Geringer RF-Komplexität Massive MIMO Systemen: Antennenselektion und Hybrid Analog-Digital Strahlformung

Wireless data traffic has been increased dramatically in the last decades, and will continue to increase in the future. As a consequence, the infrastructure of wireless communication systems needs to advance on the data capacity. Massive Multiple-Input Multiple-Output (MIMO) is a promising candidate technology to meet the demand. By scaling up the conventional MIMO by orders of magnitude number of \emph{active} antennas, a massive MIMO system can harvest considerable channel degrees of freedom to increase the spectral efficiency. However, increasing the number of \emph{active} antennas needs to increase both the numbers of Radio Frequency (RF) transceivers and antenna elements \emph{at the same rate}, which will increase the RF complexity and cost dramatically. It is known that the complexity and cost of antenna elements are usually much lower than that of RF transceivers, which motivates us to scale up MIMO by a lower increasing rate of the number of RF transceivers than that of antenna elements, resulting in so-called low RF-complexity massive MIMO systems. In this thesis, we study two types of low RF-complexity massive MIMO systems, i.e., massive MIMO antenna selection systems and massive MIMO hybrid analog-digital beamforming systems. Both systems use specific RF networks to bridge a massive number of antennas and a small number of RF transceivers, leading to signal dimension reduction from antennas to RF transceivers. The RF network used in antenna selection is referred to as RF switching network; while the RF network used in hybrid beamforming is referred to as Phase Shifting Network (PSN). Both RF networks have two types of architectures, i.e., full-array architecture and sub-array architecture. The latter has lower insertion loss, lower complexity and better scalability than the former, but at the price of performance degradation caused by connection constraint, which will be studied for both low RF-complexity systems in this thesis. In addition, a low RF-complexity PSN for the hybrid analog-digital beamforming system needs also to be studied to replace the conventional high-complexity-and-cost phase-shifter-based PSN. In the antenna selection system, the upper bounds on the channel capacity using asymptotic theory on order statistics are derived at the large-scale limit. The optimal antenna selection algorithms are also developed, which are based on Branch And Bound (BAB) search algorithm. Through the theoretical and algorithm studies, it is found that the sub-array antenna selection has close performance to the full-array antenna selection. In the hybrid beamforming system, we propose to use Rotman lens as PSN, which is of lower complexity and cost than the conventional phase-shifter-based PSN. Two beam selection algorithms, i.e., sub-optimal greedy search and optimal BAB search, are also proposed. In addition, the Rotman lenses are designed, fabricated and measured. The measurement results together with the beam selection algorithms are used to perform Monte Carlo simulation. Simulation results show that the proposed Rotman-lens-based system with the sub-array architecture suffers noticeable performance degradation compared to the system with the full-array architecture when ideal Rotman lenses are used. But when practical non-ideal Rotman lens are used, the former outperforms the latter when the number of antennas is large enough. Most interestingly, with non-ideal hardware, the sub-array Rotman-lens-based system has close performance to the sub-array phase-shifter-based system, and also exhibits a wideband capability. To prove the advantage of the low RF-complexity massive MIMO, two testbeds are built up for the antenna selection and hybrid beamforming systems, respectively. The measurement results show the low RF-complexity massive MIMO systems have superior performance over the small-scale MIMO systems under the condition of the same number of RF transceivers. The results in this thesis show that the low RF-complexity massive MIMO systems proposed in this thesis are feasible in technology and promising in performance, validating its potential usage for the future 5G wireless communication systems.Der drahtlose Datenverkehr ist in den letzten Jahrzehnten dramatisch gestiegen und wird auch in Zukunft weiter zunehmen. Infolgedessen muss die Datenkapazität der drahtlosen Infrastruktur erhöht werden. Mehrantennen Systeme mit einer sehr großen Anzahl