  Multiple-input multiple-output (MIMO) and multiple-input single-output (MISO)
schemes have yielded promising results in free space optical (FSO)
communications by providing diversity against fading of the received signal
intensity. In this paper, we have analyzed the probability of error performance
of a \emph{muliple-input single-output} (MISO) free-space optical channel that
employs array(s) of detectors at the receiver. In this regard, we have
considered the \emph{maximal ratio combiner} (MRC) and \emph{equal gain
combiner} (EGC) fusion algorithms for the array of detectors, and we have
examined the performance of these algorithms subject to phase and pointing
errors for strong atmospheric turbulence conditions. It is concluded that when
the variance of the phase and pointing errors are below certain thresholds,
signal combining with a single array of detectors yields significantly better
performance than a multiple arrays receiver. In the final part of the paper, we
examine the probability of error of the single detector array receiver as a
function of the beam radius, and the probability of error is minimized by
(numerically) optimizing the beam radius of the received signal beams.
