Browsing by Author "Riebl, Raphael"

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    Enhanced Inter-Vehicular relative positioning
    (IEEE, 2016-12-26) Speth, T.; Riebl, Raphael; Brandmeier, T.; Facchi, Christian; Al-Bayatti, Ali Hilal; Jumar, U.
    Intelligent Transportation System (ITS) applications for integral and cooperative vehicle safety as well as some Advanced Driver Assistance Systems (ADASs) benefit from precise determination of relative positions between dynamic traffic objects. With conventional Global Navigation Satellite System (GNSS) measurements, e.g. using Global Positioning System (GPS), the required accuracy cannot be achieved. For this reason, an exchange of GNSS observations via Vehicular Ad-Hoc Network (VANET) is proposed in this paper. In particular, the European Inter-Vehicle Communication (IVC) protocol stack ITS-G5 is employed. With these exchanged GNSS observations, Differential GNSS (DGNSS) or Real-Time Kinematic (RTK) calculations provide a precise relative position vector. However, due to relative movement of traffic objects, this position vector becomes obsolete for increasing transmission delays. For this reason, a mitigating kinematic model is set up and validated experimentally. With respect to fixed RTK solutions, this kinematic model reduces the errors by an average of 61% compared to position calculations ignoring IVC latency.
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    Improved Security Performance for VANET Simulations
    (Elsevier, 2016-12-06) Riebl, Raphael; Monz, Markus; Varga , Simon; Janicke, Helge; Maglaras, Leandros; Al-Bayatti, Ali Hilal; Facchi, Christian
    Upcoming deployments of Vehicular Ad Hoc Networks (VANETs) in Europe are expected to sign and verify packets secured by cryptographic signatures by default. Thus, when VANET simulations are used for development and test of applications building upon vehicular communication, the overhead induced by security extensions to the ITS-G5 protocol stack shall not be neglected. This paper presents a standard compliant simulation model capable to handle secured messages. Beside its suitability for Hardware-in-the-Loop simulations employing secured communication, the model's major advantage is the minimisation of the simulation environment's performance penalty linked with cryptographic computations.
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    Limitations of HIL Test Architectures for Car2X Communication Devices and Applications
    (2019-09-13) Al-Bayatti, Ali Hilal; Obermaier, Christina; Khan, Sarmadullah; Facchi, Christian; Riebl, Raphael
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    Measuring the Realtime Capability of Parallel-Discrete-Event-Simulations
    (MDPI, 2021-03-10) Obermaier, Christina; Riebl, Raphael; Al-Bayatti, Ali Hilal; Khan, Sarmadullah; Facchi, Christian
    Speeding up Discrete Event Simulations (DESs) is a broad research field. Promising Parallel Discrete Event Simulation (PDES) approaches with optimistic and conservative synchronisation schemes have emerged throughout the years. However, in the area of real-time simulation, PDESs are rarely considered. This is caused by the complex problem of fitting parallel executed DES models to a real-time clock. Hence, this paper gives an extensive review of existing conservative and optimistic synchronisation schemes for PDESs. It introduces a metric to compare their real-time capabilities to determine whether they can be used for soft or firm real-time simulation. Examples are given on how to apply this metric to evaluate PDESs using synthetic and real-world examples. The results of the investigation reveal that no final answer can be given if PDESs can be used for soft or firm real-time simulation as they are. However, boundary conditions were defined, which allow a use-case specific evaluation of the real-time capabilities of a certain parallel executed DES. Using this in-depth knowledge and can lead to predictability of the real-time behaviour of a simulation run.
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    Quality of Service in Vehicular Ad Hoc Networks: Methodical Evaluation and Enhancements for ITS-G5
    (De Montfort University, 2021-05) Riebl, Raphael
    After many formative years, the ad hoc wireless communication between vehicles has become a vehicular technology available in mass production cars in 2020. Vehicles form spontaneous Vehicular Ad Hoc Networks (VANETs), which enable communication whenever vehicles are nearby without need for supportive infrastructure. In Europe, this communication is standardised comprehensively as Intelligent Transport Systems in the 5.9 GHz band (ITS-G5). This thesis centres around Quality of Service (QoS) in these VANETs based on ITS-G5 technology. Whilst only a few vehicles communicate, radio resources are plenty, and channel congestion is a minor issue. With progressing deployment, congestion control becomes crucial to preserve QoS by preventing high latencies or foiled information dissemination. The developed VANET simulation model, featuring an elaborated ITS-G5 protocol stack, allows investigation of QoS methodically. It also considers the characteristics of ITS-G5 radios such as the signal attenuation in vehicular environments and the capture effect by receivers. Backed by this simulation model, several enhancements for ITS-G5 are proposed to control congestion reliably and thus ensure QoS for its applications. Modifications at the GeoNetworking (GN) protocol prevent massive packet occurrences in a short time and hence congestion. Glow Forwarding is introduced as GN extension to distribute delay-tolerant information. The revised Decentralized Congestion Control (DCC) cross-layer supports low-latency transmission of event-triggered, periodic and relayed packets. DCC triggers periodic services and manages a shared duty cycle budget dedicated to packet forwarding for this purpose. Evaluation in large-scale networks reveals that this enhanced ITS-G5 system can reliably reduce the information age of periodically sent messages. The forwarding budget virtually eliminates the starvation of multi-hop packets and still avoids congestion caused by excessive forwarding. The presented enhancements thus pave the way to scale up VANETs for wide-spread deployment and future applications.