Transcript Optical Wireless Communication using Digital Pulse

Free Space Optical
Communications
Professor Z. GHASSEMLOOY
Associate Dean for Research
Optical Communications Research Group,
School of Computing, Engineering and Information Sciences
The University of Northumbria
Newcastle, U.K.
http://soe.unn.ac.uk/ocr/
Northumbria University at Newcastle, UK
2
Outline
 Introduction to FSO
 FSO
 Applications
 Issues
 Results
 Simulation
 Experimental
 Final remarks
3
Free Space Optical
(FSO)
Communications
When Did It All Start?
800BC
150BC
1791/92
- Fire beacons (ancient Greeks and Romans)
- Smoke signals (American Indians)
- Semaphore (French)
1880
- Alexander Graham Bell demonstrated the photophone1 – 1st
FSO (THE GENESIS)
(www.scienceclarified.com)
1960s
- Invention of laser and optical fibre
1970s
- FSO mainly used in secure military applications
1990s to date - Increased research & commercial use due to successful trials
1Alexander
Graham Bell, "On the production and reproduction of sound by light," American Journal of Sciences, Series 3, pp. 305 - 324, Oct. 1880.
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The Problem?
AND THAT IS ?
….. BANDWIDTH when and where required.
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.
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7
FSO - Features
No
trenches
No
electromagnetic
interference
Used in the following
protocols: Ethernet, Fast Ethernet,
Gigabit Ethernet, FDDI, ATM, Optical
Carriers (OC)-3, 12, 24, and 48.
Complements
No
other access
Huge bandwidth
license
network
similar to fibre
fee
technologies
No multipath fading – Intensity
Secure
modulation and direct detection
transmission
Quick to install; only
takes few hours
Requires no right of way
Achievable range limited by thick fog to ~500m
Over 3 km in clear atmosphere
steering and tracking capabilities
Access Network Bottleneck
(Source: NTT)
8
8
9
Cellular Network Bottleneck
• Microwave radio links (installed or leased)
• More than one BS is connected to MSN
PTSN
Switching centre
Backhaul “last mile”
Microwave link
RF
Core network
MU
BS
Mobile switching
node
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Cellular Network Bottleneck
Medium capacity microwave link
BS C
High capacity
microwave link
BS B
Hub BS
Optical fibre
BS A
Mobile
switching
node
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Hub
Core
BS
“Regional”
BACKHAUL
“Last mile”
MSN
Iran 2008
12
Plaintree Systems Inc.
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www.geodesy-fso.com
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2009 MRV
Access Network Technology
xDSL
 Copper based (limited bandwidth)- Phone and data combine
 Availability, quality and data rate depend on proximity to service provider’s
C.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 ~1km
Cable
 Shared network resulting in quality and security issues.
 Low data rate during peak times
FTTx
 Expensive
 Right of way required - time consuming
 Might contain copper still etc
FSO
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FSO - Basics
SIGNAL
PROCESSING
Cloud
Rain
Smoke
Gases
Temperature variations
Fog and aerosol
PHOTO
DETECTOR
DRIVER
CIRCUIT






The transmission of optical radiation through the
atmosphere obeys the Beer-Lamberts’s law:
Preceive = Ptransmit * exp(-αL)
α : Attenuation coefficient
POINT A
This equation fundamentally ties FSO to the
atmospheric weather conditions
Link Range L
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POINT B
Optical Components – Light Source
Operating
Wavelength
(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 to
40Gbps
~10,000
Quantum cascade Expensive, very fast and highly
laser (QCL)
sensitive
For indoor applications LEDs are used.
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Optical Components – Detectors
Material/Structure
Wavelength
(nm)
Responsivity
Typical
(A/W)
sensitivity
Gain
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
Quantum –well and
Quatum-dot
(QWIP&QWIP)
10
~10,000
Germanium only detectors are generally not used in FSO because of their high dark current.
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Receiver Sensitivity Vs. Detector Area
-20
(155Mbit/s)
PIN
-30
Sensitivity
(dBm)
-40
APD
-50
0.01
0.1
1
10
2
Photodiode area (mm )
19
100
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
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Safety Classifications - Point Source
Emitter
500
√ with holography
class
3B
class
3B
Total
power
in a 5cm
Lens
(mW)
class
3B
class
3B
50mW
45mW
class
3A
5.0
1.0
0.2
class
3A
class
2
class
1
650
visible
class
3A
10mW
8.8mW
2.5mW
0.5mW
class
3A
class
1
class
1
880
indoor
1310
infra-red
Wavelength (nm)
21
class
1
√
1550
indoor
Source:BT
Power Spectra of Ambient Light Sources
Normalised power/unit wavelength
1.2
Pave)amb-light >> Pave)signal (Typically 30 dB with no optical filtering)
Sun
1
Incandescent
0.8
1st window IR
0.6
2nd window IR
Fluorescent
0.4
x 10
0.2
0
1.5
1.4
1.3
1.2
Wavelength (m)
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
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Cost Comparison
Source:
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25
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FSO – System Requirement







