Intruder detection system

• US 8,354,928 B2
• Filed: 11/12/2007
• Issued: 01/15/2013
• Est. Priority Date: 11/14/2006
• Status: Expired due to Fees

• Current Assignee: Instro Precision Limited (S. Reisman Ltd.)
• Original Assignee: Instro Precision Limited (S. Reisman Ltd.)
• Inventors: Morcom, Christopher John
• Primary Examiner(s): Tweel, Jr., John A
• Application Number:
  US12/514,789
• Publication Number:
  US 20100097216A1
• Time in Patent Office: 1,891 Days
• Field of Search: 340/555, 340/556, 340/572.1, 340/541
• US Class Current: 340/555
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G01S 17/26 wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals
• CPC Class Codes: G08B 13/181 using active radiation detection systems
• CPC Class Codes: G08B 13/187 by interference of a radiation field
• CPC Class Codes: G08B 13/19695 Arrangements wherein non-video detectors start video recording or forwarding but do not generate an alarm themselves
• CPC Class Codes: G08B 13/2491 Intrusion detection systems, i.e. where the body of an intruder causes the interference with the electromagnetic field

Abstract

An intruder detection system comprises an illumination means for illuminating a field of view with a modulated optical signal, modulated by a modulation signal; an optical receiver for receiving a delayed reflected signal; a cross correlator for calculating a cross correlation function between the modulation signal and the received delayed reflected signal; and means for detecting changes in the cross correlation function, a change being used to provide intruder detection. This system uses optical sensing and cross correlation calculation to enable an intruder detection signal to be obtained. This can enable a solid state, low cost, and reliable sensor to be provided for detecting intruders.

Claims

1. An intruder detection system, comprising:

an illumination means for illuminating a field of view with a modulated optical signal, modulated by a modulation signal;

an optical receiver for receiving a delayed reflected signal;

a cross correlator for calculating a cross correlation function between the modulation signal and the received delayed reflected signal; and

means for detecting changes in the cross correlation function by comparing the cross correlation function received with an average of previously received cross correlation functions, a change being used to provide intruder detection.

2. A system as claimed in claim 1, wherein the correlation function comprises a series of correlation calculations for different time shift values.

3. A system as claimed in claim 1 or 2, further comprising threshold detection means for threshold detection within a difference signal between the cross correlation function and the average of previously received cross correlation functions.

4. A system as claimed in any preceding claim, wherein the optical receiver comprises an array of photodetectors.

5. A system as claimed in any preceding claim, further comprising time of flight measurement circuitry for calculating a range to an intruder based on the detected changes in the cross correlation function.

6. A system as claimed in any preceding claim, further comprising means for storing an image from the optical receiver.

7. A system as claimed in any preceding claim, further comprising means for deriving a direction to an intruder from the cross correlation function.

8. A system as claimed in claim 7, wherein the optical receiver comprises a multi region photosensor array, and wherein the means for deriving a direction determines which region or regions of the detector result in the intruder detection signal.

9. A system as claimed in claim 7 or 8, further comprising a camera, and a controller for controlling a direction of the camera based on the derived direction.

10. A system as claimed in any preceding claim, further comprising an electronic tag for an authorised intruder, wherein the system is adapted to provide an alarm if a non-authorised intruder is detected, and not to provide an alarm if an authorised intruder is detected.

11. A system as claimed in claim 10, wherein the tag comprises a code generator and optical transmitter, for transmitting a modulated code signal in response to detection of the modulated optical signal.

12. A system as claimed in claim 11, wherein the tag comprises means for synchronising the modulated code signal with the detected modulated optical signal.

13. A system as claimed in claim 12, wherein the means for synchronising comprises a tag cross correlator and a peak detector for deriving a synchronisation signal from the detected modulated optical signal.

14. A system as claimed in any one of claim 10 to 13, further comprising means for extracting a code from the signal received by the optical receiver which receives the delayed reflected signal.

15. A system as claimed in claim 14, wherein the means for extracting a code receives the output from the system cross correlator.

16. An intruder detection system comprising means for emitting a modulated optical signal and detecting a delayed reflected version of the optical signal from an intruder, and further comprising an electronic tag for an authorised intruder, wherein the system is adapted to provide an alarm if a non-authorised intruder is detected, and not to provide an alarm if an authorised intruder is detected.

17. A system as claimed in claim 16, wherein the tag is adapted to detect the modulated signal and provide a signal in response which encodes electronic tag identification information.

18. A method of detecting an intruder, comprising:

illuminating a field of view with a modulated optical signal, modulated by a modulation signal;

receiving a delayed reflected signal;

calculating a cross correlation function between the modulation signal and the received delayed reflected signal; and

detecting changes in the cross correlation function by comparing the cross correlation function received with an average of previously received cross correlation functions, a change being used to provide intruder detection.

19. A method as claimed in claim 18, wherein calculating a correlation function comprises deriving a series of correlation calculations for different time shift values.

20. A method as claimed in claim 18 or 19, further comprising performing threshold detection within a difference signal between the cross correlation function and the average of previously received cross correlation functions.

21. A method as claimed in any one of claims 18 to 20, further comprising performing time of flight measurement to determine a range to an intruder based on the detected changes in the cross correlation function.

22. A method as claimed in any one of claims 18 to 21, further comprising deriving a direction to an intruder from the cross correlation function.

23. A method as claimed in claim 22, wherein receiving a delayed reflected signal comprises operating a multi region photosensor array, and wherein deriving a direction comprises determining which region or regions of the detector result in the intruder detection.

24. A method as claimed in claim 22 or 23, further comprising controlling a direction of a camera based on the derived direction.

25. A method as claimed in any one of claims 18 to 24, further comprising providing an authorised intruder with an electronic tag and providing an alarm if a non-authorised intruder is detected, and not providing an alarm if an authorised intruder is detected.

26. A method as claimed in claim 25, comprising, in the tag, transmitting a modulated code signal in response to detection of the modulated optical signal.

27. A method as claimed in claim 26, comprising, in the tag, synchronising the modulated code signal with the detected modulated optical signal.

28. A method as claimed in claim 27, wherein the synchronising comprises cross correlation and peak detection to derive a synchronisation signal from the detected modulated optical signal.

29. A method as claimed in any one of claims 25 to 28, further comprising extracting a code when receiving the delayed reflected signal.

30. A computer program comprising computer program code means adapted to perform all of the steps of any one of claims 18 to 29 when said program is run on a computer.

31. A computer program as claimed in claim 30 embodied on a computer readable medium.