Radio transponder and method for data transmission between a radio transponder reader and the radio transponder

A radio transponder and method for data transfer between a radio transponder reading device and the radio transponder, wherein a control unit of the radio transponder controls a change in a load impedance via a control signal having a selected switching pulse frequency and a selected switching pulse quantity to produce a response signal, where the control unit codes multiple-valued at least ternary symbols into the control signal, and where symbol values are assigned to respective switching pulse sequences each having a unique combination of switching pulse frequency, switching pulse number and phase shift such that only combinations for which the quotient of switching pulse number and switching pulse frequency lies within a predefined value range are selected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2019/065811 filed 17 Jun. 2019. Priority is claimed on European Application No. 18185432.4 filed 25 Jul. 2018, the content of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio transponder and method for data transmission between a radio transponder reader and the radio transponder.

2. Description of the Related Art

Radio transponders may be, for example, RFID (radio-frequency identification) tags that are fitted to respective items in order to identify or locate them. RFID tags comprise a memory unit, the content of which can be read, but also altered, via an RFID reader. RFID tags usually each store at least one identifier. In order to read information stored in RFID tags, RFID readers each transmit a request signal by generating an electromagnetic alternating field. This electromagnetic alternating field is firstly used to supply power to, in particular passively operated, RFID tags that have no power source of their own. The electromagnetic alternating field is secondly modulated by RFID tags, such as via load modulation or by varying their antenna impedance, in order to transmit a response signal.

Radio transponder systems for industrial automation systems must meet particular requirements with respect to reliable data transmission, authenticity of transmitted data and insensitivity toward jamming transmitters. Industrial automation systems are used for monitoring, controlling and regulating technical processes, in particular in the field of production. As such, process and buildings automation, perturbed or manipulated radio transponder systems can have serious consequences, where interruption of an automation system can occur in the worst case.

U.S. Pat. No. 9,112,543B2 discloses a radio transponder system in which a signal for supplying power to a communication device is transmitted during one time period. During a second time period, a data signal is transmitted to the communication device based on phase shift keying, frequency shift keying or quadrature amplitude modulation. A larger Q factor is selected for an antenna system that is used during the first time period than during the second time period.

U.S. Pat. No. 7,932,813B2 describes an RFID system having an RFID reader that uses synchronized sampling to receive a modulation signal from an RFID tag, specifically irrespective of whether the RFID tag uses amplitude shift keying, frequency shift keying or phase shift keying for this purpose. A modulation signal generated by the RFID tag comprises one or more subharmonics of an electromagnetic field generated by the RFID reader, where the RFID reader performs synchronized sampling around the frequency of the electromagnetic field. This cushions a loading by the modulation signal on the electromagnetic field generated by the RFID reader.

In HF-RFID systems, a data transmission from a transponder to a reader/writer is usually effected by virtue of an RF carrier signal, which is simultaneously used for supplying power to the transponder, having its amplitude changed by connecting an additional load resistor. This is accomplished by using a control signal that has a selected control signal auxiliary carrier frequency and a selected number of control pulses or oscillations. Reducing the number of control pulses or increasing the control signal switching frequency allows a data rate increase in principle. However, this leads to a shorter range for the data transmission from transponders to readers/writers or to increased sensitivities toward interference. Specifically, under application conditions in industrial automation systems, a reduction in the number of control pulses is critical in regard to an associated loss of redundancy.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention to provide a radio transponder and method for data transmission between a radio transponder reader and the radio transponder that allows an increased data rate from the radio transponder to the radio transponder reader without limitations in regard to range or reliability.

This and other objects and advantages are achieved in accordance by the invention by radio transponder and a method for data transmission between a radio transponder reader, in particular a radio transponder reader/writer, and the radio transponder, where the radio transponder reader modulates at least one control command onto a stipulated radio carrier signal and transmits the modulated radio carrier signal to the radio transponder. By way of example, the radio transponder reader can code the control command and subsequently modulate it onto the stipulated radio carrier signal. The radio transponder receives the modulated radio carrier signal via an inductive antenna arrangement to which a load modulation unit is connected that comprises a variable load impedance. A control unit of the radio transponder generates a response signal by controlling a change of the load impedance via a control signal that has a selected switching pulse frequency and a selected number of switching pulses.

In accordance with the invention, the control unit codes multi-value, at least ternary, symbols into the control signal. Symbol values are respectively assigned to switching pulse sequences that each have a unique combination of switching pulse frequency, number of switching pulses and phase shift. Only combinations whose quotient of number of switching pulses and switching pulse frequency is within a stipulated range of values are selected. The symbols coded into the control signal therefore comprise an increased information content, which results in an increased data rate. In particular, this is possible without increasing the switching pulse frequency and without reducing the number of switching pulses. The increased data rate thus has no adverse effects on range or interference immunity or redundancy. The symbols are preferably coded using at least a first and a second switching pulse frequency, a first and a second number of switching pulses and a first and a second phase shift.

