Fso Iran Stu2008

8/9/2019 Fso Iran Stu2008

1/75

Iran 2008

1

Professor Z GHASSEMLOOY

Associate Dean for ResearchOptical Communications Research Group,

School of Computing, Engineering and Information Sciences

The University of Northumbria

Newcastle, U.K.

http://soe.unn.ac.uk/ocr/

Free Space OpticalCommunications


2/75

Iran 2008

2

Northumbria University at Newcastle, UK

2


3/75

Iran 2008

3

Outline

Introduction

Why the need for optical wireless?

FSO

FSO - Issues

Some results Final remarks

3


4/75

Optical Communications

Optical FibreCommunications

PhotonicSwitching

Indoor

Wired Wireless

Free-SpaceOptics(FSO)

Free-SpaceOptics(FSO)

OCRG - Research Areas

Chromatic dispersioncompensation using

optical signal processing Pulse Modulations Optical buffers Optical CDMA

Pulse Modulations Equalisation Error control coding

Artificial neural network &Wavelet based receivers

Fast switches All optical routers

Subcarrier modulation Spatial diversity Artificial neural

network/Waveletbased receivers

4HK Poly-Univ. 2007


5/75

Staff Prof. Z Ghassemlooy J Allen R Binns K Busawon

Wai Pang Ng

Visiting AcademicsProf. Jean Pierre, Barbot

France

Prof. I. DarwazehUCL

Prof. Heinz DringHochschule Mittweida Univ.

of Applied Scie. (Germany) Dr. E. Leitgeb

Graz Univ. of Techn. (Austria)

OCRG -People

PhD M. Amiri M. F. Chiang: S. K. Hashemi R. Kharel

W. Loedhammacakra V. Nwanafio E. K. Ogah W. O. Popoola S. Rajbhandari (With IMLab)

Shalaby S. Y Lebbe

MSc and BEng A Burton D Bell G Aggarwal M Ljaz O Anozie W Leong

(BEng) S Satkunam (BEng)


6/75

Iran 2008

6

Photonics - Applications

Long-Haul Metropolitan Home access

Board -> Inter-Chip -> Intra-Chi

Photonics in communications: expanding and scaling

Health(bio-photonics)

Environmentsensing

Securityimaging

Photonics: diffusing into other application sectors


7/75

RF & Optical Communications -

Integration

TraditionalRadio

TraditionalRadio

TraditionalOptics

TraditionalOptics

Radio onFibre

Radio onFibre

OpticalWireless

FibreFibre Free SpaceFree SpaceL

ightw

ave

L

ightwave

RF

RF

Transmission ChannelTransmission Channel

Source

Sourc

e


8/75

Free Space Optical(FSO)Communications


9/75

.. BANDWIDTH when and where required.

AND THAT IS ?

Over the last 20 years deployment of optical fibre cables in the backbone

and metro networks have made huge bandwidth readily available to

within one mile of businesses/home in most places.

But, HUGE BANDWIDTH IS STILL NOT AVAILABLE TO THE END

USERS.

The Problem?

9


10/75Iran 2008

10

Optical Wireless Communication

Abundance of unregulated bandwidth - 200 THz in the 700-1500nm range

Abundance of unregulated bandwidth - 200 THz in the 700-1500nm range

Whatdoes

ItOffer

?

No multipath fading - Intensity modulation and direct detectionNo multipath fading - Intensity modulation and direct detection

Secure transmissionSecure transmission

High data rate In particular line of sight (in and outdoors)

High data rate In particular line of sight (in and outdoors)

Improved wavelength reuse capabilityImproved wavelength reuse capability

Flexibility in installationFlexibility in installation

Flexibility - Deployment in a wide variety of network architectures.Installation on roof to roof, window to window, window to roof or

wall to wall.

