Experimental Investigations of Millimeter Wave Beamforming

The millimeter wave (mmW) band, commonly referred to as the frequency band between 30 GHz and 300 GHz, is seen as a possible candidate to increase achievable rates for mobile applications due to the existence of free spectrum. However, the high path loss necessitates the use of highly directional antennas. Furthermore, impairments and power constraints make it difficult to provide full digital beamforming systems. In this thesis, we approach this problem by proposing effective beam alignment and beam tracking algorithms for low-complex analog beamforming (ABF) systems, showing their applicability by experimental demonstration. After taking a closer look at particular features of the mmW channel properties and introducing the beamforming as a spatial filter, we begin our investigations with the application of detection theory for the non-convex beam alignment problem. Based on an M-ary hypothesis test, we derive algorithms for defining the length of the training signal efficiently. Using the concept of black-box optimization algorithms, which allow optimization of non-convex algorithms, we propose a beam alignment algorithm for codebook-based ABF based systems, which is shown to reduce the training overhead significantly. As a low-complex alternative, we propose a two-staged gradient-based beam alignment algorithm that uses convex optimization strategies after finding a subregion of the beam alignment function in which the function can be regarded convex. This algorithm is implemented in a real-time prototype system and shows its superiority over the exhaustive search approach in simulations and experiments. Finally, we propose a beam tracking algorithm for supporting mobility. Experiments and comparisons with a ray-tracing channel model show that it can be used efficiently in line of sight (LoS) and non line of sight (NLoS) scenarios for walking-speed movements

