Method and apparatus for geolocating a wireless communications device

• US 20050184907A1
• Filed: 04/18/2005
• Published: 08/25/2005
• Est. Priority Date: 03/18/2002
• Status: Active Grant

• Current Assignee: Christopher J. Hall, Clay S. Turner, Jimmy C. Ray
• Original Assignee: Christopher J. Hall, Clay S. Turner, Jimmy C. Ray
• Inventors: Hall, Christopher J., Ray, Jimmy C., Turner, Clay S.
• Granted Patent: US 7,057,556 B2
• Time in Patent Office: Days
• US Class Current: 342/387
• 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: H04M 2207/18 wireless networks
• CPC Class Codes: H04M 2242/30 Determination of the location of a subscriber
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

The time difference of arrival for a signal received at two or more receiving sites as transmitted from a wireless communications device, is determined by a frequency domain technique. The constituent frequencies of the signals received at the two or more receiving sites are determined, including the phase, or a value representative of the phase, of each frequency component. The phase values for the same frequency are subtracted to yield a phase difference values as a function of frequency. The slope of the function represents the time difference of arrival for the wireless communications device signal as received at the two receiving sites. To determine the mobile location based on the determined time difference of arrival values, a seed or initial location is first assumed for the wireless communications device and the distance difference of arrival (the time difference of arrival multiplied by the speed of light) is calculated. The calculated time difference of arrival is then used to adjust the distance difference of arrival by continuously iterating the position of the wireless communications device until the calculated distance of arrival and the calculated time difference of arrival (as multiplied by the speed of light) are within a predetermined margin.

Claims

1-60. -60. (canceled)

61. A method for determining a time difference of arrival of a signal received at two or more receiving sites, the method comprising:

(a) transforming each one of the two or more signals to a frequency domain representation comprising a plurality of frequency components, each frequency component having a phase associated therewith;

(b) operating in the frequency domain, determining a Hermitian product for like-frequency components in the frequency domain representation of each of the two or more signals;

(c) operating in the frequency domain, determining a phase angle of each Hermitian product determined at the step (b), wherein each product is a function of frequency;

(d) combining the phase angles determined at the step (c) to determine a statistical representation of the phase angles; and

(e) determining the time difference of arrival from the statistical representation.

62. The method of claim 61 wherein the signal is transmitted from a transmitting unit selected from among a mobile communications device, a portable communications device, a personal communications device, a cellular communications device, a push-to-talk communications device and a trunked radio.

63. The method of claim 61 wherein the two or more receiving sites comprises N receiving sites, and wherein the time difference of arrival is determined pairwise among N receiving sites.

64. The method of claim 61 wherein the step (a) further comprises transforming each one of the two or more signals using a transformation process selected from among a Fourier transform integral, a fast Fourier transform algorithm, a discrete Fourier transform, a Hartley transform, a Hilbert transform and a Laplace transform.

65. The method of claim 61 further comprising a step (f) determining the location of the transmitting unit from the time difference of arrival determined at the step (e).

66. The method of claim 61 wherein the step (e) comprises generating a phase angle versus frequency function and determining the location from the slope of the function.

67. The method of claim 66 wherein a y-intercept of the phase angle versus frequency function represents a frequency offset between the signal received by the at least two of the plurality of receiving sites.

68. The method of claim 67 wherein each receiving site comprises signal receiving apparatuses and further comprising a step (f) returning the signal receiving apparatuses at the receiving sites to reduce the frequency offset.

69. The method of claim 61 wherein the step (d) comprises combining the phase angles utilizing a regression analysis or a weighted regression analysis to determine the statistical representation of the phase angles.

70. The method of claim 61 wherein the signal is transmitted from a cellular telephone and the two or more receiving sites comprise two or more cellular base stations.

71. The method of claim 61 wherein the signal is transmitted from a cellular telephone and the two or more receiving sites are selected from among two or more cellular base stations, two or more cellular monitoring stations, and a combination of cellular base stations and cellular monitoring stations.

