Next-generation cellular systems will rely on millimeter wave (mmWave) bands to meet the increasing demand for wireless connectivity from end user equipment. Given large available bandwidth and small-sized antenna elements, mmWave frequencies can support high communication rates and facilitate the use of multiple-input-multiple-output (MIMO) techniques to increase the wireless capacity. However, the small wavelength of mmWave yields severe path loss and high channel uncertainty. Meanwhile, using a large number of antenna elements requires a high energy consumption and heavy communication overhead for MIMO transmissions and channel measurement. To facilitate efficient mmWave communications, in this dissertation, the challenges of energy efficiency and communication overhead are addressed. First, the use of unmanned aerial vehicle (UAV), intelligent signal reflector, and device-to-device (D2D) communications are investigated to improve the reliability and energy efficiency of mmWave communications in face of blockage. Next, to reduce the communication overhead, new channel modeling and user localization approaches are developed to facilitate MIMO channel estimation by providing prior knowledge of mmWave links. Using advance mathematical tools from machine learning (ML), game theory, and communication theory, this dissertation develops a suite of novel frameworks using which mmWave communication networks can be reliably deployed and operated in wireless cellular systems, UAV networks, and wearable device networks. For UAV-based wireless communications, a learning framework is developed to predict the cellular data traffic during congestion events, and a new framework for the on-demand deployment of UAVs is proposed to offload the excessive traffic from the ground base stations (BSs) to the UAVs. The results show that the proposed approach enables a dynamical and optimal deployment of UAVs that alleviates the cellular traffic congestion. Subsequently, a novel energy-efficient framework is developed to reflect mmWave signals from a BS towards mobile users using a UAV-carried intelligent reflector (IR). To optimize the location and reflection coefficient of the UAV-carried IR, a deep reinforcement learning (RL) approach is proposed to maximize the downlink transmission capacity. The results show that the RL-based approach significantly improves the downlink line-of-sight probability and increases the achievable data rate. Moreover, the channel estimation challenge for MIMO communications is addressed using a distributional RL approach, while optimizing an IR-aided downlink multi-user communication. The results show that the proposed method captures the statistic feature of MIMO channels, and significantly increases the downlink sum-rate. Moreover, in order to capture the characteristics of air-to-ground channels, a data-driven approach is developed, based on a distributed framework of generative adversarial networks, so that each UAV collects and shares mmWave channel state information (CSI) for cooperative channel modeling. The results show that the proposed algorithm enables an accurate channel modeling for mmWave MIMO communications over a large temporal-spatial domain. Furthermore, the CSI pattern is analyzed via semi-supervised ML tools to localize the wireless devices in the mmWave networks. Finally, to support D2D communications, a novel framework for mmWave multi-hop transmissions is investigated to improve the performance of the high-rate low-latency transmissions between wearable devices. In a nutshell, this dissertation provides analytical foundations on the ML-based performance optimization of mmWave communication systems, and the anticipated results provide rigorous guidelines for effective deployment of mmWave frequency bands into next-generation wireless systems (e.g., 6G). / Doctor of Philosophy / Different kinds of new smart devices are invented and deployed every year. Emerging smart city applications, including autonomous vehicles, virtual reality, drones, and Internet-of-things, will require the wireless communication system to support more data transmissions and connectivity. However, existing wireless network (e.g., 5G and Wi-Fi) operates at congested microwave frequency bands and cannot satisfy needs of these applications due to limited resources. Therefore, a different, very high frequency band at the millimeter wave (mmWave) spectrum becomes an inevitable choice to manage the exponential growth in wireless traffic for next-generation communication systems. With abundant bandwidth resources, mmWave frequencies can provide the high transmission rate and support the wireless connectivity for the massive number of devices in a smart city. Despite the advantages of communications at the mmWave bands, it is necessary to address the challenges related to high-frequency transmissions, such as low energy efficiency and unpredictable link states. To this end, this dissertation develops a set of novel network frameworks to facilitate the service deployment, performance analysis, and network optimization for mmWave communications. In particular, the proposed frameworks and efficient algorithms are tailored to the characteristics of mmWave propagation and satisfy the communication requirements of emerging smart city applications. Using advanced mathematical tools from machine learning, game theory, and wireless communications, this dissertation provides a comprehensive understanding of the communication performance over mmWave frequencies in the cellular systems, wireless local area networks, and drone networks. The anticipated results will promote the deployment of mmWave frequencies in next-generation communication systems.