Link specifications / data rate
Response time
Timeliness / latency
Data throughput
Reliability
Availability
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FSO – System Requirement
M. Löschnigg, P. Mandl, E. Leitgeb, 2009
Hybrid FSO/RF Wireless Networks

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 by
rain

A Hybrid FSO/RF Link
- High availability (>99.99%)
- Much higher throughput than RF alone
- For greatest flexibility need unlicensed RF band
LOS - Hybrid Systems
Video-conference for Tele-medicine CIMIC-purpose and disaster recovery
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FSO - Applications
In addition to bringing huge bandwidth to businesses /homes FSO also finds
applications in :
Hospitals
Others:
 Inter-satellite communication
 Disaster recovery
 Fibre communication back-up Multi-campus university
 Video conferencing
 Links in difficult terrains
 Temporary links
e.g. conferences
FSO challenges…
Cellular communication back-haul
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FSO - Applications
Ring Topology
Star Topology
FSO - Challenges
Major challenges are due to the effects of:
CLOUD,
GASES,
SIGNAL
PROCESSING
SMOKE,
PHOTO
DETECTOR
DRIVER
CIRCUIT
RAIN,
TEMPERATURE VARIATIONS
FOG & AEROSOL
To achieve optimal link performance,
system design involves
tradeoffs of the different parameters.
POINT A
POINT B
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3rd ECAI – Romania, 3-5 July 2009
FSO Challenges – Rain & Snow
 = 0.5 – 3 mm
Snow attenuation
Effects
Photon absorption
Options
Remarks
Increase
transmit Effect not significant
optical power
• A heavy rainfall of 15 cm/hour causes 20 - 30 dB/km loss in optical power
• Light snow about 3 dB/km power loss
• Blizzard could cause over 60 dB/km power loss
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3rd ECAI – Romania, 3-5 July 2009
FSO Challenges - Physical Obstructions
Pointing Stability and Swaying Buildings
Effects
Loss of signal
 Multipath induced
Distortions
 Low power due to
beam divergence and
spreading
 Short term loss of
signal

Solutions
Spatial diversity
 Mesh architectures: using
diverse routes
 Ring topology: User’s n/w
become nodes at least one
hop away from the ring
 Fixed tracking (short
buildings)
 Active tracking (tall buildings)

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Remarks

May be used for
urban areas,
campus etc.
Low data rate
 Uses feedback

3rd ECAI – Romania, 3-5 July 2009
FSO Challenges – Aerosols Gases &
Smoke
Effects
 Mie scattering
 Photon absorption
 Rayleigh scattering
These contribute to signal
loss:
Solutions
 Increase transmit
power
 Diversity techniques
Remarks
 Effect not
severe
 ()   m ()   a ()  m ()  a ().
Absorption coefficient Scattering coefficient
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3rd ECAI – Romania, 3-5 July 2009
FSO Challenges - Fog
 = 0.01 - 0.05 mm
Using Mie scattering to predict fog attenuations
m and r are the refractive index and radius of the fog droplets, respectively. Qext is the
extinction efficiency and n(r) is the modified gamma size distribution of the fog droplets.
Effects
Options
Increase transmit
optical power
 Hybrid FSO/RF

Mie scattering
 Photon absorption

Remarks
Thick fog limits link
range to ~500m
 Safety requirements
limit maximum optical
power

