  This paper investigates the asymptotic BER performance of coherent optical
wireless communication systems in Gamma-Gamma turbulence when applying the
V-BLAST MIMO scheme. A new method is proposed to quantify the performance of
the system and mathematical solutions for asymptotic BER performance are
derived. Counterintuitive results are shown since the diversity gain of the
V-BLAST MIMO system is equal to the number of the receivers. As a consequence,
it is shown that when applying the V-BLAST MIMO scheme, the symbol rate per
transmission can be equal to the number of transmitters with some cost to
diversity gain. This means that we can simultaneously exploit the spatial
multiplexing and diversity properties of the MIMO system to achieve a higher
data rate than existing schemes in a channel that displays severe turbulence
and moderate attenuation.