Flexibility - Deployment in a wide variety of network architectures.Installation on roof to roof, window to window, window to roof or

wall to wall.10


11/75Iran 2008

11

Drawba

cks

Multipath induced dispersion (non-line of sight, indoor) - Limiting data rateMultipath induced dispersion (non-line of sight, indoor) - Limiting data rate

SNR can vary significantly with the distance and the ambient noise(Note SNR Pr

2)

SNR can vary significantly with the distance and the ambient noise(Note SNR Pr

2)

Limited transmitted power - Eye safety (indoor)Limited transmitted power - Eye safety (indoor)High transmitted power - OutdoorHigh transmitted power - Outdoor

Receiver sensitivityReceiver sensitivity

Large area photo-detectors - Limits the bandwidthLarge area photo-detectors - Limits the bandwidth

May be high cost - Compared with RFMay be high cost - Compared with RF

Limited range: Indoor: ambient noise is the dominant (20-30 dB larger than

the signal level. Outdoor: Fog and other factors

Limited range: Indoor: ambient noise is the dominant (20-30 dB larger than

the signal level. Outdoor: Fog and other factors

Optical Wireless Communication

11


12/75Iran 2008

12

12

(Source:NTT)

Access Network bottleneck

12


13/75Iran 2008

13

13

xDSL Copper based (limited bandwidth)- Phone and data combine Availability, quality and data rate depend on proximity to serviceprovidersC.O.

Radio link Spectrum congestion (license needed to reduce interference) Security worries (Encryption?) Lower bandwidth than optical bandwidth At higher frequency where very high data rate are possible,atmospheric

attenuation(rain)/absorption(Oxygen gas) limits link to ~1kmCable

Shared network resulting in quality and security issues. Low data rate during peak times

FTTx Expensive Right of way required - time consuming

Access Network Technology


14/75Iran 2008

14

Optical Wireless Communications

Using optical radiation to communicatebetween two points through unguided

channels

Types

- Indoor

- Outdoor (Free Space Optics)

14


15/7515

DRIVER

CIRCUIT

SIGNAL

PROCESSING

PHOTO

DETECTOR

Link Range L

FSO - Basics

Cloud Rain Smoke Gases Temperaturevariations Fog and aerosol

Transmission of optical radiation through the atmosphere obeys the Beer-Lambertss law:

: Attenuation coefficient dB/km Not controllable and is roughly independent ofwavelength in heavy attenuation conditions.

d1 and d2: Transmit and receive aperture diameters (m)

D: Beam divergence (mrad)(1/e for Gaussian beams; FWHA for flat top beams),

This equation fundamentally ties FSO to the atmospheric weather conditions

10/

22

1

2

2 10)(

L

trLDd

dPP

=

Dominant term at99.9% availabilityDominant term at99.9% availability


16/75

FSO Link

Transmitter Lasers 780,850,980,1550nm, also 10 microns Beam control optics

o Multiple transmit apertures to reduce scintillation problems

o Tracking systems to allow narrow beams and reduced geometric losses

Receiver Collection lens Solar radiation filters (often several) Photodetector - Large area and low capacitance (PIN/APD) Amplifier and receiver

o Wide dynamic range requirement due to very high clear air link margin

o Automatic gain and transmitter power control


17/75

Iran 2008

17

Optical Components Light Source

OperatingWavelength

(nm)

Laser type Remark

~850 VCSEL Cheap, very available, no active cooling,reliable up to ~10Gbps,

~1300/~1550 Fabry-Perot/DFB Long life, compatible with EDFA, up to40Gbps5065 times as much power comparedwith 780-850 nm

~10,000 Quantum cascadelaser (QCL) Expensive, very fast and highly sensitiveIdeal for indoor (no penetration throughwindow)

For indoor applications LEDs are also used17

Eye safety - Class 1MEye safety - Class 1M


18/75

Iran 2008

18

Optical Components Detectors

Material/StructureWavelength

(nm)Responsivity

(A/W)Typical

sensitivityGain

Silicon PIN 300 1100 0.5 -34dBm@155Mbps

1

InGaAs PIN 1000 1700 0.9 -46dBm@155Mbps 1

Silicon APD 400 1000 77 -52dBm@155Mbps

150

InGaAs APD 1000 1700 9 10

Quantum well andQuatum-dot(QWIP&QWIP)

~10,000

Germanium only detectors are generally not used in FSO because of their high dark current.

