الفهرس 
Motivation for OCDMAOnly 14 pages are availabe for public view
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Abstract
Optical fiber offers large bandwidth and high speed communication so the demand on optical fiber communication systems increased. Therefore, multiple access techniques come up to use in optical fiber to meet the increase in the capacity of users by allowing multiple users to share the same transmission media. The most famous multiple access technique is Optical Code Division Multiple Access (OCDMA). OCDMA system has several advantages such as supporting asynchronous access to the networks, enabling multiple users to use the same spectrum, and enhancing information security. So, it has attracted the attention of researchers recently.
However, there main problems in OCDMA system are the Multiple Access Interference (MAI) introduced from users transmitting simultaneously limits the performance of the system and reduces the number of active users. Also, the Phase Induced Intensity Noise (PIIN) which is correlated to the MAI because of the spectral duplication from various users when inconsistent optical fields are combined and directed on a photo detector. The phase noise fields produce intensity noise in the photo detector output marked as PIIN. So, many studies have been introduced to solve these issues.
Moreover, the properties of codes used in OCDMA system to encode data play an important role in system performance. Orthogonality between codes is critical to avoid MAI and PIIN as the OCDMA receiver consider other user’s signal a noise. To ensure Orthogonality between codes the cross correlation should equal to zero and the autocorrelation should equal to one to be able to recover information at the receiver. The receiver design as well has an effect on system performance, complexity, and cost.
This thesis started by a comparison between the performance of various Spectral Amplitude Coding SAC-OCDMA codes in both Free Space Optics (FSO) under different rain weather conditions and turbulence and Optical Fiber System (OFS) under nonlinear effects, attenuation, and dispersion to investigate the performance of codes as the performance of codes is media-dependent. Then, as code construction play a critical role in system performance. We have proposed a novel code called Cyclic Shift (CS) code able to overcome all the restrictions contained in previous generated codes. CS code has a zero cross correlation. Therefore, it has eliminated both MAI and PIIN. Moreover, our novel code has provided better performance than other codes and has overcome the drawbacks that existed in them. CS code can support a larger number of users with a practical code length and large cardinality in selecting the code weight and the supported users. It also has a simple receiver structure as its frequency bins exist next to each other which reduce the number of filters needed to encode or decode the data.
In addition, we modified Multi-service (MS) code to overcome the drawbacks exist on it and provide a proposed modified code can give better performance. Finally, we have investigated the performance of both NAND subtraction and Spectral Direct Detection (SDD) techniques using Diagonal Eigenvalue Unity (DEU) code as a promising code for future optical network. Also, the variable weight DEU code was discussed and demonstrated success for triple-play services (audio, video, and data) using the SDD to provide different Quality of Service (QoS) to users.