Transcript MICROSOFT EXCEL - Department of Electrical Engineering

EE566: Optical Communication
Optical CDMA
Presented by: George Partasides
http://partasides.da.ru
Optical CDMA Electrical 
EE 566: Optical Communications
Overview
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
History Overview (CDMA)
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1938, in the field of radar systems, examples
of frequency hopping signal patterns were
patented
During and after WWII the fact of BW
expansion without pulse narrowing could also
provide finer time resolution.
1950s Sol Golomb first Books on CDMA
Early system are ARC-50 by Magnavox and
satellite radios as well as few GPS systems
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
History Overvirew (Optical CDMA)
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Relatively new technique in Optical
Fiber communications and seems to
outperform traditional TDM and WDM
First applied in mid 1980’s by A.Salehi
Prucnal and some others.
Aim for Terabit performance on
Broadband Networks by reducing the
cost of every aspect in optical network.
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
Introduction
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CDMA used extensively in radio
frequency communication systems,
especially in 2G and 3G cellular
telephone networks.
Basic Advantage is the way it handles a
finite BW among a large number of
users (more users can transmit the
same data over the same Bandwidth)
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
…introduction (comparison)
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TDMA and WDMA schemes present
significant drawbacks in Local Area
Systems when large number of users
must be considered.
TDMA: one user tx at a time 
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System capacity = users * tx rate
WDMA: Four wave mixing as discussed
(next slide)
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
Drawbacks DWDM (revisited)
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Dispersion
Attenuation
Four wave mixing
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Non-linear nature of refractive index of optical
fiber
Limits channel capacity of the DWDM System
Difficult to construct for dynamic set of multiple
users because of the significant amount of
coordination among the nodes required for
successful operation.
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
…comparison
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Optical CDMA does not need time and
frequency management because all the users
transmit using the whole BW at the same
time!
It can also operate asynchronously (as in
wireless applications) without packet
collisions.
Slot allocation requirements are not needed
here in contradiction to TDMA and WDMA
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
…comparison (Advantages)
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Simple implementation, using existing fiber
networks
Reduce the cost in every aspect:
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Equipment , outside plant
Facilities , Operational Support systems
SECURITY
Eliminate many of intermediate time-division
multiplexing steps required by SONET
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
How does o-CDMA work
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The principle is the same as in wireless
application. Each user is assigned a unique
code (spreading length -L-) which is
multiplied by each bit. This code is only
known to the receiver in order to demodulate
the data.
The most important part for correct detection
is the code. This code must be uncorrelated
from other user’s codes and be orthogonal.
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
Orthogonal Code example
Two optical orthogonal Code with length L = 32 and λα = λc =1.
(a) First code is represented
by placing a pulse at the
1st, 10th 13th and 28th chip
positions.
(b) Second code is
represented by placing a
pulse at the 1st, 5th 12th
and 31st chip positions.
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
…how does o-CDMA works
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O-CDMA divides the fiber spectrum into
individual codes, all derived from a
single broadband optical source (WDM
divides the spectrum into narrow optical
wavelengths)
It is a simple 3 – step process:
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Source – Filter – Modulator
Filter: Spatial Filter can be thought an optical Bar code
(fixed or programmable)
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
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Optical CDMA is a broadcast technology, with all
information going to all parts of the network.
When a receiver is placed anywhere on the network
with a bar code that matches a transmitter, that
signal alone is decoded and extracted from the
network.
The second requirement for an all-optical network,
the ability to economically add users.
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A simple tap and insert coupler is installed in the lateral
fiber run to multiple users, and a receiver is installed at each
terminating location
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
Internet Traffic – The need 
The increase of data through network
and specifically LANS
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
Internet Traffic some statistics
250% increase in internet traffic in our University in one year
time!
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
References
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Spread Spectrum CDMA Systems for wireless Communications (savo
Glisic , Branka Vucetic)
Spread Spectrum Communications Handbook(Marvin K. Simon, Jim K.
Omura, Robert A. Scholtz, Barry K.Levitt)
Wireless Network Evolution 2G to 3G (Vijay K. Garg)
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Textbooks
Links
Optical CDMA with Optical Orthogonal Code
Effects of Optical Layer Impairments on 2.5 Gb/s Optical CDMA Transmission
http://www.tks.buffalo.edu/usg/Public/Mail/Imap-s/Stats/lookup.html
http://www.technologie.pl/fiber/zalacznik/artykuly/
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http://www.technologie.pl/fiber/zalacznik/artykuly/report09981.htm
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http://telephonyonline.com/ar/telecom_seamless_mobility_real/index.htm
 Optical CDMA Electrical by George Partasides
EE 566: Optical Communications
 Optical CDMA Electrical by George Partasides