Lab 1

Lab 1

Camera Communication

Platform – Same as in-class #2

• USRP + LED as Tx

• Raspberry pi camera

• Boost your data rate !! Up to 8kbps

Camera

• Raspberry pi

• Frame rate 30fps

• Shutter speed = 1us

• Resolution 1920*1080

Grading criteria

• Unawareness + workable – 20%

• Intensity stays constant over any 15ms ( 60Hz )

• Transmit 8bps ( in-class #2 )

• Baseline – 40%

• 128 bps

• Boost data rate – 30%

• 5% for each 2x. Maximum rate up to 128 × 2⁶ = 8192 bps

• Report – 10%

• Encode / decode explanation + work division

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

Find signal start

• Preamble

• Indicate the start(/end) of the signal

• Tx / Rx do not sync

• E.g. Tx transmits -> random ( 10ms, 100ms ) -> Rx camera start

• Unique symbol (sequence)

• Unused frequency in FSK

• Long bright/dark in Manchester coding

• May not follow symbol duration

• Need to have a clear “ending”

• Counter example : long bright + 1^st symbol Manchester ‘0’

( bright/dark)

Signal Loss handling

Signal Time Rolling Shutter

Tr (Read-out time)

Varies with camera models 𝑇𝑖𝑚𝑒 𝐺𝑎𝑝 = 1

𝑓𝑝𝑠 − 𝑇_𝑟 × #𝑟𝑜𝑤𝑠

𝑇 _𝑟 Calculation

• Transmit a data of known frequency

• Calculate the strip width

• Example : transmit 1 kHz cosine wave, 1 bright + 1 dark = 1ms = 1 strip

• 19 strips in image ( 1 black + 1 white ) occupying 888 pixels

• 𝑇_𝑟 = ^1𝑚𝑠

#𝑟𝑜𝑤𝑠 𝑝𝑒𝑟 𝑐𝑦𝑐𝑙𝑒 = ^1𝑚𝑠

(888/19) = 21.4𝑢𝑠

1

Signal Loss handling – long symbol

Signal Time Rolling Shutter

𝑇𝑖𝑚𝑒 𝐺𝑎𝑝

• Symbol duration > Gap

• Each symbol will be captured

• e.g. 1/30 s

• Each symbol carry multiple bits

• Multiple frequencies in FSK

• Multiple amplitude in ASK

Signal Loss handling – long symbol

• Each symbol will last over 1 frames

• Large symbol – more complex decoding

• Reference

• RollingLight :

http://www.csie.ntu.edu.tw/~hsinmu/wiki/_media/pap er/mobisys15.pdf

Symbol splitter ( optional )

• A fixed small symbol << symbol duration

• between 2 symbols to split symbol ( in case 2 consecutive same symbols )

• Similar to preamble, maybe a unique intensity in ASK or frequency in FSK

Signal Loss handling – short symbol

Signal Time Rolling Shutter

𝑇𝑖𝑚𝑒 𝐺𝑎𝑝

• Symbol duration < Gap and frame

• Some symbol loss

• Need to calculate symbol loss rate

Signal Loss handling – small symbol

• Single frame contains multiple symbol

• Small symbol – heavy coding + parity to recover

• Coding rate > symbol loss rate

• https://en.wikipedia.org/wiki/Forward_error_correction

#List_of_error-correcting_codes

Sequence number ( optional )

• Detect loss symbol in time gap

• “number” each symbol

• E.g. 24 symbols into 3 groups { A,B,C }, 8 symbols in each group = 3 bit per symbol

• Transmit symbol in group order ( cyclic )

• data = [110] [001] [010] [111] [101] [000]

• Sym. = [A6] [B1] [C2] [A7] [B5] [C0]

• If group order skipped in decode -> symbol loss

• E.g. [A6] [B1] [A7] -> [C?]

Lab #1 : CamCom

• 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 [email protected]:~/ook-vlc/

Lab #1 : CamCom

• Rx

• Raspberry camera

• Fixed 30fps 1920*1080 mp4

• Captured video in

• http://mvnl.csie.ntu.edu.tw/~wnfa/wn17fall/

• CLEAR in 10/1 (Sun.) 23:59

• 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

Grading criteria

• Demo : Unawareness + workable – 20%

• Intensity stays constant over any 15ms ( 60Hz )

• Transmit 8bps ( in-class #2 )

• Demo : Baseline – 40%

• 128 bps

• Demo : Boost data rate – 30%

• 5% for each 2x. Maximum rate up to 128 × 2⁶ = 8192 bps

Demo

• 10/26 (Thur.)

• 15 min per team

• Whole day available, book the time slot at

https://docs.google.com/spreadsheets/d/1Gt0kPk DGTFpR8MTsswOTMN4ZozkOdAH661KgcRgJIoc/edi t?usp=sharing

• Please feel free to email us if both of you are not available

Submit

• courses.dlc.ntu.edu.tw

• Lab > Lab1

• .zip containing encode.m/ decode.m/ report.pdf