Method of and apparatus for deriving a signal for enabling a radio wave source location to be derived

• US 20030043072A1
• Filed: 08/30/2001
• Published: 03/06/2003
• Est. Priority Date: 08/30/2001
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Carrott, David T.
• Granted Patent: US 6,639,552 B2
• Time in Patent Office: Days
• US Class Current: 342/442
• CPC Class Codes: G01S 5/02585 at least one of the measurements being a non-radio measurement
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

The location of a cellular telephone handset relative to the sites of two pairs of fixed cellular transceivers is determined by responding to the phase difference of radio waves the handset emits, as coupled to the sites. The phase difference is detected by supplying replicas of the waves received at the first and second sites to first and second electro-acoustical transducers at opposite ends of a Bragg cell. One Bragg cell is thus associated with each pair of cellular transceivers. A laser beam incident on each Bragg cell is deflected by a moving optical grating resulting from the interaction of acoustic waves applied by the electro-acoustical transducers to the particular Bragg cell. The laser beam deflection angle for each Bragg cell determines the relative phase angle of the acoustic waves in that cell. Indications of the deflection angles, positions of the transceivers and propagation speeds of replicas of the radio waves propagating in communication links between the sites are combined to indicate the handset location.

Claims

1. Apparatus for deriving a signal indicative of a possible position of a radio wave source relative to a pair of receiver sites having known positions, the radio wave source being arranged for emitting a radio wave to which receivers at the sites are arranged to be responsive, the apparatus comprising an optically diffractive medium capable of having a moving optical grating induced therein in response to acoustic waves propagating therein, first and second electro-acoustic transducers coupled to the optically diffractive medium for launching first and second acoustic waves toward each other in the optically diffractive medium in response to electric excitation of the first and second transducers by replicas of the radio waves to which the pair of receivers are responsive, the transducers being positioned and arranged so that the first and second acoustic waves interact with each other in the medium, an optical source for illuminating the medium, and an optical detector arrangement arranged to be responsive to optical energy from the source and modulated by the moving grating for deriving a signal indicative of the relative phase angle of the radio wave replicas exciting the first and second transducers.

2. The apparatus of claim 1 wherein the acoustic waves propagate in a direction between the transducers, the detector arrangement including plural individual detector elements positioned in an array that extends in the same direction as the direction the acoustic waves propagate, the signal indicative of the relative phase angle being derived in response to an indication of the location of the detector element which has the greatest intensity of optical energy incident on it.

3. The apparatus of claim 2 wherein the optical source is coherent and is arranged for projecting a beam that is incident on the medium at an angle that differs from a line normal to the acoustic wave propagation direction by the Bragg angle of the diffractive medium.

4. The apparatus of claim 3 wherein the optical detector arrangement is arranged to derive a signal indicative of the angle of the maximum intensity of the modulated optical energy relative to the propagation direction of the acoustic waves in the medium, the signal indicative of the relative phase angle being derived in response to the signal indicative of the angle of the maximum intensity of the modulated optical energy relative to the propagation direction of the acoustic waves in the medium.

5. The apparatus of claim 4 wherein the optical source is coherent and is arranged for projecting a beam that is incident on the medium at an angle that differs from a line normal to the acoustic wave propagation direction by the Bragg angle of the diffractive medium.

6. The apparatus of claim 1 wherein the apparatus is also arranged for determining the location of the radio wave source relative to at least three receiver sites having known positions, each arranged to be responsive to the radio wave, the apparatus further comprising a second optically diffractive medium capable of having a second moving optical grating induced therein in response to acoustic waves propagating therein, third and fourth electro-acoustic transducers coupled to the second optically diffractive medium for launching third and fourth acoustic waves toward each other in the second optically diffractive medium in response to electric excitation of the third and fourth transducers by replicas of the radio waves to which the receivers at another pair of the sites are responsive, the third and fourth transducers being positioned and arranged so that the third and fourth acoustic waves interact with each other in the second medium, a second optical source for illuminating the second medium, a second optical detector arrangement arranged to be responsive to optical energy from the second optical source and modulated by the second moving grating for deriving a second signal indicative of the relative phase angle of the radio wave replicas exciting the third and fourth transducers, and a processor responsive to both of the signals indicative of relative phase angles and indications of the known positions of the receiver sites for deriving an indication of the location of the radio wave source relative to the known positions.

