Objectives: The first installed optical fiber links were used for transmitting the telephony signals about 6 Mb/s over distance of around 10 km. Since the demand on communication network increases for bandwidth hungry services such as voice, video and data, telecommunication companies greatly enhanced the capacity of fiber lines. As increasing in the research further more leads to development in Wireless optical communication. These systems work in the same IR range in which normally the Optical fiber systems work. Methods/Statistical analysis: The Free-space optical interconnection (FSOI) technology enables high interconnection speed in next-generation services. FSOI uses laser links between the transmitter and receiver provides a lower propagation delay due to the line-of-sight (LOS) path and lower index of refraction of air. The performance of the links highly dependent on different weather conditions such as Fog, Turbulence and Rain. In this paper the combined result of Fog, Rain and Turbulence on FSOI links are compared and the suitable modulation technique is suggested to increase the spacing between optical transmitter and receiver. Findings: This paper gives the idea of which modulation technique is better for outdoor environment and to multiple users. This paper shows that maximum distance of 4 km between transmitter and receiver is possible by using M-QAM (M=16). Application/Improvements: Longer distance transmission provided with less loss of data even in high attenuation (30 dB/km) also provides multi user transmission. © 2017 IEEE.