Yes / This paper presents empirical results of an innovative beam scanning leaky-wave antenna (LWA) which enables scanning over a wide angle from -35o to +34.5o between 57 GHz and 62 GHz, with broadside radiation centered at 60 GHz. The proposed LWA design is based on composite right/left-handed transmission-line (CRLH-TL) concept. The single layer antenna structure includes a matrix of 3×9 square slots that is printed on top of the dielectric substrate; and printed on the bottom ground-plane are Π and Tshaped slots that enhance the impedance bandwidth and radiation properties of the antenna. The proposed antenna structure exhibits metamaterial property. The slot matrix provides beam scanning as a function of frequency. Physical and electrical size of the antenna is 18.7×6×1.6 mm3 and 3.43􀣅􀫙×1.1􀣅􀫙×0.29􀣅􀫙, respectively; where 􀣅􀫙 is free space wavelength at 55 GHz. The antenna has a measured impedance bandwidth of 10 GHz (55 GHz to 65 GHz) or fractional bandwidth of 16.7%. Its optimum gain and efficiency are 7.8 dBi and 84.2% at 62 GHz. / Partially supported by innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET- 722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1.

As multimedia devices advance, current high-speed wireless standards may soon struggleto support their growing demand for data speeds. This results in limitations in bandwidthfor applications, notably affecting activities like streaming high-definition television andultra-high-definition video. The proposed solution is to go up in frequency (millimeterwaves) allowing for use of greater bandwidths, in new bands. A problem is, however,that the path loss at mmWave frequencies is substantially greater than at frequencies below6GHz, currently the main frequency range used by both cellular and Wi-Fi. In order tocompensate for the increase in pathloss, wireless systems operating at mmWave frequenciesneed to use high gain antennas e.g. antenna arrays. Such arrays operate using digital oranalog beamforming. In this thesis the design, fabrication and verification of an analogbeamforming network connected to a four-antenna element patch array implemented at26GHz on a four-layer printed circuit board is presented. The components of the structuresof the Butler matrix beamforming network were designed and evaluated in simulationsusing CST. The stack up is a four-layer PCB-board with antenna elements and feedingnetwork on opposite outer layers. All structures in the Butler matrix were constructedin micro strip line with characteristic impedance of 50 ohm on Rogers RT-duroid 5880substrate to reduce dielectric losses. The designed 4x4 Butler matrix aimed at four set stateswith progressive phase differences ±45 and ±135 resulting in main lobes with direction -40,-15, 14 and 39 degrees. In the simulation, a progressive phase difference up to a deviationof up to 8.6 degrees was observed for all states. The fabricated Butler matrix was verified onan antenna measurement range to have main lobe directions of -45, -15, 15 and 40 degreesand with half power beam widths (HPBW) of 27.5, 25, 25 and 27.5 degrees respectively.The nulls between each lobe in the radiation pattern had a relative gain compared to peakvalue of -12.2 dBi resulting in similar magnitude as noise floor. The side lobe suppressionwere evaluated to minimum of 6.3 dB. The high directivity and well-defined nulls confirmthe hybrid couplers properties of equal power division as well as phase difference betweenoutput ports. The patch antennas were verified to have a dominant linear polarization butthe peak value for all lobes shows a deviation of -4.1 dB for all measurements comparedto simulation. In conclusion the final patch antenna array and Butler matrix performed asexpected from the simulation. Indicating that the proposed analog beam forming antennadesign is robust and well suited to be used in e.g. Open RAN applications.

Terrestrial mobile peer-to-peer millimeter wave networks will likely use beamforming arrays with narrow beams. Aligning narrow beams is difficult. One consideration for aligning narrow beams is co-channel interference. Beams can be aligned either on a per-link basis where co-channel interference is ignored, or on a global basis where co-channel interference is considered. One way to align beams on a global basis is coordinated beamforming. Coordinated beamforming can be defined as alignment of beams on a global basis, so as to jointly optimize the signal-to-interference-plus-noise ratio (SINR) of all links operating in a network. In this work, we explore coordinated beamforming in peer-to-peer networks and demonstrate its efficacy. Networks with varying numbers of links are simulated in scenarios with and without obstructions. The coordinated beamforming schemes presented in this work significantly improve link SINR statistics in these scenarios. Greater improvement was found in networks with higher numbers of links and in networks in terrain with obstructions. / Master of Science / Wireless communication links can interfere with each other. Interference can be mitigated by adjusting the antennas with which the links are formed. One method of mitigating interference is coordinated beamforming. Coordinated beamforming can be defined as a method of adjusting antennas to jointly optimize the strength of the links operating in a network. In this work, we explore coordinated beamforming in terrestrial mobile peer-to-peer communication networks and demonstrate its efficacy. Networks with varying numbers of links are simulated in scenarios with and without obstructions. The coordinated beamforming schemes presented in this work significantly improve link strength statistics in these scenarios. Greater improvement was found in networks with higher numbers of links and in networks in terrain with obstructions.

