• 천문학회지
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• 제28권1호
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• pp.71-75
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• 1995

In the previous work we made a long term evolution code for the central black hole in an active galactic nucleus under the assumption that the Blandford-Znajek process is the source of the emission. Using our code we get the evolution of the angular velocity of the precession for a supermassive black hole. We consider a hole at the center of an axisymmetric, ellipsoidal galactic nucleus. Our numerical results show that, only for the cases such that the stellar density or the mass of the black hole is large enough, the precession of the black hole - presumably the precession of the galactic jet - is interestingly large.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.5-6
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• 2008

With the continued evolution of third-generation cellular systems and the introduction of 3GP P LTE, there is considerable progress for the new mobile wireless markets. Recently, 3GPP LTE standards are accelerated by mobile operators supporting LTE deployment and special working groups such as LSTI are working for LTE IOT and trials. In this paper, we introduce the current status of LTE activities in the mobile communications industry.

• IEIE Transactions on Smart Processing and Computing
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• 제2권1호
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• pp.36-43
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• 2013

This paper provides an overview of the security in the System Architecture Evolution (SAE) / Long-Term Evolution (LTE) system. Security is an integral part of SAE/LTE with improvements over the Third Generation (3G) system. This paper reviews the SAE/LTE system architecture, and discusses the security requirements, algorithms, Authentication and Key Agreement (AKA), Security Mode Command (SMC), key hierarchy and security for mobility.

• 정보와 통신
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• 제25권9호
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• pp.32-40
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• 2008

본고에서는 현재 3GPP (3rd Generation Partner Project)에서 표준화 작업이 마무리중인 LTE (Long Term Evolution) 시스템에서 Medium Access Control의 구조, 절차 및 PDU 포멧 등에 대해 알아본다.

• Journal of Astronomy and Space Sciences
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• 제25권2호
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• pp.71-76
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• 2008

Study of terrestrial impact craters is important not only in the field of the solar system formation and evolution but also of the Galactic astronomy. The terrestrial impact cratering record recently has been examined, providing short- and intermediate-term periodicities, such as, ${\sim}26$ Myrs, ${\sim}37$ Myrs. The existence of such a periodicity has an implication in the Galactic dynamics, since the terrestrial impact cratering is usually interpreted as a result of the environmental variation during solar orbiting in the Galactic plane. The aim of this paper is to search for a long-term periodicity with a novel method since no attempt has been made so far in searching a long-term periodicity in this research field in spite of its great importance. We apply the cepstrum analysis method to the terrestrial impact cratering record for the first time. As a result of the analysis we have found noticeable peaks in the Fourier power spectrum appear ing at periods of ${\sim}300$ Myrs and ${\sim}100$ Myrs, which seem in a simple resonance with the revolution period of the Sun around the Galactic center. Finally we briefly discuss its implications and suggest theoretical study be pursued to explain such a long-term periodicity.

• Journal of Biosystems Engineering
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• 제25권2호
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• pp.123-130
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• 2000

A forcasting scheme for daily solar irradiance on agricultural field sis proposed by application of chaos theory to a long term observation data. It was conducted by reconstruction of phase space, attractor analysis, and Lyapunov analysis. Using the methodology , it was determined whether evolution of the five climatic data such as daily air temperature , water temperature , relative humidity, solar radiation, and wind speed are chaotic or not. The climatic data were collected for three years by an automated weather station at Hwasung-gun, Kyonggi-province. The results showed that the evolution of solar radiation was chaotic , and could be predicted. The prediction of the evolution of the solar radiation data was executed by using ' local optimal linear reconstruction ' algorithm . The RMS value of the predicting for the solar radiation evolution was 4.32 MJ/$m^2$ day. Therefore, it was feasible to predict the daily solar radiation based on the chaos theory.

• 대한전자공학회논문지TC
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• 제49권5호
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• pp.91-98
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• 2012

최근 국내외 주요 이동통신 사업자들이 본격적으로 4G 무선표준 방식인 LTE (Long Term Evolution) 서비스를 시작 하면서 LTE 방식을 지원하는 이동단말의 MIMO (Multi Input-Multi Output) OTA (Over The Air) 성능 평가 방법의 필요성이 중요해 지고 있다. 본 논문에서는 3GPP (3rd Generation Partnership Project)에서 논의되고 있는 MIMO OTA 시스템에서의 LTE 이동 단말기의 핸드 효과에 의한 안테나의 특성변화를 이론 및 실험적으로 검증하였다. 핸드 효과에 의한 LTE 이동 단말기의 성능은 MIMO OTA 시스템에서의 LTE PDSCH throughput 비교를 통해 link level에서 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2626-2646
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• 2014

This study presents a power and Physical Resource Blocks (PRBs) joint allocation algorithm to coordinate uplink (UL) interference in the device-to-device (D2D) underlaying Long Term Evolution-Advanced (LTE-A) networks. The objective is to find a mechanism to mitigate the UL interference between the two subsystems and maximize the weighted sum throughput as well. This optimization problem is formulated as a mixed integer nonlinear programming (MINLP) which is further decomposed into PRBs assignment and transmission power allocation. Specifically, the scenario of applying imperfect channel state information (CSI) is also taken into account in our study. Analysis reveals that the proposed PRBs allocation strategy is energy efficient and it suppresses the interference not only suffered by the LTE-A system but also to the D2D users. In another side, a low-complexity technique is proposed to obtain the optimal power allocation which resides in one of at most three feasible power vectors. Simulations show that the optimal power allocation combined with the proposed PRBs assignment achieves a higher weighted sum throughput as compared to traditional algorithms even when imperfect CSI is utilized.

• Journal of electromagnetic engineering and science
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• 제14권1호
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• pp.1-8
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• 2014

A differential-cascode CMOS power amplifier (PA) with a supply modulator for envelope tracking (ET) has been implemented by 0.18 ${\mu}m$ RF CMOS technology. The loss at the output is minimized by implementing the output transformer on a FR-4 printed circuit board (PCB). The CMOS PA utilizes the $2^{nd}$ harmonic short at the input to enhance the linearity. The measurement was done by the 10MHz bandwidth 16QAM 6.88 dB peak-to-average power ratio long-term evolution (LTE) signal at 1.85 GHz. The ET operation of the CMOS PA with the supply modulator enhances the power-added efficiency (PAE) by 2.5, to 10% over the stand-alone CMOS PA for the LTE signal. The ET PA achieves a PAE of 36.5% and an $ACLR_{E-UTRA}$ of -32.7 dBc at an average output power of 27 dBm.

• 한국통신학회논문지
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• 제41권11호
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• pp.1440-1442
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• 2016

LTE (Long Term Evolution) 네트워크를 기반으로 하는 공공안전 및 재난통신 관련 연구가 활발히 진행되고 있으며, 기지국의 도움 없이 직접통신이 가능한 D2D (Device-to-Device) 통신 기술은 차세대 공공안전 및 재난통신망의 기반 기술로 각광받고 있다. 본 논문에서는 재난 지역의 기지국이 붕괴되었거나 통신 폭주로 인해 자원 할당이 지연되는 경우에 D2D 단말 탐색을 활용하여 재난 지역 단말들의 통신을 위한 신속하고도 정확한 주파수 자원 확보 기술을 제안한다.