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3rd ECAI – Romania, 3-5 July 2009
Fog - Predicted specific attenuation at 10 ºC
for moderate continental fog
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FSO Challenges - Fog
Weather
condition
Precipitation
Amount
(mm/hr)
Visibility
Dense fog
Thick fog
dB
Loss/km
Typical Deployment Range
(Laser link ~20dB margin)
0m
50 m
-271.65
122 m
200 m
-59.57
490 m
500 m
-20.99
1087 m
Moderate fog
Snow
Light fog
Snow
Cloudburst
100
770 m
1 km
-12.65
-9.26
1565 m
1493 m
Thin fog
Snow
Heavy rain
25
1.9 km
2 km
-4.22
-3.96
3238 m
3369 m
Haze
Snow
Medium
rain
12.5
2.8 km
4 km
-2.58
-1.62
4331 m
5566 m
Light haze
Snow
Light rain
2.5
5.9 km
10 km
-0.96
-0.44
7146 m
9670 m
Clear
Snow
Drizzle
0.25
18.1 km
20 km
-0.24
-0.22
11468 m
11743 m
23 km
50 km
-0.19
-0.06
12112 m
13771 m
Very clear
(H.Willebrand & B.S. Ghuman, 2002.)
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FSO – Fog Experimental Data
City of Nice – Jan –July 2006
Ref: E Leitgeb et al 2009
City of Graze – Jan - July
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FSO Attenuation
3rd ECAI – Romania, 3-5 July 2009
FSO Challenges - Others




Background radiation
LOS requirement
Laser safety
Turbulence (scintillation)
3rd ECAI – Romania, 3-5 July 2009
FSO Challenges - Turbulence
Effects
Irradiance fluctuation
(scintillation)
 Image dancing
 Phase fluctuation
 Beam spreading
 Polarisation
fluctuation

Options
Diversity techniques
 Forward error control
control
 Robust modulation
techniques
 Adaptive optics
 Coherent detection not
used due to Phase
fluctuation

42
Remarks
Significant for long
link range (>1km)
Turbulence and thick
fog do not occur
together
 In IM/DD, it results in
deep irradiance
fades that could last
up to ~1-100 μs

FSO Challenges - Turbulence
Cause: Atmospheric inhomogeneity / random temperature variation along beam
path.  changes in refractive index of the channel
P:
Channel pressure, Te: Channel temperature
The atmosphere behaves like prism
of different sizes and refractive indices
Phase and irradiance
fluctuation
• Zones of differing density act as lenses,
scattering light away from its intended path.
• Thus, multipath.
Result in deep
signal fades that
lasts for ~1-100 μs
Depends on:
 Altitude/Pressure, Wind speed,
 Temperature and relative beam size.
3rd ECAI – Romania, 3-5 July 2009
Turbulence – Channel Models
Irradiance PDF:
pI (I ) 
 (ln( I / I 0 )   l 2 / 2) 2 
1
exp 

2  l I


2 l 2
1
I 0
Model
Comments
Log Normal
Simple; tractable
Weak regime only
I-K
Weak to strong
turbulence regime
K
Strong regime only
Rayleigh/Negative
Exponential
Gamma-Gamma
Saturation regime only
Based on the modulation process the received
irradiance is
x
y
I  I I
Irradiance PDF by Andrews et al (2001):
 ) / 2
(
2()(
p( I ) 
I
()()
 
) 1
2
   (2 I )
2
 
 
0.49l
  1
  exp 
12 / 5 7 / 6 
  (1  1.11l )  
1
2
 
 
0.51l

  1
  exp 
12 / 5 5 / 6 
(
1

0
.
69

)
l
 
 
1
All regimes
I 0
Ix:
due to large scale effects;
obeys Gamma distribution
Iy:
due to small scale effects;
obeys Gamma distribution
Kn(.): modified Bessel function
of the 2nd kind of order n
σl2 : Log irradiance variance
(turbulence strength indicator)
To mitigate turbulence effect we, employ subcarrier modulation
3rd ECAI – Romania, 3-5 July 2009
with spatial diversity
Turbulence Effect on OOK
Using optimal maximum a posteriori (MAP) symbol-by-symbol detection with
equiprobable OOK data: dˆ (t )  arg maxd P(ir / d (t ))
The threshold depends on the noise level and turbulence strength 

2
2

  ((ir  RI )  ir ) 

