Localization of a signal emitting source

• US 6,765,533 B2
• Filed: 10/01/2002
• Issued: 07/20/2004
• Est. Priority Date: 03/23/2000
• Status: Expired due to Fees

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Szajnowski, Wieslaw J
• Primary Examiner(s): Phan, Dao
• Application Number:
  US10/239,407
• Publication Number:
  US 20030112183A1
• Time in Patent Office: 658 Days
• Field of Search: 342/450, 342/451, 342/457, 342/463, 342/465
• US Class Current: 342/465
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: G01S 5/18 using ultrasonic, sonic, or infrasonic waves

Abstract

A source localising method comprises the steps of measuring the power received by a set of sensors and selecting N measurements from respective sensors, where N is an even number and at least four. N−1 different direct power ratios are constructed each derived from the N power measurements, with different numerators and denominators derived from respective halves of the measurements in each case. The construction of N−1 direct power ratios is facilitated by the use of a suitably constructed Hadamard matrix. Each direct power ratio may be converted with a logarithmic transformation into a linear combination of measured powers.

Claims

1. A method of locating a signal emitting source comprising the steps of:

a) selecting N measurements of power from the source from measurements made by sensors positioned at difference locations, where N is an even number and at least four; and

characterised by

b) constructing N−

1 direct power ratios each derived from the N power measurements, each power ratio having a numerator which is the product of the values of a subset comprising N/2 of the N power measurements and a denominator which is the product of the values of the remaining N/2 of the N power measurements falling outside the subset, each direct power ratio being derived from a difference combination of numerator and denominator power measurements; and

c) calculating the source location from the (N−

1) direct power ratios.

2. A method of locating a signal emitting source as claimed in claim 1 characterised in that the even number of N measurements is comprised from an odd total number of measurements and at least one of the odd total number of measurements is duplicated in the selection N.

3. A method as claimed in claim 1 characterised in that the construction of the (N−

1) direct power ratios is facilitated by the use of a suitably configured Hadamard matrix.

4. A method as claimed in claim 1 characterised in that N=2^M where M is and integer and a Fast Hadamard Transform is used to perform the multiplications.

5. A method as claimed in claim 1 characterised in that step c) comprises the step of:

d) calculating predicted power ratios for each of a plurality of hypothesised source locations;

e) comparing the direct power ratios with the predicted power ratios; and

f) identifying the hypothesised source location having the smallest discrepancy between the predicted power ratios and the direct power ratios.

6. A method as claimed in claim 1, characterised in that each power ratio is converted with a logarithmic transformation into a linear combination of measured powers.

7. A method of as claimed in claim 6 characterised in that the measure of the discrepancy between the predicted power ratios and the direct power ratios utilises the absolute difference between the logarithms of the respective ratios.

8. A method as claimed in claim 7 characterised by;

formulating a vector q where q =(in r₁, ln r₂, ln r_i . . . ln r_N)^T where T is transpose and r is the rms value of the power of a signal received at sensor i;

multiplying the vector q by a Hadamard matrix, the vector v for each grid location, v =[H_N]) q;

where v =(v₁, v₂ . . . v_N)^T

formulating a vector q⁺where q⁺=(ln r⁺₁, ln r⁺₂, . . . ln r⁺_N)^T, wherein ln r⁺₁=-ln d_i wherein d_i is the distance of a sensor i from the signal emitting source;

multiplying the vector q⁺ by a Hadamard matrix, the vector v⁺ for each grid location, v⁺=[H_N]q⁺;

where v⁺=(v⁺₁, v⁺₂, . . . v⁺_N)^T

determining for each grid location the difference between v and v⁺; and

determining a point (x_o, y_o) where the sum of the squared values of the difference calculated between v and v⁺ achieves a minimum.

9. A method as claimed in claim 1 characterised in that the source emits one of an electromagnetic and an acoustic signal.

10. A method as claimed in claim 1 characterised in that the signal emission comprises one of a continuous, intermittent and pulsed signal.

11. A method as claimed in claim 1 characterised in that at least some of the N measurements are taken by moving at least one of the sensors between different positions, the location of which is determined.

12. A system for locating a signal emitting source according to the method of claim 1 comprising;

a) means for selecting the N power measurements from the measurements made by the-sensors;

b) means for constructing the (N−

1) power ratios; and

c) means for calculating the source location from the (N−

1) direct power ratios.

13. A system as claimed in claim 12 characterised in that the means a), b), and c) are provided by a computer apparatus the computer apparatus being configured to receive measurements of power made by the sensors and being programmed to carry out the objectives a), b), and c).

14. A computer program for use in locating a signal emitting source and arranged to control a computer to perform the method of claim 1.

15. A carrier medium carrying the computer program of claim 14.

16. A method according to claim 1 in which the N selected measurements of power from the source are selected from a set of M measurements where M is greater than N.

17. A method according to claim 16 in which steps (a) and (b) are applied to each of two subsets of the M measurements and the source location is calculated from the direct power ratios derived from each of the two subsets.

18. A method according to claim 17 in which the two subsets have members in common.

19. A method according to claim 17 in which some of the measurements in the set of more than N measurements are not present in either of the two subsets.

20. A method according to claim 16 in which M is not a multiple of 4.