Position determination by directional broadcast

• US 7,576,693 B2
• Filed: 03/24/2006
• Issued: 08/18/2009
• Est. Priority Date: 03/24/2006
• Status: Expired due to Fees

• Current Assignee: Free Alliance Sdn., Bhd.
• Original Assignee: Free Alliance Sdn., Bhd.
• Inventors: Morris, Martin
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): LIU, HARRY K
• Application Number:
  US11/388,280
• Publication Number:
  US 20070222679A1
• Time in Patent Office: 1,243 Days
• Field of Search: 34235701-357017, 342/407, 342/30, 340/825.37
• US Class Current: 342/407
• CPC Class Codes: G01S 13/426 Scanning radar, e.g. 3D radar G01S13/66 takes precedence
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence

Abstract

Methods and systems to determine the position of objects indoors or in confined areas are disclosed. A multitude of broadcast stations are transmitting an omni-directional reference signal and directional signals having each a phase-shift depending upon their specific direction. The objects whose positions are to be identified have a transponder and a means to measure the phase-shift between the omni-directional reference signal and a directional signal received. The measured time-difference indicating the relative direction to the broadcast station, which has sent the directional signal, is sent back to the broadcast station. The absolute position of the object can be determined by the results of an angular measurement of a second broadcast station. The broadcast stations can communicate amongst each other. A post-processing unit can initiate actions according to the position of an object identified.

Claims

1. A method to determine the position of one or more objects in a single plane comprising the steps of:

providing a system comprising a multitude of broadcast stations broadcasting via antennas with a length in the order of 1.2 cm, communicating among each other and one or more objects whose positions are to be determined, wherein each of these objects has a transponder, an identifying code, and a means to measure phase shifts of signals;

using the identifying code of each object whose position is to be determined as input in a nearest broadcast station;

broadcasting inside or outside of buildings in a frequency range of 6 GHz from multiple broadcast stations an omni-directional reference signal and directional signals having each a phase shift characterizing their direction;

calculating the directions of said object relative to at least two of said broadcast stations using the phase difference between the reference signal and one of said directional signals measured at the object'"'"'s site;

calculating the position of said object using the directions calculated in previous step; and

displaying position of said object.

2. The method of claim 1 wherein said directional signals from adjacent broadcast stations are transmitted sequentially to avoid interference.

3. The method of claim 1 wherein relative directional signal strength is used to interpolate a direction in case a transponder receives two directional signals from a same broadcast station.

4. The method of claim 1 wherein an code identifying each broadcast station is embedded in the omni-directional reference signal.

5. The method of claim 1 wherein the calculation of a position of an object is performed by a broadcast station based upon the measurements provided by said transponder.

6. The method of claim 1 wherein the calculation of a position of an object is performed by a post-processing unit based upon the measurements provided by said transponder.

7. The method of claim 1 wherein the calculation of a position of an object is performed by said transponder.

8. The method of claim 1 wherein said phase difference is measured by a digital counter.

9. The method of claim 8 wherein said digital counter times the relationship between zero crossings of the omni-directional reference signal and the directional signal using internal clock cycles.

10. The method of claim 8 wherein for the measurement of the phase difference the ratio between rising crossings of the two signals to the time between rising crossings of the reference signal is used, followed by averaging multiple measurements.

11. The method of claim 1 wherein for the measurement of the phase difference the reference signal is delayed by a variable phase-shift in the analog domain until it coincides with a directional signal, wherein the time-span of this delay is a measure for the phase-shift.

12. The method of claim 1 wherein multiple frequencies are used to identify the broadcast stations.

13. The method of claim 1 wherein the broadcast stations are identified by externally synchronizing the broadcast stations and wherein a broadcast station ID is by turns transmitted and periodically modulated onto the omni-directional reference signal.

14. The method of claim 1 wherein the broadcast station communicate among each other using a wireless network.

15. The method of claim 1 wherein the broadcast station communicate among each other using a LAN network by wire.

16. The method of claim 1 wherein a transponder transmits its identification code and the results of the measurements taken at the object'"'"'s site.

17. The method of claim 1 wherein for each broadcast stations a post-processing node is provided.

18. The method of claim 1 wherein a transponder is only performing measurement of phase differences and related transmission after a request by a message from a broadcast station, wherein this message is embedded in the omni-directional reference signal.

19. The method of claim 1 wherein a transponder takes the measurement of said phase difference only periodically after a defined time span and transmits the result only when said phase difference is different from a previous measurement.

