• Journal of Hydrogen and New Energy
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• v.24 no.1
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• pp.36-43
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• 2013

In this paper, a three-dimensional hydrogen desorption model is applied to a thin double-layered annulus ZrCo hydride bed and validated against the temperature evolution data measured by Kang et al. The present model reasonably captures the bed temperature evolution behavior and the 90% hydrogen discharging time. In addition, the performance of thin double-layered annulus bed is evaluated by comparing with a simple cylindrical bed using hydrogen desorption model. This study provides multi-dimensional contours such as temperature and H/M atomic ratio in the metal hydride region. This numerical study provides fundamental understanding during hydrogen desorption process and indicates that efficient design of the metal hydride bed is critical to achieve rapid hydrogen discharging performance. The present three-dimensional hydrogen desorption model is a useful tool for the optimization of bed design and operating conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.12
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• pp.2719-2730
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• 2009

In this paper, we implement the measurement functionality for performance measurements of EDGE (Enhanced Data Rates for GSM Evolution) terminal by using software. Generally speaking, the receiving algorithms in normal MODEM cannot be used directly to a measurement system due to the lack of accuracy. Therefore, we propose a new receiver algorithm for precise EDGE signal measurements. In the proposed algorithm, 2-stage (coarse stage, fine stage) parameters estimation (symbol-timing, frequency offset, carrier phase) scheme is used. To improve the estimation accuracy, we increase the number of the received signal samples by interpolation. The proposed EDGE signal measurement algorithm can be used for verifying the hardware measurement system, and also can be used for the commercial systems through software optimization.

• Journal of Information Processing Systems
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• v.14 no.3
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• pp.569-589
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• 2018

Cloud computing, also known as "country as you go", is used to turn any computer into a dematerialized architecture in which users can access different services. In addition to the daily evolution of stakeholders' number and beneficiaries, the imbalance between the virtual machines of data centers in a cloud environment impacts the performance as it decreases the hardware resources and the software's profitability. Our axis of research is the load balancing between a data center's virtual machines. It is used for reducing the degree of load imbalance between those machines in order to solve the problems caused by this technological evolution and ensure a greater quality of service. Our article focuses on two main phases: the pre-classification of tasks, according to the requested resources; and the classification of tasks into levels ('odd levels' or 'even levels') in ascending order based on the meta-heuristic "Bat-algorithm". The task allocation is based on levels provided by the bat-algorithm and through our mathematical functions, and we will divide our system into a number of virtual machines with nearly equal performance. Otherwise, we suggest different classes of virtual machines, but the condition is that each class should contain machines with similar characteristics compared to the existing binary search scheme.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.2
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• pp.96-101
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• 2021

Developing effective and earth-abundant electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for the commercialization of a water splitting system. In particular, the overpotential of the OER is relatively higher than the HER, and thus, it is considered that one of the important methods to enhance the performance of the electrocatalyst is to reduce the overpotential of the OER. We report effects of incorporation of metalloid into Ni(OH)2 microcrystal on electrocatalytic activities. In this study, Te incorporated Ni(OH)2 (��Te-Ni(OH)2) were grown on three-dimensional porous NF by a facile solvothermal method with �� = 1, 3 and 5. Homogeneous microplate structure on the NF was clearly observed for the Ni(OH)2/NF and ��Te-Ni(OH)2/NF samples. However, irregular and collapsed nanostructures were found on the surface of nickel foam when Te precursor ratio is (��) over 3. Electrocatalytic OER properties were analysed by Linear sweep voltammetry (LSV) and Electrochemical impedance spectroscopy (EIS). The amount of Te incorporation used in the electrocatalytic reaction was found to play a crucial role in improving catalytic activity. The optimum Te amount (��) introduced into the Ni(OH)2/NF was discussed with respect to their OER performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2113-2120
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• 2011

In this paper, so as to improve spectral efficiency for cell-boundary users, we introduce a coordinated multi-point (CoMP) system, which is one of inter-cell cooperative transmission strategies studied in 3GPP long-term evolution-advanced (LTE-A) systems, and develop a system-level simulator to evaluate performance. To identify performance improvement of the system with inter-cell cooperative transmission, we select a 3GPP LTE system as a reference, which shows the highest performance among the existing mobile communication systems, and conduct a performance comparison. System-level simulation is performed based on widely-used OPNET tool. We implement modules including central unit (CU), CoMP eNodeB (CeNB), user equipment (UE), and multiple-input multiple-output (MIMO) channel model, while designing the inter-cell cooperative transmission system. Under WINNER wireless channel model and international telecommunication union (ITU) network model environments, we then evaluate the performance of edge users who belong to the lower 5% in terms of spectral efficiency. It is finally shown that throughput of the proposed CoMP system gets improved up to 2.5 times compared to that of the 3GPP LTE reference system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1C
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• pp.120-130
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• 2009

