• Journal of Positioning, Navigation, and Timing
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• 제6권2호
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• pp.53-57
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• 2017

eLoran refers to a terrestrial navigation system using high-power low-frequency signals. Thus, it can be regarded as a positioning, navigation and timing (PNT) system to back up a global navigation satellite system (GNSS) or an alternative to GNSS. South Korea is vulnerable to interference such as GNSS jamming in particular. Therefore, South Korea has made an effort to develop an independent navigation system through eLoran system. More particularly, an eLoran testbed has been developed to be used in the northwest sea area and research on applicability of eLoran in South Korea has been underway. The present study analyzes expected performance of eLoran according to locations of newly built eLoran transmitting stations as part of the eLoran testbed research. The performance of eLoran is analyzed in terms of horizontal position accuracy, and horizontal dilution of precision (HDOP) information was used since it affects accuracy significantly. The target service areas of the eLoran testbed are Incheon and Pyeongtaek Ports, and the required target performance is positioning accuracy of 20 m position within 30 km coverage of the target service area.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1234-1238
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• 2005

As the low power GPS signal is susceptible to interference, interference can seriously degrade the performance of GPS receiver. This paper designs a ANIEF(Adaptive Narrowband Interference Excision in Frequency domain) filter that removes narrow band interferences with low signal loss. This filter uses the pre-correlation technique and attempts to filter out the interference in the frequency domain. The interference excision performance of the designed filter is evaluated for various interferences using the ANIEF filter inserted GPS software receiver and the interference generator. Interferences considered in this paper are single-tone CWI(Continuous Wave Interference), multi-tones CWI, pulsed CWI, and swept CWI. The narrowband interference excision filter in frequency domain is very effective against various interferences and the strong interference with a simple structure. However, the signal power loss is unavoidable while transforming. In this paper, the hamming window and overlap technique are adopted to reduce the signal power loss. Finally, the interference excision performance and the reduced signal power loss of the ANIEF filter are shown.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.905-913
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• 2008

The water resource depending on mostly surface water has many problems, such as contaminated and unpredicted contamination event. For this reason, it has been employed highly technical treatment method for them, such as ground water dam and river bank filtration. it has been developed the radial collector wells in kind of bank filtration to increase efficiency for in-taking the water resource insead of the vertical well needed many wells to take more resource. But it has many problems with the incumbent method to bore the horizontal hole for radial collector wells, such as filling with the filter material outside of a strainer by watering, jamming as retrieving the casing tube with the filter material, eccentric boring etc. To reduce the problems of incumbent equipment, it has been developed the horizontal boring equipment and performed the field trial tests several times, which have bits and water jetting system with rotating the cone-shaped front to be excavated easily. In this paper, it was compared the brand-new with the incumbent non-rotating pressing insertion method. Also it was shown the problems of the incumbent method was reduced effectively.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 춘계종합학술대회
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• pp.183-187
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• 2000

본 논문에서는 다중사용자 환경 및 Rayleigh 페이딩 통신로 환경으로 모델링 되는 DS-CDMA 와 FH-CDMA 통신 시스템의 성능을 비교 분석하였다. 성능 개선기법으로는 MRC다이버시티 기법을 적용하여 두 시스템간의 개선 정도를 구하여 비교 분석하였다. 동일한 조건에서 두시스템의 성능을 비교하기위해 동일통신대역(300kHz)을 사용, 재밍신호 10∼20dB, 사용자 데이터율 300bps의 조건에서 사용자 수를 증가시키면서 BER성능을 분석하였다 결과에 의하면 다중사용자 환경에서의 DS방식과 FH방식은 Rayleigh 페이딩 환경하에서 현저하게 열화되지만 MRC 다이버시티 수신기법을 적용함으로써 열화된 시스템의 성능을 개선 시킬 수 있었고 특히 DS시스템에서의 MRC기법을 적용하였을때가 FH시스템보다 약 9.5배의 우수한 성능개선을 보임을 알 수 있었다.

• 한국군사과학기술학회지
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• 제15권1호
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• pp.66-74
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• 2012

The virtual target signal generator was developed to verify the shipborne tracking radar performance. It was used to DRFM(Digital RF Memory) method to generate the virtual moving targets. The target signal includes Doppler shift and RCS according to the target motion. And the signal generator can make jamming signal and clutter to test shipborne radar performance at real environmental condition. This paper described the functional diagram and the hardware configuration items to meet the test requirements for the tracking radar. And it showed the critical design points for the sub-systems. The signal generator which was developed in this paper shared the operational information of the radar with the radar command and control part. To test the frequency agility of the radar, it had the local oscillator which could do high speed frequency switching according to radar information. By communicating between the signal generator and the radar command and control part, the local oscillator of signal generator could be controlled every pulse. It reduced the instantaneous bandwidth of signal generator and minimized the spurious. So it lowered the probability of generating wrong targets.

