arXiv subjects

Mohammed Elamassie

Publications and source records attributed to Mohammed Elamassie.

4 recordsLinked to original sources

arXiv2026

Progressively Attenuated Multi-Branch Reception for Inter-HAPS Optical Links

Inter HAPS optical links can experience receiver saturation at short separations and become signal to noise ratio (SNR) limited at longer distances. This work proposes a saturation aware spatial multi branch intensity modulation direct detection receiver using nonoverlapping apertures with progressive attenuation and selection of the nonsaturated branch with the highest instantaneous SNR. A Gaussian beam model with finite aperture pointing loss and common two dimensional pointing jitter yields closed form branch level expressions for saturation, insufficient SNR, usability, and outage probabilities. Results show that additional branches suppress short range saturation outage, shift the minimum outage point toward shorter separations, and enable progressive attenuation to control the saturation SNR tradeoff. Monte Carlo simulations closely match the analytical results. Overall, the proposed architecture provides a low complexity approach to extending the usable dynamic range of inter HAPS optical receivers.

eess.SP↗

arXiv2026

A Novel Piecewise Atmospheric Attenuation Model for Free Space Optical Links in Vertical Heterogeneous Networks

Free-space optical (FSO) communication is emerging as a key backhaul technology for next-generation vertical heterogeneous networks (VHetNets), whose architecture spans satellites, high-altitude platform stations (HAPS), unmanned aerial vehicles (UAVs), and terrestrial nodes. Along these vertical and slant paths, optical beams traverse successive atmospheric layers that may contain clouds, fog, rain, and aerosols, conditions that conventional single-coefficient Beer-Lambert models typically handle only in isolation. Instead of such simplified formulas, we present a unified attenuation model that incorporates aerosols, fog, rain, cloud layers, and drizzle, accounts for the zenith angle, and provides a holistic estimate of the cumulative power loss across atmospheric layers. Numerical results show several-decibel attenuation variations across representative weather scenarios, while the difference between the proposed model predictions and the layer-resolved MODTRAN simulations remains within 1 dB, thereby validating the accuracy of the proposed model and its practical relevance for VHetNet link-budget studies.

eess.SP↗

arXiv2021

Hybrid RF/VLC Systems: A Comprehensive Survey on Network Topologies, Performance Analyses, Applications, and Future Directions

Wireless communications refer to data transmissions in unguided propagation media through the use of wireless carriers such as radio frequency (RF) and visible light (VL) waves. The rising demand for high data rates, especially, in indoor scenarios, overloads conventional RF technologies. Therefore, technologies such as millimeter waves (mmWave) and cognitive radios have been adopted as possible solutions to overcome the spectrum scarcity and capacity limitations of the conventional RF systems. In parallel, visible light communication (VLC) has been proposed as an alternative solution, where a light source is used for both illumination and data transmission. In comparison to RF links, VLC links present a very high bandwidth that allows much higher data rates. VLC exhibits also immunity to interference from electromagnetic sources, has unlicensed channels, is a very low power consumption system, and has no health hazard. VLC is appealing for a wide range of applications including reliable communications with low latency such as vehicle safety communication. Despite the major advantages of VLC technology and a variety of its applications, its use has been hampered by its cons such as its dependence on a line of sight connectivity. Recently, hybrid RF/VLC systems were proposed to take advantage of the high capacity of VLC links and better connectivity of RF links. Thus, hybrid RF/VLC systems are envisioned as a key enabler to improve the user rates and mobility on one hand and to optimize the capacity, interference and power consumption of the overall network on the other hand. This paper seeks to provide a detailed survey of hybrid RF/VLC systems. This paper represents an overview of the current developments in the hybrid RF/VLC systems, their benefits and limitations for both newcomers and expert researchers.

eess.SP↗

arXiv2020

Spatial power spectrum of natural water turbulence with any average temperature, salinity concentration and light wavelength

The power spectrum of water optical turbulence is shown to vary with its average temperature $\left\langle T \right\rangle$ and average salinity concentration $\left\langle S \right\rangle$, as well as with light wavelength $λ$. This study explores such variations for $\left\langle T \right\rangle \in \left[ {0\ ^\circ\rm{C},30\ ^\circ\rm{C}} \right]$, $\left\langle S \right\rangle \in \left[ {0\ \rm{ppt},40\ \rm{ppt}} \right]$ covering most of the possible natural water conditions within the Earth's boundary layer and for visible electromagnetic spectrum, $λ\in \left[400\ nm, 700\ nm \right]$. For illustration of the effects of these parameters on propagating light we apply the developed power spectrum model for estimation of the scintillation index of a plane wave (the Rytov variance) and the threshold between weak and strong turbulence regimes.

physics.ao-ph↗