Performance Analysis of Fault Tolerant TTCAN System

Continuous demand for fuel efficiency mandate “Drive-by-Wire” systems. The goal of Drive-by-Wire is to replace nearly every automotive hydraulic/mechanical system with electronics. Drive-by-Wire and active collision avoidance systems need fault tolerant networks with time triggered protocols, to guarantee deterministic latencies. CAN is an event triggered protocol which has features like high bandwidth, error detection, fault confinement and collision avoidance based on message priority. However, CAN do not ensure message latency, which is critical for real time application. TTCAN (Time Triggered CAN) removes this fallacy of CAN by providing exclusive time windows for those messages that need deterministic latencies. In addition to the exclusive windows, there are arbitration windows too, which make way for event triggered communications. In TTCAN, if an error occurs within an exclusive or arbitration window, retransmission of the message is not allowed. If the message that encountered the error is a safety critical message, then the transmission error can compromise the safety of the vehicles. In this paper, we propose a fault tolerant TTCAN system that uses a secondary bus to tolerate faults on the primary bus. To keep the cost down, we can use the same secondary bus to connect various partitions in the in-vehicle network. Each partition of the network takes care of a particular type of functionality of the vehicle. Thus the same secondary bus can tolerate faults on the primary busses of various partitions. The paper will show analysis done on a realistic TTCAN system. Our results show that even using a low bandwidth secondary bus, the performance of a Drive-by-Wire system can be significantly improved under various types of transmission errors on the primary busses.