Analysis and design of millimeter-wave integrated circuits for emerging communication/sensing and cryogenic applications with an emphasis on transistor model verification.

Emerging wireless networks are foreseen as an integration of heterogeneous spectrum bands, wireless access technologies, and backhaul solutions, as well as a large-scale interconnection of devices, people, and vehicles. Such a heterogeneity will range from the proliferation of multi-tasking user devices with different capabilities such as smartphones and tablets to the deployment of multi-mode access points that can operate over heterogeneous frequency bands spanning both sub-6 GHz microwave and high-frequency millimeter wave (mmW) frequencies bands. This heterogeneous ecosystem will yield new challenges and opportunities for wireless resource management. On the one hand, resource management can exploit user and network-specific context information, such as application type, social metrics, or operator pricing, to develop application-driven, context-aware networks. Similarly, multiple frequency bands can be leveraged to meet the stringent and heterogeneous quality-of-service (QoS) requirements of the new wireless services such as video streaming and interactive gaming. On the other hand, resource management in such heterogeneous, multi-band, and large-scale wireless systems requires distributed frameworks that can effectively utilize all available resources while operating with manageable overhead. The key goal of this dissertation is therefore to develop novel, self-organizing, and low-complexity resource management protocols -- using techniques from matching theory, optimization, and machine learning -- to address critical resource allocation problems for emerging heterogeneous wireless systems while explicitly modeling and factoring diverse network context information. Towards achieving this goal, this dissertation makes a number of key contributions. First, a novel context-aware scheduling framework is developed for enabling dual-mode base stations to efficiently and jointly utilize mmW and microwave frequency resources while maximizing the number of user applications whose stringent delay requirements are satisfied. The results show that the proposed approach will be able to significantly improve the QoS per application and decrease the outage probability. Second, novel solutions are proposed to address both network formation and resource allocation problems in multi-hop wireless backhaul networks that operate at mmW frequencies. The proposed framework motivates collaboration among multiple network operators by resource sharing to reduce the cost of backhauling, while jointly accounting for both wireless channel characteristics and economic factors. Third, a novel framework is proposed to exploit high-capacity mmW communications and device-level caching to minimize handover failures as well as energy consumption by inter-frequency measurements, and to provide seamless mobility in dense heterogeneous mmW-microwave small cell networks (SCNs). Fourth, a new cell association algorithm is proposed, based on matching theory with minimum quota constraints, to optimize load balancing in integrated mmW-microwave networks. Fifth, a novel medium access control (MAC) protocol is proposed to dynamically manage the wireless local area network (WLAN) traffic jointly over the unlicensed 60 GHz mmW and sub-6 GHz bands to maximize the saturation throughput and minimize the delay experienced by users. Finally, a novel resource management approach is proposed to optimize device-to-device (D2D) communications and improve traffic offload in heterogeneous wireless SCNs by leveraging social context information that is dynamically learned by the network. In a nutshell, by providing novel, context-aware, and self-organizing frameworks, this dissertation addresses fundamentally challenging resource management problems that mainly stem from large scale, stringent service requirements, and heterogeneity of next-generation wireless networks. / Ph. D. / The emergence of bandwidth-intensive applications along with vast proliferation of smart, multi-tasking handhelds have strained the capacity of wireless networks. Furthermore, the landscape of wireless communications is shifting towards providing connectivity, not only to humans, but also to automated cars, drones, and robots, among other critical applications. These new technologies will enable devices, machines, and things to be more intuitive, while being more capable, in order to improve the quality of life for human. For example, in future networked life, smartphones will predict our needs and help us with providing timely and relevant information from our surrounding. As an another example, autonomous vehicles and smart transportation systems with large number of connected safety features will minimize road incidents and yield a safe and joyful driving experience. Turning such emerging services into reality will require new technology innovations that provide high efficiency and substantial levels of scalability. To this end, wireless communication is the key candidate to provide large-scale and ubiquitous connectivity. However, existing wireless networks operate at congested microwave (µW) frequency bands and cannot manage the exponential growth in wireless data traffic or support low latency and ultra-high reliability communications, required by many emerging critical applications. Therefore, the goal of this dissertation is to develop novel network resource utilization frameworks to efficiently manage the heterogeneous traffic in next-generation wireless networks, while meeting their stringent quality-of-service (QoS) requirements. This transformative, fundamental research will expedite the deployment of communications at very high frequencies, at the millimeter wave (mmW) frequency bands, in next-generation wireless networks. The developed frameworks will advance new concepts from matching theory and machine learning for resource management in cellular networks, wireless local area networks (WLANs), and the intersection of these systems at both mmW and µW unlicensed frequency bands. This multi-band networking will leverage the synergies between mmW and µW wireless networks to provide robust and cost-effective solutions that enable the support of heterogeneous traffic from future wireless services. The anticipated results will transform the way in which spectral and time resources are used in both cellular networks and WLANs.

