This document summarizes a seminar presentation on Optical Code Division Multiple Access (OCDMA). OCDMA allows multiple users to transmit simultaneously over the same bandwidth using unique optical codes. It provides advantages over TDMA and FDMA such as supporting more users and asynchronous transmission without packet collisions. The presentation describes OCDMA network implementation using optical orthogonal codes assigned to transmitters and receivers for communication. It also discusses enhanced security provided by OCDMA through increasing the signal-to-noise ratio required for eavesdropping.

1. SEMINAR ON
“OPTICAL CODE DIVISION MULTIPLE ACCESS “
Submitted by
MURTADHA ALI NSAIF SHUKUR
(M.Tech(ECE) ―First semester ‖1ST
year)

2. INTRODUCTION
CDMA: 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.

3. 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.

4. 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

5. 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 .

6. IMPLEMENTATION IN OCDMA
fig. (1) block diagram of generator optical orthogonal
code

7. IMPLEMENTATION IN OCDMA

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

9. 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

10. 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.

11. 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.