Optimization of FSO system in tropical weather using multiple beams

Abstract

The presentation covers the design and analysis of optimum free space optics (FSO) system to setup communication in a typical tropical weather link. It is a known fact that single-beam FSO system is vulnerable to atmospheric attenuation, so to overcome this, a multiple beam FSO system has become prominent and is usually used. Single beam and multiple beam FSO system is designed and analyzed to produce the best system capable of tackling the effect of tropical weather. The performance evaluation and applicability of multi-beam beam FSO system, in tropical weather is explored and investigated using wavelength division multiplexing (WDM). The study is carried out based on simulation, and verified using on-site attenuation and rain intensity measurements. The study considered the received power, geometrical losses, and atmospheric losses due to heavy rain. Two types of FSO system were considered: single beam FSO system and multiple beams FSO system and how to design optimum system that can operate in severe tropical weather with high data rate and enhanced scalability. The performance of single beam FSO system was analyzed for heavy rain rate intensities for the period of six months in typical Malaysian weather, using the average value. The hybrid WDM/multi-beam FSO network is proposed to provide a significant improvement in the link distance, received optical power, geometrical loss, and scalability. Comparison is made in terms of received optical power, geometrical losses, atmospheric losses, and bit error rate (BER) on using different number of optical beams, at data rate of 1 Gb/s. It is clear from the results, that the multiple FSO system provides a significant improvement in the link distance, received optical power, and geometrical loss, under heavy rain with an attenuation of 19.2dB/km. It is found that the quality of received power is improved by using up to four beams, along with link distance up to 1141.2 m as compared to one-beam, two-beam, and three-beam, with link distances 833.3 m, 991.0 m, 1075.4 m, respectively. It was realized that four-beam FSO system can operate successfully for a link distance of 1141.2 m at BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> with a received optical power of -34.5 dBm, proving the fact that multi beam FSO is sensitive even to very low optical power. Comparing the four systems in terms of previously noted parameters, the four-beam FSO system is much superior.