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In this paper, a broadband circularly polarized (CP) antenna array with stable radiation pattern is proposed for satellite communication applications. The antenna array consists of a 2 $ \times $ × 2 planar antenna array and a feeding network. Based on the magneto-electric (ME) dipole antenna structure, the electric dipoles are modified, and a pair of shorting pins are introduced to adjust the surface current. The bandwidth problems of circular polarization are effectively improved. Then the 2 $ \times $ × 2 broadband CP antenna array is designed and fabricated. The measured results show that the −10 dB impedance bandwidth of 56.3% from 11.1 to 19.79 GHz, and the 3 dB axial ratio (AR) bandwidth of 32.1% from 11.72 to 16.20 GHz. The 3 dB gain bandwidth of 44.2% from 11.10 to 17.40 GHz, and the peak gain is 11.07 dBi. Owing to the above excellent performance, the proposed antenna array can be a candidate for satellite communications. [ABSTRACT FROM AUTHOR]

This paper presents a 2×2 antenna array prototype operating at both uplink and downlink Kubands for satellite applications. The proposed array employs four proximity coupled elliptical antennas fed by three equal Wilkinson power dividers (WPDs) constituting the feeding network. Each antenna element is fed by two parallel connected lines below the major and minor elliptical axes for achieving dual operational bands. For a reflection coefficient (S11) less than -10 dB, the proposed array impedance bandwidth ranges from 11.7 to 12.2 GHz for the downlink and from 14 to 14.96 GHz for the uplink. Over the operational frequency ranges, the suggested array design demonstrates a front-to-back ratio (FBR) ranging between 17 and 20 dB, a radiation efficiency of 86.4 %, and a reakized gain of 11.6 dBi. The antenna array is manufactured, measured, and simulated. The measured and simulated results show good agreement. The suggested array's enhanced performance qualifies it as a viable option for Kuband satellite communications. [ABSTRACT FROM AUTHOR]

In today's modern and globalized world, connectivity is a key factor for businesses, production facilities, sensor networks, and ordinary people. However, there are still populated areas which are not covered by ground-based telecommunications infrastructure. This is where telecommunication satellite constellations come in, as they can provide coverage to remote and uninhabited regions and fill existing connectivity gaps to ensure data transfer. LoRa is one of the technologies designed for data transmissions over long distances with low power consumption. Alongside with other technologies of the Low-Power Wide Area Network family, it is widely used for Internet of Things applications. LoRa chirp spread spectrum modulation is robust against the Doppler frequency shifts encountered in low earth orbits, and it has already been used in IoT satellite communications. Due to the low transmitted signal power, the achieved data rate is not high, making it a suitable technology for telecommunications payloads on CubeSat platforms for messaging services. As compared to existing traditional communication satellite systems, CubeSat constellations are low-cost and may offer an affordable connectivity service to developing regions. This study is divided in two parts. In Part I the demand model is built based on the population distribution not covered by cell towers. The LoRa link performance is analyzed, considering the impact of LoRa channel parameters variation, such as spreading factor and channel bandwidth, while satellite orbital height, transmission antenna beamwidth, and transmitter peak power have a direct impact on the payload mass. Among thousands of possible configurations, 73 feasible payload designs have been downselected. In Part II of the study, the satellite mass and the total system cost are estimated based on the payload parameters obtained. Messages transmission simulation via a constellation is conducted in order to identify optimal constellation architectures for messaging service, as well as the main drivers of the system economic profitability. The presented analysis results provide a deeper understanding of LoRa connectivity advantages and limitations together with the performance drivers, which will support the optimization of future LoRa-based satellite communication systems and other IoT satellite constellations. • A general framework for communications satellite constellation is suggested. • LoRa technology feasibility for messaging service via satellites has been proved. • LoRa channel capacity is sufficient for 1 message per day per uncovered user. • SF drives achievable channel capacity, orbit height and antenna beamwidth. • 73 payloads were downselected, with 2x2-8x8 patch antennas and transceivers of 1-2W. [ABSTRACT FROM AUTHOR]

