Ph.D. defence by Stanislav Zhekov
05.12.2018 kl. 12.30 - 16.00
‘Radio Propagation Aspects of Future Mobile Communication Systems’
The mobile communications, as one of the most successful technology innovations in the modern history, have undergone a significant development in the past years. Driving force behind this progress is the people’s demand for better quality of service. It is expected that, with the extensive adoption of mobile devices (e.g. smartphones and tablets), in the next couple of years the mobile traffic will increase on the order of hundreds of times compared to what we experience today.
Therefore, serious research efforts should be made in order to meet these demands. The radio channel places fundamental limitations on the performance of any wireless communication system. As a concept, radio channel encompasses fields like antennas, electromagnetic wave propagation and front end, and each of them has to be thoroughly studied for the sake of successful designing of a mobile communication system.
This thesis considers various topics related to radio channel. The entire work can be divided into several groups of studies. At first place, ultrawideband antenna for channels sounding purposes is proposed. Such antenna is very beneficial for the characterization of channels in legacy as well as in 5G communication systems.
The operation of a dual-element MIMO handset antenna array in close vicinity to a human hand is studied. The degradation of the antenna performance for different usage cases is analyzed as well as the exposure of the human tissue by antenna radiation is discussed. In order to ensure repeatability and that such studies, conducted by different researchers, are comparable, phantoms mimicking human hands have been developed. However, the dielectric properties of human hand have been specified only up to 6 GHz and nowadays more and more wireless communication systems are or expected to be deployed at higher frequencies. Due to that, study aiming to obtain data for the complex permittivity of human hand at high frequencies is performed and presented.
The finite-difference time-domain (FDTD) method suffers from the so-called numerical anisotropy, the presence of which can significantly reduce the accuracy of this numerical procedure especially in case of electrically large problems. An investigation on the error arising in the local-mean electric field, due to the numerical anisotropy, obtained by using a coarse FDTD mesh is discussed. Knowledge of the dielectric properties of common building materials is of a great importance when conducting numerical studies of electromagnetic wave propagation. At present, the available data in the literature on that topic is mainly limited to low frequencies and over narrow frequency bands.
This thesis presents experimental results for the complex permittivity of multiple materials over an ultrawide frequency band which can be used for radio propagation simulations.
Information about the attenuation introduced by building materials is needed for estimating the network coverage. Due to that, measurements of the power loss experienced by electromagnetic waves propagating through various structures are performed and the results presented. Apart of the frequency dependence of the attenuation, the polarization response of the materials is also analyzed in order to see whether the use of one polarization combination (vertical-vertical or horizontal-horizontal) is more beneficial, i.e. brings to lower loss and thus can be employed to improve the coverage..
Head of R&D, Dr. Sc. (ETHZ), Sven Kühn, Schmid & Partner Engineering AG, Zürich
Professor Rodney Grant Vaughan, School of Engineering Science, SFU Burnaby BC, Canada
Associate Professor Jan H. Mikkelsen (Chairman), Aalborg University
Professor Gert F. Pedersen, Aalborg University
Associate Professor Hans Ebert, Aalborg University
After the defence there will be a reception in the canteen next to the auditorium
Please feel free to join
Free of charge
The Antennas, Propagation and Millimetre-wave Systems (APMS), Department of Electronic Systems
The auditorium – Novi 8, Niels Jernes Vej 27