Atmospheric channel effects on terrestrial free space optical communication links

Abstract. This paper illustrates the challenges imposed by the atmospheric channel on the design of a terrestrial laser communication link. The power loss due to scattering effect is described using the Kim/Kruse scattering model while the effect and the penalty imposed by atmospheric turbulence is highlighted by considering the bit error rate (BER) of an On-Off Keying modulated link in an optical Poisson channel. The power loss due to thick fog can measure over 100 dB/km while snow and rain result in much lower attenuation. We show that non-uniformity in the atmospheric temperature also contributes to performance deterioration due to scintillation effect. At a BER of 10-4, for a channel with a turbulence strength of>0.1, the penalty imposed by turbulence induced fading is over 20 photoelectron counts in order to achieve the same level of performance as a channel with no fading. The work reported here is part of the EU COST actions and EU projects.

Performance Investigation of OFDM-FSO System under Diverse Weather Conditions of Bangladesh

Free space optical (FSO) communication systems which are deployed for last mile access, being considered as a suitable alternative technology for optical fiber networks. It is one of the emerging technologies for broadband wireless connectivity which has also been receiving growing attention due to high data rate transmission capability with low installation cost and license free spectrum. However, the widespread use of FSO technology has been hampered by the randomly time varying characteristics of propagation path mainly due to atmospheric turbulence, sensitivity to diverse weather conditions and the nonlinear responsivity of laser diode. This paper presents the performance investigation of an OFDM-FSO system over atmospheric turbulence channels under diverse weather conditions of Bangladesh. The channel is modeled with gamma-gamma distribution using 16-QAM modulation format and 4×4 multiple transceiver FSO system. All possible challenges are imposed on the system performance such as atmospheric attenuation, turbulence, pointing error, geometric loss etc. The refractive index structure parameter and atmospheric attenuation coefficient for different weather conditions are calculated by using the data, collected from Bangladesh Meteorological Department. The acquired results can be fruitful for scheming, forecasting and assessing the OFDM-FSO system’s ability to transmit wireless services over turbulent FSO links under actual conditions of Bangladesh

Laser based Optical Wireless Communication using Log Normal Distribution and SIM BPSK Modulation

Laser based Optical Wireless Communication(OWC) is emerging as one of the key advancements for the 5G and beyond technologies. This technology provides high bandwidth, extremely high data rate and high speed communication due to the use of optical waves for data transmission in the field of wireless communication. The system performance is limited due to the presence of turbulence in the atmosphere.We have developed system model using log normal channel distribution in the weak to moderate atmospheric turbulence. Closed form of expression is derived which provides the channel capacity in the presence of weak turbulence using log normal distribution. Subcarrier Internsity Modulation (SIM) BPSK modulation  technique is used in OWC system which  provides bettter performance in terms of received BER as compared to NRZ – OOK modulation