Massive MIMO for Dependable Communication

Cellular communication is constantly evolving; currently 5G systems are being deployed and research towards 6G is ongoing. Three use cases have been discussed as enhanced mobile broadband (eMBB), massive machine-type communication (mMTC), and ultra-reliable low-latency communication (URLLC). To fulfill the requirements of these use cases, new technologies are needed and one enabler is massive multiple-input multiple-output (MIMO). By increasing the number of antennas at the base station side, data rates can be increased, more users can be served simultaneously, and there is a potential to improve reliability. In addition, it is possible to achieve better coverage, improved energy efficiency, and low-complex user devices. The performance of any wireless system is limited by the underlying channels. Massive MIMO channels have shown several beneficial properties: the array gain stemming from the combining of the signals from the many antennas, improved user separation due to favourable propagation -- where the user channels become pair-wise orthogonal -- and the channel hardening effect, where the variations of channel gain decreases as the number of antennas increases. Previous theoretical works have commonly assumed independent and identically distributed (i.i.d.) complex Gaussian channels. However, in the first studies on massive MIMO channels, it was shown that common outdoor and indoor environments are not that rich in scattering, but that the channels are rather spatially correlated. To enable the above use cases, investigations are needed for the targeted environments. This thesis focuses on the benefits of deploying massive MIMO systems to achieve dependable communication in a number of scenarios related to the use cases. The first main area is the study of an industrial environment and aims at characterizing and modeling massive MIMO channels to assess the possibility of achieving the requirements of URLLC in a factory context. For example, a unique fully distributed array is deployed with the aim to further exploit spatial diversity. The other main area concerns massive MIMO at sub-GHz, a previously unexplored area. The channel characteristics when deploying a physically very large array for IoT networks are explored. To conclude, massive MIMO can indeed bring great advantages when trying to achieve dependable communication. Although channels in regular indoor environments are not i.i.d. complex Gaussian, the model can be justified in rich scattering industrial environments. Due to massive MIMO, the small-scale fading effects are reduced and when deploying a distributed array also the large-scale fading effects are reduced. In the Internet-of-Things (IoT) scenario, the channel is not as rich scattering. In this use case one can benefit from the array gain to extend coverage and improved energy efficiency, and diversity is gained due to the physically large array

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

Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks

Soaring capacity and coverage demands dictate that future cellular networks need to soon migrate towards ultra-dense networks. However, network densification comes with a host of challenges that include compromised energy efficiency, complex interference management, cumbersome mobility management, burdensome signaling overheads and higher backhaul costs. Interestingly, most of the problems, that beleaguer network densification, stem from legacy networks' one common feature i.e., tight coupling between the control and data planes regardless of their degree of heterogeneity and cell density. Consequently, in wake of 5G, control and data planes separation architecture (SARC) has recently been conceived as a promising paradigm that has potential to address most of aforementioned challenges. In this article, we review various proposals that have been presented in literature so far to enable SARC. More specifically, we analyze how and to what degree various SARC proposals address the four main challenges in network densification namely: energy efficiency, system level capacity maximization, interference management and mobility management. We then focus on two salient features of future cellular networks that have not yet been adapted in legacy networks at wide scale and thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and device-to-device (D2D) communications. After providing necessary background on CoMP and D2D, we analyze how SARC can particularly act as a major enabler for CoMP and D2D in context of 5G. This article thus serves as both a tutorial as well as an up to date survey on SARC, CoMP and D2D. Most importantly, the article provides an extensive outlook of challenges and opportunities that lie at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201

Smart Beamforming for Direct Access to 5G-NR User Equipment from LEO Satellite at Ka-Band

Study how spatial diversity can help in massive IoT and develp signal processing access for MIMO beamformingNon-Terrestrial Networks (NTN), in particular LEO Satellite Networks, are expected to play a key role in extending and complementing terrestrial 5G networks in order to provide services to air, sea and un-served or under-served areas. This work proposes the implementation of a novel scheme called Resource Sharing Beamforming Access (RSBA), which seems a promising solution to deal with scenarios where Bit Error Rate (BER), probability of collision and/or achievable rate are important aspects of study. Given the system architecture presented in this work, RSBA will be proposed as solution in the 5G-NR Sat-IoT scenario. As it is expected, a huge amount of IoT devices will be transmitting in the uplink, and being the case of Non-Orthogonal-Multiple-Access (NOMA), the risk of collisions between devices will increase. The idea, after assessing the channel impairments of a direct link between a LEO Satellite and a NB-IoT device, it to study how spatial diversity via smart beamforming at the receiver will reduce the probability of collision between the devices, and thus increasing the number of users that can access to the media

Evaluation of Sigma-Delta-over-Fiber for High-Speed Wireless Applications

Future mobile communication networks aim to increase the communication speed,\ua0provide better reliability and improve the coverage. It needs to achieve all of these enhancements, while the number of users are increasing drastically. As a result, new base-station (BS) architectures where the signal processing is centralized and wireless access is provided through multiple, carefully coordinated remote radio heads are needed. Sigma-delta-over-fiber (SDoF) is a communication technique that can address both requirements and enable very low-complexity, phase coherent remote radio transmission, while transmitting wide-band communication signals with high quality. This thesis investigates the potential and limitations of SDoF communication links as an enabler for future mobile networks.In the first part of the thesis, an ultra-high-speed SDoF link is realized by using state-of-the-art vertical-cavity surface-emitting-lasers (VCSEL). The effects of VCSEL characteristics on such links in terms of signal quality, energy efficiency and potential lifespan is investigated. Furthermore, the potential and limitations of UHS-SDoF are evaluated with signals having various parameters. The results show that, low-cost, reliable, energy efficient, high signal quality SDoF links can be formed by using emerging VCSEL technology. Therefore, ultra-high-speed SDoF is a very promising technique for beyond 10~GHz communication systems.In the second part of the thesis, a multiple-input-multiple-output (MIMO) communication testbed with physically separated antenna elements, distributed-MIMO, is formed by multiple SDoF links. It is shown that the digital up-conversion, performed with a shared local-oscillator/clock at the central unit, provides excellent phase coherency between the physically distributed antenna elements. The proposed testbed demonstrates the advantages of SDoF for realizing distributed MIMO systems and is a powerful tool to perform various communication experiments in real environments.In general, SDoF is a solution for the downlink of a communication system, i.e. from central unit to remote radio head, however, the low complexity and low cost requirement of the remote radio heads makes it difficult to realize the uplinks of such systems. The third part of this thesis proposes an all-digital solution for realizing complementary uplinks for SDoF systems. The proposed structure is extensively investigated through simulations and measurements and the results demonstrate that it is possible realize all-digital, duplex, optical communication links between central units and remote radio heads.In summary, the results in this thesis demonstrate the potential of SDoF for wideband, distributed MIMO communication systems and proposes a new architecture for all-digital duplex communication links. Overall, the thesis shows that SDoF technique is powerful technique for emerging and future mobile communication networks, since it enables a centralized structure with low complexity remote radio heads and provides high signal quality