Multi-Antenna Techniques for Next Generation Cellular Communications

Future cellular communications are expected to offer substantial improvements for the pre- existing mobile services with higher data rates and lower latency as well as pioneer new types of applications that must comply with strict demands from a wider range of user types. All of these tasks require utmost efficiency in the use of spectral resources. Deploying multiple antennas introduces an additional signal dimension to wireless data transmissions, which provides a significant alternative solution against the plateauing capacity issue of the limited available spectrum. Multi-antenna techniques and the associated key enabling technologies possess unquestionable potential to play a key role in the evolution of next generation cellular systems. Spectral efficiency can be improved on downlink by concurrently serving multiple users with high-rate data connections on shared resources. In this thesis optimized multi-user multi-input multi-output (MIMO) transmissions are investigated on downlink from both filter design and resource allocation/assignment points of view. Regarding filter design, a joint baseband processing method is proposed specifically for high signal-to-noise ratio (SNR) conditions, where the necessary signaling overhead can be compensated for. Regarding resource scheduling, greedy- and genetic-based algorithms are proposed that demand lower complexity with large number of resource blocks relative to prior implementations. Channel estimation techniques are investigated for massive MIMO technology. In case of channel reciprocity, this thesis proposes an overhead reduction scheme for the signaling of user channel state information (CSI) feedback during a relative antenna calibration. In addition, a multi-cell coordination method is proposed for subspace-based blind estimators on uplink, which can be implicitly translated to downlink CSI in the presence of ideal reciprocity. Regarding non-reciprocal channels, a novel estimation technique is proposed based on reconstructing full downlink CSI from a select number of dominant propagation paths. The proposed method offers drastic compressions in user feedback reports and requires much simpler downlink training processes. Full-duplex technology can provide up to twice the spectral efficiency of conventional resource divisions. This thesis considers a full-duplex two-hop link with a MIMO relay and investigates mitigation techniques against the inherent loop-interference. Spatial-domain suppression schemes are developed for the optimization of full-duplex MIMO relaying in a coverage extension scenario on downlink. The proposed methods are demonstrated to generate data rates that closely approximate their global bounds

Sistemas MIMO auxiliados por grandes superfícies refletoras como novidade para tecnologias 6G

