Location of Wideband OFDM Transmitters With Limited Receiver Bandwidth

• US 20080137524A1
• Filed: 12/12/2006
• Published: 06/12/2008
• Est. Priority Date: 12/12/2006
• Status: Active Grant

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: Anderson, Robert J., Mia, Rashidus S.
• Granted Patent: US 7,844,280 B2
• Time in Patent Office: Days
• US Class Current: 370/203
• CPC Class Codes: G01S 5/0205 Details
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

One illustrative embodiment takes the form of a system for locating wireless transmitters employing an Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme. The OFDM scheme comprises transmitting signal components over narrowband frequency channels spanning a wideband channel. The system includes a first receiving system configured to receive a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the narrowband frequency channels, and to process the fraction of the signal components to derive location related measurements. The system further includes at least a second receiving system configured to receive the fraction of the signal components transmitted by the first wireless transmitter, and to process this fraction of the signal components to derive location related measurements. The system also includes a processing system configured to use location related measurements from the first and second receiving systems to compute the location of the wireless transmitter.

Claims

1. A system for locating wireless transmitters employing an Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme, wherein said OFDM scheme comprises transmitting signal components over a plurality of predefined narrowband frequency channels spanning a predefined wideband channel, comprising:

a first receiving system configured to receive a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the predefined narrowband frequency channels, and to process said fraction of the signal components to derive location related measurements;

a second receiving system configured to receive said fraction of the signal components transmitted by said first wireless transmitter, and to process said fraction of the signal components to derive location related measurements; and

a processing system, operatively coupled to said first and second receiving systems, wherein said processing system is configured to use location related measurements from said first and second receiving systems to compute the location of said wireless transmitter.

2. A system as recited in claim 1, wherein said location related measurements derived by said first and second receiving systems comprise time difference of arrival (TDOA) measurements.

3. A system as recited in claim 1, wherein said location related measurements derived by said first and second receiving systems comprise time of arrival (TOA) measurements.

4. A system as recited in claim 1, wherein said location related measurements derived by said first and second receiving systems comprise angle of arrival (AOA) measurements.

5. A system as recited in claim 1, wherein said location related measurements derived by said first and second receiving systems comprise round trip time measurements.

6. A system as recited in claim 1, wherein said location related measurements derived by said first and second receiving systems comprise received power measurements.

7. A system as recited in claim 1, wherein said fraction of the predefined narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy, and wherein said first or second receiving systems are configured to use signal components in said pilot channel to aid in signal acquisition and demodulation.

8. A system as recited in claim 1, wherein said fraction of the predefined narrowband frequency channels excludes guard channels in which said first wireless transmitter transmits minimal energy.

9. A system as recited in claim 1, wherein said first and second receiving systems each include a radio frequency (RF) filter, and wherein the first and second receiving systems are each configured to receive signal components within a bandwidth compatible with said RF filter.

10. A system as recited in claim 1, wherein said first and second receiving systems each include an intermediate frequency (IF) filter, and wherein the first and second receiving systems are each configured to receive signal components within a bandwidth compatible with said IF filter.

11. A system as recited in claim 1, wherein said first and second receiving systems each include an analog to digital converter (ADC) characterized by a sample rate, and wherein the first and second receiving systems are each configured to receive signal components within a bandwidth compatible with said sample rate.

12. A system as recited in claim 11, wherein said ADCs are further characterized by a sample rate after decimation, and wherein the first and second receiving systems are configured to receive signal components within a bandwidth compatible with said sample rate after decimation.

13. A system as recited in claim 1, wherein said first and second receiving systems each include available memory for storing data representing received signal components, and wherein said first and second receiving systems are configured to receive signal components within a bandwidth compatible with said available memory.

14. A system as recited in claim 1, wherein said first and second receiving systems each include digital signal processors (DSPs) characterized by DSP processing throughput, and wherein said first and second receiving systems are configured to receive signal components within a bandwidth compatible with said DSP processing throughput.

15. A system as recited in claim 1, wherein said first and second receiving systems are configured to receive signal components within a bandwidth compatible with a current load on the receiving system.

16. A system as recited in claim 1, wherein said first and second receiving systems are configured to tune to a plurality of channels to receive signals from a plurality of wireless transmitters to be located.

17. A system as recited in claim 1, wherein said first and second receiving systems are configured to tune to a plurality of selected channels, wherein said selected channels are determined based upon interference levels.

18. A system as recited in claim 17, wherein said selected channels are determined based upon measurements of received signals.

19. A system as recited in claim 17, wherein said selected channels are determined based upon spectrum usage.

20. A system as recited in claim 1, wherein said first and second receiving systems are configured for collection of multiple slices of spectrum for bandwidth synthesis.

