Reconstructing light-based communication signals using an alias frequency

• US 9,564,966 B1
• Filed: 09/30/2015
• Issued: 02/07/2017
• Est. Priority Date: 09/30/2015
• Status: Active Grant

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Original Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Inventors: Breuer, Christian, Aggarwal, Anant, Stout, Barry
• Primary Examiner(s): Leung, Danny
• Application Number:
  US14/870,445
• Time in Patent Office: 496 Days
• US Class Current: 1/1
• CPC Class Codes: H04B 10/0795 Performance monitoring; Measurement of transmission parameters
• CPC Class Codes: H04B 10/116 Visible light communication
• CPC Class Codes: H04W 4/023 using mutual or relative location information between multiple location based services [LBS] targets or of distance thresholds

Abstract

Methods and systems are described for sampling an LCOM message signal at a rate less than the Nyquist rate (i.e., an “alias frequency”) and accurately reconstructing the entire LCOM message using a light receiver (e.g., digital camera) of a typical mobile computing device, such as a smartphone, tablet, or other mobile computing device. The described methods and system take advantage of the repetition of LCOM signals, sampling an LCOM signal at a frequency less than the Nyquist frequency over at least two repetitions of a signal waveform, thereby collecting sufficient samples to accurately reconstruct the signal. The samples of each successive signal waveform repetition are offset from one another so that different points on the waveform are sampled, thus facilitating reconstruction of the signal.

Claims

1. A method for sampling a light-based communication signal, the light-based communication signal repeated a plurality of times, the method for sampling comprising:

capturing first light intensity data of the light-based communication signal, the capturing performed at a sampling rate less than a Nyquist sampling rate for the light-based communication signal, the capturing of the first light intensity data initiated at a first location of a first repetition of the light-based communication signal, the first location between a start location and an end location of the first repetition of the light-based communication signal;

determining a capture offset that is a non-integer multiple of a sampling period divided by a signal period of the light based communication signal; and

capturing second light intensity data of the light-based communication signal at the sampling rate, the capturing of the second light intensity data initiated at the first location plus the capture offset.

2. The method of claim 1, further comprising:

capturing at least one additional light intensity data of the light-based communication signal, each of the at least one additional light intensity data initiated at the first location plus a non-integer multiple of the capture offset, each of the at least one additional sets of light intensity data captured at a different non-integer multiple of the capture offset.

3. The method of claim 1, further comprising reconstructing the light-based communication signal by merging the first and the second light intensity data as a function of time between the start time and end time of the repetition of the signal.

4. The method of claim 1, wherein the capturing is performed using an image capture device of a mobile computing device configured to include at least one of a global shutter and a rolling shutter.

5. The method of claim 1, wherein the capturing is performed using a light sensor of a mobile computing device.

6. The method of claim 1, wherein the capturing is performed using a camera of a mobile computing device.

7. The method of claim 1, further comprising synchronizing the capturing sampling rate to a transmission frequency of the light-based communication signal, the synchronizing storing each of a plurality of captured signals in each of a plurality of trial buffers.

8. The method of claim 7, wherein the synchronizing further comprises:

configuring a first trial buffer of the plurality with a maximum buffer size based on a signal length plus a maximum deviation;

configuring each remaining buffer of the plurality of trial buffers to have a buffer size reduced by a different multiple of a function inversely proportional to a product of baud rate and a number of captured data to sample the signal; and

determining a score for each buffer of the plurality, the score indicating a degree of synchronization between the signal length and the buffer length.

9. The method of claim 1, wherein determining the capture offset further comprising adjusting a sampling period to cause the sampling period divided by the signal period of the light based communication signal to be a non-integer multiple.

10. A computer program product for sampling a light-based communication signal, wherein the light-based communication signal is repeated a plurality of times, the computer program product comprising at least one non-transitory computer-readable storage medium containing computer program code that, when executed by one or more processors, causes a method to be performed, the method comprising:

capturing first light intensity data of the light-based communication signal, the capturing performed at a sampling rate less than a Nyquist sampling rate for the light-based communication signal, the capturing of the first light intensity data initiated at a first location of a first repetition of the light-based communication signal, the first location between a start location and an end location of the first repetition of the light-based communication signal;

determining a capture offset that is a non-integer multiple of a sampling period divided by a signal period of the light based communication signal; and

capturing second light intensity data of the light-based communication signal at the sampling rate, the capturing of the second light intensity data initiated at the first location plus the capture offset.

11. The computer program product of claim 10, further comprising:

capturing at least one additional light intensity data of the light-based communication signal, each of the at least one additional light intensity data initiated at the first location plus a non-integer multiple of the capture offset, each of the at least one additional sets of light intensity data captured at a different non-integer multiple of the capture offset.

12. The computer program product of claim 10, further comprising reconstructing the light-based communication signal by merging the first and the second light intensity data as a function of time between the start time and end time of the repetition of the signal.

13. The computer program product of claim 10, wherein the capturing is performed using a camera of a mobile computing device, the camera configured as a global shutter.

14. The computer program product of claim 10, wherein the capturing is performed using a light sensor of a mobile computing device.

15. The computer program product of claim 10, wherein the capturing is performed using a camera of a mobile computing device.

16. The computer program product of claim 10, further comprising synchronizing the capturing sampling rate to a transmission frequency of the light-based communication signal, the synchronizing storing each of a plurality of captured signals in each of a plurality of trial buffers.

17. The computer program product of claim 16, wherein the synchronizing further comprises:

configuring a first trial buffer of the plurality with a maximum buffer size based on a signal length plus a maximum deviation;

configuring each remaining buffer of the plurality of trial buffers to have a buffer size reduced by a different multiple of a function inversely proportional to a product of baud rate and a number of captured data to sample the signal; and

determining a score for each buffer of the plurality, the score indicating a degree of synchronization between the signal length and the buffer length.

18. The computer program product of claim 10, wherein determining the capture offset further comprising adjusting a sampling period to cause the sampling period divided by the signal period of the light based communication signal to be a non-integer multiple.