an Antennen (engl. Massive Multiple-Input Multiple-Output (MIMO)) sind vielversprechende Technologiekandidaten, um diese Nachfrage zu erfüllen. Durch die Hochskalierung der Antennenanzahl eines konventionellen MIMO um mehrere Größenordnungen kann ein Massive MIMO-System erhebliche Kanalfreiheitsgrade erlangen, um die spektrale Effizienz zu verbessern. Allerdings muss mit der Anzahl der \emph{aktiven} Antennen sowohl die Anzahl der Hochfrequenz (engl. Radio Frequency (RF)) Transceiver als auch die der Antennenelemente \emph{im gleichen Maße} vergrössert werden, was die RF-Komplexität und Kosten dramatisch erhöht. Dabei ist bekannt, dass die Komplexität und die Kosten von Antennenelementen in der Regel viel niedriger sind als die von RF-Transceivern. Dies führt uns dazu dass wir das MIMO-System um eine im Verhältnis zur Antennenzahl geringere Anzahl von RF-Transceivern erweitern wollen, den so genannten Massive MIMO-Systemen mit geringer RF-Komplexität. In dieser Arbeit untersuchen wir zwei Arten von Massive MIMO-Systemen mit geringer RF-Komplexität, nämlich Massive MIMO-Antennenselektionssysteme und Massive MIMO-Hybrid-Analog-Digital-Strahlformungssysteme. Beide Systeme verwenden spezielle RF-Netzwerke, um eine größere Anzahl von Antennen von einer kleineren Anzahl von RF-Transceivern zu versorgen, was zu einer Signalraumreduktion von den Antennen zu den RF-Transceivern führt. Das bei der Antennenselektions verwendete RF-Netzwerk wird als RF-Koppelfeld bezeichnet, während das RF-Netzwerk, das bei der Hybrid-Strahlformung verwendet wird, als Phasenverschiebungsnetzwerk (engl. Phase Shifting Network, PSN) bezeichnet wird. Beide RF-Netzwerke können als Voll-Array-Architektur oder als Sub-Array-Architektur realisiert werden. Letztere hat eine geringere Einfügedämpfung, eine geringere Komplexität und eine bessere Skalierbarkeit als die erstere, aber zum Preis der Leistungsverschlechterung, die durch eine eingeschränkung Anzahl von Antennen-Transceiver-Verbindungen verursacht wird. Die vorliegende Arbeit untersucht dies für beide Systeme mit niedriger RF-Komplexität. Darüber hinaus wird auch ein PSN mit niedriger RF-Komplexität für das Hybride-Analog-Digital- Strahlformungssystem untersucht, das das herkömmliche hochkomplexe und kostenintensive PSN ersetzen soll. Im Antennenselektionssystem werden die Obergrenzen der Kanalkapazität unter Verwendung der Asymptoten Theorie der Ordnungsstatistik im Grenzverhalten abgeleitet. Die optimalen Antennenselektions-Algorithmen, die auf dem Branch and Bound (BAB) Suchalgorithmus basieren, werden ebenfalls entwickelt. Die theoretischen und algorithmischen Untersuchungen zeigen, dass die Leistung der Sub-Array-Antennenauswahl dicht bei der der Voll-Array-Antennenselektions liegt. Im Hybrid-Strahlformungssystem schlagen wir vor, eine Rotman-Linse als PSN zu verwenden, die von geringerer Komplexität und Kosten ist als das herkömmliche auf Phasenverschiebung basierende PSN. Es werden zwei Strahlauswahlalgorithmen vorgeschlagen, eine suboptimale Greedy-Suche und eine optimale BAB-Suche. Darüber hinaus wird die Rotman-Linse entworfen, gefertigt und vermessen. Die Messergebnisse werden zusammen mit den Strahlselektionsalgorithmen zur Durchführung einer Monte-Carlo-Simulation verwendet. Simulationsergebnisse zeigen, dass das vorgeschlagene Rotman-Linsen-basierte System mit der Sub-Array-Architektur eine spürbare Leistungsverschlechterung im Vergleich zum System mit der Full-Array-Architektur erleidet, wenn ideale Rotman-Linsen verwendet werden. Aber wenn reale nicht-ideale Rotman-Linsen verwendet werden, übertrifft erstere die zweite, wenn die Anzahl der Antennen groß genug ist. Noch interessanter, mit nicht-idealer Hardware, zeigt das Sub-Array Rotman-Linsen-basierte System in etwa die gleiche Leistung wie das Sub-Array Phasenschieber-basierte System und weist auch Breitbandfähigkeiten auf. Um den Vorteil der Massive MIMO-Systeme mit geringer RF-Komplexität zu beweisen, werden zwei Testumgebungen für die Antennenauswahl- und Hybrid-Strahlformungssysteme aufgebaut. Die Messergebnisse zeigen, dass, unter der Bedingung einer gleichen Anzahl von RF-Transceivern, die Massive MIMO-Systeme mit geringer RF-Komplexität in der Leistung den normalen MIMO-Systemen überlegen sind. Die Ergebnisse meiner Arbeit zeigen, dass die von mir vorgeschlagenen Massive MIMO-Systeme mit geringer RF-Komplexität technisch machbar und vielversprechend in der Leistung sind und bestätigen damit deren potentielle Nutzung für die zukünftigen 5G-Funkkommunikationssysteme

