Abstract:
Free Space Optical (FSO) communication involves the transmission of signal-modulated optical
radiation from a transmitter to a receiver through the atmosphere or outer space. The locationvariant
atmospheric channel degrades the performance of an FSO system under severe
atmospheric conditions such as the presence of fog, rain, haze, smoke, and atmospheric
turbulence, thus necessitating local atmospheric attenuation studies. One-year archived visibility
data and in - situ measured 1-minute integration time rain rate data at Akure were obtained from
Nigerian Meteorological Agency (NIMET) and the Department of Physics, Federal University of
Technology, Akure respectively. Fog-induced specific attenuation was computed at five optical
wavelengths of 650, 750, 850, 950, and 1550 nm, at two transmittance thresholds of 2% and 5%
using both Kruse and Kim Model. The rain-induced specific attenuation was computed using
Carbournea Model. The performances of Single-Input Single-Output (SISO) and Multi-Input
Multi-Output (MIMO) FSO systems in the presence of different attenuation was studied using
the parameters of a commercial optical transceiver (TereScope 5000) in OptiSystem 13.0
simulation software. A maximum fog-induced specific attenuation of about 122.14 dB/km was
observed on the 35th, 269th and 317th days of the year with visibility value as low as 0.3 km.
Generally speaking, the specific attenuations were observed to reduce with increasing optical
wavelengths, however, such improvement was equally observed to decline with increasing link
distance. A maximum rain - induced specific attenuation of about 10.93 dB/km was observed in
May, 2012. However, the attenuation values were generally observed to be much lower to those
that are fog - induced. The performance of the SISO - FSO system was seen to be adequate in the
clear sky and short link distances, but deteriorated at reduced visibility, higher turbulence
regimes and longer link distances. The performance was however improved with the introduction
V
of the MIMO technique which showed higher Q-factor values, „eye‟ height, increased received
power and lower bit error rate. It was observed that the extent of FSO system improvement was
higher at the 2% transmittance threshold than at 5%. The overall result will serve as a good tool
for planning FSO systems in the study area.