7. The apparatus of claim 6 wherein the second optical detector arrangement is arranged to derive a second signal indicative of the angle of the maximum intensity of the modulated optical energy relative to the propagation direction of the acoustic waves in the second medium, the second signal indicative of the relative phase angle being derived in response to the second signal indicative of the angle of the maximum intensity of the modulated optical energy relative to the propagation direction of the acoustic waves in the second medium.

8. A system for deriving a signal indicative of a possible position of a radio wave source relative to a pair of sites having known positions, the system comprising a receiver at each of the sites for receiving the radio wave, an optically diffractive medium capable of having a moving optical grating induced therein in response to acoustic waves propagating therein, first and second electro-acoustic transducers coupled to the optically diffractive medium for launching first and second acoustic waves toward each other in the optically diffractive medium in response to electric excitation of the first and second transducers by replicas of the radio waves to which the pair of receivers are responsive, the transducers being positioned and arranged so that the first and second acoustic waves interact with each other in the medium, an optical source for illuminating the medium, and an optical detector arrangement arranged to be responsive to optical energy from the source and modulated by the moving grating for deriving a signal indicative of the relative phase angle of the radio wave replicas exciting the first and second transducers.

9. The system of claim 8 wherein the optical detector arrangement is arranged to derive a signal indicative of the angle of the maximum intensity of the modulated optical energy relative to the propagation direction of the acoustic waves in the medium, the signal indicative of the relative phase angle being derived in response to the signal indicative of the angle of the maximum intensity of the modulated optical energy relative to the propagation direction of the acoustic waves in the medium.

10. The system of claim 9 wherein the optical source is coherent and is arranged for projecting a beam that is incident on the medium at an angle that differs from a line normal to the acoustic wave propagation direction by the Bragg angle of the diffractive material.

11. The system of claim 8 wherein the system is also arranged for determining the location of the radio wave source relative to at least three receiver sites having known positions, each arranged to be responsive to the radio wave, the system further including a receiver for the radio wave at each of the sites, a second optically diffractive medium capable of having a second moving optical grating induced therein in response to acoustic waves propagating therein, third and fourth electro-acoustic transducers coupled to the second optically diffractive medium for launching third and fourth acoustic waves toward each other in the second optically diffractive medium in response to electric excitation of the third and fourth transducers by replicas of the radio waves to which the receivers at another pair of the sites are responsive, the third and fourth transducers being positioned and arranged so that the third and fourth acoustic waves interact with each other in the medium, a second optical source for illuminating the second medium, a second optical detector arrangement arranged to be responsive to optical energy from the second optical source and modulated by the second moving grating for deriving a second signal indicative of the relative phase angle of the radio wave replicas exciting the third and fourth transducers, and a processor responsive to both of the signals indicative of relative phase angles and indications of the known positions of the receiver sites for deriving an indication of the location of the radio wave source relative to the known positions.

12. The system of claim 11 wherein the radio wave source comprises a cellular telephone handset and each of the receivers is included in a fixed cellular telephone transceiver.

13. The system of claim 12 wherein a plurality of the sites include:

said first and second optically diffractive media, said first, second, third, and fourth transducers, said first and second optical sources, said first and second optical detector arrangements, and said processor;

the processors of the sites being coupled together to select the site receiving the greatest signal strength of the radio wave for deriving an indication of the cellular telephone handset positions.

