Ratna Kalos Zakiah Sahbudin

Performance analysis of a variable-weight OCDMA system under the impact of fiber impairments

The impact of Chromatic Dispersion (CD) and Non-Linear Effects (NLE) including Self-Phase Modulation (SPM) and Four-Wave Mixing (FWM), on the performance of a Variable-Weight Optical Code Division Multiple Access (VW-OCDMA) system at 1.25 Gbps is analyzed by simulation. The results show that CD is the most dominant effect, which increases the users bit error rate (BER) especially for the users with higher weights. In order to investigate the performance of system in service differentiation for users with different weights, Dispersion Compensating Fiber (DCF) is used to mitigate the effect of CD caused by Single Mode Fiber (SMF). The results show that users with higher weights have better performance as expected and impact of NLE is negligible for distance up to 150 km, considering low launched power.

Performance comparison of OCDMA codes for quasi-distributed fiber vibration sensing

The performance of Khazani Syed (KS) code based fiber vibration measurement for distributed sensing has been investigated. The setup was aimed at implementing quasi distributed vibration sensing with less complexity and optimum performance against Multiple Access Interference. The three sensor points system were compared with existing Optical Orthogonal Code (OOC) and Modified Congruence Code (MQC) in terms of level of power received, supported fiber length and complexity in implementation. Slightly better received power and longer fiber length were demonstrated by the system employing MQC code but a wide gap to OOC code. However, since KS code is implemented with less number of components which tends to reduce the cost and complexity of the system which becomes obvious as the sensor points grow, KS code is recommended for the quasi distributed vibration sensing.

Performance analysis of hybrid SAC-OCDMA/WDMA system using Random Diagonal code

A hybrid Spectral-Amplitude-Coding (SAC) - Optical Code Division Multiple Access (OCDMA) /Wavelength - Division-Multiple-Access (WDMA) using Random Diagonal (RD) code is proposed in this paper. The RD code is used in the proposed system due to its receivers flexibility. The system is simulated using OptiSystem software. In our proposed system, four users of WDMA system with bit rate of 10Gbps is coupled with users of OCDMA system performing on bit rate of 1.25Gbps. Comparing to hybrid SAC-OCDMA /WDMA using KS code, the proposed system offers better performance in term of lower code length and lower bit error rate (BER) at the expense of higher number of filters. The result also shows that the BER of nine RD users are maintained at not more than 10-9 up to 75 km.

Fiber non-linear effects in multiple-wavelengths optical CDMA systems

Abstract Multi-wavelength Optical Code Division Multiple Access (OCDMA) systems suffer from fiber impairments including non-linear effects (NLE), especially when the number of wavelengths and input power level increase. In this paper, a review of NLE, including self-phase modulation, cross-phase modulation, four wave mixing (FWM), stimulated Brillouin scattering and stimulated Raman scattering on the system performance of OCDMA systems is presented. As some of the non-linearities may have correlated effects on the performance of the system, the relations between these effects are also investigated. Bit error rate results reveal that the most important unwanted effect was caused by FWM.

Performance Comparison of Complementary and AND Subtraction Detection Techniques for Hybrid SCM SAC-OCDMA System

The subtraction detection techniques for a hybrid SCM spectral-amplitude-coding (SAC) OCDMA using double weight (DW) code family are investigated. The experimental simulation results show that the proposed new subtraction detection technique provides a better system performance.

Variable weight Khazani-Syed code using hybrid fixed-dynamic technique for optical code division multiple access system

Abstract. Future Internet consists of a wide spectrum of applications with different bit rates and quality of service (QoS) requirements. Prioritizing the services is essential to ensure that the delivery of information is at its best. Existing technologies have demonstrated how service differentiation techniques can be implemented in optical networks using data link and network layer operations. However, a physical layer approach can further improve system performance at a prescribed received signal quality by applying control at the bit level. This paper proposes a coding algorithm to support optical domain service differentiation using spectral amplitude coding techniques within an optical code division multiple access (OCDMA) scenario. A particular user or service has a varying weight applied to obtain the desired signal quality. The properties of the new code are compared with other OCDMA codes proposed for service differentiation. In addition, a mathematical model is developed for performance evaluation of the proposed code using two different detection techniques, namely direct decoding and complementary subtraction.

Proposal of multi-service (MS) code to differentiate quality of services for OCDMA systems

The emergence of a broad range of network-driven applications (e.g. multimedia, online gaming) rises the demand for network environments with ability to provide multiservice capabilities with diverse Quality of Service (QoS) requirements. In this paper, a new code family of novel spreading sequences, called Multi-Service (MS) code has been constructed in order to support multiple services in OCDMA system. The performance of the proposed code is demonstrated using mathematical analysis. Different numbers of basic users are used to support triple-play services (audio, data and video) with different QoS requirements. Results indicate that the technique can clearly provide a relative QoS differentiation. Lower value of basic users can support larger number of subscribers as well as delivering better performance in terms of acceptable BER of 10-9 at fixed code weight.

Wavelength Shifting in the Fiber Bragg Grating (FBG) based Encoder and Decoder Modules for SAC-OCDMA System

This project concentrates on the design of Fiber Bragg Grating (FBG) based encoder and decoder modules for Spectral Amplitude Coding of Optical Code Division Multiple Access (SAC-OCDMA) system. In SAC-OCDMA system, the unique code sequence is formed by using spectral components which are inherently arranged. This is done by multiplexing the Bragg wavelengths from an array of FBGs. However, the Bragg wavelength is largely depends on the strain and temperature experienced by the gratings. This paper presents the effects of the Bragg wavelength shifting of the uniform FBG used in the encoder and decoder modules for an SAC-OCDMA code to the system performance. The results show a sharp increase of bit error rate (BER) from 10-12 and 10-14 to 10-4 and 10-5 for Channel 1 and Channel 2 respectively at 0.01 nm Bragg wavelength left and right shifts. It shows that the system performance is significantly affected by the shifting of the Bragg wavelength.

Performance of SAC-OCDMA codes for multipoint fiber vibration sensing

Performance of Spectral Amplitude Coding - Optical Code Division Multiple Access (SACOCDMA) based fiber vibration sensor multiplexing using Multi-Service (MS) code has been investigated. The aim of the setup was to implement a multipoint fiber vibration sensing with less complexity, efficient performance against multiple access interference (MAI) and phase induced intensity noise (PIIN) which degrade performances. Comparison was made of the three sensing points with other existing SAC codes such as the Khazani Syed (KS) code, Modified Congruence Code (MQC) and Optical Orthogonal Code (OOC) in terms of level of signal power received, fiber length supported and complexity of system implementation. MS code has advantage of better received power hence supported longer fiber length, flexibility in increasing the number of sensors, service differentiation and shorter code length. Moreover, it has some close chips which can be filtered using single FBG therefore reduces the cost and complexity in sensor multiplexing.

Effects of fiber dispersion on the performance of optical CDMA systems

Abstract In recent years, Optical Code Division Multiple Access (OCDMA) system had received great attentions due to its potential to support applications with various data rates and Quality of Service requirements in physical layer. Since the main part of any fiber-based transmission system is the optical fiber itself, OCDMA also suffers from fiber impairments especially dispersion. In this paper, a review of fiber dispersion effects on system performance of different coding techniques is presented, focusing on single mode fiber. The different coding techniques include direct-sequence, spectral amplitude encoding and wavelength hopping/time spreading. In addition, the basic dispersion compensation approaches, which have been proposed in the literature, for these particular coding schemes are also discussed.