Coherent decoding of visible light communication (VLC) signals

Patent metadata

Field	Value
Publication number	US-9660727-B2
Application number	US-201514832259-A
Country	US
Kind code	B2
Filing date	Aug 21, 2015
Priority date	Apr 28, 2015
Publication date	May 23, 2017
Grant date	May 23, 2017

Abstract

Disclosed are methods, systems, devices, apparatus, computer-/processor-readable media, and other implementations, including a method to decode a visible light communication (VLC) signal by capturing images of a light source emitting a light modulated signal comprising a temporal sequence of symbols to determine decoded symbols and to further determine at least one codeword from a list of candidate codewords.

First claim

What is claimed is:

1. A method to decode a visible light communication (VLC) signal, the method comprising:
capturing an image of a light source emitting a light modulated signal comprising a temporal sequence of symbols;
determining a time-domain signal from the captured image;
identifying from the time-domain signal an at least one decoded symbol from a set of possible symbols based, at least in part, on known pre-determined durations associated with each of the possible symbols; and
determining at least one codeword from a list of candidate codewords based on the identified at least one decoded symbol from the time-domain signal and on an inter-symbol time measured between the at least one decoded symbol and an earlier at least one decoded symbol determined from an earlier time-domain signal from an earlier captured image.

2. The method of claim 1 , wherein determining the at least one codeword from the list of candidate codewords comprises:
eliminating a first codeword from the list of candidate codewords based on the identified at least one decoded symbol, or selecting a second codeword from the list of candidate codewords for further processing based on the identified at least one decoded symbol and on the measured inter-symbol time.

3. The method of claim 1 , wherein capturing the image of the light source comprises:
capturing the image of the light source with a CMOS camera including a rolling shutter.

4. The method of claim 1 , further comprising:
measuring the inter-symbol time according to edge information for the at least one decoded symbol and for the earlier at least one decoded symbol.

5. The method of claim 1 , wherein determining the at least one codeword comprises:
measuring the inter-symbol time between a time of the at least one decoded symbol for the image and an earlier time of the earlier at least one decoded symbol for the earlier captured image; and
identifying from the list of candidate codewords a candidate codeword including the at least one decoded symbol for the image and the earlier at least one decoded symbol for the earlier captured image when the measured inter-symbol time substantially equals a predicted inter-symbol time period between the earlier at least one decoded symbol in a first occurrence of the candidate codeword and the at least one decoded symbol in a second occurrence of the candidate codeword, the predicted inter-symbol time period computed based on a sum of pre-determined symbol durations of symbols appearing in the candidate codeword between a first position of the earlier at least one decoded symbol in the first occurrence of the candidate codeword and a second position of the at least one decoded symbol in the second occurrence of the candidate codeword.

6. The method of claim 1 , wherein identifying from the time-domain signal the at least one decoded symbol comprises:
determining duration of a pulse occurring in the time-domain signal from the captured image; and
selecting from the set of possible symbols, with each of the possible symbols associated with a respective one of the known pre-determined durations, at least one symbol with an associated pre-determined duration that is at least equal to the determined duration of the pulse occurring in the time-domain signal.

7. The method of claim 1 , wherein determining the at least one codeword from the list of candidate codewords comprises:
eliminating the at least one codeword based further on the earlier at least one decoded symbol identified in the earlier time-domain signal determined from the earlier captured image of the light source emitting the light modulated signal.

8. The method of claim 1 , further comprising:
measuring the inter-symbol time, including measuring a symbol start time of the at least one decoded symbol relative to an image start time for the image.

9. The method of claim 8 , wherein measuring the inter-symbol time further comprises:
measuring an end time of the earlier at least one decoded symbol relative to an earlier image start time for the earlier captured image.

10. The method of claim 1 , further comprising:
outputting a decoded codeword when the at least one codeword determined from the list of candidate codewords contains only one remaining candidate codeword, the decoded codeword being the one remaining codeword.

11. A mobile device comprising:
an image capture unit including a gradual-exposure module configured to capture an image of a light source emitting a light modulated signal comprising a temporal sequence of symbols;
memory configured to store the captured image; and
one or more processors coupled to the memory and the image capture unit, and configured to:
determine a time-domain signal from the captured image;
identify from the time-domain signal an at least one decoded symbol from a set of possible symbols based, at least in part, on known pre-determined durations associated with each of the possible symbols; and
determine at least one codeword from a list of candidate codewords based on the identified at least one decoded symbol from the time-domain signal and on an inter-symbol time measured between the at least one decoded symbol and an earlier at least one decoded symbol determined from an earlier time-domain signal for an earlier captured image.

12. The mobile device of claim 11 , wherein the one or more processors configured to determine the at least one codeword from the list of candidate codewords are configured to:
eliminate a first codeword from the list of candidate codewords based on the identified at least one decoded symbol, or select a second codeword from the list of candidate codewords for further processing based on the identified at least one decoded symbol and on the measured inter-symbol time.

13. The mobile device of claim 11 , wherein the image capture unit including the gradual-exposure module comprises a CMOS camera including a rolling shutter.

14. The mobile device of claim 11 , wherein the one or more processors configured to determine the at least one codeword are configured to:
measure the inter-symbol time between a time of the at least one decoded symbol for the image and an earlier time of the earlier at least one decoded symbol for the earlier captured image; and
identify from the list of candidate codewords a candidate codeword including the at least one decoded symbol for the image and the earlier at least one decoded symbol for the earlier captured image when the measured inter-symbol time substantially equals a predicted inter-symbol time period between the earlier at least one decoded symbol in a first occurrence of the candidate codeword and the at least one decoded symbol in a second occurrence of the candidate codeword, the predicted inter-symbol time period computed based on a sum of pre-determined symbol durations of symbols appearing in the candidate codeword between a first position of the earlier at least one decoded symbol in the first occurrence of the candidate codeword and a second position of the at least one decoded symbol in the second occurrence of the candidate codeword.

15. The mobile device of claim 11 , wherein the one or more processors configured to identify from the time-domain signal the at least one decoded symbol are configured to:
determine duration of a pulse occurring in the time-domain signal from the captured image; and
select from the set of possible symbols, with each of the possible symbols associated with a respective one of the known pre-determined durations, at least one symbol with an associated pre-determined duration that is at least equal to the determined d

Assignees

• Qualcomm Inc

Inventors

• Jovicic Aleksandar
• Pillai Perumal Mahadevi
• Vavreck Kenneth

Classifications

• H04B10/116 Primary

  Visible light communication · CPC title

• H04B10/0795

  Performance monitoring; Measurement of transmission parameters · CPC title

• H04N25/531

  by controlling rolling shutters in CMOS SSIS · CPC title

• H04N5/3532

  Electricity · mapped topic