Reliability-related safety analyses for satellite navigationsystems

摘要

Safety and reliability are two interrelated attributes forsafety-critical systems. While the typical safety analysis focuses onpreventing hazards associated with erroneous safety critical outputs,this paper introduces an equally important hazard for the loss ofcritical functionality, referred to as the“loss-of-function” hazard. Tradeoffs are studied among threesafety/reliability measures, i.e., the probability of working correctly,the probability of generating erroneous outputs and the probability oflosing critical functionality. One of the goals for this study is toassist system engineers in making correct and timely design decisions. Amajor problem encountered in computing the probabilities of the varioussafety hazards is the initial condition consideration. This is because afault-tolerant system can have various operational conditions and ahazard can occur under any of the working conditions, each withdifferent probabilities. To provide a reasonable estimation, a measuringmethod that incorporates all possible initial conditions is proposed