الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
Abstract
Spectral Amplitude Code (SAC) is widely used in Optical Code Division Multiple Access (OCDMA) network to eliminate some sort of dominant noise, this appropriate noise would be in the state of the art of Multi Access Interference (MAI). In this thesis, a comparison study was conducted between the different types of SAC_OCDMA in order to obtain the best performance of the system in terms of safety for data transmission through the optical fiber channel and overcome the problem of MAI. First, the proposed realization aims to demonstrate the construction of the actual Modified Walsh Code (MWC) with respect to beat noise, phase incoherent intensity noise and thermal noise. In addition, a complete comparison study has been manipulated according to the performance of the proposed MWC and some existing codes such as: Modified Frequency Hopping (MFH) code, Hadamard (HD) code, Modified Quadratic Congruence (MQC) Code, Unipolar Walsh Code (UWC) and Random Diagonal (RD) code. Numerical simulations have been introduced and discussed, in order to illustrate the effectiveness of the actual MWC method to eliminate dominant noise. Numerical results have forwarded the research to the following facts; the SNR and BER for MWC under the presence of the previous discussed signal degradation is equal 1.0799e+02 and 7.2503e-08 respectively according to a predefined number of users (150). A simulation model of optical code division multiple access system has been presented by using walsh code based on Matlab graphical user interface for such three users case study. The performance of the MWC has been introduced in terms of safety, so some parameters have to be discussed. Simulation results of the research have returned the following facts; the Mean Square Error (MSE), Peak Signal to Noise Ratio (PSNR), Entropy, CORRELATION, Number of Pixels Change Rate (NPCR) and Unified Average Change in Intensity (UACI) for MWC is equal 1.2953 ,43.6057 ,7.8263, -0.0071,0.9982 and 0.3587 respectively. So the MWC has the best performance comparing with other SAC-OCSMA as Unipolar Walsh Code (UWC), Random Diagonal (RD) Code, Muti- Diagonal (MD) Code, Modified Double-Weight (MDW) code, Zero Cross Correlation (ZCC) and Dynamic cyclic shift (DCS) code. Second, a modified topology has been proposed which combining between Orthogonal Frequency Division Multiplexing and Spectral Amplitude Coding in Optical Code Division Multiple Access (OFDM/SAC-OCDMA). OFDM based the operation of Fast Fourier Transform (FFT) which used to eliminate the distortion noises and used to increase the number of subcarriers. Such analysis aims to explain the effect of spectral efficiency with respect to MD code. The new proposed technique introduces a fusion system between the two-code keying scheme and the Forward Error Correction (FEC). The fact of FEC has been used for error detection and correction not enough but used for enhancing the value of Spectral Efficiency (SE). The introduced analysis has targeted the effect of Signal to Noise Ratio (SNR), Bit Error Rate (BER), and spectral efficiency with the presence of beat noise, phase incoherent intensity noise, and thermal noise.Numerical simulations are discussed, in order to illustrate the effectiveness of the MD code method to eliminate dominant noise. Numerical outputs have forwarded the research to the following facts; the SNR and BER under the presence of the previous discussed signal degradation is equal 2.65e+02 and 1.1504 e-10 respectively according to a predefined number of users (150). The proposed unipolar encoding with direct detection technique based OFDM/SAC-OCDMA scheme introduced an enhancement in the performance of SE over the unipolar encoding with direct detection technique based SAC-OCDMA technique by 3.455dB.The proposed two keying scheme based OFDM/SAC-OCDMA introduces an enhancement in the performance of the SE over the unipolar encoding with direct detection technique based OFDM/SAC-OCDMA technique by 2.8859 dB. Forward error correction (FEC) has been applied in order to increase the spectral efficiency for different BERs, Which the numerical results show that FEC provides 1.7457 dB. Finally, the total enhancement for SE was about 8.0866 dB.