Thomas Kürner

Short-Range Ultra-Broadband Terahertz Communications: Concepts and Perspectives

We propose the concept of ultra-broadband terahertz communication, based on directed non-line-of-sight (NLOS) transmissions. Potential applications of such a system supporting multi-gigabit data rates are given, and put into the context of currently emerging WLANs/WPANs. The technology and propagation constraints serve as boundary conditions for the determination of the required antenna gain to support ultra-broadband communication. Resulting high-gain antenna requirements will necessitate highly directed transmissions. We propose the use of omni-directional dielectric mirrors to support directed NLOS paths. Their performance is investigated with ray-tracing simulations of a terahertz propagation channel in a dynamic office environment, which is calibrated with measured building-material and mirror parameters. We demonstrate that a directed NLOS path scheme will make a terahertz communication system robust to shadowing. Furthermore, we show that dielectric mirrors covering only parts of the walls will significantly enhance the signal coverage in a typical indoor scenario.

Handover Parameter Optimization in LTE Self-Organizing Networks

This paper presents a self-optimizing algorithm that tunes the handover (HO) parameters of a LTE (Long-Term Evolution) base station in order to improve the overall network performance and diminish negative effects (call dropping , HO failures). The proposed algorithm picks the best hysteresis and time-to-trigger combination for the current network status. We examined the effects of this self-optimizing algorithm in a realistic scenario setting and the results show an improvement from the static value settings.

Scattering Analysis for the Modeling of THz Communication Systems

Modeling propagation channels for future pico-cellular indoor THz communication systems requires the knowledge of the reflective properties of building materials. The reflectivity of smooth, optically thick materials can be modeled with Fresnel equations. In case of materials with a rough surface, diffuse scattering reduces the power reflected in the specular direction. Kirchhoff scattering theory can be employed to derive modified Fresnel equations which account for these losses by introducing a Rayleigh roughness factor calculated from the measured surface height distribution of the sample under observation. Using the resulting, analytically derived reflection coefficient based on material parameter and surface measurements in propagation models enables the simulation of arbitrary configurations. We present a set of calculated and measured reflection coefficients for a selection of common indoor building materials which are in good agreement, thus verifying our modeling approach. Furthermore, we illustrate by ray-tracing simulations the effect of wall and ceiling roughness on propagation in future indoor scenarios. Both, absolute power levels and propagation patterns are shown to be strongly influenced by scattering. In some cases, reflected transmissions with longer propagation paths can be more efficient than the shorter ones in terms of incurred losses.

Omnidirectional terahertz mirrors: A key element for future terahertz communication systems

We present an omnidirectional mirror for the terahertz range made from polypropylene and high-resistivity silicon. The structure is characterized by time-domain terahertz spectroscopy. The experimental data are in good agreement with transfer matrix calculations. In the frequency band between 319 and 375GHz the mirror is highly reflecting for all incidence angles and s as well as p polarization.

Performance Analysis of Future Multigigabit Wireless Communication Systems at THz Frequencies With Highly Directive Antennas in Realistic Indoor Environments

In this paper, a simulation environment encompassing realistic propagation conditions and system parameters is employed in order to analyze the performance of future multigigabit indoor communication systems at tetrahertz frequencies. The influence of high-gain antennas on transmission aspects is investigated. Transmitter position for optimal signal coverage is also analyzed. Furthermore, signal coverage maps and achievable data rates are calculated for generic indoor scenarios with and without furniture for a variety of possible propagation conditions.

