• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2014.11a
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• pp.252-253
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• 2014

최근 채널 효율을 향상시키기 위하여 다중안테나(MIMO, multi-input multi-output) 기술이 연구되고 있다. 다중안테나 기술은 송 수신 안테나 개수를 증가시켜 수신 성능을 향상시키고 대역 효율을 향상시키지만 송신 안테나 개수를 늘려야만 대역 효율을 증가시킬 수 있으므로 기존 방송 시스템에 적용하기에는 비용이 많이 드는 단점이 있다. 이에 본 논문은 방송 시스템에 적합한 SIMO(single-input multi-output) 시스템에 FTN(faster than Nyquist)을 적용하여 대역 효율을 증가시키고 수신 성능을 향상시키고자 한다. 또한 MRC(maximum ratio combining) 및 경판정(hard decision)을 적용하여 수신 안테나 개수에 따른 수신 성능을 컴퓨터 실험을 통하여 알아본다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2005.11a
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• pp.95-98
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• 2005

이 논문에서는 동일채널 간섭이 존재하는 채널 환경에서 OFDM(Orthogonal Frequency Division Multiplexing) 시스템의 수신 다이버시티 결합 방법을 제시한다. 제시된 방법에서는 각 수신 안테나로부터의 수신 신호를 주파수 영역에서 부반송파 단위로 결합하며, 잡음과 간섭 전력을 고려한 MRC(Maximum Ratio Combining)를 적용한다. 잡음과 간섭 전력은 채널의 제한된 지연확산에 기인하는 주파수 대역에서의 상관특성(coherency)을 이용하여 인접한 몇 개의 부채널에 대해 잡음과 간섭 전력의 평균을 취함으로써 더 정확한 추정치를 얻는다. IEEE 802.11a 무선 LAN 규격에서 모의실험 결과 제안방법은 기존 방시에 비해 SNR을 2-4 dB 개선하였으며, 정확하게 SINR을 추정한 경우에 대해 1 dB 이내로 접근하는 결과를 나타내었다.

• Journal of information and communication convergence engineering
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• v.11 no.4
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• pp.223-228
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• 2013

Cognitive radio has been recently considered a promising technology to improve spectrum utilization by enabling secondary access to licensed bands that are not used by primary users temporarily or spatially. A prerequisite to this secondary access is the lack of interference to the primary system. This requirement makes spectrum sensing a key process for cognitive radio. In this study, we consider amplify and forward (AF)-based cooperative spectrum sensing for cognitive radio networks where multiple relay nodes are utilized to amplify and forward the primary user signal for better spectrum sensing, and maximum ratio combining is used for fusion detection by a cognitive coordinator. Further, the detection probability and the bit error rate of AF-based cooperative spectrum sensing are analyzed in fading multiple cognitive relay channels. The simulation results show that the AF-based cooperative spectrum sensing scheme outperforms the conventional scheme.

• Journal of the Institute of Convergence Signal Processing
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• v.10 no.2
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• pp.136-140
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• 2009

The performances of M-ary signals using L-branch maximum ratio combining (MRC) diversity reception in correlated Nakagami fading channels are derived theoretically. The coherent reception of M-ary differential phase shift keying (MDPSK), phase shift keying (MPSK), and quadrature amplitude modulation (MQAM) is considered. It is assumed that the fading parameters in each diversity branch are identical. The general formula for evaluating symbol error rate (SER) of M-ary signals in the independent branch diversity system is presented using the integral-form expressions. Until now, results did not extend to the various M-ary case for a coherent reception. The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.1250-1252
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• 2009

Cellular 망에서의 무선통신은 일반적으로 하나의 송수신안테나를 사용하거나 둘 이상의 송수신 안테나를 사용한다. MRRC(Maximum Ratio Receiver Combining)기법의 경우 여러 안테나를 사용하여 신호룰 수신하는 시스템이며, 이 경우 각 안테나의 채널에 따른 이득과 손실을 고려한 수신기가 제안되었다. Cellular model에서의 SINR 값에 따른 추정을 통해 최적 결합 기법을 적용한 MRRC 수신기를 사용하는 경우, 이에 따른 Cellular modeling을 이용하여 시스템 레벨에서의 MRRC 기법과 Optimum-MRRC 기법을 도입으로 인한 성능의 개선을 알 수 있다.

• International Journal of Contents
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• v.2 no.1
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• pp.29-33
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• 2006

The common-source low noise amplifier(LNA) with inductive degeneration using a genetic algorithm is designed and tested for a down converter in an industrial, scientific and medical (ISM) band application and a wireless broadband internet service (WiBro). The genetic algorithm optimizes the reflection coefficients to be well matched the input and output ports between multistage transistor amplifiers, and it generates low voltage standing wave ratio as well as gain flatness of the amplifier. The stability and the gain flatness of the LNA have been improved by combining the matching circuits and the series feedback microstrip lines with inductive degeneration at common-source port. In the frequency range of ISM band and WiBro application operating at $2.3GHz{\sim}2.5GHz$, the measured power gain and maximum voltage standing wave ratio (VSWR) of the LNA are $41{\pm}0.5dB$ and 1.3, and the noise figure of the LNA is lower than 0.85dB. The above results are agreed well with the theoretical values of the amplifiers.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.7
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• pp.1299-1305
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• 2017

