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- 저자 : Qingxian Wu (검색결과 5 건)
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Qingxian Jia,Lina Wu,Huayi Li 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.2
This paper addresses the problem of robust actuator fault reconstruction for Takagi-Sugeno (T-S) fuzzy systems subjects to actuator faults, unknown inputs and time-varying delays via a Fuzzy Synthesized Learning and Luenberger Observer (FSL2O). Through a coordinate transformation, the original T-S fuzzy system is decomposed into two subsystems: subsystem-1 effected by actuator faults and subsystem-2 effected by unknown inputs. In the presented FSL2O methodology, a Reduced-Order Fuzzy Learning Observer (ROFLO) is explored for the subsystem1 to reconstruct actuator faults accurately while a Reduced-Order Fuzzy State (Luenberger) Observer (ROFSO) is designed for the subsystem-2 based on the H∞ control technique such that it has strong robustness against the unknown inputs. The synthesized design of the ROFLO and the ROFSO is formulated in a unified manner in terms of Linear Matrix Inequalities (LMIs) that can be conveniently solved using LMI optimization technique. In addition, as a comparison, a full-order FLO is suggested for robust actuator fault reconstruction. Finally, a numerical exampleand simulation are provided to demonstrate the effectiveness of the proposed approaches.
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( Zehui Wu ),( Qiang Wei ),( Kailei Ren ),( Qingxian Wang ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.2
Software Defined Network (SDN) realizes management and control over the underlying forwarding device, along with acquisition and analysis of network topology and flow characters through south bridge protocol. Data path Identification (DPID) is the unique identity for managing the underlying device, so forged DPID can be used to attack the link of underlying forwarding devices, as well as carry out DoS over the upper-level controller. This paper proposes a dynamic defense method based on Client-Puzzle model, in which the controller achieves dynamic management over requests from forwarding devices through generating questions with multi-level difficulty. This method can rapidly reduce network load, and at the same time separate attack flow from legal flow, enabling the controller to provide continuous service for legal visit. We conduct experiments on open-source SDN controllers like Fluid and Ryu, the result of which verifies feasibility of this defense method. The experimental result also shows that when cost of controller and forwarding device increases by about 2%-5%, the cost of attacker`s CPU increases by near 90%, which greatly raises the attack difficulty for attackers.
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Shixun Xiong,Qingxian Wu,Yu-Hui Wang 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.10
This paper studies the dynamic output feedback consensus control problem of linear heterogeneous multi-agent systems under the leader-follower formation with a dynamic quantizer. In the practical engineering, the status information of the unmanned aircraft vehicle (UAV) and the unmanned underground vehicle (UGV) is normally unmeasurable, which is difficult to design the state feedback controller for the UAV-UGV formation. Besides, in the communication topology of the leader-follower formation based on UAVs and UGVs, the signals should be quantized in each follower. However, the traditional static quantizer has a quantization error, which affects the formation stability. Therefore, the control objective is to guarantee the UAV-UGV formation tracking consensus while improving the precision of the quantization. First, the followers and leader systems are based on the discretetime model, and the output trajectory of the leader is time-varying. Then, a dynamic output feedback controller is provided with a dynamic quantizer to guarantee the tracking performance of the heterogeneous multi-agent systemswith a leader. The followers can asymptotically track the leader system with L2 − L∞ control gains by solving a set of linear matrix inequalities (LMIs). Finally, simulation results demonstrate the effectiveness of the designed control strategies.
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EPfuzzer: Improving Hybrid Fuzzing with Hardest-to-reach Branch Prioritization
( Yunchao Wang ),( Zehui Wu Qiang Wei ),( Qingxian Wang ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.9
Hybrid fuzzing which combines fuzzing and concolic execution, has proved its ability to achieve higher code coverage and therefore find more bugs. However, current hybrid fuzzers usually suffer from inefficiency and poor scalability when applied to complex, real-world program testing. We observed that the performance bottleneck is the inefficient cooperation between the fuzzer and concolic executor and the slow symbolic emulation. In this paper, we propose a novel solution named EPfuzzer to improve hybrid fuzzing. EPfuzzer implements two key ideas: 1) only the hardest-to-reach branch will be prioritized for concolic execution to avoid generating uninteresting inputs; and 2) only input bytes relevant to the target branch to be flipped will be symbolized to reduce the overhead of the symbolic emulation. With these optimizations, EPfuzzer can be efficiently targeted to the hardest-to-reach branch. We evaluated EPfuzzer with three sets of programs: five real-world applications and two popular benchmarks (LAVA-M and the Google Fuzzer Test Suite). The evaluation results showed that EPfuzzer was much more efficient and scalable than the state-of-the-art concolic execution engine (QSYM). EPfuzzer was able to find more bugs and achieve better code coverage. In addition, we discovered seven previously unknown security bugs in five real-world programs and reported them to the vendors.
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An OpenFlow User-Switch Remapping Approach for DDoS Defense
( Qiang Wei ),( Zehui Wu ),( Kalei Ren ),( Qingxian Wang ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.9
DDoS attacks have had a devastating effect on the Internet, which can cause millions of dollars of damage within hours or even minutes. In this paper we propose a practical dynamic defense approach that overcomes the shortage of static defense mechanisms. Our approach employs a group of SDN-based proxy switches to relay data flow between users and servers. By substituting backup proxy switches for attacked ones and reassigning suspect users onto the new proxy switches, innocent users are isolated and saved from malicious attackers through a sequence of remapping process. In order to improve the speed of attacker segregation, we have designed and implemented an efficient greedy algorithm which has been demonstrated to have little influence on legitimate traffic. Simulations, which were then performed with the open source controller Ryu, show that our approach is effective in alleviating DDoS attacks and quarantining the attackers by numerable remapping process. The simulations also demonstrate that our dynamic defense imposes little effect on legitimate users, and the overhead introduced by remapping procedure is acceptable.
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