arXiv subjects

Nicholas Vaiopoulos

Publications and source records attributed to Nicholas Vaiopoulos.

5 recordsLinked to original sources

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.

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arXiv2025

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.

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arXiv2025

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.

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arXiv2024

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.

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arXiv2023

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.

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