In accordance with an advantageous embodiment of the present invention, the symbols are coded using at least a first and a second switching pulse frequency and a first and a second number of switching pulses. A quotient of first number of switching pulses and first switching pulse frequency and a quotient of second number of switching pulses and second switching pulse frequency differ from one another by no more than 10%. The data rate therefore remains relatively constant regardless of the respectively coded symbol value.

In addition to the aforementioned symbol values that are respectively assigned to switching pulse sequences having a unique combination of switching pulse frequency, number of switching pulses and phase shift, precisely one symbol value is preferably used that has an assigned tiny switching pulse sequence. This tiny switching pulse sequence deactivates a load modulation for a stipulated period. This stipulated period is advantageously within the stipulated range of values of the quotient of number of switching pulses and switching pulse frequency. In particular, the control unit can use the switching pulse sequences assigned to the symbol values to control a load modulation using combined frequency shift keying, phase shift keying and modulation deactivation.

In accordance with a preferred embodiment of the present invention, the control signal has essentially square-wave pulses or temporarily no signal strength. In particular, the square-wave pulses preferably each have a pulse duration that corresponds to half of one period duration. This allows simple and reliable demodulation at the reader.

The control unit advantageously assigns the symbol values to switching pulse sequences in accordance with a code table stored in a memory unit of the radio transponder. The radio transponder reader also stores a corresponding code table. Furthermore, selected symbol values can represent control commands for data flow control between the radio transponder reader and radio transponder, for collision detection during simultaneous transmission attempts by multiple radio transponders and/or for identification of a start or end of a data frame. This allows a further improvement in reliability and efficiency for the data transmission.

The radio transponder in accordance with the invention is intended to perform the method in accordance with the above-disclosed embodiments and comprises an inductive antenna arrangement configured to receive a modulated radio carrier signal, transmitted by a radio transponder reader, which comprises at least one control command modulated onto a radio carrier signal. Additionally, the radio transponder has a load modulation unit, connected to the antenna arrangement, which comprises a variable load impedance. Furthermore, control unit is provided which is configured to generate a response signal by controlling a change of the load impedance via a control signal that has a selected switching pulse frequency and a selected number of switching pulses. In addition, the control unit is configured to code multi-value, at least ternary, symbols into the control signal.

In accordance with the invention, the radio transponder is configured to respectively assign symbol values to switching pulse sequences that each have a unique combination of switching pulse frequency, number of switching pulses and phase shift. Only combinations whose quotient of number of switching pulses and switching pulse frequency is within a stipulated range of values are selectable.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The radio transponder system schematically depicted inFIG. 1comprises a radio transponder reader/writer200and a radio transponder100inductively couplable thereto. Accordingly, the radio transponder100and the radio transponder reader/writer200each have an inductive antenna arrangement101,201. The antenna arrangements101,201are therefore depicted as inductances coupled to one another inFIG. 1. The radio transponder reader/writer200in the present exemplary embodiment additionally comprises a data input202for receiving control commands to be transmitted to the radio transponder100, a modulation unit203, a demodulation unit204and a data output205for providing information read from the radio transponder100. In the present exemplary embodiment, the radio transponder100is an RFID tag. Accordingly, the radio transponder reader/writer200is an RFID reader/writer.

The radio transponder100comprises a load modulation unit formed by a load impedance102and by a control unit104for the load impedance102. Additionally, the radio transponder100has a memory unit105that can be read or written to via the radio transponder reader/writer200. The memory unit105stores at least one identifier assigned to the radio transponder100, which identifier is not usually changed. The control unit105and the memory unit105in the present exemplary embodiment are integrated in a circuit110that comprises both units.

The radio transponder100additionally comprises a capacitor arrangement103arranged in parallel with the antenna arrangement101and the load impedance102. The capacitor arrangement103is preferably variable with respect to its capacitance and in particular forms a tunable resonant circuit with the antenna arrangement101. To adjust its capacitance, the capacitor arrangement103can have, for example, a plurality of capacitors arranged in parallel with one another that are each arranged in series with a fuse and can be disconnected via the respective fuse to tune the resonant circuit. In the present exemplary embodiment, the radio transponder100is operated passively, i.e., the transponder100has no power supply of its own, but rather is supplied with power via an electromagnetic alternating field generated by the radio transponder reader/writer200.

For the purpose of data transmission between the radio transponder reader/writer200and the radio transponder100, the radio transponder reader/writer200uses its antenna arrangement100to generate an electromagnetic alternating field that comprises at least one carrier frequency selected on the radio transponder reader/writer200. In particular, the radio transponder reader/writer200modulates at least one coded control command onto a radio carrier signal at the selected carrier frequency and transmits the modulated radio carrier signal1to the radio transponder100.

