A. K. Rahman

Improve the Bit Error Rate Performance of Free Space Optical Communication due to Atmospheric Turbulence Effect through the Robust Modulation

This paper focus on improvement bit error rate (BER) performance due to atmospheric turbulence effect in free space optical communication (FSOC) using new modulation technique that is dual diffuser modulation (DDM) technique. This technique uses two transmitter and differential mode detection at the receiver. The combination of dual diffuser with differential detection mode at receiver produce the superior modulation against the turbulence especially reducing the scintillation index, overcome the signal detection with fix zero threshold and improve the power received. These three element factors are important in order to improve the overall performance of free space optical system. The analysis result shows that under strong turbulence condition, the BER can improve 42 percent in term of FSO distance propagation.

Study of rain attenuation with diversity of wavelengths propagation transmission in tropical rainforest region

This paper examine about the selecting of wavelength in effecting the laser transmission over the free space spatial under the rain circumstances. The wavelengths used in these computation experiment theory are 780 nm, 850 nm, 1550 nm and 10000 nm. Comparison of the experiment result is measured in various types of rain such as drizzle, light rain, medium rain, heavy rain, cloudburst, extreme rain and very extreme rain. Visual range and scattering coefficient of rain is depending on wavelength utilize. This observation is based on an extensive literature search and from Mie scattering calculation.

Performance analysis of new multiplexed patten for duty-cycledivision multiplexing over optical communication system

This paper develops new coding technique to generate multiplexed patterns for Duty-Cycle Division Multiplexing (DCDM) which allows users to share the single transmission medium by assigning different duty cycles for each user. This coding technique aims to reduce the amount of noise which is added due to multilevel signalling. Single channel back-to-back optical fibre system is designed based on the proposed coding technique. The performance analysis is based on the comparison between the proposed pattern with normal DCDM in terms of optical signal-to-noise ratio (OSNR), and receiver sensitivity. The results show that at the optimum performance, DCDM with the proposed pattern is improved by 1.6 dB OSNR and 1.3 dB receiver sensitivity than conventional pattern.

NRZ and RZ analysis for optical CDMA based on radio over fiber (RoF) technique

In this paper, we will focus on the modulation format used to produce the optical pulses, which are return to zero (RZ), and non-return to zero (NRZ). Bit error rate (BER) performance is assessed for OCDMA-RoF system. OCDMA-RoF system is viewed as a promising method for improving spectral efficiency and in the meantime diminish hardware equipment. The execution of RZ against NRZ is looked at through software simulation. We utilized two systems designed as follows: the first system used a RZ pulse generator and the second system used is NRZ pulse generator, and both frameworks were tried with 8 Optical Line Terminal (OLT) at the transmitter and 8 Optical Network Units (ONU) at the receiver without an erbium doped fiber amplifier (EDFA). It has been found that the NRZ pulse generator in this framework is prevalent than the RZ pulse generator for all re-enactment results. The performances are described through the received power at various bit rates and also an RF spectrum signal of NRZ and RZ format.

Link budget analysis for free space optical (FSO) communication under haze condition with adverse wavelength

This paper presents the link budget analysis for free space optical (FSO) communication and the studies on how to reduce the attenuation effect to improve FSO link. The effects are primarily focused on the atmospheric attenuation on the received power. Transmission power is the main priority in link budget. The power used to transmit data is gradually decreased along the path due to attenuation effects such as weather conditions. Theoretically, more transmission power is received at the receiver when scattering is low due to low level of attenuation. Despite this limitation, FSO performance could be enhanced more by using various wavelengths of laser beam. The conventional generally used wavelengths are 785 nm, 850 nm, and 1550 nm. The result analysis shows that wavelength 1550 nm is better than the wavelength 785 nm and 850 nm due to the attenuation effect and link range. Wavelength 1550 nm has improved 83%, 89%, 24% and 26% on the system compared to the wavelength 850 nm and 785 nm based on the attenuation and distance at power received -50 dB, respectively. There is a huge difference in the attenuation effect and obviously wavelength 1550 nm capable to reduce the power loss more than wavelength 785 nm and 850 nm as it is not affected much by the heavy attenuation.

Performance analysis of optical CDMA based on radio over fiber (RoF) technique

This paper presents an improvement design of an Optical Code Division Multiple Access for Radio over Fiber (OCDMA-RoF) system. This improved system is divided into two main subsystems, Central Stations (CS) and Base Station (BS). Implement OCDMA code into RoF system promised a secure, cost-effective, and high-capacity mobile and multimedia wireless services. The analysis was made based on the relationship between length of fiber, frequency carrier, BER performance and number of optical line terminal (OLT) and optical network unit (ONU). The Bit Error Rate (BER) performance was measured, evaluated, and compared through software simulation. Results demonstrate the proposed framework can expand the fiber cable up to 60km and maintain the performance until 500Mbps data bit rate while keep up the BER at 10-9 that is coordinating the understanding of hypothetical expectations and huge change over the past outline of OCDMA-RoF framework. The work exhibited has significant ramifications for future investigations of the OCDMA-RoF framework and may one-day take care of the issue of fiber optic long transmission.

Noise suppression of optical CDMA system via utilizing wavelength/time 2-D MDW code

This paper organizes the performance of two-dimensional (2-D) Modified Double Weight (MDW) code for Optical Code Division Multiple Access (OCDMA) system by employing Avalanche Photodiodes (APD) as a gain. To accomplish the perfection system capacity, their cardinality, bit error rates (BER) and noise interferences are analyzed. With 2-D MDW with APD able to recovered the cardinality at least 61%, which able to reduce the BER of 10-9 Obviously, the proposed system maximally suppressed PIIN and shot noise which is a major factor affecting BER at high effective received power (Psr). Thus, this system shows an improvement of the system by applying APD instead of PIN diodes.

Investigation of haze effects via utilizing different wavelength on free space optical communication

This paper demonstrates the effect of haze condition on free space optical (FSO) communication and to thin out the attenuation effects. The effects in the main focus on the atmospheric attenuation effects due the visibility and link range (length). Visibility is the main concern in utilizing the FSO communication system. The higher visibility, the longer transmission link. Hence, FSO performance could be enhanced and increased efficiency by using different wavelengths of laser beam. The conventions generally used wavelengths are 785 nm, 850 nm, and 1550 nm. The analysis result shows that the wavelength 1550 nm is better than 785 nm and 850 nm due to the less attenuation performance. Wavelength 1550 nm had improved 33%, 67%, 80% and 100% compared to the wavelength 850 nm and 785 nm due to the visibility and distance of 3 km, respectively. Higher wavelength able to thin out the attenuation effects on FSO links. Wavelength 1550 nm is sufficient enough to penetrate haze dense without giving harm to the eyes.

Enhancement of free space optical communication system modulation using DDM technique

Many FSO communication systems are using a conventional technique that is OOK technique in the system. Some enhancement of technique is explained in this paper to decrease the error rate that occurs in the system. The comparison between OOK technique and DDM technique is investigated in order to compare the error rate and power received. The result shows that the performance of DDM technique generates improvement as much as 21% magnitude of BER in the system.

Performance of hybrid subcarrier multiplexed — optical CDMA system based on different detection methods

In this article, a subcarrier-multiplexed Optical CDMA system utilizing the direct and AND subtraction method in receivers detection is explored. The OCDMA part exploits the Recursive Combinatorial (RC) code for its algorithm. The two different designs are then simulated and the performances are compared. Results indicate that the hybrid SCM/OCDMA system using direct detection technique could transmit to a longer distance of up to 50 km with better quality than that with AND subtraction detection for acceptable communication error rate of BER of 10-9.