January 2016 doc.: IEEE 802.15-16-0018-00-007a Project: IEEE … · 2016. 1. 10. · doc.: IEEE...

doc.: IEEE 802.15-16-0018-00-007a

Submission Slide 1

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: National Taiwan University 802.15.7r1 OCC Proposal

Date Submitted: 10 January, 2016Source: Hsin-Mu Tsai, National Taiwan UniversityAddress: No.1, Sec. 4, Roosevelt Rd., Taipei 10617, TaiwanVoice: +886 2 33664888 ext. 316, E-Mail: [email protected]

Re: CFP Response

Abstract: CFP Response

Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

<Hsin-Mu Tsai>, <National Taiwan University>

January 2016

doc.: IEEE 802.15-16-0018-00-007a

Submission

January 2016

<Hsin-Mu Tsai>, <National Taiwan University>Slide 2

National Taiwan University802.15.7r1 OCC Proposal

Hsin-Mu (Michael) [email protected]

doc.: IEEE 802.15-16-0018-00-007a

Submission

Table of Content

• Requirements• Background• PHY proposal – RS-FSK• MAC proposal –

Frame Format for RS-FSK

<January 2016>


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REQUIREMENTS

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Transmitter RequirementsOverall objective:Retain the transmitter’s original function • The transmission should not create flickers visible to

human eyes• The transmitting LED should still retain dimming

capability• Use only ON and OFF – binary levels to modulate data

(simple transmitter design, minimum modifications to existing systems, cost efficient)

• Color is not used to modulate data (color is determined by user preference)

<January 2016>


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Receiver Requirements

Overall Objective: Use existing hardware

• Use off-the-shelf, unmodifiedrolling shutter camera as the receiver– Adding software (e.g. smartphone app) instantly gives

existing devices the reception capability– The start of the exposure duration is assumed NOT

controllable (unsynchronized channel)– Camera frame rate is NOT accurate and can vary over

time

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Receiver Requirements• Cameras using different image sensors should be

able to demodulate the same transmissionsimultaneously– Parameters that could be different include

• Resolution• Row read-out duration• Frame rate • Exposure duration• TX-RX distance

• Camera receiver should be able to receive even when the transmitter does not occupy the entire image (operate at longer distance & in line-of-sightscenarios)

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BACKGROUND

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Light-to-Rolling-Shutter-Camera Channel

• Main characteristics:1. Rolling exposure process

(rolling shutter sampling)2. Time gap 3. Low-pass filtering due to integration

during exposure

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Global versus Rolling Shutter

<January 2016>


Global Shutter:All pixels exposedat the same time

Rolling Shutter:Pixels are exposed

row by row

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Comparison of Sampling Schemes<January 2016>


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Idle Period<January 2016>


Time

Idle

Exposure(1st frame)

Exposure(2nd frame)

s1

s2s3

s4s5

s6

s7

s8

s9s10

s11

s12

Signal Loss

Symbol Loss

Receiving CameraTransmitted Signal

Idle period results in significant signal & symbol loss

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Idle Period + Un-occupied Area<January 2016>


Time

Idle

Exposure(1st frame)

Exposure(2nd frame)

s1

s2s3

s4s5

s6

s7

s8

s9s10

s11

s12

Signal Loss

Symbol Loss


Smaller light in the image results in even more loss

No signal

No signal

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Idle Period + Un-occupied Area<January 2016>


Time

Idle

Exposure(1st frame)

Exposure(2nd frame)

s1

s2s3

s4s5

s6

s7

s8

s9s10

s11

s12

Signal Loss

Symbol Loss


Different light location results in different portion

of signal / symbol loss

No signal

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Idle Period + Un-occupied Area = Time gap = Lossy Channel

<January 2016>


Transmitting Light

Phone 1Phone 2 Phone 3

Time

Exposure(1st frame)

Exposure(2nd frame)

Idle (17%)

Exposure(1st frame)

Exposure(2nd frame)

Idle (38%)

Exposure(1st frame)

Exposure(2nd frame)

Idle (33%)

2m 1m15cm

Loss 60%

Loss 40% Loss

50%

Different cameras have diverse loss ratio !

