Performance analysis of DW code family for OCDMA, FTTH network

Multiple access techniques are required to meet the demand for high-speed and largecapacity communications in optical networks, which allow multiple users to share the fiber bandwidth. Optical Code-Division Multiple-Access (OCDMA) is receiving increased attention due to its potential applications for local area optical networks. OCDMA systems, however, generally, suffers from Multiple Access Interference (MAI) noise which originated from other simultaneous users severely increases the likelihood of occurrence of bit errors. To mitigate this limitation, Spectral Amplitude Coding (SAC) OCDMA is used throughout this thesis. The advantage of SAC-OCDMA over conventional OCDMA systems is that, when using appropriate detection technique, the MAI can totally be suppressed. This either reduces the effect of MAl or improves the performance even in the presence of MAL Many codes have been proposed for SAC-OCDMA systems such as Hadamard code, Modified Quadratic Congruence (MQC) code, Modified Frequency Hopping (MFH) code, Double Weight (DW) code and Random Diagonal (RD) code. The motivation of this research is to evaluate the performance of Modified Double Weigh (MOW) code and Enhanced Double Weigh (EDW) to enhance the overall performance of optical OCDMA systems. Three stages are divided in this research. Firstly, a comprehensive discussion takes place on all important aspects of MOW codes from advantages point of view. Secondly, a software simulation for SAC OCDMA system with the MOW code families using a commercial optical system, "Optisysem ™ ver.7.0" is conducted. Finally, experimental simulation tests to analyze the performance of a realistic OCDMA network have been evaluated. This analysis has been carried out including realistic system parameters such as chromatic dispersion, Multiple Access Interference (MAl), receiver noises (dark current, short noise and receiver thermal noise) and photodiode bandwidth. We analyze the error probability of the network taking into account these parameters. The performance of OCDMA system has been analyzed and compared with different signal formats (NRZ & RZ) at the transmitter part, and with the various photo detectors (PIN & APD) at the receiver part. The system parameters based on the MOW and EDW codes are carried out taking into account various design parameters; distance, bit rate, input power, received power and chip spacing. The effect of these parameters on the system is evaluated in terms of bit error rate (BER) values. It has been shown that an NRZ format with a Bit Error Rate (BER) of2.2xl0-23 is improved over the RZ with a BER of 1.03x10-18.however, the APD photodetector ofBER 6.9xi0-22 enhances the overall MDW-OCDMA system performance compared with a BER 6.2xl0·15 photodetector.It is also shown that the system using AND-Subtraction detection technique (with a BER of2.2xl o-16 )offers better system performance compared with Complementary detection technique (with a BER of4.0lxl0-11) .Fiber-To-The Home (FTTH) technology is a promising solution of the next generation OCDMA networks for faster networks and higher- bandwidth applications. The comparisons between the transmitter with a Light Emitting Diode (LED) of -6d8m transmitted power, and the receiver component are suitable for a point-to-point FTTH application up to 80 Km transmission distance with a received output power of -14 dBm.