System and method for analog cellular radio geolocation

• US 6,845,240 B2
• Filed: 12/11/2001
• Issued: 01/18/2005
• Est. Priority Date: 12/11/2000
• Status: Expired due to Term

• Current Assignee: Allen Telecom LLC (CommScope Holding Company, Inc.)
• Original Assignee: Grayson Wireless
• Inventors: Kennedy, Jr., Joseph P., Gravely, Thomas Booker, Carlson, John Peter
• Primary Examiner(s): Hudspeth, David
• Assistant Examiner(s): Afshar, Kamran
• Application Number:
  US10/011,783
• Publication Number:
  US 20020128020A1
• Time in Patent Office: 1,134 Days
• Field of Search: 455/456.1, 455/456.2, 455/456.3, 455/456.4, 455/456.6, 455/67.11, 455560-5621, 455/404.1, 455/404.2, 342/464, 342/457, 342/387, 342/465, 701/207
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/0081 Transmission between base stations
• 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: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming

Abstract

A system and method for determining the geolocation of autonomous mobile appliances emitting analog waveforms is disclosed. More specifically, the inventive system and method is used to geolocate FM analog signals such as those used in the AMPS cellular radio air standard by using a time difference of arrival (“TDOA”) approach. The inventive system and method uses a novel approach to minimize the amount of data sent between location sensors and the central location processor comprising adaptive signal combining from N channel to a single channel, FM demodulation to reduce bandwidth, Fourier transformation for signal compression, and segmentation of the location sensors into primary and secondary modes to allow for parallel processing to ease the computational burden on the central location processor.

Claims

1. A method for geolocating a mobile appliance transmitting an FM analog signal which can be received by a plurality of wireless location sensors each including at least one antenna, comprising the steps of:

(a) sending a first geolocation reference signal from each of a plurality of wireless location sensors to a central node, comprising the steps of;

(i) receiving a first FM analog signal on one or more of the at least one antennas;

(ii) digitizing the received signals;

(iii) time-stamping the digitized signals;

(iv) combining the time-stamped signals if received on more than one antenna;

(v) providing a location identification stamp for the combined signal to thereby produce a first location-identified signal;

(vi) frequency demodulating the first location-identified signal;

(vii) transforming the demodulated signal from the time domain to the frequency domain;

(viii) providing the first geolocation reference signal including a select portion of the frequency domain signal; and

(ix) sending the first geolocation reference signal to a central node;

(b) determining at the central node a primary wireless location sensor including the steps of;

(i) receiving the first geolocation reference signals from each of the plurality of wireless location sensors;

(ii) providing a predetermined quality factor;

(iii) comparing each of the first geolocation reference signals with the predetermined quality factor to thereby determine a primary geolocation reference signal;

(iii) identifying a primary wireless location sensor from the location identification stamp for the primary geolocation reference signal; and

(iv) sending a control signal to the primary wireless location sensor;

(c) receiving a second FM analog signal at each of the plurality of wireless location sensors, comprising the steps of;

(i) repeating steps (a)(i) through (a)(v) for said second FM analog signal to thereby produce a second location-identified signal; and

(ii) buffering the second location-identified signal to thereby produce a buffered signal;

(d) sending a reference signal from the primary wireless location sensor to the central node, comprising the steps of;

(i) repeating steps (a)(vi) and (a)(vii) for the second location-identified signal in response to receipt of the control signal from the central node;

(ii) providing the reference signal including a select portion of the frequency domain signal from step (d)(i); and

(iii) sending the reference signal to the central node;

(e) sending the reference signal from the central node to each one of the plurality of wireless location sensors in response to receipt at the central node of the reference signal from the primary wireless location sensor;

(f) sending a geolocation time of arrival signal from each of the plurality of wireless location sensors to a central node, comprising the steps of;

(i) receiving the reference signal from the central node;

(ii) transforming the reference signal from the frequency domain to the time domain to thereby create a time domain reference signal;

(iii) providing a carrier signal representative of the FM analog signal carrier wave;

(iv) modulating the carrier signal with the time domain reference signal;

(v) comparing the buffered signal with the time domain reference signal to thereby determine the time of arrival of the second FM analog signal at the wireless location sensor; and

(vi) sending the geolocation time of arrival signal which is representative of the time of arrival of the second FM analog signal to the central node;

(g) receiving the geolocation time of arrival signals from the plurality of wireless location sensors;

(h) determining the geolocation of the mobile appliance at the central node from the geolocation time of arrival signals.