In this paper, we consider a beamforming game between the transmitters in a two-user multiple-input single-output interference channel using limited feedback and investigate how each transmitter is able to find a modified strategy from the quantized channel state information (CSI). In the beamforming game, each of the transmitters (i.e., a player) tries to maximize the achievable rate (i.e., a payoff function) via a proper beamforming strategy. In our case, each transmitter's beamforming strategy is represented by a linear combining factor between the maximum ratio transmission (MRT) and the zero forcing (ZF) beamforming vectors, which is the Pareto optimal achieving strategy. With the quantized CSI, the transmitters' strategies may not be valid because of the quantization errors. We propose a modified solution, which takes into account the effects of the quantization errors.

• Structural Engineering and Mechanics
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• v.90 no.1
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• pp.27-40
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• 2024

The prediction of VIV amplitude is essential for the design and fatigue life estimation of steel tubes in tubular transmission towers. Limited to costly and time-consuming traditional experimental and computational fluid dynamics (CFD) methods, a machine learning (ML)-based method is proposed to efficiently predict the VIV amplitude of steel tubes in transmission towers. Firstly, by introducing the first-order mode shape to the two-dimensional CFD method, a simplified response analysis method (SRAM) is presented to calculate the VIV amplitude of steel tubes in transmission towers, which enables to build a dataset for training ML models. Then, by taking mass ratio M^*, damping ratio ξ, and reduced velocity U^* as the input variables, a Kriging-based prediction method (KPM) is further proposed to estimate the VIV amplitude of steel tubes in transmission towers by combining the SRAM with the Kriging-based ML model. Finally, the feasibility and effectiveness of the proposed methods are demonstrated by using three full-scale steel tubes with C-shaped, Cross-shaped, and Flange-plate joints, respectively. The results show that the SRAM can reasonably calculate the VIV amplitude, in which the relative errors of VIV maximum amplitude in three examples are less than 6%. Meanwhile, the KPM can well predict the VIV amplitude of steel tubes in transmission towers within the studied range of M^*, ξ and U^*. Particularly, the KPM presents an excellent capability in estimating the VIV maximum amplitude by using the reduced damping parameter S_G.

• Journal of the Korean Solar Energy Society
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• v.29 no.3
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• pp.19-27
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• 2009

In this study, Urban Climate Simulation was performed by 3-Dimensional Urban Canopy Model. The characteristics of urban climate were analyzed combining artificial land coverage, building size, heat production from the air conditioning and topographic conditions as physical variables which affects urban climate characteristics. The results are as follows. (1) The aspects of the urban climatal change is derived to be related to the combination of the building coverage ratio, building height and shading area. According to the building height, the highest temperature was increased by $2.1^{\circ}C$ from 2-story to 5-story building and the absolute humidity by 2.1g/kg maximum and the wind velocity by 1.0m/s was decreased from 2-story to 20-story building. (2) Whole heat generation was influenced by the convective sensible heat at the lower building height and by the artificial heat generation at the higher one over 20-story building influence to some extent of the building coverage ratio. The effect of the altitude is not more considerable than the other variables as below $1^{\circ}C$ of the air temperature. In the last, deriving the combination of building coverage and building height is needed to obtain effectiveness of the urban built environment planning at the point of the urban climate. These simulation results need to be constructed as DB which shows urban quantitative thermal characters by the urban physical structure. These can be quantitative base for suggesting combinations of the building and urban planning features at the point of the desirable urban thermal environment as well as analyzing urban climate phenomenon.

• Journal of Korean Society on Water Environment
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• v.18 no.4
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• pp.379-386
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• 2002

In this study, estimation model for iron compound originated from upflow, anaerobic fixed bed reactor, which treats sewage domestic wastewater, was developed. The estimation model was formulated by a mathematical expression which was based on the mass balance. Below the HRT of 60 minute, sulfide concentration combining with iron $FeS_2$ is the highest because the maximum sulfate consumption rate $V_{maxS}$ and half-saturation constant of sulfate $K_{mS}$ exert an important effect on the estimation model as temperature was increased. But increment of $FeS_2$ concentration is weakened above the HRT of 60 minutes and represent the lowest value at the HRT of 108 minutes. It implies that liquid phase distribution ratio of sulfide ${\alpha}r$ becomes lower as temperature was increased. While phosphorus concentration combining with iron $Fe_3(PO_4)_3$ is increased as HRT and temperature are increased, which is affected by phosphorus removal rate constant $k_p$. As the result of estimating the iron concentrations of corrosion by the model, the concentration of iron corrosion is higher than any other at the HRT of 108 minute and $20^{\circ}C$. The predicted values were compared with measured ones at different HRT(13.5, 27, 54, 108 min) and temperature(20, 25, $30^{\circ}C$). The experimental data could be fitted with the simulated curves. Therefore, the mathematical expression could be applicable to design full-scale wastewater treatment plants.