Compressed sensing has been proposed as a computationally efficient method to estimate the finite-dimensional signals. The idea is to develop an undersampling operator that can sample the large but finite-dimensional sparse signals with a rate much below the required Nyquist rate. In other words, considering the sparsity level of the signal, the compressed sensing samples the signal with a rate proportional to the amount of information hidden in the signal. In this dissertation, first, we employ compressed sensing for physical layer signal processing of directional millimeter-wave communication. Second, we go through the theoretical aspect of compressed sensing by running a comprehensive theoretical analysis of compressed sensing to address two main unsolved problems, (1) continuous-extension compressed sensing in locally convex space and (2) computing the optimum subspace and its dimension using the idea of equivalent topologies using Köthe sequence. In the first part of this thesis, we employ compressed sensing to address various problems in directional millimeter-wave communication. In particular, we are focusing on stochastic characteristics of the underlying channel to characterize, detect, estimate, and track angular parameters of doubly directional millimeter-wave communication. For this purpose, we employ compressed sensing in combination with other stochastic methods such as Correlation Matrix Distance (CMD), spectral overlap, autoregressive process, and Fuzzy entropy to (1) study the (non) stationary behavior of the channel and (2) estimate and track channel parameters. This class of applications is finite-dimensional signals. Compressed sensing demonstrates great capability in sampling finite-dimensional signals. Nevertheless, it does not show the same performance sampling the semi-infinite and infinite-dimensional signals. The second part of the thesis is more theoretical works on compressed sensing toward application. In chapter 4, we leverage the group Fourier theory and the stochastical nature of the directional communication to introduce families of the linear and quadratic family of displacement operators that track the join-distribution signals by mapping the old coordinates to the predicted new coordinates. We have shown that the continuous linear time-variant millimeter-wave channel can be represented as the product of channel Wigner distribution and doubly directional channel. We notice that the localization operators in the given model are non-associative structures. The structure of the linear and quadratic localization operator considering group and quasi-group are studied thoroughly. In the last two chapters, we propose continuous compressed sensing to address infinite-dimensional signals and apply the developed methods to a variety of applications. In chapter 5, we extend Hilbert-Schmidt integral operator to the Compressed Sensing Hilbert-Schmidt integral operator through the Kolmogorov conditional extension theorem. Two solutions for the Compressed Sensing Hilbert Schmidt integral operator have been proposed, (1) through Mercer's theorem and (2) through Green's theorem. We call the solution space the Compressed Sensing Karhunen-Loéve Expansion (CS-KLE) because of its deep relation to the conventional Karhunen-Loéve Expansion (KLE). The closed relation between CS-KLE and KLE is studied in the Hilbert space, with some additional structures inherited from the Banach space. We examine CS-KLE through a variety of finite-dimensional and infinite-dimensional compressible vector spaces. Chapter 6 proposes a theoretical framework to study the uniform convergence of a compressible vector space by formulating the compressed sensing in locally convex Hausdorff space, also known as Fréchet space. We examine the existence of an optimum subspace comprehensively and propose a method to compute the optimum subspace of both finite-dimensional and infinite-dimensional compressible topological vector spaces. To the author's best knowledge, we are the first group that proposes continuous compressed sensing that does not require any information about the local infinite-dimensional fluctuations of the signal.

This thesis discusses the investigation and utilization of a new promising thin-film material, liquid crystal polymer (LCP), for microwave and millimeter-wave (mm-wave [>30 GHz]) components and packages. The contribution of this research is in the determination of LCP's electrical and mechanical properties as they pertain to use in radio frequency (RF) systems up to mm-wave frequencies, and in evaluating LCP as a low-cost substrate and packaging material alternative to the hermetic materials traditionally desired for microwave circuits at frequencies above a few gigahertz (GHz). A study of LCP's mm-wave material properties was performed. Resonant circuit structures were designed to find the dielectric constant and loss tangent from 2-110 GHz under both ambient and elevated temperature conditions. Several unique processes were developed for the realization of novel multilayer LCP-based RF circuits. These processes include thermocompression bonding with tight temperature control (within a few degrees Celsius), precise multilayer alignment and patterning, and LCP laser processing with three different types of lasers. A proof-of-concept design that resulted from this research was a dual-frequency dual-polarization antenna array operating at 14 and 35 GHz. Device characterization such as mechanical flexibility testing of antennas and seal testing of packages were also performed. A low-loss interconnect was developed for laser-machined system-level thin-film LCP packages. These packages were designed for and measured with both RF micro-electromechanical (MEM) switches and monolithic microwave integrated circuits (MMICs). These research findings have shown LCP to be a material with uniquely attractive properties/capabilities for vertically integrated, compact multilayer LCP circuits and modules.

