”On Communication Requirements for Control-by-Wire Applications”

Abstract

Many control-by-wire applications are inherently safety critical. For distributed control systems, the communication subsystem as the backbone is a critical component. Thus it is vital that dependability requirements gathered from the application are well considered in the design of the communication component. However, dependability is costly and thus, it is important to carefully assess these requirements. With essential requirements from distributed control-by-wire applications in mind, we discuss the central role of the communication subsystem for system safety with focus on dependability and economy issues.

Applications of particular interest today are fly-, steer-, and brake-by-wire. From these applications we identify differences and similarities in e.g. fault-tolerance, intrinsic redundancy and production volume. Requirements on fault-tolerance states how faults should be tolerated before system failure. We acknowledge case specific redundancy, and exploit how it can be utilized to accomplish sufficiently high level of system safety. Production volume influence distribution between development and recurrent costs.

A common set of requirements for the communication sub-system have been established. We identify a set of features and properties that are the core requirements. This can serve as a foundation for any fault tolerant control-by-wire protocol definition. Finally, we compare this hypothetical protocol with four existing protocols intended for control-by-wire applications; FlexRay, SAFEbus, TTCAN, and TTP/C.

Keywords: Keywords: communication protocol, safety critical, system analysis