HAPS based FSO Links Performance Analysis and Improvement with Adaptive
Optics Correction
Abstract
This paper investigates the performance of high altitude platforms
(HAPS) based free-space optical (FSO) communication links including
HAPS-to-ground station (downlink), ground-to-HAPS (uplink) and
HAPS-to-HAPS (horizontal link) communications. The effects of
attenuation loss, atmospheric turbulence, pointing error and
angle-of-arrival (AOA) are taken into account. Also, the application of
adaptive optics correction, one of the most effective turbulence
mitigation techniques, is analyzed using the Zernike polynomials
representation. Closed-form expressions are obtained for probability
density function (PDF), cumulative distribution function (CDF), Rytov
variance, adaptive optics filter function and outage probability mainly
in terms of Meijer’s G function when both no adaptive optics correction
is used and adaptive optics correction is applied. Some selected results
are presented depending on the various parameters such as the HAPS
altitude, the ratio of vertical and horizontal deviations, beam waist,
Zenith angle, height of ground station, receiver aperture diameter,
channel state threshold and wind speed. The performance improvement with
adaptive optics correction is investigated by removing different Zernike
modes. We show that the downlik performance outperforms the uplink, the
performance of the horizontal link sharply increases above certain
altitude and communication links benefit from the adaptive optics
correction up to a certain level in terms of performance improvement.