Andreas Lehner

Channel Model for Train to Train Communication Using the 400 MHz Band

This paper presents a channel model for direct train- to-train communication appropriate for the 400 MHz band. Extrapolation of theoretical and experimental results obtained for the planning of other railway communication systems like GSM-R is not obvious due to the difference in frequencies, antenna height and absence of base stations. In this paper, the analysis of the channel model covers different radio phenomena including path loss, Doppler, fading, and delay spread. Concretely we consider three scenarios (train stations, shunting yards and regional networks), for which the propagation channel characteristics are discussed. Furthermore, influence of special railway environments like cuttings which can be found near cities and towns, tunnels and bridges are encountered.

Measurement and analysis of train motion and railway track characteristics with inertial sensors

This paper presents measurements of train motion with a low-cost inertial measurement unit (IMU) based on micro electro mechanical systems (MEMS). The measurements were recorded on-board a train during normal passenger transport service on a network with dense urban railway environment as well as a rural, regional network environment. Sensor measurements from several train runs were therefore analyzed and the data is presented with a discussion on typical characteristics, noise and dynamics. As the train motion is dependent on the track, local track characteristics are inferred from the train motion measurements. Finally, the inertial measurements are analyzed toward track feature detection for feature based localization purposes.

Characterization of the aeronautical satellite navigation channel through high-resolution measurement and physical optics simulation

In this paper we discuss the results of a measurement campaign investigating the environment of satellite navigation receivers for aeronautical applications, where reflections on the plane as well as from the ground decrease the accuracy of the positioning. The focus is on the most critical flight phase—the final approach. For this scenario a wideband model is derived, which allows to investigate the performance of present and future global navigation satellite systems. The work was carried out under an European Space Agency contract (ESTEC Contract number 16059/02/NL/DS) entitled ‘Navigation signal measurement campaign for critical environments’, by Joanneum Research (Austria) with subcontracts to DLR (Germany) and the University of Vigo (Spain). Copyright

Probabilistic localization method for trains

The localization of trains in a railway network is necessary for train control or applications such as autonomous train driving or collision avoidance systems. Train localization is safety critical and therefore the approach requires a robust, precise and track selective localization. Satellite navigation systems (GNSS) might be a candidate for this task, but measurement errors and the lack of availability in parts of the railway environment do not fulfill the demands for a safety critical system. Therefore, additional onboard sensors, such as an inertial measurement unit (IMU), odometer and railway feature classification sensors (e.g. camera) are proposed. In this paper we present a top-down train localization approach from theory. We analyze causal dependencies and derive a general Bayesian filter. Furthermore we present a generic algorithm based on particle filter in order to process the multi-sensor data, the train motion and a known track map. The particle filter estimates a topological position directly in the track map without using map matching techniques. First simulations with simplified particular state and measurement models show encouraging results in critical railway scenarios.

A multi-broadcast communication system for high dynamic vehicular ad-hoc networks

The implementation of safety of life (SoL) services in transportation systems, e.g. for applications like collision avoidance of vehicles, requires reliable and instantaneous information exchange. In this paper we present the design of an infrastructure-less ad-hoc inter-vehicle communication system that fulfills these requirements with respect to the boundary conditions in the railway environment, where a limited communication range and relatively high speeds of nodes cause the network to be highly dynamic. Moreover, in areas with high user densities the common media access is a challenge due to limited bandwidth and interference from other wireless systems.

On the Performance of TETRA DMO Short Data Service in Railway VANETs

In this paper we present the results of an empirical study investigating the performance of TETRA (TErrestrial Trunked RAdio) in a Vehicular Ad-hoc Network (VANET) for safety related railway traffic applications. The Short Data Service (SDS) of TETRA in the Direct Mode Operation (DMO) allows an infrastructure-less exchange of traffic relevant information between vehicles in range of the communication. The propagation channel in case of such a direct (base station free) communication between railway vehicles underlies specific effects, which are not equivalent to other well known terrestrial mobile scenarios. We will present measurements covering urban, suburban and rural environments along a regional railway network in the south of Bavaria. Beside different operational conditions such as front, rear, and flank approaches of trains, we investigated several topological scenarios on both, single and double track sections along the line. We will also discuss the observed characteristic changes in narrow band signal attenuation and Doppler spectra for passages through forests, hilly areas, stations and a tunnel. We determined statistics for the transmission delay of messages and the message erasure rates for single and multi user access on a single common carrier for different transmission intervals. Finally, the quality of service for the envisaged safety applications is assessed.

COMB: Cell Based Orientation Aware MANET Broadcast MAC Layer

The design of a collision avoidance system for trains implies the design of a MAC layer for their specific requirements. It should be efficient, reliable, use broadcast and support wireless mobile ad hoc networks (MANETs) with high user speeds. Therefore we are using awareness techniques, which allow a certain channel assignment, despite the absence of infrastructure. This paper presents a new MAC layer protocol designed for broadcast MANETs called COMB (Cell-based Orientation-aware MANET Broadcast). In principle, COMB allows the realization of a collision free transmission, high speed is supported and no handshake is required. COMB is based on localization aware cross layer dimensioned CDMA cells, and uses the SOTDMA protocol as intra cell scheme, while the inter cell scheme relies on direction and speed awareness.

Performance of MAC protocols in beaconing mobile ad-hoc multibroadcast networks

The investigation of infrastructureless safety applications in different transportation systems is a hot research topic. The nodes in the network are designed to advertise to the rest of the nodes informationa-bout the current traffic situation by means of short beacon messages containing speed, direction, positions and other relevant safety information. The scheduling should be organized by the MAC layer so that the transmitted messages arrive successfully as soon as possible at the receiver. The networks that support these kind of applications are Mobile Ad-hoc Multibroadcast Networks (MAMNETs). In this paper we present the challenges the MAC layer for MAMNETs should overcome. We discuss the most important performance metrics of the MAC layers in order to obtain a system independent analysis and show a survey of the factors that may influence the behavior of the MAC layers.

Measurement and analysis of the direct train to train propagation channel in the 70 cm UHF-band

In this paper we present first analyses and results of a comprehensive measurement campaign investigating the propagation channel in case of direct (base station free) communication between railway vehicles. The measurements cover urban, suburban and rural environments along a multifaceted regional railway network in the south of Bavaria. Beside different operational conditions like front, rear, and flank approaches of trains, we investigated several topological scenarios on both, single and double track sections along the line. We will also discuss the observed characteristic changes in narrow band signal attenuation and Doppler spectra for passages through forests, hilly areas, stations and a tunnel.

Bayesian GNSS/IMU tight integration for precise railway navigation on track map

The localization of a train on a railway network with onboard sensors has been usually tackled by matching an estimated position fix on a track map. In this paper, we face the navigation problem directly in the topological domain of the map without computing an initial global position. We develop a tightly coupled scheme to fuse the raw measurement of Global Navigation Satellite System (GNSS), Inertial Measurement Unit (IMU) and the information of a digital track map. We model this problem using a Dynamic Bayesian Network (DBN) and we derive a particle filter to handle the discrete and nonlinear nature of the map in the estimation process and to detect the correct path after a train switch. Real measurements are finally used to test the method and analyze the role of raw GNSS measurements and satellite geometry in precision. Results suggest that reliable navigation can be achieved even when less than four satellites are in view.