PhD Oral Exam - Shahram Shahkar, Electrical and Computer Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

The present thesis proposes resilient methodologies against three different classes of security threats that are involved with Cyber-Physical Systems (CPS), presented in Chapters 2 to 4, respectively. The first chapter involves time-delay and Denial of Service (DoS) cyberattacks inflicted on the information tele-communication signals exchanged between subsystems of the CPS. The problem assumes a generic case where the subsystems in a CPS receive anonymous information (information from sources with unknown identities). This is a particularly important assumption in many emerging CPS applications, and the author of this thesis believes that it invalidates a significant fraction of the research work available in the literature as of today, making the second chapter of the thesis a relatively major contribution. The proposed solution involves a set of equivalent interconnected filters to be located at the input channels of all transceivers at every subsystem, in such a way that the output of each filter feeds the input of its neighbouring subsystems, hence, cooperative filters. It will be shown that the cooperative filtering scheme proposed in the thesis will be capable of making the CPS resilient to all random and unknown time-delays that may inflict (any unknown number of) communication channels, as long as the filters make a connected graph. Theoretical results have been validated through simulation of a controversial CPS application known as the Load Frequency Control (LFC) problem in Smart Grids.\\

The second problem of the thesis (discussed in Chapter 3) involves a different class of cyberthreats where False Data Injection (FDI) cyberattacks inflict sensor output of subsystems in a CPS framework. Navigation of autonomous vehicles in GNSS denied environments is known to be a particular type of CPS open problems that belong to this class of cyber-threats, and is the focus of Chapter 3. This problem is known to be among the most challenging problems associated with autonomous control of aerial and ground vehicles, and the thesis proposes a novel cooperative localization filtering scheme that tends to share the \say{perceived} location of all vehicles with their neighbours in order for the vehicle community to cooperate and compensate the estimation error associated with individual vehicles.\\

The third and final problem that is addressed in the 4th chapter of this thesis associates the navigation commands (i.e., waypoint and airspeed commands) transmitted from a Ground Control Stations (GCS) to a vehicle in modern autonomous urban transportation systems, which is an example of an FDI on the actuator channels of systems in a CPS. In this example the vehicles have to authenticate the commands they receive from their GCS and have to decide whether the commands are legitimate commands (and are trustworthy to be obliged by the autopilot) or have to be rejected and replaced by \say{trustworthy} alternatives. The vehicles assume that prior commands are legit and contemplate the physical and dynamic characteristics of their autopilots, as well as traffic and geofencing rules broadcasted from the traffic control center to create a set of constraints and ensure that the commands meet these constraints and make authentication decisions accordingly. The vehicles use onboard filters to process waypoint commands to formulate a real-time authentication function in order to build a \say{trustworthy} map of the airspace, for their future navigation. The theoretical results obtained from Chapters 3 and 4 have been verified using simulated flocks of aerial vehicles.