On the practicability of full-duplex relaying in OFDM systems

A full-duplex relay is spectrally more efficient than a half-duplex relay because it uses the full band of available frequencies to receive and transmit signals simultaneously. However, the loop interference arriving at the receiver of the relay due to its own transmission is a major hindrance that must be overcome before the idea of full-duplex relaying can be put to practice. The simple technique of subtractive cancellation alone, in theory, could eliminate the loop interference completely from the received signal. In practice, however, the nonidealities inherent in the actual components within the relay transceivers create less than ideal conditions for the cancellation to work perfectly. This thesis studies the effect of such nonidealities on the performance of a single-input-single-output (SISO) full-duplex relay. The primary focus is on formulating an analytical framework that helps evaluate the feasibility of such a relay. The outcome illustrates that a number of factors determine whether the idea of a full-duplex relay with subtractive loop interference cancellation can be implemented in practice. As expected, it is necessary to have an analogy to-digital converter (ADC) with a large dynamic range at the receiver to ensure that the incoming can be digitized with sufficient accuracy. Another important requirement is to have an excellent transmitter with a very small error vector magnitude (EVM) because the contribution of the unknown random error in the transmitted signal to the loop interference cannot be cancelled no matter how accurately the incoming signal is digitized. Moreover, the physical design of the relay must, by itself, be able to provide a certain amount of natural isolation between the transmitting and receiving antennas; otherwise, the part of the loop interference resulting from the transmitter error alone can be sufficient to drown the useful signal beyond recovery

Feedback Mechanisms for Centralized and Distributed Mobile Systems

The wireless communication market is expected to witness considerable growth in the immediate future due to increasing smart device usage to access real-time data. Mobile devices become the predominant method of Internet access via cellular networks (4G/5G) and the onset of virtual reality (VR), ushering in the wide deployment of multiple bands, ranging from TVWhite Spaces to cellular/WiFi bands and on to mmWave. Multi-antenna techniques have been considered to be promising approaches in telecommunication to optimize the utilization of radio spectrum and minimize the cost of system construction. The performance of multiple antenna technology depends on the utilization of radio propagation properties and feedback of such information in a timely manner. However, when a signal is transmitted, it is usually dispersed over time coming over different paths of different lengths due to reflections from obstacles or affected by Doppler shift in mobile environments. This motivates the design of novel feedback mechanisms that improve the performance of multi-antenna systems. Accurate channel state information (CSI) is essential to increasing throughput in multiinput, multi-output (MIMO) systems with digital beamforming. Channel-state information for the operation of MIMO schemes (such as transmit diversity or spatial multiplexing) can be acquired by feedback of CSI reports in the downlink direction, or inferred from uplink measurements assuming perfect channel reciprocity (CR). However, most works make the assumption that channels are perfectly reciprocal. This assumption is often incorrect in practice due to poor channel estimation and imperfect channel feedback. Instead, experiments have demonstrated that channel reciprocity can be easily broken by multiple factors. Specifically, channel reciprocity error (CRE) introduced by transmitter-receiver imbalance have been widely studied by both simulations and experiments, and the impact of mobility and estimation error have been fully investigated in this thesis. In particular, unmanned aerial vehicles (UAVs) have asymmetric behavior when communicating with one another and to the ground, due to differences in altitude that frequently occur. Feedback mechanisms are also affected by channel differences caused by the user’s body. While there has been work to specifically quantify the losses in signal reception, there has been little work on how these channel differences affect feedback mechanisms. In this dissertation, we perform system-level simulations, implement design with a software defined radio platform, conduct in-field experiments for various wireless communication systems to analyze different channel feedback mechanisms. To explore the feedback mechanism, we then explore two specific real world scenarios, including UAV-based beamforming communications, and user-induced feedback systems

Powerline Kommunikation: Wesentliche Technologien um PLC in CE-Geräte zu integrieren

