Rate adaptive resource allocation with fairness control for OFDMA networks

The use of opportunistic radio resource allocation techniques in order to efficiently manage the resources generates a low fairness among the users in a cellular system due to uneven Quality of Service (QoS) distribution. Some classic rate adaptive policies tried to tackle this problem for OFDMA systems by proposing solutions to maximize capacity, maximize fairness, or find a static trade-off between these two objectives. This work generalizes these classic policies and propose a dynamic fairness/rate adaptive technique based on dynamic sub-carrier assignment and equal power allocation that considers a new fairness constraint in the optimization problem. By means of extensive system-level simulations, it is demonstrated that the proposed technique is able to provide an instantaneous (short-term) fairness control, which provides to the network operator the flexibility to operate on any desired trade-off point.Peer ReviewedPostprint (published version

Towards THz Communications -Status in Research, Standardization and Regulation

Abstract In the most recent years, wireless communication networks have been facing a rapidly increasing demand for mobile traffic along with the evolvement of applications that require data rates of several 10s of Gbit/s. In order to enable the transmission of such high data rates, two approaches are possible in principle. The first one is aiming at systems operating with moderate bandwidths at 60 GHz, for example, where 7 GHz spectrum is dedicated to mobile services worldwide. However, in order to reach the targeted date rates, systems with high spectral efficiencies beyond 10 bit/s/Hz have to be developed, which will be very challenging. A second approach adopts moderate spectral efficiencies and requires ultra high bandwidths beyond 20 GHz. Such an amount of unregulated spectrum can be identified only in the THz frequency range, i.e. beyond 300 GHz. Systems operated at those frequencies are referred to as THz communication systems. The technology enabling small integrated transceivers with highly directive, steerable antennas becomes the key challenges at THz frequencies in face of the very high path losses. This paper gives an overview over THz communications, summarizing current research projects, spectrum regulations and ongoing standardization activities

Reconfigurable antennas and radio wave propagation at millimeter-wave frequencies

For the last decades we have been witnessing the evolution of wireless radio networks. Since new devices appear and the mobile traffic, as well as the number of users, grows rapidly, there is a great demand in high capacity communications with better coverage, high transmission quality, and more efficient use of the radio spectrum. In this thesis, reconfigurable antennas at micro- and millimeter-wave frequencies and peculiar properties of radio wave propagation at mm-wave frequencies are studied. Reconfigurable antennas can improve radio link performance. Recently, many different concepts have been developed in the reconfigurable antenna design to control the antenna bandwidth, resonant frequency, polarization, and radiation properties. In the first part of the thesis, we investigate mechanically tunable antennas operating at microwave frequencies with the ability to change the shape of the conductor element and, consequently, to control the radiation properties of the antenna. Also in the first part, we study conformal antenna arraysfor 60 GHz applications based on cylindrical structures. Beam switching technology is implemented by realizing several antenna arrays around the cylinder with a switching network.Scanning angles of +34˚/-32˚ are achieved. Moreover, it is vital to study radio wave propagation peculiarities at mm-wave frequencies in indoor and outdoor environments to be able to deploy wireless networks effectively. The propagation part of the thesis focuses on several aspects. First, we investigate how the estimation of optimum antenna configurations in indoor environment can be done usingrealistic propagation models at 60 GHz. Ray tracing simulations are performed and realistic human blockage models are considered. Second, we present the results from a measurement campaign where reflection and scattering properties of two different built surfaces are studied in the millimeter-wave E-band (71-76 and 81-86 GHz). Next, we present a geometry based channel model for a street canyon scenario, using angular-domain measurement results to calculate realistic power angular spectra in the azimuth and elevation planes. Then, we evaluate propagation effects on the radio channel on the rooftop of the buildings bymeasurements and simulations. We have used unmanned aerial vehicles and photogrammetrytechnique to create a highly accurate 3D model of the environment. Based on a comparison of the measured and simulated power delay profiles, we show that the highly accurate 3D modelsare beneficial in radio wave propagation planning at mm-wave frequencies instead of using simple geometrical models

