Position location using broadcast digital television signals

• US 20030052822A1
• Filed: 07/31/2002
• Published: 03/20/2003
• Est. Priority Date: 02/02/2001
• Status: Active Grant

• Current Assignee: TruePosition Incorporated
• Original Assignee: Rosum Corporation (Liberty Broadband Corp.)
• Inventors: Rabinowitz, Matthew, Spilker, James J. Jr.
• Granted Patent: US 6,861,984 B2
• Time in Patent Office: Days
• US Class Current: 342/464
• CPC Class Codes: A63F 2300/205 for detecting the geographical location of the game platform
• CPC Class Codes: G01C 21/206 specially adapted for indoor navigation
• CPC Class Codes: G01S 19/46 the supplementary measurement being of a radio-wave signal type
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/0054 of actual mobile position, i.e. position calculation on base station
• CPC Class Codes: G01S 5/0081 Transmission between base stations
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/02213 Receivers arranged in a network for determining the position of a transmitter
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: G01S 5/145 Using a supplementary range measurement, e.g. based on pseudo-range measurements
• CPC Class Codes: H04N 21/25841 involving the geographical location of the client retrieval from the Internet by querying based on geographical locations G06F16/9537; arrangements for identifying locations of receiving stations in broadcast systems H04H60/51; location of the user terminal in data switching networks H04L67/52; services making use of the location of users or terminals in wireless networks H04W4/02; locating users or terminals in wireless networks H04W64/00
• CPC Class Codes: H04N 21/2662 Controlling the complexity of the video stream, e.g. by scaling the resolution or bitrate of the video stream based on the client capabilities
• CPC Class Codes: H04N 21/2668 Creating a channel for a dedicated end-user group, e.g. insertion of targeted commercials based on end-user profiles information retrieval from the Internet by querying with filtering and personalisation G06F16/9535; arrangements for replacing or switching information during the broadcast H04H20/10; push services over packet-switching network H04L12/1859; adaptation of message content in packet-switching networks H04L51/063
• CPC Class Codes: H04N 21/41422 located in transportation means, e.g. personal vehicle arrangements specially adapted for transportation systems in broadcast systems H04H20/62
• CPC Class Codes: H04N 21/615 Signal processing at physical level signal processing in analog two-way television systems H04N7/173
• CPC Class Codes: H04N 21/8126 involving additional data, e.g. news, sports, stocks, weather forecasts

Abstract

A computer program product, apparatus, and method for determining the position of a user terminal. It includes receiving at the user terminal a plurality of digital television (DTV) broadcast signals from a plurality of DTV transmitters, determining a pseudo-range between the user terminal and each DTV transmitter based on the DTV broadcast signals, and determining a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

Claims

1. A method for determining the position of a user terminal, comprising:

receiving at the user terminal a plurality of digital television (DTV) broadcast signals from a plurality of DTV transmitters;

determining a pseudo-range between the user terminal and each DTV transmitter based on the DTV broadcast signals; and

determining a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

2. The method of claim 1, wherein determining a position of the user terminal comprises:

adjusting the pseudo-ranges based on a difference between a transmitter clock at one of the DTV transmitters and a known time reference; and

determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

3. The method of claim 1, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the pseudo-ranges are determined based on a known digital sequence in the ATSC frame.

4. The method of claim 3, wherein the known digital sequence is a synchronization code.

5. The method of claim 4, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

6. The method of claim 4, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

7. The method of claim 1, wherein determining a position of the user terminal comprises:

determining an offset between a local time reference in the user terminal and a master time reference; and

determining the position of the user terminal based on the pseudo-ranges, the location of each of the DTV transmitters, and the offset.

8. The method of claim 7, further comprising:

determining a subsequent position of the user terminal using the offset.

9. The method of claim 1, wherein determining a pseudo-range comprises:

storing a portion of each of the DTV signals; and

subsequently correlating each of the stored portions and a signal generated by the user terminal to produce the pseudo-ranges.

10. The method of claim 1, wherein determining a pseudo-range comprises:

correlating each of the DTV signals with a signal generated by the user terminal as the DTV signals are received to produce the pseudo-ranges.

11. The method of claim 1, wherein determining a position of the user terminal comprises:

determining a general geographic area within which the user terminal is located; and

determining the position of the user terminal based on the pseudo-ranges and the general geographic area.

12. The method of claim 11, wherein the general geographic area is a footprint of an additional transmitter communicably linked to the user terminal.

