Hilal A. Fadhil

Improved BER based on intensity noise alleviation using developed detection technique for incoherent SAC-OCDMA systems

The major drawback of incoherent spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems is their inherent intensity noise originating due to the incoherency of the broadband light sources. In this paper, we propose a developed detection technique named the modified-AND subtraction detection for incoherent SAC-OCDMA systems. This detection technique is based upon decreasing the received signal strength during the decoding process by dividing the spectrum of the utilized code sequence. The proposed technique is capable of mitigating the intensity noise effect, as well as suppressing the multiple-access interference impact. Based on modified quadratic congruence (MQC) code, the analytical results reveal that the modified-AND detection offer best bit-error rate (BER) performance and enables MQC code to support higher transmission rate up to 1.25 Gb/s compared to conventional AND detection. Furthermore, we ascertained that the proposed technique enhances the system performance using a simulation experiment.

Improving spectral efficiency of SAC-OCDMA systems by SPD scheme

This letter presents a single photodiode detection (SPD) as an effective technique for eradicating both multiple-access interference (MAI) and phase-induced intensity noise (PIIN) in spectral amplitude coding optical code-division multiple-access (SAC-OCDMA) systems. Mathematical analysis and simulation experiments are used to investigate the spectral efficiency (SE) of SAC-OCDMA systems utilizing different detection techniques. Results show that the SPD technique significantly enhances the SE compared to AND as well as modified-AND subtraction detections.

Performance comparison of different detection techniques in long-haul fiber SAC-OCDMA systems

Progress in fiber optic technology have made long-haul communications systems reach distance that were once unheard of. This distance is made possible by using modulation techniques that do not require a complex link design which best applied in spectral-amplitude coding optical code-division multiple access (SAC-OCDMA) system. In this paper, we investigate the use of different detection schemes namely the modified-AND subtraction detection as well as AND subtraction detection for SAC-OCDMA systems. We simulate the system performance of the mentioned detection approaches using OptiSystem7.0 software. The entire effects of fiber nonlinearities, dispersion and attenuation were considered in the simulation of SAC-OCDMA systems. Based on modified double weight (MDW) codes, the simulation results revealed that the modified-AND subtraction detection improves SAC-OCDMA system performance significantly compared to the conventional AND subtraction detection. Moreover, for the same quality of service (QoS) for bit-error rate (BER) of 10-20 and data rate of 622 Mbps, modified-AND subtraction detection allows longer transmission distance of 30 % in the fiber length as compared to AND detection.

Analytical comparison of various SAC-OCDMA detection techniques

This paper presents the performances comparison of the Modified Double Weight (MDW), Enhanced Double Weight (EDW) and Zero Cross Correlation (ZCC) codes using different detections technique, which are complementary subtraction, AND subtraction and spectral direct detection (SDD). The MDW and EDW codes are the modification of the double weight (DW) code, which has the variable code weight that greater than DW code. The MDW code has an even code weight which is greater than two while the EDW code has the odd code weight which is greater than three. The ZCC code is a code that is built using the concept of “non-overlapping of bit 1” in a codeword among users who can suppress phase induced intensity noise (PUN) and also prevent the interference between users. Theoretically, for all mentioned SAC-OCDMA, SDD shows a better performance than complementary subtraction and AND subtraction through the analysis of the eye diagram, bit error rate (BER) and signal to noise ratio (SNR).

SOA/SPD-based incoherent SAC-OCDMA system at 9×5Gbps

To boost the performance of spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems, the need for an effective solution to diminish phase-induced intensity noise (PIIN) is becoming progressively more crucial. In this letter, two PIIN suppression approaches: semiconductor optical amplifier (SOA)-based noise cleaning, and single photodiode detection (SPD) are employed. The performance of the hybrid SOA/SPD scheme is validated through simulation experiments. Our results show that SOA/SPD scheme remarkably improves the performance and increases the throughput of SAC-OCDMA system.

