Abstract:
Free Space Optical (FSO) communication has been the most promising technology to overcome
bandwidth shortage of a continuously crowded wireless available spectrum. Over a terrestrial
FSO link, atmospheric turbulence caused fading along free space optic link. In order to mitigate
the effect, aperformance analysis for a single transmitter with N number of receiver in FSO
communication system employing Binary Phase Shift Keying (BPSK) Subcarrier Intensity
Modulation (SIM) in a gamma-gamma turbulent atmospheric channel was simulated using
MATLAB computational Software. A random binary sequence of +1′s and -1′s was generated in
conformity to source data modulated with BPSK modulation, the symbols are multiply with the
turbulent channel. The fading effect was also generated through the Probability Density Function
(PDF) of gamma-gamma model of the turbulent channel and additive white Gaussian noise was
added. The received signals are linearly combined using different diversity combiners such
Maximal Ratio Combiner (MRC), Equal Gain Combiner (EGC) and Selection Combiner (SC).
The effect of irradiance fading was mitigated by diversity combiners. The Bit Error Rates
(BER)and Signal to Noise Ratio (SNR) for respective EGC, MRC and SC are observedunder
gamma-gamma intensity fluctuations with log irradiance variance ( ) of 0.8, 1.6 and 3.5 and
validated with Additive White Gaussian Noise (AWGN) without combiner. The simulation
results show that at N number of receiver, MRC compensated for about 13% than EGC and 69%
SC in signal to noise. Alsoat 6dB and 12dB with different normalized log irradiance variance, it
has minimal value in bit error rate than other diversity combiners when compared with an ideal
channel. MRC has the best performance in the three diversity receptions employed. The overall
results also suggest the model capability of mitigatingatmospheric turbulence especially for the
5G wireless network in terrestrial link.
