Intermodulation mitigation technique in an RFID system

• US 8,810,403 B2
• Filed: 07/19/2012
• Issued: 08/19/2014
• 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
• Primary Examiner(s): Wu, Daniel
• Assistant Examiner(s): Tang, Son M
• Application Number:
  US13/553,379
• Publication Number:
  US 20130119132A1
• Time in Patent Office: 761 Days
• Field of Search: 340/928, 340/933, 340/935, 340/825.73, 340/572.1, 340/571, 340/572.4, 340/825.52, 340/825.49, 340/10.1, 340/5.8, 340/10.42, 340/13.26
• US Class Current: 340/572.2
• 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 transponder for receiving an interrogation signal from a reader at a first frequency and sending a response signal from the transponder at the first frequency, while mitigating interference effects from an interfering signal at a second frequency, the transponder comprising:

an antenna for receiving an interrogation signal from the reader;

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

wherein the low-pass filter has a cutoff frequency that is less than a difference between the first frequency and the second frequency.

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

3. The transponder of claim 1, wherein the interrogation signal comprises a downlink signal from the reader, and the interfering signal comprises a downlink signal from a neighboring reader.

4. The transponder of claim 1, wherein the cutoff frequency eliminates the interference effects from the interfering signal at the second frequency.

5. 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 transponders comprising;

an antenna for receiving one of the interrogation signals from one the plurality of readers;

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

wherein the low-pass filter has a cutoff frequency that is less than a difference between a frequency at which the reader operates and a frequency at which an adjacent one of the readers operates.

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

7. The system of claim 5, wherein the plurality of locations are locations in a highway toll barrier.

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

(a) receiving at an antenna, the interrogation signal from the reader;

(b) detecting at a detector, the interrogation signal and outputting a baseband analog signal representing the interrogation signal received by the antenna;

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

(d) performing at signal processing circuits, signal processing on the analog signal with the reduced interference to extract information from the analog signal with the reduced interference;

wherein the low-pass filter has a cutoff frequency that is less than a difference between the first frequency and the second frequency.

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

10. 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.

11. The method of claim 10, wherein the first reader and the second reader are disposed in a highway toll barrier.

12. The method of claim 8, wherein the interrogation signal comprises a downlink signal from the reader, and the interfering signal comprises a downlink signal from a neighboring reader.

13. The method of claim 8, wherein the cutoff frequency eliminates the interference effects from the interfering signal at the second frequency.

14. 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 the transponders 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) providing the plurality of transponder readers in the system,

wherein the low-pass filter has a cutoff frequency that is less than a difference between the frequencies of operation selected in step (a) for adjacent ones of the readers.

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

16. The method of claim 14, wherein the plurality of transponder readers are located at a highway toll barrier.