Determining a position of a tag

• US 7,932,860 B2
• Filed: 07/07/2009
• Issued: 04/26/2011
• Est. Priority Date: 01/08/2007
• Status: Active Grant

• Current Assignee: U-Blox AG (u-blox Holding AG)
• Original Assignee: Omnisense Ltd.
• Inventors: Bartlett, David
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): LIU, HARRY K
• Application Number:
  US12/459,733
• Publication Number:
  US 20100013711A1
• Time in Patent Office: 658 Days
• Field of Search: 342/442
• US Class Current: 342/442
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

A tag transmits signals having at least two different frequency components. The signals are receivable by at least some of a plurality of spaced receivers. Each receiver, in response to receiving a signal, measures respective phases of the first and second frequency components and a frequency offset between the tag and the receiver. The frequency offset is dependent upon a difference in frequencies of respective clocks in the tag and the receiver. A position processor obtains a difference in phases of the first and second frequency components for a signal, a frequency offset between the receiver and tag and determines the position of the tag in dependence upon the difference between respective phases of the first and second frequency components and in dependence upon the frequency offset.

Claims

1. A method, comprising:

receiving a first phase difference between phases of two frequency components of a first signal transmitted by a tag at a first time and measured by a receiver;

receiving a frequency offset between the tag and the receiver for the first signal;

receiving a second phase difference between phases of two frequency components of a second signal transmitted by the tag at a second time and measured by the receiver; and

determining a position of the tag in dependence upon the phase differences and the frequency offset.

2. The method of claim 1, further comprising

receiving a second frequency offset between the tag and the receiver for the second signal;

and

determining a position of the tag in dependence upon the phase differences and the frequency offsets.

3. The method of claim 1, further comprising:

receiving at least three phase differences for each of at least two signals transmitted by the tag, each signal comprising at least two frequency components and each of the at least three phase differences corresponding to phases measured by a different one of a plurality of receivers;

receiving at least three frequency offsets for each of the at least two signals, each of the at least three frequency offsets measured by a different one of a plurality of receivers; and

determining at least one position of the tag in dependence upon the phase differences and the frequency offsets.

4. The method of claim 3 wherein the at least two signals form a sequence of signals within a larger sequence of signals.

5. The method of claim 1 wherein the frequency offset is dependent upon a difference in frequencies of clocks in the tag and the receiver and upon a velocity of the tag at time of transmission of the signal.

6. The method of claim 1 further comprising providing a range equation dependent upon the phase differences.

7. The method of claim 6 wherein the tag has a first clock and the receiver has a second clock and wherein the range equation is also dependent upon a phase offset between the first clock in the tag and the second clock in the receiver.

8. The method of claim 6 wherein the tag has a first clock and the receiver has a second clock and wherein the range equation is dependent upon a frequency offset between the first clock in the tag and the second clock in the receiver.

9. The method of claim 6 wherein the range equation includes an error term and the equation is rearranged to equal zero.

10. The method of claim 6 wherein the tag has a first clock and the receiver has a second clock and wherein the range equation is dependent upon a phase offset between the first and second clocks and is further dependent upon a frequency offset between the first and second clocks, the method further comprising determining the velocity of the tag in dependence upon the phase difference and frequency offset.

11. The method of claim 5 further comprising providing a velocity equation dependent upon the frequency offset.

12. The method of claim 11 wherein the tag has a first clock and the receiver has a second clock and wherein the velocity equation is dependent upon a frequency difference between the first and second clocks.

13. The method of claim 11 wherein the velocity equation includes an error term and the equation is rearranged to equal zero.

14. The method of claim 1 further comprising determining a velocity of the tag in dependence upon the phase differences and the frequency offset.

15. The method of claim 1, further comprising:

receiving a plurality of phase differences between phases of two frequency components of a plurality of signals transmitted by the tag and measured by a plurality of receivers;

receiving a plurality of frequency offsets for the plurality of signals transmitted by the tag and measured by a plurality of receivers; and

determining a plurality of positions of the tag in dependence upon the phase differences and the frequency offsets.

16. The method of claim 15, further comprising:

preparing a first set of equations for at least one signal and a plurality of receivers, each equation of the first set being a function of position of the tag and a respective phase difference and including a respective residual error;

preparing a second set of equations for at least two signals and a plurality of receivers, each equation of the second set being a function of position of the tag and a respective pair of frequency offsets and including a respective residual error; and

solving the equations to obtain at least one position of the tag.

17. The method of claim 16, wherein solving the equations to obtain at least one position of the tag includes combining the equations to provide a cost function and to minimize cost.

18. The method of claim 17 wherein combining the equations further includes providing a respective weighting for each equation.

19. The method of claim 15, further comprising:

determining a first count of the equations;

determining a second count of unknowns in the equations; and

preparing further equations until the first count is equal to or greater than the second count.

20. The method of claim 19 further comprising preparing further equations until the first count exceeds the second count.