2. A method for geolocating a mobile appliance transmitting an FM analog signal which can be received by a plurality of wireless location sensors, comprising the steps of:

(a) receiving a first FM analog signal at each of the plurality of wireless location sensors;

(b) sending a first geolocation reference signal from each of the plurality of wireless location sensors to a central node wherein said first geolocation reference signal is a digitized, time and location stamped frequency domain signal including a select portion of the first FM analog signal;

(c) determining at the central node a primary geolocation reference signal by comparing each of the first geolocation reference signals with a predetermined quality factor to thereby determine a primary geolocation reference signal and designating the wireless location sensor that sent the primary geolocation reference signal as the primary wireless location sensor;

(d) sending a control signal to the primary wireless location sensor;

(e) receiving a second FM analog signal at each of the plurality of wireless location sensors and buffering the digitized, time and location stamped second FM analog signal to thereby create a buffered signal;

(f) sending a first reference signal from the primary wireless location sensor to the central node wherein said reference signal comprises a digitized, time and location stamped frequency domain signal including a select portion of the second FM analog signal;

(g) sending the first reference signal from the central node to each one of the plurality of wireless location sensors in response to receipt at the central node of the first reference signal from the primary wireless location sensor;

(h) receiving the first reference signal from the central node at each of the plurality of wireless location sensors;

(i) providing at each of the plurality of wireless location sensors a second reference signal comprising a time domain FM modulated version of the first reference signal;

(j) comparing at each of the plurality of wireless location sensors the buffered signal to the second reference signal to thereby determine the time of arrival of the second FM analog signal at each of the plurality of wireless location sensors;

(k) sending a geolocation time of arrival signal from each of the plurality of wireless location sensors to a central node wherein the geolocation time of arrival signal is representative of the time of arrival of the second FM analog signal;

(l) receiving at the central node the geolocation time of arrival signals from the plurality of wireless location sensors;

(m) determining the geolocation of the mobile appliance at the central node from the geolocation time of arrival signals.

3. A method of geolocating a mobile appliance transmitting an FM analog signal comprising the steps of:

(a) receiving at a plurality of wireless location sensors a first FM analog signal from the mobile appliance and sending in response thereto a first reference signal representative of the first FM analog signal to a central node;

(b) comparing at the central node the first reference signals from the plurality of wireless location sensors to thereby determine a primary wireless location sensor and sending a control signal to the primary wireless location sensor;

(c) receiving at each of the plurality of wireless location sensors a second FM analog signal from the mobile appliance and producing in response thereto a buffered signal representative of the second FM analog signal;

(d) sending from the primary wireless location sensor via the central node to each of the plurality of wireless location sensors a second reference signal representative of the second FM analog signal as received at the primary wireless location sensor;

(e) comparing at each of the plurality of wireless location sensors the buffered signal to the second reference signal to thereby produce a geolocation reference signal;

(f) sending from each of the plurality of wireless location sensors to the central node the geolocation reference signal;

(g) receiving at the central node the geolocation reference signals from each of the plurality of wireless location sensors and calculating the geolocation of the mobile appliance therefrom.

4. In a system for geolocating a mobile appliance transmitting an FM analog signal that can be received by a plurality of geographically spaced-apart wireless location sensors each including at least one antenna for receiving the FM analog signal, where geolocation information is sent between the wireless location sensors and a central signal processing node, the improvement of using at at least one of the wireless location sensors an adaptive signal combining circuit for combining the FM analog signals received on the at least one antenna to thereby reduce the amount of information to be sent between the wireless location sensors and the central processing node.

5. The system of claim 4 including an FM demodulation circuit to provide bandwidth reduction so as to further reduce the amount of geolocation information to be sent between the wireless location sensors and the central signal processing node.

6. The system of claim 4 including a Fourier Transform circuit to provide signal compression so as to further reduce the amount of geolocation information to be sent between the wireless location sensors and the central signal processing node.

7. The system of claim 6 wherein the Fourier Transform circuit is a Fast Fourier Transform circuit.

8. In a system for geolocating a mobile appliance transmitting an FM analog signal that can be received by a plurality of geographically spaced-apart wireless location sensors each including at least one antenna for receiving the FM analog signal, wherein geolocation information is sent between the wireless location sensors and a central signal processing node, the improvement of using, at at least one of the wireless location sensors, an adaptive signal combining stage for reducing the number of channels of information to be processed, an FM demodulation stage to provide bandwidth reduction, and a Fourier Transform stage to provide signal compression so as to reduce the amount of geolocation information to be sent between the wireless location sensors and the central signal processing node.