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Submission

Examples of Camera Parameters<January 2016>


ImageResolution

(X x Y)

Frame Rate (fps)

Measured Read-out

Duration (𝝁s)

Time Gap (ms)

(Percentage of Frame Duration)

AppleiPhone 6 Plus

1920x1080 30 21.42 10.20 (30.60%)

Apple iPhone 5s

1920x1080 29.98 20.65 11.03 (33.10%)

AppleiPhone 4s

1920x1080 29.87 24.48 7.04 (21.03%)

HTC New One

1920x1080 29.94 19.08 12.79(38.30%)

Samsung Galaxy S4

1920x1080 29.93 25.53 5.84 (17.48%)

Point Grey Flea3

2048x1080 30 14.73 17.42 (52.27%)

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Submission

Low-pass Filtering due to Exposure

• Pixel intensity of y-th row of pixel(s):

– 𝑟(𝑦, 𝑡): received signal of the y-th row at time t– 𝑇*: start of exposure for this image frame– 𝑇+: exposure duration– 𝑇,: row read-out duration

• Long 𝑇+ results in significant low-pass filtering!

<January 2016>


I[y] =

Z T0+(y�1)Tr+Te

T0+(y�1)Tr

r(y, t)dt

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PHY PROPOSAL -ROLLING-SHUTTERFREQUENCY SHIFT KEYING

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Submission

Recap: Rolling Shutter

Sampling

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Submission

Rolling Shutter –Frequency Shift Keying (RS-FSK)

Slide 20Time

Low frequencysquare wave

High frequencysquare wave

Wide Strip Narrow Strip

TX: Use signal frequency to represent data.RX: Use strip width to demodulate data.

Time

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to represent bits.

Relation between Frequency and Strip Width

Slide 21

Time

estimates withselects a frequency from :

Transmitter Receiver

Transmitted SignalImage Y axis

……

……

.: read-out duration.

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RS-FSK Advantages1. Average intensity stays the same for different symbols

over one symbol period (avoid flickers) 2. The waveform can be demodulated by receivers with

different (rolling shutter) sampling rates (i.e., read-out duration)

3. Demodulation is possible even when partial symbol is lost(cope with lossy channel)

4. Low-pass filtering does not destroy the signal as long as the exposure duration is not an integer multiples of the signal period

5. Dimming can be realized by changing the duty cycle of the signal

<January 2016>


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YIN - Accurate Frequency Estimation for RXAdvantages:1. Time-domain autocorrelation

handles variable signal length2. Parabolic interpolation

improves accuracy when is not an integer3. Measures to handle slow varying DC,

i.e., non-uniform illumination surface

<January 2016>


S4(front) S4(back) One(back) iP5s(front) iP5s(back)0%

25%50%75%

100%

Prob

abilit

y

loss mixed redundancy

S4(front) S4(back) One(back) iP5s(front) iP5s(back)0

0.250.5

0.751

PRR

raw splitter splitter+parity


1215

Smartphone−Camera

Thro

ughp

ut(B

ps)


Experimental resultsshow that all test camerascan all decode the sametransmission!

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Submission Slide 25

Time

……

……

Exposureof

1st frame

Exposureof

2nd frame

Idle (not receiving)

s1

s2

s3

Low SymbolRate

s1s2s3s4

……

s8s9

High SymbolRate

For better throughput:High-order modulation is required!

<January 2016>


High-Order Modulation - Partial Symbol Loss

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Z Te

r(i+ 1, t)dt

=

Ion

+ Io↵

2

· k · 1f+ I

on

(Te mod

1

f)

RS-FSK When Considering Exposure

<January 2016>


1/ft

𝐼./

𝐼.00

𝑟𝑜𝑤3

𝑇+

1/ft

𝐼./

𝐼.00

𝑟𝑜𝑤345

𝑇+

Average intensityover k signal period bright!

