arXiv subjects

Harilaos G. Sandalidis

Publications and source records attributed to Harilaos G. Sandalidis.

8 recordsLinked to original sources

arXiv2026

Optimizing Coverage in Convex Quadrilateral Regions with a Single UAV

The integration of unmanned aerial vehicles (UAVs) into next-generation wireless networks has emerged as a promising solution for providing flexible and efficient coverage. This paper investigates the optimal deployment of a single UAV over an arbitrary convex quadrilateral region, employing a directional antenna with adjustable tilt that results in an elliptical ground coverage footprint. Two coverage scenarios are considered: (i) the largest inscribed ellipse, which maximizes coverage within the quadrilateral while excluding boundary regions, and (ii) the smallest circumscribed ellipse, which guarantees full coverage of the entire area. An optimization framework is developed to determine the optimal UAV altitude by examining path loss, signal-to-noise ratio (SNR), and energy consumption. Based on a widely adopted path loss model, the altitude that minimizes the maximum path loss is derived, while the effect of antenna directivity on maximizing the minimum SNR at the coverage boundary is also analyzed. Furthermore, UAV energy consumption is evaluated by accounting for hovering, forward flight, and vertical take-off operations. Numerical results illustrate the trade-offs among coverage efficiency, communication performance, and energy consumption under different propagation environments and antenna configurations. The analysis is further extended to all feasible inscribed and circumscribed ellipse configurations, providing a complete parametric characterization of the optimal altitude. In addition, a large-scale evaluation over randomly generated convex quadrilaterals offers a statistical assessment of the proposed framework and demonstrates its robustness under geometric variability.

eess.SY↗

arXiv2026

Parametrization of microbial survival models under UVC exposure

This work presents a unified framework for the parametrization and comparison of microbial survival models under UVC exposure. Four dose-response models - the single-target, multi-target, linear-quadratic, and two-stage decay models - are analyzed with respect to their mathematical structure, parameter identifiability, and biological interpretability, while ensuring physically meaningful parameter estimates. To address the limited size and lack of replication in published datasets, parameter uncertainty is quantified using a parametric bootstrap approach under multiplicative dose uncertainty. Model comparison combines goodness-of-fit in logarithmic survival space, the Akaike Information Criterion corrected for small samples, and identifiability considerations. Application to data for 32 microorganisms shows that no single model is universally optimal, highlighting that reliable model selection requires combining statistical performance with physical and biological consistency, and providing a robust basis for UVC survival analysis and disinfection modeling.

physics.med-ph↗

arXiv2026

Distance Distributions Between Nodes in Concentric Disk-Annulus or Sphere-Shell Regions

This letter derives closed-form expressions for the probability density function of the distance between two nodes located in heterogeneous concentric geometries, namely a disk or sphere and a surrounding annulus or spherical shell. Two scenarios are considered: (i) both nodes are independently distributed in different regions, disk or sphere and annulus or shell, and (ii) one node is static in the outer region while the other follows the stationary distribution of the random waypoint model in the inner region. The resulting expressions provide a tractable analytical tool for performance evaluation in concentric wireless regions.

cs.IT↗

arXiv2026

Internodal Distance Distributions for Static and Mobile Nodes in 2D/3D Wireless Networks

This letter presents a unified analytical framework for internodal distance distributions in 2D and 3D wireless networks, with nodes confined to concentric circular or spherical regions. Four deployment scenarios are considered, covering all combinations of static (uniform) and mobile (random waypoint-based) nodes. For each scenario, closed-form expressions for the internodal distance probability density functions are derived, incorporating both geometric constraints and spatial effects introduced by mobility. Equal-radius cases are also addressed. Beta-distribution approximations and Monte Carlo simulations demonstrate the accuracy and validity of the analytical results.

eess.SP↗

arXiv2026

Efficient UAV Coverage in Large Convex Quadrilateral Areas with Elliptical Footprints

