• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.889-897
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• 2002

In this paper, we propose an improved block coding scheme for PAPR reduction in the OFDM communication system. Unlike the conventional block coding scheme which uses one block encoder of subcarrier N, two block encoders of subcarrier N/2 is used for the proposed block coding scheme. This not only improves the coding gain, but enhances the spectral efficiency by twice due to the increment of code rate. PAPR Reduction performance is the same as the conventional block coding. When BER is $10^{-4}$, the proposed block coding scheme has coding gain of 0.5 dB than the conventional scheme.

• The Journal of the Korea Contents Association
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• v.11 no.9
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• pp.54-62
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• 2011

This paper proposes both global and local mobility management (MM) scheme improved from Multi Protocol Label Switching (MPLS)-based Mobility Management scheme (MPLS-MOB) for seamless service in Next Generation Network (NGN). The proposed scheme adds local MM on the existing MPLS-MOB which supports global MM by processing handover signaling by 2.5 layer switching via Label Switch Path (LSP) of MPLS. We numerically analyze and verify that the proposed scheme has lower handover latency time than the existing ones, such as micro-MM methods using MPLS as well as MIP and an interworking scenario between PMIP and MIP.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.7
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• pp.570-577
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• 2016

This paper proposes the design of a novel distributed message management scheme using a message-oriented management and analysis tool (MOMAT) for naval combat system (NCS) middle-ware. If a message is not guaranteed real-time of the NCS with each node, it causes the loss of data and decreases the reliability of systems. To solve these problems, improved message management schemes are proposed. Message management schemes are considering a real-time user management scheme and a real-time traffic management scheme. The proposed schemes are simulated with a developed simulation tool, data publisher, and subscriber connected through nodes in middle-ware. The simulation results show improved results in terms of message round-trip time (RTT), End-to-End delay, and throughput.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.12
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• pp.5529-5552
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• 2016

Mobile cloud computing (MCC) has revolutionized the way in which the services can be obtained from the cloud service providers. Manifold increase in the number of mobile devices and subscribers in MCC has further enhanced the need of an efficient and robust authentication solution. Earlier, the subscribers could get cloud-computing services from the cloud service providers only after having consulted the trusted third party. Recently, Tsai and Lo has proposed a multi-server authenticated key agreement solution for MCC based on bilinear pairing, to eliminate the trusted third party for mutual authentication. The scheme has been novel as far as the minimization of trusted party involvement in authenticating the user and service provider, is concerned. However, the Tsai and Lo scheme has been found vulnerable to server spoofing attack (misrepresentation attack), de-synchronization attack and denial-of-service attack, which renders the scheme unsuitable for practical deployment in different wireless mobile access networks. Therefore, we have proposed an improved model based on bilinear pairing, countering the identified threats posed to Tsai and Lo scheme. Besides, the proposed work also demonstrates performance evaluation and formal security analysis.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.5 no.4
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• pp.18-29
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• 1994

In this paper, the performance of stepped serial search scheme and matched filter scheme for code acqusition in FH / CDMA are evaluated under land mobile radio communication channel environments. And delay lock loop scheme is used as code tracking system. As the results for code acquisition system, it is shown that the performance of stepped searial scheme is superior to matched filter scheme, because system complexity is reduced and system performance is improved by increasing the hopping frequency not to substitute for special hardware. Also, it is shown that its performance is improved under Rayleigh/ Rician fading environments. As the results for code tracking system, it is found that mean hold time is increased due to the increase of the number of lock state and hopping frequency, M.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.211-220
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• 2007

This work presents an iterated improved reduced system (IIRS) procedure combined with sub-structuring scheme for large structures. Iterated IRS methods are usually more efficient than others because the dynamic condensation matrix is updated repeatedly until the desired convergent values are obtained. However, using these methods simply for large structures causes expensive computational cost and even makes analyses intractable because of the limited computer storage. Therefore, the application of sub-structuring scheme is necessary. Because the large structures are subdivided into several (or more) sub-domains, the construction of dynamic condensation matrix does not require much computation cost in every iteration. This makes the present method much more efficient to compute the eigenpairs both in lower and intermediate modes. In Part I, iterated IRS method combined with sub-structuring scheme for undamped structures is presented. The validation of the proposed method and the evaluation of computational efficiency are demonstrated through the numerical examples.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.3
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• pp.281-285
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• 2008

Eigenvalue reduction schemes approximate the lower eigenmodes that represent the global behavior of the structures. In the previous study, we proposed a two-level condensation scheme (TLCS) for the construction of a reduced system. And we have improved previous TLCS with combination of the iterated improved reduced system method (IIRS) to increase accuracy of the higher modes intermediate range. In this study, we apply previous improved TLCS to multi-level sub-structuring scheme. In the first step, the global system is recursively partitioned into a hierarchy of sub-domain. In second step, each uncoupled sub-domain is condensed by the improved TLCS. After assembly process of each reduced sub-eigenvalue problem, eigen-solution is calculated by Lanczos method (ARPACK). Finally, Numerical examples demonstrate performance of proposed method.

• Journal of Korea Multimedia Society
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• v.20 no.3
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• pp.500-510
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• 2017

Recently Lee et al. proposed an improved symmetric key-based remote user authentication scheme to eliminate the security weaknesses of Kumari et al.'s scheme. They hence claimed that their scheme is secure to various well-known attacks. However, we found that Lee et al.'s scheme is still insecure against outsider attack, smart card stolen and off-line password guessing attack. To overcome these security vulnerabilities, we propose an enhanced authentication scheme with key-agreement which is based on the fuzzy-extractor. Furthermore, we prove that the proposed scheme is more secure, and that it serves to gratify all of the required security properties. Finally, we compare the performance and functionality of the proposed scheme with those of previous schemes.

• Journal of Computing Science and Engineering
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• v.5 no.1
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• pp.19-31
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• 2011

In this paper, we propose two new routing schemes for double-layered peer-to-peer systems; a shorter-lower mobility routing scheme and a reverse path routing scheme. The shorter-lower mobility routing scheme first chooses shortest routing paths among possible routing paths and selects the path associated with the relay peer who has lower mobility to improve the reliability of the system. The reverse path routing scheme carries out unicasting (instead of multicasting) based on the reverse path information that can be obtained during the initial file search to further reduce network traffic. The experimental results showed that a double-layered peer-topeer system with the proposed hybrid scheme improved the reliability of the system about 1.5% over the hop count scheme and reduced network traffic by about 0.5% compared to the hop count scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.9
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• pp.2153-2169
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• 2012

Femtocells provide high quality indoor communications with low transmit power. However, when femtocells are applied in cellular systems, a co-channel interference problem between macrocells and femtocells occurs because femtocells use the same spectrum as do the macrocells. To solve the co-channel interference problem, a previous study suggested a resource allocation scheme in LTE cellular systems using FFR. However, this conventional resource allocation scheme still has interference problems between macrocells and femtocells near the boundary of the sub-areas. In this paper, we define an optimization problem for resource allocation to femtocells and propose a femtocell resource allocation scheme to solve the optimization problem and the interference problems of the conventional scheme. The evaluation of the proposed scheme is conducted by System Level Simulation while varying the simulation environments. The simulation results show that the proposed scheme is superior to the conventional scheme and that it improves the overall performance of cellular systems.