Energy Efficient Large Scale Antenna Systems for 5G Communications and Beyond

The increasing popularity of mobile devices has fueled an exponential growth in data traffic. This phenomenon has led to the development of systems that achieve higher spectral efficiencies, at the cost of higher power consumptions. Consequently, the investigation on solutions that allow to increase the maximum throughput together with the energy efficiency becomes crucial for modern wireless systems. This thesis aims to improve the trade-off between performances and power consumption with special focus toward multiuser multiple-antenna communications, due to their promising benefits in terms of spectral efficiency. Research envisaged massive Multi-Input-Multi-Output (MIMO) systems as the main technology to meet these data traffic demands, as very large arrays lead to unprecedented data throughputs and beamforming gains. However, larger arrays lead to increased power consumption and hardware complexity, as each radiating element requires a radio frequency chain, which is accountable for the highest percentage of the total power consumption. Nonetheless, the availability of a large number of antennas unveils the possibility to wisely select a subset of radiating elements. This thesis shows that multiuser interference can be exploited to increase the received power, with significant circuit power savings at the base station. Similarly, millimeter-wave communications experienced raising interest among the scientific community because of their multi-GHz bandwidth and their ability to place large arrays in limited physical spaces. Millimeter-wave systems inherit same benefits and weaknesses of massive MIMO communications. However, antenna selection is not viable in millimeter-wave communications because they rely on high beamforming gains. Therefore, this thesis proposes a scheme that is able to reduce the number of radio frequency chains required, while achieving close-to-optimal performances. Analytical and numerical results show that the proposed techniques are able to improve the overall energy efficiency with respect to the state-of-the-art, hence proving to be valid candidates for practical implementations of modern communication systems

