This paper proposes weak TDMA (WTDMA) as a new method for slotted medium access on the controller area network (CAN). Different from TDMA, WTDMA does not require guard times for the temporal isolation of different time slots. Instead, a certain degree of overlap of time slots can be tolerated due to the usage of Carrier Sense Multiple Access/Collision Resolution (CSMA/CR) and the non-preemptive message transmission on CAN. WTDMA can be realized in software with a moderate accuracy of the synchronized clocks of different CAN nodes and without any modifications to the CAN standard. The paper provides sufficient conditions for the correct operation of WTDMA and performs a comprehensive experimental evaluation. We show that bus loads above 90% can be achieved, whereby the message latencies are mostly determined by the message transmission times in the order of hundreds of microseconds. In addition, WTDMA is robust to disturbances such as bit errors. These properties are vital for contemporary mission-critical real-time vehicle applications.

Accurate timestamps are important for clock synchronization (CS) and cyber-security on the controller area network (CAN). This article proposes a new predictable timestamping (TS) method on CAN. Different from existing TS methods, our method reduces the effect of uncertainties that are caused by the CAN bit timing, oscillator drifts, and different cable lengths. Accordingly, our TS method provides an improved TS quality, which is confirmed in comprehensive hardware experiments. We further show the positive impact of our TS method on CS for CAN with clock accuracies below 100 ns.

The heterogeneity of vehicles is an important factor when realizing cooperative adaptive cruise control (CACC) in practice. Specifically, it has to be considered that platoons generally consist of vehicles with both different dynamic properties and actuator limits on the engine and braking force, which is expected to have a negative impact on important properties such as string stability. Accordingly, the subject of this paper is the preservation of string stability for CACC in heterogeneous vehicle strings with potential actuator saturation. To this end, the paper formulates a velocity-dependent force bound that enables the derivation of sufficient conditions for preserving string stability during velocity changes of heterogeneous platoons. These conditions are then used for the analytical computation of trajectories for time-optimal velocity changes. The formal results of the paper are supported by an illustrative simulation study.

Modern vehicles, that have to be considered as safety-critical cyber-physical systems, require highly accurateclock synchronization(CS) among their distributed computing devices. Since Controller Area Network (CAN) is the predominant in-vehicle communication bus, it is highly relevant to support CS for CAN. This article proposes an original CS method for distributed in-vehicle networks based on CAN with bothoffsetanddrift correction. While offset correction is performed based on timestamps in periodic reference messages (RMs), our new method benefits from the re-synchronization mechanism of the CAN bit timing to apply highly accurate drift correction. Our algorithm does not make any modifications to the CAN protocol but requires the measurement of the phase error from the CAN controller. We derive analytical bounds for the expected clock differences and further validate the practicability of the proposed method by comprehensive experiments. As the main result, our method achieves a clock accuracy below$2\;\mu$s independent of important parameters such as the bit rate, RM period, bus utilization and time-varying clock drifts.

Synchronizing clocks is crucial for distributed safety-critical in-vehicle applications. Since Controller Area Network (CAN) is the predominant in-vehicle communication bus, it is highly relevant to realize clock synchronization (CS) on CAN. This paper proposes a new software-based CS (SW-CS) algorithm based on the periodic transmission of reference messages (RMs) by a Master node and discrete-time feedback control. Different from existing algorithms, that only update clocks after receiving a RM, our algorithm corrects the clock drift between RMs. Measurements on a hardware setup show a decrease of the clock differences by more than one order of magnitude.

Multifunction Vehicle Bus (MVB) is a highly robust real-time field bus for rail vehicles. On MVB, periodic process data and sporadic message data are transmitted in the form of telegrams. The main focus of this paper is the development of heuristic scheduling algorithms for periodic telegrams on MVB. We first propose two heuristics that find the best location of individual telegrams in the MVB schedule based on different criteria. Then, we introduce a new swap operation that allows improving MVB schedules by exchanging the locations of telegrams. A comprehensive evaluation based on a large number of test cases shows that the proposed heuristics are able to find feasible and close-to-optimal MVB schedules with practical computation times. In particular, our heuristics clearly outperform an existing ILP formulation, that cannot find optimal or even feasible schedules in cases with large telegram sets.

Safety-critical in-vehicle applications require an accurate global time in order to coordinate their actions. Although Controller Area Network (CAN) is the most widely used in-vehicle communication bus, it does not support synchronized clocks. Hence, the realization of clock synchronization on CAN is highly relevant. This paper develops two new ideas for the clock synchronization on CAN. The first contribution is a new software-based algorithm based on periodic reference messages. Different from existing algorithms, the proposed algorithm enables the use of timestamps that are taken close to the reference message transmission hence improves the clock accuracy. The second contribution of the paper is an original method for correcting clocks between reference messages. In particular, the proposed algorithm updates local clocks based on the bit timing on the CAN bus. Results from simulation experiments show an improvement of about 60% in the clock precision.

