriers, which priority rule depends on the identification tag. An instruction which is transmitted from the data station to the data carriers then advantageously need not contain any variable elements for the bit value defining the further course of the arbitration. Alternatively or in addition to this, it can be provided for the bit value to be set as a function of the signal field strength for the continuation of the arbitration method. If reception of a signal is weak, this means that the data carrier has either just entered the reception area or is leaving it again. The reception connection between the data station and the data carrier then either becomes even better or is probably interrtipted. It is therefore advantageous to give priority in the arbitration to that data carrier whose signal is received more strongly. Once a bit value for the further interrogation of the identification tags has been defined in this way, the data station transmits an instruction by means of which the other data carriers, which do not have the defined bit value at this bit position, are changed to the passive state so that they no longer take part in the further data traffic for the time being. Once the arbitration method has been completed for a data carrier and the subsequent data traffic with this data carrier, the data station reactivates the arbitration method from the start with these other data carriers which have not yet been processed. The arbitration method is repeated until all the data carriers located in the reception area -4- of the data station have been processed. The arbitration method can be speeded up in that, when two different bit values of the identification tag are detected at one bit position, only that part after this bit position is used for the further transmission of the identification tags by the data carriers. In addition, after identification of the reception of different bit values at a bit position in the identification tag, the data station can interrupt its further transmission of the identification tag by means of an instruction which is transmitted to the data carriers. Frequency modulation is carried out for the bit values of the identification tag to be transmitted, in order to implement a data carrier and a data station. A first modulation frequency is assigned to a first logic state of a bit position in the identification tag, and a second modulation frequency (PSK - Frequency Shift Keying) is assigned to a second logic state. The FSK signal is modulated onto a carrier, for example by amplitude or phase modulation or a combination thereof. This is achieved, for example, by a component being connected to the coil of the tuned circuit in the data carrier via a switch which is clocked at the first frequency or at the second frequency. Depending on the component used, for example a resistor, diode or capacitor, and depending on the circuit type, for example a serial circuit or parallel circuit, the current and/or voltage on the coil is varied in time with the modulation frequency. In consequence, side bands which depend on the clock frequency are modulated onto the carrier. These side bands can be demodulated in a corresponding manner in the data station in order to recover the transmitted bit values. The reception carrier frequency is expediently used as the carrier, by means of which the tuned circuit of the data carrier is energized by the data station, or a sub-carrier, for example a signal obtained by division from the energized carrier. The reception circuits in the data station are - 5 - designed in such a manner that both modulation frequencies can be identified alongside one another, in order to confirm the presence of two different bit values at one bit position in the identification tag. To this end, the received signal is expediently filtered by one bandpass filter acting at the first modulation frequency and by another bandpass filter acting at the second modulation frequency, and is subsequently compared with a threshold. A control device determines therefrom the presence of two different bit values at one bit position in the identification tag. The control device advantageously also evaluates the reception level of the first frequency or second frequency, in addition, in order to control the further course of the arbitration method as a function thereof. The invention is explained in more detail in the following text with reference to the figures which are illustrated in the accompanying drawing and in which: Figures 1 (a) to (d) show bit patterns for identification tags of various data carriers and bit patterns received in the data station relating to specific method sections, and Figure 2 shows a circuitry implementation for a data carrier and a data station. A data carrier for message traffic without direct contact, and having one data station is, for example, a smart card without direct contact. It contains a tuned circuit 50 (Figure 2) which is inductively coupled to a tuned circuit 60 in the data station 61. The data carrier 51 obtains its power supply from the signal which is emitted from the tuned circuit 60. Carrier frequencies and clock frequencies in the data carrier 51 are likewise derived from the signal emitted by the data station 61. Each of the three data carriers which are illustrated symbolically in Figure 2 has a unique identification number which is assigned only to it and is normally stored by the manufacturer. The ID numbers thus differ at at least one bit position. Figure 1 (a) shows three examples of 8-bit long ID numbers. In practice, the ID - 6 - number will be considerably longer because of a very high number of data carriers. In order to carry out arbitration, that is to say prioritization in the processing of the data carriers 51 by the data station 61, an instruction is transmitted by the data station 61, which instruction can be received by all the data carriers located in the reception area of the data station, as a result of which the data carriers are caused to transmit their ID numbers. The transmission of the ID numbers is carried out synchronously for all the data carriers, on the basis of the clock coupling to the transmission frequency of the data carrier 61. The bit sequence in Figure 1 (b) is then received in the data station. As is explained in more detail below, the data station 61 is designed such that it can simultaneously identify different bit values "1" and "0" at a bit position. Two logic states "1" and "0" are identified simultaneously at the third bit position