METHOD AND SYSTEM FOR SECURELY COMMUNICATING INFORMATION USING MULTIPLE RF CARRIERS

• US 20080188257A1
• Filed: 09/28/2007
• Published: 08/07/2008
• Est. Priority Date: 09/29/2006
• Status: Active Grant

• Current Assignee: University of Pittsburgh of The Commonwealth System of Higher Education
• Original Assignee: University of Pittsburgh of The Commonwealth System of Higher Education
• Inventors: Mickle, Marlin H., Lovell, Michael R., Maina, Joshua Y., Schaefer, Laura A.
• Granted Patent: US 7,747,274 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H04B 5/77 for interrogation
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

Amplitude modulation of multiple carriers provides a pulse width modulated train resulting in a novel and effective communication mechanism to overcome difficulties in certain RF applications, particularly in the area of Radio Frequency Identification (RFID). A novel conceptual pulse is formed and developed using a set of RF frequencies, such as ultra wideband frequencies, amplitude modulated to form a pulse width modulated binary coded signal. The concept is to wirelessly convey information only to a receiver at a specified distance or range. The RF energy may continue on in space, but receivers of the same design would only receive information from a transmitter if the receivers are located at a specified distance. Equivalent receivers at all other distances would see noise.

Claims

1. A method of communicating information from a first location to a second location based on a first pulse train having a first pulse width representing a first data value and a second pulse train having a second pulse width representing a second data value, said method comprising:

choosing a plurality of RF frequencies;

selectively transmitting a first combined RF signal from said first location, said first combined RF signal being based on a plurality of first RF signals, wherein each respective first RF signal has a frequency equal to a respective one of said RF frequencies and a power equal to a respective first transmission power level;

selectively transmitting a second combined RF signal from said first location, said second combined RF signal being based on a plurality of second RF signals, wherein each respective second RF signal has a frequency equal to a respective one of said RF frequencies and a power equal to a respective second transmission power level;

receiving said first combined RF signal at said second location, wherein the first transmission power levels are chosen so that as a result of attenuation of the first combined RF signal between said first location and said second location, said first pulse train may be reconstructed from the received first combined RF signal; and

receiving said second combined RF signal at said second location, wherein the second transmission power levels are chosen so that as a result of attenuation of the second combined RF signal between said first location and said second location, said second pulse train may be reconstructed from the received second combined RF signal.

2. The method according to claim 1, wherein said first combined RF signal is generated by generating said plurality of first RF signals and combining said first RF signals to form said first combined RF signal, and wherein said second combined RF signal is generated by generating said plurality of second RF signals and combining said second RF signals to form said second combined RF signal.

3. The method according to claim 1, wherein the first transmission power levels are chosen so that if said first combined RF signal is received at a location different from said second location, said first pulse train may not be reconstructed from the received first combined RF signal, and wherein the second transmission power levels are chosen so that if said second combined RF signal is received at a location different from said second location, said second pulse train may not be reconstructed from the received second combined RF signal.

4. The method according to claim 1, wherein said second location is a defined area surrounding a predetermined point in space.

5. The method according to claim 4, wherein said first combined RF signal and said second combined RF signal are transmitted using a directional antenna.

6. The method according to claim 1, wherein said second location comprises a plurality of points forming a circle around said first location wherein said first location is located at the center of said circle.

7. The method according to claim 6, wherein said first combined RF signal and said second combined RF signal are transmitted using an omni-directional antenna.

8. The method according to claim 1, wherein said RF frequencies do not have a harmonic relationship among one another.

9. The method according to claim 1, wherein said first data value is a logic 1 and said second data value is a logic 0.

10. The method according to claim 1, wherein said steps of selectively transmitting a first combined RF signal and selectively transmitting a first combined RF signal are repeatedly performed in a predetermined order in order to create a desired data stream.

