الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Optical code division multiple access (OCDMA) is a multiple access technique with numerous advantages as allows multiple users to access the same fiber channel asynchronously without delays, enhanced privacy and increased capacity in bursty networks. So, it become the most advanced multiple access technology in optical communication. OCDMA systems, however, generally, suffer from multiple access interference (MAI) which increases the bit error rate (BER). Spectral amplitude coding (SAC-OCDMA) can eliminate MAI when using appropriate detection technique. To mitigate this limitation, SAC-OCDMA is used with AND subtraction detection technique and single photodiode detection technique (SPD) throughout this thesis. Modified double weight (MDW) codes, enhanced double weight (EDW) codes and diagonal double weight codes (DDW) are used in SAC-OCDMA as signature codes in thesis because of their ideal cross correlation. The advantage of using these detection techniques are eliminating MAI and phase induced intensity noise (PIIN) which is related to MAI due to overlapping of the spectra from the different users. Also, Orthogonal frequency division multiplexing (OFDM), is a good method of data transmission in fading and multipath channels. OFDM systems that use FFT have many advantages such as provision for a higher number of subcarriers and high data rate. Therefore the use of OFDM technique with SAC-OCDMA can provide good spectrum utilization, increased transmission rate and high number of generated subcarriers. This thesis presents extensive research on how to improve the performance of OCDMA system. Different proposed models are investigated a comparison also is carried between them to show which model give better performance. Performance are related to BER, signal to noise ratio (SNR) and maximum allowable number of users can access with higher data bit rate. First investigation is that, three codes SAC-OCDMA are proposed and compared in terms of system performance including bit error rate BER, number of active users, high achievable data rate, SNR and the minimum received power that the OCDMA system supports to achieve a minimum BER value. The proposed codes are DDW codes, MDW codes and EDW codes. Different detections as AND subtraction detection technique and SPD are investigated to reduce the effect of both the MAI and PIIN. The obtained results show that SAC-OCDMA using EDW code with SPD detection can achieve large number users with better BER (~ 10-9), SNR (> 20 dB), and minimum received power (~ -20 dBm) relative to the other codes with other detection techniques. Second investigation is, a performance comparison for spectral amplitude coding SAC-OCDMA using MDW codes with SPD detection technique and different detectors at different transmission distances as well as different data bit rates. Simulation results show that the system using avalanche photodetector (APD) have longer transmission distances than that using positive intrinsic negative (PIN), with enhanced bit error rate (BER). Finally, a new OFDM-SAC-OCDMA system using three different codes which are DDW codes, MDW codes and EDW codes with two different detection techniques, AND subtraction and SPD detection techniques is investigated. The obtained results show that the performance of the OFDM-SAC-OCDMA/DDW code system using SPD detection technique is better than that of OFDM-SAC-OCDMA systems using MDW and EDW with AND subtraction detection technique. Finally, this research made improvement in OCDMA system performance.