Granted Patent B2

US 8,242,888 · App. 12/134,103 · Granted Aug 14, 2012

Abstract

Claims (34)

1. A method implemented in a radio frequency identification (RFID) system, the method comprising:

interrogating an RFID device by an RFID reader using radio frequency electromagnetic waves;

receiving at least one radio frequency signal from the RFID device, comprising receiving a first signal at a first antenna and a second signal at a second antenna;

determining a frequency difference between the first signal received at the first antenna and the second signal received at the second antenna;

detecting a Doppler frequency shift based on the frequency difference; and

calculating a motion parameter of the RFID device, based on the Doppler frequency shift.

2. The method of claim 1 , wherein the motion parameter comprises position, speed, acceleration or jerk.

3. The method of claim 1 , further comprising transmitting a radio frequency electromagnetic wave from the RFID device, the radio frequency electromagnetic wave independent of electromagnetic waves from the RFID reader; wherein the radio frequency electromagnetic wave is received as the first signal at the first antenna and the second signal at the second antenna.

4. The method of claim 1 , further comprising the RFID device reflecting an interrogating electromagnetic wave from the first antenna to provide the first signal and reflecting an interrogating electromagnetic wave from the second antenna to provide the second signal.

5. The method of claim 1 , wherein in response to a command from the RFID reader, the RFID device reflects a radio frequency electromagnetic wave transmitted from the RFID reader to generate a backscattered wave which is received as the first signal at the first antenna and the second signal at the second antenna.

6. The method of claim 1 , wherein the at least one radio frequency signal is received from the RFID device in response to the RFID reader interrogating the RFID device.

7. The method of claim 6 , wherein the at least one radio frequency signal is received from the RFID device in response to the RFID reader interrogating a plurality of RFID devices, including the RFID device.

8. The method of claim 7 , wherein the RFID reader communicates with the plurality of RFID devices to silent the plurality of RFID devices except the RFID device to receive the at least one radio frequency signal.

9. The method of claim 1 , wherein the receiving of the at least one radio frequency signal from the RFID device comprises:

maintaining by the RFID reader transmission of an interrogating electromagnetic wave for a period of time;

operating the RFID device in a mode of increased backscatter of the interrogating electromagnetic wave; and

receiving in the RFID reader the interrogating electromagnetic wave backscattered from the RFID device.

10. A radio frequency identification (RFID) system, comprising:

an RFID device; and

an RFID reader within a radio communication range from the RFID device, the RFID reader configured to identify the RFID device using an interrogating electromagnetic wave transmitted from the RFID reader and to receive at least one radio frequency signal from the RFID device during interrogation of the RFID device, including a first signal received at a first antenna and a second signal received at a second antenna, the RFID reader configured to determine a frequency difference between the first signal received at the first antenna and the second signal received at the second antenna, determine a Doppler frequency shift based on the frequency difference signal and calculate a motion parameter of the RFID device based on the determined Doppler frequency shift.

11. The radio frequency identification (RFID) system of claim 10 , wherein the RFID device is instructed by the RFID reader to operate in a mode of increased backscatter of the interrogating electromagnetic wave; the RFID reader is configured to maintain transmission of the interrogating electromagnetic wave for a period of time, to receive the interrogating electromagnetic wave backscattered from the RFID device to determine the Doppler frequency shift.

12. The radio frequency identification (RFID) system of claim 11 , wherein the RFID device comprises a transceiver circuit to reflect the interrogating electromagnetic wave at a frequency having a predetermine relation with a frequency of the interrogating electromagnetic wave received at the RFID device.

13. The radio frequency identification (RFID) system of claim 12 , wherein the transceiver circuit comprises a diode coupled to an antenna of the RFID device to reflect the interrogating electromagnetic wave at a frequency that is twice the frequency of the interrogating electromagnetic wave received at the RFID device.

14. A radio frequency identification (RFID) reader, comprising:

an oscillator to generate an interrogating electromagnetic wave;

at least one antenna and a transceiver coupled to the oscillator to transmit the interrogating electromagnetic wave and to receive at least one radio frequency signal from an RFID device, including a first signal received at a first antenna and a second signal received at a second antenna; and

a processor coupled to the memory and transceiver to identify the RFID device and configured to determine a frequency difference between the first signal received at the first antenna and the second signal received at the second antenna, determine a Doppler frequency shift based on the frequency difference and determine a speed of the RFID device from the Doppler frequency shift.

15. The radio frequency identification (RFID) reader of claim 14 , wherein the at least one antenna includes a plurality of antennas to receive a plurality of radio frequency signals; and the processor is configured to combine the plurality of radio frequency signals received from the RFID device to detect the Doppler frequency shift.

16. A machine readable media storing instructions, the instructions causing a radio frequency identification (RFID) system to perform a method, the method comprising:

interrogating an RFID device by an RFID reader via radio frequency electromagnetic waves;

receiving at least one radio frequency signal from the RFID device, including receiving a first signal at a first antenna and a second signal at a second antenna;

determining a frequency difference between the first signal received at the first antenna and the second signal received at the second antenna;

detecting a Doppler frequency shift based on the frequency difference; and

calculating a motion parameter of the RFID device, based on the Doppler frequency shift.

Assignments (8)