Abstract. This paper describes a context modelling approach using ontologies as a formal fundament. We introduce our Aspect-Scale-Context (ASC) model and show how it is related to some other models. A Context Ontology Language (CoOL) is derived from the model, which may be used to enable context-awareness and contextual interoperability during service discovery and execution in a proposed distributed system architecture. A core component of this architecture is a reasoner which infers conclusions about the context based on an ontology built with CoOL.

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.

Future safety-related vehicular applications require reliable information exchange provided by cooperative Vehicular Ad-hoc NETworks (VANETs). Although the vehicular WLAN standard IEEE 802.11p has been adapted to the challenging vehicular environment, it has not been adapted to the stringent communication requirements imposed by vehicular applications. In particular, broadcast transmissions are mostly periodic and initiated at common TX powers. This makes potential interferences recurring instead of spurious and lowers the performance of medium access for vehicular applications.In this paper, we propose to leverage recurring interferences by randomly selecting each TX power following a given probability distribution. Such randomization reduces the chances of recurring interferences, and the probability distribution provides control to the applications regarding the required Awareness Quality, in particular by providing a higher Awareness Quality at close range. This concept also reduces congestions by transmitting less at high distances. It is transparent to the applications, and manages to improve the Awareness Quality in a dense highway by a factor 2 to 20, yet at a factor 2 to 3 lower channel load.

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.

Cooperative safety applications require Dedicated Short-Range Communications (DSRC) to provide position-awareness of neighboring vehicles at a specific level of reliability, i.e. awareness-quality, up to a given distance, i.e. awareness-range. However, heavy communication loads negatively impact such awareness requirements due to communication impairments, ranging from strict capacity limitations of DSRC channels to correlated packet collisions due to periodic communication patterns. Transmission control strategies may adapt power or rate to control such impairments but risk missing the requirements of cooperative safety applications. In this paper, we design a new awareness control strategy by implementing a spatial awareness framework. Specifically, we adapt the distribution of the awareness-quality as a function of the awareness-range. Therefore, we first propose Random Transmit Power Control (RTPC), which manages to provide different levels of awareness-quality at different ranges, while mitigating correlated packet collisions by randomizing them in space. As RTPC is able to reduce the channel load, we secondly propose to combine RTPC with Transmit Rate Control (TRC) and to benefit from the gained channel resources by subsequently increasing the update-rate and by implication, the quality of position-awareness. The spatial awareness control capability of RTPC+TRC has been evaluated through simulations. We discuss the influence of RTPC+TRC on cooperative safety applications exemplarily for the Forward Collision Warning (FCW) application.

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Within the next decades the railway systems will change to fully autonomous high speed trains (HSTs). An increase in efficiency and safety and a reduction of costs would go hand in hand. Today's centralized railway management system and established regulations can not cope with trains driving within the absolute braking distance as it would be necessary for electronic coupling or platooning maneuvers. Hence, to ensure safety and reliability, new applications and changes in the train control and management are necessary. Such changes demand new reliable control communication links between train-to-train (T2T) and future developments on train-to-ground (T2G). T2G will be covered by long term evolution-railway (LTE-R) which shall replace today's global system for mobile communications-railway (GSM-R). The decentralized T2T communication is hardly investigated and no technology has been selected. This publication focuses on the wide band propagation for T2T scenarios and describes a extensive channel sounding measurement campaign with two HSTs. First results of T2T communication at high speed conditions in different environments are presented. Index Terms-train-to-train, high speed train, propagation, measurement.

Forward collision warning systems, lane change assistants or cooperative adaptive cruise control are examples of safety relevant applications that rely on accurate relative positioning between vehicles. Current solutions estimate the position of surrounding vehicles by measuring the distance with a RADAR sensor or a camera system. The perception range of these sensors can be extended by the exchange of GNSS information between the vehicles using an inter-vehicle communication link. In this paper we analyze two competing strategies against each other: the subtraction of the absolute positions estimated in each vehicle and the differentiation of GNSS pseudoranges. The aim of the later approach is to cancel out correlated errors in both receivers and, thus, achieve a better relative position estimate. The theoretical analysis is backed with Monte-Carlo simulations and empirical measurements in real world scenarios. Further on, two Bayesian approaches that make use of pseudorange differences are proposed. In a Kalman Filter pseudorange and Doppler measurements are used to estimate the baseline between two vehicles. This is extended in a second filter using on-board inertial and speed sensors following a multisensor fusion approach. The performance is evaluated in both, a highway and an urban scenario. The multisensor fusion approach proves to be able to stabilize the baseline estimate in GNSS challenging environments, like urban canyons and tunnels.