18


19/75

Existing System Specifications

Range: 1-10 km (depend on the data rates) Power consumption up to 60 W

15 W @ data rate up to 100 mbps and =780nm, short range 25 W @ date rate up to 150 Mbps and = 980nm 60 W @ data rate up to 622 Mbps and = 780nm 40 W @ data rate up to 1.5 Gbps and = 780nm

Transmitted power: 14 20 dBm Receiver: PIN (lower data rate), APD (>150 mbps) Beam width: 4-8 mRad Interface: coaxial cable, MM Fibre, SM Fibre Safety Classifications: Class 1 M (IEC) Weight: up to 10 kg

19


20/75

Iran 2008

20

Power Spectra of Ambient Light Sources

Wavelength ( m)

Norma

lise

dp

ower/unitw

aveleng

th

0

0.2

0.4

0.6

0.8

1

1.2

0.3

0.

4

0.5

0.6

0.7

0.8

0.9

1.0

1.

1

1.

2

1.3

1.

4

1.5

Sun Incandescent

x 10

1st window IR

Fluorescent

Pave)amb-light >> Pave)signal (Typically 30 dB with no optical filtering)

2nd window IR

20


21/75

Iran 2008

21

FSO - Characteristics

Narrow low power transmit beam- inherent security Narrow field-of-view receiver Similar bandwidth/data rate as optical fibre No multi-path induced distortion in LOS

Efficient optical noise rejection and a high optical signalgain Suitable to point-to-point communications only (out-door

and in-door) Can support mobile users using steering and tracking

capabilities Used in the following protocols:- Ethernet, Fast Ethernet, Gigabit Ethernet, FDDI, ATM- Optical Carriers (OC)-3, 12, 24, and 48.

Cheap (cost about $4/Mbps/Month according to fSONA)21


22/75

Iran 2008

22

22Source:

Cost Comparison


23/75

Existing Systems

Auto tracking systems - 622 Mbps [Canobeam] TereScop - 1.5 Mbps to 1.25 Gbps (500m 5km)

Cable Free - 622 Mbps to 1.25 Gbps (High power class 3BLaser at 100 mW)

Microcell and cell-site backbone GSM, GPRS, 3G and EDGE traffico No Frequency license

o No Link Engineering

o Management via SNMP, RS232

o or GSM connection

Last mile

o 155 Mbps STM-1 links

o 622 Mbps ATM link for Banks etc


24/75

Iran 2008

24

800BC - Fire beacons (ancient Greeks and Romans)150BC - Smoke signals (American Indians)1791/92 - Semaphore (French)

1880 - Alexander Graham Bell demonstrated the photophone 1st FSO (THE GENESIS)

(www.scienceclarified.com)

1960s - Invention of laser and optical fibre1970s - FSO mainly used in secure military applications1990s to date - Increased research & commercial use due to successful trials

When Did It All Start?

24


25/75

Iran 2008

25

25

In addition to bringing huge bandwidth to businesses /homes FSO also findsapplications in :

Multi-campus universityHospitals

Others: Inter-satellite

communication

Disaster recovery

Fibre communication

back-up

Video conferencing Links in difficult terrains

Temporary links

e.g. conferences

Cellular communication

back-haul

FSO challengesFSO challenges

FSO - Applications
http://www.mobilecomms-technology.com/contractors/last_mile/pav/http://www.mobilecomms-technology.com/contractors/last_mile/pav/http://www.mobilecomms-technology.com/contractors/last_mile/pav/http://www.mobilecomms-technology.com/contractors/last_mile/pav/


26/75

RF wireless networks- Broadcast RF networks are not scaleable

- RF cannot provide very high data rates

- RF is not physically secure- High probability of detection/intercept

- Not badly affected by fog and snow, affected byrain

A Hybrid FSO/RF Link- High availability (>99.99%)

- Much higher throughput than RF alone

- For greatest flexibility need unlicensed RF band

Hybrid FSO/RF Wireless Networks


27/75

Iran 2008

27

LOS - Hybrid Systems

Video-conference for Tele-medicine CIMIC-purpose and disaster recovery27


28/75

Iran 2008

28

DRIVER

CIRCUI

T

POINT APOINT B

SIGNAL

PROCESSIN

G

PHOTO

DETECTOR

Major challenges are due to the effectsof:

CLOUD,

RAIN,

SMOKE, GASES,

TEMPERATURE VARIATIONSFOG & AEROSOL

FSO - Challenges

To achieve optimal link performance,

system design involvestradeoffs of the different parameters.