in the received data according to Figure 1 (b) . This is a result of the fact that the three ID numbers according to Figure 1 (a) both have logic states at the third bit position. Both states are also received in a corresponding manner at the sixth, seventh and eighth bit positions. After the reception of both logic states at the third bit position has been identified in the data station, a bit value is defined for the further communication in the course of the arbitration method, which bit value the ID cards, with which the arbitration will be continued, must have. In the present case, arbitration is continued with those ID cards which have a "1" at the third bit position in the ID number. The other ID cards, specifically those which have a "0" at the third bit position in their ID number, are changed to a passive state by an instruction from the data station, so that they no longer take part in the further course of this arbitration method, until a single data carrier has been selected and the data traffic with this data carrier has been completed. The other data carriers are then reactivated again by an instruction from the data - 7 - station. The data carriers having the bit value "1" at the third bit position are requested by the data station to transmit their ID numbers once again. Different bit values are now received at the sixth bit position. Once again, that ID card which has the bit value "0" at the sixth bit position is changed to the passive state by the data station; the communication is continued with the other card which has the bit value "1" there, the data station once again requesting the ID card to transmit its ID number. There is now no ambiguity at any bit position in the received ID data (Figure 1 (d)) . There is now only a single data carrier which is still activated. The data station now carries out the desired message traffic with the said data carrier. After completion of the data traffic, this data carrier is deactivated as having been processed and the other data carriers are reactivated. A further data carrier is selected for message communication, using the same arbitration method. The data station acts as a so-called master during the arbitration method. According to a development, if two different bit values are received, according to Figure 1 (b) , at the third bit position, the transmission of the other bit positions 4 to 8 is interrupted by the data station, by means of an instruction. In addition, after the identification of different bit values at the third bit position in the case of Figure 1 (c), the data carriers can be caused subsequently to transmit only the bit values of bit positions 4 to 8 or, in the case of Figure 1 (d), only the bit values of bit positions 7 to 8. This speeds up the arbitration method. In the case of the selection of the bit value "1" or "0" for the continuation of the arbitration method after the identification of an ambiguity at a bit position, one of the logic states can be specified unconditionally by the data station. This results in an automatic priority rule depending on the ID number. In addition or alternatively, it is expedient to select that bit value which supplies the higher reception level and thus, from experience, can currently carry out the most - 8 - reliable and the least disturbed transmission and reception operation. In the case of the outline circuitry illustration of one of the data carriers 51 and of the data station 61, only those circuit units are indicated which are essential in the context of the invention. In particular, reception and evaluation devices in the data carrier 51, as well as transmission devices in the data station 61, are not illustrated, for the sake of simplicity. The data carrier 51 contains a transmission tuned circuit 50, which contains a coil 52. A resistor 53 can be connected in parallel with the coil 52, clock-controlled via a switch 54. The switch 54 is switched on and off in a clock manner by a control device 55. The switching signal emitted by the control device 55 is at a first switching frequency f1 when a bit value "0" is to be transmitted, and is at a second switching frequency f2, which differs from the first switching frequency, when a bit value "1" is to be transmitted. As a result of the resistor 53 being connected in parallel with the coil 52 of the tuned circuit 50 in a clocked manner, side bands are modulated onto the transmission carrier with which the tuned circuit is fed. The modulated frequencies in this case differ corresponding to the bit value "0" or "1" to be transmitted. A large number of other electronic components are possible instead of the resistor 53, preferably capacitors or else non-linear elements such as diodes, which produce a distortion factor and thus side bands at multiples of the carrier frequency. The carrier frequency transmitted by the data station can be used as the carrier frequency. A frequency which differs from the carrier of the data station but is derived from it, for example by division, a so-called sub-carrier, is advantageously used. The modulation frequencies f1 and f2 must be located with respect to the carrier in such a manner that the desired bit rate for the data transmission can be achieved. The data station 61 can be arranged to be stationary, in a fixed position, or, for its part, can - 9 - also be mobile, for example as a handset. The data carriers 51, in contrast, are always freely mobile. The data station 61 contains a receiving tuned circuit 60 with a tuned-circuit coil 62. The received signal is selected, converted into baseband and amplified by means of a conventional receiver 63 . The received signal is fed for demodulation of the bit values "0" and "1" to a first filter 64, which filters out signals at the first frequency fl, and to a second filter 65, which filters out signals at the second frequency f2. A threshold detector 66 or 67, respectively, is connected downstream from each of the filters 64, 65. In this way, both reception states "0" and "1" for a bit position can be detected simultaneously in the case of the ID numbers transmitted synchronously by the data carriers. The output signals of the detectors 66, 67 are evaluated in a control device 68 for the presence of the "1", "0" or "1/0" state. The control device 68 also defines the bit values with which the arbitration method is continued when different bit values "l/0n are detected at a bit position. In order to continue with that bit value which has the higher reception level, the detectors 66, 67 also