Unmanned Aerial Vehicles (UAVs) have gained significant attention for improving wireless communication, especially in emergencies or as a complement to existing cellular infrastructure. This letter addresses the problem of efficiently covering a large convex quadrilateral using multiple UAVs, where each UAV generates elliptical coverage footprints based on its altitude and antenna tilt. The challenge is approached using circle-packing techniques within a unit square to arrange UAVs in an optimal configuration. Subsequently, a homography transformation is applied to map the unit square onto the quadrilateral area, ensuring that the UAVs' elliptical footprints cover the entire region. Numerical simulations demonstrate the effectiveness of the proposed method, providing insight into coverage density and optimal altitude configurations for different placement scenarios. The results highlight the scalability and potential for improving UAV-based communication systems, focusing on maximizing coverage efficiency in large areas with irregular shapes.

eess.SP↗

arXiv2025

On the Terminal Location Uncertainty in Elliptical Footprints: Application in Air-to-Ground Links

Wireless transmitters (Txs) that radiate downward in a direction often generate circular footprints on the ground. The configurational flexibility of these footprints is inherently limited as coverage adjustments are restricted to variations in radius, the only parameter available for tuning. This simplification is inadequate for scenarios that require asymmetric coverage, extended service areas, or dynamic footprint adaptation due to antenna tilt or changes in altitude of unmanned aerial vehicles (UAVs). In specific scenarios, the use of elliptical cells can offer increased flexibility for providing user coverage due to unique network characteristics. For example, an elliptical footprint can be produced when a practical directional antenna with unequal azimuth and elevation half-power beamwidths is used in high-speed railway networks. Another common scenario involves the production of an elliptical footprint when an airborne Tx radiates at an angle by tilting its directional antenna by a few degrees. This paper aims to investigate for the first time the association between the random location of the user within an elliptical coverage area and the performance of a wireless communication link considering these scenarios. We assume a UAV as a Tx, although a tall cellular base station tower could also be employed without losing generality. To gain a deeper understanding of the impact of random location, we derive the relevant distance and signal-to-noise ratio metrics and examine the outage probability for a single-user link, as well as the throughput in a multiuser scenario. This analysis accounts for both random terminal locations and fading impairments in both cases. The findings provide valuable insights into the performance of comparable wireless systems.

eess.SP↗

arXiv2022

Performance Analysis of Multi-Reconfigurable Intelligent Surface-Empowered THz Wireless Systems

In this paper, we introduce a theoretical framework for analyzing the performance of multi-reconfigurable intelligence surface (RIS) empowered terahertz (THz) wireless systems subject to turbulence and stochastic beam misalignment. In more detail, we extract a closed-form expression for the outage probability that quantifies the joint impact of turbulence and misalignment as well as the effect of transceivers' hardware imperfections. Our results highlight the importance of accurately modeling both turbulence and misalignment when assessing the performance of multi-RIS-empowered THz wireless systems.

eess.SP↗

arXiv2021

Cascaded Composite Turbulence and Misalignment: Statistical Characterization and Applications to Reconfigurable Intelligent Surface-Empowered Wireless Systems

Reconfigurable intelligent surfaces (RISs) empowered high-frequency (HF) wireless systems are expected to become the supporting pillar for several reliability and data rate hungry applications. Such systems are, however, sensitive to misalignment and atmospheric phenomena including turbulence. Most of the existing studies on the performance assessment of RIS-empowered wireless systems ignore the impact of the aforementioned phenomena. Motivated by this, the current contribution presents a theoretical framework for analyzing the performance of multi-RIS empowered HF wireless systems. More specifically, we statistically characterize the cascaded composite turbulence and misalignment channels in terms of probability density and cumulative distribution functions. Building upon the derived analytical expressions, we present novel closed-form formulas that quantify the joint impact of turbulence and misalignment on the outage performance for two scenarios of high interest namely cascaded multi-RIS-empowered free space optics (FSO) and terahertz (THz) wireless systems. In addition, we provide an insightful outage probability upper-bound for a third scenario that considers parallel multi-RIS-empowered FSO systems. Our results highlight the importance of accurately modeling both turbulence and misalignment when assessing the performance of such systems.

eess.SP↗