The integration of uncrewed aerial vehicles (UAVs) with fifth-generation (5G) cellular networks has been a prominent research focus in recent years and continues to attract significant interest in the context of sixth-generation (6G) wireless networks. UAVs can serve as aerial wireless platforms to provide on-demand coverage, mobile edge computing, and enhanced sensing and communication services. However, UAV-assisted networks present new opportunities and challenges due to the inherent size, weight, and power constraints of UAVs, their controllable mobility, and the line-ofsight (LoS) characteristics of communication channels. This article discusses these opportunities and challenges from the viewpoint of mobile network operators (MNOs), and offers a novel perspective on efficiently utilizing modern city infrastructures for UAV deployment in typical urban scenarios. In these scenarios, UAV-mounted base stations (UAV-BSs) can significantly improve service continuity and network energy efficiency. We compare system performance in terms of user satisfaction and energy efficiency between conventional UAV deployment, which follows demand dynamics, and an alternative approach where UAVs land on urban infrastructure equipped with charging stations. To identify the preferred UAV locations, while considering the limited availability of such stations and environmental dynamics, we employ a data-driven genetic algorithm. This algorithm closely approximates the true optimal locations subject to a moderate computational budget.

Non-terrestrial networks (NTNs) have recently emerged as a promising paradigm for computation-intensive six-generation (6G) applications, which may range from augmented reality to disaster relief. Moreover, NTNs can cater to uninterrupted connectivity needs in both rural and urban areas. In urban settings, uncrewed aerial vehicles (UAVs) and high-altitude platform stations (HAPS) play crucial roles in supporting delay-sensitive computation applications for terrestrial UEs when terrestrial networks face limitations. Given the emerging interest in multi-connectivity for NTNs, this letter investigates UAV- and HAPS-assisted multi-connectivity computation offloading in urban areas. Specifically, we propose two novel multi-connectivity offloading strategies to improve the probability of timely task computation, along with a framework for optimizing the corresponding offloading probabilities onto HAPS and UAVs. Our results demonstrate that utilizing multi-connectivity in NTN-assisted offloading can achieve a 75% reduction in task computation delay as compared to scenarios with no offloading.

Pulsed laser deposition in vacuum at 220°C of GaAs layers heavily doped with Mn and/or Bi has been used to form nanostructures on i-GaAs (100) substrates. It is shown that, for the electrical activation of manganese, it is expedient to use subsequent annealing with an excimer laser pulse with a wavelength of 248 nm and a duration of 30 ns. The structures show an anomalous Hall effect with a hysteresis loop on the magnetic field dependence up to a Curie temperature of about 70 K. Negative magnetoresistance is observed up to temperatures of ≈150 K. Bismuth does not prevent the activation of Mn atoms during annealing and contributes to an increase in the coercive field of the GaMnAs ferromagnetic semiconductor.

The work examines the features of the magnetotransport and magnetooptical properties of a GaAs structure with a Mn S-layer located near an In0.25Ga0.75As/GaAs quantum well with high charge carrier mobility. It is shown that in the initial structure, conduction occurs predominantly in the quantum well region, that leads to the dominance of magnetotransport phenomena of a Lorentzian nature (ordinary Hall effect and positive magnetoresistance). After suppression of the conduction channel through the quantum well using ion irradiation, an anomalous Hall effect and negative resistance are observed. It has been established that the experimental magnetic field dependences of the Hall resistance in ferromagnetic nanostructures with multiple conduction channels may not reflect the real magnetic properties of the structures.

Integrated Access and Backhaul (IAB) represents a fast and cost-efficient network deployment technology that enhances the coverage of millimeter-wave (mmWave) 5G networks. In addition to the conventional challenges of wireless multi-hop relaying such as, e.g., increased interference and packet delays, traffic asymmetry can lead to significant delay degradation. While centralized coordination can mitigate these challenges, it may also lead to unnecessary overheads. In this paper, we propose an effective delay-aware distributed solution for joint access and backhaul link scheduling and route selection designed to function with limited information, which relies only on the knowledge collected from immediate neighbors. We formulate the joint upstream and downstream routing and scheduling problem, which is solved in a distributed manner for the IAB system with diverse delay requirements. To effectively tackle this problem, we employ deep reinforcement learning (DRL) algorithms. Our numerical results demonstrate that the proposed distributed solution provides improved scalability as compared to the centralized approach without a significant performance loss.