In-house PLT (Powerline Telecommunication) enables new and highly convenient networking functions without the need for additional cables on mains-powered devices. Since wireless networks are not able to reach sufficient throughput between different rooms or even floors, PLC is considered to be the ideal backbone home network medium, providing complementary and seamless interaction with wireless networks. The need to communicate information is not new. The historical overview of this thesis compares the development of PLT to radio broadcast technologies. The consumer expects technologies to operate without interferences. Today, there are coexistence problems between these two technologies. Why does this happens, and how the problems can be resolved are the main issues of this thesis. Initial calculations of the channel capacity provide encouraging results for using the mains cabling as a communication medium. Chapter 3 forecasts how PLT modems could develop in the future. The usage of frequencies above 30 MHz will increase the throughput rate. Next, the utilization of the 3rd wire (the protective earth) for communication enhances the coverage and the reliability of powerline transmissions. The reception of common mode signals and the usage of MIMO technologies enable 8 transmission paths between one pair of outlets, which improves the performance of the bad, strongly attenuated channels. Today, the main challenge for the mass deployment of PLT is the lack of harmonized international standards on interoperability and electromagnetic interference. The absence of a standard results in the undesirable situation of PLT modems interfering with technologies from different vendors and also with radio applications. Solutions for solving these problems are given in chapter 4 and chapter 5. The approach of ‘Smart Notching’ - monitoring the existence of receivable radio broadcast stations at the time and location where a PLT modem is operating, received wide resonance in the PLT and radio broadcast communities. ‘Smart Notching’, also called ‘Dynamic Notching’ or ‘Adaptive Notching’ is considered to be the key factor in solving the endless discussions about the interferences to HF radio broadcast. Details on the creation of ETSI TS 102 578 and the implementation of a demonstrator system is documented in chapter 5. Field tests conducted together with the EBU verified the efficiency of the concept. The jointly executed tests by representatives from the radio broadcast and the PLT communities became a historical event which brought the two technologies, radio receivers and PLT modems, back into one house. Finally, a vision of the future coordination of EMC and conclusions are presented.Heutige Modems zur Powerline Telekommunikation (PLT) können im Betrieb den Empfang von Kurzwellen-Rundfunk beeinträchtigen, wenn Modem und Rundfunk-Empfänger in unmittelbarer Nachbarschaft betrieben werden. Eine neue Generation von PLT Modems, in denen das Konzept von 'Smart Notching' - dem intelligenten Einfügen von Lücken in das Kommunikationsspektrum - implementiert ist, zeigt keine Interferenzen mit dem Empfang von Rundfunkdiensten. Das Rauschen auf der Niederspannungsinstallation enthält neben sonstigen Signalen - durch andere Geräte hervorgerufen - aufgrund der Antennenwirkung Information über Rundfunksender. Beim ‚Smart Notching’ erkennen PLT Modems am Betriebsort die Existenz von Rundfunksignalen, indem sie das Signalspektrum auf der Netzleitung messen. Die Echtzeit- Bewertung der aktuellen Situation am Betriebsort ermöglicht eine Adaption des PLT Systems. Damit wird die Elektromagnetische Verträglichkeit nicht a priori (zum Herstellungs-Zeitpunkt) durch Schirmung oder eine globale Reduktion des Sendepegels, sondern durch Design des Verfahrens (welches während des Betriebs angewendet wird) hergestellt. Diese Doktorarbeit beschreibt nach einem kurzen Überblick zur Historie des Rundfunks und der Datenübertragung über das Energieverteilnetz Messungen zur Ermittlung der theoretischen Kanalkapazität. Anschließend wird ein Ausblick gegeben, wohin sich zukünftige PLT Modems entwickeln werden. Dies sind vor allem der Frequenzbereich oberhalb von 30 MHz sowie die Nutzung der dritten Kupferader in den Netzleitungen: der Schutzerde. Die Verwendung von MIMO-Algorithmen (aus der kabellosen Funkübertragung (z.B. WiFi) bereits bekannt) verbessert vor allem die Wahrscheinlichkeit, eine hohe Datenrate im Gebäude sicher zu verteilen. Sorge bereitet bei PLT ebenfalls die Koexistenz mit weiteren PLT-Systemen, sowie zu xDSL. Hierfür wird ein Vorschlag gemacht, um die Interferenzen zu nicht kompatiblen PLToder DSL-Systemen zu vermeiden, ohne dass die Systeme sich gegenseitig gezielt Informationen zusenden. Das bereits oben erwähnte Konzept des ‚Smart Notching’ wird detailliert erläutert und die Implementierung eines Demonstrators auf FPGA-Basis dokumentiert. Abschließend wird noch beschrieben, wie ‚Smart Notching’ gemeinsam mit der EBU getestet wurde und wie es seinen Weg in die Welt der Standardisierung gefunden hat. Der Veröffentlichung des Standards ETSI TS 102 578 wurde im Juli 2008 einstimmig von ETSI PLT zugestimmt

