SUMMARY
Free Space Optics (FSO) is an emerging solution for the last mile broad band connectivity where deployment of fiber is expensive. This wireless technology has attracted the researchers due to the ease of erecting along the windows and terrace and the abundant bandwidth available in the unlicensed band. Combining OFDM with FSO gives a hybrid technique - OFDM based FSO or FSO-OFDM in which OFDM symbol modulates the light that passes through free space. Various predictable and unpredictable phenomena cause variation in the light that causes the fading effect of the received signal. Besides the atmospheric effect, the signal power varies within the symbol. The link availability has been calculated by setting threshold power at the receiver. The simulation of the OFDM based FSO system under three climatic conditions namely summer, winter and rainy has been observed that shows the link availability is 99.3% for summer, 98.32% for winter and 98.99% for rainy condition. Under worst climatic condition link availability is 98.17%. Thus FSO- OFDM is able to provide better connectivity even under any atmospheric condition.