• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.3 no.1 s.4
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• pp.109-116
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• 2004

The signal in wireless multi-path channel is affected by fading and ISI because of high data rate transmission, so the signal has the high error rate. The present modulation and demodulation method of DSRC system can not expect sufficient for providing data service over 1 Mbps, so the channel equalization and advanced modulation and demodulation methods are required. OFDM method is generally Inon as an effective technique for high data rate transmission system, since it can prevent ISI by inserting a guard interval. However, a guard interval longer than channel delay spread has to be used in each OFDM symbol period, thus resulting a considerable loss in the efficiency of channel utilization. Therefore the equalizer is necessary to cancel ISI to accommodate advanced ISI service with higher bit rate and longer channel delay spread condition. In this thesis, the channel equalizer for the OFDM-DSRC system was designed and its performance in a multi-path fading environment was evaluated with computer simulation. As a result, the performance of Pseudo LMMSE equalizer for the OFDM-DSRC has been improved comparing with LS equalizer at higher bit rate transmission system.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.161-166
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• 1999

The global trends of mobile communication system is moving toward digitizing, high-speed and large-capacity. Also, to utilize the limited frequency-resource efficiently, spread spectrum system is a mainstream. In this study we are concerning with the fast frequency-hopping system. Instead of the PLL with many problems such as phase-noise, we used the DDS is popular in these days minimizes the disadvantage of PLL. In the case the FFH system is designed using the PLL, it is difficult to be satisfied of the design conditions such as RF badwidth and the settling time of PLL, and it has limitation because of complex circuit by using the balanced modulator. In this study, we evaluated the performance in order to design the FFH system using the DDS. The system that has the improvement of error rate, 1Mhps hopping rate and 5MHz RF bandwidth is designed and evaluated.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.313-336
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• 2007

Unlike a conventional railway system, a high-speed rail system experiences various aerodynamic problems in tunnel sections. Trains running at a high speed in a small tunnel, when compared with the open field, face significant air pressure, resulting in reduced operating stability and fast change in pressure inside the tunnel. These phenomena further cause some unexpected problems such as the passengers onboard feeling an aural discomfort and an impulsive noise at the tunnel exit. To solve these problems, this paper introduces analysis of aerodynamic characteristics for determination of tunnel cross section. The optimum cross-section that satisfies the criteria of aural discomfort was reviewed through lots of numerical simulation analysis. Also, the pressure inside the passenger car of a train operating on Kyungbu HSR line was measured, and the pressure inside the tunnel and the micro-pressure waves at tunnel exit were measured at Hwashin 5 Tunnel. At the same time, a test of train operation model was performed and then the measurement results and test results were compared to verify that various parameters used as input conditions for the numerical simulations were appropriate.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.329-333
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• 2005

Total temperature distribution in high speed fee & wall jet regions was investigated using the total temperature probe. For the free jet, the distance of probe from the nozzle exit is changed in the range of 1, 2, 4 and 6 times o nozzle exit diameter. Energy separation phenomenon was observed on shear layer between jet and ambient. In wall jet region, impinging plate was fixed at Z/D=2 and total temperature distribution has been measured for various radial distance($R/D=1.25\sim2.0$). Energy separation phenomenon was found at wall jet boundary and near wall, and was compared with measured adiabatic wall temperature value.

• Journal of Navigation and Port Research
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• v.29 no.1 s.97
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• pp.23-28
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• 2005

The signal in wireless multi-path channel is affected by fading and ISI because of high data rate transmission, so the signal has the high error rate. The present modulation and demodulation method of DSRC system can not expect sufficient for providing data service over 1 Mbps, so the channel equalization and advanced modulation and demodulation methods are required. OFDM is generally known as an effective technique for high data rate transmission system, since it can prevent ISI by inserting a guard interval. However, a guard interval longer than channel delay spread has to be used in each OFDM symbol period, thus resulting a considerable loss in the efficiency of channel utilization Therefore the equalizer is necessary to cancel ISI to accommodate advanced ITS service with higher bit rate and longer channel delay spread condition In this paper, the channel equalizer for the OFDM -DSRC system was designed and its performance in a multi-path fading environment was evaluated with computer simulation.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2005.11a
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• pp.347-352
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• 2005

