Thomas Herpel

Stochastic and deterministic performance evaluation of automotive CAN communication

The performance of communication systems can be evaluated using various distinct techniques and paradigms, e.g. queuing theory, simulation or worst case analysis. Mean values for performance measures like transmission delay, queue length or system utilization are valuable information for network dimensioning. However, in many cases, quantile-based approaches or deterministic upper bounds are indispensable, especially for systems that need real-time guarantees. A typical application area are safety-critical functions in automotive environments, where hard real-time transmission deadlines have to be met to assure safe operation of the vehicle. In this paper, we investigate a contemporary automotive in-car communication system, the Controller Area Network (CAN). A simulation study of the system yields stochastic quantile-related use case performance measures for non-time-critical communication. It is complemented by a deterministic evaluation using Network Calculus, which allows to determine worst case transmission times and provides closed and easily applicable formulas for delay bounds of messages on all priority levels. Comprising the outcomes from this dual evaluation approach supports the design, dimensioning and parameterization of the overall CAN bus system with respect to both hard real-time demands and performance characteristics in typical use case scenarios.

Enhanced downlink capacity in UMTS supported by direct mobile-to-mobile data transfer

The goal of this work is first to analyze the feasibility of a peer-to-peer file sharing technique in mobile cellular environments, taking into account key characteristics and peculiarities of the UMTS Radio Access Network (UTRAN). The concept is referred here to as mobile-to-mobile (m2m). Next, our research efforts explore the performance benefits of m2m file sharing applications in UMTS networks in terms of releasing overall downlink capacity, which can be used to provide better Quality of Service (QoS) for real-time services. To evaluate the performance of the proposed m2m concept we conducted extensive simulation studies with appropriately modified radio propagation models for low antenna heights for both, transmitter and receiver, as it is typical for m2m. Two alternative scenarios of serving user requests (m2m network mode and conventional UMTS mode) have been constructed and analyzed. The results indicate a dramatic increase in service probability and overall throughput gain of up to 85 % in a UMTS network, supported by the m2m data transmission mode. Furthermore, results show that by a well-designed m2m routing policy and proper utilization of currently not used uplink resources (due to asymmetric uplink/downlink traffic load) substantial reduction of the expected file download time can be achieved.

Dependency-Based Test Case Selection and Prioritization in Embedded Systems

Embedded systems in automotive engineering are getting more and more complex due to a higher rate of integration and shared usage of sensor signals. A common solution to testing these systems is deriving test cases from models, so called model-based testing. In practice, generated test suites are typically very huge and have to be reduced by methods of regression-test selection and prioritization. In our field of application, we additionally suffer from the lack of knowledge on system internals like the source code. Therefore, our approach is based on dependences between the components of embedded systems. The model we use is derived from the system architecture and system requirements. We are using graph algorithms for selecting and prioritizing test cases to run on a certain system version. First statistical evaluations and the current implementation already have shown promising reduction of test-cases for regression testing.

Multi-sensor data fusion in automotive applications

The application of environment sensor systems in modern - often called ldquointelligentrdquo - cars is regarded as a promising instrument for increasing road traffic safety. Based on a context perception enabled by well-known technologies such as radar, laser or video, these cars are able to detect threats on the road, anticipate emerging dangerous driving situations and take proactive actions for collision avoidance. Besides the combination of sensors towards an automotive multi-sensor system, complex signal processing and sensor data fusion strategies are of remarkable importance for the availability and robustness of the overall system. In this paper, we consider data fusion approaches on near-raw sensor data (low-level) and on pre-processed measuring points (high-level). We model sensor phenomena, road traffic scenarios, data fusion paradigms and signal processing algorithms and investigate the impact of combining sensor data on different levels of abstraction on the performance of the multi-sensor system by means of discrete event simulation.

Real-Time Guarantees for CAN Traffic

Modern cars comprise a multitude of electronic features which are implemented in tens of communicating control units. To connect these in-car embedded systems, the CAN bus offers a sustainable performance, hence it is used as a widespread communication infrastructure, even for safety critical applications. However, CAN media access is priority based and performed competitive and non-preemptive. Thus, assessing the worst case end-to-end delay is inevitable in order to provide safe and efficient operation of functions with hard real-time properties. In this paper, we use the analytical method of network calculus to determine guaranteed upper bounds for transmission delays of all CAN priorities. We demonstrate the applicability of our approach by investigating current real-life CAN communication data from the German car manufacturer Audi.