In the realm of satellite communication, where the importance of efficient spectrum utilization is growing day by day due to the increasing significance of this technology, dynamic resource management has emerged as a pivotal consideration in the design of contemporary multi-beam satellites, facilitating the flexible allocation of resources based on user demand. This research paper delves into the pivotal role played by machine learning and artificial intelligence within the domain of satellite communication, particularly focusing on spot beam satellites. The study encompasses an evaluation of machine learning’s application, whereby an extensive dataset capturing user demand across a specific geographical area is subjected to analysis. This analysis involves determining the optimal number of beams/clusters, achieved through the utilization of the knee-elbow method predicated on within-cluster sum of squares. Subsequently, the demand data are equitably segmented employing the weighted k-means clustering technique. The proposed solution introduces a straightforward yet efficient model for bandwidth allocation, contrasting with conventional fixed beam illumination models. This approach not only enhances spectrum utilization but also leads to noteworthy power savings, thereby addressing the growing importance of efficient resource management in satellite communication.

From its early days as a fledgling technology, satellite communication has come a long way to become a flourishing component of the global technological ecosystem that determines our increasingly interdependent world. This scholarly essay provides a comprehensive analysis of current developments in satellite communication technology and the several fields in which they might be applied. The essay dives into major inventions that have catapulted this discipline to unparalleled heights, and it spans from the historical origins to the modern accomplishments. This overview elucidates the enormous influence that satellite communication has had on modern civilization, highlighting its central position in allowing global connection, data dissemination, and transformational applications across a variety of industries.

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Beyond-5G (B5G) technology plays a pivotal role in the next generation of communication infrastructure to support the future Society 5.0, a concept introduced in the 5th Basic Plan for Science and Technology by the Japanese Cabinet to define the long-term growth strategy for reconciling economic development with the resolution of social issues through the promotion of science and technologies. Free-space laser communication is a key element in boosting the data transmission capabilities required for B5G applications. The NICT will complete in 2024 the first fully functional prototypes of a series of miniaturized laser-communication terminals for multiple platforms. These terminals are designed to adapt to a wide range of requirements to address scenarios where laser communications can offer a competitive, enhanced solution compared to existing technologies. This paper provides an overview of these terminals' capabilities and the plans for their functional validation, as well as preliminary data from the first full-system tests. A number of innovations integrated into the terminals are introduced, such as the manufacture of the smallest miniaturized EDFA with integrated HPA and LNA and full space qualification to date, the first-ever integration of a beam-divergence control system in a practical communication terminal, the development of the most compact Tbit/s-class modem prototype documented in the literature, and the smallest gimbal design integrated in a lasercom terminal. Furthermore, this paper outlines the mid-term plans for demonstration in the most significant realistic scenarios, emphasizing the use of High-Altitude Platform Stations (HAPSs) and ultra-small satellites. [ABSTRACT FROM AUTHOR]

The research paper presents the novel solution for dynamic resource management in contemporary multibeam satellite communication systems, addressing the imperative need for efficient resource allocation using machine learning (ML) tool. Initially, employing unsupervised ML via weighted K-means clustering, geographical areas are evenly partitioned into 71 clusters. Subsequently, to address the variability in user demand on an hourly basis, supervised ML techniques, particularly Linear Regression (LR), are utilized to forecast demand trends. Based on these predictions, bandwidth allocation to each cluster is dynamically adjusted hourly to accommodate demand fluctuations. This innovative approach offers a simple yet effective model for optimizing bandwidth assignment, thereby facilitating significant power savings and enhancing overall system efficiency. The proposed solution represents a crucial advancement in addressing the complex challenges associated with dynamic resource management in modern satellite communication networks. [ABSTRACT FROM AUTHOR]

This paper presents the design of a two-port dual-band dual-circularly-polarized dielectric resonator antenna (DRA). The proposed DRA is formed by stacking two dielectric resonators (DRs) of different shapes, including a hexagonal DR on top and a cross-shaped DR on the bottom. It is designed to resonate at two near-degenerate orthogonal modes of TE111 and TE113, and an aperture-coupled feeding through a cross-like slot is used to achieve dual-band impedance matching simultaneously for right- and left-handed circular polarizations. Tests were conducted on a prototype working in C-band to verify the design concept. The experiment results demonstrate that the proposed DRA has exceptional performance with measured −10 dB reflection bandwidths of 24.4% and 17.4%, 3 dB axial ratio bandwidths of 21.2% and 16.3%, and maximum gains of 5.64 and 8.13 dBic for the lower and upper bands, respectively. Moreover, the measured channel isolation is more than 15.8 dB. The results obtained from the experiments show good agreement with the simulation, and hence, it can be concluded that the proposed DRA is a promising solution that can be used for various wireless communication applications. [ABSTRACT FROM AUTHOR]

