US5608410A — System for locating a source of bursty transmissi…

Claim 1

Independent Claim 299 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites: (b) digitalizing the received bursty responsive transmission at each of said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the step of estimating the position of the mobile transmitter comprises making a coarse estimate by creating a grid of possible latitude and longitude positions for each antenna site pair; calculating, for pairs of antenna sites, theoretical time difference of arrival values from points on the grid; determining a function of a sum of squares of the measured time differences of arrival minus the computed time differences of arrival; and coarsely estimating the position as the point at which the function of the sum of squares is a minimum.

Claim 2

Dependent Claim 299 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites: (b) digitalizing the received bursty responsive transmission at each of said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the step of estimating the position of the mobile transmitter comprises making a coarse estimate by creating a grid of possible latitude and longitude positions for each antenna site pair; calculating, for pairs of antenna sites, theoretical time difference of arrival values from points on the grid; determining a function of a sum of squares of the measured time differences of arrival minus the computed time differences of arrival; and coarsely estimating the position as the point at which the function of the sum of squares is a minimum.

Claim 3

Dependent Claim 64 words

A process as recited in claim 1, wherein the coarse estimation step further includes deriving quality factors representing the quality of the signal received at the antenna sites of said pairs, and the determination of the function of the sum of squares includes weighting the squares of the measured time differences of arrival minus the computed time differences of arrival by the quality factor.

Claim 4

Dependent Claim 42 words

A process as recited in claim 1, further comprising providing a confidence interval along with the location estimate, wherein said confidence interval defines an area around the estimated location and there is a probability the mobile transmitter is located within said area.

Claim 5

Dependent Claim 403 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites; (b) digitalizing the received bursty responsive transmission at each of said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; (e) determining first, second, and third frequency differences of arrival, said first frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and second antenna sites, said second frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and third antenna sites, and said third frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said second and third antenna sites; and (f) estimating the velocity of said standard mobile transmitter on the basis of at least said first, second, and third frequency differences of arrival; wherein the step of estimating the velocity of the mobile transmitter comprises making a coarse estimate by creating a grid or table of possible velocities; calculating, for pairs of antenna sites, theoretical frequency difference of arrival values corresponding to said possible velocities; determining a function of a sum of squares of the measured frequency differences of arrival minus the computed frequency differences of arrival; and coarsely estimating the velocity as the velocity at which the function of the sum of squares is a minimum.

Claim 6

Dependent Claim 403 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites; (b) digitalizing the received bursty responsive transmission at each of said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; (e) determining first, second, and third frequency differences of arrival, said first frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and second antenna sites, said second frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and third antenna sites, and said third frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said second and third antenna sites; and (f) estimating the velocity of said standard mobile transmitter on the basis of at least said first, second, and third frequency differences of arrival; wherein the step of estimating the velocity of the mobile transmitter comprises making a coarse estimate by creating a grid or table of possible velocities; calculating, for pairs of antenna sites, theoretical frequency difference of arrival values corresponding to said possible velocities; determining a function of a sum of squares of the measured frequency differences of arrival minus the computed frequency differences of arrival; and coarsely estimating the velocity as the velocity at which the function of the sum of squares is a minimum.

Claim 7

Dependent Claim 421 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites; (b) digitalizing the received bursty responsive transmission at each of said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the reception and processing of the responsive signal at each antenna site comprises the stems of receiving the responsive signal with an antenna array at each antenna site and providing a high quality signal for further processing; wherein the high quality baseband signals are provided at the respective antenna sites by coherently combining multiple baseband signals so as to reduce the effects of multipath; and further comprising the steps of: (1) generating a substantially unimpaired representation of the baseband signal by remodulating a demodulated signal; (2) determining which antenna in the array likely received the transmission over the shortest and most direct path; (3) performing a correlation between the generated, unimpaired representation of the signal and each of the signals received through each of the antennas, and generating a correlation output function for each signal; (4) determining the relative amount of multipath impairment that may have occurred at each antenna by measuring the width of each correlation output function at a predefined point on the correlation output function; (5) coherently combining the signals that appear to have similar multipath impairments to increase the quality of the signal representation; and (6) estimating a quality factor that is indicative of the relative amount of impairment that will remain in the signal after processing.