New Radio Small Cell Propagation Environment

The characterization of the wireless medium in indoor small cell networks is essential to obtain appropriate modelling of the propagation environment. This dissertation on ”MeasurementBased Characterization of the 5G New Radio Small Cell Propagation Environment” has been developed in an experimental environment. The underlying tasks are divided into three phases. The first phase took place in the laboratory of the Instituto de Telecomunicações – Covilhã, located in the Departamento de Engenharia Electromecânica of Universidade da Beira Interior. During this part of the research, spectrum measurements and the characterization of the S11 parameter (response in the first port for the signal incident in the first port) have been made experimentally through the printed circuit board antennas in the 2.6 GHz and 3.5 GHz frequency bands operating in the 2.625 GHz and 3.590 GHz center frequency, manufactured by us. The fabrication of the antennas was preceded by the simulation in the student version CST STUDIO software. In this phase, the spectrum measurements and the characterization of Smith Chart have been made to measure gain and impedance using the Rohde & Schwarz Vector Network Analyzer (VNA) from IT laboratory. Based on mathematical calculations and considerations on the conductivity and permeability of the environment, the antennas were built for use in indoor and outdoor environments. The developed antennas are characterized by their bandwidth and their radiation characteristics. The second phase took place in the three rooms adjacent to the laboratory, in which the srsLTE emulation software was applied to the 4G indoor scenario. The experimental setup includes three elements, namely a base station (BS or 4G eNodeB), which transmits the communication signal and which served as a signal source, a user equipment (UE), and an interfering eNodeB. The size of each room is 7.32 × 7.32 square meters. While room 1 is the room of interest, where theoretical and practical measurements took place, BSs that act as wireless interfering nodes are also separately considered either in room 2 or room 3. By varying the UE positions within room 1, it was possible to verify that the highest values of the received power occur close to the central BS. However, the received power does not decrease suddenly because of the reduced gain in the radiation pattern in the back part of the antenna. In addition, it was demonstrated that there is an effect of “wall loss”proven by the path loss increase between room 1 and room 2 (or between room 2 and 3). If we consider an attenuation for each wall of circa 7-9 dB the trend of the WINNER II at 2.625 GHz model for the interference coming across different walls is verified. Future work includes to investigate the 3.5 GHz frequency band. The third phase is being carried out at the facilities of the old aerodrome of Covilhã which, using a temporary license assigned to us by Instituto de Comunicações Português (ICP-ANACOM) as the two first phases. The aim of this phase is to investigate the two-slope behaviour in the UMi scenario. Very initial LTE-Advanced tests have been performed to verify the propagation of the two ray (with a reflection in the asphalt) from BS implemented with USRP B210 and srsLTE system by considering an urban cell with a length of 80 m and an interfering base station at 320 m, at 2500 - 2510 MHz (DL - Downlink) by now, mainly due to the current availability of a directional antenna in this specific band.A investigação de sinais rádio em comunicações sem fios continua a gerar considerável interesse em todo mundo, devido ao seu amplo leque de aplicações, que inclui a troca de dados entre dois ou mais dispositivos, comunicações móveis e via Wi-Fi, infravermelho, transmissão de canais de televisão, monitorização de campos, proteção e vigilância costeira e observação ambiental para exploração. A tecnologia de ondas de rádio é o um dos vários recursos que viabilizam as comunicações de alta velocidade e encurta distâncias entre dois pontos em comunicação. Na realidade, caracterização da comunicação em redes com pequenas células é essencial para obter uma modelização apropriada de ambiente de propagação. Esta dissertação sob o tema ”Measurement-Based Characterization of the 5G New Radio Small Cells Propagation Envioronment” foi desenvolvida num ambiente experimental, cujas tarefas foram divididas em fases. A primeira fase teve lugar no laboratório do Instituto de Telecomunicações da Covilhã (IT), afeto ao Departamento de Engenharia Eletromecânica. Nela foram feitas as simulações das antenas no software CST STUDIO, versão do estudante que foram utilizadas nos equipamentos durante as medições. Seguiu-se a padronização das mesmas nas faixas dos 2.6 GHz e 3.5 GHz, nas frequências centrais de 2.625 GHz e 3.590 GHZ, usando placas de circuitos impressos. Em seguida, foram feitas as medições do espectro e a caraterização do S11 e da carta de Smith para medir a impedância de entrada e o ganho. As medições foram feitas com recurso ao Vector Network Analyzer (VNA). Com base em cálculos matemáticos e considerações sobre a condutividade e permeabilidade do ambiente, as antenas foram construídas para uso em ambientes internos e externos e com ou sem interferentes. As antenas desenvolvidas são caracterizadas por sua largura de banda e suas características de radiação. A segunda fase decorreu nas três salas adjacentes ao laboratório de Telecomunicações, na qual foi montada a topologia com o sistema srsLTE associado aos USRP B210 ligados aos computadores com o sistema operativo Linux com três componentes, nomeadamente uma estação base (BS), que serviu de fonte do sinal de comunicação com um equipamento de utilizador (UE) que o recebe, e dois interferentes. Importa realçar que esta segunda fase foi dividida em duas etapas, das quais uma sem interferente para medir a potência recebida da própria estação base e outra com os interferentes mais próximo e mais afastado da sala do sinal da própria célula. O objetivo desta fase foi o de verificar o modelo de propagação do sinal de comunicação da tecnologia LTE e medir a potência recebida pelo utilizador com recurso ao Analisador de Espectro portátil FSH8 da Rohde & Schwarz capaz de medir de 10 kHz a 8 GHz, feita na frequência central de 2.625 GHz. Nas medições feitas em ambiente interior, o tamanho de cada uma das três salas é 7.32 × 7.32 metros quadrados. Embora a sala 1 seja a sala de interesse, onde ocorreram as medições teóricas e práticas, as BSs que atuam como nós interferentes também são consideradas separadamente na sala 2 ou na sala 3. Ao variar as posições de UE dentro da sala 1, foi possível verificar que os valores superiores da potência recebida ocorrem próximos à BS central. No entanto, a potência recebida não diminui repentinamente por causa do efeito do ganho reduzido no diagrama de radiação na parte traseira da antena. Além disso, foi demonstrado que existe um efeito de “atenuação da parede” comprovado pelo aumento da atenuação de trajeto entre a sala 1 e a sala 2 (ou entre a sala 2 e 3). Se considerarmos uma atenuação para cada parede de cerca de 7-9 dB, verifica-se a tendência do modelo WINNER II a 2.625 GHz para a interferência que atravessa as diversas paredes. Trabalhos futuros incluem a investigação da banda de frequência de 3.5 GHz. Já a terceira fase foi realizada nas instalações do antigo aeródromo da Covilhã, e em todas as fases servimo-nos de uma licença concedida pela Entidade Reguladora do Espectro (ICPANACOM), que permitiu realizar testes de verificação da propagação do sinal no ambiente livre na faixa de frequência dos 2.6 GHz com 2500 – 2510 MHz (UL - Uplink) e 2620 – 2630 MHz (DL - Downlink). A terceira fase ainda está a decorrer nas instalações do antigo aeródromo da Covilhã, mediante a mesma licença temporária que nos foi atribuída pelo Instituto de Comunicações de Portugal ou Autoridade Nacional de Comunicações (ICP-ANACOM) sendo esta reguladora do espectro. O objetivo é continuar a investigar o comportamento de duas inclinações no cenário UMi. Testes muito iniciais LTE-Advanced foram realizados para verificar a propagação dos dois raios (direto e refletido, com uma reflexão no asfalto) do BS implementado com o sistema USRP B210 e srsLTE, considerando uma célula urbana com um comprimento de 80 metros uma estação base interferente em 320 metros, a operar, provisoriamente, a 2500 - 2510 MHz (na ligação descendente, DL - Downlink, devido à disponibilidade de uma antena direcional específica para esta banda). Finalmente este trabalho de investigação pode ser resumidamente dividido em três categorias, nomeadamente investigação de análises teóricas e matemáticas relevantes da propagação de ondas de rádio em meios com e sem interferência significativa. Medições para verificar o comportamento do sinal de propagação da tecnologia LTE-Advanced com recursos ao analisador de espectro, simulação das antenas, fabricação e medição das características de radiação das mesmas. Assim, as antenas concebidas com bons resultados foram fabricadas nas instalações da Faculdade de Ciências no Departamento de Física da Universidade da Beira Interior, sendo de seguidas testadas e caracterizadas com o auxílio do Vector Nettwork Analyzer disponível no Laboratório de Telecomunicações do Departamento de Engenharia Eletromecânica da Universidade da Beira Interior. E, finalmente, os cálculos estatísticos que incluem o teste de normalidade de Kolmogorov-Smirnov com recurso ao software estatístico SPSS para validar os resultados obtidos seguida da construção dos gráficos no Matlab em 3D, conforme a superfície da sala

