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Scheduling Algorithms For Time-Triggered Communication Protocols
Author: Jan Dvořák
Modern automotive systems present a number of new technological challenges for developers and researchers in the field of electronic control systems. There appear efforts to replace the originally mechanical, hydraulic, or pneumatic components with electronic systems. Steer-by-wire, break-by-wire, or x-by-wire systems are examples of emerging technologies, where the original mechanical connection is replaced by an electrical or electromechanical connection. However, such an electrical connection puts high demands on the reliability and time-determinism of the entire system, an important part of which is the communication system. Moreover, the requirement to use a shared communication system for the whole system, which leads to cost savings and thus better competitiveness of the final product, is also frequent. The problem becomes even more complicated as the number of assistance systems in cars and, consequently, the units that need to be interconnected is increasing. In addition, the approaching era of vehicles with autopilot features requires high volume demanding communication, such as signals from cameras or lidars, be part of the control loop of the system. Therefore, they have to meet high reliability too. As a result, modern automotive systems require communication systems that are able to transfer large volumes of data reliably and deterministically. Time-triggered communication protocols such as FlexRay or TTEthernet have been designed for this purpose. However, their reliability and efficiency are closely tied to the quality of the schedule that communication follows.
This work deals with the problem of scheduling time-triggered communication on FlexRay and TTEthernet protocols. The first part of the work focuses on the problem of communication scheduling of FlexRay, which provides two communication channels that can be used independently. Since electronic units can be connected to only one channel, the scheduling method aims to determine which channel the unit will be connected to, so that the resulting communication schedule is as efficient as possible. The second part is also focused on creating schedules for FlexRay. Here, however, the issue of scheduling in the development process, where it is necessary to take into account several variants of the product and also backward compatibility with previous products, is studied. An example of such a development process can be found in the automotive industry, where multiple variants of a car are created on a common platform, and they are required to be compatible with each other. The third part of the study is focused on scheduling time-triggered communication in the TTEthernet network. In compliance with the second part of the study, it is required to maintain backward compatibility with its predecessor.
Each part of the study includes an analysis of related works and a formal definition of the problem to be solved. Subsequently, the proposed algorithm that solves the defined problem is described. The algorithm is then verified from the qualitative and quantitative point of view, and the phenomena of given specific problems that are reflected in the resulting schedules are studied in experiments.