recent progress in optical wireless communication giulio cossu, wajahat ali, raffaele corsini,...

INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

Recent Progress in Optical Wireless Communication

Giulio Cossu, Wajahat Ali, Raffaele Corsini, Ernesto Ciaramella


Summary

• Overlook on Optical Wireless Communication (OWC)

– Motivations and applications

– Devices

• Visible Light Communication (VLC) experiments

– Indoor applications

– Vehicle to vehicle communication

– Underwater communication

• OW for HEP and medical imaging

– Preliminary results


Introduction

• Optical Wireless (OW):

• Wavelengths from infrared to ultraviolet

• Free-space as optical medium

• Visible Light Communication (VLC):

• e.g. synergy between illumination and data transmission


Light Emitting Diodes (LEDs)

Phosphorescent white LEDBlue chips + phosphorus layerLimited bandwidth due to the slow phosphor layer (2-3 MHz)Original frequency response restored with blue filter (10-15 MHz)

RGB white LEDMix of Red + Green + Blue chipsFull bandwidth without optical filterAllows Wavelength Division Multiplexing (WDM)

0 10 20 30 40 50-30

-25

-20

-15

-10

-5

0

Nor

mal

ized

am

plitu

de (d

B)

Frequency (MHz)

White Response Blue Response400 450 500 550 600 650 7000

0,2

0,4

0,6

0,8

1,0

Nor

mal

ized

am

plitu

de (a

.u.)

Wavelength (nm)

Cool White Warm White

400 450 500 550 600 650 7000,0

0,2

0,4

0,6

0,8

1,0

Nor

mal

ized

am

plitu

de (a

.u.)

Wavelength (nm)

Lower power consumption, lower voltage, longer lifetime, smaller size, cooler operation and faster response


Differences between OW and RF technologies

Property of medium Radio Optical

Bandwidth regulation Yes No

Electromagnetic interf. Yes No

Power limitation Radio law Eye safety/illumination

Multipath fading Yes No

Passes though walls Yes No

Physical security Low High

Input x(t) Amplitude Power (always positive)

Detection type Coherent/Incoherent Incoherent


Link Configuration


Modulation format

Single-carrier modulation (power efficiency)

o On-Off Keying (OOK)• DC-balanced coding

Multi-carrier modulation (High speed)

o Orthogonal Frequency Division Multiplexing (OFDM)• Discrete Multi-Tone (DMT)

• IM/DD scheme• x(t) > 0

• Power efficiency• High speed

Discrete Multi-tone – Advantages

Advantages

• Spectral efficiency: bit-power

loading

• Easy frequency equalization

• Able to contrast the multipath


VLC Applications


High-speed OWC link – Introduction

Achieved results

(2012) 1 Gbit/s @ 15 cm – Phosphorescent LED (single channel) [Photonics journal]

(2012) 2.1 Gbit/s @ 15 cm – RGB LED (WDM channel) [ECOC]

(2012) 3.4 Gbit/s @ 15 cm – RGB LED (WDM channel) [Optics Express]

(2014) 5.2 Gbit/s @ 3 m – RGBY LED (WDM channel) [ECOC]

Goal: Highest speed operation (with low-cost components)

• Minimization of power losses -> Directed Line-of-sight configuration

• Narrow emission beam

• Narrow acceptance angle

• WDM operation (different colors transmit different data)


High-speed OWC link – Experimental Setup

Downlink: 12 chips (3 for each color). 22° Lambertian emission

Uplink: IR-LED emitting at 850 nm, 130° Lambertian emission

DMT signals N=512 subcarriers

BW=220 MHz 400 450 500 550 600 650 7000

0,2

0,4

0,6

0,8

1,0

91%72%71%

Nor

mal

ized

am

plitu

de (a

.u.)

Wavelength (nm)

92%


High-speed OWC link – Experiment

1,5 2 2,5 3 3,5 4900

1000

1100

1200

1300

1400

1500

1600720 490 300 200 168 128

Illuminance (lx)

Bit r

ate

(Mbi

t/s)

Distance Tx-Rx (m)

Red channel Green channel Blue channel Amber channel

1,5 2 2,5 3 3,5 44000

4500

5000

5500

6000

Downlink: aggregate

Distance Tx-Rx (m)

Bit r

ate

(Mbi

t/s)

500

1000

1500

2000

2500

Bit rate (Mbit/s)

Uplink: infrared channel

Summary: ≥ 5 Gbit/s with distance ≤ 3.5 m

(downlink)

Uplink ranges from 1.1 to 1.5 Gbit/s (4

-> 1.5 m)

WORLD RECORD


High-mobility OWC link – Introduction

Achieved results

(2013) 200 Mbit/s @ 2.4 m – Phosphorescent LED (uni-directional)

(2014) 250 Mbit/s @ 2 m – Phosphorescent LED/IR-LED (bi-directional)

(2014) 400 Mbit/s @ 2 m – RGB LED/IR-LED (bi-directional)

Goal: High speed operation in high mobility

• Non Directed Line-of-sight scheme

• Trade-off between diffuse links and high speed of LOS links.

• Scenario closer to typical indoor topology: synergy

illumination and data

• Robust to indoor ambient light

Custom RGB LED: blue @ 470 nm (local minimum of the Ph-LED)

Aux LED: Cool white phosphoroscent LED (to emulate ambient light)

120° Lambertian emission

DMT signals N=512 subcarriers BW=75 MHz

TxDownli

nk

400 450 500 550 600 650 7000

0,2

0,4

0,6

0,8

1,0

Nor

mal

ized

am

plitu

de (a

.u.)

