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CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 1
Optical Wireless: Benefits and Challenges
Maha Achour, Ph.D.President and CTO
machour@ulmtech.comwww.ulmtech.com
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 2
About UlmTech..
• Two Divisions: Free-Space optics and e-Learning
• Free-Space Optics Division:
• Developing the first commercial software that simulates atmospheric propagation of optical wireless signals, the Simulight™ (release date: March 01, 2002);
• e-Learning Division:
• Intelligent Real-Time Multimedia Platform for Online Learning and Collaboration;
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 3
Telecom Vertical Markets
Component Boards
Emerging Industry
Products
CashBoxes Service
Provider
Corporate
• Collapse of data delivery business model,
• Telecom Deregulation Act 1996,
• Lack of the killer innovative application led to end-user slow broadband adoption.
• Last mile connectivity.
• Will e-Learning be the solution ?
Added-Value
Services
Individual
VoIP Games Video on Demand
e-Learning
….
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 4
Broadband Access• Service providers need to access paying customers quickly, cost effectively and reliably.
• Fiber often does not reach paying customers.
• Only 3% of worldwide Businesses are on fiber, and 75% are within a mile from fiber.
• Speed limitation, cost and asymmetrical properties of DSL, Cable, Satellite and other existing technologies.
• Broadband wireless communications, with Unlicensed Wireless Technologies UWT in particular will play major role in Broadband connectivity.
• At the end of the day someone, besides investors, needs to pay for all those tremendous optical and networking advances and improvements.
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 5
Unlicensed Wireless Technologies (UWT)
FCC part 15.249. No IEEE standards
Radios in this band are provided by Sierra Digital and are affected by rain.
24.05-24.250 GHz
ISM Band: FCC part 15.247 and 15.249. No IEEE standard
Open in Asia and part of Europe, DS spread spectrum, and some radios with 25 Mbps speed.
5.725-5.85 GHz
• UNII band: FCC part 15.407 • IEEE standard 802.11a
Limited global coverage, Hiperlan in Europe (B1 and B2), indoor/outdoor (B2 and B3), 54 Mbps using OFDM on twelve non-overlapping 20 MHz bands, and some non-IEEE radios support 450 Mbps using QAM.
B1 5.15-5.25 B2 5.25-5.35 B3 5.725-5.825
• ISM band: FCC part 15.247 and 15.249 • IEEE standard 802.11b,g
Worldwide Coverage, indoor/outdoor, 11 and 22 Mbps, up to 15 miles, DS spreading and OFDM.
2.4 – 2.4825 GHz
Regulations and StandardsTechnologySpectrum Band
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 6
Unlicensed Wireless Technologies (Cont.)
• Eye-safety IEC, FDA and ANSI regulation•No FCC regulation• No standards
Free-Space Optics (FSO) using short (785-850nm), mid (1550nm) and long (10µm)wavelengths, OOK modulation, no delay, speeds up to 2.5 Gbps and few kilometers in distances.
200-300 THz
FCC part 15.255 and 15.249. No IEEE standards.
Radios with Gigabit speeds, OOK modulation, no delay, few hundred meters in range due to Oxygen absorption.
57-64 GHz (90 GHz and 120 GHz in progress)
Regulations and StandardsTechnologySpectrum Band
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 7
Quick Deployment• No licenses required on a global scale, • No frequency planning due to narrow Optical Beam,• Practical size units that look like security cameras,• Safe when units comply with the IEC safety standard,• Protocol independent,
Optical Wireless: Benefits
Low Cost / Scalability• Uses off-the-shelf components from the Fiber industry,• Highly scalable in bandwidth, • Low power consumption, with some do not require EOE conversion,
Reliability • Reliable hardware• Communication link availability is based on the location, deployed unit and distance.
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 8
Wide Technologies
• Short Wavelengths: 750-850 nm
• Mid Wavelengths: 1300-1550 nm ex: Terabeam @ 1550 nm
AOptix (Adaptive Optics)
• Long Wavelengths: 10 µmex: Maxima Corporation
Optical Wireless: Benefits
Terabeam Elliptica:
• About the size of a slightly deflated basketball.
• The laser is a CDRH Class 1 laser, meaning it is so eye-safe as to not require any warning labels.
Source: Terabeam
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 9
• Microwave signals above 10 GHz are mostly affected by rain.
• The availability of extensive global precipitation databases and rain fade (rainfall) simple modeling accurately estimates microwave deployment link availability.
• Free-Space Optics is affected by various weather conditions with Fog (visibility, fog type) in particular → channel modeling (Simulight™) and weather databases.
