Dooyoung Kim

WAP: Wormhole Attack Prevention Algorithm in Mobile Ad Hoc Networks

In wireless ad hoc networks, nodes compromise to forward packets for each other to communicate beyond their transmission range. Therefore, networks are vulnerable to wormhole attacks launched through compromised nodes because malicious nodes can easily participate in the networks. In wormhole attacks, one malicious node tunnels packets from its location to the other malicious node. Such wormhole attacks result in a false route with fewer. If source node chooses this fake route, malicious nodes have the option of delivering the packets or dropping them. It is difficult to detect wormhole attacks because malicious nodes impersonate legitimate nodes. Previous algorithms detecting a wormhole require special hardware or tight time synchronization. In this paper, we develop an effective method called wormhole attack prevention (WAP) without using specialized hardware. The WAP not only detects the fake route but also adopts preventive measures against action wormhole nodes from reappearing during the route discovery phase. Simulation results show that wormholes can be detected and isolated within the route discovery phase.

Structure of Concentrated-Flux-Type Interior Permanent-Magnet Synchronous Motors Using Ferrite Permanent Magnets

Interior permanent magnet synchronous motors (IPMs) usually use NdFeB for achieving high-torque and high-efficiency performance. This paper reviews the performance of concentrated-flux-type ferrite magnet motors (CFFMs) that use ferrite, as an alternative to the general type of IPMs that use NdFeB. A structure to reduce the motor volume and improve the torque density of CFFMs is suggested in this paper. The characteristics of CFFMs for different rotor types are analyzed. The motor parameters are analyzed. Using 2-D finite element analysis (FEA), the efficiency and size of the CFFMs are compared with each other. This paper discusses the results of stress analysis for each rotor type using 2-D FEA. Finally, it suggests a CFFM structure to replace the general type of IPMs that use NdFeB. The proposed LC-type has the highest torque density among all the ferrite rotor types. It is seen that the proposed LC-type ferrite-model replacement for the Nd model is the best choice of all the types.

Multi-Stage Intrusion Detection System Using Hidden Markov Model Algorithm

Intrusion detection systems are the basis of system protection from network attacks. However, intrusions are increasingly taking multi-stage procedures to attack a system, and cannot be detected by existing single stage intrusion detection systems. This paper proposes a multi-stage intrusion detection system architecture using hidden Markov model algorithm. This system considers every stage used by recent intrusions and applies them to the hidden Markov model algorithm to determine which intrusion is used in the audit data. This architecture reduces overheads of intrusion agents and raises efficiency of the whole system.

Efficient Parallel Scan Test Technique for Cores on AMBA-based SoC

Today’s System-on-a-Chip (SoC) is designed with reusable IP cores to meet short time-tomarket requirements. However, the increasing cost of testing becomes a big burden in manufacturing a highly integrated SoC. In this paper, an efficient parallel scan test technique is introduced to minimize the test application time. Multiple scan enable signals are adopted to implement scan architecture to achieve optimal test application time for the test patterns scheduled for concurrent scan test. Experimental results show that testing times are considerably reduced with little area overhead.

Mobile agent based intrusion detection system adopting hidden Markov model

Mobile agent based intrusion detection systems distribute detection agents to prevent system from shutting down when an agent becomes breaks. Because in this system agents are distributed, it can reduce network delay and network load, and each agent can operate independently. Agents can also be easily added or deleted. In this paper we propose an enhanced design of mobile agent based intrusion detection system using Hidden Markov Model algorithm for detection. Hidden Markov Model algorithm is used to detect abnormal behavior pattern by analyzing log information. By adopting this algorithm to the mobile intrusion detection agents, detection performance can be improved.

Hybrid Test Data Transportation Scheme for Advanced NoC-Based SoCs

Network-on-chip (NoC) has evolved to overcome the issues of traditional bus-based on-chip interconnect. In NoC-reuse as TAM, the test schedulers are constrained with the topological position of cores and test access points, which may negatively affect the test time. This paper presents a scalable hybrid test data transportation scheme that allows to simultaneously test multiple heterogeneous cores of NoC-based SoCs, while reusing NoC as TAM. In the proposed test scheme, single test stimuli set of multiple CUTs is embedded into each flit of the test stimuli packets and those packets are multicast to the targeted CUTs. However, the test response packets of each CUT are unicast towards the tester. To reduce network load, a flit is filled with maximum possible test response sets before unicasting towards the tester. With the aid of Verilog and analytical simulations, the proposed scheme is proved effective and the results are compared with some recent techniques.

