Performance Evaluation of Vehicle Network Protocols for X-By-Wire Using Simulation

Automakers have been pushing harder for the development of a safety-critical bus for the past years since there are many advantages of x-by-wire systems including steer-by-wire, brake-by-wire and throttle-by-wire. Such systems allow automakers to eliminate heavy hydraulic actuators and they offer the possibility of creating smarter and more efficient components that can be connected to a network bus. However, automakers and vendors know that a reliable, fault-tolerant bus is needed for such applications. Controller Area Network (CAN) buses, which are commonly used for powertrain and other automotive controls, are not considered reliable enough for drive-by-wire. The problem with CAN is that it is only event-based, so there is always a possibility that a message won't get through. For important applications, time-triggered architectures are needed because as time goes on, a slot for important messages is always assigned. In this paper, the performance evaluations of CAN, TTP and Byteflight are presented to explain which aspects are different and how the system should be designed for these protocols for x-by-wire systems. For evaluations, the simulation models were developed by using a discrete event simulation language, SIMAN. Based on these models numerous experiments were conducted for the comparable factors such as the probability of transmission failure, the average transmission delay and the maximum transmission delay. From the performance evaluation results, we can conclude that TTP exhibits a very stable performance over an extended traffic load while it lacks the flexibility for system changes. In addition, CAN and Byteflight show very good performance under low traffic while the performance deteriorates very fast as traffic exceeds a certain threshold.