This paper presents the development of a four-port dual-band dual-polarized antenna for transmitting/receiving (Tx/Rx) applications in Ku-band satellite communications. The antenna consists of two antenna elements sharing a common radiating aperture, a low-band element formed by an L-probe proximity-fed square-ring radiator for operation at the Rx band of 10.7–12.75 GHz, and a high-band element realized by a stacked-patch radiator for operation at the Tx band of 13.75–14.5 GHz. Within a compact multilayer structure, the antenna achieves wide dual-band operation, with each band having the ability to simultaneously operate with dual polarization. An antenna prototype is fabricated and tested to verify its performance. The experimental results show that the proposed antenna achieves an impedance bandwidth of 9.28–12.96 GHz (13.21–15.32 GHz), an isolation value between two orthogonal polarizations of 12 dB (12.4 dB), and a peak gain of 6.63 dBi (5.42 diBi) at the low band (high band). Tx/Rx isolation of more than 14 dB is achieved in both the Rx band and Tx band. [ABSTRACT FROM AUTHOR]

Satellite communication is proposed to fulfill the ubiquitous coverage for next-generation wireless networks. Considering the propagation delay and path loss, low-earth orbit (LEO) satellites are widely adopted. However, since the beam boresight directions become close in quasi-earth-fixed cells (QEFC) scenarios at low elevation angles, the interference increases and causes low communication quality. This paper introduces the optimal beamwidth maximizing uplink coverage probability scheme for quasi-earth-fixed cells in LEO satellite communication systems. The proposed scheme dynamically adjusts the beamwidth to achieve max uplink coverage probability at different elevation angles. The simulation results show that the proposed scheme matches the exhaustive search method in different scenarios and target signal-to-interference-plus-noise ratios. Furthermore, the proposed scheme significantly mitigates interference and improves the uplink coverage probability. Compared with the 3GPP setting, the proposed scheme improves the uplink coverage probability by 0.93 at time 100 s, and compared with the three-color frequency reuse, the proposed scheme improves the uplink coverage probability by 0.195 at time 100 s. The dynamic beamwidth and boresight direction adjustments enable the satellite to maintain seamless and reliable communication services across a wide range of operating conditions, ultimately realizing the goal of ubiquitous communications in the QEFC LEO satellite system. [ABSTRACT FROM AUTHOR]

Fifth Generation (5G) mobile networks considers an expansive set of heterogeneous services with stringent Quality of Service (QoS) requirements, and traffic demand with inherent spatial-temporal distribution, which places the backhaul network deployment under potential strain. In this paper, we propose to harness network slicing, Integrated Access and Backhaul (IAB) technology coupled with satellite connectivity to build a dynamic wireless backhaul network that can provide additional backhaul capacity to the base stations on demand when the wired backhaul link is temporarily out of capacity. To construct the network design, Deep Reinforcement Learning (DRL) models are used to select, for each network slice of the congested base station, an appropriate backhaul link from the pool of available IAB and satellite links that meets the QoS requirements (i.e., throughput and latency) of the slice. Simulation results show that around 20 episodes are sufficient to train a Double Deep Q-Network (DDQN) agent, with one fully-connected hidden layer and Rectified Linear Unit (ReLU) activation function, that adjusts the topology of the backhaul network.

