• 한국항공운항학회지
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• 제20권3호
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• pp.22-27
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• 2012

In oceanic flight routes, HF radio and satellite data links have been used for air-to-ground communication, but these systems have long propagation delay and low data throughput. In this paper, we propose a reliable system to overcome the weakness of current HF radio and satellite communication systems for oceanic aeronautical flight routes. The proposed scheme uses only one aeronautical VHF channel in multi-hop oceanic communication environments and supports a hybrid type of multiple access, which consists of random access and TDMA (Time Division Multiple Access) scheme. The proposed system improves performance on delay and throughput as an effective solution to communicate end-to-end on the oceanic flight routes and strengthens the reliability of oceanic aeronautical communication.

• 디지털산업정보학회논문지
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• 제17권4호
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• pp.31-42
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• 2021

In the modern era, radio wave analysis is necessary for various fields of engineering, and interpretation of this is also indispensable. Self-driving cars need multiple different electronic components, and thus accurate and fast electromagnetic simulator for this kind of complex radio environment is required for self-driving simulations. Accordingly, the demand for self-driving simulators as well as existing electromagnetic analysis software has increased. This paper briefly describes the characteristics of numerical analysis techniques for electromagnetic analysis, self-driving simulation software, and conventional electromagnetic simulation software and also summarizes the characteristics of each software. Finally, the verification of the result from in-house code compared to HFSS is demonstrated.

• 천문학회보
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• 제43권2호
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• pp.38.2-38.2
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• 2018

To understand the assembly of the galaxy population in clusters today, it is important to first understand preprocessing, the impact of environments prior to cluster infall. We use 15 cluster samples from YZiCS, a hydrodynamic cluster zoom-in simulation to determine the significance of preprocessing, and focus on the tidal mass loss of dark matter halos. We find ~48% of the cluster member halos were once satellites of another host. The preprocessed fraction depends on each cluster's recent mass growth history. Also, we find that the total mass loss is a clear function of the time spent in a host. However, two factors can increase the mass loss rate considerably. First, if the satellite mass is approaching the mass of its host. Second, when the halo suffers tidal mass loss at a higher redshift. Being in hosts before cluster infall enables halos to experience tidal mass loss for an extended period of time.

• Journal of Positioning, Navigation, and Timing
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• 제13권2호
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• pp.207-213
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• 2024

This paper examines the frame boundary detection performance for a satellite navigation augmentation signal orthogonally modulated with Hadamard code to determine the number of message preamble bits. Simulation results show that, even in weak signal environments, designing the message preamble with 32 bits is recommended for achieving stable frame boundary detection.

• 디지털산업정보학회논문지
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• 제16권2호
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• pp.27-33
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• 2020

Backward compatibility is one of the key issues for radio equipment supporting IEEE 802.11, the typical wireless local area networks (WLANs) communication protocol. For a successful packet decoding with the backward compatibility, the frame format detection is a core precondition. This paper presents a novel frame format detection method based on a deep learning procedure for WLANs affiliated with IEEE 802.11. Considering that the detection performance of conventional methods is degraded mainly due to the poor performances in the symbol synchronization and/or channel estimation in low signal-to-noise-ratio environments, we propose a novel detection method based on convolutional neural network (CNN) that replaces the entire conventional detection procedures. The proposed deep learning network provides a robust detection directly from the receive data. Through extensive computer simulations performed in the multipath fading channel environments (modeled by Project IEEE 802.11 Task Group ac), the proposed method exhibits superb improvement in the frame format detection compared to the conventional method.

• 천문학회보
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• 제36권2호
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• pp.109.1-109.1
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• 2011

Shock waves are ubiquitous in astrophysical environments. In particular, shocks formed by merger of subclumps, infall of matter and internal flow motion in intracluster media (ICMs) and cluster outskirts are relatively weak with Mach number M ${\lesssim}$ a few. At such weak shocks, it has been believed that the diffusive shock acceleration (DSA) of cosmic rays is rather inefficient. Yet, the presence of nonthermal phenomena, such as radio halos and relics, suggests that contrary to the expectation, DSA as well as magnetic field amplification should operate at weak shocks in cluster environments. We recently initiated a study of weak, collisionless, astrophysical shocks using a PIC(Particle-in-Cell) code. The PIC code describes the motion of electron and ion particles under the electromagnetic field which is represented in grid zones. Here, we present a preliminary work of one-dimensional simulations. We show how shocks are set up as the turbulent electromagnetic field is developed in the shock transition layer, and discuss the implication on DSA and magnetic field amplification.

