State-Estimation for Delay-Management in Distributed Real-Time Co-Simulation via the Internet

Typical distributed embedded real-time systems are composed of several subsystems developed by different, geographically distributed manufacturers. During the development process, these subsystems have to be integrated via real-time communication networks and tested. The verification can be simplified combining co-simulation and Software- and Hardware-In-The-Loop (SIL/HIL) testing in a distributed co-simulation framework. In such a framework, software (SIL) and hardware (HIL) components can be tested against the model of a simulated plant. This way it is possible to detect design faults and integration problems while the subsystems are still located at their manufacturers' sites.Real-time systems impose strict temporal and reliability requirements on the communication network connecting the subsystems. However, these requirements cannot be achieved using the Internet for communication in the distributed co-simulation framework. In this paper we introduce state-estimation as a delay-management technique to provide required subsystem inputs in time. Based on previous outputs and a simulation model of the remaining system, the mechanism estimates a subsystem's future inputs. Using scheduling information about the real-time communication in the system, the framework can determine if an input packet is received in time. If not, the estimated packet is forwarded. As soon as the real input packet is received later, its content is compared with the estimated input and the operator is notified if the error between estimated and real input exceeds a configurable threshold.