  According to the physical phenomena of atmospheric channels and wave
propagation, performance of wireless communication systems can be optimized by
simply adjusting its parameters. This way is more economically favorable than
consuming power or using processing techniques. In this paper for the first
time an optimization problem is developed on the performance of free-space
optical multi-input multi-output (FSO-MIMO) communication system. Also it is
the first time that the optimization of FSO is developed under saturated
atmospheric turbulences. In order to get closer to the actual results, the
effect of pointing error is taken into considerations. Assuming MPSK, DPSK
modulation schemes, new closed-form expressions are derived for Bit Error Rate
(BER) of the proposed structure. Furthermore, an optimization is developed
taking into account the beam width as the variable parameter, and BER as the
objective function, there is no constraint in this system. The obtained results
can be a useful outcome for FSO-MIMO system designers in order to limit effects
of pointing error as well as atmospheric turbulences and thus achieves optimum
performance.
