Secure State Estimation Of Cyber-Physical Systems With State Delay And Sparse Sensor Attacks

Cyber-physical systems(CPS)are systems that integrate computing,communication and physical processes deeply.Such systems can fully realize the functions of distributed sensing,real-time information processing,rapid information transmission,real-time information feedback and dynamic control.Hence,CPS are widely used,and they have attracted a lot of attention of people from all walks of life.Sensor network is an essential component of CPS,and is also the main target of various external attacks,which leads to a series of security problems.CPS have a high requirement for real-time performance,but their complex structure will cause time-delay.The environment of CPS is complex and changeable,so timely observation of the state of the system is of great practical significance for the control of the system performance.Therefore,on the basis of summarizing the research work at home and abroad,this thesis focuses on the safety state estimation of CPS with state delay.The specific research contents are as follows:1.For the continuous linear CPS model with state delay and sparse sensor attacks,a secure state observer based on adaptive switching mechanism is constructed.On the one hand,the candidate attack sets are determined by a set cover approach,which can effectively reduce the search space of the candidate attack sets and improve the search speed of attack sets.On the other hand,in the estimation process,adaptive switching mechanism is used to determine the correct attack sets from the candidate attack sets.The most critical is that based on the improved LK stability theorem for continuous linear systems with time delay,the sufficient condition for the existence of the designed observer is determined.The designed observer can quickly locate the correct attack sets,and finally achieve the desired estimation within the allowable estimation error.Finally,two simulation examples are given to verify the effectiveness and rapidity of the designed observer.2.For the discrete linear CPS model with state delay and sparse sensor attack,a security state observer based on projection operator is constructed.Firstly,the projection operator is used to determine the correct attack set,and the corresponding switching gain matrix is obtained.This method can effectively avoid the problem of estimation error surge.In addition,based on the improved LK stability theorem for discrete linear time delay systems,the sufficient condition for the existence of the secure state observer and the design method is determined.The designed observer has high estimation accuracy,which is verified by two simulation examples.Finally,we summarize the work done in this thesis and point out the directions for the next step.