Professor Yeng Chai SOH
Xiang Shen

Professor of ISchool of Electrical and Electronic Engineering

Nanyang Technological University, Singapore


Yeng Chai SOH received the B.Eng. degree in electrical and electronic engineering from the University of Canterbury, New Zealand, in 1983, and the Ph.D. degree in control engineering from the University of Newcastle, Australia, in 1987. He joined the Nanyang Technological University, Singapore, in 1987, where he is currently a professor in the School of Electrical and Electronic Engineering. From 1995 to 2005, he was the Head of the Division of Control and Instrumentation, and from 2007 to 2011, he was the Associate Dean (Research) of the College of Engineering. Dr Soh also served as the founding director of NTU’s High Performance Computing Centre, from 2009 to 2015.


Dr Soh has served on several grants and awards committees of the Agency for Science, Technology and Research (A*STAR), the Ministry of Education, and the Economic Development Board of Singapore. He was a member of the Singapore’s Science and Technology Plan 2010 Committee which is tasked to formulate science and technology roadmaps for Singapore’s future R&D funding, and he chaired the Technology Scan Committee on “Intelligent Systems and Sensor Networks”.


Dr Soh’s research interests are in robust control and applications, estimation and filtering, sensor networks and sensor fusion, decentralized optimization, machine learning, and energy efficient systems. He has published more than 300 refereed international journal papers and 190 conference papers in these areas. His research efforts in optical signal processing and waste treatment automation have been recognised with several internal awards and national awards. Dr Soh is a Fellow of the Academy of Engineering Singapore.



Stability and Performance Analysis of Networked Control System under DOS Attack


A Networked Control System (NCS) is a type of control systems that use communication networks to exchange data between sensors, controllers, and actuators and to close control loops. This offers many advantages, such as increased flexibility in control system designs, reduced wiring costs, and better monitoring and diagnostic capabilities. Thus, NCSs have numerous and diverse applications in industrial automation, transportation, energy systems, robotics, environmental monitoring, and medical devices. However, NCSs are also vulnerable to various cyber-attacks, including Denial of Service (DOS) attacks which attempt to disrupt the normal functioning of a network by flooding it with traffic or overloading its resources. In the context of NCS, a DOS attack can disrupt communication between the various components of the system, leading to time-varying delay, loss of data, and even system failure. DoS attacks can be in the form of volumetric attacks, which flood the target network or website with a large volume of traffic, or protocol attacks, which exploit vulnerabilities in network protocols to disrupt communication, or application-layer attacks, which target the application layer of the network or website, such as a specific webpage or service. This keynote will discuss some effective techniques that can maintain the stability and performance of NCS even in the presence of DOS attacks.


To deal with the DOS problem, an important understanding is that a DoS attack can cause the Transmission Control Protocol/Internet Protocol (TCP/IP) three-way handshake to become unresponsive. This can happen when an attacker floods a network with a high volume of traffic, overwhelming the system's resources and causing it to stop responding to legitimate traffic. In this situation, when a client sends an SYN (synchronize) request to the server, it does not receive the expected SYN-ACK (synchronize-acknowledgment) response from the server. As a result, the client repeatedly resends the SYN request, leading to a build-up of half-open connections and eventually exhausting system resources. This can cause network congestion, slow response times, and even complete system failure. We need an effective analysis technique to analyse the control system’s behaviour when under DOS attack. In this regard, the Lyapunov-Krasovskii function offers an effective solution to deal with the delay differential inequality. It incorporates the time-varying delays into the Lyapunov stability analysis to establish stability conditions for systems with time-varying delays, which can then be used to design control strategies to stabilize the system. These stability conditions are typically expressed in terms of linear matrix inequalities, which can be solved using numerical methods.