9 research outputs found
Analytical Channel Model and Link Design Optimization for Ground-to-HAP Free-Space Optical Communication Networks
Integrating high altitude platforms (HAPs) and free-space optical (FSO)
communications is a promising solution to establish high data rate aerial links
for the next-generation wireless networks. However, practical limitations such
as pointing errors and angle-of-arrival (AOA) fluctuations of the optical beam
due to the orientation deviations of hovering HAPs make it challenging to
implement HAP-based FSO links. For a ground-to-HAP FSO link, tractable,
closed-form statistical channel models are derived in this paper to simplify
the optimal design of such systems. The proposed models include the combined
effects of atmospheric turbulence regimes (i.e., log-normal and gamma-gamma),
pointing error induced geometrical loss, pointing jitter variance caused by
beam wander, detector aperture size, beam-width, and AOA fluctuations of the
received optical beam. The analytical expressions are corroborated by
performing Monte-Carlo simulations. Furthermore, closed-form expressions for
the outage probability of the considered link under different turbulence
regimes are derived. Detailed analysis is carried out to optimize the
transmitted laser beam and the field-of-view of the receiver for minimizing
outage probability under different channel conditions. The obtained analytical
results can be applied to finding the optimal parameter values and designing
ground-to-HAP FSO links without resorting to time-consuming simulations.Comment: 11 pages, 13 figures, accepted on May 22, 2020, for publication in
IEEE/OSA Journal of Lightwave Technolog
Analytical Channel Model and Link Design Optimization for Ground-to-HAP Free-Space Optical Communications
Integrating high altitude platforms (HAPs) and free-space optical (FSO)
communications is a promising solution to establish high data rate aerial links
for the next-generation wireless networks. However, practical limitations such
as pointing errors and angle-of-arrival (AOA) fluctuations of the optical beam
due to the orientation deviations of hovering HAPs make it challenging to
implement HAP-based FSO links. For a ground-to-HAP FSO link, tractable,
closed-form statistical channel models are derived in this paper to simplify
the optimal design of such systems. The proposed models include the combined
effects of atmospheric turbulence regimes (i.e., log-normal and gamma-gamma),
pointing error induced geometrical loss, pointing jitter variance caused by
beam wander, detector aperture size, beam-width, and AOA fluctuations of the
received optical beam. The analytical expressions are corroborated by
performing Monte-Carlo simulations. Furthermore, closed-form expressions for
the outage probability of the considered link under different turbulence
regimes are derived. Detailed analysis is carried out to optimize the
transmitted laser beam and the field-of-view of the receiver for minimizing
outage probability under different channel conditions. The obtained analytical
results can be applied to finding the optimal parameter values and designing
ground-to-HAP FSO links without resorting to time-consuming simulations.Comment: 11 pages, 13 figures, accepted on May 22, 2020, for publication in
IEEE/OSA Journal of Lightwave Technolog
Performance Evaluation of Coagulation Process in Removal of Low Turbidity and Color from Water Using Different Inorganic Coagulants
This research work was carried out in lab scale using a Jar-test set up. In order to compare the performance of four inorganic coagulants (poly aluminum chloride, ferro sulfate, ferric chloride, aluminum sulfate) in removal of turbidity and color from water, three independent variables (turbidity, color and coagulants dosage) were investigated. The region of exploration for the process was taken as the area enclosed by turbidity (10, 20, 50 NTU), color (5, 10 TCU) and concentration of coagulants (5, 10, 15, 120, 25, 30 mg/l) boundaries. The rapid and slow mixing steps were provided by the rate of 80 rpm for 1 min and 30 rpm for 20 min, respectively. The samples were then remained for 30 min as settling stage. Four parameters including turbidity, electrical conductivity (EC), pH and color were measured from the samples supernatant. Settling characteristics of the flocs formed were descriptively reported as poor, fair, good and excellent. From the results, poly aluminum chloride with concentration of 5 mg/l was found to be the best for the removal of turbidity (99-99.8 %) and color (100 %). However, fine flocs with very good settling velocity was observed at the condition with initial turbidity of 10, 20, 50 NTU. Increase in EC along with decrease in alkalinity was obtained as the coagulants concentrations were increased. The maximum and minimum amount of increase in EC and TDS were resulted from ferric chloride and poly aluminum chloride, respectively