• International Journal of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.67-72
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• 2020

The fifth generation (5G) mobile communication has an impact on the human life over the whole world, nowadays, through the artificial intelligence (AI) and the internet of things (IoT). The low latency of the 5G new radio (NR) access is implemented by the state-of-the art technologies, such as non-orthogonal multiple access (NOMA). This paper investigates a practical issue that in NOMA, for the practical channel models, such as fading channel environments, the successive interference cancellation (SIC) should be performed on the stronger channel users with low power allocation. Only if the SIC is performed on the user with the stronger channel gain, NOMA performs better than orthogonal multiple access (OMA). Otherwise, NOMA performs worse than OMA. Such the superiority requirement can be easily implemented for the channel being static or slow varying, compared to the block interval time. However, most mobile channels experience fading. And symbol by symbol channel estimations and in turn each symbol time, selections of the SIC-performing user look infeasible in the practical environments. Then practically the block of symbols uses the single channel estimation, which is obtained by the training sequence at the head of the block. In this case, not all the symbol times the SIC is performed on the stronger channel user. Sometimes, we do perform the SIC on the weaker channel user; such cases, NOMA performs worse than OMA. Thus, we can say that by what percent NOMA is better than OMA. This paper calculates analytically the percentage by which NOMA performs better than OMA in the practical mobile communication systems. We show analytically that the percentage for NOMA being better than OMA is only the function of the ratio of the stronger channel gain variance to weaker. In result, not always, but almost time, NOMA could perform better than OMA.

• Journal of Digital Contents Society
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• v.5 no.1
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• pp.28-34
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• 2004

In this paper, we have analyzed the block error probability of orthogonal multicarrier 16 QAM signal in a frequency selective Rician fading environment. The block error probability is evaluated with several parameters such as normalized propagation delay $(\gamma/T_S),$, bit energy to noise power ratio $(E_b/N_0),$ and desired signal to undesired signal power ratio (DUR) in fast fading and slow fading channels. In the fast fading channel, The result shows that the block error probability rather in the fast fading channel achieves better performance than in the slow fading channel, when the error correction capability is one or two.

• Journal of Communications and Networks
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• v.16 no.1
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• pp.1-9
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• 2014

Block diagonalization (BD) has been proposed as a simple and effective technique in multiuser multiple-input multiple-output (MU-MIMO) broadcast channels. However, when channel state information (CSI) knowledge is limited at the transmitter, the performance of the BD may be degraded because inter-user interference cannot be completely eliminated. In this paper, we propose an efficient CSI quantization technique for BD precoded systems with limited feedback where users supported by a base station are selected by dynamic scheduling. First, we express the received signal-to-interference-plus-noise ratio (SINR) when multiple data streams are transmitted to the user, and derive a lower bound expression of the expected received SINR at each user. Then, based on this measure, each user determines its quantized CSI feedback information which maximizes the derived expected SINR, which comprises both the channel direction and the amplitude information. From simulations, we confirm that the proposed SINR-based channel quantization scheme achieves a significant sum rate gain over the conventional method in practical MU-MIMO systems.

• Journal of the Korea Convergence Society
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• v.11 no.12
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• pp.15-22
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• 2020

In this paper, we proposed a deep learning based super-resolution method that combines Channel Attention and Spatial Attention feature enhancement methods. It is important to restore high-frequency components, such as texture and features, that have large changes in surrounding pixels during super-resolution processing. We proposed a super-resolution method using feature enhancement that combines Channel Attention and Spatial Attention. The existing CNN (Convolutional Neural Network) based super-resolution method has difficulty in deep network learning and lacks emphasis on high frequency components, resulting in blurry contours and distortion. In order to solve the problem, we used an emphasis block that combines Channel Attention and Spatial Attention to which Skip Connection was applied, and a Residual Block. The emphasized feature map extracted by the method was extended through Sub-pixel Convolution to obtain the super resolution. As a result, about PSNR improved by 5%, SSIM improved by 3% compared with the conventional SRCNN, and by comparison with VDSR, about PSNR improved by 2% and SSIM improved by 1%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.512-518
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• 2002

The real chip and similarity model were used to investigate the thermal behavior and velocity distribution of air from the heat source with the location and the amount of heat experimentally and numerically, and compared. The heat generated in the block is not cooled by convection and show the high temperature by the stagnation of heat flow. After maintaining the high temperature of block by the natural convection, the sudden drop of temperature with the air flow was shown in the channel but the decreasing rate was small with the time. The inward block was effected by infinitesimal air flow generated between block and channel and outward block was effected by the entry condition.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.22-32
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• 2011