exp

 
2
2

0




  ln( I / I )   2 / 2

0
l
exp 
2
2 l


0.5
Noise variance

2
1
2 l
2


dI


0.5*10-2
0.45
10-2
3*10-2
0.4
Threshold level, i
th
5*10-2
0.35
OOK based FSO requires
adaptive threshold to perform
Optimally.
0.3
0.25
0.2
0.15
0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Log Intensity Standard Deviation
0.8
0.9
1
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3rd ECAI – Romania, 3-5 July 2009
1
.
I
SIM – System Block Diagram
DC bias
m(t)
d(t)
Data in Serial/parallel
converter
.
.
Subcarrier
modulator
.
.
m(t)+bo
Summing
circuit
Optical
transmitter
Atmospheric
channel
ir
d’(t)
.
.
Parallel/serial
Data out
converter
Spatial
diversity
combiner
Subcarrier
demodulator
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Photodetector
array
3rd ECAI – Romania, 3-5 July 2009
Subcarrier Intensity Modulation
 No need for adaptive threshold
 To reduce scintillation effects on SIM
 Convolutional coding with hard-decision Viterbi decoding (J. P. KIm
et 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 a
coding gain >20 dB compared with similarly coded OOK (I. B. Djordjevic, et
al 2007)
 SIM with space-time block code with coherent and differential
detection (H. Yamamoto, et al 2003)
 However, error control coding introduces huge processing
delays and efficiency degradation (E. J. Lee et al, 2004)
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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 by birds and misalignment when
combined with a wide laser beamwidth, therefore no need for an active
tracking
 provides independent aperture averaging with multiple separate
aperture system, than in a single aperture where the aperture size has
to be far greater than the irradiance spatial coherence distance (few
centimetres)
 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 alternative
configuration 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
3rd ECAI – Romania, 3-5 July 2009
Subcarrier Modulation - Transmitter
A1
A2
Input
data
d (t )
Serial to
Parallel
Converter
.
.
.
.
.
.
AM
g(t)
PSK modulator
at coswc1t
g(t)
PSK modulator
at coswc2t
m(t ) 
M
 A j g (t ) cos(wcj t   j )
j 1
Σ m(t)
Σ
Laser
driver
Atmopsheric
channel
DC bias
b0
g(t)
PSK modulator
at coswcMt
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SIM - Receiver
PSK Demodulator
SNRele 
( IRA )
2 2
2
x
g(-t)
Sampler
coswc1t
Photodetector
ir
PSK Demodulator
at coswc2t
Parallel
to Serial
Converter
dˆ (t )
Output
data
.
.
.
Photo-current
PSK Demodulator
at coswcMt
ir (t )  R I (1  m(t ))  n(t )
R = Responsivity, I = Average power,  =
Modulation index, m(t) = Subcarrier signal
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3rd ECAI – Romania, 3-5 July 2009
Subcarrier Modulation
 Performs optimally without adaptive threshold as in OOK
 Use of efficient coherent modulation techniques (PSK, QAM etc.)
- bulk of the signal processing is done in RF where matured devices like stable,
low phase noise oscillators and selective filters are readily available.
 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
But..
 The average transmit power increases as the number of subcarrier
increases or suffers from signal clipping.
 Intermodulation distortion due to multiple subcarrier impairs its
performance
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SIM - Spatial Diversity
 Single-input-multiple-output
 Multiple-input-multiple-output (MIMO)
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3rd ECAI – Romania, 3-5 July 2009
SIM - Spatial Diversity
Combiner
F
S
O
i1 (t )
C
H
A
N
N
E
L
i2 (t )
iN (t )
Assuming identical PIN photodetector on each
links, the photocurrent on each link is:
a1
a2
.
.
.
.
a
N

iT (t )
M
R 
iri (t ) 
I i 1   A j g (t ) cos(wcj t   j
N 
j
PSK
dˆ (t )

)   ni (t )


Subcarrier
Demodulator
ai is the scaling
factor
Diversity Combining Techniques
Maximum Ratio
Combining (MRC)
[Complex but optimum]
ai
 ii
Equal Gain
Combining (EGC)
Selection Combining
(SELC). No need for phase
a1  a2  ...  a N
iT (t )  max( i1 (t ), i2 (t )...i N (t ))
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information
3rd ECAI – Romania, 3-5 July 2009
SIM Spatial Diversity – Assumptions
Made
 The spacing between detectors > the transverse correlation
size ρo of the laser radiation, because ρo = a few cm in
atmospheric turbulence
 The beamwidth at the receiver end is sufficiently broad to
cover the entire field of view of all N detectors.
 Scintillation being a random phenomenon that changes
with time makes the received signal intensity time variant
with coherence time o of the order of milliseconds.
 With the symbol duration T << o the received irradiance is
time invariant over one symbol duration.
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3rd ECAI – Romania, 3-5 July 2009
Subcarrier Modulation - Spatial Diversity
One detector
Two detectors
Three detectors
A typical reduction in intensity fluctuation with spatial diversity
Eric Korevaar et. al
3rd ECAI – Romania, 3-5 July 2009
 Free Space Optics
 Characteristics
 Challenges
 Turbulence
- Subcarrier intensity multiplexing
- Diversity schemes

