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Optical CDMA Presented by: George Partasides http://partasides.da.ru Overview History Overview (CDMA) 1938, in the field of radar systems, examples of frequency hopping signal patterns were patented

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optical cdma

Optical CDMA

Presented by: George Partasides


history overview cdma
History Overview (CDMA)
  • 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
history overvirew optical cdma
History Overvirew (Optical CDMA)
  • 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.
  • 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)
introduction comparison
…introduction (comparison)
  • 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 
    • System capacity = users * tx rate
  • WDMA: Four wave mixing as discussed (next slide)
drawbacks dwdm revisited
Drawbacks DWDM (revisited)
  • Dispersion
  • Attenuation
  • Four wave mixing
    • 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 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
comparison advantages
…comparison (Advantages)
  • Simple implementation, using existing fiber networks
  • Reduce the cost in every aspect:
    • Equipment , outside plant
    • Facilities , Operational Support systems
    • Eliminate many of intermediate time-division multiplexing steps required by SONET
how does o cdma work
How does o-CDMA work
  • 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.
two optical orthogonal code with length l 32 and c 1
Two optical orthogonal Code with length L = 32 and λα = λc =1.

Orthogonal Code example

  • First code is represented by placing a pulse at the 1st, 10th 13th and 28th chip positions.
  • Second code is represented by placing a pulse at the 1st, 5th 12th and 31st chip positions.
how does o cdma works
…how does o-CDMA works
  • 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:
    • Source – Filter – Modulator

Filter: Spatial Filter can be thought an optical Bar code (fixed or programmable)

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.
    • 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
internet traffic the need
Internet Traffic – The need -
  • The increase of data through network and specifically LANS
internet traffic some statistics
Internet Traffic some statistics

250% increase in internet traffic in our University in one year time!

    • Textbooks
  • 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)
    • Links
  • Optical CDMA with Optical Orthogonal Code
  • Effects of Optical Layer Impairments on2.5 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/
  • http://www.technologie.pl/fiber/zalacznik/artykuly/report09981.htm
  • http://telephonyonline.com/ar/telecom_seamless_mobility_real/index.htm