Visible light communication system and method
A system and method are provided herein for communicating with and controlling various devices using visible light communication (VLC). According to one embodiment, a method is provided for extending a communication range of a VLC system comprising a plurality of controlled devices and a remote control device. Such a method may include, for example, transmitting a communication message from a remote control device to a first controlled device located within range of the remote control device, wherein the communication message is transmitted through free space using visible light, and extending the communication range of the VLC system to a second controlled device, which is located outside of the range of the remote control device, by using the first controlled device to retransmit the communication message through free space using visible light to the second controlled device.
1. A visible light communication system comprising:
a lighting fixture that comprises a visible light source and a visible light detector, wherein the lighting fixture is configured to;
generate a common timing reference;
periodically turn off the visible light source based on the timing reference;
when the visible light source is periodically turned off, receive via the visible light detector visible light transmitted by a control device;
decode data modulated onto the visible light received from the control device;
receive a first message from the control device via the visible light detector while the visible light source is turned off;
adjust a bit timing in response to receiving the first message; and
based on the adjusted bit timing, retransmit the first message via the visible light source to at least one other lighting fixture such that the retransmitted first message is in synchronization with a second message transmitted by the control device, the second message transmitted at a fixed time after the first message is transmitted, the second message substantially identical to the first message.
2. The visible light communication system as recited in claim 1 , wherein the lighting fixture is further configured to;
be coupled to an alternating current (AC) power source;
generate the common timing reference by locking onto an AC signal provided by the AC power source; and
using the timing reference, synchronously modulate data onto visible light transmitted by the visible light source.
3. The visible light communication system as recited in claim 1 , wherein the data modulated onto the visible light comprises information indicating that the data modulated onto the visible light either be retransmitted from the control device or be retransmitted from the visible light source when the visible light source is periodically turned on.
4. The visible light communication system as recited in claim 1 , wherein the data modulated onto the visible light comprises a repeat field that specifies a number of times the data modulated onto the visible light should be retransmitted.
5. The visible light communication system as recited in claim 1 , wherein the data modulated onto the visible light comprises a plurality of data fields, which includes one or more of:
a repeat field that specifies a number of times the data modulated onto the visible light should be retransmitted;
a preamble field containing a unique data sequence that identifies a start of the data modulated onto the visible light;
an address field containing a code specifying a lighting fixture targeted by the data modulated onto the visible light;
a command field containing a code specifying an action to be taken by the lighting fixture;
a data field containing a data value associated with the command field code; and
a Cyclic Redundancy Check (CRC) checksum field containing a CRC code.
6. The visible light communication system as recited in claim 1 , wherein the lighting fixture further comprises a visible light communication network controller configured to receive visible light modulated with data sent from other lighting fixtures arranged in a communication network.
7. The visible light communication system as recited in claim 1 , wherein the visible light detector is one or more of a plurality of light emitting diodes (LEDs) used as the visible light source.
8. The visible light communication system as recited in claim 1 , wherein the visible light source comprises one or more of a plurality of light emitting diodes (LEDs).
9. The visible light communication system as recited in claim 1 , wherein the visible light source and the visible light detector are coupled to an AC mains and are synchronized with each other.
10. The visible light communication system as recited in claim 9 , wherein a current supplied to the visible light source is periodically decreased to produce communication gaps at regular, periodic intervals of each cycle of the AC mains.
11. A visible light communication method in a visible light communication system comprising a light fixture comprising a visible light source and a visible light detector, the method comprising:
generating a common timing reference;
periodically turning off the visible light source based on the timing reference;
when the visible light source is periodically turned off, receiving via the visible light detector visible light transmitted by a control device;
decoding data modulated onto the visible light received from the control device;
receiving a first message from the control device via the visible light detector while the visible light source is turned off;
adjusting a bit timing in response to receiving the first message; and
based on the adjusted bit timing, retransmitting the first message via the visible light source to at least one other lighting fixture such that the retransmitted first message is in synchronization with a second message transmitted by the control device, the second message transmitted at a fixed time after the first message is transmitted, the second message substantially identical to the first message.
12. The visible light communication method as recited in claim 11 , the method further comprising;
coupling the lighting fixture to an alternating current (AC) power source;
generating the common timing reference by locking onto an AC signal provided by the AC power source; and
using the timing reference, synchronously modulating data onto visible light transmitted by the visible light source.
13. The visible light communication method as recited in claim 12 , wherein the data modulated onto the visible light transmitted by the visible light source comprises information indicating that the data modulated onto the visible light transmitted by the visible light source either be retransmitted from the control device or be retransmitted from the visible light source when the visible light source is periodically turned on.
14. The visible light communication method as recited in claim 12 , wherein the data modulated onto the visible light transmitted by the visible light source comprises a repeat field that specifies a number of times the data modulated onto the visible light transmitted by the visible light source should be retransmitted.
15. The visible light communication method as recited in claim 12 , wherein the data modulated onto the visible light transmitted by the visible light source comprises a plurality of data fields, which includes one or more of:
a repeat field that specifies a number of times the data modulated onto the visible light should be retransmitted;
a preamble field containing a unique data sequence that identifies a start of the data modulated onto the visible light;
an address field containing a code specifying a lighting fixture targeted by the data modulated onto the visible light;
a command field containing a code specifying an action to be taken by the lighting fixture;
a data field containing a data value associated with the command field code; and
a Cyclic Redundancy Check (CRC) checksum field containing a CRC code.
16. The visible light communication method as recited in claim 11 , wherein the lighting fixture further comprises a visible light communication network controller configured to receive visible light modulated with data sent from other lighting fixtures arranged in a communication network.
17. The visible light communication method as recited in claim 11 , wherein the visible light detector is one or more of a plurality of light emitting diodes (LEDs) used as the visible light source.
18. The visible light communication method as recited in claim 11 , wherein the visible light source comprises one or more of a plurality of light emitting diodes (LEDs).
19. The visible light communication method as recited in claim 11 , further comprising:
coupling the visible light source and the visible light detector to an AC mains; and
synchronizing the visible light source and the visible light detector with each other.
20. The visible light communication method as recited in claim 19 , further comprising:
supplying current to the visible light source; and
periodically decreasing the current supplied to the visible light source to produce communication gaps at regular, periodic intervals of each cycle of the AC mains.