Visible to the public Biblio

Filters: Author is Chuchu Fan, University of Illinois at Urbana-Champaign  [Clear All Filters]
2016-12-14
Zhenqi Huang, University of Illinois at Urbana-Champaign, Chuchu Fan, University of Illinois at Urbana-Champaign, Alexandru Mereacre, University of Oxford, Sayan Mitra, University of Illinois at Urbana-Champaign, Marta Kwiatkowska, University of Oxford.  2016.  Automatic Safety Verification of Implantable Medical Devices.

Presented at the NSA Science of Security Quarterly Meeting, July 2016.

2016-07-13
Zhenqi Huang, University of Illinois at Urbana-Champaign, Chuchu Fan, University of Illinois at Urbana-Champaign, Sayan Mitra, University of Illinois at Urbana-Champaign.  2016.  Bounced Invariant Verification for Time-delayed Nonlinear Networked Dynamical Systems. Journal of the IFAC, International Federation of Automatic Control, Nonlinear Analysis: Hybrid Systems.

We present a technique for bounded invariant verification of nonlinear networked dynamical systems with delayed interconnections. The underlying problem in precise boundedtime verification lies with computing bounds on the sensitivity of trajectories (or solutions) to changes in initial states and inputs of the system. For large networks, computing this sensitivity
with precision guarantees is challenging. We introduce the notion of input-to-state (IS) discrepancy of each module or subsystem in a larger nonlinear networked dynamical system. The IS discrepancy bounds the distance between two solutions or trajectories of a module in terms of their initial states and their inputs. Given the IS discrepancy functions of the modules, we show that it is possible to effectively construct a reduced (low dimensional) time-delayed dynamical system, such that the trajectory of this reduced model precisely bounds the distance between the trajectories of the complete network with changed initial states. Using the above results we develop a sound and relatively complete algorithm for bounded invariant verification of networked dynamical systems consisting of nonlinear modules interacting through possibly delayed signals. Finally, we introduce a local version of IS discrepancy and show that it is possible to compute them using only the Lipschitz constant and the Jacobian of the dynamic function of the modules.
 

2015-11-17
Zhenqi Huang, University of Illinois at Urbana-Champaign, Chuchu Fan, University of Illinois at Urbana-Champaign, Alexandru Mereacre, University of Oxford, Sayan Mitra, University of Illinois at Urbana-Champaign, Marta Kwiatkowska, University of Oxford.  2015.  Simulation-based Verification of Cardiac Pacemakers with Guaranteed Coverage. Special Issue of IEEE Design and Test. 32(5)

Design and testing of pacemaker is challenging because of the need to capture the interaction between the physical processes (e.g. voltage signal in cardiac tissue) and the embedded software (e.g. a pacemaker). At the same time, there is a growing need for design and certification methodologies that can provide quality assurance for the embedded software. We describe recent progress in simulation-based techniques that are capable of ensuring guaranteed coverage. Our methods employ discrep- ancy functions, which impose bounds on system dynamics, and proceed through iteratively constructing over-approximations of the reachable set of states. We are able to prove time bounded safety or produce counterexamples. We illustrate the techniques by analyzing a family of pacemaker designs against time duration requirements and synthesize safe parameter ranges. We conclude by outlining the potential uses of this technology to improve the safety of medical device designs.