Free Space Optics (FSO) is a current well-known technology, that utilizes light to transmit data, offering high data rates and easy deployment. This technology has been widely acknowledged as an alternative solution to the bandwidth constraints of the RF counterpart, although are limited with weather-prone conditions. The use of light as transmission medium leaves the FSO channel with huge bandwidth capacity to be efficiently utilized. Hence, this work proposes on the design and investigations of Optical Single Sideband (OSSB) modulation with Subcarrier Multiplexing (SCM) and Wavelength Division Multiplexing (WDM) in FSO systems. OSSB modulation can reduce bandwidth utilized per one user and improve spectral efficiency, while SCM and WDM can increase data capacity. This proposed architecture is designed using Optisystem software tool and the system performances are analysed based on simulation results presented by the Bit Error Rate (BER) and eye diagram performance metrices under various atmospheric conditions. Results shows that in clear condition, channels with two and three SCM can go more than 450 m, while for the same number in moderate fog conditions, a quality transmission could not transmit more than 200 m distances. Results also reveals that having more subchannels in the architecture do not have huge impact to the system performances compared to weather conditions impacts. This technique provides a useful insight on potential solutions for the emerging 5G standards which require accesses of multiple standards simultaneously.