Results and discussions

Final remarks
3rd ECAI – Romania, 3-5 July 2009
Error Performance – No Spatial Diversity
Normalised SNR at BER of 10-6 against the number of subcarriers for various
turbulence levels for BPSK
Normalised SNR @ BER = 10-6 (dB)
20
15
Increasing the number of
subcarrier/users, results
In increased SNR
10
5
0
Log intensity
variance
0.1
0.2
0.5
0.7
-5
-10
1
2
3
4
5
6
7
Number of subcarrier
8
9
SNR gain compared
with OOK
10
3rd ECAI – Romania, 3-5 July 2009
Error Performance – No Spatial Diversity
BPSK BER against SNR for M-ary-PSK for log intensity variance = 0.52
DPSK
BPSK
16-PSK
8-PSK
-2
10
10
BER
BPSK based subcarrier
modulation is the most
power efficient
Log intensity
-4
variance = 0.52
-6
10
BER 
-8
10


2 
Q SNRe log 2 M sin( / M ) p( I )dI
log 2 M 0
-10
10
20
30
25
SNR
35
40
(dB)
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Spatial Diversity Gain
Spatial diversity gain with EGC against Turbulence regime
2 Photodetectors
3 Photodetectors
70
Saturation
Diveristy Gain (dB)
60
50
40
Moderate
30
20
10
Weak
Turbulence Regime
3rd ECAI – Romania, 3-5 July 2009
Spatial Diversity Gain for EGC and SeLC
25
Link margin (dB)
Log Intensity
Variance
0.22
20
0.52
0.72
1
15
Link margin for SelC is lower
than EGC by ~1 to ~6 dB
10
5
0
Dominated by received irradiance,
reduced by factor N on each link.
-5
-10
EGC
Sel.C
BER = 10-6
1
Pe ( SelC ) 
2
3
N
2
N
4
5
6
No of Receivers
n
7
[ w 1  erf ( x )


i 1
N 1
i
i
8
.e
9
10
(  K 0 2 exp( 2 xi 2 l   l 2 ))
Zeros of the n order w n = Weight factor of the nth order
xi n = Hermite
i
Hermite polynomial
polynomial
th
i 1
i 1
]
K 0  RI0 A 2  2 N
3rd ECAI – Romania, 3-5 July 2009
Spatial Diversity Gain for EGC and MRC
30
BER = 10-6
Log Intensity
variance

1  /2
 
0
25
Spatial Diversity Gain (dB)
Pe ( EGC) 
1

20
0
1

m
2 u  u )
 wi Q( K1e ( x
i
)
1
MRC
EGC

15
Pe ( MRC ) 
2
0.5



 
 ( I ) dI
Q

/
I
P
MRC
I

0
10
5
0


K12
2
exp  
Z
P ( Z ) d dZ
 2 sin 2 ( )
 Z



0.22
1
2
3
Most diversity gain
region
4
6
5
No of Receivers
7
8
1

 /2
 S ( )
N
d ,
0
10
9
The optimal but complex MRC diversity is marginally superior
to the practical EGC
61
3rd ECAI – Romania, 3-5 July 2009
62
Temporal Diversity
Retransmission on different subcarriers
Other possibilities: different wavelengths
different polarisations
Delay ≥ Channel coherence time
This process is reversed at the receiver side to recover the data
Temporal Diversity Gain
No fading
No TDD
1-TDD
3-TDD
5-TDD
2-TDD
-2
10
-4
BER
10
-6
10
Single delay path
is the optimum
-8
10
BER =10-9
-10
10
Rb = 155Mbps
Log irradiance
var =0.3
-32
-30
-28
-26
-24
-22
-20
Receiver sensitivity, Io (dBm)
-18
-16
No TDD
-17.17
Io (dBm)
(no fading: -27.05)
Fading penalty (dB) 9.88
Diversity gain (dB) 0
(gain / path)
(0)
1-TDD 2-TDD
-19.17 -19.85
3-TDD
-20.13
5-TDD
-20.3
7.88
2
(2)
6.92
2.96
(0.99)
6.75
3.13
(0.63)
7.2
2.68
(1.34)
Multiple-Input-Multiple-Output
Combiner
It1
It2
d(t)
BPSK
ModuLator
and
.
.
.
Laser
driver
ItH
F
S
O
i1 (t )
C
H
A
N
N
E
L
i2 (t )
iN (t )
a1

a2
.
.
.
.
a
iT
BPSK
Subcarrier
Demodulator
dˆ (t )
N
By linearly combining the photocurrents using MRC, the individual SNRe on each
link
SNRele i

RA
 
2
 2 N H
64


I

ij 
j 1

H
2
3rd ECAI – Romania, 3-5 July 2009
MIMO Performance
-3
10
At BER of 10-6:
1X5MIMO
1X8MIMO
4X4MIMO
2X2MIMO
1X4MIMO
-4
10

2 x 2-MIMO requires additional ~0.5
dB of SNR compared with 4photodetector single transmittermultiple photodetector system.