Z Te

r(i, t)dt

=

Ion

+ Io↵

2

· k · 1f+ I

on

(Te mod

1

f)

“variation”:

Average intensityover k signal period bright!“variation”:

Tr

Actual captured image

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Z Te

r(i+ 3, t)dt

=

Ion

+ Io↵

2

· k · 1f+ I

o↵

(Te mod

1

f)

RS-FSK When Considering Exposure

<January 2016>


1/ft

𝐼./

𝐼.00

𝑟𝑜𝑤346

𝑇+

Average intensityover k signal period

mixed“variation”:

1/ft

𝐼./

𝐼.00

𝑇+

𝑟𝑜𝑤347

Average intensityover k signal period

dark!“variation”:

Z Te

r(i+ 2, t)dt

=

Ion

+ Io↵

2

· k · 1f

+ {↵ · Ion

+ (1� ↵) · Io↵

} (Te mod

1

f)

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Submission

The Case Where RS-FSK is not Observed

<January 2016>


1/ft

𝐼./

𝐼.00

𝑟𝑜𝑤3 𝑇+Average intensityover k signal period

No “variation”! No stripe pattern!

When exposure is an integer multiple of the signal period

Te = k · 1f

𝑇+

The result stays the same for all rows!

𝑟𝑜𝑤8

Z Te

r(i, t)dt

=

Ion

+ Io↵

2

· k · 1f+ I(Te mod

1

f)

) Te mod

1

f= 0

0

doc.: IEEE 802.15-16-0018-00-007a

Submission

RS-FSK with Different Exposure Durations

<January 2016>


1/ft

𝐼./

𝐼.00

𝑟𝑜𝑤3

1/ft

𝐼./

𝐼.00

𝑟𝑜𝑤3

Te

Te = k · 1f+ (Te mod

1

f)

Z Te

r(i, t)dt

=

Ion

+ Io↵

2

· k · 1f+ I(Te mod

1

f)

Te

k = 1

k = 3 Average intensityover k signal period

”Variation” over

As the exposure duration increases, “variation” becomes small compared to the average intensity

Te

Te mod

1

f

doc.: IEEE 802.15-16-0018-00-007a

Submission

RS-FSK with Exposure / Low-pass Filtering1. In most cases, with arbitrary exposure duration

setting, RS-FSK signal remains detectable in the received images.

– The observed signal frequency in the images is the same as the transmitted signal frequency

2. When the exposure duration is (approximately) an integer multiple of the signal period, the signal is NOT detectable.

– This can be regarded as channel fading for that signal frequency3. As the exposure duration increases, the difference

between bright and dark strips (ON/OFF states) becomes small.

– When this difference becomes less than the intensity resolution of the image, the signal is no longer visible.

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Validation with Experimental Results

<January 2016>


0.00 3.66 7.33 10.99 14.65 18.31 21.98 25.64 29.300%

20%

40%

60%

80%

100%

Exposure Duration (ms)

Det

ectio

n Er

ror P

roba

bilit

y

FFTDIPYIN

Reasonable error probability up to tens of milliseconds

• Tested with 3 flavors of algorithms

• Each demodulation is regarded as erroneous if the estimated signal period is off by more than one read-out duration

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Submission







<January 2016>


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Submission

Dimming with Duty Cycle

<January 2016>


t

𝐼./

𝐼.00

𝐼./

𝐼.001/f t1/f

50% duty cycle 25% duty cycle

𝐼./

𝐼.00t1/f

75% duty cycle

• Change square wave duty cycle to adjust observed brightness

• Duty cycle is independent of and does not affect signal frequency f

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MAC PROPOSAL –FRAME FOR RS-FSK

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Submission

MAC Proposal

Main Objective: Compensate for significant signal loss and unsynchronized channelProblems & Proposed Solutions:1. Mis-aligned symbol boundary

