Traditional cellular base stations with downtilted antennas are designed primarily to serve ground users. However, the advancements of drone technology and the increasing number of aerial users have made it challenging to provide reliable cellular coverage in the sky using conventional infrastructure. To address this, we propose overlaying a portion of existing terrestrial base stations with uptilted antennas, while retaining their downtilted antennas for ground coverage. This approach aims to provide seamless cellular connectivity for aerial users without compromising ground user performance. Using stochastic geometry, we analyze the coverage probability for aerial users and examine interference dynamics from uptilted and downtilted antennas. Our results demonstrate significant coverage improvements for aerial users even with small overlay percentages, offering a cost-effective solution. Furthermore, we find that this approach does not adversely affect ground user performance. These insights provide valuable guidelines for future research and deployment of overlaid networks supporting both aerial and ground users.

Unmanned Aerial Vehicles (UAVs) are increasingly used in a plethora of applications such as shipping, surveillance, and search-and-rescue. For UAVs to operate safely, reliable cellular connectivity is essential. Utilizing the terrestrial networks for aerial connectivity has been proposed, but the 3D radiation pattern of base station antennas significantly affects the performance of aerial links. To address this, we evaluate the coverage probability of cellular-connected UAVs, considering vertical antenna gain, by leveraging tools from stochastic geometry. We also analyze how the UAV hovering height, tilt angle and 3D antenna beamwidth influence the reliability of the communication link. Our results show that a down-tiled antenna does not only improve the connectivity of terrestrial users but also its cellularconnected UAVs counterpart. Moreover, the coverage probability of the UAV-UE becomes saturated at large down-tilt angles at the TBSs due to the antenna sidelobe gain at the serving and interfering TBSs. We also found that the significant increase of the vertical antenna beamwidth improves the UAV user coverage probability especially at relatively low hovering altitudes thanks to the increase of the desired signal strength compared to the interference power.

On-board battery consumption, cellular disconnectivity, and frequent handoff are key challenges for unmanned aerial vehicle (UAV) based delivery missions, a.k.a., cargo-UAV. Indeed, with the introduction of UAV technology into cargo shipping and logistics, designing energy-efficient paths becomes a serious issue for the next retail industry transformation. Typically, the latter has to guarantee uninterrupted or slightly interrupted cellular connectivity for the UAV’s command and control through a small number of handoffs. In this paper, we formulate the trajectory planning as a multi-objective problem aiming to minimize both the UAV’s energy consumption and the handoff rate, constrained by the UAV battery size and disconnectivity rate. Due to the problem’s complexity, we propose a dynamic programming based solution. Through simulations, we demonstrate the efficiency of our approach in providing opti-mized UAV trajectories. Also, the impact of several parameters, such as the cargo-UAV altitude, disconnectivity rate, and type of environment, are investigated. The obtained results allow to draw recommendations and guidelines for cargo-UAV operations.

In this paper, we analyze the downlink coverage probability and rate of an aerial user in vertical HetNets (VHetNets) comprising aerial base stations (aerial-BSs) and terrestrial-BSs. The locations of terrestrial-BSs are modeled as an infinite 2-D Poisson Point Process (PPP), while the locations of aerial-BSs are modeled as a finite 2-D Binomial Point Process (BPP). Our cellular-to-air (C2A) channel model incorporates line-of-sight (LoS) and non-LoS transmissions between terrestrial-BSs and a typical aerial user, while we assume LoS transmissions for all aerial links. We assume that the aerial user is associated with an aerial-BS or terrestrial-BS that provides the strongest average received power. Using stochastic geometry, we derive exact and approximate expressions of the coverage probability and rate in terms of interference power's Laplace transform. The expressions are simplified assuming only LoS transmissions for the C2A channels. This enables easy-to-compute equations with good accuracy at elevated aerial user heights. We find that aerial users hovering at low altitudes tend to connect to aerial-BSs in denser terrestrial environments. Employing directive beamforming at aerial-BSs guarantees an acceptable performance at the aerial user by reducing interference signals received from the aerial-BSs. In denser terrestrial networks, the performance at the aerial user degrades substantially despite beamforming.

Unmanned aerial vehicles (UAVs) can be users that support new applications, or be communication access points that serve terrestrial and/or aerial users. In this paper, we focus on the connectivity problem of aerial users when they are exclusively served by aerial base stations (BS), i.e., UAV-BSs. Specifically, the 3D placement problem of a directional-antenna equipped UAV-BS, aiming to maximize the number of covered aerial users under a spectrum sharing policy with terrestrial networks, is investigated. Given a known spectrum sharing policy between the aerial and terrestrial networks, we propose a 3D placement algorithm that achieves optimality. Simulation results show the performance of our approach, in terms of number of covered aerial users for different configurations and parameters, such as the spectrum sharing policy, antenna beamwidth, transmit power, and aerial users density. These results represent novel guidelines for exclusive aerial networks deployment and applications, distinctively for orthogonal and non-orthogonal spectrum sharing policies with terrestrial networks.

Ubiquitous wireless connectivity is critical for the operation of aerial users. In this paper, we investigate the downlink coverage probability of a typical aerial user served by a network of terrestrial-BSs and aerial-BSs, which we refer to as the vertical HetNet (VHetNet). We model the terrestrial- BSs as an infinite 2-D Poisson point process (PPP) and aerial-BSs as a finite 2-D Binomial point process (BPP). A typical aerial user is assumed to be associated with the BS that provides the strongest biased average received signal power. Closed-form expressions for the association probabilities to a terrestrial-BS and an aerial-BS are derived. Under the assumption of an interference-limited network, we derive an expression for the coverage probability in terms of the Laplace transform of the aggregate interference power. Several design insights are presented, showing that the coverage probability does not have a steady behavior with the aerial user height; and a denser aerial-BS network improves the overall coverage probability. Moreover, the results reveal that the coverage probability under unbiased aerial user association always outperforms its biased counterpart.

In this paper, we unify the performance analysis for the outage probability (OP) and the bit-error rate (ABER) of relay-assisted dual-hop free-space optics (FSO) transmission under heterodyne detection and intensity modulation/direct detection (IM/DD). The FSO link experiences the generalized Malaga-m distribution with pointing errors. under the assumption of fixed and variable gain relaying schemes, we derive the analytical closedform expressions for the performance metrics in terms of bivariate Fox-H function (FHF). Finally, we present some Monte-carlo simulation results to corroborate the new derived expressions.

This paper investigates the impact of radio frequency (RF) cochannel interference (CCI) on the performance of dual-hop free-space optics (FSO)/RF relay network. The considered FSO/RF system operates over mixed Malaga-M/composite fading/shadowing generalized-K (GK) channels with pointing errors. The H-transform theory, wherein integral transforms involve Fox's H-functions as kernels, is embodied into a unifying performance analysis framework that encompasses closed-form expressions for the outage probability, the average bit error rate (BER), and the ergodic capacity. By virtue of some H-transform asymptotic expansions, the high signal-to-interference-plus-noise ratio (SINR) analysis culminates in easy-to-compute expressions of the outage probability and BER.