28


29/75

Iran 2008

29

29

Effects Options Remarks

Photon absorption

Increase transmitoptical power Effect not significant

FSO Challenges - Rain

= 0.5 3 mm


30/75

FSO Challenges - Physical Obstructions

Pointing Stability and Swaying Buildings

Effects Solutions Remarks Loss of signal Multipath induced

Distortions

Low power due tobeam divergence and

spreading Short term loss of

signal

Spatial diversity Mesh architectures: using

diverse routes Ring topology: Users n/w

become nodes at least onehop away from the ring

Fixed tracking (short

buildings) Active tracking (tall buildings)

May be used for

urban areas,

campus etc.

Low data rate Uses feedback

30


31/75

FSO Challenges Aerosols Gases &

Smoke

Mie scattering Photon absorption

Rayleigh scattering

Increase transmitpower

Diversity techniques

Effect not severe

Effects Solutions Remarks

31


32/75

Iran 2008

32

32


Mie scattering Photon absorption

Increase transmit

optical power Hybrid FSO/RF

Thick fog limits link

range to ~500m Safety requirements

limit maximum optical

power

FSO Challenges - Fog

= 0.01 - 0.05 mmIn heavy fog conditions, attenuation is

almost constant with wavelength over the7801600 nm region.

In fact, there are no benefits until one gets

to millimeter-wave wavelengths.

In heavy fog conditions, attenuation isalmost constant with wavelength over the

7801600 nm region.In fact, there are no benefits until one gets

to millimeter-wave wavelengths.


33/75

Iran 2008

33

33

Weathercondition

Precipitation Amount(mm/hr)

Visibility dBLoss/km

Typical Deployment Range(Laser link ~20dB margin)

Dense fog 0 m50 m -271.65 122 m

(H.Willebrand & B.S. Ghuman,2002.)

Very clear 23 km50 km

-0.19-0.06

12112 m13771 m

Thick fog 200 m -59.57 490 m

Moderate fog Snow 500 m -20.99 1087 m

Light fog Snow Cloudburst 100 770 m1 km

-12.65-9.26

1565 m1493 m

Thin fog Snow Heavy rain 25 1.9 km2 km

-4.22-3.96

3238 m3369 m

Haze Snow Medium rain 12.5 2.8 km4 km

-2.58-1.62

4331 m5566 m

Light haze Snow Light rain 2.5 5.9 km10 km -0.96-0.44 7146 m9670 m

Clear Snow Drizzle 0.25 18.1 km20 km

-0.24-0.22

11468 m11743 m

FSO Challenges - Fog


34/75

FSO Challenges - Beam Divergence

Beam width Typically, for FSO transceiver is relatively wide: 210-mrad

divergence, (equivalent to a beam spread of 210 m at 1 km), as isgenerally the case in non-tracking applications.

Compensation is required for any platform motion By having a beam width and total FOV that is larger than either

transceivers anticipated platform motion.

For automatic pointing and tracking, Beam width can be narrowed significantly (typically, 0.051.0 mrad

of divergence (equivalent to a beam spread of 5 cm to 1 m at 1 km)- further improving link margin to combat adverse weather conditions.

- However, the cost for the additional tracking feature can be significant.


35/75

Iran 2008

35

Background radiation

LOS requirement

Laser safety

FSO Challenges - Others


36/75

Free Space Optics Characteristics Challenges Turbulence

- Subcarrier intensity multiplexing- Diversity schemes

Results and discussions

Wavelet ANN Receiver

Final remarks


37/75


Irradiance fluctuation

(scintillation)

Image dancing

Phase fluctuation Beam spreading Polarisation

fluctuation

Diversity techniquesForward error control

control

Robust modulationtechniques

Adaptive opticsCoherent detection not

used due to Phasefluctuation

Significant for longlink range (>1km)

Turbulence and thickfog do not occurtogether

In IM/DD, it results in

deep irradiance

fades that could last

up to ~1-100 s

FSO Challenges - Turbulence

37


38/75

Iran 2008

38

Cause:Atmospheric inhomogeneity / random temperature variation along beam path.