Spectral efficiency comparison of SAC-OCDMA systems using unipolar and bipolar encoding techniques

We compare the spectral efficiency of unipolar and bipolar encoding for spectral-amplitude coding optical code-division multiple access (SAC-OCDMA) systems operating with incoherent sources considering the intensity noise as the primary noise source. For both encoding techniques, the spectral efficiency of four SAC codes such as Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC) is evaluated and compared as a function of the number of users and code length for a BER= 10−10. Analytical derived equations and results verified that ZCC code can support high number of users and leads to the best achievable spectral efficiency than other SAC codes considered. Furthermore, bipolar encoding improves the spectral efficiency as compared to unipolar technique, e.g., bipolar ZCC has 7.7 dB spectral efficiency advantage than unipolar ZCC.

Enhanced performance of SAC-OCDMA system based on SPD detection utilizing EDFA for access networks

In this paper, we present the impact of an EDFA (Erbium Doped Fibre Amplifier) for high data rate in Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) networks. A Single photodiode (SPD) detection structure for SACOCDMA system is presented. The SPD detection can be flexibly constructed for any weight and number of users by using a single photodiode. Several advantages of using EDFA for simultaneous noise suppression and improved the signal quality. Thus, these features show the SPD combined with EDFA be a solution to enhance the overall system performance of SAC-OCDMA access networks. Based on the theoretical and simulation evaluation, Modified Double Weight (MDW) code is shown to provide a much better performance compared to existing SAC-OCDMA codes. The ability of the MDW code based SAC-OCDMA system utilizing EDFA to support simultaneous transmissions at different data rate has been successfully established through the simulated results of the (622 Mbps×3 users) at bit error rate of 10. 

Performance enhancement of SAC-OCDMA system using modified-AND subtraction detection

Technology is already on the move towards exploiting the limits of the fibers physical properties and more sophisticated techniques will be needed to increase the throughput and counteract the transmission impairments. In this paper, we present a new detection technique called the modified-AND subtraction detection for spectral-amplitude coding optical code-division multiple access (SAC-OCDMA) systems. This detection technique is based upon decreasing the received signal strength to the decoders branches by dividing the weight of the utilized code sequence. The new technique is capable of mitigating the intensity and shot noise impacts, as well as eliminating the multiple access interference (MAI) influence. We simulate the system performance of the proposed detection technique using OptiSystem 9.0 software. The entire practical effects of fiber nonlinearities, dispersion and attenuation were considered in the simulation of SAC-OCDMA system. Based on modified double-weight (MDW) code, the simulation results revealed that the modified-AND subtraction detection improves SAC-OCDMA system performance significantly compared to the conventional AND subtraction detection.

Spectral efficiency of unipolar SAC-OCDMA system considering noise effects

In this paper, we evaluate the spectral efficiency of unipolar spectral-amplitude coding optical code-division multiple access (SAC-OCDMA) system operating with incoherent sources in the present of intensity, shot, and receiver thermal noises. The spectral efficiency achievable by four SAC codes such as Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC) is evaluated and compared against the number of active users and code length for a bit error rate (BER) of 10−10. Analytical results indicated that ZCC code can support more users and leads to the best achievable spectral efficiency than other SAC codes considered. Moreover, the effect of shot and receiver thermal noise degrades the SAC-OCDMA system performance, e.g., when the number of users equal to 80, ZCC has 1.8 dB spectral efficiency penalty by considering these noises as additional to intensity noise.

Investigation of transmission performance for SAC-OCDMA system under long haul transmission distance based on single photodiode detection technique

In order to meet the ultra-high speed and ultra-long haul transmission distance in spectral amplitude coding optical code division multiple access (SAC-OCDMA) system, the dispersion impairment affecting the overall system performance should be minimized. In this paper, the transmission performance of SAC-OCDMA system is investigated based on single photodiode detection technique when a conventional single-mode fiber G.652 (SMF) is used as a transmission link. On the other hand, the grating filter represents as one of the critical parameters in contusing to a high performance fiber Bragg grating (FBG) dispersion compensator. Comparison reveals that the dispersion compensating fiber (DCF) results best performance for chromatic dispersion compensator over FBG dispersion compensator. Furthermore, we have found that, a transmission length of 125 km and 135 km have been achieved for a bit error rate (BER) <;10-9 when FBG compensator and dispersion compensating fiber are present, respectively. Finally, the proposed investigation is considered an ideal solution to achieve long haul transmission for SAC-OCDMA system with minimized dispersion affects.