• Journal of Aerospace System Engineering
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• v.17 no.4
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• pp.58-66
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• 2023

The latest global issues are the Space economy and low-orbit Space communication. 3GPP announced Release 17 standardization in June 2022, and in this regard, the United States prepared a strategy to enhance the competitiveness of the low-orbit 5G-NTN Space industry, and create an ecosystem at the national level in March 2023. Global smartphone semiconductor manufacturers have announced the development and verification results of standard-based chip technology, and satellite communication operators are launching low-orbit 5G-NTN Space communication services and rate products through convergence between terrestrial communication networks. This study diagnoses the current status of Korea's low-orbit 5G-NTN space communication ecosystem. We present our ecosystem creation strategy in terms of fair competition in the market, the service legal system, and the national R&D governance system.

• Journal of the Korea Society of Computer and Information
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• v.14 no.4
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• pp.119-129
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• 2009

In The increasing use of computers and high-speed Internet network has greatly influenced education, causing a veering away from the typical and traditional way of delivering instruction. Specifically, the various kinds of Web-based multimedia technology, the interactive activities on the Internet, and satellite broadcasting technology are accelerating the emergence of a virtual-lectures-based educational model, which transcends time and space. Such virtual lectures make it possible for the entire teaching-learning process to be done in a virtual learning environment, thus giving rise to problem regarding learning guidance, feedback, and appraisal. In this paper, we propose a system for attendance appraisal for learner participation degree based virtual lecture, an appraisal element in virtual learning environments. This appraisal model can set the elements of virtual learning environments in such a way as to reflect in the attendance appraisal of the opened virtual learning environment information regarding the learner's participation in class. In addition, this model motivates the learners to actively participate in the virtual learning environment and to support instructors by accomplishing the activities that are needed for attendance appraisal.

• 한국공간정보시스템학회:학술대회논문집
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• 2001.11a
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• pp.143-160
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• 2001

최근 들어 무선인터넷 및 모바일 컴퓨팅 기술의 급속한 발전과 함께 향후 그 수요가 폭발적으로 증대될 것으로 예상되는 분야가 위치기반서비스(LBS, Location Based Service) 기술이다. 이동통시산업이 발달한 미국 및 유럽의 선진국에서는 지난 수년에 걸쳐 지속적으로 축적되어 온 정보기술을 통하여 현재 수많은 LBS 관련 기술개발이 활발히 진행되고 있다. 1999년 미국의 FCC(미연방통신위원회)는 무선 E119 규칙을 제정하였는데, 이 규칙은 LBS를 주목하게 한 결정적인 계기가 되었다. FCC는 미국내의 망 사업자들이 2001년 10월까지 이동전화 사용자가 응급 호출(911)을 하였을 때 67%는 100M 이내의 위치오차로, 95%는 300M 이내의 위치오차로 응급호출자의 위치정보를 제공해야 한다는 규정을 제정했다. 이때부터 각종 관련 회사들이 생겨나기 시작했으며, 사람들이 LBS에 관심을 가지기 시작하였다. 국내에서도 이동통신사업자 및 IMT-2000 사업자를 중심으로 LBS 도입을 적극 준비하고 있는 상황이다. 그러나 위치정보라는 것은 오래 전부터 사람들이 알고있던 사항이다. 이미 GPS라는 것을 이용하여 국방분야, 환경분야, 교통 및 물류 분야에서 많이 활용되고 있었기 때문이다. 그런데 왜 같은 위치정보를 활용하는 분야인데 LBS는 이토록 많은 관심을 불러일으키는가? 그것에 대한 답변은 바로 위치정보가 이동통신망과 연결되면서 대중적이고 일반적인 서비스가 가능해졌기 때문이다. 특히, LBS는 GIS가 정보통신 기술과 융합되면서 앞으로 추구해야 할 차세대 정보기술 분야라는 점에서 그 의미는 더 크다고 할 수 있다. 평균(平均) 0.322였다. 그리고 RaA를 모핵종(母核種)으로 가정(假定)했을 때 각핵종간(各核種間)의 방사평형비(放射平衡比)는 대개 $C_1>C_2>C_3$인 것으로 나타났다. 여기서 $C_1,\;C_2$ 및 $C_3$는 각각 RaA, RaB 및 RaC의 농도(濃度)를 나타낸다.0cm 깊이에서는 Pythium균(菌)과 Fusarium균(菌)을 제외(除外)하고 모두 14일간(日間)에 사멸(死滅)하였다. 6. 최고(最高)에 달(達)했다가 최저(最低)에 이르는 온도(溫度)의 반복적(反復的)인 파동(波動)이 있는 것에서 없는 것보다 단시간(短時間)에 사멸(死滅)하였다. 이상(以上)의 결과(結果)에서 볼 때 하기고온기(夏期高溫期)의 재배(栽培) 휴한기(休閑期)에 PVC film을 사용(使用)하여 하우스를 밀폐(密閉)하거나 턴널을 만들어서 태양열(太陽熱)을 이용(利用)한 토양소독(土壤消毒)의 가능성(可能性)이 충분(充分)히 있는 것으로 생각된다.종합적(綜合的)으로 볼 때, diazinon 과 decamethrin의 처리(處理)는 포장(圃場)에서 벼멸구의 산란력(産卵力)과 성충수명을 증대(增大)시키고, 식이활동(食餌活動)을 촉진(促進)함으로서 벼멸구의 resurgence를 유발(誘發)하고 아울러 수도체(水稻體)의 hopperbun을 가속화시킬 가능성(可能性)이 있음을 알 수 있었다.는 점차 약하여 졌으나 catalase, invertase는 그 활성도가 일단 숙성중기에 높아졌다가 낮아졌다.n 이 pH 4.2이고 temperature는 $60^{\circ}C$이었다. 그리고

