초록 ▼

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 m

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.

대표청구항 ▼

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 t

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; andmeans 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; anddetecting 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.