• ETRI Journal
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• 제33권1호
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• pp.1-5
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• 2011

Downlink transmit power allocation schemes are proposed for soft fractional frequency reuse (FFR) in loose and tightly coordinated systems. The transmit powers are allocated so that the loss of spectral efficiency from the soft FFR is minimized, and the required cell edge user throughput is guaranteed. The effect of the soft FFR on spectral efficiency is evaluated depending on the power allocation schemes and the number of subbands. Results show that the loss of spectral efficiency from the soft FFR can be reduced by configuring an appropriate number of subbands in the loosely coordinated systems. In tightly coordinated systems, results show that the loss of spectral efficiency can be minimized regardless of the number of subbands due to its fast coordination.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.259-260
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• 2008

This paper presents fractional frequency reuse (FFR) with sub-channel borrowing to improve spectral efficiency of the wireless broadband (WiBro) system. FFR has constraints on usable sub-channels to balance the interference and cell capacity. Our FFR with sub-channel borrowing allows use of the dedicated sub-channels assigned to neighboring cells. Simulation results show that the proposed FFR with sub-channel borrowing improves the performance of the WiBro system.

• 한국통신학회논문지
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• 제37권7B호
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• pp.505-516
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• 2012

4G 이동통신 핵심 기술 중 펨토셀 시스템 실제 구현 시에 매크로셀과 펨토셀이 동일 주파수를 사용하면 동일채널 간섭이발생되기 때문에 이를 해결하기 위해 주파수 자원을 서로 다르게 할당하는 간섭 회피 기술이 필요하다. 본 논문에서는 매크로셀과 펨토셀 간의 기존 자원 할당 방식을 분석하여, 문제점을 도출하고 이를 기반으로, 본 논문에서는 FFR (Fractional Frequency Reuse) 기반의 펨토셀이 분포된 환경에서 셀 용량을 증가시키고 주파수 효율을 최대화하기 위한 적응 주파수 자원 할당 방식에 대해 제안하였다. 모의 실험 수행 결과, 기존 방식과 비교하여 SINR (Signal to Interference Noise Ratio) 분포에서는 근소한 개선 효과를 보였고, 전체 셀 용량에서는 큰 개선 효과를 보여주었다. 본 논문의 현실적인 구현을 위해 펨토 및매크로 유저 분포의 검출 방안 등에 대한 연구 및 전력 제어나 다중 신호 간섭 검출을 통해 간섭을 완화하는 방안 과의 결합방식 들에 대한 연구가 향후 추가 적으로 더 진행 되어야 할 것으로 생각 된다.

• Journal of Chest Surgery
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• 제55권6호
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• pp.442-451
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• 2022

Background: This meta-analysis was conducted to evaluate the effect of fractional flow reserve (FFR) on clinical outcomes after coronary artery bypass grafting (CABG). Methods: Five online databases were searched for studies that (1) enrolled patients who underwent isolated CABG or CABG with aortic valve replacement and (2) demonstrated the effect of an FFR-guided strategy on major adverse cardiac events (MACE) after surgery based on a randomized controlled trial or adjusted analysis. MACE included cardiac death, acute myocardial infarction (MI), and repeated revascularization. The primary outcomes were all MACE outcomes and a composite of all-cause death and MI, and the secondary outcomes were the individual MACE outcomes. Publication bias was assessed using a funnel plot and the Egger test. Results: Six articles (3 randomized and 3 non-randomized studies: n=1,027) were selected. MACE data were extracted from 4 studies. The pooled analyses showed that the risk of MACE was not significantly different between patients who underwent FFR-guided CABG and those who underwent angiography-guided CABG (hazard ratio [HR], 0.80; 95% CI, 0.57-1.12). However, the risk of the composite of death or MI was significantly lower in patients undergoing FFR-guided CABG (HR, 0.62; 95% CI, 0.41-0.94). The individual MACE outcomes were not significantly different between FFR-guided and angiography-guided CABG. Conclusion: FFR-guided CABG might be beneficial in terms of the composite outcome of death or MI compared with angiography-guided CABG although data are limited.

• 전자공학회논문지C
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• 제36C권4호
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• pp.1-16
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• 1999

본 논문에서는 테스트 생성 과정에서 자주 사용되는 임계의 확장 개념으로 임계-쌍을 정의한다. 그리고 임계의 특성을 나타내는 요소로서 임계성, 임계율, 임계설정율 등을 정의한다. 이 요소들을 이용하여 임계-쌍의 사용이 단일 임계의 사용보다 더 효율적이라는 것을 입증하고, FFR에서의 테스트 패턴 생성 시에 임계값에 대한 평가 회수, 경로선의 탐색 회수 및 생성 시간에서 더 효율적이라는 것을 보여준다. 시뮬레이션을 통해서 ISCAS85 벤치마크 테스트 회로에 대한 실험 결과를 비교 분석한다.

