Non-Terrestrial Networks (NTNs) will be an es-sential element in Beyond -5G (BSG) and 6G ecosystems, with the purpose of enabling seamless and global coverage, as well as supporting high data rate services. To achieve that, Full Frequency Reuse (FFR) schemes, along with digital beamforming techniques to cope with the Co-Channel Interference (CCI), are considered as promising strategies in 6G NTN. In this paper, we address the design of Cell-Free (CF) MIMO algorithms in NTN composed of multiple swarms of Non-GeoSynchronous Orbit (NGSO) nodes, in which each swarm performs distributed digital beamforming schemes. Furthermore, aiming at increasing the directivity of on-board antenna arrays for each NGSO node and enhancing the interference mitigation, we propose a Limited Field of View (LFoV) planar array architecture built up of smaller planar subarrays. We evaluate the performance of distributed beamforming schemes including both Channel State Information (CSI)-based, e.g., digital Minimum Mean Square Error (MMSE), and position-based such as analog Conventional Beamforming (CBF). We provide a numerical analysis of the performance in terms of per-user spectral efficiency. The results show that our proposed sub arrayed architecture designed for federated CF-MIMO beamforming outperforms the reference approach without subarraying in the proposed NTN system architecture.

This paper describes the integration of Terrestrial and Non-Terrestrial Networks, wherein space-based network entities collaborate with traditional and emerging terrestrial communication frameworks to furnish pervasive, resilient, and three-dimensional wireless connectivity worldwide toward the 6th Generation of communication networks. This integration supports heterogeneous services, such as enhancing coverage, user experience, system capacity, service reliability, and availability, while also providing high-speed connectivity in remote or disaster-affected areas, improving existing 5th Generation technologies. Various Use Cases are detailed, highlighting the pivotal roles that Non-Terrestrial Networks play in distinguishing between urban/suburban and rural environments, with particular emphasis on transportation ecosystems. Through this analysis, Key Performance Indicators and requirements are delineated to characterize the requisite service quality for these diverse Use Cases. The paper further presents an overview of potential and standards-compliant integrated Terrestrial/Non-Terrestrial architectures, delineating their roles both in backhauling and access across different layers of Non-Terrestrial systems and elements. These insights are derived from studies conducted within the Integrated Terrestrial And Non-Terrestrial Networks (ITA-NTN) project, part of the European Union initiative defined as the Italian National Recovery and Resilience Plan (NRRP) RESTART Research Program.

With the evolution process of the 5G into the 6G, there will be an exponential growth of the Internet of Things (IoT) devices, offering ubiquitous and continuous connectivity services in all areas of our life. In order to deal with such huge amount of IoT devices, and to satisfy the large capacity requirements of the most advanced of them, non-terrestrial networks (NTNs) will play a pivotal role to assist and complement the terrestrial systems. However, one of the major challenges of the NTN channel is represented by the large delay which hampers the different communication phases, such as the Random Access (RA) procedure. In this paper, we provide an assessment of the system level performances, in terms of access delay and access success probability, of the Narrowband IoT (NB-IoT) devices in typical satellite scenarios defined by the 3GPP. In particular, we provide a detailed analysis under different network densities, for various combinations of the related configuration parameters, and for different system architectures supporting the NB-IoT over NTN. The analysis led to a useful comparison of the RA performances obtained with 3GPP compliant configurations for access parameters and satellite configuration with the aim to maximize the access success probability and minimize the access time in a NB-IoT NTN system.

Satellite Communications systems are a promising solution to extend and support terrestrial networks in un- or under-served areas. In Release 17, 3GPP initiated a Study Item for IoT over Non-Terrestrial Networks (NTN) to assess and adapt the NB-IoT air interface to the NTN characteristics. One of the main objective of the study is the evaluation of the Random Ac-cess procedure and the estimation of the up-link synchronization parameters at the satellite. In this context, it is essential that the detection algorithms of the NB-IoT preamble, at the receiver, satisfy the user detection requirements as well as the timing synchronization accuracy. This is not a trivial task, especially in satellite channels where the carrier frequency offset (CFO) is more severe than that of terrestrial links. In order to cope with this problem, we propose a new algorithm based on a non-decimated dyadic wavelet transform. This method is able to detect the incoming preambles and to estimate their time of arrival, without having to compensate the CFO first. The performance of the proposed algorithm is compared with a classical estimation approach based on the Fast Fourier Transform, substantiating the significant advantage obtained in the considered NTN scenarios.

