T. Kayser

Capability of 3-D Ray Tracing for Defining Parameter Sets for the Specification of Future Mobile Communications Systems

Three-dimensional (3-D) ray tracing has advanced to such a degree that it can provide channel parameters like delay spread, Doppler spread, angular spread, and distribution functions of long- and short-term fading with high accuracy for fixed to mobile and mobile to mobile communications. These parameters are absolutely required during the specification phase of future mobile communications systems in order to define the air interface and a variety of other relevant system parameters. This paper describes state-of-the-art ray tracing capabilities. A 3-D ray tracing model developed at the Universitaumlt Karlsruhe is presented. Important characteristic channel parameters are briefly discussed. Based on these parameters the model is verified by wideband nondirectional and directional measurements at 2 and 5.2 GHz, respectively, showing a good agreement. The proposed 3-D ray tracing model can therefore be used in order to extract parameter sets for the specification of future mobile communications systems and to optimize existing ones

Deterministic UWB Wave Propagation Modeling for Localization Applications based on 3D Ray Tracing

For the assessment of radio based localization applications deterministic channel models are required that allow for the simulation of wave propagation in realistic environments. This paper describes the extension of the deterministic narrow-band wave propagation modeling approach of ray tracing to ultra wideband (UWB) channels. A channel model is presented that permits the simulation of wave propagation in realistic three-dimensional environments over the entire frequency range of UWB applications from 3.1 to 10.6 GHz. Simulation results for the impulse response and the power delay profile in a typical indoor scenario are shown. From a set of simulation results statistics are extracted and compared to already standardized statistical UWB channel models

High-Accuracy Range Detection Radar Sensor for Hydraulic Cylinders

Industrial automation requires highly precise distance measurement sensors. Accurate detection of the piston position is indispensable for the control and monitoring of hydraulic cylinder applications. Known external and integrated solutions are subject to many limitations as for example in accuracy, in measurement length, or in price. A promising approach consists in the use of precise and low-cost radar sensors. The developed K-band frequency modulated continuous wave (FMCW) radar system in this paper detects the piston position in a hydraulic cylinder based on the guided propagation of a radar signal. The dielectric characteristics of the hydraulic oil are obtained for this purpose by permittivity measurement methods. Influences of the hydraulic oil on wave propagation in cylindrical waveguides as well as mechanical requirements associated with this new approach are investigated. The design of an adapted oil- and pressure-resistant transition between the radar sensor and the hydraulic cylinder and a novel calibration method will be described and verified under real measurement conditions. At a measurement repetition rate of 2 kHz, an accuracy of well below 200 μm was achieved for a hydraulic cylinder of 1 m in length.

Verification of a Hybrid Ray-Tracing/FDTD Model for Indoor Ultra-Wideband Channels

For development and optimization of ultra-wideband (UWB) based localization and imaging algorithms deterministic channel models are needed, which provide realistic channel impulse responses for given indoor scenarios. As the considered frequency band is 3.1 to 10.6 GHz the dimensions of objects in most indoor scenarios are small compared to the wavelength at lower frequencies. To simulate wave propagation properties in such scenarios an existing ray-tracing model has been combined with the finite difference time domain method (FDTD). The scattering properties of small objects are computed using FDTD and incorporated in a ray-tracing simulation as single scattering points. The simulation results are compared to measurements in a complex laboratory scenario. This comparison shows that the combined ray-tracing/FDTD model provides in complex indoor scenarios higher precision for propagation paths with small delay time. However the overall improvement of the simulation quality is limited and in comparison to the potential improvement by considering the diffuse scattering in the ray-tracing simulation almost negligible.

A versatile measurement system for the determination of dielectric parameters of various materials

In this paper, a versatile method for the determination of the complex permittivity of materials from measured scattering parameters is presented. The measurement set-up consists of a waveguide applicator for housing the material sample. The considered frequency range is 2?3 GHz. The complex scattering parameters are measured by a vector network analyser. The algorithm for computing the complex permittivity from the measured scattering parameters is shown in detail and an error estimation is performed. Depending on the waveguide layout liquid, granular and solid materials can be measured. To measure granular and liquid samples two dielectric walls inside the waveguide are used to house the samples. The dielectric parameters of different soils as well as of some liquids are determined with consideration of their moisture content and temperature. In contrast to several other techniques, this measurement set-up is also suited for high loss materials. The set-up has also been successfully used for measurements of anisotropic materials.

