Dirk Didascalou

A stochastic spatial channel model based on wave-propagation modeling

A novel stochastic spatial propagation channel model for wide-band spread spectrum applications is presented. The model is set up for indoor scenarios, although in principle it can be extended easily to urban environments. Deterministic ray-tracing results are used to produce the huge data sets required for the statistical evaluation of the parameters of the proposed model. The approach for the stochastic model is based on physical wave-propagation, where the channel is described by multipath components including angles of arrival at the receiver and angles of transmission at the transmitter. In each modeling step, path properties change according to the movement of the radio stations (RSs). The appearance and disappearance of multipath components is modeled by a genetic process. Especially, changing delay times of the propagation paths yield a realistic Doppler behavior of the channel. A new approach to model the directions of multipath components in three dimensions has been developed. By relating the angles of arrival (or transmission) to the direct line between transmitter and receiver, a universal modeling approach, which is independent of the actual geometry, becomes possible. The novel stochastic spatial channel model allows the simulation of complex systems including arbitrary antenna configurations and patterns. A detailed description of the overall model is presented together with some initial simulation results.

Ray-density normalization for ray-optical wave propagation modeling in arbitrarily shaped tunnels

This work is concerned with the calculation of natural electromagnetic (EM) wave propagation and the determination of the propagation channel characteristics in highway or railway tunnels in the ultrahigh-frequency (UHF) range and above (>300 MHz). A novel ray-tracing technique based on geometrical optics (GO) is presented. Contrary to classical ray tracing, where the one ray representing a locally plane wave front is searched, the new method requires multiple representatives of each physical EM wave at a time. The contribution of each ray to the total field at the receiver is determined by the proposed ray-density normalization (RBN). This technique has the further advantage of overcoming one of the major disadvantages of GO, the failure at caustics. In contrast to existing techniques, the new approach does not use ray tubes or adaptive reception spheres. Consequently, it does not suffer their restrictions to planar geometries. Therefore, it allows one to predict the propagation of high-frequency EM waves in confined spaces with curved boundaries, like tunnels, with an adequate precision. The approach is verified theoretically with canonical examples and by various measurements at 120 GHz in scaled tunnel models.

Subway tunnel guided electromagnetic wave propagation at mobile communications frequencies

A measurement campaign has been carried out in the Berlin subway to characterize electromagnetic wave propagation in underground railroad tunnels. The received power levels at 945 and 1853.4 MHz are used to evaluate the attenuation and the fading characteristics in a curved arched-shaped tunnel. The measurements are compared to ray-optical modeling results, which are based on ray density normalization. It is shown that the geometry of a tunnel, especially the cross-sectional shape and the course, is of major impact on the propagation behavior and thus on the accuracy of the modeling, while the material parameters of the building materials have less impact.

A novel approach in the determination of visible surfaces in 3D vector geometries for ray-optical wave propagation modelling

Image theory as a ray-tracing method is a well known but cumbersome tool for propagation modelling. A promising way to enhance its efficiency is a prior reduction of complexity of the scenario under consideration. Only the visible surfaces from the receiver and transmitter locations are potential ray interceptors. Thus, only they have to be subject to the imaging algorithm. The determination of the visible surfaces is discussed. The proposed algorithm is based on a successive dimensional reduction of the problem. In the first step the whole 3D scenario is projected perspectively in several 2D planes. The spatial information is hereby preserved. The resulting 2D polygons, which represent the surfaces, are tested for overlap. This is efficiently done by applying a sweep-line algorithm. With the knowledge of the relative surface positions a graph theory based polygon subtraction is applied to determine the visible surfaces. An inverse projection into 3D space yields the actual visible 3D polygons.

Impact of road surfaces on millimeter-wave propagation

Future intelligent transportation systems (ITSs) will deeply rely on millimeter waves for communication and sensing purposes. This results in the need of a precise description of the propagation properties at these frequencies. In this paper, the propagation mechanisms reflection and diffraction of millimeter waves at realistic road surfaces and geometries are investigated theoretically and validated by measurements at 77 GHz. The effect of guided waves underneath a vehicles underbody is observed, which can be exploited in a favorable way for range extension in obstructed sight situations. It is also shown that the local curvature of common road surfaces leads to focusing and defocusing effects of the transmitted energy, resulting in an increased signal fluctuation. Furthermore, the importance of diffraction phenomena at road crests is stressed, which were formerly neglected but may play an important role in security sensitive applications like collision avoidance systems etc.