13. The method of claim 1, wherein determining a position of the user terminal comprises:

determining a tropospheric propagation velocity in a vicinity of the user terminal;

adjusting the value of each pseudo-range based on the tropospheric propagation velocity; and

determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

14. The method of claim 1, wherein determining a position of the user terminal comprises:

adjusting each pseudo-range based on a terrain elevation in a vicinity of the user terminal; and

determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

15. The method of claim 1, further comprising:

selecting the DTV signals based on an identity of an additional transmitter communicably linked to the user terminal and a stored table correlating the additional transmitter and the received DTV broadcast signals.

16. The method of claim 1, further comprising:

accepting a location input from a user; and

selecting the DTV signals based on the location input.

17. The method of claim 1, further comprising:

scanning available DTV signals to assemble a fingerprint of the location; and

selecting the DTV broadcast signals used to determine the pseudo-ranges based on the fingerprint and a stored table that matches known fingerprints with known locations.

18. The method of claim 1, further comprising:

using receiver autonomous integrity monitoring (RAIM) to check the integrity of each pseudo-range based on redundant pseudo-ranges from the DTV transmitters.

19. A method for determining the position of a user terminal, comprising:

receiving at the user terminal a plurality of digital television (DTV) broadcast signals from a plurality of DTV transmitters;

determining a pseudo-range between the user terminal and each DTV transmitter based on the DTV broadcast signals; and

transmitting the pseudo-ranges to a location server configured to determine a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

20. The method of claim 19, wherein determining a pseudo-range comprises:

determining a time of transmission from one of the DTV transmitters of a component of the DTV broadcast signal;

determining a time of reception at the user terminal of the component; and

determining the difference between the time of transmission and the time of reception.

21. The method of claim 19, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the component is a known digital sequence in the ATSC frame.

22. The method of claim 21, wherein the component is a synchronization code.

23. The method of claim 22, wherein the synchronization code is a field synchronization segment within an ATSC data frame.

24. The method of claim 22, wherein the synchronization code is a synchronization segment within a data segment within an ATSC data frame.

25. The method of claim 19, wherein determining a pseudo-range comprises:

storing a portion of each of the DTV signals; and

subsequently correlating each of the stored portions and a signal generated by the user terminal to produce the pseudo-ranges.

26. The method of claim 19, wherein determining a pseudo-range comprises:

correlating each of the DTV signals with a signal generated by the user terminal as the DTV signals are received to produce the pseudo-ranges.

27. A method for determining the position of a user terminal, comprising:

receiving a plurality of pseudo-ranges from a user terminal, each pseudo-range determined between the user terminal and one of a plurality of DTV transmitters based on DTV signals broadcast by the DTV transmitters; and

determining a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

28. The method of claim 27, wherein determining a position of the user terminal comprises:

adjusting the pseudo-ranges based on a difference between a transmitter clock at one of the DTV transmitters and a known time reference; and

determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

29. The method of claim 27, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the pseudo-ranges are determined based on a known digital sequence in the ATSC frame.

30. The method of claim 29, wherein the known digital sequence is a synchronization code.

31. The method of claim 30, wherein the synchronization code is a field synchronization segment within an ATSC data frame.

32. The method of claim 30, wherein the synchronization code is a synchronization segment within a data segment within an ATSC data frame.

33. The method of claim 27, wherein determining a position of the user terminal comprises:

determining an offset between a local time reference in the user terminal and a master time reference; and

determining the position of the user terminal based on the pseudo-ranges, the location of each of the DTV transmitters, and the offset.

34. The method of claim 33, further comprising:

determining a subsequent position of the user terminal using the offset.

35. The method of claim 27, wherein determining a position of the user terminal comprises:

determining a general geographic area within which the user terminal is located; and

determining the position of the user terminal based on the pseudo-ranges and the general geographic area.

36. The method of claim 35, wherein the general geographic area is a footprint of an additional transmitter communicably linked to the user terminal.

37. The method of claim 27, wherein determining a position of the user terminal comprises:

determining a tropospheric propagation velocity in a vicinity of the user terminal;

adjusting the value of each pseudo-range based on the tropospheric propagation velocity; and

determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

38. The method of claim 27, wherein determining a position of the user terminal comprises:

adjusting each pseudo-range based on the terrain elevation in the vicinity of the user terminal; and

determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

39. An apparatus for determining the position of a user terminal, comprising:

means for receiving at the user terminal a plurality of digital television (DTV) broadcast signals from a plurality of DTV transmitters;

means for determining a pseudo-range between the user terminal and each DTV transmitter based on the DTV broadcast signals; and

means for determining a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

40. The apparatus of claim 39, wherein means for determining a position of the user terminal comprises:

means for adjusting the pseudo-ranges based on a difference between a transmitter clock at one of the DTV transmitters and a known time reference; and

means for determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

41. The apparatus of claim 39, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the pseudo-ranges are determined based on a known digital sequence in the ATSC frame.