Routing of Safety-Relevant Messages in Automotive ECU Networks

Modern cars comprise tens of electronic control units, serving for various purposes like entertainment, drivers comfort or occupant protection. To connect these networked embedded systems inside the car, widespread bus systems like CAN or FlexRay are used, each one offering projecting abilities and specific limitations for certain application areas. In order to point out the suitability of a certain in-car network topology for the transmission of highly time- and safety-critical data content, we investigated effects of routing by a central gateway on the communication delay. In cooperation with the German car manufacturer Audi, we installed a prototype measurement infrastructure and collected meaningful communication data samples for up-to-date and future in-car networks. The results we obtained from the data samples allow for a sophisticated evaluation of the in-car communication network with respect to the demands of time- and safety-critical functions at an early stage of system development. Keywords-Automotive Embedded Systems; ECUs; CAN; FlexRay; In-Car Communication; Safety-Relevant Applications

Improving Downlink UMTS Capacity by Exploiting Direct Mobile-to-Mobile Data Transfer

The goal of this work is to analyze the feasibility of a peer-to-peer file sharing technique in mobile cellular environments, taking into account key characteristics and peculiarities of the UMTS radio access network (UTRAN). The concept is referred here to as mobile-to-mobile (m2m). Our research efforts explore the performance benefits of m2m file sharing applications in UMTS networks in terms of releasing overall downlink capacity. In our concept the users that are interested in downloading a popular file form a mobile cooperative community and using the fact that traffic load of multimedia services is asymmetrically distributed between uplink and downlink, contribute their own currently not used uplink capacity for providing the packets of the content to other users within the group in multicast mode on the uplink carrier frequencies. As a result a major part of the traffic is shifted away from the downlink, making the released downlink capacity available for providing better quality of service (QoS) for real-time services. Two alternative scenarios of serving user requests (m2m and conventional UMTS mode) have been analyzed. The results indicate a dramatic increase in service probability and overall throughput gain of up to 85 % in a UMTS network, supported by the m2m data transmission mode. Furthermore, results show that by a well-designed m2m routing policy and proper utilization of uplink resources substantial reduction of the expected file download time can be achieved.

Assessing the CAN communication startup behavior of automotive ECUs by prototype measurements

Applications of modern automotive electronics often rely on data from various electronic control units (ECUs). A widespread communication system to enable the data exchange is the Controller Areas Network (CAN), implementing a priority-based media access scheme. Assessing important aspects of data transmission is done in both the early phase of system design by means of simulation or analytical evaluation of the in-car communication system, and in terms of measurements in real test cars by logging and analyzing communication data in prototype installations. For the latter alternative, we want to show a methodology in this paper, how to obtain meaningful communication data samples and how to analyze this data thoroughly in order to derive the important measurement of durations of controller startup phases. We use commonly applied data logging and evaluation tools from CONDALO™ and Vector™ and we present results for networked applications in current upper class series vehicles from the German car manufacturer Audi. The outcomes allow for a sophisticated analysis of CAN communication at an early stage of prototype hardware installations.

Trade-off between coverage and robustness of automotive environment sensor systems

Car manufacturers, research institutions and governments are challenged by decreasing the number of road traffic fatalities in spite of rapidly increasing traffic volumes. One approach is to enhance the ldquointelligencerdquo of modern cars in anticipating dangerous driving situations. Besides wireless communications with the traffic environment, context perception enabled by well-known technologies such as radar, laser or video is regarded as a promising instrument in driver assistance and collision avoidance. There is a rich variety of both hardware configurations of automotive environment sensor systems and strategies for sensor data fusion and processing. For sensor systems assembled of multiple devices, the trade-off between increased spatial coverage, robustness against interfering factors and accuracy of measured data is a crucial aspect of system design. We investigate up-to-date automotive sensor systems with respect to detection performance and detection quality. We built UML-based discrete-event simulation models to resemble sensors, context perception, signal processing and data fusion in realistic road traffic scenarios. Our results allow for a sound comparison on sensor systems and data acquisition strategies at an early stage of system development.

Efficiency and Dependability of Direct Mobile-to-Mobile Data Transfer for UMTS Downlink in Multi-Service Networks

This paper is a sequel of previous work, in which we proposed a concept based on direct mobile-to-mobile (m2m) data exchange on uplink channels for distribution of large popular content in dynamic wireless environment. We showed the feasibility and performance benefit of m2m file sharing applications in terms of thereby released overall downlink capacity in UTRA-FDD systems, where multiple m2m user groups coexist in the network. A pure m2m traffic scenario was investigated and the wireless interference only among the neighboring groups was taken into account. The present paper extends the basic model by introducing a hybrid case of traffic. We consider an UMTS system scenario with coexisting conventional UMTS users and m2m file sharing participants and analyze the cross-traffic impact in order to find out the degree of m2m data transfer performance degradation due to increased uplink interference. The results indicate a slight performance degradation of m2m file sharing applications, in terms of relative losses of m2m link quality (number of corrupted data) caused by additional interference from cross-traffic. Nevertheless, no dramatic decrease in service probability and overall throughput for m2m applications in an UMTS network was observed. Furthermore, results show that by a well-designed m2m routing policy the ability to interconnect wireless devices on the partly unused uplink carrier frequencies (due to typical asymmetric uplink/downlink traffic load) might be a profitable goal and offers a promising alternative for distribution of popular content.