Analysis of atmospheric effects on free space earth-to-satellite optical links in Malaysia

Abstract

Free Space Optics (FSO) has become one of the most promising technologies whereby optical transceivers transmit high bandwidth laser beams directly through the air. FSO offers extra inherent advantages which include fast and easy deployment by saving time and cost, license free spectrum, and has immunity to radio frequency interferences. In spite of these advantages, FSO is very sensitive towards atmospheric phenomena because it solely employs the air as transmission medium. Hence, atmospheric effects greatly affect the FSO transmission performances. Very few researches were conducted to study feasibility of FSO from earth-to-satellite links. None of these studies investigate the vulnerability of FSO links towards environmental effects from ground to space in tropical regions. Therefore, this research aims to provide feasibility analysis on establishing FSO links from earth-tosatellite, especially Low Earth Orbit (LEO) satellite. It evaluates the impact of several atmospheric phenomena that occurs in tropical regions specifically Malaysia. A measuring system was setup at Faculty of Engineering, International Islamic University Malaysia (IIUM) Kuala Lumpur campus in order to collect rain intensity, visibility variations, and received signal level from 800 m long FSO link concurrently. The FSO links availability has been predicted by estimating the effects of geometrical attenuation, absorption, scintillation, haze attenuation, and rain attenuation. The analyses are based on the prediction models as well as from the measured data collected from experimental FSO links. It was found that FSO links could be well established at LEO satellite during clear weather conditions with most sophisticated available optical devices, while during hazy conditions, the link depends on the visibility range. At 10 km visibility and 50 degree elevation angle, 52 dB link margin is achieved. During rainy event, the highest availability of establishing the FSO links is at 99.9% provided elevation angle must be higher than 50 degree. Note that, elevation angle and beam divergence angle are critical parameters trade in FSO slant path links that must be resolved to obtain a successful optical wireless system. Finally, the result of this analysis will contribute sufficient information for applying FSO in longer distances and determining the operability of FSO system and will be a benchmark for future designs.