42. The apparatus of claim 41, wherein the known digital sequence is a synchronization code.

43. The apparatus of claim 42, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

44. The apparatus of claim 42, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

45. The apparatus of claim 39, wherein means for determining a position of the user terminal comprises:

means for determining an offset between a local time reference in the user terminal and a master time reference; and

means for determining the position of the user terminal based on the pseudo-ranges, the location of each of the DTV transmitters, and the offset.

46. The apparatus of claim 45, further comprising:

means for determining a subsequent position of the user terminal using the offset.

47. The apparatus of claim 39, wherein means for determining a pseudo-range comprises:

means for storing a portion of each of the DTV signals; and

means for subsequently correlating each of the stored portions and a signal generated by the user terminal to produce the pseudo-ranges.

48. The apparatus of claim 39, wherein means for determining a pseudo-range comprises:

means for correlating each of the DTV signals with a signal generated by the user terminal as the DTV signals are received to produce the pseudo-ranges.

49. The apparatus of claim 39, wherein means for determining a position of the user terminal comprises:

means for determining a general geographic area within which the user terminal is located; and

means for determining the position of the user terminal based on the pseudo-ranges and the general geographic area.

50. The apparatus of claim 49, wherein the general geographic area is a footprint of an additional transmitter communicably linked to the user terminal.

51. The apparatus of claim 39, wherein means for determining a position of the user terminal comprises:

means for determining a tropospheric propagation velocity in the vicinity of the user terminal;

means for adjusting the value of each pseudo-range based on the tropospheric propagation velocity; and

means for determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

52. The apparatus of claim 39, wherein means for determining a position of the user terminal comprises:

means for adjusting each pseudo-range based on a terrain elevation in a vicinity of the user terminal; and

means for determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

53. The apparatus of claim 39, further comprising:

means for selecting the DTV signals based on an identity of an additional transmitter communicably linked to the user terminal and a stored table correlating the additional transmitter and the received DTV broadcast signals.

54. The apparatus of claim 39, further comprising:

means for accepting a location input from a user; and

means for selecting the DTV signals based on the location input.

55. The apparatus of claim 39, further comprising:

means for scanning available DTV signals to assemble a fingerprint of the location; and

means for selecting the DTV broadcast signals used to determine the pseudo-ranges based on the fingerprint and a stored table that matches known fingerprints with known locations.

56. The apparatus of claim 39, further comprising:

means for using receiver autonomous integrity monitoring (RAIM) to check the integrity of each pseudo-range based on redundant pseudo-ranges from the DTV transmitters

57. An apparatus for determining the position of a user terminal, comprising:

means for receiving at the user terminal a plurality of digital television (DTV) broadcast signals from a plurality of DTV transmitters;

means for determining a pseudo-range between the user terminal and each DTV transmitter based on the DTV broadcast signals; and

means for transmitting the pseudo-ranges to a location server configured to determine a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

58. The apparatus of claim 57, wherein means for determining a pseudo-range comprises:

means for determining a time of transmission from one of the DTV transmitters of a component of the DTV broadcast signal;

means for determining a time of reception at the user terminal of the component; and

means for determining the difference between the time of transmission and the time of reception.

59. The apparatus of claim 57, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the component is a known digital sequence in the ATSC frame.

60. The apparatus of claim 59, wherein the component is a synchronization code.

61. The apparatus of claim 60, wherein the synchronization code is a field synchronization segment within an ATSC data frame.

62. The apparatus of claim 60, wherein the synchronization code is a synchronization segment within a data segment within an ATSC data frame.

63. The apparatus of claim 57, wherein means for determining a pseudo-range comprises:

means for storing a portion of each of the DTV signals; and

means for subsequently correlating each of the stored portions and a signal generated by the user terminal to produce the pseudo-ranges.

64. The apparatus of claim 57, wherein means for determining a pseudo-range comprises:

means for correlating each of the DTV signals with a signal generated by the user terminal as the DTV signals are received to produce the pseudo-ranges.