14. A method of deriving a signal indicative of a possible position of an emitted radio wave source relative to a pair of receiver sites having known positions, the method comprising receiving the emitted radio wave at the pair of sites, processing replicas of the radio waves received at the pair of sites by supplying to an optically diffractive medium acoustic replicas of the received radio waves, the acoustic replicas propagating toward each other and meeting in the optically diffractive medium, causing an optical beam to be incident on the acoustic replicas propagating in the medium, the acoustic replicas meeting in the medium causing modulation and deflection of the optical beam, and responding to an indication of the deflection angle of the optical beam to derive a response determined by the relative phase of the replicas of the radio waves received at the pair of sites.

15. The method of claim 14 wherein the radio wave source comprises a cellular telephone handset and cellular network transceivers at the sites receive the emitted radio wave.

16. The method of claim 14 further comprising determining the location of the radio wave source relative to at least three sites having known positions, each site including a receiver for the emitted radio wave, receiving the emitted radio wave at receivers at a second pair of the sites, processing replicas of the radio waves received at the second pair of sites by supplying to a second optically diffractive medium second acoustic replicas that propagate toward each other and meet in the second optically diffractive medium, the second acoustic replicas meeting in the second medium causing modulation and deflection of the second optical beam, responding to an indication of the deflection angle of the second optical beam to derive a second response determined by the relative phase of the replicas of the radio waves received at the second pair of sites, and combining both responses to derive an indication of the radio wave source location.

17. The method of claim 16 wherein the radio wave source comprises a cellular telephone handset and cellular network transceivers at the sites receive the emitted radio wave.

18. The method of claim 17 further including detecting which of the sites receives the strongest signal strength radio wave, and deriving the indication of the radio wave source location at the site detected as receiving the strongest signal strength radio wave.

19. Apparatus for determining the location of a radio wave source relative to at least three receiver sites having known positions, each of the sites being arranged to be responsive to the radio wave, the apparatus comprising an optically diffractive medium arrangement capable of having several optical gratings induced therein in response to acoustic waves propagating therein, electro-acoustic transducers connected to be responsive to replicas of the radio wave at the sites and coupled to the optically diffractive medium arrangement for launching several acoustic waves in the optically diffractive medium arrangement, the acoustic waves being replicas of the radio waves at the sites, a pair of said electro-acoustic transducers being coupled with the optically diffractive medium arrangement to cause a pair of acoustic waves to be launched toward each other so the pair of acoustic waves interact with each other in the optically diffractive medium arrangement, an optical source arrangement for illuminating the optically diffractive medium arrangement, the several acoustic waves in the optically diffractive medium arrangement causing deflection of optical energy from the optical source arrangement, an optical-electric detector arrangement arranged to be responsive to optical energy from the optical source arrangement, and a processor arrangement connected to be responsive to the optical-electric detector arrangement and indications of the known positions for deriving a signal indicative of the location of the radio wave source.

20. The apparatus of claim 19 wherein the apparatus is included in a system including the sites, the system including:

at least one of the sites including the optically diffractive medium and the processor.

21. The apparatus of claim 19 wherein the apparatus is included in a system including the sites, the system including:

a plurality of the sites including the optically diffractive medium and the processor arrangement, a communication link coupling the plurality of sites to each other, the processor arrangements at the sites being connected to be responsive to the links for detecting the site receiving the radio wave having the greatest signal strength and for causing the processor arrangement at the site receiving the radio wave having the greatest signal strength to perform the processing for deriving the signal indicative of the location of the radio wave source.

22. A method of determining the location of a wave emitted by a wave source comprising the steps of receiving the wave at three or more sites having known positions, launching in an optical diffracting medium arrangement several acoustic waves that are replicas of the wave, as received at the sites, the acoustic waves being launched while the optical energy is incident on the diffracting medium, the waves being launched so that pairs of them propagate toward each other and meet in the medium arrangement to cause deflection of the optical energy incident on the medium arrangement, and responding to the deflected optical energy to indicate the position of the wave source.