Ergodic capacity and outage capacity analysis for multiple-input single-output free-space optical communications over composite channels

Free-space optical (FSO) communications have attracted significant attention recently. The ergodic capacity and outage capacity of a multiple-input single-output FSO communication system are investigated. Initially, a composite channel model including distance-dependant atmospheric loss, pointing error, and atmospheric turbulence is derived. To show different weather conditions, both the weak and strong atmospheric turbulence conditions are taken into account. Moreover, the statistical characteristics of two composite channels (i.e., weak turbulence composite channels and strong turbulence composite channels) are provided. Furthermore, approximated expressions of the ergodic capacity and closed-form expressions of the outage capacity are derived under the two composite channels, respectively. Numerical results finally substantiate that the derived theoretical expressions can provide a very good approximation to the simulation results.