4 x 4-MIMO requires ~3 dB and ~0.8
dB lower SNR compared with
single transmitter with 4 and 8photodetectors , respectively.
-5
BER
10
-6
10
-7
10
-8
10
-9
10
log intensity variance= 0.52
12
14
16
18
20
22
2
(dB)
SNR (R*E[I]) / No
1
Pe 

/ 2
 S ()
N
d,
24
26
S () 
2


K2

w j exp  
exp[
2
(
x
2



)]

j
u
u 
2
 j 1
 2 sin 

1
m
K2 
0
65
RI 0 A
2 N 2 H
3rd ECAI – Romania, 3-5 July 2009
FSO – Turbulence Chamber
Thermometers, T4
Laser Module
(Direct Modulation)
Power = 3mW
λ = 785nm
OOK & BPSK Modulator + Demodulator
Turbulence chamber
Heaters + Fans
Reflecting mirror
PIN Detector +
Amplifier
Optical power meter head
Reflecting mirror
BPSK modulator
•Carrier
•Data rate
Turbulence chamber
•Dimension
•Temp. range
1.5 MHz
A few kHz
140 x 30 x 30 cm
24oC – 60oC 3rd ECAI – Romania, 3-5 July 2009
FSO – With Scintillation Effect
Received mean signal + Noise + Scintillation
Signal Distribution
Histogram of mean signal - no scintillation
Gaussian fit
Mean = -0.0012
Variance = 5e-5
16
Gaussian fit
Gaussian fit
14
Bin Size
12
10
8
6
4
2
0
-0.05
2.5
Observations
-0.04
-0.03
-0.02
-0.01
0
0.01
With scintillation
Signal level
Lognormal fit
Mean =1
Variance = 9e-3
0.02
0.03
0.04
Lognormal fit
• Total fluctuation variance =
• Weak scintillation obeys Lognormal
distribution (variance < 1)
• Simulated turbulence is very weak.
9.10-3
(V2)
Bin Size
2
Lognormal fit
1.5
1
0.5
0
0.85
3rd ECAI – Romania, 3-5 July 2009
0.9
0.95
1
1.05
Signal level
2.93 V
1.1
1.15
FSO – OOK With Scintillation Effect
8
7.5
7
No scintillation
Received Signal
Threshold position. ith
Bin Percentage
6.5
6
5.5
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
Received
Transmitted
0
-0.2492 -0.1992 -0.1492 -0.0992 -0.0492 0.0008 0.0508
Signal Level
0.1008
0.1508
0.2008 0.2492
1.4
With scintillation
1.3
1.2
Received Signal ≈ 400mV p-p
1.1
Threshold
range
Bin Percentage
1
0.9
0.8
0.7
Observation:
The optimum symbol decision
position in OOK depends on
scintillation level
0.6
0.5
0.4
0.3
0.2
0.1
0
-0.3488
-0.2488
-0.1487
-0.0487
0.0513
Signal Level
0.1513
0.2513
0.35130.3987
3rd ECAI – Romania, 3-5 July 2009
FSO – BPSK-SIM With Scintillation
Effect
3.5
3.4
Received Signal
No scintillation
3.2
3
2.8
2.6
Demodulated
No low
Pass filtering
BIn Percentage
2.4
2.2
2
1.8
1.6
1.4
1.2
1
Before
demodulation
0.8
0.6
0.4
0.2
0
-0.2
-0.15
-0.1
-0.05
3.5
3.4
3.2
0
0.05
Singal Level
0.1
0.15
0.2
Demodulated Signal ≈ 400mV p-p
With scintillation
3
2.8
2.6
Bin Percentage
2.4
2.2
2
Observation:
Scintillation does not affect the
symbol decision position in BPSK SIM
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
Signal Level
0.1
0.15
0.2
0.25
3rd ECAI – Romania, 3-5 July 2009
FSO Network – Linking Two Universities
in Newcastle
Agilent Photonic
Research Lab
Optical Fibre @1550 nm
Specifications:
• 4x4 Du-plex communication link (The FlightStrata 155E)
• VCSEL @ 650 nm wavelength
• Si APD
• Data rate: 155 Mbps
• Maximum length: 3.5 km
• Automatic Power Control and Auto Tracking
rd
3 ECAI – Romania, 3-5 July 2009
Collaborators
• Graz Technical University, Austria
• Houston University, USA
• UCL
• Hong-Kong Polytechnic University
• Tarbiat Modares University, Iran
• Newcastle University
• Ankara University, Turkey
• Agilent
• Cable Free
• Technological University of Malaysia
• Others
•
3rd ECAI – Romania, 3-5 July 2009
72
Summary

