Improved clock synchronization start-up time for Ethernet AVB-based in-vehicle networks

Clock synchronization is a necessary feature in in-vehicle time- and safety-critical networks. The reason is that exact timing information has to be maintained in nodes, for instance for time stamps of messages that are important for safety-critical functions. A common time base has to be established at start-up time before time-sensitive data handling can begin. In vehicular applications, this clock initialization phase is only one part of tasks that have to be finished before the vehicle is fully functional. To avoid lengthy delays after vehicle ignition, this start-up phase has to be very short depending on the requirements of functions. Advanced driver assistance systems require high-bandwidth communication such as Ethernet Audio Video Bridging (AVB). Its corresponding IEEE 802.1 AS time synchronization protocol is, however, not able to guarantee fast synchronization start-up in conformance with automotive applications. This paper thus proposes and analyzes several variants of the time synchronization protocol to achieve a shorter start-up time. Simulation-based performance analysis shows that start-up times can be reduced by a factor of 40 compared to the standard IEEE 802.1 AS with the proposal, without considerably affecting synchronization error.