SMARAD - Centre of Excellence in Smart Radios and Wireless Research - Activity Report 2008 - 2010

Centre of Excellence in Smart Radios and Wireless Research (SMARAD), originally established with the name Smart and Novel Radios Research Unit, is aiming at world-class research and education in Future radio and antenna systems, Cognitive radio, Millimetre wave and THz techniques, Sensors, and Materials and energy, using its expertise in RF, microwave and millimetre wave engineering, in integrated circuit design for multi-standard radios as well as in wireless communications. SMARAD has the Centre of Excellence in Research status from the Academy of Finland since 2002 (2002-2007 and 2008-2013). Currently SMARAD consists of five research groups from three departments, namely the Department of Radio Science and Engineering, Department of Micro and Nanosciences, and Department of Signal Processing and Acoustics, all within the Aalto University School of Electrical Engineering. The total number of employees within the research unit is about 100 including 8 professors, about 30 senior scientists and about 40 graduate students and several undergraduate students working on their Master thesis. The relevance of SMARAD to the Finnish society is very high considering the high national income from exports of telecommunications and electronics products. The unit conducts basic research but at the same time maintains close co-operation with industry. Novel ideas are applied in design of new communication circuits and platforms, transmission techniques and antenna structures. SMARAD has a well-established network of co-operating partners in industry, research institutes and academia worldwide. It coordinates a few EU projects. The funding sources of SMARAD are diverse including the Academy of Finland, EU, ESA, Tekes, and Finnish and foreign telecommunications and semiconductor industry. As a byproduct of this research SMARAD provides highest-level education and supervision to graduate students in the areas of radio engineering, circuit design and communications through Aalto University and Finnish graduate schools such as Graduate School in Electronics, Telecommunications and Automation (GETA). During years 2008 – 2010, 21 doctor degrees were awarded to the students of SMARAD. In the same period, the SMARAD researchers published 141 refereed journal articles and 333 conference papers

Compact antenna arrays in mobile communications: A quantitative analysis of radiator coupling

To meet the ongoing demand for higher data rates and greater user mobility, modern mobile communications systems increasingly employ adaptive antenna arrays. By moving antenna elements closer together, to fit them inside a cellular phone for instance, mutual coupling effects impair their radiation capabilities. To describe these impairments more descriptively in contrast to current approaches, the present thesis extends the familiar notion of radiation efficiency from a single radiator to arbitrary antenna arrays by introducing an orthogonal set of radiating degrees of freedom. Detailed examples illustrate the effects of mutual coupling. Decoupling and matching networks are introduced to counteract mutual coupling. Thus, a design method applicable to a broad class of antenna arrays is described and verified by numerous examples, thereby ohmic losses and narrow bandwidths are identified as major weaknesses of decoupling and matching networks in general. For an investigation of the influence of mutual coupling on a mobile diversity receiver system, closed-form expressions for its diversity gain are derived and discussed. The analysis is complemented by a comprehensive receiver noise model. Practical diversity and noise measurements confirm the validity of the theoretical concepts developed. The present work aims to convey a more descriptive understanding of radiator coupling and to raise awareness of the fact that aspects of the entire system must be accounted for for an objective assessment of the potentials of mutually coupled antenna arrays