Access bottleneck has been discussed

FSO introduced as a complementary technology

Atmospheric challenges of FSO highlighted

Subcarrier intensity modulated FSO (with and
without spatial diversity) discussed

Wavelet ANN based receivers

72
3rd ECAI – Romania, 3-5 July 2009
73
Acknowledgements
 To many colleagues (national and international)
and in particular to all my MSc and PhD students
(past and present) and post-doctoral research
fellows
3rd ECAI – Romania, 3-5 July 2009
74
LS Series Specifications
Model
WBLS10
WBLS100
WBLS100U
Ultra-Wide
Data Rate
10Mbps Full Duplex
10Mbps Full Duplex
10Mbps Full Duplex
Distance (meters)
up to 800m
up to 500m
custom
Network Protocol
Ethernet
Fast Ethernet
Fast Ethernet
Network Interface
10Base-T (RJ45) x1
100Base-Tx (RJ45) x1
100Base-Tx (RJ45) x1
Transmitter
IR - LED Class 1
IR -LED Class 1
IR - LED Class 1
Wavelength
800-900nm
800-900nm
800-900nm
Beam width
17mrad
17mrad
custom
Power
POE or 48V DC
POE or 48V DC
POE or 48V DC
Housing
Weatherproof
Weatherproof
Weatherproof
Operating Temp.
-40° C to 70° C
-40° C to 70° C
-40° C to 70° C
Relative Humidity
5% to 95%
5% to 95%
5% to 95%
Dimensions
9” x 6.0” x 12”
9” x 6.0” x 12”
9” x 6.0” x 12”
Weight
3.2Kg, 7.5lbs
3.2Kg, 7.5lbs
3.2Kg, 7.5lbs
Mounting Options
Wall/Tower, Roof,
Non-penetrating
Wall/Tower, Roof,
Non-penetrating
Wall/Tower, Roof,
Non-penetrating
Iran 2008
75
Model
WBLS T1/E1
WBLS 4T1/4E1
Data Rate
4 x 1.54 Mbps or
4 x 2.048 Mbps
1 x 1.54 Mbps or
1 x 2.048 Mbps
Distance (meters)
Up to 800m
up to 1600m
Network Protocol
ATM
ATM
Network Interface
4 x RJ48C
1 x RJ48C
Transmitter
IR - LED Class 1
IR - LED Class 1
Wavelength
800-900nm
800-900nm
Beam width
17mrad
17mrad
Power
48V DC
48V DC
Housing
Weatherproof
Weatherproof
Operating Temp.
-40° C to 70° C
-40° C to 70° C
Relative Humidity
5% to 95%
5% to 95%
Dimensions
9” x 6.0” x 12”
9” x 6.0” x 12”
Weight
3.2Kg, 7.5lbs
3.2Kg, 7.5lbs
Mounting Options
Wall/Tower, Roof,
Non-penetrating
Wall/Tower, Roof,
Non-penetrating
Iran 2008
76
400/500 Series
Specifications
Model
WB410
WB4100
WB4155
WB510
Data Rate
10Mbps Full Duplex
100Mbps Full Duplex
155Mbps Full Duplex
10Mbps Full Duplex
Distance (meters)
1500m
750m
750m
2000m
Network Protocol
Ethernet
Fast Ethernet
Clear Channel
Ethernet
Network Interface
10Base-T (RJ45) x1
100Base-Tx (RJ45) x1
SPF- LC Fiber Connect
10Base-T (RJ45) x1
Transmitter
IR - LED Class 1
IR -LED Class 1
IR - LED Class 1
IR - LED Class 1
Wavelength
Beam width
Power
800-900nm
17mrad
POE or 48V DC
800-900nm
17mrad
POE or 48V DC
800-900nm
custom
48V DC
800-900nm
17mrad
POE or 48V DC
Housing
Weatherproof
Weatherproof
Weatherproof
Weatherproof
Operating Temp.
-40° C to 70° C
-40° C to 70° C
