Performability of Integrated Networked Control Systems

A direct sensor to actuator communication model (S2A) for unmodified Ethernet-based Networked Control Systems (NCSs) is presented in this research. A comparison is made between the S2A model and a previously introduced model including an in-loop controller node. OMNET simulations showed the success of the S2A model in meeting system delay with strict zero packet loss (with no over-delayed packets) requirements. The S2A model also showed a reduction in the end-to-end delay of control packets from sensor nodes to actuator nodes in both Fast and Gigabit switched Ethernet-Based. Another major improvement for the S2A model is accommodating the increase in the amount of additional load compared to the in-loop model. Two different controller-level fault-tolerant models for Ethernet-based Networked Control Systems (NCSs) are also presented in this research. These models are studied using unmodified Fast and Gigabit Ethernet. The first is an in-loop fault-tolerant controller model while the second is a fault-tolerant direct Sensor to Actuator (S2A) model. Both models were shown via OMNeT++ simulations to succeed in meeting system end-to-end delay with strict zero packet loss (with no over-delayed packets) requirements. Although, it was shown that the S2A model has a lower end-to-end delay than the in-loop controller model, the fault-tolerant in-loop model performs better than the fault-tolerant S2A model in terms of less total end-to-end delay in the fault-free situation. While, on the other hand, in the scenario with the failed controller(s), the S2A model was shown to have less total end-to-end delay. Performability analysis between the two fault-tolerant models is studied and compared using fast Ethernet links relating controller failure with reward, depending on the system state. Meeting control system\u27s deadline is essential in Networked Control Systems and failing to meet this deadline represents a failure of the system. Therefore, the reward is considered to be how far is the total end-to-end delay in each state in each model from the system deadline. A case study is presented that simultaneously investigates the failure on the controller level with reward

Hierarchical fault tolerance in wireless networked control systems

Wireless Networked Control Systems (WNCS) have recently emerged as a replacement for wired control networks. Wireless networked control systems are more suitable for environments that require higher flexibility and robustness. In previous literature a wireless manufacturing line was proposed. The work-cells communication was through IEEE 802.11 technologies and a switched Ethernet backbone. This thesis is aiming to improve the current solution by adding a supervisor to the existing system. The supervisor could be either in passive or active mode. Passive supervisor would intervene when all controllers in the network fail, while active supervisor would act once any controller on the line fail. The system was simulated using OPNET software with 95% confidence analysis. The ability of the system to withstand external interference was assessed through adding a single band jammer to the OPNET simulation. The system was able to hold up to 8KB interfering file sent from a single band jammer affecting the full Wi-Fi spectrum. All results were subjected to a 95% confidence analysis The performability of passive and active supervisor systems was compared. A Markov model of both systems was built. It was shown that by time, the performability of a passive supervisor system is enhanced while that of an active supervisor system degraded. However, the active supervisor showed a better performability in all cases

Networked control systems for intelligent transportation systems and industrial automation

This thesis presents a study of two different applications of Networked Control Systems. The first is: Ethernet Networked Control System On-board of Train-wagons. An Ethernet backbone is shared between control and entertainment. The wagon contains a dedicated control server and a dedicated entertainment server, which act as fault-tolerant machines for one another. In the event of a server failure, the remaining machine can serve both entertainment and/or control. The study aims at enhancing system design in order to maximize the tolerable entertainment load in the event of a control/entertainment server failure, while not causing any control violations. This fault-tolerant system is mathematically analyzed using a performability model to relate failure rates, enhancements and rewards. The model is taken further to test two identical wagons, with a total of four fault-tolerant servers. All possible failure sequences are simulated and a different communication philosophy is tested to further minimize the degradation of the entertainment load supported during the failure of up to three of the four servers. The system is shown to be capable of operating with minimal degradation with one out of four servers. The second is: Wireless Networked Control Systems (WNCS) for Industrial Automation. A WNCS using standard 802.11 and 802.3 protocols for communication is presented. Wireless Interface for Sensors and Actuators (WISA) by ABB is used as a benchmark for comparison. The basic unit is a single workcell, however, there is a need to cascade several cells along a production line. Simulations are conducted and a nontraditional allocation scheme is used to ensure correct operation under the effect of co-channel interference and network congestion. Next, fault-tolerance at the controller level is investigated due to the importance of minimizing downtime resulting from controller failure. Two different techniques of interconnecting neighboring cells are investigated. The study models both a two and three-cell scenario, and all systems show that fault-tolerance is achievable. This is mathematically studied using a performability analysis to relate failure rates with rewards at each failure state. All simulations are conducted on OPNET Network Modeler and results are subjected to a 95% confidence analysis

Experimental evaluation of the service time for industrial hybrid (wired/wireless) networks under non-ideal environmental conditions

none3nononeSeno, Lucia*; Vitturi, Stefano; Tramarin, FedericoSeno, Lucia; Vitturi, Stefano; Tramarin, Federic

Integrating wireless technologies into intra-vehicular communication

With the emergence of connected and autonomous vehicles, sensors are increasingly deployed within car. Traffic generated by these sensors congest traditional intra-vehicular networks, such as CAN buses. Furthermore, the large amount of wires needed to connect sensors makes it hard to design cars in a modular way. These limitations have created impetus to use wireless technologies to support intra-vehicular communication. In this dissertation, we tackle the challenge of designing and evaluating data collection protocols for intra-car networks that can operate reliably and efficiently under dynamic channel conditions. First, we evaluate the feasibility of deploying an intra-car wireless network based on the Backpressure Collection Protocol (BCP), which is theoretically proven to be throughput-optimal. We uncover a surprising behavior in which, under certain dynamic channel conditions, the average packet delay of BCP decreases with the traffic load. We propose and analyze a queueing-theoretic model to shed light into the observed phenomenon. As a solution, we propose a new protocol, called replication-based LIFO-backpressure (RBL). Analytical and simulation results indicate that RBL dramatically reduces the delay of BCP at low load, while maintaining its high throughput performance. Next, we propose and implement a hybrid wired/wireless architecture, in which each node is connected to either a wired interface or a wireless interface or both. We propose a new protocol, called Hybrid-Backpressure Collection Protocol (Hybrid-BCP), for the intra-car hybrid networks. Our testbed implementation, based on CAN and ZigBee transceivers, demonstrates the load balancing and routing functionalities of Hybrid-BCP and its resilience to DoS attacks. We further provide simulation results, obtained based on real intra-car RSSI traces, showing that Hybrid-BCP can achieve the same performance as a tree-based protocol while reducing the radio transmission power by a factor of 10. Finally, we present TeaCP, a prototype Toolkit for the evaluation and analysis of Collection Protocols in both simulation and experimental environments. TeaCP evaluates a wide range of standard performance metrics, such as reliability, throughput, and latency. TeaCP further allows visualization of routes and network topology evolution. Through simulation of an intra-car WSN and real lab experiments, we demonstrate the functionality of TeaCP for comparing different collection protocols