BPSK Subcarrier Intensity Modulated Free-Space
Optical Communications in Atmospheric Turbulence
Wasiu O. Popoola, Student Member, IEEE, and Zabih Ghassemlooy, Senior Member, IEEE
Abstract—Free-space optical communications (FSO) propagated
over a clear atmosphere suffers from irradiance fluctuation
caused by small but random atmospheric temperature fluctuations.
This results in decreased signal-to-noise ratio (SNR) and
consequently impaired performance. In this paper, the error
performance of the FSO using a subcarrier intensity modulation
(SIM) based on a binary phase shift keying (BPSK) scheme in
a clear but turbulent atmosphere is presented. To evaluate the
system error performance in turbulence regimes from weak to
strong, the probability density function (pdf) of the received
irradiance after traversing the atmosphere is modelled using the
gamma-gamma distribution while the negative exponential distribution
is used to model turbulence in the saturation region and
beyond. The effect of turbulence induced irradiance fluctuation
is mitigated using spatial diversity at the receiver. With reference
to the single photodetector case, up to 12 dB gain in the electrical
SNR is predicted with two direct detection PIN photodetectors in
strong atmospheric turbulence
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