• Journal of The Korean Astronomical Society
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• v.28 no.1
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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.

• Proceedings of the IEEK Conference
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• 2008.06a
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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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• v.2 no.1
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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.

• Information and Communications Magazine
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• v.25 no.9
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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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• v.25 no.2
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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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• v.25 no.2
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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.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.5
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• pp.91-98
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• 2012

Since the major cellular data service providers in U.S, Japan as well as in Korea started the LTE (Long Term Evolution) service, there has been more strong need for the methods that can accurately measure the MIMO (Multi Input-Multi Output) OTA (Over The Air) performance of LTE handsets because the performance of the MIMO antenna determines the data throughput in the downlink. In this paper, the hand effect on the MIMO antenna performance is analyzed by numerically and experimentally. The hand effect on the LTE mobile handset is analyzed by measuring the link level performance in the MIMO OTA system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.8
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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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• v.14 no.1
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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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1440-1442
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• 2016

As long term evolution (LTE) is the most widely deployed broadband communication technology so far, efforts are being made to develop LTE-based mission critical public safety (PS) communication systems. In this paper, we propose a device-to-device (D2D) discovery-based radio resource acquisition scheme to support the LTE D2D communication to PS systems and the realization of resource forwarding for user equipments in emergency area.