Konferenzbeiträge

The analysis of wireless communication channels at the mmWave, sub-THz and THz bands gives rise to difficulties in the construction of antenna arrays due to the small maximum inter-element spacing constraints at these frequencies. Arrays with uniform spacing greater than half the wavelength for a certain carrier frequency exhibit aliasing side-lobes in the angular domain, prohibiting non-ambiguous estimates of a propagating wave-front’s angle of arrival.In this paper, we present how wide-band modelling of the array response is useful in mitigating this spatial aliasing effect. This approach aims to reduce the grating lobes by exploiting the angle- and frequency-dependent phase-shifts observed in the response of the array to a planar wave-front travelling across it.Furthermore, we propose a method by which the spatial correlation characteristics of an array operating at 33 GHz carrier frequency with an instantaneous bandwidth of 1 GHz can be improved such that the angular-domain side-lobes are reduced by 5-10 dB. This method, applicable to arbitrary antenna array manifolds, makes use of a linear operator that is applied to the base-band samples of the channel transfer function measured in space and frequency domains. By means of synthetically simulated arrays, we show that when operating with a bandwidth of 1 GHz, the use of a derived linear operator applied to the array output results in the spatial correlation characteristics approaching those of the array operating at a bandwidth of 12 GHz. Hence, non-ambiguous angle estimates can be obtained in the field without the use of expensive high-bandwidth RF front-end components.

The emergence of new electric vehicle (EV) corner concepts with in-wheel motors offers numerous opportunities to improve handling, comfort, and stability. This study investigates the potential of controlling the vehicle's corner positioning by changing wheel toe and camber angles. A high-fidelity simulation environment was used to evaluate the proposed solution. The effects of the placement of the corresponding actuators and the actuation point on the force required during cornering were investigated. The results demonstrate that the toe angle, compared to the camber angle, offers more effect for improving the vehicle dynamics. The developed direct yaw rate control with four toe actuators improves stability, has a positive effect on comfort, and contributes to the development of new active corner architectures for electric and automated vehicles.

A recurring discussion is whether it is useful to specify a typical exposure in addition to the theoretical maximum exposure for massive-MIMO systems, but currently no reliable method exists. Therefore, typical 5G use cases are investigated, grouped according to their throughput, and three typical data rates are derived. To evaluate the reproducibility of data rates and corresponding exposures, three measurement runs have been performed at four measurement points (MP) with different cell utilization by other users, while a 5G UE generated the typical data rates in the vicinity of the MP. Furthermore, temporal variations have been considered by evaluating three different averaging times. The results demonstrate that the exposure values are reproducible within typical measurement uncertainty across different averaging times and even across different measurement runs. Therefore, this method is considered to be capable of providing reproducible measurements of the typical exposure in addition to the maximum possible exposure.

Ongoing mobile radio small cell deployment requires detailed analysis of the electromagnetic exposure which is dependent on the installation environment. To facilitate site-specific small cell exposure analysis, a hybrid exposure assessment approach is utilized which combines antenna nearfield measurement and post-processing. An equivalent current antenna model is investigated under virtually varying installation conditions, considering three real applications of small cell installation. The equivalent current antenna model's results are in good agreement with reference measurements and geometry-based simulations. Antenna pattern deviations vary between 0.9 dB and 2.9 dB, depending on the installation environment selected. This highlights the advantages of using the hybrid exposure assessment approach which adequately captures and reflects changes in the installation surroundings. Additionally, it yields comparable results to established methods and provides extensive flexibility for virtual exposure estimations by taking into account varying installation environments.

Measurements of RF exposure to mobile radio base stations are important for risk communication. We measured instantaneous exposure with a focus on 5G with an exposimeter on an identical route on three afternoons to study the reproducibility. Due to different walking speeds, the relationship between time and place was not identical for the measurements, so time is not suitable as a reference for comparison. When the distance walked was used as reference, accuracy problems of the exposimeter's internal GPS system occurred, resulting in a mismatch between the actual location and the GPS location. This problem was successfully corrected by using the gradient descent with momentum method. The three measurements show a variation in maximum measured exposure of up to 5.4 dB for a selected section of the route, which is reduced to 2.8 dB when averaged over 6-minute intervals, which is acceptable given typical measurement uncertainties of ±3 dB.