Browsing by Author "Khallaf, H. S."

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    Composite fading model for aerial MIMO FSO links in the presence of atmospheric turbulence and pointing errors
    (IEEE, 2021-06) Khallaf, H. S.; Kato, K.; Mohamed, E. M.; Sait, S. M.; Yanikomeroglu, H.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    In this letter, we introduce accurate approximation expressions for composite fading channel model and outage probability of multiple-input multiple-output (MIMO) free space optical (FSO) link between two unmanned aerial vehicles (UAVs) in hovering state. In our derivations, we consider the effects of weather attenuation, random fluctuations in UAVs' positions and orientations, and atmospheric turbulence. Our proposed model is unified with respect to turbulence effect, which means it is valid for different atmospheric turbulence models. We show the accuracy of the proposed model through comparisons with Monte Carlo simulations under different channel conditions.
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    Comprehensive study on UAV-based FSO links for high-speed train backhauling
    (The Optical Society, 2021-09-20) Khallaf, H. S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
    In this paper, we introduce the idea of using unmanned aerial vehicle (UAV)-based free-space optical communication systems to backhaul high-speed trains. We introduce a composite channel model that includes effects of both atmospheric turbulence and pointing errors due to position/orientation deviation. Based on the derived fading model, we present an approximation expression for the outage probability. The performances of the proposed air-relay and traditional ground-relay systems are compared under fair conditions. Pointing-acquisition-tracking (PAT) complexity and coverage distance under different weather conditions and different fading levels are considered as comparison metrics. Furthermore, we investigate the effect of several parameters such as beam divergence angle, displacement deviation variance, and UAV operation altitude on system performance. Our results reveal that air relay helps in mitigating the fog effect, can achieve longer coverage distance, and relaxes PAT system design.
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    Wi-Fi assisted two-hop relay probing in WiGig device to device networks
    (IEEE, 2021-06) Mohamed, E. M.; Khallaf, H. S.; Uysal, Murat; Elhalawany, B. M.; Fouda, M. M.; Electrical & Electronics Engineering; UYSAL, Murat
    Relaying is a key technology for millimeter wave communications to extend the range and to route around blockages. In practical implementation of relaying systems, probing is required to identify proper neighbor terminals which will serve as relays. There is however an inherent trade-off between relay probing and required overhead. In this paper, we consider WiGig (IEEE 802.11ad) devices, which are multiband capable with Wi-Fi support, and propose a Wi-Fi assisted relay probing for WiGig device-to-device networks. In the proposed scheme, Wi-Fi received signal strengths are used to pre-select the WiGig relays expected to maximize the spectral efficiency of the overall system. Then, only these pre-selected relays are used in online relay probing step. Simulation analysis demonstrate improvements in throughput and energy consumptions over existing relay probing schemes.