An Introduction to Probability Theory and its Applications, Volume I

The use of networks for communications between the electronic control units (ECU) of a vehicle in production cars dates from the beginning of the 1990s. The specific requirements of the different car domains have led to the development of a large number of automotive networks such as Local Interconnect Network, J1850, CAN, TTP/C, FlexRay, media-oriented system transport, IDB1394, etc. This paper first introduces the context of in-vehicle embedded systems and, in particular, the requirements imposed on the communication systems. Then, a comprehensive review of the most widely used automotive networks, as well as the emerging ones, is given. Next, the current efforts of the automotive industry on middleware technologies, which may be of great help in mastering the heterogeneity, are reviewed. Finally, we highlight future trends in the development of automotive communication systems.

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Trends in Automotive Communication Systems

An Introduction to Probability Theory and Its Applications. Volume II By William Feller. Pp. xviii, 626. 90s. 1966. (Wiley)

Wireless networked control systems (WNCS) are composed of spatially distributed sensors, actuators, and con- trollers communicating through wireless networks instead of conventional point-to-point wired connections. Due to their main benefits in the reduction of deployment and maintenance costs, large flexibility and possible enhancement of safety, WNCS are becoming a fundamental infrastructure technology for critical control systems in automotive electrical systems, avionics control systems, building management systems, and industrial automation systems. The main challenge in WNCS is to jointly design the communication and control systems considering their tight interaction to improve the control performance and the network lifetime. In this survey, we make an exhaustive review of the literature on wireless network design and optimization for WNCS. First, we discuss what we call the critical interactive variables including sampling period, message delay, message dropout, and network energy consumption. The mutual effects of these communication and control variables motivate their joint tuning. We discuss the effect of controllable wireless network parameters at all layers of the communication protocols on the probability distribution of these interactive variables. We also review the current wireless network standardization for WNCS and their corresponding methodology for adapting the network parameters. Moreover, we discuss the analysis and design of control systems taking into account the effect of the interactive variables on the control system performance. Finally, we present the state-of-the-art wireless network design and optimization for WNCS, while highlighting the tradeoff between the achievable performance and complexity of various approaches. We conclude the survey by highlighting major research issues and identifying future research directions.

Wireless Network Design for Control Systems: A Survey

We investigate the optimal estimation problem in lossy networked control systems where the control packets are randomly dropped without acknowledgment to the estimator. Most existing results for this setup are concerned with the design of controller, while the optimal estimation and its performance evaluation have been rarely treated. In this paper, we show that, unlike many other cases such as intermittent observations or TCP-like systems, the system state follows a Gaussian mixture distribution with exponentially increasing terms, which leads to a Gaussian sum filter-based optimal estimation. We develop an auxiliary estimator method to establish necessary and sufficient conditions for the stability of the mean estimation error covariance matrices. It is revealed that the stability is independent of the packet loss rate, and is not affected by the lack of acknowledgment. A suboptimal filtering algorithm with improved computational efficiency is then developed. Numerical examples and simulations are employed to illustrate the theoretical results.

Optimal Estimation in UDP-Like Networked Control Systems With Intermittent Inputs: Stability Analysis and Suboptimal Filter Design

http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac11-proceedings/data/html/papers/1098.pdf

Analysis of Networked Event-Based Control with a Shared Communication Medium: Part I – Pure ALOHA

Within this paper, we consider the feedback control of an unstable system, which runs in open loop from time to time due to failures like packet losses in a Networked Control System. Up to now, this problem is most often analyzed with a probabilistic description of the failure process. This approach allows to guarantee stability in the mean square sense, i.e., the convergence of the first and second moment of the state, but not in the classical sense of Lyapunov. Moreover, even when the closed loop is stable in the mean square sense, there is no guarantee that the state does not exceed an arbitrarily large bound. In contrast to these works, we use the ideas of weakly hard real-time constraints to describe the failure process in a non-probabilistic and more precise way. In doing so, we derive conditions to guarantee stability of the entire system in the classical sense of Lyapunov despite failures in updating the control input.

Towards Networked Control Systems with guaranteed stability: Using weakly hard real-time constraints to model the loss process

The Controller Area Network (CAN) is a robust, low-cost, and simple event-triggered technology for connecting electronic control units in the manufacturing industry and vehicles. Today's real-time control systems are distributed over a multitude of CAN systems (domains) which are connected via embedded gateways. A failure or overload situation in the gateway can affect several domains. Furthermore, gateways often become bottlenecks between the domains and in the case of CAN buses they can pose further problems with respect to the priority-based network access method. Due to this access method and the limited resources (e.g., buffer capacity) embedded CANCAN gateways have to be dimensioned accurately. Otherwise, unacceptable processing delay and message loss within the gateway can occur. The main contribution of this paper is to investigate the optimized dimensioning of an embedded CAN-CAN gateway with regard to minimizing gateway resources in terms of processing and buffer capacity and decreasing message loss at the same time. For that purpose a CAN bus and a gateway model are described and used to investigate scenarios with two domains connected via a gateway.

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Optimized Resource Dimensioning in an embedded CAN-CAN Gateway

When analyzing networked control systems, where the control loop is closed over a communication system, it is crucial to take the communication system into account. Hence, time-triggered and event-based control of an integrator system with noise over a shared communication system is analyzed. Thereby, analytical models of different communication systems are used and the analysis is focused on the effect of the communication system on the performance, as well as the interaction between control and communication. For time-triggered control, where the event times are known in advance, a deterministic communication protocol can be used. Hence, time-triggered control with the two most well-known deterministic communication protocols, time division multiple access (TDMA) and frequency division multiple access (FDMA), is analyzed. For event-based control, where the events appear at random times, a contention-based communication protocol should be used. Hence, event-based control is analyzed with different contention-based communication protocols: pure ALOHA, slotted ALOHA, a queueing system, and Erlang’s loss model. It turns out that time-triggered control with either TDMA or FDMA outperforms event-based control with pure or slotted ALOHA. However, event-based control with a properly designed queueing system gives an even better performance. Thus, we conclude that it is crucial to take the details of the communication system into account.

Rainer Blind

Papers

Analysis of Networked Event-Based Control with a Shared Communication Medium: Part I – Pure ALOHA

Towards Networked Control Systems with guaranteed stability: Using weakly hard real-time constraints to model the loss process

Optimized Resource Dimensioning in an embedded CAN-CAN Gateway

On time-triggered and event-based control of integrator systems over a shared communication system

Optimal and optimal-linear control over lossy, distributed networks