Claim 8

Dependent Claim 421 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites; (b) digitalizing the received bursty responsive transmission at each of said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the reception and processing of the responsive signal at each antenna site comprises the stems of receiving the responsive signal with an antenna array at each antenna site and providing a high quality signal for further processing; wherein the high quality baseband signals are provided at the respective antenna sites by coherently combining multiple baseband signals so as to reduce the effects of multipath; and further comprising the steps of: (1) generating a substantially unimpaired representation of the baseband signal by remodulating a demodulated signal; (2) determining which antenna in the array likely received the transmission over the shortest and most direct path; (3) performing a correlation between the generated, unimpaired representation of the signal and each of the signals received through each of the antennas, and generating a correlation output function for each signal; (4) determining the relative amount of multipath impairment that may have occurred at each antenna by measuring the width of each correlation output function at a predefined point on the correlation output function; (5) coherently combining the signals that appear to have similar multipath impairments to increase the quality of the signal representation; and (6) estimating a quality factor that is indicative of the relative amount of impairment that will remain in the signal after processing.

Claim 9

Dependent Claim 332 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites; (b) digitalizing the received bursty responsive transmission at each said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the reception and processing of the responsive signal at each antenna site comprises the steps of receiving the responsive signal with an antenna array at each antenna site; and providing a high quality signal for further processing; and wherein the step of providing a high quality signal comprises sampling a signal from each antenna in said array and formatting the samples into frames of digital data; and providing, on the basis of the frames of data, a high quality digital baseband signal for further processing; and further comprising extracting selected signal characteristics from the high quality baseband signal; compressing the high quality baseband signal so as to retain the selected characteristics; and forwarding the compressed signal to a prescribed location for further processing.

Claim 10

Dependent Claim 332 words

A process for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising the steps of: (a) receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third ground-based antenna sites; (b) digitalizing the received bursty responsive transmission at each said first, second, and third antenna sites; (c) determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the reception and processing of the responsive signal at each antenna site comprises the steps of receiving the responsive signal with an antenna array at each antenna site; and providing a high quality signal for further processing; and wherein the step of providing a high quality signal comprises sampling a signal from each antenna in said array and formatting the samples into frames of digital data; and providing, on the basis of the frames of data, a high quality digital baseband signal for further processing; and further comprising extracting selected signal characteristics from the high quality baseband signal; compressing the high quality baseband signal so as to retain the selected characteristics; and forwarding the compressed signal to a prescribed location for further processing.

Claim 11

Dependent Claim 26 words

A process as recited in claim 6, wherein the selected characteristics include timing, power, frequency, phase, and a factor representing the quality of the baseband signal.

Claim 12

Independent Claim 306 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the means for estimating the position of the mobile transmitter comprises means for making a coarse estimate by creating a grid of possible latitude and longitude positions for each antenna site pair; calculating, for pairs of antenna sites, theoretical time difference of arrival values from points on the grid; determining a function of a sum of squares of the measured time differences of arrival minus the computed time differences of arrival; and coarsely estimating the position as the point at which the function of the sum of squares is a minimum.

Claim 13

Independent Claim 306 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; wherein the means for estimating the position of the mobile transmitter comprises means for making a coarse estimate by creating a grid of possible latitude and longitude positions for each antenna site pair; calculating, for pairs of antenna sites, theoretical time difference of arrival values from points on the grid; determining a function of a sum of squares of the measured time differences of arrival minus the computed time differences of arrival; and coarsely estimating the position as the point at which the function of the sum of squares is a minimum.

Claim 14

Dependent Claim 58 words

A system as recited in claim 8, wherein the means for making a coarse estimation further includes means for deriving quality factors representing the quality of the signal received at the antenna sites of said pairs, and weighting the squares of the measured time differences of arrival minus the computed time differences of arrival by the quality factor.

Claim 15

Dependent Claim 44 words

A system as recited in claim 8, further comprising means for providing a confidence interval along with the location estimate, wherein said confidence interval defines an area around the estimated location and there is a probability the mobile transmitter is located within said area.

Claim 16

Independent Claim 412 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; (e) means for determining first, second, and third frequency differences of arrival, said first frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and second antenna sites, said second frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and third antenna sites, and said third frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said second and third antenna sites; and (f) means for estimating the velocity of said standard mobile transmitter on the basis of at least said first, second, and third frequency differences of arrival; wherein the means for estimating the velocity of the mobile transmitter comprises means for making a coarse estimate by creating a grid of possible velocities; calculating, for pairs of antenna sites, theoretical frequency difference of arrival values from points on the grid; determining a function of a sum of squares of the measured frequency differences of arrival minus the computed frequency differences of arrival; and coarsely estimating the velocity as the velocity at which the function of the sum of squares is a minimum.

