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The profound knowledge of radio wave propagation is essential for the design and test of wireless communication systems especially in demanding environments and for mobile transmitters and receivers. In this article we provide an accurate description of the relevant propagation parameters for train-to-train scenarios considering typical environments such as railway stations, open field and hilly terrain with cutting. At the beginning of this contribution we shortly describe the comprehensive train-to-train measurement campaign which is the basis for all further evaluations. We treat the stationarity of the channel in time and frequency and derive power delay profiles, and the Doppler spectral densities. Furthermore, distance-variant statistics about the $k$ -factor, delay spread and Doppler frequency spread are presented. We show that these parameters change very much for different environments and distances. For all stochastic channel parameters we propose distance dependent model parameters.

Device-free localization systems infer presence and location of moving users by measuring user-induced perturbations in the signal power between wireless network nodes. Thereby, users not only induce perturbations to the power of the line-of-sight, but also to the power of reflected and scattered signals which are observed in the received signal as multipath components. Since the propagation paths of multipath components differ inherently from the line-of-sight path, these propagation paths can be considered as additional network links. This extended network determines the multipath-enhanced device-free localization system. Based on empirical models that relate perturbations in the power of multipath components to the user location, the localization problem can be solved by nonlinear Bayesian filtering. In this work, we therefore investigate the point mass filter and the particle filter as possible solutions. Using simulations, we demonstrate the applicability of these filter solutions for multipath-enhanced device-free localization. The overall localization performance is comparable for both filters. Further, the simulation results indicate an improvement of the localization performance of multipath-enhanced device-free localization compared to device-free localization.

State-of-the-art device-free localization systems infer presence and location of users based on received signal strength measurements of line-of-sight links in wireless networks. In this letter, we propose to enhance device-free localization systems by exploiting multipath propagation between the individual network nodes. Particularly indoors, wireless propagation channels are characterized by multipath propagation, i.e., received signals comprise multipath components due to reflection and scattering. Given prior information about the surrounding environment, e.g., a floor plan, the individual propagation paths of multipath components can be derived geometrically. Inherently, these propagation paths differ spatially from the line-of-sight propagation path and can be considered as additional links in the wireless network. This extended network determines the novel multipath-enhanced device-free localization system. Using theoretical performance bounds on the localization error, we show that including multipath components into device-free localization systems improves the overall localization performance and extends the effective observation area significantly.

Operating remotely piloted aircraft is not imaginable without a continuous data exchange between the air vehicle and the remote pilot. This data exchange requires reliable data links. One approach for such a data link discussed in the community is a terrestrial system deployed in C-band. A good knowledge of the physical conditions of the communication channel, in this case the air-ground/ground-air channel, is indispensable for the development of wireless data links. Therefore we carried out a 50MHz bandwidth channel sounding campaign with a terrestrial transmitter and an airborne receiver. In this paper we give a detailed description of our campaign setup and the processing of the collected data. The campaign covered several flight scenarios, such as take-off, taxiing, and multiple en-route maneuvers. We furthermore present results on the received power and the amplitude distribution of the first resolvable path of the received signal for the different flight scenarios. We observed significant drops in reception power during certain maneuvers that need to be considered in the design process of a data link for unmanned aviation. Additionally, we show that the amplitude distribution follows the distributions commonly used in statistical channel modeling of wireless channels to some extent. We finally present parameter sets for multiple flight scenarios for scaling the amplitude distributions to allow a statistical channel modeling of the reception power of the first resolvable signal path.

Mobile robotics will play a key role in future space, ocean and deep sea exploration activities. Besides the actual development of the robotic systems, the different ways of commanding those systems, using technologies varying from teleoperation with the human in the loop, through shared autonomy towards highly autonomous systems, will be the main challenges of these missions. This paper describes the robotic activities of the DLR institutions within the Helmholtz projects ROBEX and ARCHES, dealing with robots for autonomous space and ocean exploration applications. Furthermore, it describes the challenges, the overlap and the synergies of those domains, the different approaches of operating robots from far distances in extreme environments and gives an outlook on future mission possibilities.

In this contribution, we present a method to analyze the effectiveness of multipath mitigation by extended averaging in the context of terrestrial radionavigation. We derive the requirements of extended averaging on the geometry between a ground station and an aircraft. Using that knowledge we are able to analyze the effectiveness of extended averaging for real world flight trajectories.

Rain attenuation has a significant impact on the availability of millimeter wave communication systems. In order to dynamically simulate such radio systems, several generators of artificial time series of rain attenuation have been developed. This paper briefly describes the DLR channel model and presents the results of model parameter extraction from time series measured on terrestrial microwave paths in the Czech Republic.