20. The method of claim 1 wherein a transponder takes the measurement of said phase difference followed by a transmission of the measurement results when a physical movement of its object is sensed by an acceleration sensor.

21. The method of claim 1 wherein a transponder sends an alarm when its battery is losing power.

22. The method of claim 1 wherein more than one of said systems comprising broadcast stations are operated.

23. The method of claim 22 wherein these systems are interconnected by a WLAN network.

24. The method of claim 22 wherein these systems are interconnected by a LAN by wire.

25. A system to determine the position of an object in a single plane is comprising:

a multitude of broadcast stations inside or outside of buildings each of them comprising;

a transmitter broadcasting in a frequency range of 6 MHZ an omni-directional reference signal and directional signals in different directions wherein each of said directional signals has a specific phase-shift relative to said omni-directional reference signal;

a set of antennas with a length in the order of 1.2 cm, and

a receiver receiving signals from a transponder of an object whose position is to be determined, wherein said signals are related to an identification and direction from a broadcast station towards said object; and

an object whose position has to be determined comprising;

a means to measure the phase difference between said omni-directional reference signal and one or more directional signal received; and

a transponder to receive said omni-directional reference signal and a directional signal and to transmit said phase difference back to a broadcast station, which has sent said directional signal.

26. The system of claim 25 wherein a post-processing unit prepares reports about all objects in identified in an area.

27. The system of claim 25 wherein a post-processing unit initiates actions correspondent to the position of an object whose position has been determined.

28. The system of claim 25 wherein said transponder is switched off after the position of its correspondent object has been determined and is switched on when said object is being moved.

29. The system of claim 25 wherein said directional signals from adjacent broadcast stations are transmitted sequentially to avoid interference.

30. The system of claim 25 wherein relative directional signal strength is used to interpolate a direction in case a transponder receives two directional signals from a same broadcast station.

31. The system of claim 25 wherein an code identifying each broadcast station is embedded in the omni-directional reference signal.

32. The system of claim 25 wherein a calculation of a position of an object is performed by a broadcast station based upon the measurements provided by said transponder.

33. The system of claim 25 wherein a calculation of a position of an object is performed by a post-processing unit based upon the measurements provided by said transponder.

34. The system of claim 25 wherein a calculation of a position of an object is performed by said transponder.

35. The system of claim 25 wherein said means to measure said phase difference is a digital counter.

36. The system of claim 35 wherein said digital counter times the relationship between zero crossings of the omni-directional reference signal and the directional signal using internal clock cycles.

37. The system of claim 25 wherein said means to measure said phase difference uses the ratio between rising crossings of the two signals to the time between rising crossings of the reference signal, followed by averaging multiple measurements.

38. The system of claim 25 wherein said means for measurement of said phase difference delays the reference signal by a variable phase-shift in the analog domain until it coincides with a directional signal, wherein the time-span of this delay is a measure for the phase-shift.

39. The system of claim 25 wherein multiple frequencies are used to identify the broadcast stations.

40. The system of claim 25 wherein the broadcast stations are identified by externally synchronizing the broadcast stations and wherein a broadcast station ID is by turns transmitted and periodically modulated onto the omni-directional reference signal.

41. The system of claim 25 wherein the broadcast station communicate among each other using a wireless network.

42. The system of claim 25 wherein the broadcast station communicate among each other using a LAN network by wire.

43. The system of claim 25 wherein a transponder transmits its identification code and the results of the measurements taken at the object'"'"'s site.

44. The system of claim 25 wherein for each broadcast stations a post-processing node is provided.

45. The system of claim 25 wherein a transponder is only performing measurement of phase differences and related transmission after a request by a message from a broadcast station, wherein this message is embedded in the omni-directional reference signal.

46. The system of claim 25 wherein a transponder takes the measurement of said phase difference only periodically after a defined time span and transmits the result only when said phase difference is different from a previous measurement.

47. The system of claim 25 wherein a transponder takes the measurement of said phase difference followed by a transmission of the measurement results when a physical movement of its object is sensed by an acceleration sensor.

48. The system of claim 25 wherein a transponder sends an alarm when its battery is losing power.

49. The system of claim 25 wherein more than one of said systems comprising broadcast stations are operated.

50. The system of claim 49 wherein these systems are interconnected by a WLAN network.

51. The system of claim 49 wherein these systems are interconnected by a LAN by wire.