-40° C to 70° C
-40° C to 70° C
Relative Humidity
5% to 95%
5% to 95%
5% to 95%
5% to 95%
Dimensions
15.8" x15.3" x 19"
15.8" x15.3" x 19"
15.8" x15.3" x 19"
15.8" x15.3" x 19"
Weight
Mounting Options
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
Iran 2008
77
Model
WB5100
WB5155
WB5 T1/E1
WB5 T4/E4
Data Rate
100Mbps Full Duplex
155Mbps Full Duplex
1 x 1.54 Mbps or
1 x 2.048 Mbps
4 x 1.54 Mbps or
4 x 2.048 Mbps
Distance (meters)
1000m
1000m
3500m
2000m
Network Protocol
Fast Ethernet
Clear Channel
ATM
ATM
1 x RJ48C
4 x RJ48C
Network Interface
100Base-Tx (RJ45) x1 SPF- LC Fiber Connect
Transmitter
IR - LED Class 1
IR - LED Class 1
IR - LED Class 1
IR - LED Class 1
Wavelength
Beam width
Power
800-900nm
17mrad
POE or 48V DC
800-900nm
17mrad
48V DC
800-900nm
17mrad
48V DC
800-900nm
17mrad
48V DC
Housing
Weatherproof
Weatherproof
Weatherproof
Weatherproof
Operating Temp.
-40° C to 70° C
-40° C to 70° C
-40° C to 70° C
-40° C to 70° C
Relative Humidity
5% to 95%
5% to 95%
5% to 95%
5% to 95%
Dimensions
15.8" x15.3" x 19"
15.8" x15.3" x 19"
15.8" x15.3" x 19"
15.8" x15.3" x 19"
Weight
Mounting Options
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
9.0Kg, 20lbs
Wall/Tower, Roof,
Non-penetrating
Iran 2008
78
XT Series Specifications
Model
WBXT10
WBXT100
WBXT155
Data Rate
10Mbps Full Duplex
100Mbps Full Duplex
155Mbps Full Duplex
Distance (meters)
3000m
2000m
2000m
Network Protocol
Ethernet
Fast Ethernet
Clear Channel
Network Interface
10Base-T (RJ45) x1
100Base-Tx (RJ45) x1
SPF- LC Fiber Connect
Transmitter
IR - LED Class 1
IR -LED Class 1
IR - LED Class 1
Wavelength
Beam width
Power
800-900nm
17mrad
POE or 48V DC
800-900nm
17mrad
POE or 48V DC
800-900nm
custom
48V DC
Housing
Operating Temp.
Weatherproof
-40° C to 70° C
Weatherproof
-40° C to 70° C
Weatherproof
-40° C to 70° C
Relative Humidity
5% to 95%
5% to 95%
5% to 95%
Dimensions
Weight
Mounting Options
19" x 11" x 32"
15Kg, 30lbs
Wall/Tower, Roof,
Non-penetrating
19" x 11" x 32"
15Kg, 30lbs
Wall/Tower, Roof,
Non-penetrating
19" x 11" x 32"
15Kg, 30lbs
Wall/Tower, Roof,
Non-penetrating
Iran 2008
79
Model
WBXT T1/E1
WBXT T4/E4
Data Rate
1 x 1.54 Mbps or
1 x 2.048 Mbps
4 x 1.54 Mbps or
4 x 2.048 Mbps
Distance (meters)
4000m
3000m
Network Protocol
ATM
ATM
Network Interface
1 x RJ48C
4 x RJ48C
Transmitter
IR - LED Class 1
IR - LED Class 1
Wavelength
800-900nm
800-900nm
Beam width
17mrad
17mrad
Power
48V DC
48V DC
Housing
Weatherproof
Weatherproof
Operating Temp.
-40° C to 70° C
-40° C to 70° C
Relative Humidity
5% to 95%
5% to 95%
Dimensions
19" x 11" x 32"
19" x 11" x 32"
Weight
15Kg, 30lbs
15Kg, 30lbs
Mounting Options
Wall/Tower, Roof,
Non-penetrating
Wall/Tower, Roof,
Non-penetrating
Iran 2008