Depends on: Altitude/Pressure, Wind speed, Temperature and relative beam size. Can change by more than an order of magnitude during the course of a day, being the

worst, or most scintillated, during midday (highest temperature). However, at ranges < 1 km, most FSO systems have enough dynamic range or margin to

compensate for scintillation effects.

The atmosphere behaves like prismof different sizes and refractive indices

Phase and irradiancefluctuation

Zones of differing density act as lenses,scattering light away from its intended path.

Thus, multipath.

Result in deepsignal fades that

lasts for ~1-100 s

FSO Challenges - Turbulence


39/75

Iran 2008

39

Gamma-Gamma All regimes

Model Comments

Log Normal Simple; tractableWeak regime only

I-K Weak to strongturbulence regime

K Strong regime only

Rayleigh/Negative

Exponential

Saturation regime only

Irradiance PDF by Andrews et al (2001):

0)2()()(

)(2

)(

1)2(

2/)(

>

=

++

IIIIp

1

6/55/12

2

1

6/75/12

2

1)69.01(

51.0exp

1)11.11(

49.0exp

+

=

+

=

l

l

l

l

Ix: due to large scale effects;obeys Gamma distribution

Iy: due to small scale effects;

obeys Gamma distributionKn(.): modified Bessel function

of the 2nd kind of ordernl

2 : Log irradiance variance

(turbulence strengthindicator)

yxIII =

Based on the modulation process the received

irradiance is

Irradiance PDF:

02

220

2

)2/)/(ln(exp

1

2

1)(

+= I

l

l

l

I

II

IIp

To mitigate turbulence effect we, employ subcarrier modulationwith s atial diversit

Turbulence Channel Models


40/75

Iran 2008

40

40

A

No Pulse Bit 0 Pulse Bit 1

No Intensity Fading

With Intensity Fading

A

Threshold level

A/2

All commercially available systems use OOK with fixed threshold whichresults in sub-optimal performance in turbulence regimes

Turbulence Effect on OOK


41/75

( )dI

II

I

iRIi

l

l

l

rr

+

=

2

220

20

2

22

2

2/)/ln(exp

.1

2

1

2

))((exp

))(/()(maxarg

tdiPtd rd=

Using optimal maximum a posteriori (MAP) symbol-by-symbol detection withequiprobable OOK data:

Turbulence Effect on OOK

0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 10 .1

0.15

0 .2

0.25

0 .3

0.35

0 .4

0.45

0 .5

L o g I n te n s i ty S t a n d a r d D e v i a t i o n

Thres

holdlevel,i

th

0.5*10-2

10-2

3*10-2

5*10-2

Noise var iance

OOK based FSO requires

adaptive threshold to perform

optimally.

.but subcarrier intensitymodulated FSO does not

41


42/75

Photo-detector

array

Atmosphericchannel

Serial/parallelconverter

Subcarriermodulator

.

.Data in

d(t)

Summingcircuit

.

.

DC bias

m(t) m(t)+bo

Opticaltransmitter

Spatialdiversitycombiner

Subcarrierdemodulator

Parallel/serialconverter .

.

Data out

d(t) ir

SIM System Block Diagram

42


43/75

Subcarrier Intensity Modulation

No need for adaptive threshold To reduce scintillation effects on SIM

Convolutional coding with hard-decision Viterbi decoding (J. P. KImet al 1997)

Turbo code with the maximum-likelihood decoding (T. Ohtsuki, 2002) Low density parity check (for burst-error medium):

- Outperform the Turbo-product codes.

- LDPC coded SIM in atmospheric turbulence is reported to achieve acoding gain >20 dB compared with similarly coded OOK (I. B. Djordjevic, etal 2007)

SIM with space-time block code with coherent and differentialdetection (H. Yamamoto, et al 2003)

However, error control coding introduces huge processingdelays and efficiency degradation (E. J. Lee et al, 2004)