9. In a method for geolocating a mobile appliance transmitting an FM analog signal that can be received by a plurality of geographically spaced-apart wireless location sensors each including at least one antenna for receiving the FM analog signal, where data representative of the received FM analog signal is sent between the wireless location sensors and a central signal processing node, the improvement of digitizing and compressing the received FM analog signals at the wireless location sensors so as to minimize the amount of data to be sent between the wireless location sensors and the central signal processing node.

10. The method of claim 9 wherein the amount of data representative of the received FM analog signal to be sent from a wireless location sensor to the central signal processing node is less than 5% of the amount of data representative of the received FM analog signal at the wireless location sensors.

11. The method of claim 9 wherein the amount of data representative of the received FM analog signal to be sent from a wireless location sensor to the central signal processing node is less than 10% of the amount of data representative of the received FM analog signal at the wireless location sensors.

12. A geolocation system for geolocating a mobile appliance transmitting an FM analog signal which can be received by a plurality of wireless location sensors comprising:

a plurality of wireless location sensors each including at least one antenna comprising;

(a) a receiver for receiving FM analog signals from ones of the at least one antennas;

(b) a first interface circuit for sending signals to a central node and for receiving signals from the central node;

(c) a first signal processing circuit comprising;

(i) a digitizer for digitizing the received FM analog signals;

(ii) time-stamping means for time-stamping the digitized signals;

(iii) a combiner for combining the time-stamped signals; and

(iv) location identification stamping means for providing a location identification stamp for the combined signal to thereby create a location-identified signal;

(d) a second signal processing circuit for producing a reference signal comprising;

(i) a demodulator for frequency demodulating the location-identified signal;

(ii) first transforming means for transforming the demodulated signal from the time domain to the frequency domain; and

(iii) selecting means for selecting a portion of the frequency domain signal to thereby produce the reference signal;

(e) a third signal processing circuit for producing a geolocation reference signal comprising;

(i) a buffer for buffering the location-identified signal to thereby produce a buffered signal;

(ii) second transforming means for transforming a reference signal sent by the central node from the frequency domain to the time domain to thereby produce a time domain reference signal;

(iii) first circuit means for providing a carrier signal representative of the FM analog signal carrier wave;

(iv) a modulator for modulating the carrier signal with the time domain reference signal;

(v) a first comparator for comparing the buffered signal with the time domain reference signal to thereby determine the time of arrival of an FM analog signal at said at least one antennas; and

(vi) second circuit means for producing the geolocation reference signal representative of said time of arrival of an FM analog signal;

a central node comprising;

(a) a second interface circuit for sending signals to the plurality of wireless location sensors and for receiving signals from the wireless location sensors;

(b) second circuit means for providing a predetermined quality factor;

(c) a second comparator for comparing the reference signals from each of the plurality of wireless location sensors with the predetermined quality factor to thereby determine a primary geolocation reference signal;

(d) third circuit means for identifying a primary wireless location sensor from the location identification stamp for the primary geolocation reference signal;

(e) fourth circuit means for producing a control signal to be sent to the primary wireless location sensor; and

(f) a fourth signal processing circuit for determining the geolocation of the mobile appliance at the central node from the geolocation reference signals.

13. The system of claim 12 whereby:

each of the plurality of wireless location sensors receives a first FM analog signal from the mobile appliance and sends a first reference signal representative of the first FM analog signal to the central node in response thereto,

the central node compares the first reference signals from the plurality of wireless location sensors to thereby determine the primary wireless location sensor and sends the control signal to the primary wireless location sensor,

each of the plurality of wireless location sensors receives a second FM analog signal from the mobile appliance and produces a buffered signal representative of the received second FM analog signal in response thereto,

the primary wireless location sensor sends a second reference signal representative of the second FM analog signal received at the primary wireless location sensor to each of the plurality of wireless location sensors via the central node,

each of the plurality of wireless location sensors compares the buffered signal to the second reference signal to thereby produce a geolocation reference signal and sends the geolocation reference signal to the central node,

the central node receives the geolocation reference signals from each of the plurality of wireless location sensors and determines the geolocation of the mobile appliance therefrom.