| dc.description.abstract | The spectral amplitude coding optical code division multiple access (SAC-OCDMA)
technique enables many subscribers to share a network simultaneously and
asynchronously by allocating a specific code to each subscriber. The performance of the SAC-OCDMA systems is governed by numerous parameters such as the data rate,
number of simultaneous users, the powers of the transmitter and receiver, and the type of codes. Therefore, a SAC-OCDMA system has limitations in the number of users and
bit rate because of multiple access interference (MAI) which is considered to be the
dominant degradation factor in SAC-OCDMA systems. In this work, a new approach to
the SAC-OCDMA system with Rf-subcarrier such as adaptive multicarrier modulation
(OFDM) has been developed, to accommodate a large number of users, enhance the
system capacity, and decrease the system degradation. The proposed system has been
built using the modified double weight (MDW) code family, which has various
advantages over other codes including easy code construction, simple encoder/decoder
design, existence for every natural number n, ideal cross-correlation (λ = 1) and a higher
SNR. A new mathematical framework to calculate the SNR and the BER of the SACOCDMA
system using adaptive multi-carrier modulation (OFDM) has been developed
and analysed based on the AND detection technique. It provides better spectrum use,
generates a higher number of sub-carriers, and increases transmission rates using lowcost
optical components by M-ary modulation on its sub-carriers. In addition,
mathematical models and results, based on the same code and detection technique in
order to test all possible design, have been generated for the Rf-SCM/SAC-OCDMA
system. Based on the mathematical calculations, the SAC-OCDMA system with
adaptive multi-carrier modulation (OFDM) has shown superior performance compared
to Rf-SCM/SAC-OCDMA and conventional SAC-OCDMA systems. The theoretical
and simulation results have been evaluated based on the BER and number of users as
well as on the amount of power maintained. Optisys (version 12), software was used to
simulate the designed system. The proposed system gave better performance and
maintained approximately 40% of power as well as increased the number of users
twofold compared to Rf-SCM/SAC-OCDMA system. Augmentation in performance, in
terms of the number of users, for SAC-OCDMA with adaptive multicarrier modulation
(OFDM) compared to a conventional SAC-OCDMA systems based on MDW code is
more than three times. The development of this new system has contributed to SACOCDMA
system improvement by mitigating the interference, enhancing the channel
data rate, maintaining the power, and increasing the number of users. Thus, this system
could be a promising solution to symmetric high capacity access networks because of its
high spectral efficiency, cost effectiveness, good flexibility, and enhanced security.
These features make it an attractive candidate for next-generation broadband-access
networks. | en_US |
