Course Activity
On-off keying
LED to camera communication
• CamCom
• Intuitive / Visible
• Clear and simple channel
• Easy encoding / low data rate
Camera
• Raspberry pi
• Frame rate 30fps
• Shutter speed = 1us
• Resolution 1920*1080
Camera – Rolling Shutter
Global Shutter Rolling Shutter
Pixels exposed SIMULTANEOUSLY
Pixels exposed ROW BY ROW
How rolling shutter works ?
Signal Time
Global Shutter
1/30 s (1/fps)
Rolling Shutter
Tr (Read-out time)
Varies with camera models Time Gap
On-Off keying
• 1 = bright = on
• 0 = dark = off
• 1 second = 30 frames = 30 samples
• Symbol duration = 1/15 second
• Self designed preamble ( e.g. 1/5 second bright
On-Off keying
Time Intensity
1/15 s
Discard mixed frame, 1~2 frames = 1 bit, 3 frames = 2 bit
On-Off keying
• Problem : #On != #off, intensity changes
• No synchronization between Tx / Rx
• E.g. Rx = 28 fps, Tx = 30fps
• 30 consecutive ‘1’ s fail
Manchester coding
• 1 = dark -> bright
• 0 = bright -> dark
• Intensity changes in EVERY symbol
• Provide synchronization
• Symbol duration = 1/15 second
• Self designed preamble ( e.g. 1/5 second bright
Manchester coding
Time Intensity
1/15 s
Discard mixed frame, 1~2 frames = 1 bit, 3 frames = 2 bit
1 1 0 1 0
Manchester decoding
Time
Intensity 1 1 0 1 0
D DB BD DB BB BD DD DB BB BD D
Time
Intensity 1 1 0 1 0
DD BB DD BB BB DD DD BB BB DD
Course Activity
• In-class exercise
• Deadline : Wednesday ( maybe extended )
• Inter/ inner group discussion ok !
• Inter group code exchange FORBIDDEN
• DO NOT SHOW YOUR CODE TO OTHERS EXCEPT YOUR TEAMATE
Activity #2 : CamCom Manchester
• Tx
• USRP control LED
• Fixed Sampling rate : 200K
• 1 = bright, 0 = dark. Linear scale ( 0.5 = half intensity) Sample MATLAB file create bin file
• https://drive.google.com/file/d/0B_Z- TUMjZ2A8ZDNLM0FMQ0U1TUU/view
• Upload your bin file through
• scp teamN_v#.bin wn@10.5.7.182:~/ook-vlc/
• Password: wnfa2017
Activity #2 : CamCom Manchester
• Rx
• Raspberry camera
• Fixed 30fps 1920*1080 mp4
• Captured video in
• http://mvnl.csie.ntu.edu.tw/~wnfa/wn17fall/
• test.mp4 – sample video for 1kHz cosine wave
• Download the video and decode
• Read video sample code in
• https://www.dropbox.com/s/5zx14ozqg408san/OOKRxDemo.m
?dl=0
Requirement
• Decode 1 byte ( 1 char ) from 1s video
Submit
• courses.dlc.ntu.edu.tw
• Exercise > OOK
• .zip containing encode.m/ decode.m/ report.pdf
Activity #2 : Rolling Shutter Manchester
• Tx
• USRP control LED
• Fixed Sampling rate : 200K
• 1 = bright, 0 = dark. Linear scale ( 0.5 = half intensity)
• Sample bin file created by MATLAB
• Sample MATLAB file create bin file
• Upload your bin file to
Activity #2 : Rolling Shutter Manchester
• Rx
• Raspberry camera
• Fixed 30fps 1920*1080 mp4
• Captured video in
• http://mvnl.csie.ntu.edu.tw/~wnfa/wn17fall/
• test.mp4 – sample video for 1kHz cosine wave
• Download the video and decode
• Read video sample code in
• https://www.dropbox.com/s/5zx14ozqg408san/OOKRxDemo.m
?dl=0
Requirement
• Decode 1 byte ( 1 char ) from 1s video
Submit
• courses.dlc.ntu.edu.tw
• Exercise > Rolling OOK
• .zip containing encode.m/ decode.m/ report.pdf