21. A system as recited in claim 1, wherein said first and second receiving systems are configured for use of a sequential pattern of re-tuning a frequency agile receiver to cover a substantial part of an OFDM waveform spectrum.

22. A system as recited in claim 1, wherein said system is configured for use of a bandwidth synthesis process to provide increased resolution in a cross-correlation function to reduce multipath delay spread.

23. A system as recited in claim 1, wherein said system is configured to use a station-based processing method.

24. A system as recited in claim 1, wherein said first or second receiving systems include means for performing OFDM receiving and demodulation processing.

25. A system as recited in claim 1, wherein said first and second receiving systems include narrowband receivers.

26. A system as recited in claim 1, wherein said first and second receiving systems include wideband receivers.

27. A method for locating wireless transmitters employing an Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme, wherein said OFDM scheme comprises transmitting signal components over a plurality of narrowband frequency channels spanning a wideband channel, comprising:

at a first receiving system, receiving a fraction of the signal components transmitted by a first wireless transmitter to be located in a fraction of the narrowband frequency channels, and processing said fraction of the signal components to derive location related measurements;

at a second receiving system, receiving said fraction of the signal components transmitted by said first wireless transmitter, and processing said fraction of the signal components to derive location related measurements; and

processing said location related measurements from said first and second receiving systems to compute the location of said wireless transmitter.

28. A method as recited in claim 27, wherein said location related measurements comprise time difference of arrival (TDOA) measurements.

29. A method as recited in claim 27, wherein said location related measurements comprise time of arrival (TOA) measurements.

30. A method as recited in claim 27, wherein said location related measurements comprise angle of arrival (AOA) measurements.

31. A method as recited in claim 27, wherein said location related measurements comprise round trip time measurements.

32. A method as recited in claim 27, wherein said location related measurements comprise received power measurements.

33. A method as recited in claim 27, wherein said fraction of the narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy, and wherein signal components in said pilot channel are used to aid in signal acquisition and demodulation.

34. A method as recited in claim 27, wherein said fraction of the narrowband frequency channels excludes guard channels in which said first wireless transmitter transmits minimal energy.

35. A method as recited in claim 27, wherein said first and second receiving systems each include a radio frequency (RF) filter, and wherein the method includes receiving signal components within a bandwidth compatible with said RF filter.

36. A method as recited in claim 27, wherein said first and second receiving systems each include an intermediate frequency (IF) filter, and wherein the method includes receiving signal components within a bandwidth compatible with said IF filter.

37. A method as recited in claim 27, wherein said first and second receiving systems each include an analog to digital converter (ADC) characterized by a sample rate, and wherein the method includes receiving signal components within a bandwidth compatible with said sample rate.

38. A method as recited in claim 37, wherein said ADCs are further characterized by a sample rate after decimation, and wherein the method includes receiving signal components within a bandwidth compatible with said sample rate after decimation.

39. A method as recited in claim 27, wherein said first and second receiving systems each include available memory for storing data representing received signal components, and wherein the method includes receiving signal components within a bandwidth compatible with said available memory.

40. A method as recited in claim 27, wherein said first and second receiving systems each include digital signal processors (DSPs) characterized by DSP processing throughput, and wherein the method includes receiving signal components within a bandwidth compatible with said DSP processing throughput.

41. A method as recited in claim 27, wherein the method includes, at the first receiving system, receiving signal components within a bandwidth compatible with a current load on the first receiving system.

42. A method as recited in claim 27, wherein the method includes, at the first and second receiving systems, tuning to a plurality of channels to receive signals from a plurality of wireless transmitters to be located.

43. A method as recited in claim 27, wherein the method includes, at the first and second receiving systems, tuning to a plurality of selected channels, wherein said selected channels are determined based upon interference levels.

44. A method as recited in claim 43, wherein said selected channels are determined based upon measurements of received signals.

45. A method as recited in claim 43, wherein said selected channels are determined based upon spectrum usage.

46. A method as recited in claim 27, wherein the method further comprises, at the first and second receiving systems, collection of multiple slices of spectrum for bandwidth synthesis.

47. A method as recited in claim 27, wherein the method further comprises, at the first and second receiving systems, use of a sequential pattern of re-tuning a frequency agile receiver to cover a substantial part of an OFDM waveform spectrum.

48. A method as recited in claim 27, wherein the method further comprises, at the first and second receiving systems, use of a bandwidth synthesis process to provide increased resolution in a cross-correlation function to reduce multipath delay spread.

49. A method as recited in claim 27, further comprising the use a station-based processing method.

50. A method as recited in claim 27, wherein the method further comprises, at the first or second receiving systems, performing OFDM receiving and demodulation processing.