Integrated Access and Backhaul (IAB) is a cost-efficient network densification technology for improving the coverage and capacity of the millimeter-wave (mmWave) cellular networks. In IAB systems, user traffic is forwarded to/from the wired base station by one or more relay stations, known as IAB nodes. Due to the multi-hop relaying, these systems may be subject to large packet delays and poor performance when the load is unevenly distributed among nodes. Addressing this limitation via delay-aware access and backhaul link scheduling in IAB networks is challenging due to potentially large network scale, complex topology, half-duplex, and interference constraints. In this paper, the topical link scheduling problem is formulated as a Markov decision problem (MDP) for a single-donor IAB system with a general topology that allows for users with different delay requirements and traffic dynamics. The proposed link scheduling strategy jointly optimizes (i) user traffic routing and (ii) multiplexing of access and backhaul links under half-duplex constraints and non-negligible interference that may arise in dense IAB systems even with high beam directionality. To address the complexity of our formulated MDP, we consider several approximation methods, namely, Q-learning, Monte Carlo Tree Search (MCTS), and genetic algorithms (GAs). Then, we propose a customized version of the GA, which provides the preferred optimality-complexity trade-off and offers a 15% packet delay reduction as compared to the state-of-the-art backpressure algorithm.

The work shows the possibility of doping gallium arsenide with bismuth during ion implantation and the effect of rapid thermal and pulsed laser annealing on these structures. The results of a study of bismuth depth distribution profiles are presented in comparison with theoretical calculations. The influence of bismuth on the optical properties of gallium arsenide was investigated using transmittance and reflection spectroscopy methods. It has been shown that the introduction of bismuth leads to a decrease in the band gap of gallium arsenide.

The use of unmanned aerial vehicles (UAVs) is gaining significant interest for a variety of emerging applications. One of the most attractive use cases for network operators is the ability of UAVs to carry base station equipment on board. The usage of UAVs as moving base stations may enhance connectivity quality in congested areas and expand coverage. Particularly useful for millimeter-wave (mmWave) 5G New Radio (NR) networks, UAV base stations (UAV-BSs) operating at higher altitudes may benefit from broader coverage, improved line-of-sight conditions, and reduced blockage. This paper evaluates UAV-aided radio systems by employing system-level simulations and compares them with traditional terrestrial networks, where urban deployment is modeled using real-world data. Our results show improvements in the average user throughput when using UAVs as flying base stations in urban environments. On top of this, we provide an updated review of 3GPP activities related to UAVs and NR-based relaying.

Исследованы слои GaMnAs, изготовленные методом импульсного лазерного нанесения в вакууме на подложках полуизолирующего GaAs. В процессе создания структур варьировалась температура подложки в интервале от 200 до 350oC, а толщина слоев составила ~ 50 nm. Образцы изготовленных структур подвергались отжигу импульсами эксимерного KrF-лазера. Анализ спектров комбинационного рассеяния отожженных образцов с использованием аппроксимации их функциями Лоренца показал, помимо пиков в области LO- и ТО-мод GaAs, наличие связанной фонон-плазмонной моды. В результате отжига наблюдается значительное возрастание дырочной проводимости слоев (сопротивление уменьшается от значений Rs~107-109 Ω до Rs~ 900-3000 Ω). Существенным образом изменяется вид магнитополевой зависимости намагниченности при комнатной температуре: происходит переход от нелинейной характеристики с петлей гистерезиса для исходного образца (появляющейся вследствие присутствия в нем включений соединения MnAs c температурой Кюри выше комнатной) к линейному характеру поведения для отожженного образца. Изучение гальваномагнитных свойств при температурах от 10 до 150 K показывает существование ферромагнетизма в слоях GaMnAs с температурой Кюри, достигающей 90 K. Наблюдаемые эффекты позволяют заключить, что применяемое импульсное лазерное воздействие приводит к модификации (растворению) включений MnAs, электрической активации Mn и, как следствие, к образованию однофазного ферромагнитного полупроводника GaMnAs. Ключевые слова: импульсное лазерное нанесение, импульсный лазерный отжиг, ферромагнитный полупроводник.