• Journal of Korea Spatial Information System Society
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• v.8 no.1 s.16
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• pp.107-118
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• 2006

In this paper, several network algorithms were tested to find an optimal one for telecommunication network design. Algorithms such as Dijkstra's shortest path algorithm, Ford-Bellman's shortest path algorithm, Prim's minimum spanning tree algorithm, and Kruscal's minimum spanning tree algorithm were reviewed and compared in terms of feasibility and resulted network construction cost. Then an optimal algorithm that is most suitable for telecommunication network design was selected. For more specific and quantitative analysis of the selected algorithm, it was implemented to a real telecommunication network construction site. The analyzed results showed that the suggested design method when compared with the conventional one, reduced the network construction cost considerably. The total network length estimated by the conventional method were 5267 meters while the suggested method resulted in 4807 meters. Thus the new method reduced the total network length by 8.7 percent which is equivalent to 97,469,000 Won of construction cost. Considering the frequent telecommunication network constructions, due to new urban developments in the nation, the economic benefit of the suggested telecommunication network design method will be significant. In addition to the construction cost savings, the suggested telecommunication network design procedure possesses several other economic benefits. Since the design procedure can be standardized and automatized, it can reduce the design cost itself and the skill acquirement periods required for new or inapt design crews. Further, due to the standardized and automatized design procedure, any telecommunication network design results can accessed more objectively.

• Journal of Korean Society for Geospatial Information Science
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• v.23 no.4
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• pp.43-48
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• 2015

We studied on pseudo-range correction(PRC) modeling in order to improve differential GNSS(DGNSS) accuracy. The PRC is the range correction information that provides improved location accuracy using DGNSS technique. The digital correction signal is typically broadcast over ground-based transmitters. Sometimes the degradation of the positioning accuracy caused by the loss of PRC signals, radio interference, etc. To prevent the degradation, in this paper, we have designed a PRC model through polynomial curve fitting and evaluated this model. We compared two quantities, estimations of PRC using model parameters and observations from the reference station. In the case of GPS, the average is 0.1m and RMSE is 1.3m. Most of GPS satellites have a bias error of less than ${\pm}1.0m$ and a RMSE within 3.0m. In the case of GLONASS, the average and the RMSE are 0.2m and 2.6m, respectively. Most of satellites have less than ${\pm}2.0m$ for a bias error and less than 3.0m for RMSE. These results show that the estimated value calculated by the model can be used effectively to maintain the accuracy of the user's location. However;it is needed for further work relating to the big difference between the two values at low elevation.