72. The method of claim 61 wherein the signal received at the two or more receiving sites is selected from among a cell access attempt signal, a response to an incoming call, a registration signal, a control channel signal and a call requesting the dispatch of emergency or other position-relevant services.

73. The method of claim 61 wherein the step (a) further comprises determining a signal arrival time at the two or more receiving sites relative to a common time reference and determining an identification of the transmitting unit.

74. The method of claim 61 wherein the step (a) is executed at each of the two or more receiving sites.

75. The method of claim 61 further comprising providing the frequency domain representation from each of the two or more receiving sites to a processing site, and executing the steps (b)-(e) at the processing site.

76. The method of claim 75 wherein the step of providing the frequency domain representation to the processing site further comprises providing the frequency domain representation to the processing site over a narrow bandwidth transmission medium.

77. The method of claim 76 further comprising determining a location at the processing site in response to the results of the step (e).

78. The method of claim 61 wherein the result of forming the Hermeitian product is a vector comprising a plurality of elements, and wherein each element comprises a value representing the phase angle difference for a like-frequency component.

79. The method of claim 78 wherein the number of vectors is less than or equal to the number of pairwise combinations of receiving sites.

80. The method of claim 61 wherein the same time domain signal is received at the two or more receiving sites, further comprising sampling the time domain signal and providing the sampled time domain signal to a processing site, wherein the steps (a)-(e) are executed at the processing site.

81. The method of claim 61 wherein the signal has a known format, and wherein the time difference of arrival as determined for the signal received at the two or more receiving sites is responsive to a reference point within the known format.

82. The method of claim 61 further comprising:

(f) determining an estimated location of the transmitting unit from the time difference of arrival;

(g) determining an actual location of the transmitting unit; and

(h) determining a difference between the estimated location and the actual location.

83. The method of claim 61 wherein the step (a) further comprises filtering the frequency domain representation to control the effect of certain frequency domain components on the time difference of arrival determination.

84. The method of claim 83 wherein the step of filtering further comprises determining a signal quality metric for the frequency domain components, determining a signal quality metric threshold and removing frequency components having a signal quality metric below the signal quality metric threshold.

85. The method of claim 83 wherein the step of filtering further comprises determining a signal quality metric for each frequency domain component and weighting the frequency components in accordance with the signal quality metric.

86. A method for determining a time difference of arrival of a signal received at two or more receiving sites, the method comprising:

(a) transforming each one of the two or more signals to a frequency domain representation comprising a plurality of frequency components, each frequency component having a phase associated therewith;

(b) operating in the frequency domain, determining a Hermitian product for like-frequency components in the frequency domain representation of the signals received at the two or more receiving sites;

(c) operating in the frequency domain, determining a phase function representing the phase angle of each Hermitian product as a function of frequency; and

(d) determining the time difference of arrival from the phase function.

87. The method of claim 86 wherein the step (d) further comprises determining a derivative of the phase function with respect to frequency and determining the time difference of arrival from the derivative.

88. The method of claim 87 wherein the step (d) further comprises determining the time difference of arrival by performing a linear regression operation on the derivative of the phase function.

89. The method of claim 88 wherein the linear regression operation further comprises a weighted linear regression operation.

90. The method of claim 86 wherein the signal is transmitted from a transmitting unit selected from among a mobile communications device, a portable communications device, a personal communications device, a cellular communications device, a push-to-talk communications device and a trunked radio.

91. The method of claim 86 wherein the two or more receiving sites comprises N receiving sites, and wherein the time difference of arrival is determined pairwise among the N receiving sites.

92. The method of claim 86 further comprising a step (e) determining a location of the transmitting unit from the time difference of arrival determined at the step (d).

93. The method of claim 86 wherein the signal is transmitted from a transmitting unit comprising a cellular telephone and the two or more receiving sites comprise two or more cellular base stations.

94. The method of claim 86 wherein the signal is transmitted from a transmitting unit comprising a cellular telephone and the two or more receiving sites are selected from among two or more cellular base stations, two or more cellular monitoring stations, and a combination of cellular base stations and cellular monitoring stations.

