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Yongjoo Chung,Hugon Kim 한국경영과학회 2010 Management Science and Financial Engineering Vol.16 No.3
In this study, we present the exact methods of transforming the continuous solutions into the discrete ones for two types of bit?loading problem, marginal adaptive (MA) and rate adaptive (RA) problem, in multicarrier communication systems. While the computational complexity of existing solution methods for discrete optimal solutions depends on the number of bits to be assigned ( R ), the proposed method determined by the number of subcarriers ( N ), making ours be more efficient in most cases where R is much larger than N . Furthermore our methods have some strength of their simpler form to make a practical use.
Chung, Yongjoo,Paik, Chunhyun,Kim, Young Jin Elsevier 2019 International journal of greenhouse gas control Vol.81 No.-
<P><B>Abstract</B></P> <P>It is widely acknowledged that the power generation sector is a major source of greenhouse gas emissions. Especially, carbon dioxide emissions from the coal-fired power plant fleet are estimated to be 8.5 Giga tons in 2010 accounting for one-quarter of the global anthropogenic carbon emissions. It has often been claimed that the power plants retrofit may be considered one of the most promising emissions reduction alternatives. This study presents a noble approach to modeling the power plant retrofit based on the bottom-up formulation of OSeMOSYS, which provides a wide range of flexibility in energy systems modeling. The proposed approach has been demonstrated for the Korean electricity sector. The optimal solutions for the schedule of power plants retrofit have been obtained, and the effect of retrofit options on greenhouse gas emissions and associated costs has been further examined. It is shown that the power plants retrofit can be highly cost-effective for emissions reduction from the power generation sector. The proposed approach to retrofit modeling may contribute to attaining a deeper understanding on the analysis of power plants retrofit.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Modeling approach to power plants retrofit is proposed and the corresponding OSeMOSYS code is also developed. </LI> <LI> The applicability of the proposed approach is demonstrated with coal-fired power plants retrofit of the Korean electricity sector. </LI> <LI> It is shown that power plants retrofit may be considered one of the most promising mitigation measures for the power generation sector. </LI> </UL> </P>
연속 잡음 음성 인식을 위한 다 모델 기반 인식기의 성능 향상에 대한 연구
정용주(Yongjoo Chung) 한국음성학회 2008 음성과학 Vol.15 No.2
Recently, the multi-model based speech recognizer has been used quite successfully for noisy speech recognition. For the selection of the reference HMM (hidden Markov model) which best matches the noise type and SNR (signal to noise ratio) of the input testing speech, the estimation of the SNR value using the VAD (voice activity detection) algorithm and the classification of the noise type based on the GMM (Gaussian mixture model) have been done separately in the multi-model framework. As the SNR estimation process is vulnerable to errors, we propose an efficient method which can classify simultaneously the SNR values and noise types. The KL (Kullback-Leibler) distance between the single Gaussian distributions for the noise signal during the training and testing is utilized for the classification. The recognition experiments have been done on the Aurora 2 database showing the usefulness of the model compensation method in the multi-model based speech recognizer. We could also see that further performance improvement was achievable by combining the probability density function of the MCT (multi-condition training) with that of the reference HMM compensated by the D-JA (data-driven Jacobian adaptation) in the multi-model based speech recognizer.
정용주(YongJoo Chung) 한국경영과학회 2009 經營 科學 Vol.26 No.3
This study deals with the location management in WCDMA (Wideband Code Division Multiple Access) networks. The new location management method is the one of the many techniques used to provide the packet switched (PS) services effectively in WCDMA networks. WCDMA introduces RA (routing area) for the PS services in addition to LA (location area) for the circuit switched (CS) services. WCDMA system also adopts the cooperative paging and the combined area update which are to decrease signaling traffic using the PS network resources for the CS services. Considering the characteristics of the WCDMA networks, this study formulate into the mathematical programming problem for the location management. Rather than the existing researches which consider the single MSC/SGSN networks, we deal with the multi MSC/SGSN networks, where both MSC area and SGSN area should be determined as well. Fairness between traffic loads of MSC/SGSN and the system cost incurred to MSC/SGSN are also incorporated into our model, which make the model more realistic. We propose greedy algorithms for the problems, which consists of the merger of two neighboring areas and the movement of an area. Extensive experiment has been done based on the realistic problem examples. Followed by the analysis of parameter effect on the final solutions and the quality of final solutions obtained by our greedy algorithms. Our proposed model and analysis result can be used to determine WCDMA system areas and to predict the system performance measures by the determination.