21. The method of claim 19 further comprising determining a count of equations needed in dependence upon the number of receivers and the number of signals measured by the receivers.

22. The method of claim 2 wherein the tag transmits signals at least two different frequency components at different times.

23. The method of claim 2 wherein the tag transmits signals having at least four different frequency components.

24. The method of claim 2, further comprising:

receiving a difference in respective phases of two different frequency components for a given signal from a fixed tag of known position and for the receiver;

obtaining frequency offsets between the fixed tag and the receiver for at least two different signals;

receiving a difference in respective phases of two different frequency components for a given signal from the fixed tag and for a second receiver;

obtaining frequency offsets between the fixed tag and the second receiver for at least two different signals;

determining a relative phase offset between the receivers; and

determining a relative frequency offset between the receivers.

25. The method of claim 2 comprising:

receiving a difference in respective phases of two different frequency components for a given signal from a first fixed tag of known position and for the receiver;

receiving a difference in respective phases of two different frequency components for a given signal from a second fixed tag of known position and for the receiver; and

determining a relative phase offset between the first and second fixed tags.

26. The method of claim 2 wherein the tag transmits signals having at least three different frequency components, such that at least two different phase differences are obtainable corresponding to different pairs of frequency components, the method comprising:

determining a first estimate of position of the tag in dependence upon the difference between respective phases of a first pair of frequency components; and

determining a second estimate of position of the tag in dependence upon the difference between respective phases of a second pair of frequency components.

27. The method of claim 1 wherein determining the position of the tag includes limiting the position of the tag to a predefined surface.

28. A method, comprising:

receiving a phase difference between phases of two frequency components of a first signal transmitted by a transmitter at a first time and measured by a tag;

receiving a frequency offset between the tag and the transmitter for the first signal;

receiving a phase difference between phases of two frequency components of a second signal transmitted by a transmitter at a second, different time and measured by the tag; and

determining the position of the tag in dependence upon the phase differences and the frequency offset.

29. The method of claim 28, comprising:

receiving a phase difference for each signal of at least three sets of signals, each signal comprising at least two frequency components, each set of signals transmitted by a different transmitter and each set comprising at least two signals;

receiving frequency offset for each signal of the at least three sets of signals; and

determining at least one position of the tag in dependence upon the phase differences and the frequency offsets.

30. A computer readable medium which stores instructions which are executable on a computer in which the instructions perform a method for determining the position of a tag, the method comprising:

receiving a first phase difference between phases of two frequency components of a first signal transmitted by the tag at a first time and measured by a receiver;

receiving a frequency offset between the tag and the receiver for the first signal;

receiving a second phase difference between phases of two frequency components of a second signal transmitted by the tag at a second time and measured by the receiver; and

determining a position of the tag in dependence upon the phase differences and the frequency offset.

31. The computer readable medium of claim 30 wherein the method further comprises:

receiving at least three phase differences for each of at least two signals

transmitted by the tag, each signal comprising at least two frequency components

and each of the at least three phase differences corresponding to phases measured by a different one of a plurality of receivers;

receiving at least three frequency offsets for each of the at least two signals, each of the at least three frequency offsets measured by a different one of a plurality of receivers; and

determining at least one position of the tag in dependence upon the phase differences and the frequency offsets.

32. An apparatus, comprising:

means for receiving a first phase difference between phases of two frequency components of a first signal transmitted by a tag at a first time and measured by a receiver;

means for receiving a frequency offset between the tag and the receiver for the first signal;

means for receiving a phase difference between phases of two frequency components of a second signal transmitted by the tag at a second, different time and measured by the receiver; and

means for determining a position of the tag in dependence upon the phase differences and the frequency offset.

33. The apparatus of claim 32, wherein:

the phase difference receiving means is operable to receive at least three phase differences for each of at least two signals transmitted by the tag, each of the at least two signals

having at least two frequency components and each of the at least three phase differences corresponding to phases measured by a different one of a plurality of receivers;

the frequency offset receiving means is operable to receive at least three frequency offsets for each of the at least two signals, each of the at least frequency offsets measured by a different one of the plurality of receivers; and

the position determining means is operable to determine at least one position of the tag in dependence upon the phase differences and the frequency offsets.

34. A system, comprising:

a buffer arranged to receive a first phase difference between phases of two frequency components of a first signal transmitted by a tag at a first time and measured by a receiver, a frequency offset between the tag and the receiver for the first signal, a second phase difference between phases of two frequency components of a second signal transmitted by the tag at a second, different time and measured by a receiver; and

a position determination unit to determine the position of the tag in dependence upon the phase difference and the frequency offset.

35. The system of claim 34, further comprising:

at least three receivers, each receiver operable, in response to receiving a signal, to measure respective phases of the first and second frequency components and to measure a frequency offset between the tag and each receiver, the frequency offset dependent upon a difference in frequencies of respective clocks in the tag and the receivers and to transmit the phases and the frequency offset to the position determination unit.