Control of lighting devices
A network of active sensors in a control system is considered. The active sensors, which may be fixed-infrastructure sensors, provide presence detection information to a distributed lighting system. The active sensors communicate by transmitting probe signals. The communication of probe signals may result in cross-interference which may vary in time. Cross-interference is detected, and can later be avoided, by determining a difference between signals received in a first part of a timeslot and signals received in a second part of the timeslot. In order to do so probe signals comprising two non-zero pulses are transmitted in respective parts of the timeslot. Applications are, for example, active presence sensors in lighting control applications in indoor as well as outdoor environments.
1. A control system, comprising
a first active sensor comprising
a transmitter arranged to in a first timeslot transmit a first probe signal comprising two non-zero pulses transmitted in respective parts of said first timeslot; and
a second active sensor comprising
a receiving sensor array arranged to receive said first probe signal; and
a processing unit arranged to, in a second timeslot, determine a difference between signals received in a first part of said second timeslot and signals received in a second part of said second timeslot, the processing unit thereby being arranged to detect cross-interference between the active sensors, cross-interference being detected if the power in the difference signal has an absolute value that is larger than a predefined threshold value.
2. The control system according to claim 1 , wherein the second active sensor further comprises
a transmitter arranged to in said second timeslot transmit a second probe signal comprising two non-zero pulses transmitted in respective parts of said second timeslot, wherein
said receiving sensor array further is arranged to receive an echo of said second probe signal, and wherein
said processing unit, by determine said difference, thereby being arranged to cancel said two non-zero pulses of said second probe signal.
3. The control system according to claim 1 , wherein one of said respective parts corresponds to a first half, and wherein the other of said respective parts corresponds to a second half.
4. The control system according to claim 1 , wherein interference is detected by said difference having an absolute value being larger than a predetermined threshold.
5. The control system according to claim 4 , wherein said processing unit is further arranged to, in response to interference being detected, increase said predetermined threshold.
6. The control system according to claim 1 , wherein said processing unit is further arranged to discard ranges in said second timeslot where interference is detected.
7. The control system according to claim 1 , wherein said first timeslot and said second timeslot are reallocated in response to interference being detected.
8. The control system according to claim 1 , wherein the second active sensor further comprises
a transmitter arranged to in said second timeslot and in response to said receiving sensor array receiving said first probe signal transmit an announcing signal pertaining to said second active sensor being added to the control system, and wherein
the first active sensor further comprises
a receiving sensor array arranged to receive said announcing signal.
9. The control system according to claim 8 , wherein said announcing signal is a continuous sinusoidal transmitted in entire said second timeslot.
10. The control system according to claim 8 , wherein frequency content of said announcing signal is different from frequency content of said first probe signal.
11. The control system according to claim 1 , wherein said receiving sensor array is arranged to perform correlation in order to detect interference.
12. The control system according to claim 2 , wherein said first active sensor and said second active sensor are either ultrasound based sensors or radar based sensors.
13. A method of detecting interference in a control system ( 1 ), comprising
transmitting, by a first active sensor, in a first timeslot a first probe signal comprising two non-zero pulses transmitted in respective parts of said first timeslot;
receiving, by a second active sensor, said first probe signal; and
determining, by said second active sensor, in a second timeslot a difference between signals received in a first part of said second timeslot and signals received in a second part of said second timeslot, the second active sensor thereby being arranged to detect cross-interference between the active sensors, cross-interference being detected if the power in the difference signal has an absolute value that is larger than a predefined threshold value.
14. The method according to claim 13 , further comprising
transmitting, by said second active sensor, in said second timeslot a second probe signal comprising two non-zero pulses transmitted in respective parts of said second timeslot;
receiving, by said second active sensor, an echo of said second probe signal, said second active sensor, by determining said difference, thereby being arranged to cancel said two non-zero pulses of said second probe signal.
15. The method according to claim 13 , further comprising
transmitting, by said second active sensor, in said second timeslot and in response to said receiving said first probe signal an announcing signal pertaining to said second active sensor being added to the control system, and wherein
receiving, by said first active sensor, said announcing signal.