The radio transponder100receives the modulated radio carrier signal1via its inductive antenna arrangement101and uses its control unit104to decode the control command transmitted by the radio transponder reader/writer200. To generate a response signal2, the control unit104of the radio transponder100controls a change of the load impedance102via a control signal141. In this manner, the radio transponder100codes and modulates its response into the electromagnetic alternating field generated by the radio transponder reader/writer200, specifically by changing the field via load modulation.

The variable load impedance may, in the simplest case, be provided by a switchable load resistor, for example. Here, the control unit104of the radio transponder100generates the response signal2by controlling connection of the load resistor via the control signal141. When the load resistor is connected, the radio transponder100consumes an energy component of the electromagnetic alternating field generated by the radio transponder reader/writer200. This is detected by the radio transponder reader/writer200via its demodulation unit204. In this manner, the radio transponder reader/writer200can provide information read from the memory unit105of the radio transponder100, for example, at its data output204.

FIG. 2depicts a first switching pulse sequence11for the control signal141by way of illustration, where the control signal has a selected switching pulse frequency f1and a selected number of switching pulses n1(in this case: 4). This results in a symbol duration T1=n1/f1for the first switching pulse sequence that is the reciprocal of a possible data rate. An actual data rate is normally lower than this possible data rate if additional coding rules, for example, Manchester coding or pulse position coding, are also taken into consideration. These additional coding rules firstly provide opportunities for detecting transmission errors. The additional coding rules can secondly allow further functionalities, such as collision detection or insertion of additional redundancy for increased data transmission security.

Based on the first switching pulse sequence11shown inFIG. 2and further switching pulse sequences10,12,13depicted inFIG. 3, the control unit104codes symbols that each represent one of multiple values into the control signal141. In any event, the coded symbols are at least ternary, i.e., the coded symbols have 3 values. In the present exemplary embodiment, quaternary symbols are used, which can assume U, V, W or X as symbol values and therefore have an information content of 2 bits. The control unit104assigns the symbol values U-X to the switching pulse sequences10,11,12,13in accordance with a code table stored in the memory unit105of the radio transponder100. A corresponding code table is also stored in the radio transponder reader/writer200. The first switching pulse sequence11has the symbol value V assigned to it in the code table, for example, while a second switching pulse sequence12is assigned the symbol value W, a third switching pulse sequence13is assigned the symbol value X and a fourth switching pulse sequence10is assigned the symbol value U.

In the present exemplary embodiment, the first to third switching pulse sequences11,12,13each have a unique combination of switching pulse frequency f1, f2, f3=f1, number of switching pulses n1=4, n2=5, n3=4 and phase shift φ1=0°, φ2=0°, φ3=180°. Only combinations whose quotient of number of switching pulses niand switching pulse frequency fiis within a stipulated range of values Dmin−Dmaxare admissible. The symbols are preferably coded using at least a first (f1=f3) and a second (f2) switching pulse frequency and also a first (n1=n3) and a second (n2) number of switching pulses, the quotients n1/f1=n3/f3, n2/f2of which differ from one another by no more than 10%. In this manner, the possible data rate remains sufficiently constant in each case.

The fourth switching pulse sequence10assigned to the symbol value U is a tiny switching pulse sequence that comprises no switching pulses. This tiny switching pulse sequence deactivates a load modulation for a stipulated period that is within the stipulated range of values Dmin−Dmaxof the quotient of number of switching pulses niand switching pulse frequency fi. The control signal141thus either comprises essentially square-wave pulses or temporarily has no signal strength. In the present exemplary embodiment, the square-wave pulses each have a pulse duration that corresponds to half of one period duration (duty factor 50%). All in all, the control unit uses the switching pulse sequences10,11,12,13assigned to the symbol values U-X to control a load modulation using combined frequency shift keying, phase shift keying and modulation deactivation.

It is fundamentally possible for selected symbols to represent control commands for data flow control between the radio transponder reader/writer200and the radio transponder100, for collision detection during simultaneous transmission attempts by multiple radio transponders and/or for identification of a start or end of a data frame.

FIG. 4is a flowchart of the method for data transmission between a radio transponder reader100and a radio transponder200.

The method comprises modulating, by the radio transponder reader200, at least one control command onto a radio carrier signal and transmitting the modulated radio carrier signal1to the radio transponder100, as indicated in step410.

Next, the radio transponder100receives the modulated radio carrier signal1via an inductive antenna arrangement101, as indicated in step420. In accordance with the invention, a load modulation unit comprising a variable load impedance102is connected to the inductive antenna arrangement101.

Next, a control unit104of the radio transponder100generates a response signal2by controlling a change of the load impedance102via a control signal141having a selected switching pulse frequency and a selected number of switching pulses, as indicated in step430.

Next, the control unit104codes multi-value, at least ternary, symbols into the control signal141, as indicated in step440.

Next, respective symbol values U-X are assigned to switching pulse sequences10,11,12,13each having a unique combination of switching pulse frequency, number of switching pulses and phase shift, as indicated in step450. In accordance with the invention, only combinations whose quotient of number of switching pulses and switching pulse frequency is within a stipulated range of values are thus selected.