In this paper, we first analyze the differences of underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) systems and conventional terrestrial OFDM system, and give a simple introduction of the backgrounds. By considering the real UWA channel environments, the measured channel data is used to generate the UWA channel model and calculate the relative parameters for underwater OFDM systems. Practical least square (LS) based channel estimation with linear interpolation are adopted to obtain the channel state information (CSI) at receiver side. As multi-input multi-output (MIMO) processing techniques, Alamouti code is implemented and evaluated to perform for space time block coding (STBC) and space frequency block coding (SFBC) for UWA OFDM systems with the MIMO configuration of $2{\times}1$, at the same time, $1{\times}2$ maximum ratio combining (MRC) is performed for the purpose of comparison. The simulation results show that, with perfect channel estimation, SFBC failed to work duo to the serious frequency selectivity of UWA channel environments. When the practical channel estimation is applied, in the case of STBC, the proposed 4-column pilot pattern gives better performance about 7dB than SISO system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.10
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• pp.2645-2652
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• 1996

In this paper wepropose a sub-block retransmission scheme for ARQ and hybrid ARQ schemes. When the cannel is quiet the sub-block retransmission scheme behaves like a conventional ARQ or hybrid ARQ scheme. As the channel is becoming noisy, the data block is dvided into small sub-blocks for transmission. Each sub-block is encoded for error control by an apprpriate shortened code and the code length of the shortened code is being adaptive to the corresponding channel BER. the reeived block is checked for errors sub-block by sub-block. The propsoed sub-block retransmission scheme provides improved throughput over conventional schemes by retransmitting only the naked sub-blocks in the occurrence of errors. An example of transferring ATM cells is considered for simulation.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.1215-1218
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• 1998

본 논문은 Digital Audio Compression(AC-3) Standard 인 A-52를 기반으로 하였으며 Borland C++3.1 Compiler를 사용하여 AC-3 Decoding Algorithm 구현하였다. Input Stream은 DVD VOB File에서 AC-3 Stream만을 분리하여 사용하며 최종 출력은 16 Bit PCM File이다. AC-3의 Frame구조는 Synchronization Information, Bit Stream Information, Audio Block, Auxiliary Data, Error Check로 구성된다. Aduio Block 은 모두 6개의 Block으로 나뉘어져 있다. BSI와 Side Information을 참조하여 Exponent를 추출하여 Exponent Strategy에 따라 Exponent를 복원한다. 복원된 Exponent 정보를 이용하여 Bit Allocation을 수행하여 각각의 Mantissa에 할당된 Bit수를 계산하고 Stream으로부터 Mantissa를 추출한다. Coupling Parameter를 참조하ㅕ Coupling Channel을 Original Channel로 복원시킨다. Stereo Mode에 대해서는 Rematrixing을 수행한다. Dynamic Range는 Mantissa와 Exponent의 Magnitude를 바꾸는 것으로 선택적으로 사용할 수 있다. Mantissa와 Exponent를 결합하여 Floating Point coefficient로 만든 후 Inverse Transform을 수행하면 PCM Data를 얻을 수 있다. PC에서 듣기 위해서는 Multi Channel을 Stereo나 Mono로 Downmix를 수행한다. 이렇게 만들어진 PCM data는 PCM Data를 재생하는 프로그램으로 재생할 수 있다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.923-930
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• 2002

Cooling characteristics of a parallel channel with protruding heat sources using convection and conduction heat transfer are studied numerically. A two-dimensional model has been developed for numerical prediction of transient, compressible, viscous, laminar flow, and conjugate heat transfer between parallel plates with uniform block heat sources. The finite volume method is used to solve the problem. The assembly consists of two channels formed by two covers and one printed circuit board which has three uniform heat source blocks. Six different cooling methods are considered to find out the most efficient cooling method in a given geometry and heat sources. The velocity and temperature fields of cooling medium, the temperature distribution along the block surface, and the maximum temperature in each block are obtained. The results are compared to examine the cooling characteristics of the different cooling methods.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.7
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• pp.592-598
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• 2002

The characteristics of a pulsating flow field from a heated block representing heat-dissipating electronic component in a channel have been numerically investigated. At the channel inlet a pulsating sinusoidal flow is imposed. The Reynolds number based on the channel height (H) is fixed at Re=500, and the forcing frequency is varied in the range of $0\leqSt\leq2$. Numerical results on the time-dependent flow field are obtained and averaged over a cycle of pulsation. The effect of the important governing parameters such as the Strouhal number is investigated in detail. The results indicate that the recirculating flow behind the block is substantially affected by the pulsation frequency. To characterize the periodic vortex shedding due to the inflow pulsation, numerical flow visualizations are carried out.