Terrestrial network planning for digital video broadcasting to mobile receivers

The digital video broadcasting (DVB) standard offers data rates of several ten Mbit/s, using the MPEG-2 transport stream. These high data rates can be realized by cable networks (DVB-C) and by satellite transmission (DVB-S). The terrestrial DVB standard (DVB-T) has been designed to operate as a single frequency network (SFN), which means that only one frequency band is required over an arbitrarily large area. In the 8 MHz bandwidth of one analog television (TV) channel four to six digital TV programs can be stationary received with medium gain antennas in obscured line of sight (LOS) conditions. First measurement campaigns proved, that the reception for both, portable and mobile receivers is possible, but only under certain conditions. In this paper suitable parameter sets for mobile reception are determined and design rules for terrestrial transmitter networks are derived. The coverage criteria, minimum required field strength and maximum allowed bit error rate are analyzed. The results of this work are necessary to investigate whether existing transmitter locations can be used for future digital terrestrial video broadcasting networks and help to develop strategies for a SFN repeater operation.

A novel ray-optical approach to model wave propagation in curved tunnels

In this paper, a novel ray optical approach is presented to model the electromagnetic wave propagation in curved tunnels with rectangular or arched cross-sections. The modelling is performed by a stochastic ray launching technique (Monte-Carlo method), based on geometrical optics. Due to the curved surfaces, a so-called ray density normalisation is introduced in order to predict the field strength precisely. The model is verified theoretically with a corrugated circular waveguide and by various measurements at 120 GHz in scaled tunnel models.

Wideband wave propagation measurements for local multipoint distribution services (LMDS) at 26 GHz

The results of a wideband measurement campaign at 26 GHz in the inner city of Karlsruhe, Germany, are presented. The measurements are performed using the Marconi (former Bosch Telecom) Digital Multipoint System (DMS). Therefore, the results can be directly adopted for planning purposes. The measurements are carried out for two different base station heights with several terminal station positions. Thus, a large number of different propagation scenarios is investigated, such as free Fresnel zone (FFZ), obstructed Fresnel zone (OFZ), obstructed line of sight (OLOS) and non-line of sight (NLOS) scenarios. In order to characterise polarisation effects both vertical and horizontal polarisation are utilised. Furthermore, the influence of vertical misalignment of the terminal station antenna is examined in NLOS scenarios. Using strong multipath components to build up stable links in NLOS scenarios is a critical issue in LMDS planning. Therefore, closer investigations on this issue are presented. As a last point the impact of vegetation obstructing the line of sight (LOS) path is analysed. For all scenarios the delay spread and coherence bandwidth are derived from the measured average power delay profile (PDP).

Natural wave propagation in subway tunnels at mobile communications frequencies

A measurement campaign has been carried out in the Berlin subway to characterize EM-wave propagation in underground railroad tunnels. The received power levels at 945 MHz, and 1853.4 MHz are used to evaluate the attenuation and the fading characteristics in a curved, arched-shaped tunnel. The measurements are compared to ray-optical modelling results. It is shown that the geometry of a tunnel, especially the cross-sectional shape and the course, is of major impact on the propagation behaviour and thus on the accuracy of the modelling.

An investigation of millimeter wave propagation mechanisms for mobile intervehicle communications and outdoor MBS

Future intelligent transportation systems (ITS) and mobile broadband systems (MBS) will deeply rely on millimeter waves for communication purposes. Therefore their properties have to be known. In this paper, the propagation mechanisms of reflection and diffraction at curved surfaces at millimeter wave frequencies are investigated. They are classified with respect to the requirements of mobile intervehicle communications. The consideration of realistic street geometries and parameters leads to novel insights, which were formerly neglected.