New spectral amplitude coding OCDMA system using adaptive multicarrier modulation for next generation network

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.