• ETRI Journal
• /
• 제31권2호
• /
• pp.182-192
• /
• 2009

Rain attenuation and intercell interference are two crucial factors in the performance of broadband wireless access networks such as local multipoint distribution systems (LMDS) operating at frequencies above 20 GHz. Power control can enhance the performance of downlink CDMA-based LMDS systems by reducing intercell interference under clear sky conditions; however, it may damage system performance under rainy conditions. To ensure robust operation under both clear sky and rainy conditions, we propose a novel power-control scheme which applies an adaptive neuro-fuzzy inference system (ANFIS) for downlink CDMA-based LMDS systems. In the proposed system, the rain rate and the number of users are two inputs of the fuzzy inference system, and output is defined as channel quality, which is applied in the power control scheme to adjust the power control region. Moreover, ITU-R P.530 is employed to estimate the rain attenuation. The influence of the rain rate and the number of users on the distance-based power control (DBPC) scheme is included in the simulation model as the training database. Simulation results indicate that the proposed scheme improves the throughput of the DBPC scheme.

• 한국지구과학회지
• /
• 제40권1호
• /
• pp.56-67
• /
• 2019

본 연구에서는 미국 남캘리포니아 지진센터에서 개발한 물리적 지진모델링 기반 광대역 강지진동 모사 플랫폼(버전 16.5)을 활용하여, 규모 6.0, 6.5, 7.0 지진에 대한 진도 감쇠 특성 분석을 수행하였다. 지진 발생 위치는 2016년 규모 5.8 경주 지진 진앙 인근을 가정하였으나 지각 전파 모델의 경우 남캘리포니아 강지진동 모사 플랫폼에서 제공하는 미국의 대표적인 지각 모델 두 개를 사용하였다. 하나는 판 내부를 대표하는 미국 중동부 지역(Central and Eastern United States, CEUS) 모델이고 다른 하나는 판의 경계를 대표하는 미 서부 지역(LA Basin) 모델이다. 버전 16.5 플랫폼에는 5개의 모델링 방법론이 제시되고 있으며 본 연구에서는 Song 모델과 Exsim 모델을 사용하였다. 동일 규모의 지진이라 하더라도 지진발생 환경이 다른 지역(CEUS vs LA Basin)에서는 같은 진앙 거리에서 진도 2 등급에 가까운 차이가 발생할 수 있음을 본 연구를 통해서 발견하였다. 본 연구에서 나타난 지역별 진도 감쇠 특성의 차이를 감안할 때 한반도에서 좀 더 정밀한 지진재해 평가를 위해서는 지역에 적합한 진도 감쇠 특성을 이해하는 것이 중요할 것으로 판단되며 본 연구는 지역 특화된 진도 감쇠 특성을 고려하지 않을 경우 진도 감쇠 분포의 불확실성 정도를 잘 보여준다.

• 전기학회논문지
• /
• 제65권10호
• /
• pp.1774-1779
• /
• 2016

This paper proposes a portable cable fault detection system with automatic fault distinction and distance measurement using time-frequency correlation and reference signal elimination method and automatic fault classification algorithm in order to have more accurate fault determination and location detection than conventional time domain refelectometry (TDR) system despite increased signal attenuation due to the long distance to cable fault location. The performance of the developed system method was validated via an experiment in the test field constructed for the standardized performance test of power cable fault location equipments. The performance evaluation showed that accuracy of the developed system is less than 1.34%. Also, an error of automatic fault type and location by detection of phase and peak value through elimination of the reference signal and normalization of correlation coefficient and automatic fault classification algorithm not occurred.

• 설비공학논문집
• /
• 제26권3호
• /
• pp.103-107
• /
• 2014

To assess a various of workplace noise environment in the tunnel construction site, the measurement is performed while tunnel constructing work. This study focuses on the sound attenuation according to the sound frequency characteristics and the distance from various works in the tunnel. Also, the noise distribution while blasting work is measured according to distance in this study. In addition, the boring processing, muck treatment, and tunnel lining by distance are measured for the noise distributions.

