• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2153-2169
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• 2012

Femtocells provide high quality indoor communications with low transmit power. However, when femtocells are applied in cellular systems, a co-channel interference problem between macrocells and femtocells occurs because femtocells use the same spectrum as do the macrocells. To solve the co-channel interference problem, a previous study suggested a resource allocation scheme in LTE cellular systems using FFR. However, this conventional resource allocation scheme still has interference problems between macrocells and femtocells near the boundary of the sub-areas. In this paper, we define an optimization problem for resource allocation to femtocells and propose a femtocell resource allocation scheme to solve the optimization problem and the interference problems of the conventional scheme. The evaluation of the proposed scheme is conducted by System Level Simulation while varying the simulation environments. The simulation results show that the proposed scheme is superior to the conventional scheme and that it improves the overall performance of cellular systems.

• ETRI Journal
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• 제43권5호
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• pp.787-798
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• 2021

This paper applies learning automata to improve the performance of a Q-learning based random access channel (QL-RACH) scheme in a cellular machine-to-machine (M2M) communication system. A prioritized learning automata QL-RACH (PLA-QL-RACH) access scheme is proposed. The scheme employs a prioritized learning automata technique to improve the throughput performance by minimizing the level of interaction and collision of M2M devices with human-to-human devices sharing the RACH of a cellular system. In addition, this scheme eliminates the excessive punishment suffered by the M2M devices by controlling the administration of a penalty. Simulation results show that the proposed PLA-QL-RACH scheme improves the RACH throughput by approximately 82% and reduces access delay by 79% with faster learning convergence when compared with QL-RACH.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2009년도 춘계학술발표대회
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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.

• ETRI Journal
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• 제44권1호
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• pp.155-167
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• 2022

The Internet of Things (IoT) is a new paradigm that connects physical and virtual objects from various domains such as home automation, industrial processes, human health, and monitoring. IoT sensors receive information from their environment and forward it to their neighboring nodes. However, the large amounts of exchanged data are vulnerable to attacks that reduce the network performance. Most of the previous security methods for IoT have neglected the energy consumption of IoT, thereby affecting the performance and reducing the network lifetime. This paper presents a new multistep routing protocol based on cellular learning automata. The network lifetime is improved by a performance-based adaptive reward and fine parameters. Nodes can vote on the reliability of their neighbors, achieving network reliability and a reasonable level of security. Overall, the proposed method balances the security and reliability with the energy consumption of the network.

• 한국영양학회:학술대회논문집
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• 한국영양학회 2003년도 연합학술대회
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• pp.132.1-132.1
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• 2003

• Asian Pacific Journal of Cancer Prevention
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• 제15권17호
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• pp.7487-7488
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• 2014

• 대한흉부심장혈관외과학회:학술대회논문집
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• 대한흉부외과학회 1993년도 제25차년차학술대회 및 총회
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• pp.132-132
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• 1993

• Molecules and Cells
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• 제45권6호
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• pp.362-364
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• 2022

• 생물정신의학
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• 제8권1호
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• pp.3-19
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• 2001

Recent basic and clinical studies demonstrate a major role for neural plasticity in the etiology and treatment of depression and stress-related illness. The neural plasticity is reflected both in the birth of new cell in the adult brain(neurogenesis) and the death of genetically healthy cells(apoptosis) in the response to the individual's interaction with the environment. The neural plasticity includes adaptations of intracellular signal transduction pathway and gene expression, as well as alterations in neuronal morphology and cell survival. At the cellular level, repeated stress causes shortening and debranching of dendrite in the CA3 region of hippocampus and suppress neurogenesis of dentate gyrus granule neurons. At the molecular level, both form of structural remodeling appear to be mediated by glucocorticoid hormone working in concert with glutamate and N-methyl-D-aspartate(NMDA) receptor, along with transmitters such as serotonin and GABA-benzodiazepine system. In addition, the decreased expression and reduced level of brain-derived neurotrophic factor(BDNF) could contribute the atrophy and decreased function of stress-vulnerable hippocampal neurons. It is also suggested that atrophy and death of neurons in the hippocampus, as well as prefrontal cortex and possibly other regions, could contribute to the pathophysiology of depression. Antidepressant treatment could oppose these adverse cellular effects, which may be regarded as a loss of neural plasticity, by blocking or reversing the atrophy of hippocampal neurons and by increasing cell survival and function via up-regulation of cyclic adenosine monophosphate response element-binding proteins(CREB) and BDNF. In this article, the molecular and cellular mechanisms that underlie stress, depression, and action of antidepressant are precisely discussed.

• 한국통신학회논문지
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• 제38B권4호
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• pp.229-239
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• 2013

최근 셀룰라 네트워크의 주파수 효율을 높이고 다양한 사용자 경험을 제공하기 위하여 단말간 직접 통신(device-to-device, D2D) 기술이 주목을 받고 있다. 본 논문에서는 D2D 관련 표준 및 기존 연구에 대한 선행 조사를 통하여 D2D 통신이 가지는 많은 장점들과 이 장점들이 제대로 실제 시스템에 적용되기 위해서 해결되어야 할 주요 문제점들에 대해서 살펴본다. 특히, 가장 중요시 되는 셀룰라 링크와 D2D 링크간의 간섭 이슈를 고려하여 5가지 D2D 자원할당 및 간섭제어 시나리오에 대해 시스템 레벨 시뮬레이션을 수행한다. 성능 분석 결과, D2D를 사용할 경우에 주파수 재사용 및 데이터 오프로딩(off-loading) 효과로 인해 전체 셀 용량 및 D2D 사용자 전송률이 현저히 증가하며, 이들 성능을 최대화하는 최적 D2D 통신 허용 반경값이 존재함을 알 수 있다.