Machine Type Communications (MTC) and Internet of Things (IoT) applications are growing exponentially and are forecast to play an even more important role in Future Networks and Systems. The Third Generation Partnership Project (3GPP) introduced the Narrowband IoT (NB-IoT) air interface as a response to the IoT use case requirements. However, it is widely accepted that the terrestrial network alone is not able to serve the requirement of the IoT market of a truly ubiquitous coverage. To this aim, several initiatives are currently addressing the inclusion of a satellite component into the telecommunication infrastructure to extend its coverage to those areas that are unserved or underserved by the terrestrial network. The recently approved 3GPP study item on NB-IoT over Non-Terrestrial Network (NTN) is the most important of these initiatives. The study item, starting at the beginning of 2021, will assess the performance of the NB-IoT air interface over satellite and will identify which adaptations are needed to enable its use. In this context, our work provides an assessment of the system level performance, in terms of the link budget parameters, of the NB-IoT air interface in typical satellite scenarios. In particular, we provide a detailed discussion of the system architecture supporting the NB-IoT over NTN, a description of the link budget computation methodology, and the numerical results of the link budget analysis in both single-satellite and multi-satellite scenarios.

Satellite Communication systems represent a solid solution to extend and complement terrestrial networks in un-/under-served areas. The recent standardisation endeavours within 3GPP led to the Non-Terrestrial Networks (NTN) study item for New Radio, aimed at deploying satellite systems either stand-alone or as integration to terrestrial networks in mobile broadband and machine-type communication scenarios. In this context, the main focus is currently related to: i) evaluating the system level performance; and ii) understanding the impact at link level of typical satellite channel impairments on the PHY/MAC procedures. In this paper, we focus on the former; in particular, we provide: i) a detailed discussion on the current system architecture and assumptions; ii) we thoroughly describe the methodology to perform link budget computations; and iii) we show the numerical results for GEO and LEO systems.

The standardization of 5G systems is entering in its critical phase, with 3GPP that will publish the PHY standard by June 2017. In order to meet the demanding 5G requirements both in terms of large throughput and global connectivity, Satellite Communications provide a valuable resource to extend and complement terrestrial networks. In this context, we consider a heterogeneous architecture in which a LEO mega-constellation satellite system provides backhaul connectivity to terrestrial 5G Relay Nodes, which create an on- ground 5G network. Since large delays and Doppler shifts related to satellite channels pose severe challenges to terrestrial-based systems, in this paper we assess their impact on the future 5G PHY and MAC layer procedures. In addition, solutions are proposed for Random Access, waveform numerology, and HARQ procedures.

Wireless communication systems are predicted to appear massively in the future human life. In case of 5G communications, high expectations in terms of Quality of Service and reliability are foreseen. However, the development of future systems has to cope with a better exploitation of the available resources. As a matter of fact, system coexistence and frequency sharing are two of the most promising approaches to achieve spectrum efficiency. Cognitive Radio (CR) is a key enabler of these approaches, which are also arising in Satellite Communications (SatComs). In this paper, a carrier allocation based scheduling algorithm inspired by genetic algorithms (GA) is proposed by taking into account different environment conditions and service requirements of the users of the cognitive satellite system.

The increasing request of communication capacity for the introduction of modern multimedia services has collided with the problem of the spectrum shortage. One of the most known approach is represented by cognitive radios, which are supposed to exploit already deployed frequency bands in use by an incumbent system. Among other cognitive radio features, detection and estimation of the incumbent user are essential for implementing the cognitive radio system avoiding any interference. This is particularly important in SatCom cognitive scenarios due to transmission power impairments. In this paper, we focus on a joint interference and noise estimation algorithm aiming at detecting and estimating incumbent interference, for allowing the coexistence of the two systems. The behavior of the algorithm is analytically derived, and numerical results obtained through computer simulations confirm the effectiveness of the proposed approach.

In this paper, we introduce a new framework to compute the Outage Probability (Pout) and the Average Symbol Error Probability (ASEP) of dual-hop Amplify-and-Forward (AF) relaying in the presence of noise, fading, and network interference. The interfering nodes are randomly distributed in the 2D Euclidean plane according to a homogeneous Poisson point process. Our framework provides closed-form expressions of Poutand ASEP over Rayleigh fading channels, additive noise at the relay and at the destination, and network interference at the destination. The accuracy of our analytical derivation is substantiated through extensive Monte Carlo simulations.

In this paper, we introduce an analytical framework to compute the average rate of downlink heterogeneous cellular networks. The framework leverages recent application of stochastic geometry to other-cell interference modeling and analysis. The heterogeneous cellular network is modeled as the superposition of many tiers of Base Stations (BSs) having different transmit power, density, path-loss exponent, fading parameters and distribution, and unequal biasing for flexible tier association. A long-term averaged maximum biased-received-power tier association is considered. The positions of the BSs in each tier are modeled as points of an independent Poisson Point Process (PPP). Under these assumptions, we introduce a new analytical methodology to evaluate the average rate, which avoids the computation of the Coverage Probability (Pcov) and needs only the Moment Generating Function (MGF) of the aggregate interference at the probe mobile terminal. The distinguishable characteristic of our analytical methodology consists in providing a tractable and numerically efficient framework that is applicable to general fading distributions, including composite fading channels with small- and mid-scale fluctuations. In addition, our method can efficiently handle correlated Log-Normal shadowing with little increase of the computational complexity. The proposed MGF-based approach needs the computation of either a single or a two-fold numerical integral, thus reducing the complexity of Pcov-based frameworks, which require, for general fading distributions, the computation of a four-fold integral.

