Security Control Of Networked Systems Under Denial Of Service Attacks

Under open network environments,networked control system(NCS)are con-fronted with more and more potential threats,which are brought by cyber-space and physical systems.With the increasing improvement of intelligent and diversified attack-s,non-contact-style damages are achieved through the fact that attackers launch their attacks to physical systems from cyber-space.Recent security incidents become in-creasingly prominent and this attracts much attention from government and other com-munities.Meanwhile,some studies have been carried out on this field.In essence,NCSs are a class of complex networked feedback control systems which intergraded with both cyber-space and physical systems deeply.It is significan-t and meaningful,from both theory and application,to study how to secure the NCS from control theory and method when attack is an established fact.At present,secu-rity control of the NCS mainly includes security modelling,state estimation,defense and control strategies for different attack types such as DoS attacks and FDI attacks.Although some excellent results have been achieved on security control,there are still exist some deficiencies,for example,probabilistic assumptions to attacks are unseason-able,security state estimation are imprecise,new security control methods are absent,etc.As a common attack type,security analysis and control of the NCS under DoS attacks are studied in this paper.In fact,there are the following shortcomings on se-curity and control under DoS attacks:(?)Generally,a real attacker will launch their attack without following any specific rules but energy constraints.It is unreasonable to characterize DoS attacks with Bernoulli distribution.(?)There are some limitations on current security design method which compensate packet dropouts only by adjusting sampling rate,however,the controller should be given in advance.Based on the above two facts,the main contributions of this paper include the following aspects:·According to the basic problems of security control on the NCS,a comprehensive survey on attack types,mechanism with its state of art for the NCS is conducted.Further,some shortcomings on security control are presented.·Markov-based packet dropout is proposed to describe the energy constraint of DoS attacks which can overcome the shortcoming that Bernoulli process is difficult to describe this feature.Therefore,Markov jump linear systems are used to char-acterize packet dropouts caused by DoS attacks.By considering the concealing of DoS attacks,stochastic security analysis and controller design are conducted under the cases that probability transition matrix is full-known or partial-known.·The state-security-based resilient event-triggered communication scheme is pro-posed by taking full consideration of the effects caused by DoS attacks.By in-troducing state dependent information(DoS-free case)and state independent in-formation(DoS case)into event-triggered condition,the security resilient event-triggered communication scheme is well designed which includs state dependent and state independent information.Then,the security performance analysis and controller design are carried out to drive the system state into a security region.·A switch-like event-triggered communication based on the fact that the duration of DoS attacks can be converted to maximum allowable transmission interval(MATI)is proposed to characterize DoS attacks.By dividing the DoS attacks into S-interval(DoS-free case)and D-interval(DoS case)for each transmission interval,different event-triggered communication schemes are designed.The se-curity performance is analyzed under the constraint of switch frequency between different triggered conditions.Further,the duration constraint of single and total DoS attacks is characterized and controller design by considering the uncertain of networks is designed.·The security control design of the NCS under DoS attacks is investigated.Event-triggered predicative control(ETPC)strategy is proposed to deal with arbitrary bounded packet dropout under DoS attacks for the NCS.Firstly,arbitrary bounded packet dropout in event-triggered communication scheme is employed to describe the effect of DoS attacks by considering its energy-constraint and arbitrariness.Subsequently,a control gain sequence which is derived by the latest received state is predicted to compensate the packet dropouts caused by DoS attacks at the con-troller side.In what follows,the security analysis and ETPC design is conducted by Lyapunov stability theory and switched system method.The proposed ETPC method only needs the latest received state and dose not satisfy with the constrain-t of maximum allowable packets dropouts bound in traditional stability analysis method.This provides an effective solution to analysis and control of NCS with large time delay.At last,simulation results are shown to verify the proposed ETPC method.At last,some conclusions are obtained and the future research works are given in brief.