Verification of 3D Ray-tracing with Non-Directional and Directional Measurements in Urban Macrocellular Environments

3D ray-tracing has meanwhile advanced to a performance that it can provide channel parameters such as delay spread, Doppler spread, angular spread, distribution functions of long- and short-term fading with high accuracy for fixed to mobile and mobile to mobile communications. These parameters are absolutely required during the specification phase in order to define the air interface and a variety of other relevant system parameters. This paper shows state of the art 3D ray-tracing capabilities. The 3D ray-tracing model developed at the University of Karlsruhe is described and verified with wide-band non-directional and directional measurements at 2 GHz and 5.2 GHz respectively, showing a good agreement. The proposed 3D ray-tracing model can therefore be used in order to extract parameter sets for the specification of future mobile communications systems and to optimize existing ones

Microwave cavity perturbation technique for high-temperature dielectric measurements

The present work is motivated by the use of microwaves for the catalytic conversion of carbon dioxide to carbon monoxide. Chemical reactions like this are running at catalyst temperatures of more than 800 °C. The appropriate design of the microwave assisted reactor requires the exact knowledge of the dielectric properties of the catalyst and catalyst support materials up to those high temperatures. For this purpose a measurements system based on the cavity perturbation method was built. The system is using a rectangular TE104 cavity with a resonance frequency at 2.45 GHz and a quality factor Q ≈ 12000. A novel synthetic calibration method based on numerical full-wave modeling has been developed as an alternative to traditional calibration methods. The results of high temperature dielectric measurements for polyether ether ketone (PEEK), MACOR glass ceramics and zirconia are presented.

Characterisation of the time-dependent urban MIMO channel in FDD communication systems

The influence of the time dependent urban transmission channel on MIMO systems is investigated in this paper. Exploiting the full potential of MIMO systems requires the knowledge of the transmission channel matrix at the transmitter and the receiver. Channel estimation is therefore necessary. It has to be performed continuously as the transmission channel changes over time. In real communications systems it is only possible to update the channel state information in certain time intervals. During these intervals the estimated channel matrix is assumed to be constant. The difference between the real channel and the estimated one leads to non-orthogonal channels in the MIMO system. The result is inter-sub-channel interference (ISCI). The ISCI is considered as a Gaussian noise random process, which is added to the common thermal noise. Due to the increased total noise power of the resulting channel, the capacity decreases. Furthermore, a sub-channel transmission gain degradation (STGD) occurs caused by the non-orthogonal sub-channels. This results in an additional capacity loss. The dependency of ISCI and STGD on the update time interval is investigated. The considerations are based on simulations of the transmission channel in an urban environment. In order to attain realistic results, a 3D ray-tracing tool is used. An FDD communication system is assumed.

Modeling of Mutual Coupling Between Electromagnetic and Thermal Fields in Microwave Heating

This paper presents the analysis and modeling of the mutual coupling between thermal and electromagnetic fields. During the microwave heating process the microwaves are dissipated to heat due to the dielectric losses of the medium. The heat propagation inside the medium depends on its thermal parameters as well as on different propagation mechanisms. In most cases the dielectric properties are dependent on the temperature. In this paper a model is described for a microwave assisted soil decontamination system. The dielectric properties of the soil not only depend on temperature but also on the moisture content which reduces during the heating process. With changing dielectric properties of the soil the electromagnetic field distribution changes as well which again has an influence of the heat propagation. The basic principles of microwave heating and heat propagation are explained in this paper, as well as a simulation model based on an FEM code. To prove the correctness of the model a comparison with measurement results is given.

Impedance Matching of a Coaxial Antenna for Microwave In-situ Processing of Polluted Soils

Abstract The present paper is focused on the minimization of return loss of a slotted coaxial radiator proposed for a decontamination system for soils contaminated by volatile or semivolatile organic compounds such as oils or fuels. The antenna upgrade is achieved by coating it with a 5 mm thick Teflon layer. The electromagnetic characteristics reflection coefficient and power density distribution around the antenna surrounded by soils with different moisture levels are analyzed numerically. Simplified analytical approaches are employed to accelerate the optimization of the given antenna for microwave heating systems. The improved antenna design shows a good matching of the antenna to the surrounding soil with varying moisture levels. This ensures a high efficiency of the proposed in-situ soil decontamination system.