Scheduling of safety-critical time-constrained traffic with F-shaped messages

Abstract

The rapid improvement of systems that surround us such as automotive vehicles brings new challenges for system designers and manufacturers. New functionalities like advanced driver assistants leverage some responsibilities from the driver to an autonomous system. Being able to provide such functionalities requires a safety certification for the system, namely the reliability of the communication backbone. In complex systems, the safety certification is becoming a hard problem, especially in Event-Triggered environments. On the other hand, Time-Triggered communications are well-known for their determinism, reliability, and ease of certification but lack the flexibility that is required e.g. for message retransmissions. To support safety-critical applications, we improve the reliability of Time-Triggered communications even more. We build schedules that account for retransmissions of lost messages. The schedules are robust and static while encapsulating all the possible alternative execution scenarios arising from the uncertainty of transmission outcomes. However, being too robust can be very costly. Therefore, our schedules compensate retransmissions by a possibility of rejecting the transmission of less critical messages to achieve a trade-off between the safety and efficient usage of resources. To solve this complex problem, we present a novel two-stage decomposition algorithm for the synthesis of static schedules accounting for alternative execution scenarios with non-preemptive messages that are constrained by release times and deadlines. We show that our method attains solutions within 6–7% from a lower bound even for large problem instances.