Proposition of Structures for Brushless Hybrid-Excitation Synchronous Motors With Improved Rotor

Recently, studies on the hybrid excitation synchronous motor using permanent magnet (PM) together with field windings have been actively conducted. In this regard, this paper seeks to investigate brushless hybrid excitation synchronous motors with improved rotors. The design was performed using an equivalent magnetic circuit to determine the best of four possible different structures. Using a finite-element analysis (FEA), the back electromotive force (EMF) per PM usage and the phase back EMF of each type were calculated and compared, and the design that can best reduce costs and increase torque density was determined. A detailed design of one of the four structures with excellent characteristics was performed, and the associated characteristics and problems were verified. An improved rotor structure was proposed to resolve the identified problems and improve performance. The phase back EMF and the total harmonic distortion of the phase back EMF, cogging torque, load torque, and torque ripple of the improved rotor structure were verified through the application of the FEA. In addition, the prototype motor was fabricated, and a no-load test was conducted to compare the test results and analysis results on the phase back EMF. The reliability of the analysis results was confirmed by comparison between test results and analysis results on the input current, line to line voltage, and efficiency under the same output conditions through the load test.

An Asymmetric Rotor Design of Interior Permanent Magnet Synchronous Motor for Improving Torque Performance

Torque ripple is necessarily generated in interior permanent magnet synchronous motors (IPMSMs) due to the non-sinusoidal distribution of flux density in the air gap and the magnetic reluctance by stator slots. This paper deals with an asymmetric rotor shape to reduce torque ripple which can make sinusoidal flux density distribution in the air gap. Meanwhile the average torque is relatively increased by the asymmetric rotor. Response surface method (RSM) is applied to find the optimum position of the permanent magnets for the IMPSM with improved torque performance. Consequently, an asymmetric structure is the result of RSM and the structure has disadvantage of a mechanical stiffness. Finally, the performance of suggested shape is verified by finite element analysis and structural analysis is conducted for the mechanical stiffness.

Oxide Formation Mechanisms in High Manganese Steel Welds

Oxide inclusions in high-Mn steel welds were analyzed and almost all of which were found to belong to the MnO-Al2O3-SiO2 system. In this study, the inclusions were categorized based on MnS morphology into the following two types: (1) aluminosilicate with a MnS patch, or (2) aluminosilicate with a MnS shell. The most frequently detected was type 1, the formation mechanism of which was investigated using commercially available thermochemical computing software, FactSage™ (ver. 6.3). The thermodynamic calculations predicted that galaxite (MnAl2O4), tephroite (Mn2SiO4), and MnS could precipitate during solidification. However, because of the fast cooling rate in welding processes, galaxite and tephroite phases were unable to fully crystallize, but rather were supercooled as glassy phases. In order to confirm the validity of the thermodynamic calculations, the composition of the observed inclusions was compared with the MnO-SiO2-Al2O3 ternary phase diagram, resulting in remarkably good agreement. Furthermore, it was found that the type of the oxide inclusions was dependent on their location (i.e., MnS shell- and MnS patch-type oxides were detected at the dendritic core and interdendritic boundary, respectively). Both types of oxides were occasionally found in one oxide, near the interdendritic boundary. This indicates that the morphology variation originates from the redistribution of solute due to fast solidification.

An Algorithm for Acquiring Reliable Path in Abnormal Traffic Condition

Most Reliable Paths algorithm make it enable to select the most stable path on network by considering not only link cost but also link capacity, link operation probability and the size of message to be sent. But this algorithm uses a fixed value as link operation probability so that it can be applicable in the normal network state, not in the network state that traffic abnormally increase. To solve this problem, this thesis applies the packet drop probability of RED (Random Early Detection) method to the operation probability of the most reliable path algorithm so that the most reliable path can be guaranteed. For this purpose, we propose an All-Pairs Most Reliable Paths acquiring algorithm having time complexity thetas (n3) based on the All-Pairs Shortest Paths algorithm proposed by Floyd-Warshall.