Claim 17

Independent Claim 412 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; (e) means for determining first, second, and third frequency differences of arrival, said first frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and second antenna sites, said second frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said first and third antenna sites, and said third frequency difference of arrival representing a difference between the frequency of said responsive transmission as received at said second and third antenna sites; and (f) means for estimating the velocity of said standard mobile transmitter on the basis of at least said first, second, and third frequency differences of arrival; wherein the means for estimating the velocity of the mobile transmitter comprises means for making a coarse estimate by creating a grid of possible velocities; calculating, for pairs of antenna sites, theoretical frequency difference of arrival values from points on the grid; determining a function of a sum of squares of the measured frequency differences of arrival minus the computed frequency differences of arrival; and coarsely estimating the velocity as the velocity at which the function of the sum of squares is a minimum.

Claim 18

Independent Claim 460 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; comprising an antenna array at each antenna site and means for providing a high quality signal for further processing at each antenna site; wherein the means for providing a high quality signal comprises means for sampling a signal from each antenna in said array and formatting the samples into frames of digital data, and providing, on the basis of the frames of data, a high quality digital baseband signal for further processing; and wherein the high quality baseband signals are provided at the respective antenna sites by coherently combining multiple baseband signals so as to reduce the effects of multipath; and further comprising means for: (1) generating a substantially unimpaired representation of the baseband signal by remodulating a demodulated signal; (2) determining which antenna in the array likely received the transmission over the shortest and most direct path; (3) performing a correlation between the generated, unimpaired representation of the signal and each of the signals received through each of the antennas, and generating a correlation output function for each signal; (4) determining the relative amount of multipath impairment that may have occurred at each antenna by measuring the width of each correlation output function at a predefined point on the correlation output function; (5) coherently combining the signals that appear to have similar multipath impairments to increase the quality of the signal representation; and (6) estimating a quality factor that is indicative of the relative amount of impairment that will remain in the signal after processing.

Claim 19

Independent Claim 460 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; comprising an antenna array at each antenna site and means for providing a high quality signal for further processing at each antenna site; wherein the means for providing a high quality signal comprises means for sampling a signal from each antenna in said array and formatting the samples into frames of digital data, and providing, on the basis of the frames of data, a high quality digital baseband signal for further processing; and wherein the high quality baseband signals are provided at the respective antenna sites by coherently combining multiple baseband signals so as to reduce the effects of multipath; and further comprising means for: (1) generating a substantially unimpaired representation of the baseband signal by remodulating a demodulated signal; (2) determining which antenna in the array likely received the transmission over the shortest and most direct path; (3) performing a correlation between the generated, unimpaired representation of the signal and each of the signals received through each of the antennas, and generating a correlation output function for each signal; (4) determining the relative amount of multipath impairment that may have occurred at each antenna by measuring the width of each correlation output function at a predefined point on the correlation output function; (5) coherently combining the signals that appear to have similar multipath impairments to increase the quality of the signal representation; and (6) estimating a quality factor that is indicative of the relative amount of impairment that will remain in the signal after processing.

Claim 20

Independent Claim 326 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; comprising an antenna array at each antenna site and means for providing a high quality signal for further processing at each antenna site; wherein the means for providing a high quality signal comprises means for sampling a signal from each antenna in said array and formatting the samples into frames of digital data, and providing, on the basis of the frames of data, a high quality digital baseband signal for further processing; and further comprising means for extracting selected signal characteristics from the high quality baseband signal; compressing the high quality baseband signal so as to retain the selected characteristics; and forwarding the compressed signal to a prescribed location for further processing.

Claim 21

Independent Claim 326 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) means for receiving a bursty responsive transmission from said standard mobile transmitter at first, second, and third antenna sites; (b) means for digitalizing the received bursty responsive transmission at each of said first, second, and third ground-based antenna sites; (c) means for determining first, second, and third time differences of arrival, said first time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and second antenna sites, said second time difference of arrival representing a difference between the time of arrival of said responsive transmission at said first and third antenna sites, and said third time difference of arrival representing a difference between the time of arrival of said responsive transmission at said second and third antenna sites; and (d) means for estimating the location of said standard mobile transmitter on the basis of at least said first, second, and third time differences of arrival; comprising an antenna array at each antenna site and means for providing a high quality signal for further processing at each antenna site; wherein the means for providing a high quality signal comprises means for sampling a signal from each antenna in said array and formatting the samples into frames of digital data, and providing, on the basis of the frames of data, a high quality digital baseband signal for further processing; and further comprising means for extracting selected signal characteristics from the high quality baseband signal; compressing the high quality baseband signal so as to retain the selected characteristics; and forwarding the compressed signal to a prescribed location for further processing.

