Testbed Emulator of Satellite-to-Ground FSO Downlink Affected by Atmospheric Seeing Including Scintillations and Clouds  
[PERSON]  
1 Institute of Microwave and Photonic Engineering, Graz University of Technology, 12 Infeldgasse, 8010 Graz, Austria; [EMAIL_ADDRESS] (E.L.); [EMAIL_ADDRESS] (P.B. )2 Department of Information, Electronics and Telecommunications, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy; [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Information, Electronics and Telecommunications, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy; [EMAIL_ADDRESS]  
[PERSON]  
1 Institute of Microwave and Photonic Engineering, Graz University of Technology, 12 Infeldgasse, 8010 Graz, Austria; [EMAIL_ADDRESS] (E.L.); [EMAIL_ADDRESS] (P.B. )2 Department of Information, Electronics and Telecommunications, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy; [EMAIL_ADDRESS]  
[PERSON]  
1 Institute of Microwave and Photonic Engineering, Graz University of Technology, 12 Infeldgasse, 8010 Graz, Austria; [EMAIL_ADDRESS] (E.L.); [EMAIL_ADDRESS] (P.B. )2 Department of Information, Electronics and Telecommunications, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy; [EMAIL_ADDRESS]  
Footnote 1: email: {[[https://www.mdpi.com/journal/electronics/article/pdf/10](https://www.mdpi.com/journal/electronics/article/pdf/10)]([https://www.mdpi.com/journal/electronics/article/pdf/10](https://www.mdpi.com/journal/electronics/article/pdf/10))  
number of broadband services that require low-latency performance [1]. As stated in [3], the planned FSO data throughput for LEO satellites is expected to reach 200 Gbps in the foreseen future. Nevertheless, FSO technology enabling secure and extremely high data rate communication triggers a need for excessive testing and characterization of the atmospheric propagation channel. Both commercially produced scintillometers and systems based on delayed tilt anisoplanatism technology are applied for measuring atmospheric-turbulence-induced fading, used for FSO operation range between 1 km and 13.5 km [4]. Moreover, sonic anemometer-thermometer data are used in [4] to observe the wind speed and temperature changes and their influence over near-surface atmospheric turbulence within the boundary layer. Although those technologies offer decent results, they are mainly used for horizontal links. A piece of novel key equipment presented in [5] that is under extensive testing implements technology utilizing laser guide star systems installed in most observatories. While it is still in an early development phase, it is claimed that backscatter-effect-based technology applying Rayleigh beaconing and collecting telescope offers a reliable evaluation of slant atmospheric turbulence profiles. In contrast to this intricate but highly productive method, a state-of-the-art concept for a compact device implementing an interferometric refractive index sensor is given in [6]. This interferometric approach widely used in the field of meteorology science offers a solution for figuring out the fringe frequency (i.e., atmospheric refractive index) that is easy for use in an outdoor environment, and once installed in an unmanned aircraft system, a vertical atmospheric turbulence profile can be built. In parallel with those initiatives involving tremendous resources, a vertical profile of refractive index structure parameter used for investigation of clear-air scintillations in terms of space-to-ground downlinks is well approximated based on Radiosonde Observation (RAOB) data [7; 8]. Apart from the listed measurement methods, the most promising technology for the mitigation of atmospheric turbulence is adaptive optics systems. In order to compensate for the phase distortion, the reconstruction process is based on a deformable mirror controlled by a wave-front sensor.