2. Lost symbol detection

3. Recover from loss

<January 2016>


Embedded Sequence Number

Symbol Splitter

XOR-based Parity Code

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1. Problem: Mixed-Symbol Frames<January 2016>


TX & RX have different frame rates

TX & RX have the same frame rates

f1

f2

Time

TX RX

s1

s2

s3

s4

s5

s6Time

TX RX

Incorrect frequencyestimation!

firstsymbol

secondsymbol

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1. Solution: Symbol Splitter (SS)

<January 2016>


Time

TX RX

s1

ss

s2

s3

s4

f1

f2ss

ss

ssf3

firstsymbol

secondsymbol

SS

Symbol Splitter:micro symbol with known signal frequency

• Insert SS between consecutive data symbols• Linear search in the image to locate SS

(the location with strong power at SS frequency)• Separate image areas for frequency estimation

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2. Problem: Lost Symbol Detection

<January 2016>


��

��

��

��

��

��

��

When TX frame duration < RX frame duration Ts,tx T

f,rx

Entire symbol could be lost in the gap!1. How does the receiver know a symbol is lost?2. How to recover the lost data symbol?

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2. Solution: Embedded Sequence Number<January 2016>


Time

s1

s2

s3

s4

s5

s6

s7

s8

Assume no consecutive symbol losses*:

How to embed sequence numbers into symbols?

1 , 2 , 3 , 1 , 2 —> 3 is lost1 , 2 , 3 , 1 , 2 —> 2 is lost1 , 2 , 3 , 1 , 2 —> 1 is lost

XX

X

s9

seq# 1

seq# 2

seq# 3

seq# 1

seq# 2

seq# 3

seq# 1

seq# 2

seq# 3

{ }…

….

……

.

……

.] ] ]*This is true when the TX & RX frame rates are not different by more than 2 times

3 sequencenumbers needed

3 sets of frequenciesto represent3 sequence

numbers

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3. Solution: XOR-Based Parity Code

<January 2016>


Time

s1

s2

s3

s4

P

s5

f1

s6

f2

gap

TX RX

• Add parity symbol P every N-1data symbols

• Recover when 1 out of N symbol is lost

Determine N from loss probability:

Light sizeRead-out durationExposure duration

Transmitted symbol durationReceiving frame duration

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Derivation of Symbol Loss Probability

<January 2016>


Light size (number of rows)Read-out durationExposure durationTransmitted symbol durationReceiving frame duration

H :Tr :

Te :Ts,tx :Tf,rx :

Ploss

=max

✓Tgap

� Ts,tx

Tf,rx

, 0

◆

=max

✓Tf,rx � (H � 1)Tr � Te � T

s,tx

Tf,rx

, 0

◆

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Validation with Experimental Results<January 2016>


Compatible with a wide range of devices!

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Support longer distances /

smaller light!

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S4(front) S4(back) One(back) iP5s(front) iP5s(back)0%

25%50%75%

100%

Prob

abilit

y

loss mixed redundancy


0.250.5

0.751

PRR



1215

Smartphone−Camera

Thro

ughp

ut(B

ps)


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Preamble – Read-Out Duration Estimation

Slide 46

Time

Transmittedsignal

iPhone 5c iPhone 5s iPhone 6 Plus

= 108 px

250 Hz

= 164 px = 158 px

Packet format

Data ……

Preamble Symbol (known frequency 𝑓: )

Learn 𝑇, from the preamble:

Different cameras have different 𝑇, !

<January 2016>


Channel Estimation - 𝑇,

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Proposed Frame Format<January 2016>


��

��

��

��

��

��

��

��

��

Additional frame header fields for open systems:1. Selection of PHY data and SS frequencies

(Number of frequencies used: 2 byte; Actual used frequency in Hz, 2 byte per frequency)

2. Parity density N (1 byte)3. Checksum (optional, 2-4 bytes)

January 2016 doc.: IEEE 802.15-16-0018-00-007a Project: IEEE … · 2016. 1. 10. · doc.: IEEE...

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