Klaus Schmidt

Optimal Message Scheduling for the Static Segment of FlexRay

In this paper, we study the scheduling of periodic messages in the static segment of the FlexRay protocol. Our approach is based on two performance metrics. Similar to previous work, we seek to allocate a minimum number of frame IDs (FIDs) in the static segment. In addition, different from existing work, we want to minimize the message jitter, i.e., the deviation of the message transmission from the required periodicity. To this end, we first derive analytical expressions that quantify the FID allocation and the jitter, and then formulate a linear integer programming problem whose solution is the desired message schedule. An example illustrates our schedule optimization.

Schedulability Analysis and Message Schedule Computation for the Dynamic Segment of FlexRay

In this paper, we perform the schedulability analysis and schedule computation for sporadic real-time messages in the dynamic segment of the FlexRay protocol. We first formulate a linear integer programming problem that allows to determine if a given message schedule is feasible, i.e., the worst-case delay of each message is smaller than its deadline. Then, we develop a heuristic algorithm that enables the efficient computation of feasible schedules. Our results are illustrated by an experimental setup with three FlexRay nodes.

Performance evaluation of FlexRay/CAN networks interconnected by a gateway

The coexistence of both CAN and FlexRay networks in contemporary and future automobiles necessitates the use of FlexRay/CAN gateways that support the timely data exchange among the different networks. In this paper, we report on the implementation of such FlexRay/CAN gateway. Moreover, for the first time, we investigate appropriate network and gateway configurations that are beneficial for the overall network performance in the sense of small delays of gateway messages.

Brief paper: Abstraction-based verification of codiagnosability for discrete event systems

In this paper, we investigate the verification of codiagnosability for discrete event systems (DES). That is, it is desired to ascertain if the occurrence of system faults can be detected based on the information of multiple local sites that partially observe the overall DES. As an improvement of existing codiagnosability tests that resort to the original DES with a potentially computationally infeasible state space, we propose a method that employs an abstracted system model on a smaller state space for the codiagnosability verification. Furthermore, we show that this abstraction can be computed without explicitly evaluating the state space of the original model in the practical case where the DES is composed of multiple subsystems.

Abstraction-Based Control for Not Necessarily Closed Behaviours

Abstract This paper addresses abstraction-based supervisory control for plant and specification behaviours that are not necessarily ω-closed, i.e. plant behaviours that exhibit eventuality properties and specifications that impose eventuality properties on the closed loop. Technically, the core idea is to combine results from previous work on abstraction-based supervision of input-output behaviours with results on supervisory control of ω-languages. As our main result, we identify a controllability condition for the plant, that ensures a nonblocking closed-loop behaviour with a controller that has been obtained for a plant abstraction.

A longest-path problem for evaluating the worst-case packet delay of switched ethernet

In the recent years, the use of real-time Ethernet protocols becomes more and more relevant for time-critical networked industrial applications. In this context, this paper presents a method to compute the worst-case packet delays on switched Ethernet. Based on an evaluation of the packet delays at each switch port and the network topology, we construct a weighted directed graph that allows to find the worst-case end-to-end packet delay by solving a conventional longest-path problem.

Multi-objective decision making using fuzzy discrete event systems: A mobile robot example

In this paper, we propose an approach for the multi-objective control of sampled data systems that can be modeled as fuzzy discrete event systems (FDES). In our work, the choice of a “fuzzy” system representation is justified by the assumption of a controller realization that depends on various potentially imprecise sensor measurements. Our approach consists of three basic steps that are performed in each sampling instant. First, the current fuzzy state of the system is determined by a sensor evaluation. Second, the future fuzzy state is predicted for the possible control actions, and finally, a particular multi-objective weighting strategy allows to determine the control action to be applied. We demonstrate the features of our method by a mobile robot example.

Applied Supervisory Control for a Flexible Manufacturing System

Abstract This paper presents a case study in the design and implementation of a discrete event system (DES) of real-world complexity. Our DES plant is a flexible manufacturing system (FMS) laboratory model that consists of 29 interacting components and is controlled via 107 digital signals. Regarding controller design, we apply a hierarchical and decentralised synthesis method from earlier work in order to achieve nonblocking and safe closed-loop behaviour. Regarding implementation, we discuss how digital signals translate to discrete events from a practical point of view, including timing issues. The paper demonstrates how both, design and implementation, are supported by the open-source software tool libFAUDES.

An Experimental Study of the FlexRay Dynamic Segment

Abstract It is expected that the time-triggered FlexRay bus will replace the event-triggered Controller Area Network (CAN) for the high-speed in-vehicle communication in future automobiles. To this end, FlexRay provides a static segment for the transmission of periodic messages and a dynamic segment that is suitable for exchanging event-based (sporadic) messages. In this paper, we experimentally evaluate the operation of the FlexRay dynamic segment. In particular, we study how the maximum and average message delays are affected if the length of the dynamic segment , the message payload , the utilization of the dynamic segment and the priority assignment changes. Our experiments are carried out on a FlexRay network with 6 nodes.

Fuzzy Hybrid Systems modeling with application in decision making and control

Hybrid Systems are systems containing both discrete event and continuous variable components. Many recent contributions address crisp situations, where ambiguity or subjectivity in the measured data is absent. In this paper, we propose Fuzzy Hybrid Systems to account for inaccurate measurements and uncertain dynamics. We present a strategy to determine the most appropriate control actions in a sampled data setting. The proposed approach is based on three basic steps that are performed in each sampling period. First, the current discrete fuzzy state of the system is determined by a sensor evaluation. Next, the future discrete fuzzy state is predicted for the possible control actions and the best action, in respect to desired continuous states, is selected. Finally, the decision is cross-evaluated by a limited horizon prediction of the continuous system variables. The proposed method is explained and demonstrated for a variation of the a well-known two-tank scenario.