Der 60 GHz Indoor-Funkkanal - Herausforderungen menschlicher Abschattung

Driven by the ever increasing capacity of storage devices and HD video streaming applications, there will be a strong demand for wireless multi-Gbps consumer applications soon. Due to its large available bandwidth and the high allowed transmit power, the unlicensed frequency range around 60 GHz is proving ideal for the realization of such systems. During the development process of 60 GHz multi-gigabit wireless systems, a detailed knowledge of the radio channel is essential. Taking into account research gaps, this dissertation makes a significant contribution to knowledge in the field of 60 GHz channel characterization. The focus is on human shadowing and its influence on the channel characteristics, which leads to a high and time-variant path loss. In order to provide realistic results, sophisticated radio channel models are required for the 60 GHz range. In particular, they should include information in the spatial domain at the receiver and the transmitter as well as take into account time-varying human shadowing. The angular information is necessary in this case to evaluate smart antenna systems. Such comprehensive models are not yet available and therefore represent the major outcome of this dissertation.Wegen seiner großen verfügbaren Bandbreite und der hohen erlaubten Sendeleistung erweist sich der unlizensierte Frequenzbereich um 60 GHz als hervorragend geeignet für die Realisierung drahtloser Multi-Gigabit-Kommunikationssysteme. Während des Entwicklungsprozesses solcher Systeme ist eine detaillierte Kenntnis des Funkkanals unerlässlich. Unter Berücksichtigung offener Fragestellungen leistet die vorliegende Dissertation einen wesentlichen Beitrag zum Wissensstand auf dem Gebiet der 60-GHz-Kanalcharakterisierung. Im Vordergrund steht dabei die Abschattung durch Personen, die bei Trägerfrequenzen um 60 GHz zu einer hohen und gleichzeitig zeitvarianten Funkfelddämpfung führt. Um realistische Ergebnisse zu liefern, sind im 60-GHz-Bereich komplexe Funkkanalmodelle erforderlich, die insbesondere Winkelinformationen am Sender und Empfänger enthalten und die zeitvariante Abschattung durch Personen berücksichtigen sollten. Beides ist notwendig, um intelligente Antennensysteme evaluieren zu können. Solche umfassenden Modelle sind bisher nicht verfügbar und stellen deshalb das wesentliche Ziel dieser Dissertation dar

Der 60 GHz Indoor-Funkkanal - Herausforderungen menschlicher Abschattung

Driven by the ever increasing capacity of storage devices and HD video streaming applications, there will be a strong demand for wireless multi-Gbps consumer applications soon. Due to its large available bandwidth and the high allowed transmit power, the unlicensed frequency range around 60 GHz is proving ideal for the realization of such systems. During the development process of 60 GHz multi-gigabit wireless systems, a detailed knowledge of the radio channel is essential. Taking into account research gaps, this dissertation makes a significant contribution to knowledge in the field of 60 GHz channel characterization. The focus is on human shadowing and its influence on the channel characteristics, which leads to a high and time-variant path loss. In order to provide realistic results, sophisticated radio channel models are required for the 60 GHz range. In particular, they should include information in the spatial domain at the receiver and the transmitter as well as take into account time-varying human shadowing. The angular information is necessary in this case to evaluate smart antenna systems. Such comprehensive models are not yet available and therefore represent the major outcome of this dissertation.Wegen seiner großen verfügbaren Bandbreite und der hohen erlaubten Sendeleistung erweist sich der unlizensierte Frequenzbereich um 60 GHz als hervorragend geeignet für die Realisierung drahtloser Multi-Gigabit-Kommunikationssysteme. Während des Entwicklungsprozesses solcher Systeme ist eine detaillierte Kenntnis des Funkkanals unerlässlich. Unter Berücksichtigung offener Fragestellungen leistet die vorliegende Dissertation einen wesentlichen Beitrag zum Wissensstand auf dem Gebiet der 60-GHz-Kanalcharakterisierung. Im Vordergrund steht dabei die Abschattung durch Personen, die bei Trägerfrequenzen um 60 GHz zu einer hohen und gleichzeitig zeitvarianten Funkfelddämpfung führt. Um realistische Ergebnisse zu liefern, sind im 60-GHz-Bereich komplexe Funkkanalmodelle erforderlich, die insbesondere Winkelinformationen am Sender und Empfänger enthalten und die zeitvariante Abschattung durch Personen berücksichtigen sollten. Beides ist notwendig, um intelligente Antennensysteme evaluieren zu können. Solche umfassenden Modelle sind bisher nicht verfügbar und stellen deshalb das wesentliche Ziel dieser Dissertation dar