The properties of carbon layers (C-layers) formed by thermal decomposition of CCl4 at temperatures of 600-700oC on the surface of gallium arsenide structures fabricated by MOC-hydride epitaxy on n+-GaAs (100) wafers have been studied. The surface morphology of the carbon layers was studied using atomic force microscopy. The structural and optical properties were studied using Raman spectroscopy and reflection spectroscopy. It has been found that in the case of a C-layer fabricated at a temperature of 650-700oC, the atomic force microscopy image demonstrates the presence of vertical carbon nanowalls (vertical graphene) located parallel to one of the [110] directions of the GaAs crystal lattice. The characteristics of the bands observed in the Raman spectra correspond to the parameters of the spectra of vertical graphene. The reflectivity coefficient of such carbon layers significantly decreases (diffuse reflection does not exceed 25% for a layer fabricated at 700oC) in the wavelength range from 0.19 to 1.8 μm. The presence of a significant "absorbing" ability makes the obtained carbon layers promising as a conducting contact in photosensitive semiconductor device structures, which is confirmed by preliminary results of studies of the current-voltage characteristics and spectral dependences of the photocurrent. Keywords: thermal decomposition of carbon tetrachloride, gallium arsenide, vertical graphene morphology.

Low-temperature device-quality GaAs layers with high resistivity were obtained by pulsed laser deposition. The properties of GaAs layers are sensitive to the process temperature. At a growth temperature of less than 300°C, the layers have low electron mobility and a shift of the GaAs stoichiometry towards the region of arsenic enrichment at a level of 1–2 at.%. At a growth temperature of more than 300° C., the layers show an improved crystalline quality. The dependence of the relative intensity of the As 3d photoelectron line on the growth temperature confirms this trend with a change in the growth temperature.

Low-temperature device-quality GaAs layers with high resistivity were obtained by pulsed laser deposition. The properties of GaAs layers are sensitive to the process temperature. At a growth temperature of less than 300 o C, the layers have low electron mobility and a shift of the GaAs stoichiometry towards the region of arsenic enrichment at a level of 1-2 at.%. At a growth temperature of more than 300 o C, the layers show an improved crystalline quality. The dependence of the relative intensity of the As 3d photoelectron line on the growth temperature confirms this trend with a change in the growth temperature. Keywords: pulsed laser deposition, Hall effect, X-ray photoelectron spectroscopy.

GaMnAs layers made by pulsed laser deposition in vacuum on semi-insulating GaAs substrates have been studied. During the creation of the structures, the substrate temperature varied in the range from 200 to 350 o C, and the thickness of the layers was ~ 50 nm. Samples of the manufactured structures were annealed by pulses of an excimer KrF-laser. The analysis of the Raman scattering spectra of annealed samples using their approximation by Lorentz functions showed, in addition to peaks in the LO- and TO-GaAs modes, the presence of a coupled phonon-plasmon mode. As a result of annealing, a significant increase in the hole conductivity of the layers is observed (the resistance decreases from R s ~10 7 -10 9 Ω to R s ~ 900-3000 Ω). The type of magnetic field dependence of magnetization at room temperature changes significantly: there is a transition from a nonlinear characteristic with a hysteresis loop for the initial sample (appearing due to the presence of MnAs compound inclusions with a Curie temperature above room temperature) to a linear behavior for the annealed sample. The study of galvanomagnetic properties at temperatures from 10 to 150 K shows the existence of ferromagnetism in GaMnAs layers with a Curie temperature reaching 90 K. The observed effects allow us to conclude that the applied pulsed laser action leads to modification (dissolution) of MnAs inclusions, electrical activation of Mn and, as a consequence, to the formation of a single-phase ferromagnetic semiconductor GaMnAs. Keywords:: pulsed laser deposition, pulsed laser annealing, ferromagnetic semiconductor.

Extending the existing near-shore terrestrial infrastructure with non-terrestrial network capabilities helps maritime operators alleviate the high costs of communication and meet the requirements imposed by time-sensitive applications. Recognizing that the deployment of terrestrial and non-terrestrial networks necessitates selecting from the available wireless backhaul solutions, which have dissimilar data transmission costs and communication link qualities, it is essential to propose an appropriate backhaul selection policy. Specifically, in this letter, we coin a backhaul selection policy that manages the inherent trade-off between data transmission expenses and timely throughput guarantees for maritime communications. We formulate the backhaul selection problem as a Markov decision process and show that the proposed solution is not only more cost-efficient, but also satisfies the timely throughput requirements in contrast to the currently used greedy strategies.

