Enhanced position calculation

• US 6,084,547 A
• Filed: 03/26/1999
• Issued: 07/04/2000
• 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:
  US09/276,729
• Time in Patent Office: 466 Days
• Field of Search: 342/457, 342/463
• 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 determining a location of an unknown position radio transmitter under low signal-to-noise ratio conditions, comprising the steps of:

receiving a first radio signal, including a unit identification, at a first transmission time from an unknown position radio transmitter at a first of n radio receivers, where n>

2;

determining, at said first radio receiver or at a central processing device (CPD), a time of a next unknown position radio transmission;

sending the time of the next radio transmission from the first radio receiver to the other n-1 radio receivers or sending the time of the next radio transmission from the CPD to the n radio receivers;

receiving, with a signal enhancing mode, radio signals from said unknown position radio transmitter at the n radio receivers at the time of the next unknown position radio transmission; and

determining a location of said unknown position radio transmitter using said enhanced radio signals.

2. The method of claim 1, wherein said step of determining comprises:

determining the location of said unknown position radio transmission using a neural network.

3. The method of claim 1, wherein said step of determining comprises:

determining the location of said unknown position radio transmission using an associative memory.

4. The method of claim 1, wherein said step of determining comprises:

determining the time of the next unknown position radio transmission by reading an indication of the time of the next unknown position radio transmission from data contained in the first radio signal.

5. The method of claim 1, wherein said step of determining comprises:

receiving a second radio signal at a second transmission time at a second one of said n radio receivers; and

determining the time of the next unknown position radio transmission by using the first and second transmission times.

6. A digital storage medium comprising an executable computer program to perform the method of claim 1.

7. A method, tolerant of fixed obstacles, for determining a location from which an unknown position radio signal is transmitted, comprising the steps of:

a) transmitting an unknown position radio signal from an unknown location;

b) receiving said unknown position radio signal at plural radio receivers at different known locations;

c) determining reference times of reception when said unknown position radio signal is received by plural receivers;

d) communicating to a central processing device (CPD) said reference times and said unknown position radio signal;

e) designating a first of said plural radio receivers as a current receiver;

f) estimating an initial unknown location estimate, having a convergence error, of said unknown location;

g) ending the estimation process if said convergence error is less than a specified threshold;

h) reducing the time value corresponding to the current receiver to a smaller time value;

i) determining a new unknown location estimate, having a new convergence error;

j) setting the convergence error equal to the new convergence error and repeating steps g-i if the new convergence error is smaller than the previous convergence error;

k) resetting the smaller time value to the time value of step g if the new convergence error of step i was larger than the convergence error of step g; and

l) repeating steps g-k for each of said plural radio receivers that have not been designated as the current receiver.

8. A method for determining a location from which an unknown position radio signal is transmitted, comprising the steps of:

transmitting from plural known mobile locations respective mobile radio signals;

receiving said mobile radio signals at plural receivers located at different known locations, said mobile radio signals having at least one of leading edge peak and leading edge valley delay spread profile cues;

determining a reference time of reception when each mobile radio signal transmitted from said mobile known locations is received by the plural receivers which received each respective indoor signal;

communicating to a central processing device (CPD) information relating to the mobile radio signals received by the plural receivers, including the respective reference times of reception when each of the mobile radio signals were received by the respective plural receivers;

receiving at plural receivers an unknown position radio signal from an unknown location;

communicating to the CPD information relating to the unknown position radio signals received by the plural receivers receiving the unknown position radio signal, including the respective reference times of reception of the unknown position radio signal at the respective plural receivers;

transmitting from subsequent plural known mobile locations respective subsequent mobile radio signals;

receiving said subsequent mobile radio signals at plural receivers located at different known locations, said subsequent mobile radio signals having at least one of leading edge peak and leading edge valley delay spread profile cues;

determining a reference time of reception when each subsequent mobile radio signal transmitted from said subsequent mobile known locations is received by the plural receivers which received each respective subsequent mobile radio signal;

communicating to the CPD information relating to the subsequent mobile radio signals received by the plural receivers receiving the subsequent mobile radio signal, including the respective reference times of reception when each of the subsequent mobile radio signals were received by the plural receivers;

using the communicated unknown position radio signals in relation to the respective reference times of reception of the unknown position radio signals and the subsequent mobile radio signals in relation to the respective reference times of reception of the subsequent mobile position radio signals as inputs to the CPD; and

outputting from the CPD an estimate of the actual location from which the unknown position radio signal was transmitted.

9. The method of claim 8, further comprising the steps of:

training the CPD using the received mobile radio signals and the known locations from which each of the received mobile radio signals were transmitted in relation to the respective reference times of reception at the plural receivers of the received mobile radio signals, wherein the CPD comprises a neural network.

10. A system for determining a location from which an unknown position radio signal is transmitted, comprising:

means for transmitting from plural known mobile locations respective mobile radio signals;

means for receiving said mobile radio signals at plural receivers located at different known locations, said mobile radio signals having at least one of leading edge peak and leading edge valley delay spread profile cues;

means for determining a reference time of reception when each mobile radio signal transmitted from said mobile known locations is received by the plural receivers which received each respective indoor signal;

means for communicating to a central processing device (CPD) information relating to the mobile radio signals received by the plural receivers, including the respective reference times of reception when each of the mobile radio signals were received by the respective plural receivers;

means for receiving at plural receivers an unknown position radio signal from an unknown location;

means for communicating to the CPD information relating to the unknown position radio signals received by the plural receivers receiving the unknown position radio signal, including the respective reference times of reception of the unknown position radio signal at the respective plural receivers;

means for transmitting from subsequent plural known mobile locations respective subsequent mobile radio signals;

means for receiving said subsequent mobile radio signals at plural receivers located at different known locations, said subsequent mobile radio signals having at least one of leading edge peak and leading edge valley delay spread profile cues;

means for determining a reference time of reception when each subsequent mobile radio signal transmitted from said subsequent mobile known locations is received by the plural receivers which received each respective subsequent mobile radio signal;

means for communicating to the CPD information relating to the subsequent mobile radio signals received by the plural receivers receiving the subsequent mobile radio signal, including the respective reference times of reception when each of the subsequent mobile radio signals were received by the plural receivers;

means for using the communicated unknown position radio signals in relation to the respective reference times of reception of the unknown position radio signals and the subsequent mobile radio signals in relation to the respective reference times of reception of the subsequent mobile position radio signals as inputs to the CPD; and

means for outputting from the CPD an estimate of the actual location from which the unknown position radio signal was transmitted.