Abstract—Free Space Optical (FSO) communication system is an optical wireless connectivity operating at an unlicensed optical spectrum, with lots of advantages over the conventional Radio Frequency (RF) transmission. However, the performance of the FSO channel is limited due to atmospheric turbulence and severe weather conditions. There are many authors who have worked on mitigating these effects by using Spatial Diversity (SD) with 2X2-MIMO systems and few have worked up to 4X4-MIMO systems, blended with BPSK-Sub-carrier Intensity Modulation (BPSK-SIM) under the log-normal atmospheric turbulence model. However, in this paper, we extended the SD technique to higher-order configurations such as 8X8-MIMO system in order to improve the performance obtained from lower-order FSO systems. This study was considered at log-irradiance variance values of 0.1 and 0.9, representing the mildly weak and moderately weak atmospheric turbulence regimes respectively. This work has presented the performance analysis of various FSO-SD techniques. As a result, at BER of 10-9 the 1X8, 4X4, 6X6 and 8X8 higher-order SD systems were ≈46%, 55%, 61% and 69% respectively better than the "non-diversity" FSO system during the moderately weak atmospheric condition. Also, their channel capacities were ≈74%, 77%, 85% and 89% respectively better than the "non-diversity" FSO system at SNR of 30 dB. 
 

Index Terms—Atmospheric turbulence, BPSK-Sub-carrier intensity modulation, free space optical communication systems, higher-order spatial diversity technique, log-normal atmospheric turbulence model
 

Cite: Okikiade A. Layioye, Thomas J. O. Afullo, and Pius A. Owolawi, "Performance Analysis of FSO Communication Systems with Higher-Order Spatial Diversity Schemes Using BPSK-SIM over Log-Normal Atmospheric Turbulence Channels," Journal of Communications, vol. 12, no. 6, pp. 312-327, 2017. Doi: 10.12720/jcm.12.6.312-327.