11. A transponder system wherein information is communicated from a first location to a second location using a plurality of RF frequencies based on a first pulse train having a first pulse width representing a first data value and a second pulse train having a second pulse width representing a second data value, comprising:

a base station located at said first location, said base station being adapted to;

(a) selectively transmit a first combined RF signal from said first location by generating a plurality of first RF signals and combining said first RF signals to form said first combined RF signal, wherein each respective first RF signal has a frequency equal to a respective one of said RF frequencies and is generated having a respective first transmission power level, and

(b) selectively transmit a second combined RF signal from said first location by generating a plurality of second RF signals and combining said second RF signals to form said second combined RF signal, wherein each respective second RF signal has a frequency equal to a respective one of said RF frequencies and is generated having a respective second transmission power level; and

a transponder adapted to receive, as appropriate, said first combined RF signal and said second combined RF signal at said second location, wherein the first transmission power levels are chosen so that as a result of attenuation of the first combined RF signal between said first location and said second location, said first pulse train may be reconstructed from the received first combined RF signal, and wherein the second transmission power levels are chosen so that as a result of attenuation of the second combined RF signal between said first location and said second location, said second pulse train may be reconstructed from the received second combined RF signal.

12. The transponder system according to claim 11, wherein the first transmission power levels are chosen so that if said first combined RF signal is received at a location different from said second location, said first pulse train may not be reconstructed from the received first combined RF signal, and wherein the second transmission power levels are chosen so that if said second combined RF signal is received at a location different from said second location, said second pulse train may not be reconstructed from the received second combined RF signal.

13. The transponder system according to claim 11, wherein said transponder system is an RFID system, said base station is an RFID interrogator, and said transponder is an RFID tag.

14. The transponder system according to claim 11, wherein said base station includes a directional antenna, wherein said first combined RF signal and said second combined RF signal are transmitted using said directional antenna, and wherein said second location is a defined area surrounding a predetermined point in space.

15. The transponder system according to claim 11, wherein said base station includes an omni-directional antenna, wherein said first combined RF signal and said second combined RF signal are transmitted using said omni-directional antenna, and wherein said second location comprises a plurality of points substantially forming a circle around said first location and wherein said first location is located at the center of said circle.

16. A method of communicating information from a first location to a second location based on a first pulse train having a first pulse width representing a first data value and a second pulse train having a second pulse width representing a second data value, said method comprising:

choosing a plurality of RF frequencies;

selectively generating a first amplitude modulated RF signal corresponding to said first pulse train using said RF frequencies and transmitting said first amplitude modulated RF signal from said first location, said first amplitude modulated RF signal being generated using a respective first transmission power level for each RF frequency;

selectively generating a second amplitude modulated RF signal corresponding to said second pulse train using said RF frequencies and transmitting said second amplitude modulated RF signal from said first location, said second amplitude modulated RF signal being generated using a respective second transmission power level for each RF frequency;

receiving said first amplitude modulated RF signal at said second location, wherein the first transmission power levels are chosen so that as a result of attenuation of said first amplitude modulated RF signal between said first location and said second location, said first data value may be detected from the received first amplitude modulated RF signal; and

receiving said second amplitude modulated RF signal at said second location, wherein the second transmission power levels are chosen so that as a result of attenuation of said second amplitude modulated RF signal between said first location and said second location, said second data value may be detected from the received second amplitude modulated RF signal.

17. The method according to claim 16, wherein said first data value may be detected from the received first amplitude modulated RF signal by reconstructing the first pulse train from the received first amplitude modulated RF signal, and wherein said second data value may be detected from the received second amplitude modulated RF signal by reconstructing the second pulse train from the received second amplitude modulated RF signal.

18. The method according to claim 17, wherein the first transmission power levels are chosen so that if said first amplitude modulated RF signal is received at a location different from said second location, said first pulse train may not be reconstructed from the received first amplitude modulated RF signal, and wherein the second transmission power levels are chosen so that if said second amplitude modulated RF signal is received at a location different from said second location, said second pulse train may not be reconstructed from the received second amplitude modulated RF signal.

