Free Space Optical (FSO) communications is the only practical candidate for realizing universal network coverage
between ground and airborne nodes, satellites, and even moon and other nearby planets. When atmosphere (be it the
earth or Mars) is a part of the optical channel, attributes of scattering and turbulence bring about amplitude attenuation,
and scintillation, as well as beam wander and phase aberrations at the receiving aperture. Phase screens are usually used
in order to simulate the atmospheric fading channel and phase fluctuations. In this paper, different methods of generating
phase screens are compared based on their accuracy and computational complexity, as in most computer simulations, a
large ensemble of phase screens are required for averaging purposes.
To combat the focal plane intensity fading, caused by amplitude and phase variations in the received wave-front, it is
possible to replace the Single Input-Single Output (SISO) communications system with its Multiple Input Multiple
Output (MIMO) equivalent, which has the same total transmit power and receiving aperture area. Another alternative is
to equip the receiver with a state of the art Adaptive Optics (AO) correction system. Using average Bit Error Rate (BER),
as a performance metric, effectiveness of these two approaches are compared and it is shown that while a MIMO
configuration outperforms a basic AO system capable of only tilt corrections, an ideal AO system, which is able to
remove higher orders of Zernike modes can asymptotically perform as well as an equivalent MIMO configuration.