• Informatization Policy
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• v.17 no.4
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• pp.80-99
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• 2010

A substantial body of theoretical and case study literature exists about the relationship between competition and universal service in developing countries. On the one hand, many scholars have argued that state-owned monopolies in developing countries are not able to mobilize the capital needed for network expansion: the resulting unmet demand for services becomes a motivator for liberalization. On the other hand, the introduction of competition jeopardizes the internal and external subsidies through which the state-owned monopoly kept subscription rates low: the heightened concern about loss of subscribership incentivizes the creation of explicit universal service statutes and funding mechanisms concurrently with or soon after competition is introduced. This paper shows that universal service in Korea had a unique evolutionary path, which did not conform to either of these expectations. From this finding, it reaches the conclusion that the outcomes predicted by theory and observed in the case study literature are not intrinsic to the monopoly condition per se, but derive from the strategic choices made by telecommunications managers, regulators and lawmakers in developing countries.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.06a
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• pp.397-400
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• 2007

Indoor air-conditioning system(IAS) using wireless sensor network serves to reduce the amount of pollution entering the room from outside and also the pollution that is generated indoor. Small-size and lower power wireless sensor node and sensor interface board was designed for indoor air-conditioning system in buildings of offices and industrial establishments. Many sensor nodes forms Ad-hoc network topology using simple forwarding routing to transmit polluting gas concentration data from different rooms to the indoor air-conditioning system. Sensor node analyzes pollution concentration in the each room and air-conditioning system performs to air-distribution and air-inhalation according to room's pollution by regulating the fan of indoor air-conditioning system. To reduce power consumption electrochemical gas sensor was used in the design. Thus the designed system can optimize state of indoor environment. Graphic user interface displays node sate, gas concentration and temperature of each room.

• Journal of Broadcast Engineering
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• v.16 no.2
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• pp.360-371
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• 2011

T-DMB hybrid data service provides advanced data services while maintaining backward compatibility with legacy T-DMB receivers by using hybrid BIFS technology enabling distributed delivery of scene description information and object description information. This paper presents the hybrid service authoring framework implementing hybrid BIFS technology for creating contents for distributed delivery, and the results of experiments by using it. Hybrid service authoring framework is comprised of service creation system, service management system, and contents offering system. It enables the creation of combined hybrid data service and the splitting of the contents into two parts for ecah delivery network, data for broadcasting network and the data for mobile network. It also enables the managements of the contents. The feasibility of advanced data services while maintaining backward compatibility with the legacy T-DMB receiver has been proved by the contents created by using the hybrid authoring framework presented in this paper.

• Journal of Internet Computing and Services
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• v.10 no.4
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• pp.199-211
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• 2009

Recent advancements in wireless networks have enabled support for mobile applications to transfer data over heterogeneous wireless paths in parallel using data striping technique [2]. Traditionally, high performance data transfer requires tuning of multiple TCP sockets, at sender's end, based on bandwidth delay product (BDP). Moreover, traditional techniques like Automatic TCP Buffer Tuning (ATBT), which balance memory and fulfill network demand, is designed for wired infrastructure assuming single flow on a single socket. Hence, in this paper we propose a buffer tuning technique at senders end designed to ensure high performance data transfer by striping data at transport layer across heterogeneous wireless paths. Our mechanism has the capability to become a resource management system for transport layer connections running on multi-homed mobile host supporting features for wireless link i.e. mobility, bandwidth fluctuations, link level losses. We show that our proposed mechanism performs better than ATBT, in efficiently utilizing memory and achieving aggregate throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4A
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• pp.385-392
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• 2006

It is widely accepted that high user densities in mobile multimedia environments can only be achieved with micro- and pico-cell. The smaller cell size causes frequent handovers between cells, and decreases permissible handover processing delay. This may result in the handover failure, in addition to the loss of some packets during the handover. In these cases, re-transmission is needed in order to compensate errors, which in turn triggers a rapid degradation of throughput. In this paper, we propose a new handover scheme for the next generation mobile communication systems, in which the handover setup process is done in advance before a handover request by predicting the handover cell based on mobile terminal's current position and moving direction. Simulation is performed in order to analyze the handover failure rate and packet loss rate. Simulation results show that our proposed method provides a better performance than the conventional method.