Optical CDMA Presented by: George Partasides http://partasides.da.ru
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) • 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.
Introduction • 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) • 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) • 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.
…comparison • 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) • Simple implementation, using existing fiber networks • Reduce the cost in every aspect: • Equipment , outside plant • Facilities , Operational Support systems • SECURITY • Eliminate many of intermediate time-division multiplexing steps required by SONET
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 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 • 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 - • The increase of data through network and specifically LANS
Internet Traffic some statistics 250% increase in internet traffic in our University in one year time!
References • 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