Intermodulation mitigation technique in an RFID system

• US 9,558,383 B2
• Filed: 08/12/2014
• Issued: 01/31/2017
• 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.
• Primary Examiner(s): Benlagsir, Amine
• Assistant Examiner(s): Tang, Son M
• Application Number:
  US14/457,918
• Publication Number:
  US 20140347167A1
• Time in Patent Office: 903 Days
• Field of Search: 340/928, 340/933, 340/935, 340/825.73
• US Class Current: 1/1
• 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 system comprising:

a transponder;

a first reader for supplying a first interrogation signal to the transponder at a first frequency and receiving a response signal from the transponder at the first frequency;

a second reader for supplying a second interrogation signal to the. transponder at a second frequency and receiving a response signal from the transponder at the second frequency, the transponder mitigating interference effects of the second interrogation signal, wherein said first and second readers have intermodulation products that create interference;

an antenna at the transponder for receiving the first and second interrogation signals from said first and second readers;

a detector at the transponder and 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 at the transponder and 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 in which the interference is reduced; and

a signal processing circuit at the transponder and in electrical communication with the frequency-selective filter to receive the analog signal with the reduced interference, and configured to perform signal processing on the analog signal with the reduced interference to extract information from the analog signal with the reduced interference.

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

3. The system of claim 1, wherein the system uses frequency separation and time domain multiplexing to allow said first and second readers to operate closely together.

4. A system comprising:

a plurality of readers at a plurality of locations in the system for supplying interrogation signals at a downlink data rate, each of the plurality of readers operating at a different frequency, wherein a frequency difference between the different frequencies is larger than the downlink data rate and wherein intermodulation products from at least two of said plurality of readers create interference;

a plurality of transponders, each of the plurality of transponders comprising;

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

a detector, in electrical communication with the antenna, for detecting 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 in which the interference is reduced; and

a signal processing circuit at each of the plurality of transponders and in electrical communication with the frequency-selective filter to receive the analog signal with the reduced interference, and configured to perform 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 the frequency-selective filter comprises a low-pass filter.

6. The system of claim 4, wherein the system uses frequency separation and time domain multiplexing to allow the plurality of readers to operate closely together.

7. The of claim 6, wherein the plurality of readers are located in adjacent traffic lanes.

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