INTERMODULATION MITIGATION TECHNIQUE IN AN RFID SYSTEM

• US 20140347167A1
• Filed: 08/12/2014
• Published: 11/27/2014
• Est. Priority Date: 05/26/2005
• Status: Active Grant

• Current Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Original Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Inventors: TIERNAY, Robert W.
• Granted Patent: US 9,558,383 B2
• Time in Patent Office: Days
• US Class Current: 340/10.2
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures
• CPC Class Codes: G06K 7/10009 sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
• CPC Class Codes: G06K 7/10019 resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08
• CPC Class Codes: G06K 7/10069 the collision being resolved in the frequency domain, e.g. by hopping from one frequency to the other frequency hopping or spread spectrum techniques H04B7/00
• CPC Class Codes: G06K 7/10475 arrangements to facilitate interaction with further interrogation devices, e.g. such that at least two interrogation devices may function and cooperate in a network of such devices
• CPC Class Codes: G07B 15/063 using wireless information transmission between the vehicle and a fixed station identification of vehicles G08G
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

When multiple readers for RF transponders have to be placed in close proximity, such as in adjacent lanes of a highway toll barrier, they can be set to operate at different frequencies. When signals from two adjacent ones of the readers interfere, the resulting signal includes interference terms whose frequencies equal the sum of the reader frequencies and the difference between the reader frequencies. To remove such interference terms while passing the desired terms, a tag includes a low-pass or other frequency-selective filter.

Claims

1. A reader for supplying an interrogation signal to a transponder at a first frequency and receiving a response signal from the transponder at the first frequency, while mitigating interference effects from an interfering signal at a second frequency, the reader comprising:

an antenna for receiving the response signal from the transponder;

a detector, in electrical communication with the antenna, for detecting and outputting a baseband analog signal representing the response signal received by the antenna;

a frequency-selective filter, in electrical communication with the detector to receive the baseband analog signal output by the detector, for performing frequency-selective filtering of the baseband analog signal to output an analog signal with reduced interference; and

signal processing circuits, in electrical communication with the frequency-selective filter to receive the analog signal with the reduced interference, for performing signal processing on the analog signal with the reduced interference to extract information from the analog signal with the reduced interference.

2. The reader of claim 1, wherein the frequency-selective filter comprises a low-pass filter.

3. The reader of claim 2, wherein the low-pass filter has a cutoff frequency which is less than a difference between the first frequency and the second frequency.

4. A system for supplying interrogation signals to transponders and receiving response signals from the transponders, the system comprising:

a plurality of readers at a plurality of locations in the system for supplying the interrogation signals and receiving the response signals, each of the plurality of readers operating at a different frequencies;

each of the plurality of readers comprising;

an antenna for receiving the response signal from the transponder;

a detector, in electrical communication with the antenna, for detecting and outputting a baseband analog signal representing the response signal received by the antenna;

a frequency-selective filter, in electrical communication with the detector to receive the baseband analog signal output by the detector, for performing frequency-selective filtering of the baseband analog signal to output an analog signal with reduced interference; and

signal processing circuits, in electrical communication with the frequency-selective filter to receive the analog signal with the reduced interference, for performing signal processing on the analog signal with the reduced interference to extract information from the analog signal with the reduced interference.

5. The system of claim 4, wherein, in each of the readers, the frequency-selective filter comprises a low-pass filter.

6. The system of claim 5, wherein the low-pass filter has a cutoff frequency which is less than a difference between the frequency at which the reader operates and the frequency at which an adjacent one of the readers operates.

7. The system of claim 4, wherein the plurality of locations are locations in a highway toll barrier.

8. A method for receiving a response signal from a transponder at a first frequency, while mitigating interference effects from an interfering signal at a second frequency, the method comprising:

(a) receiving the response signal from the transponder;

(b) detecting and outputting a baseband analog signal representing the response signal received by the antenna;

(c) performing frequency-selective filtering of the baseband analog signal to output an analog signal with reduced interference; and

(d) performing signal processing on the analog signal with the reduced interference to extract information from the analog signal with the reduced interference.

9. The method of claim 8, wherein step (c) is performed using a low-pass filter.

10. The method of claim 9, wherein the low-pass filter has a cutoff frequency which is less than a difference between the first frequency and the second frequency.

11. The method of claim 8, wherein:

steps (a)-(d) are performed using a first reader; and

the interfering signal is a signal from a second reader which is adjacent to the first reader.

12. The method of claim 11, wherein the first reader and the second reader are disposed in a highway toll bather.

13. A method for providing a plurality of transponder readers in a system, the method comprising:

(a) selecting a frequency of operation for each of the transponder readers;

(b) providing each of the transponder readers with a frequency-selective filter for reducing interference effects caused by signals from adjacent ones of the transponder readers, the frequency-selective filter being selected in accordance with the frequencies of operation selected in step (a); and

(c) installing the plurality of transponder readers in the system.

14. The method of claim 13, wherein, in step (b), the frequency-selective filter is a low-pass filter.

15. The method of claim 14, wherein the low-pass filter has a cutoff frequency which is less than a difference between the frequencies of operation selected in step (a) for adjacent ones of the readers.

16. The method of claim 13, wherein the plurality of locations are locations in a highway toll barrier.