Coherent decoding of visible light communication (vlc) signals

Patent metadata

Field	Value
Publication number	US-2016323035-A1
Application number	US-201514832259-A
Country	US
Kind code	A1
Filing date	Aug 21, 2015
Priority date	Apr 28, 2015
Publication date	Nov 3, 2016
Grant date	—

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; 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 , wherein identifying from the time-domain signal the at least one decoded symbol comprises:
identifying from the time-domain signal the 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.

5 . 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.

6 . 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.

7 . 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 a set of possible symbols, with each of the possible symbols associated with a respective pre-determined duration, 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.

8 . 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.

9 . 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.

10 . The method of claim 9 , 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.

11 . The method of claim 1 , further comprising:
outputting a decoded codeword if the list of candidate codewords contains only one remaining candidate codeword, the decoded codeword being the one remaining codeword.

12 . 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; 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.

13 . The mobile device of claim 12 , 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.

14 . The mobile device of claim 12 , wherein the image capture unit including the gradual-exposure module comprises a CMOS camera including a rolling shutter.

15 . The mobile device of claim 12 , wherein the one or more processors configured to identify from the time-domain signal the at least one decoded symbol are configured to:
identify the 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.

16 . The mobile device of claim 12 , 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.

17 . The mobile device of claim 12 , wherein the one or more processors configured

Assignees

• Qualcomm Inc

Inventors

• Jovicic Aleksandar
• Pillai Perumal Mahadevi
• Vavreck Kenneth

Classifications

• H04B10/116 Primary

  Visible light communication · CPC title

• H04N25/531

  by controlling rolling shutters in CMOS SSIS · CPC title

• H04B10/0795

  Performance monitoring; Measurement of transmission parameters · CPC title

• H04N5/3532

  Electricity · mapped topic