report to the control device 68 information about the respective reception level. To this end, the level values are compared with one another in the control device 68, that bit value "I" or "0" being selected which has the higher reception level. We Claim: 1- System for access control from data station to mobile data carriers comprising at least two mobile data carriers 151) and one data station (61), each mobile data carrier having - a tuned circuit (50) for inductively coupled signal transmission too the data station (61), the oscillation of which tuned circuit (50) can be modulated either with a signal at a first frequency(f )or with a signal at a second frequency (f ) as 1 2 a fuction of at bit, wfaich is to be transmitted, of an identification tag, the data station having - a tuned circuit (60) for inductive reception of signals which are transmitted from the data carriers, - filter means (64,65) which are coupled to the tuned circuit (60), for separating the received signal into a frequency range containing the first frequency (f ) and a frequency range 1 containing the second frequency (f ), each frequency being 2 assigned to one bit value in the identification tag, the data carriers (51) being constructed to transmit an identification tag synchronously on request of the data station, and - a control device (68) which is coupled to the filter means (64,65) and by neans of which the reception of two different bit values located at tine same bit position in the identification tag can be confirmed, said control device (68) being constructed to control said data station (61) such that, if two different bit values have been confirmed by the control device (68) as having been received at at least one bit position in the identification tag, those data carriers (51) whose identification tag have a bit value different from the bit value defined by the data station (61) at the bit position, are changed to a passive state by an instruction from the data station and the data carriers (51) whose identification tag have at bit value defined by the data station (61) at the bit position are instructed by the data station (61) to transmit at least a part of the identificaion on tag once again. 2. System as claimed in claim 1, wherein once the reception of at least two bit values at one bit position has been confirmed by said data station (61), the transmission of the remaining bit positions of the identification tag from the mobile data carriers (51) is interrupted on request by the data station. 3. System as claimed in claim 1 or 2, wherein if two different bit values are confirmed as having been received in at least one bit position in the identification tag, those data carriers which contain a bit value at the bit position which differs from the defined bit value are caused by the data station not to carry out any further data traffic until the data traffic with those data carriers which contain) the defined value has been completed. - 12 - 4. System as claimed in one of claims 1 to 3, wherein said data station {61) is configured to allow the data carriers (51) to transmit subsequently only those bit positions which are less significant or store significant than this bit position, if two different bit values are confirmed as having been received in at least one bit position in the identification tag. 5. System as claimed in claims I to 4, wherein the identification tag comprises logic states ("0", "l") which are transmitted in a frequency-modulated manner by the data carriers and that for each respective frequency range corresponding to a logic state a filtering process (f , f ) is applied to the 1 2 received signal in the data station. 6. System as claimed in one of claims 1 to 5, wherein a first frequency (f ) is assigned to a first logic state ("O"), that a 1 second frequency (f) is assigned to a second logic state and 2 that a carrier signal corresponding to the bit value to be transmitted is modulated at the first frequency or at the second frequency. 7. System as claimed in one of claims 1 to 6, provided with a control unit (55) for transmitting a signal at a first frequency (f ) or a second frequency (f ) as a function of the bit ("0", 1 2 "1") to be modulated, and by a modulation device (54,53), which is actuated by the control unit (55) for action on the tuned circuit (50) for modulation of the carrier - 13 - 8. System as claimed in one of claims 1 to 7, wherein said tuned circuit (58) is provided with an inductance (52) and an element (53) which can be connected via a switch (54) to the inductance (52) , said switch (54) being switched by the control device (55) at the frequency (f ) which is assigned to the first 1 bit value or at the frequency (f ) which is assigned to the 2 second bit value. 9. System as claimed in one of claims 1 to 8, provided with threshold value detectors (66,67), which are connected in each respective signal path between respective filter means (64,65) and the control device (68). 10. System as claimed in one of claims 1 to 9, wherein detection means (66,67) for detection of the reception level are connected in each respective signal path between the filter means (64,65) and the control device (68), and that the decision about the bit value to be defined is made by the control device (68) as a function of the reception levels. The present invention provides a system for access control from a data station to mobile data carriers. A check is carried out to determine whether two different bit values are received at one bit position in the identification numbers which are transmitted synchronously by the data carriers. In order to continue the arbitration, those data carriers are selected which have a bit value, which is predetermined by the data station, in the identification number at that bit position. FSK modulations is expediently used for transmission of the bit values in the identification numbers. Filter means are provided in the receiving equipment in order to split the received signal between the frequencies assigned to the bit values, in order to identify the simultaneous reception of different bit values at one bit position.

Documents:

01140-cal-1996-abstract.pdf

01140-cal-1996-claims.pdf

01140-cal-1996-correspondence.pdf

01140-cal-1996-description (complete).pdf

01140-cal-1996-drawings.pdf

01140-cal-1996-form-1.pdf

01140-cal-1996-form-2.pdf

01140-cal-1996-form-3.pdf

01140-cal-1996-form-5.pdf

01140-cal-1996-gpa.pdf

01140-cal-1996-priority document others.pdf

01140-cal-1996-priority document.pdf