Electromagnetic waves propagation through the ionosphere is subject to several effects including refraction, absorption, signal delay, or Faraday rotation. A ray tracer propagator that simulates these effects is an important tool for all satellite missions relying on transionospheric communications and Earth observation. This study presents an update to the 1975 Jones and Stephenson IONORT's code by implementing the use of up-to-date ionospheric, atmospheric, and geomagnetic models (International Reference Ionosphere or NeQuick, NRLMSISE-00, and International Geomagnetic Reference Field), and a new 3-D model for equatorial plasma bubbles. The developed code is part of the Ionosphere Modular Software Package in the context of the European Space Agency project SIMIONO. High-frequency radar sounders, synthetic aperture radars, and GNSS reflectometry missions constitute the main application of this software. The ray tracer has been validated with respect to the original software and by comparing real versus simulated vertical ionograms in different locations and dates.

Orthogonal time frequency space (OTFS) modulation is strongly considered as a promising solution for high-mobility communications. In contrast to conventional modulation techniques, wherein information symbols are multiplexed in a one-dimensional time or frequency domain, OTFS employs a two-dimensional modulation scheme by multiplexing information symbols in the delay-Doppler domain. This paper presents a comprehensive survey of OTFS. It starts with an overview of OTFS, its advantages over conventional air interface techniques, general block diagrams, and implementations. Subsequently, the paper explores the potential integration of multiple-input multiple-output and OTFS techniques. The paper further discusses the feasibility of integrating OTFS into multiple access techniques as a solution for maintaining acceptable performance in high-mobility scenarios. Then, widespread applications of OTFS in satellite communications are highlighted. Also, the potential utilization of OTFS modulation in integrated sensing and communications paradigm is thoroughly treated. In addition, the survey covers further applications of OTFS in deep learning, index modulation, underwater acoustic, and unmanned aerial vehicle communications. The paper concludes by pointing out numerous challenging and promising directions for future OTFS research.

The sixth-generation (6G) network is envisioned to shift its focus from the service requirements of human beings to those of Internet-of-Things (IoT) devices. Satellite communications are indispensable in 6G to support IoT devices operating in rural or disaster areas. However, satellite networks face the inherent challenges of low data rate and large latency, which may not support computationintensive and delay-sensitive IoT applications. Mobile Edge Computing (MEC) is a burgeoning paradigm by extending cloud computing capabilities to the network edge. Using MEC technologies, the resourcelimited IoT devices can access abundant computation resources with low latency, which enables the highly demanding applications while meeting strict delay requirements. Therefore, an integration of satellite communications and MEC technologies is necessary to better enable 6G IoT. In this survey, we provide a holistic overview of satellite-MEC integration. We first categorize the related studies based on three minimal structures and summarize current advances. For each minimal structure, we discuss the lessons learned and possible future directions. We also summarize studies considering the combination of minimal structures. Finally, we outline potential research issues to envision a more intelligent, more secure, and greener integrated satellite-MEC network.

Today, the worldwide economy and society are already taking advantage of the first deployments of 5G networks. However, the challenges that will be posed by 2030 networks on the infrastructure, technologies, and performance requirements call for a further leap in mobile communications. To this aim, evolutions of the 5G concepts in 5G-Advanced, and rethinking of future Radio Access Technologies, i.e., 6G which is expected to be the next revolution in the mobile ecosystem, are already being addressed by the scientific and industrial communities. In this framework, as demonstrated by 3GPP Rel. 17 specifications, Non-Terrestrial Networks (NTN) are expected to play a vital role in near and long term mobile communications, based on the joint optimisation of the terrestrial and non-terrestrial components in a unified 3D architecture. In this paper, we extensively discuss the 3GPP normative activities for 5G (Rel. 17), 5G-Advanced (Rel. 18 onward), and 6G (Rel. 20+) in terms of enabling features, architectures and interfaces, and protocols. Then, we explore the evolution of the 5G services towards 5G-Advanced and 6G NTN applications. Finally, we discuss the evolution to 6G network infrastructures with respect to the main performance requirements.

