Method and apparatus for communication using pulse-width-modulated visible light

• US 20070024571A1
• Filed: 08/01/2005
• Published: 02/01/2007
• Est. Priority Date: 08/01/2005
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Maniam, Selvan, Keh, Kean, Yap, Eit
• Granted Patent: US 7,570,246 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: H04B 10/1141 One-way transmission
• CPC Class Codes: H04B 10/116 Visible light communication

Abstract

A visible light communications transmitter combines a modulated carrier signal with a pulse from a pulse generator. The carrier signal is modulated according to data read from a buffer during the pulse.

Claims

1. A visible light communications transmitter comprising:

a data input providing data to the visible light communications transmitter a buffer storing data;

a pulse generator generating a pulse;

a signal generator providing a carrier signal;

a modulator coupled to the pulse generator, the buffer, and the signal generator and reading data from the buffer during the pulse and modulating the carrier signal according to the data read from the buffer to produce a modulated carrier signal;

an adder adding the modulated carrier signal to the pulse to produce a modulated pulse; and

a pulse-width-modulated (“

PWM”

) light-emitting diode (“

LED”

) light source operated according to the modulated pulse so as to produce a modulated optical signal suitable for use in a visible optical communications system.

2. The visible light communications transmitter of claim 1 further comprising a data packet constructor and a coder disposed between the data input and the buffer.

3. The visible light communications transmitter of claim 2 further comprising an interleaver disposed between the coder and the buffer.

4. The visible light communications transmitter of claim 1 wherein the PWM LED light source is a backlight of a display.

5. The visible light communications transmitter of claim 1 wherein the display is the display of an electronic device.

6. The visible light communications transmitter of claim 5 wherein the electronic device is a personal computer, a notebook computer, a laptop computer, a personal digital assistant, or a mobile telephone.

7. The visible light communications transmitter of claim 4 wherein the backlight comprises white light-emitting diodes.

8. The visible light communications transmitter of claim 1 wherein the PWM LED light source comprises colored LEDs.

9. The visible light communications transmitter of claim 8 wherein outputs of the colored LEDs are combined to produce a white light.

10. The visible light communications transmitter of claim 9 wherein each of the colored LEDs are operated according to the modulated pulse so as to produce modulated white light suitable for use in a visible optical communications system.

11. The visible light communications transmitter of claim 9 wherein LEDs of a first color in the PWM LED light source are operated according to the modulated pulse so as to produce a first modulated colored light signal suitable for use in a visible optical communications system.

12. The visible light communications transmitter of claim 11 wherein LEDs of a second color in the PWM LED light source are operated according to a second modulated pulse so as to produce a second modulated colored light signal suitable for use in the visible optical communications system.

13. A method of communication using pulse-width-modulated visible light comprising the steps of:

storing data in a buffer;

generating a pulse;

reading data from the buffer during the pulse;

modulating a carrier according to the data to produce a modulated carrier signal;

combining the modulated carrier signal with the pulse to produce a modulated pulse; and

coupling the modulated pulse to a light-emitting diode light source so as to produce light from an LED light source for use in a visible light communication system.

14. The method of claim 13 wherein the step of modulating the carrier comprises frequency modulation of the carrier.

15. The method of claim 13 wherein the step of modulating the carrier comprises amplitude modulation of the carrier.

16. The method of claim 15 wherein the step of reading data includes waiting a selected period after a leading edge of the pulse before reading the data from the buffer.

17. The method of claim 16 wherein the step of reading data further includes stopping reading the data from the buffer a second selected period before a trailing edge of the pulse.

18. The method of claim 13 further comprising steps, prior to the step of storing the data, of

packetizing the data into data packets;

and

coding the data packets so as to provide forward error correction.

19. The method of claim 18 further comprising a step, prior to the step of storing the data, of interleaving data.