• 한국의학물리학회지:의학물리
• /
• 제4권1호
• /
• pp.55-71
• /
• 1993

Measured and calculated the TMR and SMR factors from percent depth dose underpartial attenuators which cover the whole part of the radiation beam with variousfilter thickness from 0 to 50 mm. This study was performed for x-ray beams generated with a 6 MV linear acceleratorat source to surface distance of 100cm in a water phantom for Lipowitz metal. TMR(0,d,t) was derived from non-linear polynomial regression with field sizedifferencies and a given filter thickness. In this experiments, the TMR(0,10,50) of 50mm of filter thickness was showed13.6 % higher than that of open field and SMR(5,10,50) was 38.5% smaller than thatof open field in same depth.

• 한국의학물리학회:학술대회논문집
• /
• 한국의학물리학회 2002년도 Proceedings
• /
• pp.263-266
• /
• 2002

We have developed a practical method for estimating high-energy x-ray spectra using measured attenuation curves. This method is based on the iterative perturbation technique proposed by Waggener et al. The principle is to minimize the difference between the measured and calculated transmission curves. The experimental study was made using 4 MV, 10 MV, and 15 MV x-ray beams. It has been found that the spectrum varies strongly with the off-axis distance.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1999년도 제14차 학술회의논문집
• /
• pp.274-277
• /
• 1999

This paper is concerned with estimating the mass of a loose part in the steam generator of a nuclear power plant. Although there is the basic principle known as “Hertz Theory”for estimating mass and energy of a spherical part impacted on an infinite flat plate, the theory is not directly applicable because real plants do not comply with the underlying ideal assumptions. (Say, the steam generator is of a cylindrical and hemisphere shape.) In this work, a practical method is developed based on the basic theory and considering amplitude and energy attenuation effects. Actually, the impact waves propagating along the plate to the sensor locations become significantly different in shape and frequency spectrum from the original waveform due to the plate and surrounding conditions, distance attenuation and damping loss. To show the validity of the present mass estimation algorithm, it has been applied to the mock-up impact test data and also to real plant data. The results show better performance comparing to the conventional Hertz schemes.

• 전기학회논문지
• /
• 제61권3호
• /
• pp.497-502
• /
• 2012

Power line communication(PLC) is a kind of communication technology, was made use of controling a frequency narrow band, but as the PLC technology developing, in the near future get to the commercial step that is broadband PLC upto 30 MHz. This paper deals with the PLC of electric railway using capacitive signal coupler. An AC arrester for catenary is used as a capacitive signal coupler, has the characteristic of capacitor. As a result of field test, a messenger wire used PLC contain much of conducted noise about overall frequency band and also signal attenuation rate increased with increasing frequency between two points. and the communication speed of PLC used messenger wire is 793kbps at a distance of 40m. Experimental results show the possibility of PLC using a messenger wire and an AC arrester for catenary at electric railway.

• 한국석유지질학회:학술대회논문집
• /
• 한국석유지질학회 2005년도 제12차 학술발표회 초록집
• /
• pp.9-16
• /
• 2005

The electromagnetic (light) waves are limited to penetrate the media, ie, water and sea-bottom layers, due to high energy attenuation, but acoustic (sound) waves play as the good messenger to gather the underwater target information. Therefore the acoustic methods are applied to almost of ocean equipments and technology in terms of in-water and sub-bottom surveys, Generally the sound character is controlled by its frequency. In case that the sound source is low frequency, the penetration is high and the resolution is low. On the other hand, its character is reversed at the high frequency. The common character at the both of light and sound is the energy damping according to the travel distance increase.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 1998년도 Proceedings of International Symposium on Remote Sensing
• /
• pp.138-148
• /
• 1998

The aim of the work described in this paper is to develop a complex underground acoustic system which detects and localizes the origin of an underground hammering sound using an array of hydrophones located about loom underground. Three different methods for the sound localization will be presented, a time-delay method, a power-attenuation method and a hybrid method. In the time-delay method, the cross correlation of the signals received from the way of sensors is used to calculate the time delays between those signals. In the power-attenuation method, the powers of the received signals provide a measure of the distances of the source from the sensors. A new hybrid method has been developed for estimating the origin of the underground acoustic source by coupling both methods. The Nelder-Meade simplex search algorithm is then used to numerically estimate the position of the source in those methods. For each method the sound localization is carried out in three dimensions underground. The distance between the true and estimated origins of the source is in some cases less than 6m for a search area of radius 250m.