Rain Attenuation Effect in Free Space Optic Propagation Based on Non-Selective Scattering Effect

Free Space Optic (FSO) is a line-of-sight technology that enable optical connectivity without involving fiber cable and security spectrum license. Since FSO propagates through the atmosphere, there is a variety of detrimental features of the atmospheric channel that could lead to a signal degradation. For FSO signal, the major obstruction is the weather condition such as snow, fog, haze and rain. In the tropical region with the absence of snow and fog, rain and haze are the limiting factors. Therefore, the focus of this research is to propose the optimum parameters in FSO system that can withstand the effect of rainfall attenuation in the atmosphere. Rain is chosen because it is considered the dominant weather in tropical region. The rain data is provided by Malaysian Meteorological Department (MMD) for Kuching, Sarawak station. The work involved the simulation using OptiSystem software to examine the performance of FSO system. Based on the simulation result, wavelength of 1550nm has better performance according to bit error rate (BER) value compared to 785nm wavelength. Narrow beam divergence angle is vital in assuring low power consumption and capable to sustain high power at the receiver. The avalanche photodiode (APD) is preferable compared to p-i-n photodiode (PIN) based on the sensitivity performance. APD photodiode is more sensitive to detect weak signal in the system. The receiver aperture size of 0.25m and transmitter aperture size of 0.05m are considered optimum specification which can reduce the loss efficiently