Claim 22

Dependent Claim 26 words

A system as recited in claim 13, wherein the selected characteristics include timing, power, frequency, phase, and a factor representing the quality of the baseband signal.

Claim 23

Independent Claim 357 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) at least three ground-based antenna site systems, each antenna site system comprising: an antenna; a sampling subsystem operatively coupled to said antenna for sampling said bursty responsive signal at a prescribed sampling frequency and formatting the sampled signal into frames of digital data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said bursty responsive transmission was received; a baseband convertor operatively coupled to said sampling subsystem for providing baseband signals derived from said frames of data; and a timing subsystem operatively coupled to said sampling subsystem for providing timing signals; and (b) a central site system operatively coupled to said antenna site systems, comprising means for processing said frames of data to generate data identifying said mobile transmitter and the differences in times of arrival of said responsive signal among said antenna site systems; and means for determining, on the basis of said times of arrival differences, the location of the mobile transmitter; and further comprising location estimation means for: (1) creating a grid of theoretical points covering a prescribed geographic area, said theoretical points being spaced at prescribed increments of latitude and longitude; (2) calculating theoretical values of time delay for a plurality of pairs of antenna sites; (3) calculating a least squares difference value based on the theoretical time delays and measured time delays for a plurality of pairs of antenna sites; (4) searching the grid of theoretical points and determining the best theoretical latitude and longitude for which the value of the least squares difference is minimized; and (5) starting at the best theoretical latitude and longitude, performing another linearized-weighted-least-squares iteration to resolve the actual latitude and longitude to within a prescribed number of degrees or fraction of a degree.

Claim 24

Independent Claim 357 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) at least three ground-based antenna site systems, each antenna site system comprising: an antenna; a sampling subsystem operatively coupled to said antenna for sampling said bursty responsive signal at a prescribed sampling frequency and formatting the sampled signal into frames of digital data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said bursty responsive transmission was received; a baseband convertor operatively coupled to said sampling subsystem for providing baseband signals derived from said frames of data; and a timing subsystem operatively coupled to said sampling subsystem for providing timing signals; and (b) a central site system operatively coupled to said antenna site systems, comprising means for processing said frames of data to generate data identifying said mobile transmitter and the differences in times of arrival of said responsive signal among said antenna site systems; and means for determining, on the basis of said times of arrival differences, the location of the mobile transmitter; and further comprising location estimation means for: (1) creating a grid of theoretical points covering a prescribed geographic area, said theoretical points being spaced at prescribed increments of latitude and longitude; (2) calculating theoretical values of time delay for a plurality of pairs of antenna sites; (3) calculating a least squares difference value based on the theoretical time delays and measured time delays for a plurality of pairs of antenna sites; (4) searching the grid of theoretical points and determining the best theoretical latitude and longitude for which the value of the least squares difference is minimized; and (5) starting at the best theoretical latitude and longitude, performing another linearized-weighted-least-squares iteration to resolve the actual latitude and longitude to within a prescribed number of degrees or fraction of a degree.

Claim 25

Dependent Claim 41 words

A system as recited in claim 15, wherein said calculating step (2) comprises accounting for any known site biases caused by mechanical, electrical, or environmental factors, said site biases determined by periodically calculating the positions of reference transmitters at known locations.

Claim 26

Dependent Claim 111 words

A system as recited in claim 15, wherein said least squares difference is given by: LSD=[Q.sub.12 (Delay.sub.-- T.sub.12 Delay.sub.-- O.sub.12).sup.2 +Q.sub.13 (Delay.sub.-- T.sub.13 -Delay.sub.-- O.sub.13).sup.2 +. . . Q.sub.xy (Delay.sub.-- T.sub.xy -Delay.sub.-- O.sub.xy).sup.2 ] where, Delay -- T xy represents the theoretical delay between antenna sites x and y, x and y being indices representative of antenna sites; Delay -- O xy represents the observed delay between antenna sites x and y; Q xy represents a quality factor for the delay measurement between antenna sites x and y, said quality factor being an estimated measure of the degree to which multipath or other anomalies may have affected a particular delay measurement.