• 대한전기학회논문지:전력기술부문A
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• 제53권7호
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• pp.405-413
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• 2004

Traditionally, electrical power systems had the vertically-integrated industry structures based on the economics of scale. However power systems have been recently reformed to increase the energy efficiency of the power system. According to these trends, Korean power industry has been partially restructured, and the competitive generation market was opened in 2001. In competitive electric markets, correct demand data are one of the most important issue to maintain the flexible electric markets as well as the reliable power systems. However, the measuring load data can have the uncertainty because of mechanical trouble, communication jamming, and other things. To obtain the reliable load data, an efficient evaluation technique to adust the missing load data is needed. This paper analyzes the load pattern of historical real data and then the turned ARIMA (Autoregressive Integrated Moving Average) model, PCHIP(Piecewise Cubic Interporation) and Branch & Bound method are applied to seek the missing parameters. The proposed method is tested under a variety of conditions and tested with historical measured data from the Korea Energy Management Corporation (KEMCO).

• Journal of Positioning, Navigation, and Timing
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• 제5권3호
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• pp.157-163
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• 2016

Clocks for time synchronization using radio signals such as global navigation satellite system (GNSS) may lose reference signals by intentional or unintentional jamming. This is called as holdover. When holdover occurs, a clock goes into free run in which synchronization performance is degraded considerably. In order to maintain the required precise time synchronization during holdover, accurate estimation on main parameters such as frequency offset and frequency drift is needed. It is necessary to implement an optimum filter through various simulation tests by creating clock noise in accordance with given specifications in order to estimate the main parameters accurately. In this paper, a method that creates clock noise in accordance with given specifications is described.

• 한국전자파학회논문지
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• 제27권8호
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• pp.676-683
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• 2016

본 논문에서는 단일포트시스템으로 설계된 배열안테나에서 재밍신호나 간섭신호 방향으로 방사패턴에 널(null)을 형성하는 적응 알고리즘을 제안한다. 제안한 적응 알고리즘은 재밍신호나 간섭신호의 크기나 입사방향에 대한 사전정보를 요구하지 않으며, 배열안테나의 일부 RF 경로의 위상을 제어하는 부분적응(partially adaptive) 알고리즘이다. 제안한 적응 알고리즘은 최적화 알고리즘의 한 종류인 PSO(Particle Swam Optimization) 알고리즘과 gradient-based 섭동 적응 알고리즘을 혼합하여 시간에 따라 간섭신호의 입사방향이 변화하는 이동형 재밍환경에서도 적응적으로 안정적인 널링 성능을 가진다.

• 한국정밀공학회지
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• 제2권3호
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• pp.28-40
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• 1985

In this study, to check up on the effect of the components of cutting resistance upon friction between drill and inside wall of hole in drilling, the experiment was performed with individual specimen of carbon steel, cast iron, aluminium alloy under various cutting conditions: depth of hole, cutting speed, feed rate, shape and material of specimen. On the basis of the experimental results, the following conclusions are drawn; 1. The components of cutting resis- tance were increased in proportion to the increase of depth of hole owing to frictional resistance of drill margin and chip-jamming. 2. As feed rates increase, torque and thrust were increased. When comparing to the increasing rate for these components respecitively, thrust is higher tendency than torque. 3. As drill diameter increase, torque and thrust were increased. When comparing to the increasing rate for these components respectively, torque is higher tendency than thrust. 4. In the case of torque, the frictional resistance between drill margin and inside wall of drilled hole accounts for about 20 percent of carbon steel, 14 of cast iron, 10 aluminium alloy in drilling. But the effect of thrust force could be negligible. 5. Comparison between the theoretical and experimental results showed a close agreement so far as depth of hole is about three times of drill diameter. But there was a wide difference between them beyond the rane of three times, because of characteristics of the drilling process.

• Journal of Advanced Marine Engineering and Technology
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• 제36권1호
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• pp.179-184
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• 2012

기존의 무선 RF 통신은 근거리에서 전력손실이 상대적으로 크고, 전파간섭 및 방해, 재밍 등에 민감하다. 이러한 단점을 보완하는 대안으로 자외선을 이용한 통신 방식에 대한 연구가 최근 관심을 받고 있다. 본 논문에서 자외선을 이용한 비가시거리 통신의 data rate 특성에 대해 시뮬레이션한 결과를 제시하였다. On-off keying 방식을 사용하는 비가시거리 자외선 통신에서 data rate는 송신 빔의 방향, 수신빔의 빔 폭, 송신 전력에 의해 큰 영향을 받는다는 것을 확인하였다.