CHANNEL MODELING FOR FIFTH GENERATION CELLULAR NETWORKS AND WIRELESS SENSOR NETWORKS

In view of exponential growth in data traffic demand, the wireless communications industry has aimed to increase the capacity of existing networks by 1000 times over the next 20 years. A combination of extreme cell densification, more bandwidth, and higher spectral efficiency is needed to support the data traffic requirements for fifth generation (5G) cellular communications. In this research, the potential improvements achieved by using three major 5G enabling technologies (i.e., small cells, millimeter-wave spectrum, and massive MIMO) in rural and urban environments are investigated. This work develops SPM and KA-based ray models to investigate the impact of geometrical parameters on terrain-based multiuser MIMO channel characteristic. Moreover, a new directional 3D channel model is developed for urban millimeter-wave (mmW) small cells. Path-loss, spatial correlation, coverage distance, and coherence length are studied in urban areas. Exploiting physical optics (PO) and geometric optics (GO) solutions, closed form expressions are derived for spatial correlation. Achievable spatial diversity is evaluated using horizontal and vertical linear arrays as well as planar 2D arrays. In another study, a versatile near-ground field prediction model is proposed to facilitate accurate wireless sensor network (WSN) simulations. Monte Carlo simulations are used to investigate the effects of antenna height, frequency of operation, polarization, and terrain dielectric and roughness properties on WSNs performance

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

Empirical multi-band characterization of propagation with modelling aspects for communictions

Diese Arbeit präsentiert eine empirische Untersuchung der Wellenausbreitung für drahtlose Kommunikation im Millimeterwellen- und sub-THz-Band, wobei als Referenz das bereits bekannte und untersuchte sub-6-GHz-Band verwendet wird. Die großen verfügbaren Bandbreiten in diesen hohen Frequenzbändern erlauben die Verwendung hoher instantaner Bandbreiten zur Erfüllung der wesentlichen Anforderungen zukünftiger Mobilfunktechnologien (5G, “5G and beyond” und 6G). Aufgrund zunehmender Pfad- und Eindringverluste bei zunehmender Trägerfrequenz ist die resultierende Abdeckung dabei jedoch stark reduziert. Die entstehenden Pfadverluste können durch die Verwendung hochdirektiver Funkschnittstellen kompensiert werden, wodurch die resultierende Auflösung im Winkelbereich erhöht wird und die Notwendigkeit einer räumlichen Kenntnis der Systeme mit sich bringt: Woher kommt das Signal? Darüber hinaus erhöhen größere Anwendungsbandbreiten die Auflösung im Zeitbereich, reduzieren das small-scale Fading und ermöglichen die Untersuchung innerhalb von Clustern von Mehrwegekomponenten. Daraus ergibt sich für Kommunikationssysteme ein vorhersagbareres Bild im Winkel-, Zeit- und Polarisationsbereich, welches Eigenschaften sind, die in Kanalmodellen für diese Frequenzen widergespiegelt werden müssen. Aus diesem Grund wurde in der vorliegenden Arbeit eine umfassende Charakterisierung der Wellenausbreitung durch simultane Multibandmessungen in den sub-6 GHz-, Millimeterwellen- und sub-THz-Bändern vorgestellt. Zu Beginn wurde die Eignung des simultanen Multiband-Messverfahrens zur Charakterisierung der Ausbreitung von Grenzwert-Leistungsprofilen und large-scale Parametern bewertet. Anschließend wurden wichtige Wellenausbreitungsaspekte für die Ein- und Multibandkanalmodellierung innerhalb mehrerer Säulen der 5G-Technologie identifiziert und Erweiterungen zu verbreiteten räumlichen Kanalmodellen eingeführt und bewertet, welche die oben genannten Systemaspekte abdecken.This thesis presents an empirical characterization of propagation for wireless communications at mm-waves and sub-THz, taking as a reference the already well known and studied sub-6 GHz band. The large blocks of free spectrum available at these high frequency bands makes them particularly suitable to provide the necessary instantaneous bandwidths to meet the requirements of future wireless technologies (5G, 5G and beyond, and 6G). However, isotropic path-loss and penetration-loss are larger with increasing carrier frequency, hence, coverage is severely reduced. Path-loss can be compensated with the utilization of highly directive radio-interfaces, which increases the resolution in the angular domain. Nonetheless, this emphasizes the need of spatial awareness of systems, making more relevant the question “where does the signal come from?” In addition, larger application bandwidths increase the resolution in the time domain, reducing small-scale fading and allowing to observe inside of clusters of multi-path components (MPCs). Consequently, communication systems have a more deterministic picture of the environment in the angular, time, and polarization domain, characteristics that need to be reflected in channel models for these frequencies. Therefore, in the present work we introduce an extensive characterization of propagation by intensive simultaneous multi-band measurements in the sub-6 GHz, mm-waves, and sub-THz bands. Firstly, the suitability of the simultaneous multi-band measurement procedure to characterize propagation from marginal power profiles and large-scale parameters (LSPs) has been evaluated. Then, key propagation aspects for single and multi-band channel modelling in several verticals of 5G have been identified, and extensions to popular spatial channel models (SCMs) covering the aforementioned system aspects have been introduced and evaluated