Recent advancements in onboard satellite communication have enhanced the capability of dynamically modifying the radiation pattern of a Direct Radiating Array (DRA). This is crucial not only for conventional communication satellites like Geostationary Orbit (GEO) but also for those in lower orbits such as Low Earth Orbit (LEO). Key design factors include the number of beams, beamwidth, Effective Isotropic Radiated Power (EIRP), and Side Lobe Level (SLL) for each beam. However, a challenge arises in multibeam scenarios when trying to simultaneously meet requirements for the aforementioned design factors which are reflected as uneven power distribution. This leads to over-saturation, especially in centrally located antenna elements due to the activation times per beam, commonly referred to as activation instances. In response to this challenge, this paper presents a method to balance the activation instances across antenna elements for each required beam. Our focus is on beams operating at 19 GHz on a CubeSat positioned 500 km above the Earth’s surface. We introduce a Genetic Algorithm (GA)-based algorithm to optimize the beamforming coefficients by modulating the amplitude component of the weight matrix for each antenna element. A key constraint of this algorithm is a limit on activation instances per element, which avoids over-saturation in the Radio Frequency (RF) chain. Additionally, the algorithm accommodates beam requirements such as beamwidth, SLL, pointing direction, and total available power. With the previous key design factors, the algorithm will optimize the required genes to address the desired beam characteristics and constraints. We tested the algorithm’s effectiveness in three scenarios using an $8\times 8$ DRA patch antenna with circular polarization, arranged in a triangular lattice. The results demonstrate that our algorithm not only meets the required beam pattern specifications but also ensures a uniform activation distribution across the antenna array.

This paper presents a novel autonomous management system for satellite-based Non-Terrestrial Networks (NTN). It addresses the challenges of managing the operations of Low Earth Orbit (LEO) constellations for the Internet of Things (IoT), emphasizing intermittent connectivity and resource constraints. This work contributes with the description of the scheduler module alongside a customized formulation of a novel multi-objective optimization problem and its associated mathematical framework. The resultant optimization algorithm is elaborated. This Constellation Management System (CMS) is validated through a real-world scenario, revealing substantial improvements of up to 40% in task assignment and throughput rates when compared to a best-effort baseline. This study underscores the CMS’s potential to enhance IoT communication with LEO constellations through resource-efficient and business-aware satellite operations scheduling.

The upper mid-band – approximately from 7 to 24 GHz — has recently attracted considerable interest for new cellular services. This frequency range has vastly more spectrum than the highly congested bands below 7 GHz while offering more favorable propagation and coverage than the millimeter wave (mmWave) frequencies. In this regard, the upper mid-band has the potential to provide a powerful and complementary frequency range that balances coverage and capacity. Realizing cellular networks that exploit the full range of these bands, however, presents significant technical challenges. Most importantly, spectrum will likely need to be shared with incumbents including communication satellites, military RADAR, and radio astronomy. Also, the upper mid-band is simply a vast frequency range. Due to this wide bandwidth, combined with the directional nature of transmission and intermittent occupancy of incumbents, cellular systems will likely need to be agile to sense and intelligently use large spatial and frequency degrees of freedom. This paper attempts to provide an initial assessment of the feasibility and potential gains of such adaptive wideband cellular systems operating across the upper mid-band. The study includes: (1) a detailed ray tracing simulation to assess potential gains of multi-band systems in a representative dense urban environment and illustrate the value of a wideband system with dynamic frequency selectivity; (2) an evaluation of potential cross-interference between satellites and terrestrial cellular services and interference nulling to reduce that interference; and (3) design and evaluation of a compact multi-band antenna array structure. Leveraging these preliminary results, we identify potential future research directions to realize next-generation systems in these frequencies.

Quantum technologies are increasingly recognized as groundbreaking advancements set to redefine the landscape of computing, communications, and sensing by leveraging quantum phenomena, like entanglement and teleportation. Quantum technologies offer an interesting set of advantages such as unconditional security, large communications capacity, unparalleled computational speed, and ultra-precise sensing capabilities. However, their global deployment faces challenges related to communication ranges and geographical boundaries. Non-terrestrial networks (NTNs) have emerged as a potential remedy for these challenges through providing free-space quantum links to circumvent the exponential losses inherent in fiber optics. Through the utilization of free-space optical (FSO) and Li-Fi links, NTNs provide an effective method for transmitting quantum states over extensive distances. This paper delves into the dynamic interplay between quantum technologies and NTNs to unveil their synergistic potential. We also investigate their integration challenges and the potential solutions to foster a symbiotic convergence of quantum and NTN functionalities while identifying avenues for enhanced interoperability. Specifically, quantum communication over NTNs imposes challenges in communication channel reliability, network flexibility, and scalability. To enhance channel reliability, multicarrier transmission techniques and spatial diversity strategies, including quantum MIMO (q-MIMO) transmission schemes, can be employed. Introducing the software defined networking (SDN) model facilitates flexible network configurations. In NTN-based quantum infrastructure, technologies like trusted relays, measurement device independent (MDI), and quantum repeaters can address scalability concerns efficiently. This paper not only offers useful insights into the mutual advantages but also presents future research directions, aiming to inspire additional studies and advance this interdisciplinary collaboration.