Formed in February 2001 to unify vendors and service providers efforts to bring proper awareness and understanding of the technology.
www.fsoalliance.com
Optical Wireless: Challenges
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 10
Meteorological Visual Range
“Using Camera Imagery to measure Visibility and fog”, MIT Lincoln Lab Report 2001
Background Contrast
Visibility: Distance for which the Contrast transmission of the atmosphere is 2% in reference to the wavelength 550 nm that the eye has the greatest sensitivity.
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 11
About Simulight™..
Simulight™ considers the following optical propagation effects:
• Low altitudes propagation,
• Haze, rain, fog, low clouds and molecular scattering,
• Geometrical beam dispersion including diffraction effects,
• Water and carbon dioxide absorption,
• Absorption due to the presence of water vapor in the air,
• It supports wavelengths that span from 750 nm to 12 µm.
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 12
Atmospheric Propagation
Modeling FSO atmospheric propagation:Deployment parameters: are related to the location and application of the FSO system installation: Range, Bandwidth, Wavelength …
FSO system parameters: are related to the deployed FSO system: location of the FSO system installation: number of transmitters (Tx) and Receivers (Rx), Tx diameter, Rx diameter, Tx power, Rx sensitivity, additional amplification, additional hardware losses..
Weather parameters: Meteorological Visual Range (Visibility), Temperature, Relative Humidity, fog model (non-selective, evolving, stable)…
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 13
Atmospheric attenuation
FSO systems are affected by the following weather conditions:
Absorption: is a Quantum effect with H2O and CO2 absorption bands defining the eight atmospheric windows 720 nm – 12000 nm (fine line absorption). Increasing humidity cause additional water absorption.
Rayleigh Scattering: due to scattering by air molecule. Very small compared to Mie scattering and is proportional to λ-4
Mie Scattering: Due to scattering by small particles of sizes comparable to wavelength.
Turbulences (scintillation): Beam deviation, wander, broadening and power fluctuation.
Rain Fade: Considered non-selective scattering. The attenuation is proportional to the rainfall rate (drop size distribution)
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 14
Scattering Effects
Scattering patterns of electromagnetic waves by spherical particles.
(a) Small Particles with diameter < λ/10
Small Particles with diameter ≅ λ/4
Small Particles with diameter > λ
Incident Beam with wavelength λ Incident Beam with wavelength λ
Incident Beam with wavelength λ
Earl J. McCartney, Optics of the Atmosphere: Scattering by Molecules and Particles,Wiley & Sons, New York, [1976].
Multiple-order scattering between Tx and Rx
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 15
Weather Parameters
Absolute Humidity: Mass of water vapor in a unit volume of air. Saturation: Refers to the maximum possible amount of water vapor that air can hold (Temperature dependent) per unit volume.
Dew Point: Is the temperature at which saturation occurs. Related to temperature and Dewpoint.
Relative Humidity: The ratio of the absolute humidity to saturation. This parameter, along with temperature, is useful to determine additional water absorption.
Visibility: Distance for which the Contrast transmission of the atmosphere is 2% in reference to the wavelength 550 nm that the eye has the greatest sensitivity. It is a function of the extinction coefficient βext(λ).
V = |ln(0.02)|/ βext(λ) = 3.91/ βext(λ=0.55µ)
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 16
Meteorological Visual Range
• Relative contrast is defined as follows:
• The above approximation holds when Lmin(0) << Lmax(0) and Lmin(0)=Lmin(V).
• If the background is the horizon, then Lmin(0)=Lmin(V).
• Complete understanding of visibility measurement is essential.
• Meteorological visual ranges V are defined with the above two approximations. .
• The problem is how to use V to derive βscat(λ).
V-
max
max
minmax
min
min
minmax e (0)L(V)L
(0)L - (0)L(0)L
(V)L(V)L (V)L
C(0)C(V) α=≅
−=
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 17
Rainfall Attenuation
• Is considered non-selective scattering because the size of a raindrop (Diameter 0.01-10 mm) is much larger than the incident wavelength.
• In 1920, F.W. Preston, in an almost forgotten paper, claimed that the obscuring power of falling rain is proportional only to the number of drops falling on unit area of the earth’s surface per second.
