• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.159-168
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• 2023

The main goal of the Korean VLBI Network Calibrator Survey (KVNCS) is to expand the VLBI calibrators catalog for KVN, KaVA (KVN and VERA Array), EAVN (East-Asian VLBI Network), and other extended regions. The second KVNCS (KVNCS2) aimed to detect VLBI fringes of new candidates for calibrators in the K band. Out of the 1533 sources whose single-dish flux density in the K band was measured with KVN telescopes (Lee et al. 2017), 556 sources were observed with KVN in the K band. KVNCS2 confirmed the detection of VLBI fringes of 424 calibrator candidates over a single baseline. All detected sources had a high Signal-to-Noise Ratio (SNR) of >25. Finally, KVNCS2 confirmed 347 new candidates as VLBI calibrators in the K band, resulting in a 5% increase in the sky coverage compared to previous studies. The spatial distribution was quasi-uniform across the observable region (Dec. > -32.5°). In addition, the possibility as calibrator candidates for the detected sources was checked, using an analysis of the flux-flux relationship. Ultimately, the KVNCS catalog will not only become the VLBI calibrator list but is also useful as a database of compact radio sources for astronomical studies.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.5
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• pp.602-611
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• 2015

Even though GNSS provides highly accurate navigation information all over the world, it is vulnerable to jamming in the electronic warfare due to its weak signal power. The United States and Korea have plans to use terrestrial navigation systems as back-up systems during outage of GNSS. In order to develop back-up systems of GNSS, an M&S software platform is necessary for performance evaluation of various vehicle trajectories and integrated navigation systems. In this paper a design method of an M&S software is proposed for evaluation of multiple radio positioning integration systems. The proposed M&S software consists of a navigation environment generation part, a navigation algorithm part, a GUI part and a coverage analysis part. Effectiveness of the proposed design method is shown by implementing an M&S software for the GPS, DME and eLoran navigation systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.7
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• pp.51-58
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• 2010

Wireless Mesh Network has drawn much attention due to wide area service coverage with low system cost. However, there is a bottleneck problem in wireless mesh network since the traffic is aggregated into a gateway. Placement of multi-radio can easy the bottleneck problem, but without careful design it results in unnecessary system cost increasement. In this paper, we propose a system cost minimization through differential antenna placement where optimum antenna placement is determined by the required wireless link capacity. With CPLEX program, optimum number of antennae is determined as a function of local user traffic and gateway capacity. From numerical analysis, it is confirmed that our proposed model can solve bottleneck problem, and at the same time save the system cost.

• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.57-63
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• 2010

Many efficient frequency sharing methods are issued in present because of increasing users with various wireless communication terminals. In the satellite communications, the service coverage is generally very wide so frequency sharing with terrestrial system is essentially needed, and the research is progressing dynamically related on this frequency sharing method. But if we adopt the terrestrial system which is commonly used, it can't avoid the interference from terrestrial service to satellite service. Therefore, this paper will introduce methods for reducing the interference from terrestrial station to earth station using cognitive radio system Satellite system is guaranteed with decreasing interference from terrestrial stations using Genetic Algorithm based power control method. Furthermore, terrestrial systems can have increased QoS because the frequency reuse factor in proposed method is higher than existing methods.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.3
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• pp.231-238
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• 2021

In addition to individual calls and group calls, the Trunked Radio System (TRS), which belongs to a group, can make calls simultaneously, and many users can use it within a limited time by adjusting the call time. Also, the LCX infrastructure network of the subway Most of the FM, firefighting radio, TRS of the National Police Agency and the terrestrial DMB service built in 2005 are commonly connected to the network for service and operation. In connection with the analysis, call reception sensitivity, handoff, interference with other signals, time delay, etc. were analyzed, and tests such as reception field strength for each output of the repeater and the success rate of the call terminal were conducted and the test results were analyzed. In addition, it will help TRS cell design and network construction by predicting equipment output capacity and service coverage based on test results.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.311-315
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• 2015

In this study, we estimated the topside scale height of plasma density (Hm) using the Swarm constellation and ionosondes in Korea. The Hm above Korean Peninsula is generally around 50 km. Statistical distributions of the topside scale height exhibited a complex dependence upon local time and season. The results were in general agreement with those of Tulasi Ram et al. (2009), who used the same method to calculate the topside scale height in a mid-latitude region. On the contrary, our results did not fully coincide with those obtained by Liu et al. (2007), who used electron density profiles from Arecibo Incoherent Scatter Radar (ISR) between 1966 and 2002. The disagreement may result from the limitations in our approximation method and data coverage used for estimations, as well as the inherent dependence of Hm on Geographic LONgitude (GLON).

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.38.4-39
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• 2015

We have been monitoring Sgr A*, the radio source at the center of our galaxy, continuously since G2 encounter was predicted. KaVA is a powerful High resolution imaging array at K and Q band, and it has a excellent uv-coverage for Sgr A*. Together with 1-Gbps recording, our observations have provided high-quality images of Sgr A* at Q-band. Our images reveal a scatter-broadened, elliptical Gaussian structure of the source. We found no significant flux or structural variation of Sgr A* in 2013-2014, which is consistent with recent simulations by Kawashima et al. Continuous monitoring in the coming few years would be able to capture the possible flux increase in the source caused by G2, which will lead to better understanding of the accretion process around supermassive black holes.

• IE interfaces
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• v.14 no.3
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• pp.318-325
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• 2001

In this paper, we estimate the investment cost for the IMT-2000 services in Korea. The network elements for the IMT-2000 system are drawn out and the required number of base stations(Node-B) is predicted by using the coverage of the base station. With the assumption of the 2-generation mobile communications network configuration, the number of radio network controllers(RNC's) and core network facilities is estimated. We also setup different scenarios by considering the utilization of the transmission facilities between base stations, RNC's and switching systems, and then evaluate the investment cost for each scenario.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.255-258
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• 2000

최근 경제 활동의 증가로 인하여 통신 서비스에 대한 이동성, 편의성, 및 개인에 대한 요구가 증대되고 있다. 현재 세계각국에서는 이동통신 서비스인 셀룰라 이동통신과 개인 휴대 통신인 PCS(Personal Communication System)가 상용화되고 있다. 1900MHz 대역은 셀룰라 800 MHz에 비해 전파 특성상 전파환경에 따른 전파의 감쇄 및 회전손실 등으로 인한 전파 경로 손실이 증가 할 것으로 본다. 본 논문에서는 바다 해수면의 영향에 따른 800MHz대역과 1900MHz 대역에서 주파수에 따른 경로 손실 차를 실측 Data를 이용하여 비교하였으며 실측 Data를 이용하여 전파모델을 만들어 LGE에서 자체 개발한 전파 분석 시뮬레이션 툴로 Coverage 영역을 비교하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.5
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• pp.2043-2060
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• 2020

Developed from Digital Multimedia Broadcasting (DMB), DMB+ changes the application focus fundamentally. The plus symbol "+" indicates that DMB+ is no longer for digital radio/videos, instead it works as a general data transmission technique. The merits of wireless transmission, broad coverage, high quality, information security and low building/maintenance cost make DMB+ suitable for a wide range of applications with numerous terminals and users, such as public information release, alarm and administration etc. The concept of DMB+ base station enables DMB+ to be used in building independent networks and for remote control and management, as well as for Industry 4.0. DMB+ will access into a new field that till now has been dominated by communication techniques, will open a huge commercial opportunity.