Delay and jitter attacks on hierarchical state estimation

State estimation is critical to ensure the stability of many non-trivial control systems where full observability cannot be maintained, and is particularly important in electrical power networks relying on wide-area measurement systems. In recent years, the problem of malicious bad data injection has been studied extensively, with a number of innovative mitigation and protection measures being proposed. Hierarchical and distributed state estimation systems require not only correct measurements and means for detecting and mitigating any faults or attacks, but also timely transmission of measurements and intermediate results. We argue that the latter has thus far not been considered adequately, and that communication channels cannot be considered to be instantaneous and reliable, nor solely be captured by stochastic models. In this paper we describe a communication channel model for hierarchical state estimators relying on the common WLS formulation and analyse the propagation of faults leading up to convergence failures in both intermediate and top-level state estimates as a consequence of interference with the communication channel. To this end we concentrate on denial of service-type attacks, limited to suppression of communication or channel manipulation resulting in delays or jitter as such attacks are feasible even where channel integrity and confidentiality are protected adequately. Analytical results showing substantial effects are supported by simulation results also reported.