• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.4
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• pp.752-757
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• 2006

In the case of the requirement of high speed transmission, OFDM is a powerful technique employed in communications systems suffering from frequency selective fading. In this paper, we apply an optimal adaptive bitloading algorithm technique. The BER performance of the fixed-rate SISO and adaptive SISO is simulated. Specially, we can decompose the MIMO channel into the SISO channel by making use of the singular value decomposition(SVD) assuming channel knowledge in a multipath environment. As a results of simulation, we confirmed that the BER enhancement of MIMO-OFDM system with the bitloadins algorithm was superior to the SISO-OFDM system.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.652-656
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• 2007

The major streams in South Korea have established the TMDL(Total Maximum Daily Loads) regulation for just 4 years. Traditional concepts in water quality management in South Korea are based upon the selection of a design streram flow which is 10-year averged flow exeedance probability 75%(Q275). That is, a single flow value based upon average long term flow conditions is chosen for application in dilution calculations, permit design, water quality modeling, etc. While these TMDLs seems to satisfy the requirement of the target water quality regulations, they have contributed little to any watershed/waterbody assessment and restoration plans. These types of TMDLs do little to characterize the problems the TMDLs are intended to address. For TMDLs to be more beneficial in the assessment and implementation process, TMDLs should reflect adequate water quality across flow conditions rather than at a single flow value such as average daily flow. In this paper, we developed LDC (load duration curve) methodology for theevaluation of Korean TMDL evaluation based on watershed scaled, physically based on SWAT(Soil and Water Assessment Tool) model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.4087-4102
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• 2014

Two-way relaying is an effective way of improving system spectral efficiency by making use of physical layer network coding. However, energy efficiency in OFDM-based bidirectional relaying with asymmetric traffic requirement has not been investigated. In this study, we focused on subcarrier transmission mode selection, bit loading, and power allocation in a multicarrier single amplified-and-forward relay system. In this scheme, each subcarrier can operate in two transmission modes: one-way relaying and two-way relaying. The problem is formulated as a mixed integer programming problem. We adopt a structural approximation optimization method that first decouples the original problem into two suboptimal problems with fixed subcarrier subsets and then finds the optimal subcarrier assignment subsets. Although the suboptimal problems are nonconvex, the results obtained for a single-tone system are used to transform them to convex problems. To find the optimal subcarrier assignment subsets, an iterative algorithm based on subcarrier ranking and matching is developed. Simulation results show that the proposed method can improve system performance compared with conventional methods. Some interesting insights are also obtained via simulation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.338-343
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• 2001

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc., In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, two kinds of spring steel(SAE 9254, DIN 50CrV4) are made. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) on low stress condition, the single stage shot peening is not affected by nonmetallic inclusion under metal. (2) it is possible that the two-stage shot peening increases the fatigue life and the high stress, but, that is affected by nonmetallic inclusion under metal. (3) so far, beeasily 50CrV4 have made high stress. But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.

• Journal of Communications and Networks
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• v.9 no.2
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• pp.112-117
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• 2007

In this paper, we focus on the total transmission power minimization problem for downlink beamforming multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems while ensuring each user's QoS requirement. Although the linear integer programming (LIP) solution we formulate provides the performance upper bound of the margin adaptive (MA) optimization problem, it is hard to be implemented in practice due to its high computational complexity. By regarding each user's equivalent channel gain as approximate independent values and using iterative descent method, we present a heuristic MA resource allocation algorithm. Simulation results show that the proposed algorithm efficiently converges to the local optimum, which is very close to the performance of the optimal LIP solution. Compared with existing space division multiple access (SDMA) OFDM systems with or without adaptive resource allocation, the proposed algorithm achieves significant performance improvement by exploiting the frequency diversity and multi-user diversity in downlink multiple-input single-output (MISO) OFDM systems.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1994.11a
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• pp.51-66
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• 1994

A divisible off-line electronic cash system based on cut-and-choose has first been proposed by [OO91] and recently more efficient single term divisible cash system was presented in [EO94] which is based on Brand's scheme [Bra93]. In this paper, we present a different type of single term divisible electronic cash system which is more efficient than previously proposed systems such as [OO91], [YLR93], and [EO94] in the standpoint of the amount of communication, the number of modular multiplications required in the payment transactions, and the storage requirement in the withdrawal protocol. Our scheme is a modified version of [LL93], where the major improvement has been made in its withdrawal transaction to introduce untraceability and multi-spendability. We have borrowed the idea of the withdrawal protocol of our scheme from [EO94] with minor modifications. Transferability in our scheme allows only a finite number of transfer. Our scheme satisfies an the desirable properties of an electronic cash system such as untraceability, divisibility and transferability. In addition, we present a n-spendable cash. The basic idea of extension to multi-spendability has been borrowed from [Bra93] with minor modifications.

• Microbiology and Biotechnology Letters
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• v.7 no.4
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• pp.211-216
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• 1979

Air lift fermentor (ALF) is widely used for production of single-cell protein (SCP) from hydrocarbon and other carbon sources, because oxygen transfer efficiency is believed to be superior in the ALF to that in other conventional fermentors. However, the performance of ALF in terms of mixing is somewhat questionable. In this research, we studied about the performance of the ALF in SCP production using methanol fermentation process as a model system. The results show that ALF could be employed for SCP production or other fermentation processes when substrate is miscible and used at low concentration. With a high substrate concentration, it must be operated under high pressure or low dilution rate to meet the adequate oxygen transfer requirement.

• Proceedings of the IEEK Conference
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• 2003.07d
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• pp.1621-1624
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• 2003

As the entities participating Grid become larger, performance requirement for the LDAP-based GIS(Grid Information Service) goes beyond that provided by a stand-alone single LDAP server. This entails the exploration of distributed LDAP systems. This paper presents the performance evaluation respectively for a distribution-based and a replication-based LDAP model. The analysis is based on an analytic performance model for each distributed system which is obtained by applying the M/M/1 queuing model. The performance evaluation made to these analytic models reveals that the distribution-based and the replication-based model show a significant tradeoff in their performance with respect to the system size as well as the amount of system load.

• Composites Research
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• v.13 no.1
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• pp.11-24
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• 2000

In this paper, finite thickness and tow phase effects on the mechanical behavior were studied numerically for plain weave textile composites. Unit cell analysis based on a superposition method was employed to simulate uniaxial tensile loading condition and macro-element post-processor was used to reduce computer resource requirement. The effective moduli and micro-stress distribution were calculated for finite thick plain weave composites with phase shifts. Single layer and infinitely thick configurations were also considered for comparison.

• The KSFM Journal of Fluid Machinery
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• v.18 no.4
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• pp.56-61
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• 2015

It is important requirement to properly evaluate the aerodynamic performance and characteristics during preliminary design of a centrifugal compressor. In this study the centrifugal compressor was calculated for variations of mass flow and blade Mach number by means of single passage steady state. A lot of quantitative performance values were obtained and through the obtained values the aerodynamic performance characteristics of designed impeller and vaned diffuser were investigated. The results were classified by blade Mach number to analyze characteristics and the aerodynamic performance was examined at choke of impeller, diffuser and separation of diffuser.