Methods and apparatus to determine a position using light sources

1. A method, comprising:

processing, via a logic circuit, an output of a photodetector based on anticipated codes to identify multiple light sources from which the photodetector receives light at a first position;

determining, using the logic circuit, locations of the identified light sources; and

determining a location of the first position based on the locations of the identified light sources, wherein determining the location of the first position comprises:

calculating, for at least three of the anticipated codes, a distance between the photodetector and the light source associated with the anticipated code based on a time at which the anticipated code was received and an expected time of transmission by the light source associated with the anticipated code, and

triangulating the location of the first position based on the calculated distances.

2. The method as defined in claim 1 , further comprising determining the anticipated codes based on a code book or code sequences associated with the light sources.

3. The method as defined in claim 1 , further comprising receiving the locations of the light sources via a data channel, and determining the locations of the identified light sources comprises determining the received locations associated with detected ones of the anticipated codes.

4. The method as defined in claim 1 , further comprising determining a time difference between a time at which a first one of the anticipated codes is received and a reference time.

5. The method as defined in claim 1 , wherein the light source comprises a visible light source in an indoor location.

6. The method as defined in claim 1 , further comprising determining a time offset between the light source and the photodetector based on the output of the photodetector.

7. A method comprising:

processing, via a logic circuit, an output of a photodetector based on anticipated codes to identify multiple light sources from which the photodetector receives light at a first position, wherein identifying the multiple light sources comprises:

demodulating the output of the photodetector to generate a demodulated signal;

correlating the demodulated signal to ones of the anticipated codes, and

identifying a first one of the anticipated codes as being in the demodulated signal based on the demodulated signal having at least a threshold correlation with the first one of the anticipated codes;

determining, using the logic circuit, locations of the identified light sources; and

determining a location of the first position based on the locations of the identified light sources.

8. An apparatus, comprising:

a photodetector to convert received light to an electrical signal;

a code extractor to identify anticipated codes in the electrical signal;

a light source identifier to identify multiple light sources and respective locations of the light sources based on the code extractor identifying the anticipated codes; and

a location determiner to determine a location based on the identified light sources and the locations of the identified light sources, wherein the location determiner is to determine the location by:

calculating, for at least three of the identified codes, a distance between the photodetector and the light source associated with the identified code based on a time at which the identified code was received and an expected time of transmission by the light source associated with the identified code; and

triangulating a position based on the calculated distances.

9. The apparatus as defined in claim 8 , wherein the location determiner is to determine a time based on one or more of the identified anticipated codes.

10. The apparatus as defined in claim 8 , further comprising a data communications interface to receive the locations of the light sources via a data channel, the location determiner to determine the locations of the identified light sources by determining the received locations associated with detected ones of the anticipated codes.

11. The apparatus as defined in claim 8 , further comprising a code book to store the anticipated codes, wherein a first one of the anticipated codes comprises a pseudorandom code associated with a first one of the light sources.

12. The apparatus as defined in claim 11 , wherein the first one of the anticipated codes is different than any other ones of the anticipated codes.

13. The apparatus as defined in claim 8 , wherein the location determiner is to synchronize a clock based on the code extractor identifying the anticipated codes.

14. The apparatus as defined by claim 8 , wherein the code extractor is to identify the anticipated codes by demodulating the electrical signal and correlating a demodulated electrical signal to the anticipated codes.

15. A tangible computer readable storage medium comprising computer readable instructions which, when executed, cause a logic circuit to at least:

process an output of a photodetector based on anticipated codes to identify multiple light sources from which the photodetector receives light at a first position, wherein the instructions are to cause the logic circuit to identify the multiple light sources by:

demodulating the output of the photodetector to generate a demodulated signal;

correlating the demodulated signal to ones of the anticipated codes, and

identifying a first one of the anticipated codes as being in the demodulated signal based on the demodulated signal having at least a threshold correlation with the first one of the anticipated codes;

determine locations of the identified light sources; and

determine a location of the first position based on the locations of the identified light sources.

16. A tangible computer readable storage medium comprising computer readable instructions which, when executed, cause a logic circuit to at least:

process an output of a photodetector based on anticipated codes to identify multiple light sources from which the photodetector receives light at a first position,

determine locations of the identified light sources; and

determine a location of the first position based on the locations of the identified light sources, wherein the instructions are to cause the logic circuit to determine the location of a first position by:

calculating, for at least three of the anticipated codes, a distance between the light source associated with the anticipated code and the photodetector based on a time at which the anticipated code was received and an expected time of transmission by the light source associated with the anticipated code, and

triangulating a position based on the calculated distances.

17. The storage medium as defined in claim 15 , wherein the instructions are further to cause the logic circuit to synchronize a clock based on the anticipated codes and the locations of the light sources.

18. A method comprising:

processing, via a logic circuit, an output of a photodetector based on anticipated codes to identify multiple light sources from which the photodetector receives light at a first position;

synchronizing a time reference for the light sources;

modulating the light sources to transmit respective pseudorandom codes in a synchronized manner via light pulses from respective ones of the light sources, each of the light sources transmitting a different pseudorandom code from others of the light sources;

determining, using the logic circuit, locations of the identified light sources; and

determining a location of the first position based on the locations of the identified light sources.

19. The storage medium as defined in claim 16 , wherein the instructions are further to cause the logic circuit to synchronize a clock based on the anticipated codes and the locations of the light sources.