arXiv subjects

Mohammad-Ali Khalighi

Publications and source records attributed to Mohammad-Ali Khalighi.

6 recordsLinked to original sources

arXiv2026

Statistical Characterization of Wind-Induced Beam Refraction and UAV Instability in Water-to-Air Optical Channels

Direct water-to-air (W2A) optical communications experience strong beam refraction at the dynamic sea surface and unmanned aerial vehicle (UAV) instability. This letter proposes a novel and tractable statistical channel model for a vertical W2A link between an underwater node and an UAV under varying wind speeds, modeling wind-induced pointing errors with a Beta mixture fitted via the Expectation-Maximization algorithm. By accounting for link interruptions due to total internal reflection (TIR) and effective receiver field-of-view limitations, we derive closed-form expressions for the channel distribution and link outage probability. Our analysis reveals a fundamental TIR-induced outage floor limiting link reliability and providing insight for robust W2A system design.

eess.SP↗

arXiv2026

Second-Order Fade Statistics in Underwater Optical Wireless Communications in Air-Bubble and Turbidity-Impaired Environments

The propagation of underwater optical signals through air-bubble-impaired channels induces irradiance fluctuations and partial line-of-sight blockages that degrade the performance of underwater optical wireless communication (UOWC) systems. Although the first-order fading statistics of such channels have been extensively investigated, their second-order statistics, namely the level crossing rate (LCR) and average fade duration (AFD), remain rather unexplored. This paper presents a theoretical and experimental characterization of the LCR and AFD in bubble-impaired UOWC channels under different bubble sizes and water turbidity conditions. Two analytical approaches are developed based on Rice's formula and on the cumulative distribution function (CDF) together with the bivariate CDF of the sampled irradiance, and are validated experimentally. The results show that water turbidity has a negligible effect on fade statistics under small-bubble conditions. In contrast, for large bubbles, turbid water leads to shorter but more frequent fades than tap water, as particle-induced beam spreading reduces the likelihood of deep fades and prolonged blockage events. Finally, the derived second-order statistics are applied to evaluate the packet outage probability (POP) performance using a two-state Markov channel model, demonstrating that the higher fade rate in the turbid water case results in a larger POP despite the shorter fade durations.

eess.SP↗

arXiv2026

Statistical Channel Model for FSO Systems Assisted by a UAV-Mounted IRS

Integrating optical intelligent reflecting surfaces (IRSs) into aerial platforms, such as unmanned aerial vehicles (UAVs), has been proposed to relax the line-of-sight (LoS) constraint, extend coverage, and enhance deployment flexibility of free space optical (FSO) systems. However, misalignment errors induced by the UAV hovering, in both position and orientation, may degrade connectivity and impair the end-to-end channel quality. In this paper, we develop novel expressions for the electric fields incident on and reflected by an optical IRS, based on the Huygens-Fresnel principle. The resulting expressions are applicable for any combination of incident and reflected propagation directions. Building on this framework, we derive a closed-form statistical channel model that captures the geometric and misalignment losses of an FSO link assisted by a UAV-mounted IRS in the presence of random UAV fluctuations. In particular, we develop a statistical model for the beam misalignment at the receiver lens, assuming Gaussian fluctuations in both the UAV position and orientation. The proposed analytical model is validated through Monte Carlo (MC) simulations and is further used to provide practical design guidelines regarding the optimal placement of the UAV-mounted IRS for the minimization of the outage probability.

eess.SP↗

arXiv2026

End-to-End Optical Propagation Modeling for Water-to-Air Channels under Sea Surface and UAV Effects

Underwater observatories have recently emerged as an efficient solution for marine biodiversity monitoring. The primary objective of this work is to enable efficient and cost-effective data muling from underwater sensors by investigating the use of optical wireless communications to transmit data from the underwater sensors to an aerial node close to the water surface, such as an unmanned aerial vehicle (UAV). More specifically, we utilize a direct water-to-air (W2A) optical communication link between the sensor node equipped with an LED emitter and the UAV equipped with an ultra-sensitive receiver, i.e., a silicon photo-multiplier. As a main contribution, we develop a comprehensive Monte Carlo-based ray-tracing algorithm to characterize this complex channel. This framework rigorously incorporates the impact of air bubbles modeled through the Mie scattering theory, a realistic sea surface representation derived from the JONSWAP spectrum, and an analytical derivation of the channel loss resulting from UAV instability under wind-induced perturbations. Furthermore, we conduct a comprehensive analysis of the W2A channel, examining the influence of key parameters such as wind speed, transmitter configurations, and receiver characteristics. The end-to-end performance evaluation demonstrates the practical feasibility of the proposed approach, achieving a bit-error rate of $10^{-3}$ at a data rate of 1 Mbps for a transmitter depth of 47 m and wind speeds up to 13 m/s.

eess.SP↗

arXiv2023

Single-Photon Counting Receivers for Optical Wireless Communications in Future 6G Networks

Optical wireless communication (OWC) offers several complementary advantages to radio-frequency wireless networks such as its massive available spectrum; hence, it is widely anticipated that OWC will assume a pivotal role in the forthcoming sixth generation wireless communication networks. Although significant progress has been achieved in OWC over the past decades, the outage induced by occasionally low received optical power continues to pose a key limiting factor for its deployment. In this work, we discuss the potential role of single-photon counting (SPC) receivers as a promising solution to overcome this limitation. We present an overview of the applications of SPC-based OWC systems in 6G networks, introduce their major performance-limiting factors, propose a performance enhancement framework to tackle these issues, and identify critical areas of open problems for future research.

cs.IT↗

arXiv2021

Resource Allocation in a Quantum Key Distribution Network with LEO and GEO trusted-repeaters

Quantum Key Distribution~(QKD) is a technology that enables the exchange of private encryption keys between two legitimate parties, using protocols that involve quantum mechanics principles. The rate at which secret keys can be exchanged depends on the attenuation that is experienced. Therefore, it is more convenient to replace many terrestrial fiber segments (and repeaters) by just few optical satellite links that would enable flexible global coverage. Then, the satellite nodes can take the role of trusted-relays, forwarding the secret keys from source to destination. However, since the rate at which secret keys can be generated in each quantum link is limited, it is very important to select the intermediate satellite nodes to inter-connect ground stations efficiently. This paper studies the most convenient allocation of resources in a QKD network that combines complementary connectivity services of GEO and LEO satellites. The aim of the centralized routing algorithm is to select the most convenient trusted-relays to forward the secret keys between pairs of ground stations, verifying the constraints that satellite-to-ground and inter-satellite quantum channels have.

eess.SP↗