19. The method according to claim 16, wherein the received first amplitude modulated RF signal comprises a plurality of first received RF signals, and wherein said first data value is detected from the received first amplitude modulated RF signal if a power level of each of said first received RF signals falls within a respective corresponding predetermined power level range, and wherein the received second amplitude modulated RF signal comprises a plurality of second received RF signals, and wherein said second data value is detected from the received second amplitude modulated RF signal if a power level of each of said second received RF signals falls within a respective corresponding predetermined power level range.

20. A transponder system wherein information is communicated from a first location to a second location using a plurality of RF frequencies based on a first pulse train having a first pulse width representing a first data value and a second pulse train having a second pulse width representing a second data value, comprising:

a base station located at said first location, said base station being adapted to;

(a) selectively generate a first amplitude modulated RF signal corresponding to said first pulse train using said RF frequencies and transmit said first amplitude modulated RF signal from said first location, said first amplitude modulated RF signal being generated using a respective first transmission power level for each RF frequency, and

(b) selectively generate a second amplitude modulated RF signal corresponding to said second pulse train using said RF frequencies and transmit said second amplitude modulated RF signal from said first location, said second amplitude modulated RF signal being generated using a respective second transmission power level for each RF frequency; and

a transponder adapted to receive, as appropriate, said first amplitude modulated RF signal and said second amplitude modulated RF signal at said second location, wherein the first transmission power levels are chosen so that as a result of attenuation of said first amplitude modulated RF signal between said first location and said second location, said first data value may be detected from the received first amplitude modulated RF signal, and wherein the second transmission power levels are chosen so that as a result of attenuation of said second amplitude modulated RF signal between said first location and said second location, said second data value may be detected from the received second amplitude modulated RF signal.

21. The transponder system according to claim 20, wherein said first data value may be detected from the received first amplitude modulated RF signal by reconstructing the first pulse train from the received first amplitude modulated RF signal, and wherein said second data value may be detected from the received second amplitude modulated RF signal by reconstructing the second pulse train from the received second amplitude modulated RF signal.

22. The transponder system according to claim 21, wherein the first transmission power levels are chosen so that if said first amplitude modulated RF signal is received at a location different from said second location, said first pulse train may not be reconstructed from the received first amplitude modulated RF signal, and wherein the second transmission power levels are chosen so that if said second amplitude modulated RF signal is received at a location different from said second location, said second pulse train may not be reconstructed from the received second amplitude modulated RF signal.

23. The transponder system according to claim 20, wherein the received first amplitude modulated RF signal comprises a plurality of first received RF signals, and wherein said first data value is detected from the received first amplitude modulated RF signal if a power level of each of said first received RF signals falls within a respective corresponding predetermined power level range, and wherein the received second amplitude modulated RF signal comprises a plurality of second received RF signals, and wherein said second data value is detected from the received second amplitude modulated RF signal if a power level of each of said second received RF signals falls within a respective corresponding predetermined power level range.

24. The transponder system according to claim 20, wherein said transponder system is an RFID system, said base station is an RFID interrogator, and said transponder is an RFID tag.

25. A method of communicating information from a first location to a second location based on a first pulse train having a first pulse width representing a first data value and a second pulse train having a second pulse width representing a second data value, said method comprising:

selectively amplitude modulating a plurality of RF carrier signals to generate a first amplitude modulated RF signal corresponding to said first pulse train and transmitting said first amplitude modulated RF signal from said first location; and

selectively amplitude modulating said plurality of RF carrier signals to generate a second amplitude modulated RF signal corresponding to said second pulse train and transmitting said second amplitude modulated RF signal from said first location;

wherein remote from said first location said first data value may be detected from said first amplitude modulated RF signal only when received at said second location, and wherein remote from said first location said second data value may be detected from said second amplitude modulated RF signal only when received at said second location.