Claim 27

Independent Claim 341 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) at least three ground-based antenna site systems, each antenna site system comprising: an antenna; a sampling subsystem operatively coupled to said antenna for sampling said bursty responsive signal at a prescribed sampling frequency and formatting the sampled signal into frames of digital data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said bursty responsive transmission was received; a baseband convertor operatively coupled to said sampling subsystem for providing baseband signals derived from said frames of data; and a timing subsystem operatively coupled to, said sampling subsystem for providing timing signals; and (b) a central site system operatively coupled to said antenna site systems, comprising means for processing said frames of data to generate data identifying said mobile transmitter and the differences in times of arrival of said responsive signal among said antenna site systems; and means for determining, on the basis of said times of arrival differences, the location of the mobile transmitter; and further comprising velocity estimation means for: (1) creating a grid of theoretical points covering a prescribed range of velocities, said theoretical points being spaced at prescribed increments; (2) calculating theoretical values of frequency difference for a plurality of pairs of antenna sites; (3) calculating a least squares difference value based on the theoretical frequency differences and measured frequency differences for a plurality of pairs of antenna sites; (4) searching the entire grid of theoretical points and determining the best theoretical velocity for which the value of least squares difference is minimized; and (5) starting at the best theoretical velocity, performing another linearized-weighted-least-squares iteration to resolve the actual velocity to within a prescribed tolerance.

Claim 28

Independent Claim 341 words

A system for determining the location of a "standard" mobile transmitter not specifically designed or altered to provide signals facilitating the location of the transmitter, said standard mobile transmitter being operative to receive a message signal and to respond to said message signal by transmitting a bursty responsive transmission indicative of the identity of the standard mobile transmitter, comprising: (a) at least three ground-based antenna site systems, each antenna site system comprising: an antenna; a sampling subsystem operatively coupled to said antenna for sampling said bursty responsive signal at a prescribed sampling frequency and formatting the sampled signal into frames of digital data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said bursty responsive transmission was received; a baseband convertor operatively coupled to said sampling subsystem for providing baseband signals derived from said frames of data; and a timing subsystem operatively coupled to, said sampling subsystem for providing timing signals; and (b) a central site system operatively coupled to said antenna site systems, comprising means for processing said frames of data to generate data identifying said mobile transmitter and the differences in times of arrival of said responsive signal among said antenna site systems; and means for determining, on the basis of said times of arrival differences, the location of the mobile transmitter; and further comprising velocity estimation means for: (1) creating a grid of theoretical points covering a prescribed range of velocities, said theoretical points being spaced at prescribed increments; (2) calculating theoretical values of frequency difference for a plurality of pairs of antenna sites; (3) calculating a least squares difference value based on the theoretical frequency differences and measured frequency differences for a plurality of pairs of antenna sites; (4) searching the entire grid of theoretical points and determining the best theoretical velocity for which the value of least squares difference is minimized; and (5) starting at the best theoretical velocity, performing another linearized-weighted-least-squares iteration to resolve the actual velocity to within a prescribed tolerance.

Claim 29

Independent Claim 284 words

A method for determining the location of a mobile transmitter operative to receive a message signal and to respond to said message signal by transmitting a responsive signal over a predefined messaging channel, said responsive signal being indicative of the identity of the mobile transmitter, comprising the steps of: (a) receiving said signal at least three separate ground-based antenna sites; (b) processing said signal at each antenna site to produce frames of data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said frames were produced at each antenna site; (c) processing said frames of data to identify said responsive signal and the differences in times of arrival of said responsive signal among said antenna sites; and (d) determining, on the basis of said times of arrival differences, the location of said mobile transmitter; and further comprising estimating the location of said mobile transmitter by performing the following steps: (1) creating a grid of theoretical points covering a prescribed geographic area, said theoretical points being spaced at prescribed increments of latitude and longitude; (2) calculating theoretical values of time delay for a plurality of pairs of antenna sites; (3) calculating a least squares difference (LSD) value based on the theoretical time delays and measured time delays for a plurality of pairs of antenna sites; (4) searching the entire grid of theoretical points and determining the best theoretical latitude and longitude for which the value of LSD is minimized; and (5) starting at the best theoretical latitude and longitude, performing another linearized-weighted-least-squares iteration to resolve the actual latitude and longitude to within a prescribed number of degrees or fraction of a degree.