43


44/75

SIM Our Contributions

Multiple-input-multiple-output (MIMO) (an array of transmitters/photodetectors) to mitigate scintillation effect in a IM/DD FSO link overcomes temporary link blockage (birds and misalignment) when

combined with a wide laser beamwidth, therefore no need for an activetracking

provides independent aperture averaging with multiple separate

aperture system, than in a single aperture where the aperture size hasto be far greater than the irradiance spatial coherence distance (fewcentimetres)

provides gain and bit-error performance Efficient coherent modulation techniques (BPSK etc.) - bulk of the

signal processing is done in RF that suffers less from scintillation

In dense fog, MIMO performance drops, therefore alternativeconfiguration such as hybrid FSO/RF should be considered

Average transmit power increases with the number of subcarriers,thus may suffers from signal clipping

Inter-modulation distortion

45


45/75

Iran 2008

45

45

=

+=M

j

jcjj twtgAtm

1

)cos()()(

Serial to

ParallelConverter

.

.

.

.

.

.

PSK m odulator

atcoswc1t

PSK m odulator

atcoswcMt

PSK m odulator

atcoswc2t

Laser

driver

)(tdInputdata

g(t)

g(t)

g(t)

A1

AM

A2

m(t)

DC b ias

b0

Atmopsher ic

channel

Subcarrier Modulation -Transmitter

1'

00,0 ][ ct NPRhModulation index is constrained to avoid over modulationModulation index is constrained to avoid over modulation

46


46/75

Iran 2008

46

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-5

-4

-3

-2

-1

0

1

2

b0 Drive current

Outputpower

m(t)2

m a xP

P=

5-subcarriers

=

+=M

jjcjj twtgAtm

1

)cos()()(

Subcarrier Modulation -Transmitter

1'

00,0 ][ ct NPRh


47/75

Photodetector

ir

x g(-t) Sampler

PSK D emodulator

atcoswc2t

PSK D emodulator

atcoswcMt

Parallelto Serial

Converter

PSK Demodulator

coswc1t

)( td Oud

.

.

.

SIM -Receiver

)())(1()( tntmIRtir ++=

Photo-current

R= Responsivity, I= Average power, =Modulation index, m(t) = Subcarrier signal

di(t) = Data

2

2

2)(

= IRASNR ele

47

{ }=

++=cN

i

iiitir tntftdPhP1

, )(2cos()(1

48


48/75

Iran 2008

48

48

Performs optimally without adaptive threshold as in OOK Use of efficient coherent modulation techniques (PSK, QAMetc.)

- bulk of the signal processing is done in RF where matureddevices like stable,

low phase noise oscillators and selective filters are readilyavailable.

System capacity/throughput can be increased Outperforms OOK in atmospheric turbulence Eliminates the use of equalisers in dispersive channels

Similar schemes already in use on existing networks The average transmit power increases as the numberof

subcarrier increases or suffers from signal clipping. Intermodulation distortion due to multiple subcarrier

impairsits performance

But..

Subcarrier Modulation


49/75

SIM - Spatial Diversity

Single-input-multiple-output

Multiple-input-multiple-output (MIMO)

49


50/75

Selection Combining(SELC). No need for phaseinformation

))()...(),(max()( 21 titititi NT =ii ia

Maximum RatioCombining (MRC)[Complex but optimum]

Naaa === ...21

Equal GainCombining (EGC)

FSO

C

HAN

NEL

PS K

SubcarrierDemodulator.

.

.

.

)( td

)(1 ti

)(2 ti

)(tiN

a2

a1

aN

Combiner

)(tiT

DiversityCombiningTechniques

ai is the scaling

factor

)()cos()(1)( tntwtgAIN

Rti i

M

jjcjjiri +

++=

SIM - Spatial Diversity

Assuming identical PIN photodetector on eachlinks, the photocurrent on each link is:

50

SIM S ti l Di it A ti


51/75

SIM Spatial Diversity Assumptions

Made

Spacing between detectors > the transverse correlationsize

oof the laser radiation, because

o= a few cm in

atmospheric turbulence

Beamwidth at the receiver end is sufficiently broad to coverthe entire field of view of all Ndetectors.

Scintillation being a random phenomenon that changeswith time makes the received signal intensity time variantwith coherence time

o

of the order of milliseconds.