The properties of carbon layers (C- layers) formed by thermal decomposition of CCl4 at temperatures of 600–700°C on the surface of gallium arsenide structures fabricated by MOС-hydride epitaxy on n+-GaAs (100) wafers have been studied. The surface morphology of the carbon layers was studied using atomic force microscopy. The structural and optical properties were studied using Raman spectroscopy and reflection spectroscopy. It has been found that in the case of a C layer fabricated at a temperature of 650–700°C, the atomic force microscopy image demonstrates the presence of vertical carbon nanowalls (vertical graphene) located parallel to one of the [110] directions of the GaAs crystal lattice. The characteristics of the bands observed in the Raman spectra correspond to the parameters of the spectra of vertical graphene. The reflection coefficient of such carbon layers significantly decreases (diffuse reflection does not exceed 25% for a layer fabricated at 700°C) in the wavelength range from 0.19 to 1.8 μm. The presence of a significant "absorbing" ability makes the obtained carbon layers promising as a conducting contact in photosensitive semiconductor device structures, which is confirmed by preliminary results of studies of the current-voltage characteristics and spectral dependences of the photocurrent.

Operation modes of laser structures with controlled polarization of light have been studied and the results of measuring polarization characteristics are presented. The possibility of controlling both the linear and circular polarizations of light with corresponding modification of the laser design is shown. In particular, stable lasing at two orthogonally polarized modes in the near-IR range with the intensity ratio of radiation components ITE/ITM ≈ 4.5 is implemented. The possibility is confirmed of generation of circularly polarized radiation in edge-emitting laser diodes by magnetization of a combined semitransparent mirror with a ferromagnetic CoPt layer deposited on the end face of the laser cavity. The degree of polarization is ±1.25% in the CoPt layer saturation magnetization mode.

Age of Information (AoI) has gained significant attention from the research community because of its applications to Internet of Things (IoT) monitoring and control. In this work, we treat multihop connections over queuing networks with tributary flows and non-preemptive service: packets cannot be discarded because they are utilized for other system objectives, such as data analytics. Without preemption, the key tool for optimizing AoI is then the scheduling policy between the different data flows at each intermediate node. This is the subject of our analysis, along with the impact of packet erasure on the age. We derive upper and lower bounds for the average AoI considering several queuing policies in arbitrary network topologies, and present the results in different scenarios. Network topology, tributary traffic load, and link characteristics such as packet erasure generate complex trade-offs, which affect the optimal operation point and the age performance. The scheduling strategy at each node can also affect performance and fairness among users, particularly at critical bottleneck links, which have a significant impact on the overall performance of the whole network.

The possibilities of controlled exposure to ion irradiation (He+ with an energy of 20 keV and a fluence in the range from 3·1014 to 3·1015 cm-2) as a method for modifying the magnetic properties and domain structure of Co0.35Pt0.65 thin ferromagnetic films have been studied. It was found that the ion irradiation causes a change in the Dzyaloshinskii--Moriya interaction constant and a change in the skyrmion density that correlates with it. This result shows the possibility of homogeneous ion irradiation as a way to control the micromagnetic structure, namely the process of formation of skyrmion states. Keywords: ferromagnetic thin films, ion irradiation, domain structure, magnetic force microscopy, Dzyaloshinskii-Moriya interaction, skyrmions.

Devices with multiple SIM cards are expected to prevail over the conventional devices with only one SIM. Despite the growing demand for such devices, only proprietary solutions are available so far. To fill this gap, the Third Generation Partnership Project (3GPP) is aiming at the development of a unified cross-platform solution for multi-SIM device coordination. This article extends the technical discussion and investigation of the 3GPP solutions for improving mobile terminated (MT) service delivery to multi-SIM devices. Implementation trade-offs, impact on quality of service, and possible future directions in 3GPP are outlined.

The GaAs semiconductor structures for the application as betavoltaic power sources were investigated. Three types of structures underwent a comparative study: a Schottky diode, a p-n junction and Schottky structure modified by deposition of a carbon layer. The power characteristics were estimated by Monte-Carlo simulation and collected current calculation using parameters obtained from the electron beam induced current technique. It was shown that carbon deposition on the top of n-GaAs allows passivating the surface states and thus improving betavoltaic performance.