This research delves into wireless communication systems, with a particular focus on initial access processes, channel modeling, and beamforming strategies. The study involves meticulous channel data collection across diverse urban, suburban, and rural terrains, each presenting unique propagation challenges. The research also simulates a typical communication network with four base stations, adjusting their configurations to suit the varied terrains. A central focus is the implementation of the cell search methodology, including the exploration of random beamforming at both system and cell levels. The findings indicate that the cell-level system configurations do not yield significant performance improvements over the baseline configuration. Furthermore, potential increased costs associated with this strategy are noted. However, it is essential to highlight that this project serves as a critical exploration of the potential benefits of random beamforming at the cell level within non-public network scenarios. While the improvements observed are minimal, the insights gained from this research are poised to guide future research endeavors and contribute to the elimination of uncertainties in the field of wireless communication. / Denna forskning fördjupar sig i trådlösa kommunikationssystem, med särskilt fokus på initiala åtkomstprocesser, kanalmodellering och strålformningsstrategier. Studien involverade noggrann kanaldatainsamling över olika urbana, förorts- och landsbygdsterränger, var och en med unika spridningsutmaningar. Forskningen simulerade också ett typiskt kommunikationsnätverk med fyra basstationer som justerade deras konfigurationer för att passa de varierande terrängerna. Ett centralt fokus var implementeringen av cellsökningsmetoden, inklusive utforskning av slumpmässig strålformning på både system- och cellnivå. Resultaten indikerade att systemkonfigurationerna på cellnivå inte gav signifikanta prestandaförbättringar jämfört med baslinjekonfigurationen. Dessutom noterades potentiella ökade kostnader förknippade med denna strategi. Det är dock viktigt att betona att detta projekt fungerade som en kritisk utforskning av de potentiella fördelarna med slumpmässig strålformning på cellnivå inom icke-offentliga nätverksscenarier. Även om de observerade förbättringarna var minimala, är insikterna från denna forskning redo att vägleda framtida forskningsinsatser och bidra till att eliminera osäkerheter inom området trådlös kommunikation.

Research interest: In recent years we have seen the emergence of commercial applications at high frequencies, such as the top part of the microwave band and the millimeter and sub-millimeter bands, and it is expected a big increase in the coming years. This growing demand requires a rapid development of low-cost technology with good performance at these frequencies, where common technologies, such as microstrip and standard waveguides, have some shortcomings. In particular, existing solutions for high-gain planar scanning antennas at these frequencies su er from the disadvantages of these technologies giving rise to high-cost products not suitable for high volume production. Objectives: The main objective of this thesis is to study the feasibility of a new proposal to improve existing solutions to date for low-cost high-gain planar scanning antennas at high frequencies. This overall objective has resulted in another central objective of this thesis, which is the research of new quasi-TEM waveguides that are more appropriate than current technologies for the realization of circuits and components at these frequency bands. These guided solutions make use of periodic or arti cial surfaces in order to con- ne and channel the elds within these waveguides. Methodology: The work follows a logical sequence of speci c tasks aimed at achieving the main objective of this thesis. Chapter 2 presents the proposed guiding solution and shows its performance numerical and experimentally. The optimized design of high-gain antennas based on waveguide slot arrays requires the development of e cient ad-hoc codes. The implementation and validation of this code is presented in Chapter 3, where a new method for the analysis of corrugated surfaces is proposed, and in Chapter 4, which extends this code to the analysis of waveguide slot arrays. The process design and optimization of a two-dimensional array is described in Chapter 5, where a preliminary experimental validation is also described. Moreover, the proposed guiding solution has inspired the development of a new guiding technology of wider bandwidth and more versatile for the realization of circuits and components at high frequencies. Chapter 6 presents the contributions to the study of this technology and its application to the design of circuits. / Alfonso Alós, E. (2011). New quasi-TEM waveguides using artificial surfaces and their application to antennas and circuits [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/11073