Massive MIMO channel models for 5G wireless communication systems and beyond

The recently standardised 5th generation (5G) wireless communication technologies and their evolution towards the 6th generation (6G) will enable low-latency, highdensity, and high-capacity communications across a wide variety of scenarios under tight constraints on energy consumption and limited availability of radio electromagnetic spectrum. Massive multiple-input multiple-output (MIMO) technologies will be key to achieve some of these goals and cover the ever-growing demand of data rates, reliability and seamless connectivity. Nowadays, the design and evaluation of new wireless communication technologies heavily rely on computationally-efficient channel models that can accurately capture essential propagation phenomena and flexibly adapt to a wide variety of scenarios. Thus, this thesis aims at providing methods of analysis of massive MIMO channels and developing advanced massive MIMO channel models that will help assess the 5G wireless communication technologies and beyond. First, key aspects of massive MIMO channels are investigated through a stochastic transformation method capable of modelling the space-time varying (STV) distribution of the delay and angle of arrival (AoA) of multi-path components (MPCs). The proposed method is followed by a channel modelling approach based on STV parameters of the AoA distribution that leads to closed-form expressions of key massive MIMO channel statistical properties. These methods are employed to analyse widelyused channel models and reveal some of their limitations. This investigation provides fundamental insights about non-stationary properties of massive MIMO channels and paves the way for developing subsequent efficient and accurate channel models. Second, three-dimensional (3D) non-stationary wideband geometry-based stochastic models (GBSMs) for massive MIMO communication systems are proposed. These models incorporate a novel approach to capture near-field effects, namely, the parabolic wavefront, that presents a good accuracy-complexity trade-off when compared to other existing techniques. In addition to cluster of MPCs (re)appearance, a Log-normal cluster-level shadowing process complements the modelling of large-scale fading over the array. Statistical properties of the models are derived and validated through simulations and measurements extracted from the available literature. Third, a highly-flexible and efficient 3D space-time non-stationary wideband massive MIMO channel model based on an ray-level evolution approach is proposed as a candidate for the design and assessment of 5G and beyond 5G (B5G) massive MIMO wireless communication technologies. The model can capture near-field effects, (dis)appearance, and large-scale fading of both clusters and individual MPCs by employing a single approach. Its efficiency relies upon a more realistic wavefront selection criterion, namely, the effective Rayleigh distance, which accounts for the limited lifespan of MPCs over the array. This novel criterion can help improve the efficiency of both existing and B5G massive MIMO channel models by greatly reducing the need for spherical wavefronts

A Vision and Framework for the High Altitude Platform Station (HAPS) Networks of the Future