Satellite networks are expected to support global connectivity via future 3GPP non-terrestrial networks (NTNs), as well as private non-geostationary satellite orbit (NGSO) constellations, e.g. OneWeb, SpaceX, and Amazon’s Kuiper. In both 3GPP and private NGSO networks, handling mobility is critical, due to the intrinsic continuous movement of the satellites. In this paper we select three representative inter-satellite handover (HO) strategies and we study their impact on the achievable space-to-ground link performance in emerging NGSO constellations. With 1) Closest Satellite HO a ground station always connects to the closest satellite, with 2) Max Visibility HO a ground station connects and remains connected to the satellite with the maximum visibility time, until this satellite stops being visible, while with 3) CINR-based HO a ground station is handed over to the closest satellite if the carrier-to-interference-and-noise ratio (CINR) decreases by 3 dB below a maximum reference level. The first two HO strategies achieve the upper and lower bounds of the satellite-to-ground link performance based on the constellation geometry, while the third one is representative of HO mechanisms triggered by signal strength measurements. We consider five private constellations with different characteristics, some of which have already been launched. The goal is to determine the most suitable HO strategy for each constellation and our results show that this depends on the constellation type, i.e. low earth orbit (LEO), medium earth orbit (MEO) and highly elliptical orbit (HEO), and design. For large LEO constellations with thousands of satellites like SpaceX and Kuiper, CINR-based HO is recommended, since it achieves a good tradeoff among the spectral efficiency, propagation delay and handover rate, while the Doppler shift is in any case high. For smaller LEO constellations with hundreds of satellites like OneWeb, Closest Satellite HO is preferred due to the highest spectral efficiency and lowest propagation delay, while the handover overhead is similar for all strategies. For MEO and HEO constellations with tens to a few hundreds of satellites like Mangata and Pleiades, Closest Satellite HO is best. This achieves the highest spectral efficiency, lowest delay and sometimes a low Doppler shift, while the handover rate is in any case low. Finally, CINR-based HO is recommended in seldom cases of strong inter-constellation interference. Overall, the results suggest that the inter-satellite HO strategy should be adjusted to the constellation specifics, where e.g. adaptive handover selection algorithms could be employed for constellations that are enhanced in time by adding new satellites and orbit types.

Rain attenuation poses a significant challenge for high-throughput communication systems. In response, this paper introduces an artificial intelligence (AI) model designed for predicting and mitigating rain-induced impairments in high-throughput satellite (HTS) to land channels. The model is based on three AI algorithms developed using 3D antenna design to characterize, analyze, and mitigate rain-induced attenuation, optimizing channel quality specifically in the United Arab Emirates (UAE). The study evaluates various parameters, including rain-specific attenuation, effective slant path through rain, rain-induced attenuation, signal carrier-to-noise ratio, and symbol error rate, for five conventional modulation schemes: Quadrature Phase-Shift Keying (QPSK), 8-Phase Shift Keying (8-PSK), 16-Quadrature Amplitude Modulation (16-QAM), 32-QAM, and 64-QAM. Additionally, the paper introduces a new database detailing rain-induced attenuation in HTS channels in the UAE at different frequencies using measured rainfall intensities. The paper concludes by proposing a smart antenna design with a frequency diversity technique for fade mitigation. Results indicate that rain-induced attenuation varies significantly based on rainfall rate and frequency. Specifically, at 25 GHz and a rainfall rate of 100 mm/h, the rain-induced attenuation can reach as high as 15 dB, resulting in a significant decline in signal quality and link performance. The