65. An apparatus for determining the position of a user terminal, comprising:

means for receiving a plurality of pseudo-ranges from a user terminal, each pseudo-range determined between the user terminal and one of a plurality of DTV transmitters based on DTV signals broadcast by the DTV transmitters; and

means for determining a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

66. The apparatus of claim 65, wherein means for determining a position of the user terminal comprises:

means for adjusting the pseudo-ranges based on a difference between a transmitter clock at one of the DTV transmitters and a known time reference; and

means for determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

67. The apparatus of claim 65, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the pseudo-ranges are determined based on a known digital sequence in the ATSC frame.

68. The apparatus of claim 67, wherein the known digital sequence is a synchronization code.

69. The apparatus of claim 68, wherein the synchronization code is a field synchronization segment within an ATSC data frame.

70. The apparatus of claim 68, wherein the synchronization code is a synchronization segment within a data segment within an ATSC data frame.

71. The apparatus of claim 65, wherein means for determining a position of the user terminal comprises:

means for determining an offset between a local time reference in the user terminal and a master time reference; and

means for determining the position of the user terminal based on the pseudo-ranges, the location of each of the DTV transmitters, and the offset.

72. The apparatus of claim 71, further comprising:

means for determining a subsequent position of the user terminal using the offset.

73. The apparatus of claim 65, wherein means for determining a position of the user terminal comprises:

means for determining a general geographic area within which the user terminal is located; and

means for determining the position of the user terminal based on the pseudo-ranges and the general geographic area.

74. The apparatus of claim 73, wherein the general geographic area is a footprint of an additional transmitter communicably linked to the user terminal.

75. The apparatus of claim 65, wherein means for determining a position of the user terminal comprises:

means for determining a tropospheric propagation velocity in a vicinity of the user terminal;

means for adjusting the value of each pseudo-range based on the tropospheric propagation velocity; and

means for determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

76. The apparatus of claim 65, wherein means for determining a position of the user terminal comprises:

means for adjusting each pseudo-range based on the terrain elevation in the vicinity of the user terminal; and

means for determining the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

77. A computer program product, tangibly stored on a computer-readable medium, for determining the position of a user terminal, comprising instructions operable to cause a programmable processor to:

receive at the user terminal a plurality of digital television (DTV) broadcast signals from a plurality of DTV transmitters;

determine a pseudo-range between the user terminal and each DTV transmitter based on the DTV broadcast signals; and

determine a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

78. The computer program product of claim 77, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

adjust the pseudo-ranges based on a difference between a transmitter clock at one of the DTV transmitters and a known time reference; and

determine the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

79. The computer program product of claim 77, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the pseudo-ranges are determined based on a known digital sequence in the ATSC frame.

80. The computer program product of claim 79, wherein the known digital sequence is a synchronization code.

81. The computer program product of claim 80, wherein the synchronization code is a Field Synchronization Segment within an ATSC data frame.

82. The computer program product of claim 80, wherein the synchronization code is a Synchronization Segment within a Data Segment within an ATSC data frame.

83. The computer program product of claim 77, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

determine an offset between a local time reference in the user terminal and a master time reference; and

determine the position of the user terminal based on the pseudo-ranges, the location of each of the DTV transmitters, and the offset.

84. The computer program product of claim 83, further comprising instructions operable to cause a programmable processor to:

determine a subsequent position of the user terminal using the offset.

85. The computer program product of claim 77, wherein instructions operable to cause a programmable processor to determine a pseudo-range comprise instructions operable to cause a programmable processor to:

store a portion of each of the DTV signals; and

subsequently correlate each of the stored portions and a signal generated by the user terminal to produce the pseudo-ranges.

86. The computer program product of claim 77, wherein instructions operable to cause a programmable processor to determine a pseudo-range comprise instructions operable to cause a programmable processor to:

correlate each of the DTV signals with a signal generated by the user terminal as the DTV signals are received to produce the pseudo-ranges.

87. The computer program product of claim 77, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

determine a general geographic area within which the user terminal is located; and

determine the position of the user terminal based on the pseudo-ranges and the general geographic area.

88. The computer program product of claim 87, wherein the general geographic area is a footprint of an additional transmitter communicably linked to the user terminal.

89. The computer program product of claim 77, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to

determine a tropospheric propagation velocity in a vicinity of the user terminal;

adjust the value of each pseudo-range based on the tropospheric propagation velocity; and

determine the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

90. The computer program product of claim 77, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

adjust each pseudo-range based on the terrain elevation in the vicinity of the user terminal; and

determine the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

91. The computer program product of claim 77, further comprising instructions operable to cause a programmable processor to:

select the DTV signals based on an identity of an additional transmitter communicably linked to the user terminal and a stored table correlating the additional transmitter and the received DTV broadcast signals.

