Optical Spatial Modulation with Diversity Combiner in Dual-Hops Amplify-and-Forward Relay Systems Over Atmospheric Impairments

In this paper, we analyzed a dual-hop optical spatial modulation channel state information-assisted amplified and forward (AF) relay system with spatial diversity combiner under the influence of gamma-gamma atmospheric turbulence induced fading and pointing error impairments. Maximum ratio combiner (MRC) and equal gain combiner (EGC) with heterodyne detection are considered at the destination as mitigation tools to improve the system error performance. The statistical characteristics of AF relay in terms of moment generating function (MGF), probability density function and cumulative density function are derived for both impairments. Based on these expressions, the average pairwise error probability for each of the combiners under study is determined and the average bit error rate (ABER) for the system is given by using union bounding technique. By utilizing the derived ABER expressions, the effective capacity for the considered system is then obtained. The effect of turbulence strength ranging from weak to strong levels and pointing errors in terms of beam width and jitter displacement are studied. The numerical results obtained show that the more the turbulence strength and/or pointing error increases, the more the error rate and effective capacity of the system deteriorates. Under the same conditions, the results confirmed that MRC system offers an optimal performance compared with EGC.