COMMUNICATING WITH AN RFID TRANSPONDER

Abstract

An RFID device is provided for communicating with at least one RFID transponder that has a transmitter, a receiver, a transmission antenna and a reception antenna for emitting and receiving RFID signals and has a control and evaluation unit that is configured to transmit and receive an RFID signal in a respective one of a plurality of frequency channels, in particular to encode RFID information into the RFID signal and/or to read information from the RFID signal in accordance with an RFID protocol and to carry out an intensity adaptation of the RFID channel in dependence on the frequency channel used for the transmission and reception.

Claims

1. An RFID device for communicating with at least one RFID transponder that has a transmitter, a receiver, a transmission antenna and a reception antenna for emitting and receiving RFID signals and a control and evaluation unit that is configured to transmit and receive an RFID signal in a respective one of a plurality of frequency channels, wherein the control and evaluation unit is furthermore configured to carry out an intensity adaptation of the RFID signal in dependence on the frequency channel used for the transmission and reception.

2. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to encode RFID information into the RFID signal and/or to read information from the RFID signal.

3. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to encode RFID information into the RFID signal and/or to read information from the RFID signal in accordance with an RFID protocol,

4. The RFID device in accordance with claim 1, wherein the RFID device is configured for the UHF range in accordance with ISO 180000-6.

5. The RFID device in accordance with claim 4, wherein the frequency channels are fixed in the ETSI or FCC band.

6. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to adapt a transmission power of the transmission antenna in dependence on an antenna characteristic of the transmission antenna over the frequency channels.

7. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to adapt an amplification of the received RFID signal in dependence on an antenna characteristic of the reception antenna over the frequency channels.

8. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to recognize a measured intensity of the received RFID signal.

9. The RFID device in accordance with claim 8, wherein the control and evaluation unit is configured to recognize anan RSSI value.

10. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to carry out the intensity adaptation in the used frequency channel in dependence on an antenna characteristic of the RFID transponder

11. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to provide an intensity at least largely independent of the frequency channel used by means of the intensity adaptation.

12. The RFID device in accordance with claim 1, wherein the control and evaluation is configured to align the intensity adaptation to the weakest frequency channel.

13. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to determine the intensity of the received RFID signal on communication with an RFID transponder in different frequency channels.

14. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to determine a required intensity adaptation per frequency channel by parameterization to a type of RFID transponders.

15. The RFID device in accordance with claim 1, wherein the control and evaluation unit is configured to determine a required intensity adaptation per frequency channel by reading intensity adaptation information from an RFID transponder.

16. A method of communicating with at least one RFID transponder, in which method a transmitter emits an RFID signal via a transmission antenna in a respective one of a plurality of frequency channels and the RFID signal is received in a receiver via a reception antenna, wherein a piece of RFID information is encoded into the transmitted RFID signal and/or is read from the received RFID signal, and wherein an intensity adaptation of the RFID signal is carried out in dependence on the frequency channel used for the transmission and reception.

17. The method in accordance with claim 16, wherein the piece of RFID information is encoded into the transmitted RFID signal and/or is read from the received RFID signal in accordance with an RFID protocol.

18. The method in accordance with claim 16, wherein a required intensity adaptation per intensity channel is determined in advance by determining the intensity of the received RFID signal in different frequency channels.

Description

[0026] The invention will be explained in more detail in the following also with respect to further features and advantages by way of example with reference to embodiments and to the enclosed drawing. The Figures of the drawing show in:

[0027] FIG. 1 a schematic overview representation of an RFID device having a plurality of RFID transponders in reading range;

[0028] FIG. 2 an exemplary frequency characteristic of an RFID transponder;

[0029] FIG. 3 a comparison of the frequency characteristics of different RFID transponders; and

[0030] FIG. 4 a schematic representation of an embodiment of an intensity adaptation in different frequency channels.

[0031] FIG. 1 shows a schematic overview representation of an RFID device 10 and of an RFID transponder 12 arranged in an exemplary manner in its reading range. The RFID device 10 in this embodiment has a respective separate transmission antenna 14a and reception antenna 14b, wherein a transmitter 16a emits an RFID signal via the transmission antenna 14a or a receiver 16b again receives the RFID signal 14d via the reception antenna. The separation at the hardware side into a transmission channel and a reception channel is also practically conceivable, but primarily serves for the conceptional representation to separately explain the effects at the transmission and reception sides. In other embodiments, a common transmission/reception antenna replaces the individual transmission antenna 14a and reception antenna 14b and/or a transceiver replaces the transmitter 16a and receiver 16b.

[0032] A control unit 18, for example having a digital module such as a microprocessor or an FPGA (field programmable gate array) controls the routines in the RFID device 10 and is able to encode RFID information into an RFID signal or to read RFID information from an RFID signal. A wired or wireless connector 20 serves to integrate the RFID reading apparatus 10 into a higher ranking system.

[0033] In detail, the communication preferably takes place in accordance with a known RFID protocol, in particular ISO 18000-6 or EPC Generation-2 UHF RFID, and the steps and components required for this are known per se. The exact setup of the RFID reading device 10 beyond the rough functional blocks is equally considered known that is in another respect only shown purely schematically in this form and can alternatively adopt any other arrangement known per se of the explained elements.

