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Terahertz communications: Physical layer enablers and analysis

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dc.contributor.author Dovelos, Konstantinos
dc.contributor.other Bellalta, Boris
dc.contributor.other Universitat Pompeu Fabra. Departament de Tecnologies de la Informació i les Comunicacions
dc.date.accessioned 2022-01-27T02:30:09Z
dc.date.available 2022-01-27T02:30:09Z
dc.date.issued 2021-11-05
dc.identifier http://hdl.handle.net/10803/673252
dc.identifier.uri http://hdl.handle.net/10230/52332
dc.description.abstract Undoubtedly, spectrum scarcity constitutes the main bottleneck of current wireless networks. It is therefore imperative to move beyond the sub-6 GHz band in order to overcome this limitation. Toward this direction, terahertz (THz) communication is deemed a promising solution for future wireless systems owing to the abundant spectrum resources at these frequencies. Despite the prospect of terabit- per-second wireless links, THz signals suffer from severe propagation losses, which can undermine the communication range and performance of THz systems. In this dissertation, we tackle this challenge by putting forward two key physical layer technologies, namely massive multiple-input multiple-output (MIMO) and intelligent reflecting surfaces (IRSs). More particularly, this dissertation consists of two parts. In the first part, we thoroughly study the spatialwideband effect in THz massive MIMO. We commence by demonstrating that conventional narrowband beamforming/combining leads to substantial performance degradation for large antenna arrays and high transmission bandwidths. With this in mind, we propose a wideband array architecture based on true-timedelay and virtual subarrays. For the channel estimation problem, we introduce a wideband dictionary along with a novel variant of the orthogonal matching pursuit algorithm. Numerical simulations are provided showcasing that the proposed design enables: i) nearly squint-free beamforming/combining with a small number of true-time-delay elements; and ii) accurate channel acquisition with reduced pilot overhead even in the low signal-to-noise-ratio regime. In the second part, we focus on the fundamentals of IRSs at THz frequencies. Specifically, we show that an IRS has the potential to improve the energy efficiency of THz MIMO, when it is placed close to one of the link ends. As a result, electrically large IRSs are expected to operate in the radiating near-field zone, where the spherical wavefront of the emitted electromagnetic (EM) waves cannot be neglected. To this end, we introduce a spherical wave channel model by leveraging EM theory, which includes far-field as special case. Furthermore, we discuss the importance of using EM principles to characterize the path loss of IRS-aided links, as simplistic models may wrongly estimate the link budget and actual system performance. Our analysis reveals that: i) conventional far-field beamforming is highly suboptimal in terms of power gain, and hence beamfocusing is the optimal mode of operation for THz IRSs; and ii) frequencydependent beamfocusing is required in wideband THz transmissions, as beam squint can substantially reduce the achievable data rate.
dc.format application/pdf
dc.format 84 p.
dc.language.iso eng
dc.publisher Universitat Pompeu Fabra
dc.rights ADVERTIMENT. Tots els drets reservats. L'accés als continguts d'aquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials d'investigació i docència en els termes establerts a l'art. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix l'autorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No s'autoritza la seva reproducció o altres formes d'explotació efectuades amb finalitats de lucre ni la seva comunicació pública des d'un lloc aliè al servei TDX. Tampoc s'autoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant als continguts de la tesi com als seus resums i índexs.
dc.rights info:eu-repo/semantics/openAccess
dc.source TDX (Tesis Doctorals en Xarxa)
dc.title Terahertz communications: Physical layer enablers and analysis
dc.type info:eu-repo/semantics/doctoralThesis
dc.type info:eu-repo/semantics/publishedVersion
dc.date.modified 2022-01-25T13:11:43Z
dc.subject.keyword Beam squint effect
dc.subject.keyword Compressive channel estimation
dc.subject.keyword Hybrid combining
dc.subject.keyword Massive MIMO
dc.subject.keyword Planar antenna arrays
dc.subject.keyword Wideband THz communications
dc.subject.keyword Far-field beamforming
dc.subject.keyword Near-field beamfocusing
dc.subject.keyword Electromagnetics
dc.subject.keyword Intelligent reflecting surfaces
dc.subject.keyword Near-field model
dc.subject.keyword 62


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