Symbol duration T


52/75

Iran 2008

52

Eric Korevaar et. alA typical reduction in intensity fluctuation with spatial diversity

One detector

Two detectors

Three detectors

Subcarrier Modulation - Spatial Diversity


53/75




Wavelet ANN Receiver Final remarks


54/75

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

-5

0

5

10

15

20

Num be r o f subca r ri e r

NormalisedSNR@B

ER=10

-6(d

B)

0.10.20.50.7

Log intensi tyvariance

Normalised SNRat BER of 10-6 against the number of subcarriers for variousturbulence levels for BPSK

Increasing the number ofsubcarrier/users, resultsIn increased SNR

SNR gain comparedwith OOK

Error Performance No Spatial Diversity

55


55/75

Iran 2008

55

2 0 2 5 3 0 3 5 4 01 0

-1 0

1 0-8

1 0-6

1 0-4

1 0-2

S N R (dB )

BER

D P S K

B P S K

1 6 -P S K

8 -P S K

Log i n ten s i t y

var ian c e = 0 .52

( )

0

22

)()/sin(loglog

2dIIpMMSNRQMBER

e

BPSK based subcarrier

modulation is the mostpower efficient

BPSK BER against SNR forM-ary-PSK for log intensity variance = 0.52

Error Performance No Spatial Diversity

56


56/75

Iran 2008

56

10

20

30

40

50

60

70

Turbulence Regime

DiveristyGain

(dB)

Weak

Saturation

Moderate

2 Photodetectors

3 Photodetectors

Spatial Diversity Gain

Spatial diversity gain with EGC against Turbulence regime


57/75

Spatial Diversity Gain for EGC and SeLC

1 2 3 4 5 6 7 8 9 10-10

-5

0

5

10

15

20

25

No of Receivers

Linkmargin(dB)

0.22

0.52

0.72

1

Log Intensity

Variance

EGC

Sel.C

BER = 10-6

[ ] ].)(1[2

))22exp((

1

1

)(

220 llixK

n

i

N

iiNSelCeexerfw

NP

=

+=

{ }ni ix

1=

= Zeros of the nth order

Hermite polynomial{ } n

i iw

1=

= Weight factor of the nth order

Hermite polynomial

NARIK 200 2 =

Dominated by received irradiance,reduced by factorNon each link.

Link margin for SelC is lower

than EGC by ~1 to ~6 dB


58/75

1 2 3 4 5 6 7 8 9 100

5

10

15

20

25

30

No of Receivers

SpatialDivers

ityGain

(dB)

MRC

EGC

Log Intensity

variance

1

0.52

0.22

Most diversity gainregion

The optimal but complex MRC diversity is marginally superior to thepractical EGC

Spatial Diversity Gain for EGC and MRC

BER = 10-6

+

=

=

mx

i

ZEGCe

uuieKQw

dZdZPZK

P

1

)2(1

0

2/

0

2

2

21

)(

)(1

)()(sin2

exp1

( )

[ ]

=

=

2/

0

0

)(

,)(1

)(/

dS

IdIPIQP

N

IMRCMRCe

58


59/75

Multiple-Input-Multiple-Output

BPSK

Modu-

Lator

and

Laser

driver

d(t) .

.

.

It1

It2

ItH

F

S

O

C

HA

N

N

E

L

BPSK

SubcarrierDemodulator.

.

.

.

)( td

)(1 ti

)(2 ti

)(tiN

a2

a1

aN

Combiner

iT

By linearly combining the photocurrents using MRC, the individual SNRe on each

link 2

122

=

=

H

j

ijieleI

HN

RASNR

59


60/75

MIMO Performance

12 14 16 18 20 22 24 26

10-9

10-8

10-7

10-6

10-5

10-4

10-3

SNR (R*E[I])2 / No (dB)

BER

1X5MIMO

1X8MIMO

4X4MIMO

2X2MIMO

1X4MIMO

[ ]

=2/

0

,)(1

dSPN

e=

+

m

j

uujj xK

wS1

2

2

2 )]2(2exp[sin2

exp1

)(

HN

ARIK

2

02

2

=

log intensity variance= 0.52

At BER of 10-6:

2 x 2-MIMO requires additional ~0.5dB ofSNRcompared with 4-photodetector single transmitter-multiple photodetector system.