In this paper, we propose a receiver structure for frequency synchronization in OFDMA (Orthogonal Frequency Division Multiple Access) system which is considered as 3GPP LTE(Long Term Evolution) downlink. In general, OFDMA frequency synchronization consists of two parts: coarse synchronization and fine synchronization. We consider P-SCH (Primary-Synchronization Channel) and CP (Cyclic Prefix) of OFDMA symbol for coarse synchronization and fine synchronization, respectively. The P-SCH signal has two remarkable disadvantages that it does not have sufficiently many sub-carriers and its differential correlation characteristic is not good due to ZC (Zadoff Chu) sequence-specific property. Hence, conventional frequency synchronization algorithms cannot obtain satisfactory performance gain. In this paper, we propose a modified differential correlation algorithm to improve performance of the coarse frequency synchronization. Also, we introduce an effective PLL (Phase Locked Loop) structure to guarantee stable performance of the fine frequency synchronization. Simulation results verify that the proposed algorithm has superior performance to the conventional algorithms and the 2nd-order PLL is effective to track the fine frequency offset even in high mobility.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3C
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• pp.302-313
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• 2010

In this paper, we propose an enhanced AGC (Automatic Gain Control) structure and P-SCH detection method for initial cell search in 3GPP (3rdGenerationPartnershipProject) LTE (Long Term Evolution) FDD(Frequency Division Duplex) / TDD (Time Division Duplex) dual mode system. Since TDD frame structure consists of uplink subframe and downlink subframe, conventional AGC structure causes P-SCH detection performance degradation by increase of AGC variation due to signal power difference between uplink and downlink subframe. Also, P-SCH detection performance is degraded by distortion of P-SCH correlation characteristic in frequency offset and multipath fading channel environments. Therefore, we propose an AGC structure which can minimize P-SCH detection performance degradation with stable operation in 3GPP LTE TDD mode as well as FDD mode. Also we propose a P-SCH detection method which can reduce distortion of correlation chareteristics in frequency offset and multipath fading environments and obtain good P-SCH detection performance. Simulation results show that the proposed AGC structure and P-SCH detection method have stable AGC operation and excellent P-SCH detection performance for 3GPP LTE TDD / FDD dual mode downlink receiver in various channel environments.

• 한국체육학회지인문사회과학편
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• v.56 no.5
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• pp.665-677
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• 2017

This study aimed to examine the evolution of exercise performance and medical assessments in U-12 youth football players. Participants were recruited from an youth football players (YFG, n=15; $11.2{\pm}0.9yrs$) and normal youth (CON, n=15; $11.5{\pm}0.6yrs$). Both groups were tested for exercise performance (health related physical fitness, skill related physical fitness, functional movement screen; FMS and Y-balance) and medical assessments (lower extremity alignment, range of motion; ROM and manual muscle test; MMT). YFG showed a positive effects on pacer in health related physical fitness, 50-m run and Single-leg standing with eyes closed in skill related physical fitness, active straight leg raise and rotary stability in FMS, non-dominant composite score in Y-balance, respectively compared to CON. However, YFG showed a negative effects on Q-angle of dominant and non-dominant in lower extremity alignment, dorsiflexion of non-dominant, plantarflexion of dominant and non-dominan in ROM, hip extension and abduction, knee flexion and extension of dominant, knee flexion and extension of non-dominant in MMT, respectively compared to CON. These results indicated that U-12 youth football players have shown excellent exercise performance, but medical assessments has proved negative effects.

• Journal of Broadcast Engineering
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• v.26 no.6
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• pp.766-777
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• 2021

This paper presents an improved scheme for detection of the physical broadcast channel (PBCH) in long-term evolution (LTE)-based fifth-generation (5G) multimedia broadcast and multicast services (MBMS) and 5G new radio (NR) for cellular broadcast. In the time domain, by combining the correlations between the received signal and primary synchronization signal (PSS) within all SS/PBCH blocks, the frame synchronization and the start position of the SS/PBCH blocks can be obtained. In this paper, to improve the detection performance of PBCH for 5G NR, a combining scheme of PBCH signals within a frame is proposed. In addition, the performance of the proposed detection scheme is evaluated and the performance is compared with the conventional scheme for PBCH detection of LTE-based 5G MBMS. The simulation results show that the detection performance of PBCH for 5G NR is improved by combining the PBCH signals and outperforms LTE-based 5G MBMS under the additive white Gaussian noise (AWGN), fixed, and mobile environments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.9
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• pp.3594-3610
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• 2015

Recent advancements in broadband wireless communication technologies enable mobile users to receive video streaming services with various smart devices. The long term evolution (LTE) network provides high bandwidth and low latency for several emerging mobile applications. This paper proposes the buffer aware scheduling (BAS) approach to schedule the downlink video traffic in LTE network. The proposed BAS scheme applies the weighting function to heuristically adjust the scheduling priority by considering the buffer status and channel condition of UE so as to reduce the time that UE stays in the connected state without receiving data. Both of 1080P and 2160P resolution video streaming sources were applied for exhaustive simulations to examine the performance of the proposed scheme by comparing to that of the fair bandwidth (FB) and the best channel quality indicator (CQI) schemes. The simulation results indicate that the proposed BAS scheme not only achieves better performance in power saving, streaming delivery time, and throughput than the FB scheme while maintaining the similar performance as the best CQI scheme in light traffic load. Specifically, the proposed scheme reduces streaming delivery time and generates less signaling overhead than the best CQI scheme when the traffic load is heavy.