Mohamad Khazani Abdullah

A new family of optical code sequences for spectral-amplitude-coding optical CDMA systems

A new code structure for spectral-amplitude-coding optical code-division multiple-access system based on double-weight (DW) code families is proposed. The DW code has a fixed weight of two. By using a mapping technique, codes that have a larger number of weights can be developed. Modified double-weight (MDW) code is a DW code family variation that has variable weights of greater than two. The newly proposed code possesses ideal cross-correlation properties and exists for every natural number n. Based on theoretical analysis and simulation, MDW code is shown here to provide a much better performance compared to Hadamard and modified frequency-hopping codes.

Spectral amplitude coding OCDMA using and subtraction technique

An optical decoding technique is proposed for a spectral-amplitude-coding-optical code division multiple access, namely, the AND subtraction technique. The theory is being elaborated and experimental results have been done by comparing a double-weight code against the existing code, Hadamard. We have proved that the and subtraction technique gives better bit error rate performance than the conventional complementary subtraction technique against the received power level.

Design and analysis of a dynamic code division multiple access communication system based on tunable optical filter

A dynamic optical code division multiple access (DOCDMA) communication system is proposed for high-bandwidth communication systems. An implementation of the system is proposed based on a fast tunable optical filter (TOF) in each encoder and decoder. This technique actively modulates the central wavelength of a TOF according to a functional code at the transmitter during the bit period before the transmission of the data. The system is modeled and analyzed taking into account multiple access interference (MAI), thermal noise, and phase-induced intensity noise (PIIN). The performance of this system is compared to that of a spectral amplitude coding system that uses either a Hadamard code or a modified quadratic congruence (MQC) code. The results show that the proposed DOCDMA system reduces the PIIN effect on the performance of the system and improves the bit error rate (BER) performance at a large number of users. Furthermore, it is found that when the effective power is large enough, the MAI becomes the main factor that limits system performance, whereas when the effective power is relatively low, both thermal noise and PIIN become the main limiting factors with thermal noise having the main influence.

Analysis of the effect of haze on free space optical communication in the Malaysian environment

This paper presents the effect of atmospheric attenuation during hazy days for free space optical (FSO) communication in point-to-point connection. The analysis focuses on scattering coefficient and atmospheric attenuation effects on low visibility, which falls in the range of 1.8 km to 4.5 km. The performance comparison is also done for the wavelength of 850 nm and 1550 nm. The result shows that the performance of 1550 nm is better than 850 nm in both performance parameters. As the link range between transmitter and receiver increases, the atmospheric attenuation increases too. Deployment distance of less than 1km can reduce the effect of atmospheric attenuation. These challenges limit FSO to the short distance application.

Characterization of a multiwavelength Brillouin–erbium fiber laser based on a linear cavity configuration

We experimentally demonstrate a simple method for generating a multiwavelength Brillouin comb by utilizing a linear cavity of hybrid Brillouin-erbium fiber lasers (BEFLs). The optimization of Brillouin pump wavelength, power, and erbium gain played a significant role in determining the maximum number of Brillouin Stokes signals generated. Simultaneous and stable multiple-wavelength laser output of 22 lines with 10.88-GHz channel spacing has been obtained with good flatness. Various parameters such as 980-nm pump power, Brillouin pump wavelength, and Brillouin pump power that affect the performance of a multiwavelength BEFL system have been investigated. An analysis of the tuning range of the system is presented.

Performance of OCDMA systems using a complementary subtraction technique

Feature Issue on Optical Code Division Multiple AccessWhat we believe to be a new code structure to reduce the multiple access interference in a spectral amplitude coding optical code-division multiple access system based on double-weight code families is proposed. Enhanced double weight (EDW) possesses ideal cross-correlation properties, and weight can be any odd number that is greater than 1. The theoretical analysis shows that EDW codes can more effectively suppress the phase-induced intensity noise and provide a significantly better performance compared with modified quadratic congruence and partial modified prime codes.

Multiple access interference elimination with enhanced chromatic dispersion tolerance in SAC OCDMA

We demonstrate a direct decoding scheme to eliminate multiple access interference in optical spectral-amplitude-coded, multiple access networks. By detecting only the non-overlapping spectrums, our scheme shows a better BER of eight orders of magnitude over the conventional complementary subtraction scheme, when 16 simultaneous channels with 10Gbps bit rate per channel are transmitted over a simulated 70km dispersion-compensated fiber span. Our direct decoding technique is also tolerant to chromatic dispersion, where the maximum achievable distance of 67km was obtained in a dispersion limited system with standard 16ps/nm.km dispersion of single mode fiber.

Duty Cycle Division Multiplexing Technique for Wireless Communications

A new multiplexing technique which is called duty cycle division multiplexing (DCDM) is presented in this paper. Theoretical and simulation studies have been carried out to evaluate the performance of this technique based on the signal energy and symbol error rate (SER). A wireless channel based on free space propagation model is considered for the simulation study. Two modulation schemes of PSK and QAM are used to evaluate the technique, against the number of users and data rates. Also, the performance of the multiplexing technique is compared with the conventional time division multiplexing (TDM) technique as well as with the multilevel M-ary signaling. The study shows that the energy per bit in the DCDM technique, unlike that of the TDM technique increases with the number of users. The simulation results correspond with the theoretical study in which the DCDM technique has better SER than that of TDM.

Duty-Cycle Division Multiplexing: Alternative for High Speed Optical Networks

Performance of 3×10 Gbps duty-cycle division multiplexing (DCDM) is analyzed. The channel demultiplexing is performed electronically at single user bit rate (10 Gbps). At 30 Gbps, null-to-null spectral width of 80 GHz is measured for DCDM technique which is 33.3% less compared to 30 Gbps conventional return-to-zero (RZ). In this system, the worst channel required a receiver sensitivity of around -25.6 dBm at bit error rate (BER) 10-9. The chromatic dispersion tolerances of the system are 210.5 and 236 ps/nm for the worst and the best channel respectively.

Multi-Rate Transmissions on SAC-OCDMA System using New Enhancement Double-Weight (EDW) Codes

This paper presents a new code structure and its ability in supporting multiple transmission rates in point to point Spectral Amplitude CodingOptical Code Division Multiple Access (SAC-OCDMA) links. The Double-Weight (DW) code family that has a basic fixed weight of 2 was proposed. Enhancement Double Weight (EDW) Code is a DW code family variation that has variable weight of greater than one. The ability of EDW codes to support simultaneous transmissions at different bit rates is shown through simulated results of the bit error rate (BER) and the eye patterns. Three EDW encoded channels were used at the bit rates of 2.5Gbps and 10Gbps. EDW code shown here significantly performs better than Hadamard and Modified Frequency Hopping (MFH) codes