System-level reliability analysis considering imperfect fault coverage

Safety-critical systems rely on redundancy schemes such as k-out-of-n structures which enable tolerance against multiple faults. These techniques are subject to Imperfect Fault Coverage (IFC) as error detection and recovery might be prone to errors or even impossible for certain fault models. As a result, these techniques may act as single points of failure in the system where uncovered faults might be overlooked and lead to wrong system outputs. Neglecting IFC in reliability analysis may lead to fatal overestimations in case of safety-critical applications. Yet, existing techniques that do consider IFC are overly pessimistic in assuming that the occurrence of an uncovered fault always results in a system failure. But often, in particular in complex systems with nested redundant structures, a fault that is not noticed by an inner redundancy scheme might be caught by an outer redundancy scheme. This paper proposes to automatically incorporate IFC into reliability models, i. e. Binary Decision Diagrams (BDDs), to enable an accurate reliability analysis for complex system structures including nested redundancies and repeated components. It also shows that IFC does not equally affect different redundancy schemes. Experimental results presented for applications in multimedia and automotive confirm that the proposed approach can analyze system reliability more accurately at an acceptable execution time and memory overhead compared to the underlying IFC-unaware technique.