Thomas Fügen

A new inter-vehicle communications (IVC) channel model

A new model of the transmission channel between moving vehicles is presented in this paper. The approach consists of three major parts: the modelling of the road traffic, the modelling of the environment adjacent to the road lane, and the actual modelling of the wave propagation between the vehicles. A ray-optical approach is used to model the wave propagation, which allows for wide-band as well as narrow-band analyses of the channel. A characteristic time series of impulse responses of the IVC-channel can therefore be calculated, which can be directly used for system simulations. Simulation results are compared to wide-band measurements at 5.2 GHz of the IVC-channel, yielding a good agreement.

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

Narrow-band measurement and analysis of the inter-vehicle transmission channel at 5.2 GHz

The inter-vehicle transmission channel is characterised based on narrow-band measurements at 5.2 GHz. The measurement setup consists of a transmitter and a receiver, which are installed in two different vehicles. While measuring the transmission channel, both vehicles are manoeuvred in realistic road traffic scenarios. Measurements are obtained for four different classes of environments: urban, suburban (village), motorway and highway. Statistical functions, such as the cumulative distribution function (CDF) of the received signal, the average Doppler power density spectrum and the level crossing rate (LCR), are derived for each class. The measured results are compared to analytical functions, such as the Rice, the Rayleigh, the Gauss or the Nakagami distribution. The least squares and the conjugate gradient method are used to fit the parameters of the analytical functions to the measurement data.

Channel Analysis for an OFDM-MISO Train Communications System Using Different Antennas

For the design of an OFDM train communications system it is essential to characterise and consider the channel parameters. The transmission channel of a high-speed train scenario is frequency selective as well as time variant. Thus, delay spread and Doppler spread are investigated as crucial parameters for the OFDM system performance. Using a ray-tracing tool realistic impulse responses of the transmission channels are simulated. The investigated system includes three base stations operating in common frequency mode along a railway track and one mobile station situated on a high-speed train. For the mobile station different antenna patterns are included in the simulation model. The results are compared and assessed with respect to delay spread, Doppler spread and receive power. When using directional antennas a distinct reduction in Doppler spread is achieved.

MIMO capacities for different antenna array structures based on double directional wide-band channel measurements

We present an approach for investigating the performance of generic multiple-input multiple-output (MIMO) wireless systems in a realistic way using wideband real-time propagation measurements of the double-directional radio channel. Applying a multidimensional high-resolution channel parameter estimation procedure the descriptive parameters for any relevant propagation path including the path weights, time-delay, Doppler shift and the propagation directions at both ends of the wireless link are extracted simultaneously from the measurement data. from the estimated parameter sets then a local reconstruction of the multidimensional wave fields in the vicinity of the measured aperture volumes in time, space and frequency is possible. Since this way the measurement antenna properties are excluded from the channel, the influence of a variety of application specific array architectures can be investigated. Here, we use this synthesis approach to analyze the performance of given target systems with smart antennas in terms of the resulting channel capacities and eigenvalue distributions.

Virtual Drive: A Complete V2X Communication and Radar System Simulator for Optimization of Multiple Antenna Systems

Vehicle-to-X (V2X) communication as well as automotive radar are fast growing areas of consumer interest. This gives rise to a challenge to a well-working communication systems in handling the V2X radio channel. The two most important components influencing the channel are the antennas and the fast changing environment, resulting in a time-variant behavior of the channel. Therefore, finding the optimal antenna configuration to ensure the best performance is a difficult task. A possible solution is the employment of measurement campaigns, but they are expensive, time consuming, and provide no repeatability. An alternative approach, based on simulations, is presented in this article. This tool, called “Virtual Drive,” consists of an environment and a traffic model and calculates the multipath propagation with a 3D ray-tracing tool. This combination yields a “virtual drive” through arbitrary scenarios and allows for the optimization of antenna configurations that are to be investigated. The different components of the Virtual Drive are described and the accuracy of the software tool is examined by a comparison with measurements. Finally, the manifold capabilities of such a software tool are demonstrated using the example of vehicular antenna optimization for cars and of radar system optimization.

Characterization of multipath clusters with ray-tracing in urban MIMO propagation environments at 2 GHz

For the design of MIMO (multiple input multiple output) systems, channel models are required that properly describe the behavior of the physical channel. The propagation environment around a mobile station (MS) and a base station (BS) is a multipath environment. Multipath components can be grouped together into so called clusters. We define a cluster as a group of paths with similar directions of departure or arrival in azimuth and elevation and similar time delay of arrival. A 3D deterministic ray-tracing tool is used to calculate the double-directional MIMO channel. The advantage of deterministic ray-tracing in contrast to measurements is that ray-tracing offers the possibility of detailed characterization of all multipaths and investigation of the propagation effects without any constraint concerning the antenna or the measurement equipment. A new automatic procedure to identify clusters in azimuth, elevation and delay at the transmitter and the receiver from ray-tracing data is presented. Based on the ray-tracing simulations, we propose a new iterative procedure to extract multipath clusters. The extracted parameters show clearly that, in macrocellular environments, the number of MS-clusters is much greater than the number of BS-clusters. The presented cluster characteristics help to parameterize MIMO channel models and to make simulation results more realistic.

Signal: SAR for ice, glacier and global dynamics

SIGNAL is an innovative earth exploration mission proposal with the main objective to estimate accurately and repeatedly topography and topographic changes associated with mass change or other dynamic effects on glaciers, ice caps and polar ice sheets. Elevation measurements are complemented with glacier velocity measurements, providing valuable additional information for a better understanding of the hydrology of glacierized basins and of the Arctic and Antarctic water cycle. SIGNAL is capable of monitoring all critical regions with a high spatial resolution and an adequate revisit time. This paper gives an overview about the actual mission design status and provides a brief description of the topography (DEM - digital elevation map) self-calibration strategy and the estimated global interferometric performance.

Channel Modelling for an OFDM Train Communications System Including Different Antenna Types

The characteristics of propagation channels between high-speed trains and fixed base stations for multimedia communications links using orthogonal frequency division multiplexing (OFDM) is investigated. To model the system behaviour realistically, impulse responses of the transmission channels are generated by a ray-tracing tool. Typical environments along a railway track are taken into account as well as the train motion. Mobile station antennas with different patterns are included in the simulation model and the results are compared and assessed with respect to characteristic channel parameters.

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