95. The method of claim 86 wherein the step (a) is executed at each of the two or more receiving sites.

96. The method of claim 86 further comprising providing the frequency domain representation at each of the two or more receiving sites to a processing site and executing the steps (b)-(d) at the processing site.

97. The method of claim 86 wherein the step (a) further comprises filtering the frequency domain representation to control the effect of certain frequency domain components on the time difference of arrival determination.

98. The method of claim 97 wherein the step of filtering further comprises determining a signal quality metric for the frequency domain components and weighting the frequency components in response to the signal quality metric.

99. The method of claim 86 wherein the step (a) further comprises transforming each one of the two or more signals to the frequency domain representation using a process selected from among, a Fourier transform integral, a fast Fourier transform algorithm, a discrete Fourier transform, a Hartley transform, a Hilbert transform and a Laplace transform.

100. A method for determining the location of a transmitting unit transmitting a signal, in response to the time difference of arrival of the signal at two or more receiving sites, comprising:

(a) selecting a location estimate for the transmitting unit;

(b) determining the pairwise distance difference of arrival from the location estimate to at least two of the two or more receiving sites;

(c) determining the error in the location estimate in response to the distance difference of arrival value determined at the step (b); and

(d) updating the location estimate in response to the error.

101. The method of claim 100 further comprising determining a predetermined threshold value and a step (e), repeating the steps (b) through (d) until the error is less than the threshold value.

102. The method of claim 100 wherein the distance difference of arrival value is the product of the time difference of arrival and the speed of light.

103. The method of claim 100 wherein the (a) further comprising selecting a location estimate of the geographic center of the two or more receiving sites.

104. The method of claim 100 wherein the step (c) further comprises:

(c1) determining a linear differential equation relating the distance difference of arrival, the geographic location of the two or more receiving sites, the location estimate and the error in the location estimate; and

(c2) solving the linear differential equation to determine the error in the location estimate.

105. The method of claim 104 wherein the step (c2) further comprises solving the linear differential equation according to a least squared error process.

106. The method of claim 100 wherein the step (b) further comprises determining the distance difference of arrival for the pairwise combinations of the receiving sites, wherein the error in the location estimate according to the step (c) further comprises the error in the location estimate with respect to each of the pairwise combinations of receiving sites.

107. The method of claim 100 wherein the location estimate includes a location estimate in three dimensions.

108. An apparatus for determining the location of a transmitting unit transmitting a signal received at two or more receiving sites, the apparatus comprising:

an antenna at each of the two or more receiving sites responsive to the signal;

a processor responsive to the antenna for determining a frequency domain representation for the signal received at the two or more receiving sites by transforming the signal received at the two or more receiving sites to a frequency domain representation comprising a plurality of frequency domain components, and wherein each frequency domain component comprises a two-dimensional number;

the processor for determining the time difference of arrival of the signal as received at the two or more receiving sites in response to the two-dimensional numbers, wherein the time difference of arrival represents the difference in the arrival time of the signal as received at the two or more receiving sites; and

the processor for determining a phase angle of a Hermitian product for like frequency components in the frequency domain representation of the signal received at the two or more receiving sites;

the processor for determining a statistical representation for the phase angles as a function of frequency in response to the phase angles of the Hermitian products;

the processor for determining the time difference of arrival of the signal as received at the two or more receiving sites in response to the statistical representation, wherein the time difference of arrival represents the difference in the arrival time of the signal as received at the two or more receiving sites; and

the processor for determining the location of the transmitting unit in response to the time difference of arrival.

109. A computer program product for determining a time difference of arrival of a signal received at two or more receiving sites, comprising:

a computer usable medium having computer readable program code modules embodied in the medium for determining the time difference of arrival;

a computer readable first program code module for transforming each one of the two or more signals to a frequency domain representation comprising a plurality of frequency components, each frequency component having a phase associated therewith;

a computer readable second program code module for determining a Hermitian product for like-frequency components in the frequency domain representation of the signals received at the two or more receiving sites;

a computer readable third program code module operating in the frequency domain, determining a phase function representing the phase angle of each Hermitian product as a function of frequency; and

computer readable fourth program code module for determining the time difference of arrival from the phase function.