Enhanced position calculation

• US 5,917,449 A
• Filed: 09/30/1997
• Issued: 06/29/1999
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: Southern Focus Investments, LLC
• Original Assignee: Sanconix Inc.
• Inventors: Poppe, Martin C., Sanderford, H. Britton
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US08/941,367
• Time in Patent Office: 637 Days
• Field of Search: 342/357, 342/457, 342/363, 701/214, 395/23
• US Class Current: 342/457
• CPC Class Codes: G01S 1/022 Means for monitoring or calibrating
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 5/0081 Transmission between base stations
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0252 Radio frequency fingerprinting
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: G01S 5/145 Using a supplementary range measurement, e.g. based on pseudo-range measurements
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

The invention discloses several computation and control techniques which use historic information as well as other cues in order to enhance the accuracy of a radio position fix. These computational techniques include neural networks, mapped grid coefficients as input to a set of simultaneous or differential equations,and table lookup of correction coefficients for known low accuracy positions. The invention further discloses techniques for receiver array synchronization so that all system elements in a particular coverage area obtain a time reference appropriate for time of flight radio location measurements. The invention further teaches techniques to enhance the accuracy of a position fix by use of both fixed references, which are located in a coverage area, as well as a mobile reference carried by a search team. The invention also discloses techniques to provide information appropriate to guide a search team to an unknown positioned transmitter that is located within a building or structure. The invention discloses techniques to train a central computing unit, by using actuarial data, so that multi-path errors resulting from fixed or mobile obstacles may be reduced.

Claims

1. A method for correcting clock drift of a time base of a radio receiver via a time reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising the steps of:

transmitting a time reference signal;

receiving said time reference signal at first and second radio receivers;

resetting first and second counters at said first and second receivers at predetermined intervals based on said time reference signal, each of said counters containing a value and receiving a clocking signal;

correcting a time base at said first and second radio receivers using the received time reference signal to correct for said clock drift;

incrementing each of said counters using the respective time base of the respective radio receiver as a clocking signal;

receiving an unknown position radio signal at said first and second receivers;

capturing the respective values of the counters when said unknown position radio signals are received;

communicating the captured values to a neural network;

using the captured values as an uncorrected timing indicator signal between the respective time reference signals and the unknown position radio signal;

inputting the uncorrected timing indicator signal to the neural network; and

outputting from the neural network a drift corrected timing indicator signal based on the captured values and the uncorrected timing indicator signal and based upon past training of the neural network.

2. The method of claim 1, further comprising the steps of:

transmitting a first radio signal from a first known location;

receiving said first radio signal at a radio receiver located at a second known location;

determining a training timing indicator signal of said first radio signal;

communicating the training timing indicator signal of said first radio signal to said neural network; and

training the neural network using the training timing indicator signal of said first radio signal.

3. The method of claim 1, wherein the step of transmitting a time reference comprises the step of:

transmitting a global positioning system reference.

4. The method of claim 1, wherein the step of transmitting a time reference comprises the step of:

transmitting a time reference from a grid synchronizing transmitter.

5. The method of claim 1, further comprising the steps of:

using said drift corrected timing indicator signal as an input to a second neural network; and

outputting from said second neural network an estimate of the actual location from which the unknown position radio signal was transmitted.

22. The method according to any one of claims 1, 10 and 17, wherein:

the step of using the captured values comprises using the captured values as relative times of arrival; and

the step of outputting comprises outputting a relative time of arrival.

24. The method according to any one of claims 1, 10 and 17, wherein:

the step of using the captured values comprises using the captured values as times of arrival; and

the step of outputting comprises outputting a time of arrival.

26. The method according to any one of claims 1, 10 and 17, wherein:

the step of using the captured values comprises subtracting pairs of the captured values to generated time differences; and

the step of outputting comprises outputting a time difference.

6. A method for correcting clock drift of a time base of a radio receiver via a time reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising the steps of:

transmitting a time reference signal;

receiving said time reference signal at first and second radio receivers;

resetting first and second counters at said first and second receivers at predetermined intervals based on said time reference signal, each of said counters containing a value and receiving a clocking signal;

correcting a time base at said first and second radio receivers using the received time reference signal to correct for said clock drift;

incrementing each of said counters using the respective time base of the respective radio receiver as a clocking signal;

receiving an unknown position radio signal at said first and second receivers;

capturing the respective values of the counters when said unknown position radio signals are received;

communicating the captured values to a neural network;

using the captured values as an uncorrected timing indicator signal between the respective time reference signals and the unknown position radio signal;

inputting the uncorrected timing indicator signal to the neural network; and

outputting from the neural network an estimate of the actual location from which the unknown position radio signal was transmitted based on the captured values and the uncorrected timing indicator signal.