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 18
Rainfall Attenuation
Simulation Results:
• Rainfall between 10-100 mm/hr
• Wavelength independent
Num
ber o
f dro
ps p
er m
3
Drop Diameter in mm Drop Diameter in mm
Rainfall rate in mm/hr
Rai
nfal
l rat
e in
mm
/hr
Rai
nfal
l atte
nuat
ion
dB/k
m
Caption:
mm/hr
(+) 10
(o) 20
(*) 30
(◊) 40
(●) 50
(x) 60
(□) 70
( ) 80
( ) 90
( ) 100
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 19
Mie Scattering
• Based on slide 14 assumptions, Visibility can be related to the extinction coefficient β(λ=0.55µ) by the following relation:
• In most literatures, relating β(λ=0.55µ) to β(λ) was performed using the following equation:
• The exponent δ = 1.6 for good visibility, 1.3 for V=6-50 Km and 0.585 V1/3 for visibility less than 6 Km.
• Problem: exponent value and the one-to-one relation between visibility and attenuation coefficient independent of droplet sizes and distributions.
)0.55(λ
3.91 )0.55(λ
ln(0.02) V
µβµβ ==
==
55.0
3.91 55.0
)0.55(λ β(λ)δδ λλµβ
−−
=
==
V(1)
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 20
Mie Scattering
• The general equation to derive scattering coefficient is:
βscatt (λ)= ∑a π a2 Na Qscatt (x)
where, x=2πa/ λ.• λ dependence is not trivial due to the analytical expression of Q.
Q(x)
x
x
x
Q(x 850/550)
Q(x)
Q(x 1550/550)
Q(x)
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 21
Mie Scattering
• Build a virtual fog/haze model that reproduces the same results as the equation below at λ = 850 nm:
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
10
20
30
40
50
60
70
80
90
100
550
3.91 550
)0.55(λ β(λ)1/31/3 V585.0V585.0 −−
=
==
λλµβV
0.5 1 1.5 2 2.5 3 3.5 40
5
10
15
20
25
30
Atte
nuat
ion
in d
B/K
m
Con
cent
ratio
n in
cm
3
Drop Radius in µm Visibility in Km
Black 785nm
Red 1550 nm
Blue 10 µm
(+) Based on Drop Distribution Model
Visibility 0.5 Km
Visibility 4 Km
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 22
Mie Scattering
• Defining Drop-sizes distribution function by identifying the peaks and the slope of the curve at both ends.
• Use the general Mie definition of the scattering coefficient.
• More choices of haze/fog/cloud distributions based on visibility than raindrops distributions based on rainfall rates: Due to the behavior of large drops in the air.
• There are other constraints that small drops need to satisfy.
• Visibility along with fog type provide sufficient information to calculate FSO attenuations.
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 23
Mie Scattering
Weather ConditionsClear: It includes light Haze and Rain: Visibilities over 4 Km.
Rain: Weather conditions that accounts of rain only.
Evolving Fog: Weather conditions between light haze, dense haze and stable fog: Visibilities between 1 and 4 Km.
Stable Fog: Foggy weather conditions: Visibilities up to 1.5 Km.
Selective Fog: Weather conditions between fog and low clouds: Visibilities up to 0.75 Km.
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 24
Mie Scattering
18.118.4512.6710,100 / 10,1003c
41.368.465.781230 /12303b
50.13Jan24 1812-1824
62.957.72750 / 6550.303a
110.42263.4213.6510,100 / 10,1002c
185.64247.33239.21230 /12302b
209.73Jan29/30 2106-2306
226.2227.06750 / 6550.075Stable2a
3.17.30.9310,100 / 10,1001c
10.617.3718.81230 / 12301b
14.16Dec 11, 222015.217.09750 / 6551Evolving1a
Equation (1) (dB/Km)
Experiment*Day/Time
Experiment*(dB/Km)
Simulight™Mie Loss (dB/Km)
Wavelength (nm)Simulight / Experiments
Visibility(Km)
FogModel
(*) Clay, M. R. and Lenham A. P., Transmission of electromagnetic radiation in fogs in the 0.53-10.1 µm wavelength range, Applied Optics, Vol. 20, No. 22, 1981, page 3831
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 25
Mie Scattering
Sample of the fog droplet distribution for case 1: Evolving 1 Km Visibility
Sample of the fog droplet distribution for case 2: Stable 75 m Visibility
CLEO / LEAP 2002, May 22, Long Beach, California Maha Achour, Ph.D. 26
Concluding Remarks
• Free-Space Optics offer quick, scalable and cost-effective solutions to the access network,
• Wide selection of products from T1 to OC48 and soon 10 Gbps speeds,
• Global deployments over the past decade,
• Need extensive weather database,
• Need to classify fogs for very low visibilities,
• Properly convey the technology limitations