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Antennas and Propagation Aspects for Emerging Wireless Communication Technologies

The increasing demand for high data rate applications and the delivery of zero-latency multimedia content drives technological evolutions towards the design and implementation of next-generation broadband wireless networks. In this context, various novel technologies have been introduced, such as millimeter wave (mmWave) transmission, massive multiple input multiple output (MIMO) systems, and non-orthogonal multiple access (NOMA) schemes in order to support the vision of fifth generation (5G) wireless cellular networks. The introduction of these technologies, however, is inextricably connected with a holistic redesign of the current transceiver structures, as well as the network architecture reconfiguration. To this end, ultra-dense network deployment along with distributed massive MIMO technologies and intermediate relay nodes have been proposed, among others, in order to ensure an improved quality of services to all mobile users. In the same framework, the design and evaluation of novel antenna configurations able to support wideband applications is of utmost importance for 5G context support. Furthermore, in order to design reliable 5G systems, the channel characterization in these frequencies and in the complex propagation environments cannot be ignored because it plays a significant role. In this Special Issue, fourteen papers are published, covering various aspects of novel antenna designs for broadband applications, propagation models at mmWave bands, the deployment of NOMA techniques, radio network planning for 5G networks, and multi-beam antenna technologies for 5G wireless communications

Antenna Designs for 5G/IoT and Space Applications

This book is intended to shed some light on recent advances in antenna design for these new emerging applications and identify further research areas in this exciting field of communications technologies. Considering the specificity of the operational environment, e.g., huge distance, moving support (satellite), huge temperature drift, small dimension with respect to the distance, etc, antennas, are the fundamental device allowing to maintain a constant interoperability between ground station and satellite, or different satellites. High gain, stable (in temperature, and time) performances, long lifecycle are some of the requirements that necessitates special attention with respect to standard designs. The chapters of this book discuss various aspects of the above-mentioned list presenting the view of the authors. Some of the contributors are working strictly in the field (space), so they have a very targeted view on the subjects, while others with a more academic background, proposes futuristic solutions. We hope that interested reader, will find a fertile source of information, that combined with their interest/background will allow efficiently exploiting the combination of these two perspectives