51. A method as recited in claim 27, wherein the method further comprises, at the first and second receiving systems, the use of narrowband receivers.

52. A method as recited in claim 27, wherein the method further comprises, at the first and second receiving systems, the use of wideband receivers.

53. A computer readable medium comprising executable instructions for use by a receiving system deployed in a system for locating wireless transmitters employing an Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme, wherein said OFDM scheme comprises transmitting signal components over a plurality of predefined narrowband frequency channels spanning a predefined wideband channel, the computer readable medium comprising executable instructions for causing a receiving system to carry out a method comprising the steps of receiving a fraction of the signal components transmitted by a wireless transmitter to be located in a fraction of the narrowband frequency channels, and processing said fraction of the signal components to derive location related measurements.

54. A computer readable medium as recited in claim 53, wherein said location related measurements comprise time difference of arrival (TDOA) measurements.

55. A computer readable medium as recited in claim 53, wherein said location related measurements comprise time of arrival (TOA) measurements.

56. A computer readable medium as recited in claim 53, wherein said location related measurements comprise angle of arrival (AOA) measurements.

57. A computer readable medium as recited in claim 53, wherein said location related measurements comprise round trip time measurements.

58. A computer readable medium as recited in claim 53, wherein said location related measurements comprise received power measurements.

59. A computer readable medium as recited in claim 53, wherein said fraction of the narrowband frequency channels includes at least one pilot channel in which said first wireless transmitter transmits energy, and wherein signal components in said pilot channel are used to aid in signal acquisition and demodulation.

60. A computer readable medium as recited in claim 53, wherein said fraction of the narrowband frequency channels excludes guard channels in which said first wireless transmitter transmits minimal energy.

61. A computer readable medium as recited in claim 53, wherein said receiving system includes a radio frequency (RF) filter, and wherein the method includes receiving signal components within a bandwidth compatible with said RF filter.

62. A computer readable medium as recited in claim 53, wherein said receiving system includes an intermediate frequency (IF) filter, and wherein the method includes receiving signal components within a bandwidth compatible with said IF filter.

63. A computer readable medium as recited in claim 53, wherein said receiving system includes an analog to digital converter (ADC) characterized by a sample rate, and wherein the method includes receiving signal components within a bandwidth compatible with said sample rate.

64. A computer readable medium as recited in claim 63, wherein said ADCs are further characterized by a sample rate after decimation, and wherein the method includes receiving signal components within a bandwidth compatible with said sample rate after decimation.

65. A computer readable medium as recited in claim 53, wherein said receiving system includes available memory for storing data representing received signal components, and wherein the method includes receiving signal components within a bandwidth compatible with said available memory.

66. A computer readable medium as recited in claim 53, wherein said receiving system includes digital signal processors (DSPs) characterized by DSP processing throughput, and wherein the method includes receiving signal components within a bandwidth compatible with said DSP processing throughput.

67. A computer readable medium as recited in claim 53, wherein the method includes, at the receiving system, receiving signal components within a bandwidth compatible with a current load on the receiving system.

68. A computer readable medium as recited in claim 53, wherein the method includes, at the receiving system, tuning to a plurality of channels to receive signals from a plurality of wireless transmitters to be located.

69. A computer readable medium as recited in claim 53, wherein the method includes, at the receiving system, tuning to a plurality of selected channels, wherein said selected channels are determined based upon interference levels.

70. A computer readable medium as recited in claim 69, wherein said selected channels are determined based upon measurements of received signals.

71. A computer readable medium as recited in claim 69, wherein said selected channels are determined based upon spectrum usage.

72. A computer readable medium as recited in claim 53, wherein the method further comprises, at the receiving system, collection of multiple slices of spectrum for bandwidth synthesis.

73. A computer readable medium as recited in claim 53, wherein the method further comprises, at the receiving system, use of a sequential pattern of re-tuning a frequency agile receiver to cover a substantial part of an OFDM waveform spectrum.

74. A computer readable medium as recited in claim 53, wherein the method further comprises, at the receiving system, use of a bandwidth synthesis process to provide increased resolution in a cross-correlation function to reduce multipath delay spread.

75. A computer readable medium as recited in claim 53, wherein the method further comprises the use a station-based processing method.

76. A computer readable medium as recited in claim 53, wherein the method further comprises, at the receiving system, performing OFDM receiving and demodulation processing.

77. A computer readable medium as recited in claim 53, wherein the method further comprises, at the receiving system, the use of narrowband receivers.

78. A computer readable medium as recited in claim 53, wherein the method further comprises, at the receiving system, the use of wideband receivers.