In this paper we propose ACCLOUD-MAN, a novel resource manager for heterogeneous cloud data centers. In heterogeneous clouds a user request can be satisfied with more than one physical resource alternative. That is, the resource manager must decide which resource alternative will be chosen, along with the decision of the server the request will be assigned to. ACCLOUD-MAN's resource management objective is to reduce the power consumption of the cloud data center. To this end, the manager is modeled as an integer linear programming problem and is implemented in MATLAB, along with a cloud data center simulation platform. Simulation results show that the proposed ACCLOUD-MAN outperforms existing resource allocation methods such as Openstack.

String stability is an essential property to ensure that the fluctuations are attenuated along vehicle strings. This paper focuses on the fulfillment of string stability in the practical case of heterogeneous vehicle strings that comprise vehicles with different dynamic properties. Using the idea of predecessor following, acceleration feedforward, predicted acceleration feedforward, and input signal feedforward are considered as different possible feedforward strategies. For all strategies, the parameter ranges of predecessor vehicles that ensure string stability of a given vehicle are characterized, computed, and validated by simulation.

The usage of the controller area network (CAN) as an in-vehicle communication bus requires finding feasible and robust priority orders such that each message transmitted on the bus meets its specified deadline and tolerates potential transmission errors. Although such priority orders can be determined by available algorithms whenever they exist, it is always assumed that a CAN priority order is computed from scratch. In practical applications, it is frequently necessary to extend an existing message set by new messages. In this case, a feasible priority order that retains the standardized IDs of the existing messages and assigns suitable priorities to the new messages needs to be found. This paper proposes an algorithm for the computation of robust priority orders that solves the stated problem of extending existing message sets. First, bounds for the priorities of new messages are determined and then the most robust priority order that keeps the IDs of the existing messages is computed. The obtained algorithms are proved to yield correct results and are illustrated by detailed scheduling examples.

In this paper, we study the diagnosability verification for modular discrete-event systems (DESs), i.e., DESs that are composed of multiple components. We focus on a particular modular architecture, where each fault in the system must be uniquely identified by the modular component where it occurs and solely based on event observations of that component. Hence, all diagnostic computations for faults to be detected in this architecture can be performed locally on the respective modular component, and the obtained diagnosis information is only relevant for that component. We define the condition of modular language diagnosability with local specifications (MDLS) in order to capture that each fault can indeed be detected in this modular architecture. Then, we show that MDLS can be formulated as a specific language-diagnosability problem. As the main contribution of this paper, we develop an incremental abstraction-based approach for the verification of MDLS, which is based on projections that fulfill the loop-preserving observer condition. In particular, our approach efficiently avoids the construction of a global system model, which is infeasible for systems of realistic size. Furthermore, we do not rely on the assumption of a live global plant, which is prevalent in previous diagnosability methods for modular DESs. We illustrate our approach and its computational savings by a manufacturing system example.

Fuzzy discrete event systems (FDESs) have been introduced in recent years to model systems whose discrete states or discrete state transitions can be uncertain and are, hence, determined by a possibility degree. This paper develops an FDES framework for the control of sampled data systems that have to fulfill multiple objectives. The choice of a fuzzy system representation is justified by the assumption of a controller realization that depends on various potentially imprecise sensor measurements. The proposed framework consists of three basic steps that are performed at each sampling instant. First, the current fuzzy state of the system is determined by a sensor evaluation. Second, the fuzzy state in the future sampling instant is predicted for all possible control actions of the system. Finally, an original multiobjective weighting strategy is proposed to determine the control action to be applied in the current sampling instant. The features of the proposed approach are demonstrated by a detailed mobile robot example, which includes a simulation study.

The automation of today's large-scale industrial systems relies on the operation of distributed controller devices that perform local computations and exchange information via communication networks. The subject of this paper is the development of a family of shared-medium industrial communication protocols that support the transmission of real-time (RT) and nonreal-time (nRT) data among distributed controller devices. Different from existing protocols, we suggest to incorporate information that is available from the control application in the protocol definition. As a result, our protocols dynamically change the bandwidth allocation on the shared medium according to the instantaneous communication requirements while ensuring hard RT guarantees. Following the recent developments in industrial automation, our protocols can be realized as software layers on top of low-cost conventional Ethernet.

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.

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.

This paper investigates how to generate cyclic gaits for multi-bodied isolated mechanical systems whose configuration space is represented by a trivial fiber bundle. We describe how to generate gaits in the base space of the fiber bundle, or the shape space of the robot on which we assume full control. Such gaits are guaranteed to generate a non-zero motion along the fiber space, i.e., a net change in the position of the robot, while making sure that the robot’s shape is unchanged after a complete cycle. The gait generation technique presented in this paper is intuitive; it involves dividing the base space into well defined regions and devising a set of simple rules on how to generate curves in such regions. Not only do such curves guarantee non-zero position change but also do allow for gait optimization.