Claim 30

Independent Claim 284 words

A method for determining the location of a mobile transmitter operative to receive a message signal and to respond to said message signal by transmitting a responsive signal over a predefined messaging channel, said responsive signal being indicative of the identity of the mobile transmitter, comprising the steps of: (a) receiving said signal at least three separate ground-based antenna sites; (b) processing said signal at each antenna site to produce frames of data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said frames were produced at each antenna site; (c) processing said frames of data to identify said responsive signal and the differences in times of arrival of said responsive signal among said antenna sites; and (d) determining, on the basis of said times of arrival differences, the location of said mobile transmitter; and further comprising estimating the location of said mobile transmitter by performing the following steps: (1) creating a grid of theoretical points covering a prescribed geographic area, said theoretical points being spaced at prescribed increments of latitude and longitude; (2) calculating theoretical values of time delay for a plurality of pairs of antenna sites; (3) calculating a least squares difference (LSD) value based on the theoretical time delays and measured time delays for a plurality of pairs of antenna sites; (4) searching the entire grid of theoretical points and determining the best theoretical latitude and longitude for which the value of LSD is minimized; and (5) starting at the best theoretical latitude and longitude, performing another linearized-weighted-least-squares iteration to resolve the actual latitude and longitude to within a prescribed number of degrees or fraction of a degree.

Claim 31

Dependent Claim 41 words

A method as recited in claim 19, wherein said calculating step (2) comprises accounting for any known site biases caused by mechanical, electrical, or environmental factors, said site biases determined by periodically calculating the positions of reference transmitters at known locations.

Claim 32

Dependent Claim 97 words

A method as recited in claim 19, wherein said least squares difference is given by: LSD=ΣQ.sub.xy (Delay.sub.-- T.sub.xy -Delay.sub.-- O.sub.xy).sup.2 where, Delay -- T xy represents the theoretical delay between antenna sites x and y, x and y being indices representative of antenna sites; Delay -- O xy represents the observed delay between antenna sites x and y; Q xy represents a quality factor for the delay measurement between antenna sites x and y, said quality factor being an estimated measure of the degree to which multipath or other anomalies may have affected a particular delay measurement.

Claim 33

Independent Claim 267 words

A method for determining the location of a mobile transmitter operative to receive a message signal and to respond to said message signal by transmitting a responsive signal over a predefined messaging channel, said responsive signal being indicative of the identity of the mobile transmitter, comprising the steps of: (a) receiving said signal at least three separate ground-based antenna sites; (b) processing said signal at each antenna site to produce frames of data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said frames were produced at each antenna site; (c) processing said frames of data to identify said responsive signal and the differences in times of arrival of said responsive signal among said antenna sites; (d) determining, on the basis of said times of arrival differences, the location of said mobile transmitter; and further comprising estimating the velocity of said mobile transmitter by performing the following steps: (1) creating a grid of theoretical points covering a prescribed range of velocities, said theoretical points being spaced at prescribed increments; (2) calculating theoretical values of frequency difference for a plurality of pairs of antenna sites; (3) calculating a least squares difference (LSD) value based on the theoretical frequency differences and measured frequency differences for a plurality of pairs of antenna sites; (4) searching the entire grid of theoretical points and determining the best theoretical velocity for which the value of LSD is minimized; and (5) starting at the best theoretical velocity, performing another linearized-weighted-least-squares iteration to resolve the actual velocity to within a prescribed tolerance.

Claim 34

Independent Claim 267 words

A method for determining the location of a mobile transmitter operative to receive a message signal and to respond to said message signal by transmitting a responsive signal over a predefined messaging channel, said responsive signal being indicative of the identity of the mobile transmitter, comprising the steps of: (a) receiving said signal at least three separate ground-based antenna sites; (b) processing said signal at each antenna site to produce frames of data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said frames were produced at each antenna site; (c) processing said frames of data to identify said responsive signal and the differences in times of arrival of said responsive signal among said antenna sites; (d) determining, on the basis of said times of arrival differences, the location of said mobile transmitter; and further comprising estimating the velocity of said mobile transmitter by performing the following steps: (1) creating a grid of theoretical points covering a prescribed range of velocities, said theoretical points being spaced at prescribed increments; (2) calculating theoretical values of frequency difference for a plurality of pairs of antenna sites; (3) calculating a least squares difference (LSD) value based on the theoretical frequency differences and measured frequency differences for a plurality of pairs of antenna sites; (4) searching the entire grid of theoretical points and determining the best theoretical velocity for which the value of LSD is minimized; and (5) starting at the best theoretical velocity, performing another linearized-weighted-least-squares iteration to resolve the actual velocity to within a prescribed tolerance.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	2000-03-03	2000-09-02	2001-03-04	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2004-03-03	2004-09-02	2005-03-04	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2008-03-03	2008-09-02	2009-03-04	$7700.00	Window Closed / Lapsed

System for locating a source of bursty transmissions cross reference to related applications

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