Clock synchronization compensation of Time-Triggered Ethernet based on least squares algorithm

Abstract

Time-Triggered (TT) communication, which enhances real-time requirement and packets transmission certainty, can satisfy the requirements of Distributed Integrated Modular Avionic (DIMA). Due to clock skew between source end and destination systems, the end to end performance is inaccurate. Therefore, clock synchronization service is crucial for TT messages transmission in Time-Triggered Ethernet (TTEthernet). There are two kinds of clock synchronization services: external synchronization service and internal synchronization service. The main difference between two services is the presence of a standard time basis. As an internal synchronization service standard of TTEthernet, AS6802 is used to calculate the average difference between timestamp values of end systems in TTEthernet. However, the clock compensation policy after calculation has not been discussed. In this paper, the compensated algorithm based on modified least squares (LS) is proposed. The clock skew can be eliminated online by LS method to get clocks perfectly synchronized. First, the basic theories about reasons of clock offset are analyzed and the process of clock synchronization in TTEthernet is researched; second, the drifted rates of clocks are changed incessantly due to temperature variation or aging. On that account, clocks are modeled as accurately as possible; besides, the simulation platform is built, including end systems, switch models, network topology to verify the effectiveness of the compensated algorithm; finally, the method of this paper compares with the traditional compensation policies. Simulation shows algorithm in the paper can obtain better clock synchronization precision than other algorithms.