In this paper, we introduce an analytical framework for performance analysis and design of Single-Input-Multiple-Output (SIMO) wireless systems in the presence of noise, fading, and radio frequency interference produced by randomly distributed active interferers surrounding an intended probe receiver. The framework leverages recent application of stochastic geometry and Poisson Point Processes (PPPs) theory to network interference modeling. To assess the impact of spatial dependence across multiple receive-antennas, three models of network interference are studied: i) the isotropic model, where all receive-antennas see interferers belonging to the same PPP; ii) the independent model, where each receive—antenna sees interferers belonging to an independent PPP; and iii) the mixture model, which is a superposition of isotropic and independent interferences. Depending on the fading distribution of the interferers, the Nakagami-m fading parameter of the probe link, and the number of receive-antennas, either exact or upper-bound formulas of the error probability averaged over noise, fading, and spatial interference are given. Our analysis shows that, depending on the interference model, performance can either improve or get worse with multiple antennas at the receiver. The proposed analytical methodology is applicable to single- and multi-PPPs interference environments.

Accurate modeling of network interference, deep understanding of its impact on the achievable performance, and development of efficient techniques to mitigate or exploit it are three important and fundamental research assets in current and next-generation cellular networks. In this context, Andrews, Baccelli, and Ganti [1] have recently introduced a new analytical approach to estimate coverage and rate of cellular networks subject to other-cell interference. In this paper, we move from the approach developed in [1], and propose an alternative analytical derivation to compute the rate of cellular networks. More specifically, by using stochastic geometry and Poisson point processes theory, we derive a simple and easy-to-compute expression of the rate, which can be used for arbitrary network and channel parameters, e.g., path-loss exponent, receiver noise, density of Base Stations (BSs), etc. Compared to [1], our framework has two main distinguishable features: i) the rate can be computed via a single numerical integral, rather than via a three-fold numerical integral; and ii) the formula is applicable to arbitrary fading distributions on the intended link, rather than being useful for Rayleigh fading only. Our analytical derivation is substantiated through extensive Monte Carlo simulations.

In this paper, we introduce a new framework to compute the Average Symbol Error Probability (ASEP) of an intended wireless communication system subject to network interference and noise. The interfering nodes are assumed to be randomly distributed in the 2D Euclidean plane according to a homogeneous Poisson point process. Our framework is applicable to performance prediction and optimization of, e.g., emerging heterogeneous cellular and cognitive radio networks. More specifically, we move from and generalize the semi-analytical framework recently introduced by Pinto and Win [1], and develop a new mathematical model which offers a simple single-integral expression of the ASEP under very general channel and interference conditions. The framework is exact, avoids Monte Carlo methods for its computation, and is applicable to asynchronous and synchronous scenarios. Our numerical examples show that both setups have almost the same performance, and that the ASEP in the presence of synchronous interference is a very tight upper-bound of the ASEP in the presence of asynchronous interference. This is a relevant result, as we show in this paper that in the former case all parameters of interest can be computed in closed-form. Our analytical derivation is substantiated through extensive Monte Carlo simulations.

The ever increasing demand for multimedia wireless communication systems is a key feature of more advanced markets. The buzzword of personal communications, meant to provide "access to anyone, anywhere, at anytime" to the wanted service, implies that spectrum demands are dramatically increasing in most developed markets. To cope with these needs, and in order to exploit the released spectrum resulting from the Digital Switchover, the last World Radiocommunication Conference (WRC-07) allocated on a co-primary basis the upper part of the UHF band to mobile services as from 2015. This will cause potentially harmful mutual interference between TV and mobile radio services, that needs to be carefully analyzed. In this paper we present a study of the co-channel interference problem, proposing a methodology to take into account the mutual interference between a LTE mobile network and a DVB-T system and highlighting the different behaviour of the two radio links.

In this paper we present the concept of cognitive satellite terrestrial radios (CSTR) for hybrid satellite-terrestrial systems (HSTS). The cognitive radio (CR) technology is being motivated by the radio regulatory bodies for efficient utilization of the radio spectrum. The future satellite ground terminals therefore need to integrate and co-exist with the spectrally crowded terrestrial wireless systems and hence we propose the idea of CSTR. The key issues are addressed and the concepts of developing CR based satellite ground terminals in HSTS for dynamic spectrum access on the ground are presented. Furthermore, the concept of 3D-Spatial reuse of the spectrum is also presented using the CSTR considering low elevated satellite ground stations. Two particular HSTS applications to illustrate the CSTR concept, a) the hybrid satellite-UWB (ultra wideband) communication system for personal area networks (PAN) with short range on ground communications, and b) the hybrid satellite-WRAN (wireless regional area networks) for long range on ground communications are presented. In both the applications the satellite uplink and the terrestrial radios adopt the CR functionalities. The key enabling technologies and their integrated architecture for the CSTR are also presented.