• 천문학회보
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• 제39권1호
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• pp.46.1-46.1
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• 2014

In understanding "cooling flow" problem and the galaxy-SMBH co-evolution, AGN feedback is considered as one of the most important phenomena. Among various AGN feedback phenomena, X-ray cavities are particularly useful for studying AGN feedback over 10 kpc scales, as the origin of X-ray cavities is believed to be related to radio jet from AGN. For a comprehensive study of X-ray cavities, we collect all available diffuse X-ray data of galaxies in various galaxy environments, ranging from field galaxies to galaxy clusters, using the Chandra X-ray data archive. As a result we build up a sample of 87 targets showing enough X-ray photons to perform the analysis. Using modeling and unsharp masking techniques, we detected X-ray cavities and measured their physical properties (i.e., cavity size) for the 49 targets. Here, we present X-ray cavity properties and discuss environmental effects.

• 전기전자학회논문지
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• 제16권4호
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• pp.290-296
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• 2012

본 논문에서는 반무반사실내에서 반사체와 시간영역 측정을 이용한 반사파의 효과적인 억제 기술을 제안하고 있다. 제안한 기법을 이용하여 측정 영역상에 전기장의 균일도를 향상시켜 완전 무반사실과 유사한 안테나 측정환경을 구현할 수 있었다. 구현한 측정환경의 성능은 측정을 통하여 검증하였으며 소형 VHF대역 안테나 측정에 사용 가능할 것으로 판단된다.

• 천문학회보
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• 제46권2호
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• pp.41.1-41.1
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• 2021

Neutral (HI) gas clouds associated with galaxies are responsible for fuelling the star-formation in the universe. In literature, the extremely strong damped Lyman-alpha absorbers (or ESDLAs) have been known to be sensitive to the effects of HI-H2 transition and star-formation in galaxies. Yet, ESDLAs are rare to probe due to the smaller cross section they subtend on the sky (similar to galaxies). In my talk, I will focus primarily on my study of the nature of ESDLAs that are observed as absorption signature along the line-of-sight (LOS) of a quasar (QSO). I will further look at the HI-H2 transition and interesting results relevant to diffuse molecular gas and the multi-phase medium (gas in different ionization states) that are associated with ESDLAs. Furthermore, I will also discuss how the ESDLA environments differ from the high star-forming and molecular environments detected in blind optical and radio surveys consecutively.

• 한국전자파학회논문지
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• 제26권10호
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• pp.841-850
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• 2015

전자 및 전파 통신기술의 급속한 발전에 따라 인류는 정보통신의 커다란 혜택을 누릴 수 있게 되었다. 그러나 전자파환경은 보다 복잡해지고, 각종 전자기기를 비롯한 인체에 다양한 영향을 미치게 되어 ANSI, FCC, CISPR 등과 같은 국제기구에서는 다양한 전자파환경을 규제하고, 효율적인 제어 및 대책을 수립해 오고 있다. 본 논문에서는 방열 기능을 가지면서 고성능의 전파흡수체 제조 방법을 제안하고, 나아가 미래의 스마트 전파흡수체의 전망을 기술하였다. 산화철($Fe_2O_3$)과 세라믹의 혼합물을 고온 열처리한 후, 탄소 물질과 배합하여 저온 열처리하고, 개구를 형성하여 2~2.45 GHz에서 방열 기능을 가지면서 흡수능이 20 dB 이상인 고성능 전파흡수체를 개발하였다. 이 스마트 전파흡수체는 다양한 전자, 통신, 제어, 전파 시스템의 회로 및 부품 보호용 소재로 활용성이 높을 것으로 보인다.