Diffraction in mm and Sub-mm Wave Indoor Propagation Channels

Current indoor wireless communication systems are shifting from classical microwave bands towards mm wave frequencies, whereas here the 60 GHz band is of special interest. Future systems are expected to work at even higher carrier frequencies in the sub-mm band beyond 300 GHz. In indoor wave propagation channels of such systems, diffraction occurs at a multitude of objects and hence must be considered for propagation simulations. Although the relevance of diffraction has been thouroughly studied at lower frequencies, it has not yet been analyzed methodically in the mm and sub-mm wave frequency range. This paper presents an extensive measurement campaign of the diffraction at objects like edges, wedges and cylinders for frequencies of 60 and 300 GHz. Different materials, realistic antennas as well as transmission through the objects are taken into account. Theoretical approaches are validated against the measurement results. Furthermore, shadowing of rays by persons is investigated and modeled with the help of diffraction. Finally, ray tracing is applied in an office scenario in order to evaluate the impact of diffraction on mm and sub-mm wave indoor channel characteristics.

Cell outage management in LTE networks

Cell outage management is a functionality aiming to automatically detect and mitigate outages that occur in radio networks due to unexpected failures. We envisage that future radio networks autonomously detect an outage based on measurements, from e.g., user equipment and base stations, and alter the configuration of surrounding radio base stations in order to compensate for the outage-induced coverage and service quality degradations and satisfy the operator-specified performance requirements as much as possible. In this paper we present a framework for cell outage management and outline the key components necessary to detect and compensate outages as well as to develop and evaluate the required algorithms.

Future railway services-oriented mobile communications network

The future development of the railway is highly desired to evolve into a new era where infrastructure, trains, travelers, and goods will be increasingly interconnected to provide high comfort, with optimized door-to-door mobility at higher safety. For this vision, it is required to realize seamless high data rate wireless connectivity for railways. To improve the safety and comfort of future railways, wireless communications for railways are required to evolve from only voice and traditional train control signaling services to various high data rate services including critical high-definition (HD) video and other more bandwidth-intensive passenger services, such as onboard and wayside HD video surveillance, onboard real-time high data rate services, train multimedia dispatching video streaming, railway mobile ticketing, and the Internet of Things for railways. Corresponding mobile communications network architecture under various railway scenarios including inter-car, intra-car, inside station, train-to-infrastructure and infrastructure- to-infrastructure are proposed in this article. Wireless coverage based on massive MIMO for railway stations and train cars is proposed to fulfill the requirement of high-data-rate and high spectrum efficiency. The technical challenges brought by the massive MIMO technique are discussed as well.

Diffuse Scattering From Rough Surfaces in THz Communication Channels

Recent years have seen a tremendous increase in the demand for wireless bandwidth. To support this demand by innovative and resourceful use of technology, future communication systems will have to shift towards higher carrier frequencies. Due to the tight regulatory situation, frequencies in the atmospheric attenuation window around 300 GHz appear very attractive to facilitate an indoor, short range, ultra high speed THz communication system. In this paper, we investigate the influence of diffuse scattering at such high frequencies on the characteristics of the communication channel and its implications on the non-line-of-sight propagation path. The Kirchhoff approach is verified by an experimental study of diffuse scattering from randomly rough surfaces commonly encountered in indoor environments using a fiber-coupled terahertz time-domain spectroscopy system to perform angle- and frequency-dependent measurements. Furthermore, we integrate the Kirchhoff approach into a self-developed ray tracing algorithm to model the signal coverage of a typical office scenario.

The Impact of Reflections From Stratified Building Materials on the Wave Propagation in Future Indoor Terahertz Communication Systems

In order to derive reliable propagation models for future terahertz indoor pico-cellular communication systems, accurate reflectivity data of building materials is necessary. Here we present reflection terahertz time domain spectroscopy (THz-TDS) measurements and matching transfer matrix simulations of the frequency dependent reflection coefficient of multi layer building materials in the frequency range from 100 to 500 GHz for a set of angles, both in TE- and TM-polarization. Two prominent stratified structures, a double pane window and white paint on plaster are investigated as they usually account for large areas in indoor environments. Communication systems located above 100 GHz are expected to be strongly affected by the variations of the reflectivity over the frequency and incident angle of such stratified materials as they will rely both on line of sight (LOS) and non line of sight (NLOS) propagation. We discuss this impact on the power distribution in a sample scenario employing the ray-tracing method.