유비쿼터스라는 새로움 페러다임의 도래로 인해 많은 IT산업이 이를 중심으로 많은 발전을 하고 있다. 이러한 유비쿼터스 관련 산업에 있어서 상당 부분 무선 통신기술인 RF를 기반으로 하고 있으며, 이를 활용하여 RFID 시스템 및 센서 네트워크 등이 발전하고 있는 추세이다. 본 논문에서 이러한 무선 통신기술에 적합한 저전력 저전압 Wireless UHF 트렌시버인 CC1020 칩을 이용하여 무선통신시스템을 구현하였다. 이 시스템을 제어하기 위해 MCU와의 Interface를 구성하고 CC1020 칩의 레지스터를 설정하기 위해 4선의 직렬 구성 인터페이스로 모토로라사에서 개발된 근거리용 고속 직렬 동기식 통신규격인 SPI 방식을 이용하였다. 따라서 레지스터 종류 및 설정순서와 타이밍에 대한 내용과 MCU와의 인터페이스 중심으로 설명하였으며, 시스템을 구현하고 실험을 통해 신호의 파형과 데이터 송수신을 확인하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.32-32
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• 1998

고체 추진제 로켓의 연소시에 발생되는 산화 알루미늄(A1$_2$O$_3$) 입자는 로켓 추진 노즐에서 팽창과정의 효율을 저하시키는 요소가 되며, 이러한 비효율성은 연소 가스와 입자간의 비평형 상태 효과와 기본적인 속도와 열적 차이에 의해서 발생된다고 보고되었다. 또한 연소시 발생된 산화 알루미늄 입자는 높은 열과 큰 운동량을 가지고 로켓 노즐 내부를 유동하게 되며, 매우 많은 량이 짧은 시간에 고온 고속으로 노즐 벽면이나 기타 구조물에 충돌 및 점착하기 때문에 로켓 노즐내의 표면이 손상을 입게 되고, 로켓의 방향 제어 및 조정 안정성이 저하되며, 구조적인 강도가 약화 될 수 있다. 또한 산화 알루미늄 액적들의 경우 노즐 벽면에 고착되게 되면 로켓의 중량 증가로 인해서 추력의 손실을 초래할 수 있다. 따라서 이러한 연소 부산물들의 운동 경로와 충돌 위치 및 표면에서의 충돌량과 그리고 충돌에 따른 마모량 및 점착 그리고 열전달 특성을 예측하는 것이 필수적이다.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.2 s.179
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• pp.81-87
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• 2006

This study has been focused on the analysis of high speed shear forming process for lead-acid battery grids. The grid plays an important role of electrical charge. It is necessary to ensure the best battery's performance that the grid should have a best quality. The clearance between punch and die, the velocity of punch and the critical damage value are very important parameters for making a good grid form. The finite element analysis of the shear forming process is carried out by measuring and optimizing these three important parameters. The result of this study concludes that these parameters has a great influence on grid quality.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.30 no.2
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• pp.23-28
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• 2007

"Getting to market first" is extremely critical in this competitive business environment. The speed at which products are developed and released to market is tightly linked to profitability and market share. Many companies that have been very skeptical of Rapid Tooling (RT) technologies developed so far are working on Hybrid Tooling (HT) that can really meet the market standards. This paper describes the experimentation how HT process has been being successfully established and effectively applied with typical case study. Through the experimentation, Ceramic-filled HT was found to be aptly suited for the low grade mold, both in terms of the lead time, dimensional accuracy, and tooling cost.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.54-58
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• 2003

Jet vane is an useful component which is installed at the end of a nozzle for the purpose of the posture control and the secure controlling stability during the initial launching of a rocket. Small space for installation and rapid response are considered as its merits but it is ablated thermally and mechanically by the combusted gas having high velocity and temperature produced in a combustion chamber. En this study, as the fundamental study for the ablation analysis of jet vane, the heat transfer into a jet vane which is located in the supersonic flow field.