4 x 4-MIMO requires ~3 dB and ~0.8dB lower SNR compared withsingle transmitter with 4 and 8-photodetectors , respectively.

60


61/75




Wavelet ANN Receiver Final remarks

62


62/75

Iran 2008

Transmission System - ReceiverModels

TX Channel

Noise

+

Slicer

MFEqualiserSlicerData out

CWTNNSlicerData out

Data in

MMSE

Wavelet - NN

Data out

63


63/75

Iran 2008

PPM System NN Equalization

PPM

Encoder

h(t)

Neural

Network

Decision

Device

Optical

Transmitter

Optical

Receiver

n(t)

PPM

Decoder

X(t)

Matched

Filter

ZjZjZj-1

.

Zj-n

.

Yj

Z(t)

M

0 0 1 0Ts = M/LRb

XjM

0 1 0 0

A feedforward back propagation neural network .

ANN is trained using a training sequence at the operating SNR.

Trained AAN is used for equalization

64


64/75

Iran 2008

Impulse Response of Equalized Channel

Pulse are spread to adjust pulse .

ISI depends on pulse spread

Equalized response in a deltafunction which is equivalent to aimpulse response of the idealchannel

Impulse response of unequalizedchannel

impulse response of equalizedchannel

65


65/75

Iran 2008

Results (1)

Adaptive linear equalizer with

least mean square (LMS)algorithm is used.

The performance of ANNequalizer is almost identical to

the linear equalizer.

Slot error rate performance of 8- PPM in diffuse channel with Drms of 5ns at 50Mbps

66


66/75

Iran 2008

Results (2)

Unequalized performance athigher data rate is

unacceptable at all SNR range

Linear and neural equalizationgive almost identical performance.

Slot error rate performance of 8- PPM in diffuse channel with Drms of 5ns at 100Mbps

67


67/75

Iran 2008

Results (3) - Wavelet-AI Receiver

SNR Vs. the RMS delay spread/bit duration

Wavelet

68


68/75

Iran 2008

Wavelet-AI Receiver - Advantages andDisadvantages

Complexity- many parameters & computations.

High sampling rates- technology limited.

Speed- long simulation times on average machines.

Similar performance to other equalisation techniques. Data rate independent

- data rate changes do not affect structure (just re-train).

Relatively easy to implement with other pulsemodulation techniques.

Vi ibl Li ht O ti l Wi l S t ith OFDM


69/75

Downlink

Uplink

Visible-light communication system

0

1

2

3

4

5

0

1

2

3

4

5

200

400

600

800

1000

1200

1400

x[m]

Distribution of horizantal illuminance [lx]

y[m]

Illuminance[lx]

Number of LEDs

60 x 60 (4 set)

Distribution of illuminance

Visible Light Optical Wireless System with OFDM

FSO Network Two Universities in


70/75

FSO Network Two Universities in

Newcastle

71


71/75

Iran 2008

Agilent Photonic Research Lab

Research Collaboration

Free space opticalDu-plex communication

link(Northumbria

and Newcastle Universities)at a data rate of 155 MbpsOptical Fibre

A-BlockAgilent PhotonicResearch Lab

C ll b t


72/75

Collaborators

Graz Technical University, Austria Houston University, USA University College London, UK Hong-Kong Polytechnic University

Tarbiat Modares University, Iran Newcastle University, UK Ankara University, Turkey Agilent, UK Cable Free, UK

Technological University of Malaysia Others

73


73/75

Iran 2008

Final Remarks

Could the promise of optical wireless live up to reality?

Yes!!

But

Optical wireless must complement radio, not compete Industry must be bold in research and development

Lower component cost, and single technology baseddeviced

Integration with existing systems Lover receiver sensitivity

Of course more research and development at alllevels

74


74/75

Iran 200874

Summary

Access bottleneck has been discussed

FSO introduced as a complementary technology

Atmospheric challenges of FSO highlighted

Subcarrier intensity modulated FSO (with andwithout spatial diversity) discussed

Wavelet ANN based receivers

75


75/75

Acknowledgements

To many colleagues (national and international)and in particular to all my MSc and PhD students

(past and present) and post-doctoral researchfellows

Fso Iran Stu2008

Documents

Transcript of Fso Iran Stu2008