Update Delay: A new Information-Centric Metric for a Combined Communication and Application Level Reliability Evaluation of CAM based Safety Applications

Standard network metrics, such as throughput, latency and reception probability, are the most popular performance indicators used in the literature to describe and compare communication protocol variations. However, these “traditional” network-centric PI are not adapted to the distributed, information-centric nature of the beaconing communication pattern, nor do they cover application level reliability or freshness of information. In this paper, we introduce a more suitable metric called Update Delay, represented as a Complementary Cumulative Distribution Function (CCDF). We will show how this single Update Delay performance indicator can be an optimal representation of the freshness and reliability of the information about a certain transmitter, i.e. awareness about vehicles and their current state in the vicinity. This paper extends on the methodological aspects of the approach, as well as introduces several concrete examples

Performance of CAM based Safety Applications using ITS-G5A MAC in High Dense Scenarios

ETSI ITS-G5 is the current vehicle-to-vehicle communication technology in Europe, which will be standardized by ETSI TC ITS. It is based on IEEE 802.11p and therefore uses a CSMA/CA scheme for Media Access Control (MAC). In this paper we analyze the performance of CAM based safety applications using the ETSI ITS-G5 MAC technology in a challenging scenario with respect to MAC issues: A suitable freeway segment with 6 lanes in each direction. The freeway scenario is thoroughly modeled and implemented in the well known ns-3 simulation environment. Based on this model, the paper shows the performance of CAM based safety applications under MAC challenging conditions. Therefore we provide a set of simulation results resting upon a particular performance metric which incorporates the key requirements of safety applications. Finally we analyze two concrete example scenarios to make a point how reliable CAM based safety applications are in high dense traffic scenarios

Innovative Zugleit- und Sicherungstechnik durch Digitalisierung

Der Fortschritt in der Elektronik sowie der Datenverarbeitung und Kommunikation hat sich in den letzten Jahren beschleunigt und führt dazu, dass immer mehr Daten verfügbar sind, die sinnvoll genutzt werden sollten. Der technische Trend wird derzeit als Digitalisierung 4.0 bezeichnet – wobei 4.0 für die 4. technische Revolution nach der Erfindung der Dampfmaschine steht. Diese 4. Generation unterscheidet sich von der vorhergehenden vor allem durch die Anwendung neuer Konzepte hinsichtlich Datenerfassung und -verarbeitung, Assistenzsysteme, Vernetzung und Integration, Dezentralisierung und Serviceorientierung, Selbstorganisation und Autonomie. Dieser Trend macht natürlich auch vor den Schienenfahrzeugen und deren Betrieb nicht halt. Perspektivisch wird die Zugleit- und Sicherungstechnik auf die bereits europaweit spezifizierte Ebene des European Train Control System (ETCS) umgestellt, um die vielen länderspezifischen Alt-Signalisierungssysteme in Europa abzulösen und damit eine Vereinheitlichung der Fahrzeugausrüstung zu ermöglichen. Mit ETCS Level 3 ist dadurch neben der Zugsicherung auch die Zugschlusserkennung technisch gelöst. Aber die Digitalisierung 4.0 im Bahnbereich bietet noch viel mehr. Dieser Beitrag zeigt an einigen Beispielen auf, wohin die Reise in der Zugleit- und Sicherungstechnik gehen wird

Train Collision Avoidance with Mobile Devices for Sparsely Used Railway Lines

This paper shows the results of a communication range measurement campaign performed with mobile onboard units of a fully de-centralized train collision avoidance safety overlay system in typical environments of sparsely used railway lines. The most critical sections of the track with respect to a direct train-to-train communication channel were identified and selected for measurements in different antenna configurations. The measurement results justify the conclusion that the direct train-to-train communication channel along typical sparsely used railway lines fits the requirements of mobile onboard units of the train collision avoidance system

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

Towards Autonomous Services for Smart Mobile Devices

In this paper a framework is presented which allows the discovery and execution of services on connected and partially autonomous mobile devices. Discovery and execution procedures are sensitive to the user's context (current location, personal preferences, current network situation etc.). We present a description language for service offers which is used to provide the necessary information for a service registry running on the mobile device itself. Services are executed in an abstract manner (in the sense of a non-specific implementation) from the user's point of view, getting an optimal result with respect to the current context out of a set of parallel invoked service implementations

Degradation of Communication Range in VANETs Caused by Interference 2.0 - Real-World Experiment

High channel load in vehicle-to-vehicle communication leads to a degradation of the vehicles’ communication range, due to interference and hence packet loss at larger distances. Packet loss results from two or more concurrent transmissions, colliding at receivers located inbetween, which is also known as the hidden station problem. In previous works, our simulation study has shown that this packet loss leads to a degradation of 90% of the communication range. In this paper, we confirm the simulation results by real-world measurements. We present a methodology for transferring the simulation scenario to a real-world measurement scenario, able to evaluate the problem of hidden stations. With three radios applying the IEEE 802.11p standard, we measure the degradation of the communication range under interference. In the measurement, we find a degradation of 50 to 70%. On the one hand, there are less collisions due to only one hidden station. On the other hand, we identify that the receiving vehicle as a shadowing object itself is an additional origin for hiding the other station which slightly increases the number of collisions even at close distances