7. The method of claim 6, further comprising the steps of:

transmitting a first radio signal from a first known location;

receiving said first radio signal at a radio receiver located at a second known location;

determining a training timing indicator signal of said first radio signal;

communicating the training timing indicator signal of said first radio signal to said neural network; and

training the neural network using the training timing indicator signal of said first radio signal.

8. The method of claim 6, wherein the step of transmitting a time reference comprises the step of:

transmitting a global positioning system reference.

9. The method of claim 6, wherein the step of transmitting a time reference comprises the step of:

transmitting a time reference from a grid synchronizing transmitter.

10. A method for compensating for clock drift of a time base of a radio receiver via a time reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising the steps of:

transmitting a periodic synchronization reference signal;

receiving said periodic synchronization reference signal at a radio receiver;

enabling a counter when said periodic synchronization reference is received, said counter having a value and receiving a clock signal;

clocking said counter using a local time base clock;

receiving an unknown position radio signal;

disabling said counter when said unknown position radio signal is received;

capturing the value of the counter when unknown position radio signal is received;

communicating the captured value to a neural network;

using the captured values as an uncorrected timing indicator signal between the respective time reference signals and the unknown position radio signal;

inputting the uncorrected timing indicator signal to the neural network; and

outputting from the neural network a drift corrected timing indicator signal based on the captured values and the uncorrected timing indicator signal and based upon past training of the neural network to compensate for said clock drift.

11. The method of claim 10, further comprising the steps of:

transmitting a first radio signal from a first known location;

receiving said first radio signal at a radio receiver located at a second known location;

determining a training timing indicator signal of said first radio signal;

communicating the training timing indicator signal of said first radio signal to said neural network; and

training the neural network using the training timing indicator signal of said first radio signal.

12. The method of claim 10, wherein the step of transmitting a periodic synchronization reference signal comprises the step of:

transmitting a periodic synchronization reference signal from a fixed reference transmitter.

13. The method of claim 10, further comprising the steps of:

using said drift corrected timing indicator signal as an input to a second neural network; and

outputting from said second neural network an estimate of the actual location from which the unknown position radio signal was transmitted.

14. A method for compensating for clock drift in a time base of a radio receiver via a time reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising the steps of:

transmitting a periodic synchronization reference signal;

receiving said periodic synchronization reference signal at a radio receiver;

enabling a counter when said periodic synchronization reference is received, said counter having a value and receiving a clock signal;

clocking said counter using a local time base clock;

receiving an unknown position radio signal;

disabling said counter when said unknown position radio signal is received;

capturing the value of the counter when said unknown position radio signal is received;

communicating the captured value to a neural network;

using captured value an uncorrected timing indicator signal between the respective time reference signals and the unknown position radio signal;

inputting the uncorrected timing indicator signal to the neural network to compensate for said clock drift; and

outputting from the neural network an estimate of the actual location from which the unknown position radio signal was transmitted based on the captured value and the uncorrected timing indicator signal.

15. The method of claim 14, further comprising the steps of:

transmitting a first radio signal from a first known location;

receiving said first radio signal at a radio receiver located at a second known location;

determining a training timing indicator signal of said first radio signal;

communicating the training timing indicator signal of said first radio signal to said neural network; and

training the neural network using the training timing indicator signal of said first radio signal.

16. The method of claim 14, wherein the step of transmitting a periodic synchronization reference signal comprises the step of:

transmitting a periodic synchronization reference signal from a fixed reference transmitter.

23. The method according to any one of claims 6, 14 and 20, wherein the step of using the captured values comprises:

using the captured values as relative times of arrival.

25. The method according to any one of claims 6, 14 and 20, wherein the step of using the captured values comprises:

using the captured values as times of arrival.

27. The method according to any one of claims 6, 14 and 20, wherein the step of using the captured values comprises:

subtracting pairs of the captured values to generate time differences.

