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THE m-STEP COMPETITION GRAPHS OF d-PARTIAL ORDERS
Jihoon Choi 충청수학회 2020 충청수학회지 Vol.33 No.1
The notion of m-step competition graph was introduced by Cho et al. in 2000 as an interesting variation of competition graph. In this paper, we study the m-step competition graphs of d-partial orders, which generalizes the results obtained by Park et al. in 2011 and Choi et al. in 2018.
Modified RLS Algorithm and Its Application to Channel Estimation for CDMA Systems
CHOI, Jihoon,JUNG, Young-Ho The Institute of Electronics, Information and Comm 2010 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.93 No.5
<P>A new adaptive algorithm is proposed by introducing some modifications to the recursive least squares (RLS) algorithm. Except for the noise variance, the proposed algorithm does not require any statistics or knowledge of the desired signal, thus, it is suitable for adaptive filtering for channel estimation in code division multiple access (CDMA) systems in cases where the standard RLS approach cannot be used. A theoretical analysis demonstrates the convergence of the proposed algorithm, and simulation results for CDMA channel estimation show that the proposed algorithm outperforms existing channel estimation schemes.</P>
Linear Fresnel Lens for a Solar Cell with above 85% Focal Efficiency
Jihoon Choi,Heeso Noh,Hyeri Jang,Jeong Seok Kang 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.8
We designed a linear Fresnel lens (LFL) for harvesting solar energy. The optimized LFL was fabricated with dimensions of 100 (W) × 100 (H) × 5 (T) mm^3, a focal length of 100 mm, and a fixed pitch size of 500 μm. The maximum focal efficiency is approximately 91%, and the half width at half maximum (HWHM) value of the focus size is approximately 130 μm. We also investigated the robustness of the LFL to changes in the incident angle, draft angle, and detection position. Simulations revealed a focal efficiency above 85% with an incident angle up to 1°, a draft angle up to 10°, and a detection position up to ±10 mm. We fabricated the LFL by using an injection molding process. The fabricated lens had a maximum focal efficiency of approximately 88% and a full width at half max (FWHM) of about 2.5 mm.
Jihoon Kim,Joo Myung Lee,Taek Kyu Park,Jeong Hoon Yang,Young Bin Song,Jin-Ho Choi,Seung-Hyuk Choi,Hyeon-Cheol Gwon,Sang Hoon Lee,Joo-Yong Hahn 대한의학회 2020 Journal of Korean medical science Vol.35 No.1
Background: Although current guidelines recommend noninvasive stress tests prior to elective percutaneous coronary intervention (PCI), it is unknown whether antecedent exercise stress test (EST) affects the outcomes of patients undergoing PCI for stable ischemic heart disease (SIHD). This study aimed to investigate long-term outcomes in patients undergoing elective PCI with or without EST. Methods: We studied 2,674 patients undergoing elective PCI using drug-eluting stents for SIHD. Patients were divided into the 2 groups: the test group underwent EST with a positive result within 180 days prior to PCI (n = 668), whereas the non-test group did not undergo any noninvasive stress tests (n = 2,006). The primary outcome was all-cause death or myocardial infarction (MI). Results: Over 5 years after the index PCI, the risk of all-cause death or MI was significantly lower in the test group than in the non-test group in overall population (3.3% vs. 10.9%; adjusted hazard ratio [HR], 0.34; 95% confidence interval [CI], 0.22–0.55; P < 0.001), and in propensity score-matched population (668 pairs) (3.3% vs. 6.3%; adjusted HR, 0.52; 95% CI, 0.30–0.89; P = 0.018). However, the incidence of any revascularization was similar between the 2 groups in overall (16.7% vs. 16.8%; adjusted HR, 0.99; 95% CI, 0.79–1.25; P = 0.962) and matched population (16.7% vs. 18.3%; adjusted HR, 0.91; 95% CI, 0.70–1.19; P = 0.509). Conclusion: Patients who underwent elective PCI with EST had a reduced risk of all-cause death or MI than those undergoing PCI without stress tests.
On the Calculation of the Maximal MOT Throughput in T-DMB
Jihoon Choi,Donghwan Lee,Jieun Yu,Kyunghwi Kim,Wonjun Lee IEEE 2007 IEEE transactions on consumer electronics Vol.53 No.3
<P>Digital multimedia broadcasting (DMB) is one of burgeoning communication technologies, which can provide audio, video, and data services to mobile terminals using broadcasting infrastructures. Data services in terrestrial- digital multimedia broadcasting (T-DMB) inherently have the disadvantage of retransmitting a lot of data unnecessarily for reliability. This paper proposes a novel optimized transmission policy using segment size and repetition number variability, which maximizes the object- level throughput as well as improves reliability. The theoretical modeling and simulation results demonstrate that our policy provides a throughput gain over the conventional protocol.</P>
Low-Complexity Multiuser MIMO Precoder Design Under Per-Antenna Power Constraints
Choi, Jihoon,Han, Suyong,Joung, Jingon IEEE 2018 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.67 No.9
<P>A new precoder design method is proposed for multi-input multioutput (MIMO) systems with per-antenna power constraints (PAPCs). In the proposed scheme, the optimal zero-forcing (ZF) based precoder maximizing the sum rate is evaluated for MIMO systems under the conventional sum power constraint (SPC), after which a new ZF-based precoder conforming to the PAPCs is designed by finding the linear precoder closest to the optimal ZF-based SPC precoder. Using the proposed design procedure, we derive an iterative algorithm based on the modified Newton's method to construct a PAPC precoder for a multiuser MIMO system. The complexity order of the proposed method is compared with those of the existing precoding schemes, and it is shown through numerical simulations that the proposed PAPC precoder achieves near-optimal performance while reducing the power consumption at macrocell base stations.</P>
Wireless Powered Information Transfer Based on Zero-Forcing for Multiuser MIMO Systems
Choi, Jihoon,Song, Choonggeun,Joung, Jingon IEEE 2018 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.67 No.9
<P>A zero-forcing (ZF)-based transmission method is proposed for a wireless powered communication network (WPCN) with multiuser multi-input multi-output (MU-MIMO) channels. We formulate the max–min user rate optimization problem based on ZF-based uplink transmission, under the transmit power constraints determined by the downlink power transfer, and derive a Newton-like iterative algorithm to find the optimal solution of the proposed problem. Using the proposed ZF-based method, we design a downlink energy beamformer, and optimize the uplink power allocation vector, precoder, and combiner in terms of the max–min user rate for a MU-MIMO WPCN system. Numerical simulations show that the proposed method provides at least 3 dB signal-to-noise ratio gain compared to the conventional transmission schemes for WPCN. Moreover, through complexity analysis and simulations, it is shown that the proposed method can reduce at least 92% of the computation load in terms of runtime with moderate achievable rate loss, compared to the optimal method obtained by the interior-point method.</P>