The Research On Strategy Of Dynamic Bandwidth Allocation For Networked Control System Under Denial Of Service Attack

Networked control system(NCS)wherein the control loops are closed through a shared,open,distributed communication network,which makes it more flexible,easy to maintain,and more economical.The deep integration of network and control system makes NCS not only inherit the advantages of information network,but also has the limitation of it,such as network-induced delay and packets dropout,etc.The distributed communication network nodes and open links in NCS make it vulnerable to being attacked.In recent years,incidents of NCS security caused by cyber attacks have happened frequently.Therefore,the security of NCS caused by attacks has become a hot research topic in NCS.Denial of Service(DoS)attack,which is the type of resource exhaustion,is the most frequently occurred in the current network environment.Once it occurs,it will seriously affect the quality of network service,and even cause the communication network to be completely unavailable.Therefore,security of NCS under DoS attack is not only academic,but also practical issues that need to be urgently solved.This thesis studies the dynamic allocation of NCS network bandwidth under DoS attack.Firstly,the queueing traffic models of DoS-induced delay and packets dropout are established by combining the characteristics of NCS communication channel and the impact of DoS attacks on the communication channe l.The attack modes of time constrained DoS attack are also thoroughly introduced.Based on the simulation of DCservo under PI controller,the quality of control under two types of DoS attack model are analyzed.Secondly,a control strategy of NCS when DoS attack occurs is given by analyzing and describing the characteristics of DoS at tack.A mathematical description of timeconstrained DoS attack is also presented by taking into consideration the unpredictable characteristics of DoS attack time,strength and frequency.The constraints on frequency and duration of DoS attack are also co nsidered in consideration of the existence of attack detection schemes and the limited energy of DoS attacks.At the same time,the evolution of NCS's system state under DoS attack is analyzed based on the proposed control strategy and DoS attack modes.The sufficient condition for guaranteeing input to state stability of NCS under DoS attack is also obtained.Finally,a method of dynamic bandwidth allocation for NCS under DoS attack is proposed based on DoS attack traffic model ?,which ca uses serious packets dropout.An algorithm,which is an assist method to help select proper sampling period that accounts for the current state error is also present.Two different coefficient selection algorithms for dynamic bandwidth allocation are also given.And,the simulation validates the advantages of the dynamic bandwidth allocation strategy against fixed-bandwidth strategies under DoS attack.