A High Altitude Platform Station (HAPS) is a network node that operates in the stratosphere at an of altitude around 20 km and is instrumental for providing communication services. Precipitated by technological innovations in the areas of autonomous avionics, array antennas, solar panel efficiency levels, and battery energy densities, and fueled by flourishing industry ecosystems, the HAPS has emerged as an indispensable component of next-generations of wireless networks. In this article, we provide a vision and framework for the HAPS networks of the future supported by a comprehensive and state-of-the-art literature review. We highlight the unrealized potential of HAPS systems and elaborate on their unique ability to serve metropolitan areas. The latest advancements and promising technologies in the HAPS energy and payload systems are discussed. The integration of the emerging Reconfigurable Smart Surface (RSS) technology in the communications payload of HAPS systems for providing a cost-effective deployment is proposed. A detailed overview of the radio resource management in HAPS systems is presented along with synergistic physical layer techniques, including Faster-Than-Nyquist (FTN) signaling. Numerous aspects of handoff management in HAPS systems are described. The notable contributions of Artificial Intelligence (AI) in HAPS, including machine learning in the design, topology management, handoff, and resource allocation aspects are emphasized. The extensive overview of the literature we provide is crucial for substantiating our vision that depicts the expected deployment opportunities and challenges in the next 10 years (next-generation networks), as well as in the subsequent 10 years (next-next-generation networks).Comment: To appear in IEEE Communications Surveys & Tutorial

Channel modelling for visible light communication systems

Visible Light Communications (VLCs) have been identified as a potential solution for mitigating the looming Radio Frequency (RF) spectrum crisis. Having the ability to provide illumination and communication at the same time, this technology has been considered as one of the most promising communication technologies for future wireless networks. VLCs are a viable candidate for short-range indoor applications with very high data rates. In terms of outdoor applications, Vehicular VLCs (VVLCs) play an important role in vehicular ad hoc networks and Intelligent Transportation Systems (ITS). Adopting visible light in vehicular networks offers a great potential to enhance road safety and traffic efficiency towards accident-free driving. For the sake of VLC system design and performance evaluation, it is indispensable to develop accurate, efficient, and flexible channel models, which can fully reflect the characteristics of VLC channels. In this thesis, we first give a comprehensive and up-to-date literature review of the most important indoor Optical Wireless Communications (OWCs) measurement campaigns and channel models, primarily for Wireless Infrared Communications (WIRCs) and VLCs. Consequently, we can identify that an appropriate channel model for VLC systems is currently missing in the literature. This Ph.D. project is therefore devoted to the modelling of VLC channels for both indoor and outdoor communication systems. Second, a new Two-Dimensional (2D) stationary Field of View (FoV) one-ring Regular-Shape Geometry Based Stochastic Model (RS-GBSM) for VLC Single-Input Single-Output (SISO) channels is proposed. The proposed model considers the Line-of-Sight (LoS) and Single-Bounce (SB) components. VLC channel characteristics are analysed based on different positions of the Photodetector (PD) and FoV constraint. Third, we propose a new 2D stationary multiple-bounce RS-GBSM for VLC SISO channels. The proposed model employs a combined two-ring and confocal ellipse model. This model is sufficiently generic and adaptable to a variety of indoor scenarios since the received signal is constructed as the summation of the LoS, SB, Double-Bounce (DB), and Triple-Bounce (TB) rays with different powers. Fourth, a new 2D mobile RS-GBSM for vehicular VLC SISO channels is proposed. The proposed model combines a two-ring model and a confocal ellipse model, and considers SB and DB components in addition to LoS component. Unlike conventional models, the proposed model considers the light that is reflected off moving vehicles around the Transmitter (Tx) and Receiver (Rx), as well as the light that is reflected off the stationary roadside environments. Vehicular VLC channel characteristics are analysed along different distance ranges between 0 and 70 m and different PD heights. Fifth, we propose a novel Three-Dimensional (3D) mobile RS-GBSM for vehicular VLC Multiple-Input Single-Output (MISO) channels. The proposed model combines two-sphere and elliptic-cylinder models. Both the LoS component and SB components, which are reflected off moving vehicles and stationary roadside environments, are considered. The proposed 3D RS-GBSM has the ability to study the impact of the vehicular traffic density on the received power and jointly considers the azimuth and elevation angles by using the von Mises-Fisher (VMF) distribution. In summary, this work proposes new realistic VLC channel models which are useful for the design, test, and performance evaluation of advanced indoor and outdoor VLC systems. Furthermore, it identifies important directions that can be considered in future research, and helps propose new applications that require the development of more realistic channel models before the actual implementation