A new three-dimensional code for OCDMA system

Abstract

Many codes have been proposed for incoherent OCDMA based on one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) by exploiting one or more resources simultaneously. The 3-D Perfect Difference (3-D PD) code has been proposed for spectral/time/spatial OCDMA system in order to increase the number of users by using shorter code lengths. But, the complexity of the system, especially the decoder, is increased. In this research, a new 3-D code namely, Three-Dimensional Diluted Perfect Difference/ Multi Diagonal (3-D DPD/MD) code is proposed for the incoherent OCDMA system, to completely cancel the Multi Access Interference (MAI), mitigate the Phase Induced Intensity Noise (PIIN), accommodate a large number of simultaneous users and reduce the complexity of the 3-D system decoder. The 3-D DPD/MD code has been developed based on the DPD and MD codes. The study of the proposed code, included the mathematical derivation of the performance equations in terms of Signal to Noise Ratio (SNR) and Bit Error Rate (BER) under the effect of receiver noises, and the validation by using optical simulation software. The system performance was investigated under the effect of data rate, distance, received power, and the photodetector type. Theoretical results showed that the 3-D DPD/MD code system achieved better performance than the 3-D PD, 2-D DPD, and 2-D PD codes of similar total users where a larger number of simultaneous users can be accommodated using the same data rate and received power. At BER of 10-9, it could support 1020 simultaneous users at 0.622 Gbps and -7 dBm compared with 660, 570 and 490 users of 3-D PD, 2-D DPD and 2-D PD codes, respectively, where the improvement factors were 54%, 78% and 108%. Also, the proposed code provided better performance than the others at 1.25 Gbps. Moreover, the 3-D DPD/MD code provided 600 active users at lower received power of -15 dBm with data rate of 0.622 Gbps. Consequently, the spectral efficiency based on the 3-D DPD/MD code was enhanced by more than 27%. In addition to that, the using of the 3-D DPD/MD code reduced the decoder complexity by more than 50% when compared with the 3-D PD code. On the other hand, the simulation results validated the proposed code to support the service differentiation in optical networks via simulation modeling. As a result, a high spectral efficiency, low system complexity, and a large number of simultaneous users can be accommodated by adopting the proposed code in the OCDMA networks.