| dc.description.abstract | The growing utilization of bandwidth hungry applications of the internet and multimedia
applications has lead to tremendous research development in optimizing the bandwidth capacity in optical communication, particularly in Optical Code Division Multiple Access (OCDMA). In
this work, a new code in the family of Spectral Amplitude Coding (SAC) OCDMA has been developed in an attempt to overcome the limitations faced by other existing codes of the same class. This work also contributes to the development of mathematical model of hybrid subcarrier multiplexed OCDMA system based on the new code and its performance evaluations.
The combination of Subcarrier Multiplexing (SCM) and OCDMA scheme can be regarded as a
new research area which is still in its infancy, since most work on SCM gives privilege to the
combination with Wavelength division multiplexing (WDM) scheme. This combination
demonstrates an improvement in bandwidth utilization of optical communication. In particular,
this thesis begins with an explicit construction of the code, namely the Recursive Combinatorial
(RC) code that is designed to have a minimum cross correlation of one, with the flexibility of
choosing the code’s parameter, such as the code weight and number of code sequences, with
minimum code length. The simple code development are based on the matrix combinatorial
method to maintain the cross correlation of one between the code sequences, that reduces the
Multiple Access Interference (MAI). The mathematical derivation of this code’s performance is
then generated to analyze its performance in the OCDMA system. Simulations are carried out to
evaluate and optimize the parameters for best performance in the system. The study focuses on
the effect of distance, bit rate, data modulation format and input power on the systems
performance. Validations of theoretical results by simulations are also conducted. It is shown
from the performance analysis that this codes exhibits better performance compared to other
codes in the same class. It is shown in term of cardinality; this code could accommodate up to
105 users simultaneously at a permissible bit error rate of 10-9. In the hybrid SCM OCDMA
using RC code, this system could accommodate up to 28 subcarrier channels for BER better
than 10-9. On the other hand, the MDW code, as compared, can only accommodate up to 20
subcarrier channels. A simulation model is also developed for the SCM OCDMA system, where
some comparisons are being made on its performances. In short, the significant contribution of
this thesis lies in the development of a new code exhibiting a very simple code construction,
which is suitable for the ease of implementation in a practical network. Adding new users in the
network using this code does not require modifying the existing network; nodes can be added at
the next available wavelength along the bandwidth occupied. At the same time, adding up the
code weight will not change any other parameters. In other words, this code design retains the
individuality of each code parameter, hence making it a more flexible code compared to others.
Apart from that, the theoretical and simulation model derived for a hybrid system of subcarrier
multiplexed OCDMA based on RC code has realized a potential approach in improving the
bandwidth utilization efficiency of optical communication. | en_US |