[0034] RFID communication takes place on one frequency channel from a plurality of frequency channels. For example, 15 frequency channels are provided in the ETSI band from 865 to 868 Hz and 52 frequency channels in the FCC band from 902 to 928 MHz The transmitted and received intensity of the RFID signal and thus the reading range vary with the frequency and therefore differ in the frequency channels. There are a plurality of possible reasons for this frequency behavior. They include the frequency characteristic of the transmission antenna 14a, the reception antenna 14b, and the transponder antenna of the RFID transponder 12. The specific application environment and the arrangements of the RFID device 10 and the RFID transponder 12 and its material can have an effect on the frequency behavior.

[0035] FIG. 2 shows by way of example the reading range in dependence on the frequency of the RFID signal for an RFID transponder having a metal substrate (on-metal) for the FCC band. The maximum reading range is achieved at approximately 905 MHz with this transponder, with a reading range of approximately 6.5 m. A maximum at 915 MHz would be better suited for an optimum coordination with the FCC band since the reading range drops to approximately 4 m at the upper end of the FCC band.

[0036] Only the total curve ca be rescaled upwardly or downwardly by conventional only across-the-board adaptation of the transmission power. This then either results in reading failures in weak frequency channels or in excess ranges in strong frequency channels. In accordance with the invention, an intensity adaptation per frequency channel is in contrast made possible by which the curve is flattened. A uniform reading range in all the frequency channels can thus be achieved. The intensity, signal strength, and reading range are coupled to one another. When an intensity adaptation is spoken of in the following, it means an adaptation of the coupled parameters without wording this separately at every point.

[0037] The frequency dependence of the intensity is in part based on properties of the RFID device 10, in particular an antenna characteristic of the transmission antenna 14a and the reception antenna 14b. The RFID transponder contributes a further portion whose transponder antenna likewise has antenna characteristic so that more or less intensity is also returned for this reason depending on the current frequency channel.

[0038] FIG. 3 shows for this purpose in a similar representation to FIG. 2 the reading range in dependence on the frequency for a plurality of different RFID transponders. The dashed curve corresponds to a well-coordinated ETSI transponder. There would be little need for action here; the curve is already per se largely flat within the ETSI band. However, this RFID transponder in the FCC band would only be readable at short ranges and less suitable for this purpose. The solid curve corresponds to an RFID transponder that attempts a compromise for a global coordination between the ETSI band and the FCC band, but only at the price of very high variations over the frequency channels. There is in particular a fall of the reading range in the FCC band from 7 m to 3.5 m. The dotted curve reduces this effect a little, but still shows values between 6.5 m and 4.5 m in the FCC band. A transponder for the FCC band could be added from FIG. 2, but it still shows a drop from 6.5 m to 4 m despite the close coordination with the FCC band.

[0039] The control and evaluation unit 18 can first compensate the frequency characteristic of its own antennas 14a-b to find a suitable intensity adaptation. The frequency characteristic for a specific type of RFID device 10 is known from the development so that the transmission power can be lowered or increased as compensation depending on the frequency channel. A further conceivable measure is an adaptation of the receiver-side amplification or a calculatory receiver-side compensation, for example by correcting an RSSI value. The frequency characteristic of the RFID transponder 12 can likewise be known from a datasheet or can be measured per type and then correspondingly compensated.

[0040] It is furthermore conceivable to measure the RFID system from the RFID device 10 and RFID transponder 12 in that communication takes place with a fixed transmission energy with a specific RFID transponder sequentially over the different frequency channels and the received intensity is measured. Curves such as those of FIGS. 2 and 3 can thereby be empirically determined. Such measurements can be carried out individually for a specific RFID system, even at its application site, but alternatively also in the lab for a specific type of RFID device 10 and/or RFID transponder 12. In an embodiment, a teaching or calibration phase in which these measurements are carried out is provided for this purpose. This is alternatively done very independently in advance and the results for a certain type of RFID transponder 12 are stored. The RFID device 10 can then later be parameterized for this, that is the transponder type can be set. In a further alternative, the RFID transponder 12 itself also communicates the information required for the intensity adaptation by means of RFID communication.

[0041] The relative strengths of the frequency channels are thus known and they can be corrected to a common level. There is still the freedom to select this common level. There are again different possibilities for this, for instance use of the maximum permitted transmission energy with the result of a maximum reading range that the weakest channel determines, but without an excess range being forced on the other channels as in the prior art. The common level is preferably coordinated such that the weakest channel achieves a specific reading range, as explained now for an exemplary specific embodiment.

[0042] FIG. 4 schematically shows the intensity adaptation in eight frequency channels by way of example here. The weakest frequency channel fixes the common level with which a desired reading range can be achieved. For this purpose, the transmitter power varies on communication over the weakest frequency channel until stable communication with an RFID transponder 12 is possible in the reading range.

[0043] The intensity is lowered or the RSSI corrected in accordance with the known frequency characteristic in all other frequency channels, as indicated by arrows. The desired reading range is thereby also only reached here and an excess width is avoided. The dependence of the intensity and thus of the reading range on the respectively used frequency channel is eliminated. In this respect, a complete leveling as in FIG. 4 is only the desired ideal state, even an only partial flattening already represents a considerable advantage.

[0044] FIG. 4 only shows a preferred embodiment. It would be conceivable even intentionally to deviate from the flattening shown, for example to have a frequency channel available that has a higher reading range as necessary. It is furthermore admittedly advantageous, but not necessary to align the common level to the weakest channel.