Competing Failure Analysis in IoT Systems with Cascading Functional Dependence

The Internet of Things (IoT) has developed rapidly and aimed to improve the quality of our modern life. Despite its considerable benefits, the IoT poses many challenges, among which assessing the reliability of an IoT system is critical since it guarantees the success rate of IoT service delivery. Functional dependence (FDEP) complicates the reliability analysis of IoT systems, where the failure of one component (trigger) causes other IoT components (dependent components) to become inaccessible or isolated, leading to competing failure effects in the time domain. Existing studies have assumed non-cascading FDEP. However, in real-world systems with hierarchical structures, cascading FDEP exists where a component can serve as a trigger and a dependent component at the same time, causing correlations among multiple FDEP groups. Based on the divide and conquer principle, this paper suggests a combinatorial solution procedure to assess reliability of IoT systems with cascading FDEP. In addition, random failure propagation time is modeled. A case study on a smart home sensor system is performed to demonstrate the considered system model and the proposed method.