Study Of Key Technological Issues In Optical Code Division Multiple Access Networks

OCDMA is the potential candidate for deployment in the future access networks because it offers several benefits such as security and easy network control and management. It results in zero waiting time to access the channels and there is no need of synchronization. Therefore interest in OCDMA is rising.In this dissertation, key issues related with OCDMA are studied and theoretical and numerical analysis of the issues is performed.Spectral amplitude coding (SAC) is a technique of OCDMA to encode and decode the data bit by using spectral components of the broadband source. Usually in this encoding scheme, ON-Off-Keying (OOK) modulation format is used. To make SAC OCDMA network spectrally efficient, higher order modulation format of DQPSK is studied and simulated. m-sequence code is encoded in the simulated setup. Performance regarding various lengths of m-sequence is also analyzed and displayed in the pictorial form. Besides, three types of detection of the received signal are studied namely balanced or complementary detection, AND detection and direct detection.The results of the simulation are evaluated with the help of electrical constellation diagram, eye diagram and bit error rate graph. All the graphs indicate better transmission quality in case of advanced modulation format of DQPSK used in SAC OCDMA network as compared with OOK.Many encoding schemes are used in OCDMA but SAC is widely used. It is considered an effective arrangement to eliminate dominant noise called multi- access interference (MAI). Various spectral amplitude codes are studied for evaluation with respect to their performance against three noises namely shot noise, thermal noise and phase induced intensity noise (PIIN). Their SNRs are calculated and BERs are computed using Gaussian distribution assumption. After analyzing the results, it is concluded that ZCC performs better than the other selected SAC codes and can serve larger number of active users than the other codes can. At various receiver power levels, analysis points out that RDC also performs better than the other codes. For the power interval between-10and-20dBm performance of RDC is ahead of that of ZCC. Their lowest BER values suggest that these codes should be part of an efficient and cost effective OCDM access network in the future.In the final part of the dissertation, long reach passive optical network (LR-PON) is studied. Access techniques such as TDMA, WDMA or hybrid of these are available options for deployment in the future optical network. OCDM A technology is preferable because of the advantages over other access technologies. It is proposed for long reach network. For this OCDMA, a2-D Prime/OOC code family is selected for encoding and decoding. The code has large cardinality and good performance characteristics. The performance of the code was evaluated analytically and displayed pictorially.OCDMA network with extended reach was simulated with two users to prove the feasibility of this scheme. The simulation was done for100km without any dispersion compensating arrangements. Results verify that this is a viable setup and can be deployed in the future access networks for cost efficiency and improved performance.