Orientador: Gustavo FraidenraichDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Large Intelligent Surfaces (LIS) é uma tecnologia promissora para a sexta geração (6G) de comunicações móveis devido ao seu potencial para melhorar a relação sinal-ruído (SNR), aumentar a eficiência espectral e ainda possibilitar a redução do consumo de energia no estação rádio base (BS) durante a transmissão. O LIS é um painel formado por células que podem refletir ondas eletromagnéticas para fazer beamforming e remover a fase do canal, a superfície é formada por metamateriais que podem alterar a fase das ondas incidentes com um ângulo quantizado que pode ser controlado digitalmente por software permitindo que o sinal resultante da soma de todas as componentes refletidas pelo LIS possua uma fase adaptada para cancelar o efeito da fase do canal. Esta fase é estimada por algoritmos de aprendizado de máquina e quanto mais eficiente a estimativa melhor será o processo de ajuste de fase, mas devido às não idealidades do sistema, temos um erro de fase residual que neste trabalho é modelado pela distribuição de Von Mises. Dividimos nosso estudo em dois capítulos, o primeiro referindo-se a sistemas com apenas uma antena na BS, considerando a presença de uma linha direta de propagação de ondas eletromagnéticas a.k.a. line of sight (LoS) com desvanecimento Nakagami-m e nós ignoramos a possibilidade de um link direto com o usuário, já na segunda parte consideramos um arranjo de antenas na estação base e incluindo um link direto entre o usuário e a BS, mas negligenciando a LoS ao considerar canais com desvanecimento Rayleigh. Para o cenário da BS de uma antena, derivamos a probabilidade de erro de bit exata considerando modulação M-QAM e BPSK quando o número de elementos do LIS, n , é igual a 2 e 3 considerando que os coeficientes de desvanecimento do canal são Nakagami-m e o LIS tem um erro de fase com distribuição de Von Mises. Além disso, com base no teorema do limite central, e considerando um grande número de elementos refletores, apresentamos uma aproximação precisa e limites superiores para a taxa de erro de bit. Por meio de várias simulações de Monte Carlo, demonstramos que todas as expressões derivadas correspondem perfeitamente aos resultados simulados. No cenário de matriz de antenas, consideramos o Rayleigh flat fading para cada subcanal entre a BS, o LIS e o usuário e aplicamos um precoder na estação base para ter a transmissão de razão máxima (MRT). Com base no teorema do limite central (CLT), concluímos que o canal total tem um desvanecimento Gamma equivalente cujos parâmetros são derivados dos momentos estatísticos do canal entre o arranjo de antenas e LIS, e também do LIS para o usuário. Assumindo que o canal equivalente pode ser modelado como uma distribuição Gama, propomos expressões de forma fechada muito precisas para a probabilidade de erro de bit e um limite superior muito restrito. Para o caso em que o LIS não é capaz de realizar o cancelamento de fase perfeito, ou seja, sob erros de fase, é possível analisar o desempenho do sistema considerando as aproximações analíticas e os resultados simulados obtidos pelo método de Monte Carlo. As expressões analíticas para os parâmetros da distribuição Gama são muito difíceis de serem obtidas devido à complexidade das transformações não lineares de variáveis aleatórias com média diferente de zero e termos correlatos. Mesmo com o cancelamento de fase perfeito, todos os coeficientes de desvanecimento são complexos devido à ligação entre o usuário e a estação base que não é negligenciada neste estudoAbstract: Large intelligent surfaces (LIS) is a promising technology for the sixth generation (6G) of mobile communications due to its potential to improve the signal to noise ratio (SNR), increase spectral efficiency, and even make it possible to reduce energy consumption in the radio base station (BS) during transmission. The LIS is a panel formed by cells that can reflect electromagnetic waves to make beamforming and cancel the channel phase, the surface is formed by metamaterials that can change the phase of the incident waves with a quantized angle that can be controlled digitally by software allowing that the signal resulting from the sum of all components reflected by the LIS has a phase adapted to nullify the effect of the channel phase. The channel information is estimated by machine learning algorithms and more efficient phase estimations implies better phase adjustments at the LIS, but due to the system's non-idealities, we have a residual phase error that in this work is modeled by the Von Mises distribution. We divided our study into two chapters, the first referring to systems with a single antenna at the BS considering the existence of a straight and unobstructed line for electromagnetic wave propagation a.k.a. line of sight (LoS) with Nakagami-m fading and we ignore the possibility of a direct link between the user, in the second part we consider an antenna array at the base station and including a direct link between the user and the BS but neglecting the LoS by considering Rayleigh fading channels. For the single antenna BS scenario, we derive the exact bit error probability considering quadrature amplitude modulation (M-QAM) and binary phase-shift keying (BPSK) when the number of LIS elements, n, is equal to 2 and 3 considering that the channel fading coefficients are Nakagami-m. Also, based on the central limit theorem (CLT), and considering a large number of reflecting elements, we present an accurate approximation and upper bounds for the bit error rate. Through several Monte Carlo simulations, we demonstrate that all derived expressions perfectly match the simulated results. In the antenna array scenario, we consider Rayleigh flat fading for each subchannel between the BS, the LIS, and the user and we apply a precoder at the base station to have the maximum ratio transmission (MRT). Based on the CLT, we conclude that the overall channel has an equivalent Gamma fading whose parameters are derived from the moments of the channel fading between the antenna array and LIS, and also from the LIS to the single user. Assuming that the equivalent channel can be modeled as a Gamma distribution, we propose very accurate closed-form expressions for the bit error probability and a very tight upper bound. For the case where the LIS is not able to perform perfect phase cancellation, that is, under phase errors, it is possible to analyze the system performance considering the analytical approximations and the simulated results obtained using the well known Monte Carlo method. The analytical expressions for the parameters of the Gamma distribution are very difficult to be obtained due to the complexity of the nonlinear transformations of random variables with non-zero mean and correlated terms. Even with perfect phase cancellation, all the fading coefficients are complex due to the link between the user and the base station that is not neglected in this studyMestradoTelecomunicações e TelemáticaMestre em Engenharia Elétrica88882.329402/2019-01CAPE

Satellite Communications

This study is motivated by the need to give the reader a broad view of the developments, key concepts, and technologies related to information society evolution, with a focus on the wireless communications and geoinformation technologies and their role in the environment. Giving perspective, it aims at assisting people active in the industry, the public sector, and Earth science fields as well, by providing a base for their continued work and thinking

MIMO antenna systems for next generation wireless communications

Multiple Input Multiple Output wireless communications systems require as the name implies multiple antennas at the transmit and receive side of a link, as all multiple elements operationally occupy the same spectrum, the capacity of carrying information is increased with no increase in the transmission bandwidth or power. Antennas destined for MIMO systems need to address the issue of adequate isolation between elements and the issue of the diversity performance of the array, these issues become challenging for mobile terminals. In this thesis dual band arrays for the mobile and the access point are proposed along with dual band mutual coupling reduction and radiation pattern improvement methods. First a dual band two element printed inverted F stacked monopole array is proposed for the mobile terminal. The single elements in the array are easily tuneable and achieve impedance matching from an open stub. The configuration is compact, with radiators distanced at 0.13λ0. By use of a grid of parasitically coupled printed lines mutual coupling is reduced by 9dB, where at the lower band at 2.4GHz, S12 = −18dB. Then a dual band two element printed dipole array is proposed for a pico–micro cell access point. The dipoles are fed by a printed balun which provides wide impedance bandwidth at two bands. To improve the radiation pattern at both frequencies the array is positioned above a dual band frequency selective surface, acting as an artificial magnetic conductor, thus allowing the screen to be placed 0.03λ0 from the array while maintaining good radiation efficiency. Finally a brief discussion of dual band surface wave suppression for printed antennas is presented. Here it is suggested that the surface waves can be eliminated by a superstrate at one band and by an EBG lattice at the second band. Initial experiments with different size superstrates and three periods of mushroom type EBG, show that mutual coupling can be reduced and the radiation pattern can be modified.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (EPSRC)GBUnited Kingdo