• 한국통신학회논문지
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• 제35권2B호
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• pp.345-351
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• 2010

DMB 2.0, Mobile IPTV 등 방송과 통신을 융합하는 서비스에 대한 관심이 최근 급증하고 있다. 유니캐스트는 수용량 제한 및 열악한 수신환경으로 인해 방송서비스를 하기 힘들기 때문에 WiBro는 MBS(Multicast Broadcast Service)를 제공하여 방송서비스를 지원한다. MBS는 MBS 존에 속한 모든 기지국이 방송서비스를 요구하는 모든 사용자에게 동일한 콘텐츠를 동시에 전송하는 방식이다. 단말은 다수의 기지국으로부터 자원을 받기 때문에 Macro diversity로 인해 SINR을 높일 수 있지만 존 외곽 셀의 경우 간섭으로 인해 여전히 SINR이 매우 낮으므로 보완책이 필요하다. 본 논문에서는 MBS 존의 내부와 외부의 성능차이를 줄이면서 전체적으로는 높은 MCS를 사용하여 전송률을 높이는 방안으로 MIMO(Multiple Input Multiple Output) STBC(Space Time Block Coding), Relay, FFR(Fractional Frequency Reuse)을 도입한다. 기본적인 시뮬레이션 환경은 SISO(Single Input Single Output)로 가정하고 transparent 중계기, MBS에서 적용가능한 FFR로 시나리오를 나누어 SISO와 MIMO STBC 환경에서 각각 성능을 평가하고 비교 분석한다.

• IMMUNE NETWORK
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• 제7권4호
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• pp.197-202
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• 2007

Background: Immunomodulators enhancing MHC-restricted antigen presentation would affect many cellular immune reactions mediated by T cells or T cell products. However, modulation of MHC-restricted antigen presentation has received little attention as a target for therapeutic immunoregulation. Here, we report that lectins isolated from mushroom Fomitella fraxinea enhance MHC-restricted exogenous antigen presentation in professional antigen presenting cells (APCs). Methods: Lectins, termed FFrL, were isolated from the carpophores of Fomitella fraxinea, and its effects on the class I and class II MHC-restricted presentation of exogenous ovalbumin (OVA) were examined in mouse dendritic cells (DCs) and mouse peritoneal macrophages. The effects of FFrL on the expression of total MHC molecules and the phagocytic activity were also examined in mouse DCs. Results: DCs cultured in the presence of FFrL overnight exhibited enhanced capacity in presenting exogenous OVA in association with class I and class II MHC molecules. FFrL increased slightly the total expression levels of both class I (H-$2K^b$) and class II (I-$A^b$) MHC molecules and the phagocytic activity of DCs. Antigen presentation-enhancing activity of FFrL was also observed in macrophages isolated from mouse peritoneum. Conclusion: Lectins isolated from the carpophores of Fomitella fraxinea increase MHC-restricted exogenous antigen presentation by enhancing intracellular processing events of phagocytosed antigens.

• International Journal of Computer Science & Network Security
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• 제22권7호
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• pp.199-205
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• 2022

The extensive growth in data rate demand by the smart gadgets and mobile broadband application services in wireless cellular networks. To achieve higher data rate demand which leads to aggressive frequency reuse to improve network capacity at the price of Inter Cell Interference (ICI). Fractional Frequency Reuse (FFR) has been recognized as an effective scheme to get a higher data rate and mitigate ICI for perfect geometry network scenarios. In, an irregular geometric multicellular network, ICI mitigation is a challenging issue. The purpose of this paper is to develop distributed dynamic power allocation scheme for FFR based on game theory to mitigate ICI. In the proposed scheme, each cell region in an irregular multicellular scenario adopts a self-less behavior instead of selfish behavior to improve the overall utility function. This proposed scheme improves the overall data rate and mitigates ICI.

• International Journal of Computer Science & Network Security
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• 제22권4호
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• pp.292-298
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• 2022

Femtocell networks can be a potential method for increasing the capacity of LTE networks, especially in indoor areas. However, unplanned deployment of femtocells results in co-tier interference and cross-tier interference problems. The interference reduces the advantages of implementing femtocell networks to a certain extent. The notion of Fractional Frequency Reuse (FFR) is proposed in order to reduce the impact of interference on the system's performance. In this paper, a dynamic approach for efficiently partitioning the spectrum is suggested. The goal is to enhance the capacity of femtocells, which will improve the performance of the system. The suggested strategy allocates less resources to the macrocell portion of the network, which has a greater number of femtocells deployed to maximize the utilization of available resources for femtocell users. The spectrum division would be dynamic. The proposed strategy is evaluated through a simulation using MATLAB tool. In conclusion, the results showed that the proposed scheme has the potential to boost the system's capacity.

• 한국전산유체공학회지
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• 제22권1호
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• pp.15-25
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• 2017

Swirl flow is often found in proximal coronary arteries, because the aortic valves can induce swirl flows in the coronary artery due to vortex formation. In addition, the curvature and tortuosity of arterial configurations can also produce swirl flows. The present study was performed to investigate fractional flow reserve alterations in a post-stenotic distal part due to the presence of pre-stenotic swirl flow by computational fluid dynamics analysis for virtual stenotic models by quantifying fractional flow reserve(FFR). Simplified stenotic coronary models were divided into those with and without pre-stenotic swirl flow. Various degrees of virtual stenosis were grouped into three grades: mild, moderate, and severe, with degree of stenosis of 0 ~ 40%, 50 ~ 60%, and 70 ~ 90%, respectively. In this study, three-dimensional computational hemodynamic simulations were performed under hyperemic conditions in virtual stenotic coronary models by coupling with a zero-dimensional lumped parameter model. The results showed that the influence of pre-stenotic swirl inflow is dominant on FFR alteration in mild stenosis, whereas stenosis is dominant on FFR alteration in moderate/severe stenosis. The decrease in FFR caused by swirl flow is more significant in mild stenosis than moderate/severe stenosis. Biomechanical modeling is useful for clinicians to provide insight for medical intervention strategies. This hemodynamic-based parameter study could play a critical role in the development of a non-invasive imaging-based strategy-support system for percutaneous transluminal angioplasty in cases of mild/moderate stenosis.