Michael A. Baldauf

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.

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.

Interference of short range radar with radio astronomy base stations

The automotive industry is considering the integration of Short Range Radar (SRR) sensors operating in the 24 GHz frequency range in order to increase traffic safety and driver comfort. The potential spread of SRRs has raised concerns about the interference threat to earth based Radio Astronomy (RA) stations. This paper derives a generic procedure for the calculation of SRR interference with ground based radio astronomy receivers. It forces the aggregate interference power from the SRRs to be less than the ambient noise power inherent to any RA antenna in order to calculate the exclusion zone required to protect RA stations. The presented results are obtained for a maximum influence of the interference, thus by setting the parameters for a worst-case scenario. The generic procedure is also suited for different research objectives by adapting the parameters to the specific scenario. Short Range Radar, Radio Astronomy, Interference, 24GHz Radar, UWB

Safety distances underneath vertically polarized base station antennas

Assessing the safety distances to base station antennas needs to be done in a quick but safe manner. The commonly performed far-field calculation leads typically to an overestimation of the safety distance in the main beam direction. However, for the vertical safety distance the straight forward application of the far-field formula might lead to an underestimation of the field strengths. Based on a computational investigation of halfwavelength dipoles, which are built in most base station antennas a new formula is presented that allows a safe assessment of the safety distance directly underneath the base station antenna.

Mobile MIMO Phones and Their Human Exposure to Electromagnetic Fields

A mobile phone equipped with a multiple antenna system is investigated with respect to its human exposure to electromagnetic fields. The channel conditions and the demanded capacity determine the required exictation voltages, which are passed to a commercial software tool. To get rid of the influence of various antenna distances to the shaped human head a dielectric cuboid is considered as absorbing medium. Utilizing MIMO techniques with channel knowledge at the transmitter allows a reduction of the exposure by some 95%.

Channel Characterisation for an OFDM-MISO Train Communications System

To design an OFDM train communications system it is essential to characterize and consider the channel parameters. For a high train scenario the transmission channel 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. Mobile station antennas with different patterns are included in the simulation model. The results are compared and assessed with respect to delay spread and Doppler spread

Exposition in Penthauswohnungen verursacht durch Mobilfunkbasisstationen

The widespread use of mobile communications in conjunction with an increasing number of new sites for base stations causes sometimes concern. The potential hazard of a mobile base staton is often estimated to be greater, the closer it is to a residential house. This article deals with the scenario where a mobile base station is directly mounted on the flat roof of a penthouse. Far field calculations cannot be applied because of the proximity of the roof to the antenna. Furthermore the damping cannot be given in general due to different angles of incidence onto the various building materials. Individual calculations are necessary. In this article a method for solving the problem is presented together with calculated power densities for different situations. Für die Dokumentation EMVU / GSM / Vollwellenmodellierung / geschichtete Medien