Optimization of Spectrum Management in Massive Array Antenna Systems with MIMO

Fifth generation (5G), is being considered as a revolutionary technology in the telecommunication domain whose the challenges are mainly to achieve signal quality and great ability to work with free spectrum in the millimetre waves. Besides, other important innovations are the introduction of a more current architecture and the use of multiple antennas in transmission and reception. Digital communication using multiple input and multiple output (MIMO) wireless links has recently emerged as one of the most significant technical advances in modern communications. MIMO technology is able to offer a large increase in the capacity of these systems, without requiring a considerable increase in bandwidth or power required for transmission. This dissertation presents an overview of theoretical concepts of MIMO systems. With such a system a spatial diversity gain can be obtained by using space-time codes, which simultaneously exploit the spatial domain and the time domain. SISO, SIMO and MISO systems are differentiated by their channel capacity and their configuration in relation to the number of antennas in the transmitter/receiver. To verify the effectiveness of the MIMO systems a comparison between the capacity of SISO and MIMO systems has been performed using the Shannon’s principles. In the MIMO system some variations in the number of antennas arrays have been considered, and the superiority of transmission gains of the MIMO systems have been demonstrated. Combined with millimetre waves (mmWaves) technology, massive MIMO systems, where the number of antennas in the base station and the number of users are large, is a promising solution. SDR implementations have been performed considering a platform with Matlab code applied to MIMO 2x2 Radio and Universal Software Peripheral Radio (USRP). A detailed study was initially conducted to analyze the architecture of the USRP. Complex structures of MIMO systems can be simplified by using mathematical methods implemented in Matlab for the synchronization of the USRP in the receiver side. SISO transmission and reception techniques have been considered to refine the synchronization (with 16-QAM), thus facilitating the future implementation of the MIMO system. OpenAirInterface has been considered for 4G and 5G implementations of actual mobile radio communication systems. Together with the practical MIMO, this type of solution is the starting point for future hardware building blocks involving massive MIMO systems.A quinta geração (5G) está sendo considerada uma tecnologia revolucionária no setor de telecomunicações, cujos desafios são principalmente a obtenção de qualidade de sinal e grande capacidade de trabalhar com espectro livre nas ondas milimétricas. Além disso, outras inovações importantes são a introdução de uma arquitetura mais atual e o uso de múltiplas antenas em transmissão e recepção. A comunicação digital usando ligaçõe sem fio de múltiplas entradas e múltiplas saídas (MIMO) emergiu recentemente como um dos avanços técnicos mais significativos nas comunicações modernas. A tecnologia MIMO é capaz de oferecer um elevado aumento na capacidade, sem exigir um aumento considerável na largura de banda ou potência transmitida. Esta dissertação apresenta uma visão geral dos conceitos teóricos dos sistemas MIMO. Com esses sistemas, um ganho de diversidade espacial pode ser obtido utilizando códigos espaço-tempo reais. Os sistemas SISO, SIMO e MISO são diferenciados pela capacidade de seus canais e a sua configuração em relação ao número de antenas no emissor/receptor. Para verificar a eficiência dos sistemas MIMO, realizou-se uma comparação entre a capacidade dos sistemas SISO e MIMO utilizado os princípios de Shannon. Nos sistemas MIMO condecideraram-se algumas variações no número de agregados de antenas, e a superioridade dos ganhos de transmissão dos sistemas MIMO foi demonstrada. Combinado com a tecnologia de ondas milimétricas (mmWaves), os sistemas massivos MIMO, onde o número de antenas na estação base e o número de usuários são grandes, são uma solução promissora. As implementações do SDR foram realizadas considerando uma plataforma com código Matlab aplicado aos rádios MIMO 2x2 e Universal Software Peripheral Radio (USRP). Um estudo detalhado foi inicialmente conduzido para analisar a arquitetura da USRP. Estruturas complexas de sistemas MIMO podem ser simplificadas usando métodos matemáticos implementados no Matlab para a sincronização do USRP no lado do receptor. Consideraram-se técnicas de transmissão e recepção SISO para refinar a sincronização (com 16-QAM), facilitando assim a implementação futura do sistema MIMO . Considerou-se o OpenAirInterface para implementações 4G e 5G de sistemas reais de comunicações móveis. Juntamente com o MIMO na pratica, este tipo de solução é o ponto de partida para futuros blocos de construção de hardware envolvendo sistemas MIMO massivos

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Reconfigurable Antennas for Beam-Space MIMO Transmission with a Single Radio

