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Weighted Sum MSE Minimization under Per-BS Power Constraint for Network MIMO Systems
Haewook Park,Seok-Hwan Park,Han-Bae Kong,Inkyu Lee IEEE 2012 IEEE COMMUNICATIONS LETTERS Vol.16 No.3
<P>We study joint processing (JP) for network MIMO systems where base stations exchange the user's message and channel state information under per-BS power constraint. In this letter, we propose a weighted sum mean square error (WS-MSE) minimization algorithm for the JP systems by considering the channel gain as the weight factor in the MSE metric. To efficiently solve the formulated WS-MSE problem, an alternating optimization method which iteratively finds a local optimal solution is employed in our algorithm. The simulation results confirm that the proposed algorithm provides the sum rate performance close to the near-optimal gradient ascent approach and outperforms conventional schemes. In addition, we also propose a modified WS-MSE design which is robust to channel mismatch caused by channel estimation and feedback errors.</P>
MMSE-Based Filter Designs for Cognitive Multiuser Two-Way Relay Networks
Haewook Park,Changick Song,Hoon Lee,Inkyu Lee IEEE 2015 IEEE Transactions on Vehicular Technology VT Vol.64 No.4
<P>This paper considers cognitive multiuser two-way relay networks (MU-TRNs) where multiple secondary users (SUs) concurrently exchange their data with other SUs with an aid of a two-way relay in licensed primary networks. In this paper, we particularly focus on linear relay filter designs that effectively minimize the mean square error of SUs while providing a certain level of quality of service for the primary network. To this end, we first propose an iterative algorithm that identifies a solution based on an alternating optimization technique. Then, a closed-form relay filter design is presented, which employs a high signal-to-noise ratio approximation to reduce the computational complexity. Through the simulation results, we confirm that the proposed closed-form relay filter design outperforms conventional approaches and provides the performance close to the proposed iterative algorithm with much reduced complexity.</P>
Park, Haewook,Lee, Seungeun,Ko, Guen Bae,Lee, Jae Sung Institute of Physics in association with the Ameri 2018 Physics in medicine & biology Vol.63 No.24
<P>Coincidence resolving time (CRT) is one of the most important physical-performance measures for positron emission tomography (PET), as reconstruction with accurate time-of-flight information enhances the lesion detectability in patient studies. Accordingly, various PET detector designs and high-performance front-end readout circuits have been actively investigated to improve timing performance. The resulting PET detectors are often evaluated using multichannel waveform digitizers for versatile data analysis of the output signals. However, we have found that inappropriate data acquisition (DAQ) using a multichannel waveform digitizer based on the domino-ring-sampler 4 (DRS4) chip can lead to a considerable error when determining CRT. To address this issue, we performed CRT measurements using a pair of Hamamatsu R9800 photomultiplier tube based PET detectors. Then, considering intra- and inter-chip sampling, we employed four different combinations of input channels into the CAEN DT5742B waveform digitizer and obtained 2D CRT maps according to the leading-edge discriminator threshold for assessing each DAQ scheme. The intra-chip CRT measurement exhibited unusual streak patterns in the 2D CRT map and yielded the artificially-low CRT information in PET detector pairs, whereas the inter-chip CRT measurement provided the reliable estimation of timing resolution. Further, we could prevent the high-frequency signal crosstalk among input channels within the DRS4 chip using the inter-chip CRT measurement. We expect that our findings will also be useful for achieving the reliable CRT measurements when using other single-chip-based multichannel waveform digitizers.</P>
저압 EGR 시스템을 이용한 V6 3.0ℓ엔진의 연비 최적화 개발
이해욱(Haewook Lee),조청훈(Chunghoon Jo),남기훈(Kihoon Nam),이세영(Seyoung Lee),이은현(Eunhyun Lee) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
As the markets require more environmentally friendly and high fuel consumption vehicle, we have to satisfy bilateral target. Though many new after-treatment techniques like LNT, SCR are investigated to meet both strong emission regulations and low fuel consumption, high cost of these techniques should be solved to adopt widely. This paper describes how to optimize the dual loop EGR as a tool to reduce CO2 emission of a HSDI diesel engine in the passenger car application. Focus is not only on the optimization to obtain the maximum CO2 reduction but also on how to assess and overcome various side effects. As a result of careful optimization, as much as 6% CO2 reduction was achieved by introduction of low pressure EGR loop, maintaining the same boundary conditions as those with high pressure EGR loop only. Not only the dual EGR system but also further improvement was applied such as combustion improvement, friction reduction and many others to achieve as much as 20% total CO2 reduction. The dual loop EGR was proven to be an effective solution to reduce CO2 and therefore it is considered to be one of the core technologies in the passenger diesel applications of Hyundai-Kia Motors to meet the future CO2 regulation.