Wavelength (nm)

Phosphorescent LED Transmitted BLUE LED Blue Filter

High-mobility OWC link – Experimental setup


High-mobility OWC link – Experiment

Measurement conditions• Vertical distance between ceiling and desktop: h = 2 m• Fixed 500 lx @ Rx• BER < 1,48 10∙ -3 (error-free after FEC decoding)

Measurements for downlink and uplink:• Maximum data rate

a) φ=ψ=0° (R=0 m),

Data rates: 400 Mbit/s (downlink) – 380 Mbit/s (uplink)

b) φ=ψ =45° (R=2 m)

Data rates: 200 Mbit/s (downlink and uplink)

Hot spot having r ≤ 2 m (≈12 m2) with a maximum of 400 Mbit/s (at the center) and a guaranteed data rate of 200 Mbit/s.


• Intelligent Transport System (ITS)• Increase safety, reduce congestion, enhancing mobility

• Vehicle-to-Infrastructure (V2I): roadside sensor, traffic lights

• Vehicle-to-Vehicle (V2V): safety-critical communication

• Common Radio Frequency (RF) solution• IEEE 802.11-based protocols: 5.9 GHz bandwidth

• Network congestion because of isotropic nature of the radio-waves

«Broadcast storm»Optical Wireless

• Low cost and limited impact: LEDs already present on the cars

• Free from broadcast storm: strong directionality


Car-to-Car communication – Preliminary results

CONFIDENTIAL

«Broadcast storm»



0,1 1 100

0,005

0,010

0,015

0,020

0,025

Bit E

rror

Rati

o

Distance Tx-Rx (m)

No lens Tx - No lens Rx 18° lens Tx - No lens Rx No lens Tx - Lens Rx 44° lens Tx - Lens Rx 18° lens Tx - Lens Rx

Step-like behavior:• No error until the distance

is such that the signal is higher than the serial port sensitivity

Maximum distance (m)

1 No lens Tx – No lens Rx 0,25

2 18° lens Tx – No lens Rx 0,5

3 No lens Tx – Lens Rx 2,6

4 44° lens Tx – Lens Rx 14,5

5 18° lens Tx – Lens Rx 31


Underwater communication - Introduction

300 400 500 600 700 8000,01

0,1

1

10

K co

effici

ent (

m-1

)

Wavelength (nm)

turb

idity

• Underwater monitoring exploiting vehicles in cooperation• needs of data exchange among vehicles

• Radio waves extremely attenuated in water• Acoustic modems for long distance suffer

• low data rate (hundreds bit/s)• latency (v=1500 m/s)• high cost

Optical Underwater Communication


Underwater communication – Preliminary results

11:00 12:00 13:00 14:00 15:00 16:000

2

4

6

8

10

Background light Signal + Background light

Time

Mea

sure

d lig

ht (V

)

0,0

0,1

0,2Peak to Peak signal (V)

Peak to Peak

11:00 12:00 13:00 14:00 15:00 16:0010-7

10-6

10-5

10-4

10-3

10-2

Bit E

rror

Rat

e

DMT, 100 Mbit/s (2,5 m)

• Almost 7 hours BER

monitoring

• Up to 100 Mbit/s

• Error free after FEC decoding


OWC for INFIERI applications

• OWC for Medical Imaging:

– To avoid strong electromagnetic interference in PET detectors

• We performed some preliminary results for the joint project with University Carlos 3 of Madrid.


Board-to-Board communication– Introduction

• OWC for HEP

• Design a Multi Gigabit OWC system for particles detectors (CMS used as a case study)

Requirements:

– Transmission distance: 10 cm

– Transmission bitrate: 2.5 Gbit/s

– Target bit error rate (BER): 10-9

– HEP environment


Board-to-Board communication – Preliminary results

Preliminary experimental results:

o Tx: Vertical Cavity Surface Emitting Laser (VCSEL)

– Relatively high output optical power: 0 dBm (1 mW)

– Medium divergence angle: 16°

– Emission wavelength: 1550 nm (no absorption with silica material)

o Rx: Photodiode

– Active area: 60 µm diameter

– Ball lens: 1.5 mm diameter

• Transmission link up to 1 cm approx.

Ray-tracing simulation (TracePro)in order to optimize the receiver



0 1 2 3 4 5 6 7 8 9 10 11 12-16

-14

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0

Tran

smis

sion

pow

er (d

Bm) @

BER

= 10

-9

Ball lens diameter (mm)

Required transmitted power vs lens diameter

• Target distance: 10 cm

• Target bitrate: 2.5 Gbit/s

• Target bit error rate (BER): 10-9

• Simulation shows 2 dB power margin respect to our transmitted power• As expected, margin increases with bigger ball lens

(together with tolerance to misalignment)



0,0 0,2 0,4 0,6 0,8 1,00

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24 1.5 mm diameter 3.0 mm diameter 5.0 mm diameter

Pow

er p

enal

ty (d

B) @

BER

= 1

0-9

Defocusing (mm)

Power penalty due to misaligment from optimal focal point in z axis

Ball lensPhotodiode

misalignment

Current condition22 dB power penalty (~150 times)

Conclusions

Optical wireless system as new technology alternative to RF

Main application: communication -> Visible Light Communication

High-speed indoor communication

5.2 Gbit/s WDM approach in directed-LOS @ 3 m (RECORD)

400 Mbit/s in Non-directed LOS @ 2 m (RECORD)

Vehicles to vehicles communication

Security message up to 31 m exploiting 1 LED

Underwater communication

Up to 100 Mbit/s error-free in 2.5 m underwater

Medical Imaging

Preliminary results: tolerance measurement at 0.5-1 m distance

High Energy Physics

Preliminary results: 1 cm transmission. Simulated: 10 cm feasible

Thanks for your [email protected]

recent progress in optical wireless communication giulio cossu, wajahat ali, raffaele corsini,...

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