BPSK Subcarrier Intensity Modulated Free-Space Optical Communications in Atmospheric Turbulence Wasiu O. Popoola, Student Member, IEEE, and Zabih Ghassemlooy, Senior Member, IEEE

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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Average Symbol Error Probability of General-Order Rectangular Quadrature Amplitude Modulation of Optical Wireless Communication Systems Over Atmospheric Turbulence Channels

Average Symbol Error Probability of General-Order Rectangular Quadrature Amplitude Modulation of Optical Wireless Communication Systems Over Atmospheric Turbulence Channels


Abstract—Using an accurate exponential bound for
the Gaussian Q-function, we derive simple approximate
closed-form expressions for the average symbol
error probability (ASEP) of a free-space optical communication
link using subcarrier intensity modulation
(SIM) with general-order rectangular quadrature
amplitude modulation (QAM) over atmospheric
turbulence channels. To model the atmospheric turbulence
conditions, the log-normal and the gammagamma
distribution are used. Extensive numerical
and computer simulation results are presented in order
to verify the accuracy of the proposed mathematical
analysis.

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Performance Analysis of a Laser Ground-Station-to-Satellite Link With Modulated Gamma-Distributed Irradiance Fluctuations

Performance Analysis of a Laser
Ground-Station-to-Satellite Link With
Modulated Gamma-Distributed
Irradiance Fluctuations






Abstract—The performance of a ground-station-to-space

laser uplink with a Gaussian-beam wave model subject to

turbulence and beam wander effects is the topic of the

present study. The modulated gamma distribution is used to

describe the combined effect of the above two deteriorating

factors. At first, a versatile expression of the above probability

density function is deduced. We then derive novel closedform

expressions for its cumulative distribution function

and the moment-generating function. The scintillation index

and the probability of fade are hence readily evaluated. The

analysis is completed with the evaluation of the bit error

rate assuming heterodyne detection with differential phaseshift

keying. In order to attain an adequate error rate target,

we incorporate diversity at the satellite receiver. A proper

simulation scenario is adopted, and numerical results are

provided to verify the accuracy of the derived expressions.

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Performance Analysis of Decode-and-Forward Relaying in Gamma-Gamma Fading Channels

Performance Analysis of Decode-and-Forward
Relaying in Gamma-Gamma Fading Channels

Manav R. Bhatnagar, Member, IEEE

Abstract—We analyze performance of the decode-and-forward
(DF) protocol in the free space optical (FSO) links following
the Gamma-Gamma distribution. The cumulative distribution
function (cdf) and probability density function (pdf) of a random
variable containing mixture of the Gamma-Gamma and Gaussian
random variables is derived. By using the derived cdf and pdf,
average bit error rate of the DF relaying is obtained.

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Average BER Analysis of Differential Modulation in DF Cooperative Communication System over Gamma-Gamma Fading FSO Links

Average BER Analysis of Differential Modulation in DF Cooperative
Communication System over Gamma-Gamma Fading FSO Links

Manav R. Bhatnagar, Member, IEEE

Abstract—In this letter, we study differential modulation for decode-and-forward (DF) based free space optical (FSO) cooperative communication system over Gamma-Gamma fading channels. We derive exact bit error rate (BER) of the differential DF FSO system in terms of power series. The diversity order

and coding gain of the differentially modulated DF FSO system are analytically obtained. It is demonstrated by analysis and simulation that the differential DF FSO system is able to achieve significant performance gain over a non-cooperative direct transmission based differential FSO system.

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