17. A method for compensating for clock drift of a time base of a radio receiver via a fixed reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising the steps of:

clocking a counter using a local clock, said counter having a value and receiving said local clock signal;

transmitting a fixed reference signal;

receiving said fixed reference signal at a radio receiver;

capturing the value of the counter when said fixed reference signal is received;

using the captured value as a first uncorrected timing indicator;

receiving an unknown position radio signal;

capturing the value of the counter when said unknown position radio signal is received;

using the captured value as a second uncorrected timing indicator;

communicating the first and second uncorrected timing indicators to a neural network;

using the captured first and second uncorrected timing indicators as inputs to said neural network to compensate for said clock drift; and

outputting from the neural network a drift corrected timing indicator signal based on the first and second uncorrected timing indicator signals and based upon past training of the neural network.

18. The method of claim 17, further comprising the steps of:

transmitting a first radio signal from a first known location;

receiving said first radio signal at a radio receiver located at a second known location;

determining a training timing indicator signal of said first radio signal;

communicating the training timing indicator signal of said first radio signal to said neural network; and

training the neural network using the training timing indicator signal of said first radio signal from a first known location a first radio signal.

19. The method of claim 17, further comprising the steps of:

using said drift corrected timing indicator signal as an input to a second neural network; and

outputting from said second neural network an estimate of the actual location from which the unknown position radio signal was transmitted.

20. A method for compensating for clock drift of a time base of a radio receiver via a fixed reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising the steps of:

clocking a counter using a local clock, said counter having a value and receiving said local clock signal;

transmitting a fixed reference signal;

receiving said fixed reference signal at a radio receiver;

capturing the value of the counter when said fixed reference signal is received;

using the captured value as a first uncorrected timing indicator signal;

receiving an unknown position radio signal;

capturing the value of the counter when said unknown position radio signal is received;

using the captured value as a second uncorrected timing indicator signal;

communicating the first and second uncorrected timing indicator signals to a neural network;

using the captured first and second uncorrected timing indicator signals as inputs to said neural network to compensate for said clock drift; and

outputting from the neural network an estimate of the actual location from which the unknown position radio signal was transmitted based on the first and second uncorrected timing indicator signals.

21. The method of claim 20, further comprising the steps of:

transmitting a first radio signal from a first known location;

receiving said first radio signal at a radio receiver located at a second known location;

determining a training timing indicator signal of said first radio signal;

communicating the training timing indicator signal of said first radio signal to said neural network; and

training the neural network using the training timing indicator signal of said first radio signal.

28. A system for correcting clock drift of a time base of a radio receiver via a time reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising:

means for transmitting a time reference signal;

means for receiving said time reference signal at first and second radio receivers;

means for resetting first and second counters at said first and second receivers at predetermined intervals based on said time reference signal, each of said counters containing a value and receiving a clocking signal;

means for correcting a time base at said first and second radio receivers using the received time reference signal to correct for said clock drift;

means for incrementing each of said counters using the respective time base of the respective radio receiver as a clocking signal;

means for receiving an unknown position radio signal at said first and second receivers;

means for capturing the respective values of the counters when said unknown position radio signals are received;

means for communicating the captured values to a neural network;

means for using the captured values as an uncorrected timing indicator signal between the respective time reference signals and the unknown position radio signal;

means for inputting the uncorrected timing indicator signal to the neural network; and

means for outputting from the neural network an estimate of the actual location from which the unknown position radio signal was transmitted based on the uncorrected timing indicator signal.

29. A system for correcting clock drift of a time base of a radio receiver via a time reference signal transmission, in order to determine with increased accuracy, a location from which an unknown position radio signal is transmitted, comprising:

means for transmitting a time reference signal;

means for receiving said time reference signal at first and second radio receivers;

means for resetting first and second counters at said first and second receivers at predetermined intervals based on said time reference signal, each of said counters containing a value and receiving a clocking signal;

means for correcting a time base at said first and second radio receivers using the received time reference signal to correct for said clock drift;

means for incrementing each of said counters using the respective time base of the respective radio receiver as a clocking signal;

means for receiving an unknown position radio signal at said first and second receivers;

means for capturing the respective values of the counters when said unknown position radio signals are received;

means for communicating the captured values to a neural network;

means for using the captured values as an uncorrected timing indicator signal between the respective time reference signals and the unknown position radio signal;

means for inputting the uncorrected timing indicator signal to the neural network; and

means for outputting from the neural network a drift corrected timing indicator signal based on the uncorrected timing indicator signal and based upon past training of the neural network.