MIMO techniques allow remarkable improvements in the reliability and/or transmission rate of wireless communication systems. However, there are several major challenges towards the implementation of conventional MIMO concept in terminals with size, cost, and power constraints. Firstly, insufficient space impedes the design of efficient and decorrelated MIMO antennas. Second, MIMO traditionally demands each antenna to be fed by its own RF chain, which in turn results in greater hardware complexity, larger power consumption, and higher implementation cost. Among all reduced-complexity and antenna-decoupling schemes proposed so far, the so-called beam-space MIMO has attracted a great deal of interest as a potential solution for addressing both problems concurrently. The key idea therein is to engineer the radiation pattern of a single-feed antenna structure for each symbol period, such that multiple independent symbols directly modulate a predefined set of orthogonal virtual patterns in the far-field, therefore allowing true MIMO transmission using a single RF chain and a compact antenna structure. More important in practice, the transmitted information can be retrieved using a conventional MIMO receiver. However, the transformation of this idea into reality entails dealing with various practical aspects that are commonly overlooked in theoretical and conceptual developments. This dissertation explores the beam-space MIMO concept from the perspective of the antenna engineering, and aims at addressing several key issues associated with the actual design and implementation of beam-space MIMO systems. The early developments of beam-space MIMO concerned switched parasitic arrays. However, the requirement of utilizing several physically-separate radiators is inconvenient for practicable implementation in compact portable devices. To solve this problem, a single-radiator load-modulated antenna solution is proposed in this dissertation. Another primary challenge consists in emulating high-order modulation schemes such as PSK with realistic hardware. Here, an efficient beam-space MIMO strategy is developed, which allows transmitting PSK data streams of any modulation order using only purely reactive reconfigurable loads, and without the need for a symbol-rate dynamic matching network. The approach is illustrated by the design and fabrication of a realistic antenna for QPSK signaling. The performance of a beam-space MIMO system which utilizes the fabricated antenna is then investigated through over-the-air experiments, and compared with conventional MIMO in realistic environments. Embedding information in the radiation patterns, beam-space MIMO systems are expected to be inherently prone to multiplexing performance degradation in the presence of external field perturbation. This makes the study of near-field interaction influence on beam-space MIMO distinct from those carried out for the case of conventional systems. This issue is considered for the first time in this dissertation. Moreover, like any reconfigurable system, a beam-space MIMO system may suffer from bandwidth expansion of the transmitted signals. The final part of the work is directed towards this important issue. To reduce out-of-band radiation effect, a solution based on shaping the time-domain response of the reconfigurable components is presented. The studies presented in this thesis constitute a crucial step towards MIMO with simpler and cheaper hardware for real-life terminals

Energy-Efficient System Design for Future Wireless Communications

The exponential growth of wireless data traffic has caused a significant increase in the power consumption of wireless communications systems due to the higher complexity of the transceiver structures required to establish the communication links. For this reason, in this Thesis we propose and characterize technologies for improving the energy efficiency of multiple-antenna wireless communications. This Thesis firstly focuses on energy-efficient transmission schemes and commences by introducing a scheme for alleviating the power loss experienced by the Tomlinson-Harashima precoder, by aligning the interference of a number of users with the symbols to transmit. Subsequently, a strategy for improving the performance of space shift keying transmission via symbol pre-scaling is presented. This scheme re-formulates complex optimization problems via semidefinite relaxation to yield problem formulations that can be efficiently solved. In a similar line, this Thesis designs a signal detection scheme based on compressive sensing to improve the energy efficiency of spatial modulation systems in multiple access channels. The proposed technique relies on exploiting the particular structure and sparsity that spatial modulation systems inherently possess to enhance performance. This Thesis also presents research carried out with the aim of reducing the hardware complexity and associated power consumption of large scale multiple-antenna base stations. In this context, the employment of incomplete channel state information is proposed to achieve the above-mentioned objective in correlated communication channels. The candidate’s work developed in Bell Labs is also presented, where the feasibility of simplified hardware architectures for massive antenna systems is assessed with real channel measurements. Moreover, a strategy for reducing the hardware complexity of antenna selection schemes by simplifying the design of the switching procedure is also analyzed. Overall, extensive theoretical and simulation results support the improved energy efficiency and complexity of the proposed schemes, towards green wireless communications systems

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin