Method and system for modifying a beacon light source for use in a light based positioning system
In one aspect, the present disclosure related to a method for modifying a beacon light source for use in a light-based positioning system. In some embodiments, the method includes selecting a modulation scheme for the light source, determining a duty cycle for the light source based on the modulation scheme, the duty cycle having a proportion of time the light source is in an on state and a corresponding proportion of time the light source is in an off state, the proportion of time the light source is in an off state resulting in reduced luminosity of the light source, and supplying additional power to the light source to compensate for the reduced luminosity of the light source by the duty cycle.
1. A method, comprising:
setting a duty cycle of a periodic modulating of a light source output of a light source based on an image sampling time of a rolling shutter camera intended to receive modulated light output by the light source, wherein:
the duty cycle has a light source ON period and a light source non-zero period in which an output level of the light source modulates between a peak output level and a bottom output level increased by an applied DC bias,
electrical power applied to the light source during the ON period is greater than electrical power applied to the light source during the non-zero period, and
the light source non-zero period is less than half of the image sampling time of the rolling shutter camera of the intended receiving device;
periodically modulating the light source output of the light source from the peak output level to the bottom output level, wherein a modulating period is set based on the duty cycle;
applying the DC bias to the light source during the periodic modulation of the light source based on the duty cycle that increases the peak output level of an unmodulated output of the light source beyond an un-modulation output of the light source corresponding to a given brightness level and to achieve an average output of the light source equal to the un-modulation output of the light source corresponding to the given brightness level; and
reducing a required power for the peak output level by the DC bias to maintain thermal heating of the light source below a threshold, wherein the threshold comprises a thermal heating level determined based on a maximum allowable droop.
2. The method of claim 1 , wherein the light source ON period is less than half of the image sampling time of the rolling shutter camera of the intended receiving device.
3. The method of claim 1 , wherein the modulating period is set based on a plurality of rolling shutter camera image sampling times.
4. The method of claim 1 , wherein the peak output level and the bottom output level comprise electrical current levels.
5. The method of claim 1 , wherein the peak output level and the bottom output level comprise voltage levels.
6. The method of claim 1 , wherein the light source comprises a light-emitting diode (LED).
7. A lighting device for use in a light based positioning system, the lighting device comprising:
a controllable light source that emits light;
a modulator comprising a data signal input and a dimming device interface; and
a driver coupled to the modulator and the light source, wherein the driver outputs driver signals in response to a data signal causing the light source to output light in accordance with the driver signals,
wherein the modulator is configured to:
receive a data signal via the data signal input;
select a modulation scheme for the light source based on the received data signal, wherein the modulation scheme periodically varies based on a selected frequency of a light source output of the light source from a peak output level to a bottom output level;
add a DC bias to the modulation scheme;
receive via the dimming device interface a dimming signal;
set a duty cycle for the pulse width modulation signal based on the received dimming signal, wherein the duty cycle is set based on an image sampling time of a rolling shutter camera intended to receive the light source output by the light source, wherein:
the set duty cycle has a light source ON period and a light source non-zero period in which the light source output by the light source modulates between the peak output level and the bottom output level,
the bottom output level is:
increased based on the applied DC bias
corresponds to the non-zero period, and
the light source non-zero period is less than half of the image sampling time of the rolling shutter camera of the intended receiving device;
output to the driver signals based on the selected modulation scheme having the selected frequency, added DC bias and the set duty cycle to cause the light source to output modulated light; and
reduce a required power for the peak output level by the DC bias to maintain thermal heating of the light source below a threshold, wherein the threshold comprises a thermal heating level determined based on a maximum allowable droop.
8. The lighting device of claim 7 , wherein the peak output level and the bottom output level comprise electrical current levels.
9. The lighting device of claim 7 , wherein the peak output level and the bottom output level comprise voltage levels.
10. The lighting device of claim 7 , wherein the duty cycle is set based on a plurality of rolling shutter camera image sampling times.
11. The lighting device of claim 7 , wherein the light source comprises a light-emitting diode (LED).
12. A modulated light source for use in a light based positioning system, the light source comprising:
an emitter with a luminosity broadcasting a modulated signal; and
a modulator for receiving a modulation scheme and driving the luminosity of the emitter by applying the modulation scheme with a DC bias to the emitter, the modulator configured to:
determine a duty cycle of periodic modulating of the emitter based on an image sampling time of a rolling shutter camera intended to receive the luminosity by the emitter, wherein:
the duty cycle has an emitter ON period and an emitter non-zero period in which a luminosity output level of the emitter modulates between a peak output level and a bottom output level increased by the DC bias, and
the emitter non-zero period is less than half of the image sampling time of the rolling shutter camera of the intended receiving device;
apply the DC bias to the emitter during modulation based on the duty cycle that increases the peak output level of an unmodulated output of the emitter beyond an un-modulation output of the emitter corresponding to a given brightness level and to achieve an average output of the emitter equal to the un-modulation output of the emitter corresponding to the given brightness level; and
reduce a required power for the peak output level by the DC bias to maintain thermal heating of the emitter below a threshold, wherein the threshold comprises a thermal heating level determined based on a maximum allowable droop.
13. The modulated light source of claim 12 , wherein the emitter ON period is less than half of the image sampling time of the rolling shutter camera of the intended receiving device.
14. The modulated light source of claim 12 , wherein the peak output level and the bottom output level comprise electrical current levels.
15. The modulated light source of claim 12 , wherein the peak output level and the bottom output level comprise voltage levels.
16. The modulated light source of claim 12 , wherein the modulating period is set based on a plurality of rolling shutter camera image sampling times.
17. The modulated light source of claim 12 , wherein the emitter comprises a light-emitting diode (LED).