Free-space optical (FSO) communication requires a line-of-sight connection\nbetween a transmitter and a receiver in which the information signal is modulated\nby an optical carrier that propagates in free space. The FSO channel is\ngreatly affected by weather conditions such as fog, rain, and snow. In the literature,\nseveral adaptive techniques, such as power control (PC), have been\nsuggested to mitigate channel link degradations. In this paper, we investigate\nthe effects of snow and rain attenuation on the bit error rate (BER) of the FSO\nsystem using two types of modulations, the on-off keying (OOK) modulation\nand the pulse-position modulation (16-PPM). The effect of PC on the performance\nof FSO communications is also examined in this study. We evaluated\nthe systemâ??s performance with two types of snow, wet snow and dry\nsnow, as well as with different rain regions. Results show that PC improves\nthe BER of the FSO system; a high rate of improvement is found for wet snow\nand rain. PC has almost no effect with dry snow because of the high attenuation\nand the limitations on transmitted power. The BER for 16-PPM is better\nthan that for OOK modulation.
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