Optical code division multiple access

SEMINAR ON “OPTICAL CODE DIVISION MULTIPLE

ACCESS “

Submitted byMURTADHA ALI NSAIF SHUKUR

( M.Tech(ECE) “First semester ”1ST year)

INTRODUCTIONCDMA: Code Division Multiple Access All users share the same radio frequency at the

same time. This approach obviously means that all users interfere with each other

Optical fibers : Circular dielectric waveguides that can transport optical energy and information. They have a central core surrounded by a concentric cladding with slightly lower refractive index , transmitter the data by light use LED and Laser diode.

OCDMA : send the data by pulse light instead of electromagnetic waves.

WIRELESS OPTICAL CDMA Optical CDMA wireless multi-user

network include some transmitter and receiver , in this network ,an optical orthogonal code (OOC) is assigned to each (Tx and Rx) to connect to its equivalent (OOC) user and after synchronization between two equivalent (OOC) user , they can send and receiver data to/from each other.

ADVANTAGE OF OCDMA

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 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 Simple implementation, using existing fiber networks

Reduce the cost in every aspect: Equipment , outside plant Operational Support systems SECURITY

IMPLEMENTATION IN OCDMA Network centralized network control to

dynamically allocate new codes to users and monitor the CDMA encoders. A distributed network control can be allowed if using an advanced code generation algorithm, show block diagram in fig. (1). In each node of the network, the level of MAI(multi access interference ) of the network is monitored and code selection logic will direct the encoder to encode the data source with the appropriate signature code. Code selection logic–Multiple code words to priority service–Different length of codeword to services–Different weight of codeword to services .

IMPLEMENTATION IN OCDMA

fig. (1) block diagram of generator optical orthogonal code

IMPLEMENTATION IN OCDMA

IMPLEMENTATION IN OCDMA

Fig.(3) Examples of sequences (a) sequence for fiber optics (b) sequence for radio frequency

ENHANCED SECURITY OF OCDMA Enhanced security has often been cited as an important

benefit of optical CDMA (O-CDMA) signaling. However, the quality and degree of security enhancement has not been closely examined in the literature. This paper examines the degree and types of security that may be provided by O-CDMA encoding. A quantitative analysis of data confidentiality is presented for O-CDMA encoding techniques that use both time spreading and wavelength hopping. The probability of successful data interception is calculated as a function of several parameters, including signal-to-noise ratio and fraction of total available system capacity. For reasonable choices of system and encoding parameters, it is shown that increasing code complexity can increase the signal-to-noise ratio (SNR) required for an eavesdropper to "break" the encoding by only a few dB.

CONCLUSION

Optical Code Division Multiple Access (OCDMA) is a multiplexing/multiple access technique adapted from the successful implementation in wireless networks. In OCDMA systems, each user is assigned with a sequence code that serves as its address. An Optical CDMA user modulates its code (or address) with each data bit and asynchronously initiates transmission. Hence, this modifies its spectrum appearance, in a way recognizable only by the intended receiver. Otherwise, only noise-like bursts are observed. The advantages of OCDM technique over other multiplexing techniques such as TDM, FDM and WDM are numerous.

REFERENCES [1] B. Mukherjee, Optical Communication Networks,

New York, McGraw–Hill, 1997. [2] P. R. Prucnal, M. A. Santoro, and T. R. Fan, “Spread

Spectrum Fiber Optic [3] Local Area Network Using Optical Processing,” IEEE

J. Lightwave Tech., vol. LT-4, no. 5, May 1986, pp. 547–54.

[4] J. A. Salehi, “Code Division Multiple-Access Techniques in Optical Fiber Networks — Part I: Fundamental Principles,” IEEE Trans. Commun., vol. 37, no. 8, Aug. 1989, pp. 824–33.

[5] J. A. Salehi and C. A. Brackett, “Code Division Multiple-Access Techniques in Optical Fiber Networks — Part II: Systems Performance Analysis,” IEEE Trans. Commun., vol. 37, no. 8, Aug. 1989, pp. 834–42.