92. The computer program product of claim 77, further comprising instructions operable to cause a programmable processor to:

accept a location input from a user; and

select the DTV signals based on the location input.

93. The computer program product of claim 77, further comprising instructions operable to cause a programmable processor to:

scan available DTV signals to assemble a fingerprint of the location; and

select the DTV broadcast signals used to determine the pseudo-ranges based on the fingerprint and a stored table that matches known fingerprints with known locations.

94. The computer program product of claim 77, further comprising instructions operable to cause a programmable processor to:

use receiver autonomous integrity monitoring (RAIM) to check the integrity of each pseudo-range based on redundant pseudo-ranges from the DTV transmitters

95. A computer program product, tangibly stored on a computer-readable medium, for determining the position of a user terminal, comprising instructions operable to cause a programmable processor to:

receive at the user terminal a plurality of digital television (DTV) broadcast signals from a plurality of DTV transmitters;

determine a pseudo-range between the user terminal and each DTV transmitter based on the DTV broadcast signals; and

transmit the pseudo-ranges to a location server configured to determine a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

96. The computer program product of claim 95, wherein instructions operable to cause a programmable processor to determine a pseudo-range comprise instructions operable to cause a programmable processor to:

determine a time of transmission from one of the DTV transmitters of a component of the DTV broadcast signal;

determine a time of reception at the user terminal of the component; and

determining the difference between the time of transmission and the time of reception.

97. The computer program product of claim 95, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the component is a known digital sequence in the ATSC frame.

98. The computer program product of claim 97, wherein the component is a synchronization code.

99. The computer program product of claim 98, wherein the synchronization code is a field synchronization segment within an ATSC data frame.

100. The computer program product of claim 98, wherein the synchronization code is a synchronization segment within a data segment within an ATSC data frame.

101. The computer program product of claim 95, wherein instructions operable to cause a programmable processor to determine a pseudo-range comprise instructions operable to cause a programmable processor to:

store a portion of each of the DTV signals; and

subsequently correlate each of the stored portions and a signal generated by the user terminal to produce the pseudo-ranges.

102. The computer program product of claim 95, wherein instructions operable to cause a programmable processor to determine a pseudo-range comprise instructions operable to cause a programmable processor to:

correlate each of the DTV signals with a signal generated by the user terminal as the DTV signals are received to produce the pseudo-ranges.

103. A computer program product, tangibly stored on a computer-readable medium, for determining the position of a user terminal, comprising instructions operable to cause a programmable processor to:

receive a plurality of pseudo-ranges from a user terminal, each pseudo-range determined between the user terminal and one of a plurality of DTV transmitters based on DTV signals broadcast by the DTV transmitters; and

determine a position of the user terminal based on the pseudo-ranges and a location of each of the DTV transmitters.

104. The computer program product of claim 103, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

adjust the pseudo-ranges based on a difference between a transmitter clock at one of the DTV transmitters and a known time reference; and

determine the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

105. The computer program product of claim 103, wherein the DTV broadcast signal is an American Television Standards Committee (ATSC) DTV signal, and the pseudo-ranges are determined based on a known digital sequence in the ATSC frame.

106. The computer program product of claim 105, wherein the known digital sequence is a synchronization code.

107. The computer program product of claim 106, wherein the synchronization code is a field synchronization segment within an ATSC data frame.

108. The computer program product of claim 106, wherein the synchronization code is a synchronization segment within a data segment within an ATSC data frame.

109. The computer program product of claim 103, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

determine an offset between a local time reference in the user terminal and a master time reference; and

determine the position of the user terminal based on the pseudo-ranges, the location of each of the DTV transmitters, and the offset.

110. The computer program product of claim 109, further comprising instructions operable to cause a programmable processor to:

determine a subsequent position of the user terminal using the offset.

111. The computer program product of claim 103, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

determine a general geographic area within which the user terminal is located; and

determine the position of the user terminal based on the pseudo-ranges and the general geographic area.

112. The computer program product of claim 111, wherein the general geographic area is a footprint of an additional transmitter communicably linked to the user terminal.

113. The computer program product of claim 103, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

determine a tropospheric propagation velocity in the vicinity of the user terminal;

adjust the value of each pseudo-range based on the tropospheric propagation velocity; and

determine the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.

114. The computer program product of claim 103, wherein instructions operable to cause a programmable processor to determine a position of the user terminal comprise instructions operable to cause a programmable processor to:

adjust each pseudo-range based on the terrain elevation in the vicinity of the user terminal; and

determine the position of the user terminal based on the adjusted pseudo-ranges and the location of each of the DTV transmitters.