• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권9호
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• pp.2590-2608
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• 2023

The high-altitude and mobility characteristics of unmanned aerial vehicles (UAVs) have made them a key element of new radio systems, particularly because they can exceed the limits of terrestrial networks. However, at high altitudes, UAVs can be significantly affected by intercell interference at a high line-of-sight probability. To mitigate this drawback, we propose an algorithm that selects the optimal beam to reduce interference and maximize transmission efficiency. The proposed algorithm comprises two steps: constructing a user-location-based fingerprint database according to the user types presented herein and cooperative beam selection. Simulations were conducted using cellular cooperative downlink systems for analyzing the performance of the proposed method, and the signal-to-interference-plus-noise cumulative distribution function and spectral efficiency cumulative distribution function were used as performance analysis indicators. Simulation results showed that the proposed algorithm could reduce the effect of interference and increase the performance of the desired signal. Moreover, the algorithm could efficiently reduce overheads and system cost by reducing the amount of resources required for information exchange.

• 전자공학회논문지
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• 제54권6호
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• pp.65-71
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• 2017

디지털 이미지나 비디오는 저장, 전송을 하는 과정에서 여러 가지 종류의 잡음이 발생하게 된다. 이러한 잡음 중 Salt & Pepper 잡음은 원본 데이터를 훼손하여 압축 효율을 저하시키고 영상 처리 방법으로 이용하는 Edge Detection이나 Segmentation에서의 성능저하를 일으키는 요인이 된다. 이 잡음을 완화하기 위한 방법으로 Median Filter, Weighted Median Filter, Center Weighted Median Filter, Switching Weighted Median Filter, Adaptive Median Filter 등이 있다. 하지만 이러한 방법들은 높은 잡음의 밀도에서 성능이 다소 미흡하다. 따라서 본 논문에서는 Salt & Pepper 잡음이 발생하는 무선 통신 환경에서 잡음 완화를 위한 새로운 형태의 필터를 제안한다. 제안한 필터는 Salt & Pepper 잡음 감지를 통해 훼손된 픽셀의 위치를 확인하고 일정 영역의 훼손되지 않은 인접 픽셀 값들을 이용하여 잡음을 완화한다. 제안하는 필터 중 $3{\times}3$ 크기의 에러 마스크를 이용하는 필터의 성능을 기존의 방법들과 비교하여 PSNR을 통해 평가하였을 때, 이미지에서 잡음의 밀도가 95%일 때, MF와 비교하여 13.24 dB, AMF와 비교하여 13.09 dB의 성능을 향상시키는 것을 확인하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.1977-1983
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• 2009

This paper described partial discharge(PD) patterns depending on types of insulation defects in CNCO-W cable(Concentric Neutral Closs-linked Polyethylene Insulated Polyolefin-Water Proof Sheathed Power Cable). The PD measurement system consists of a coupling network, a detection impedance, and a low noise amplifier. A 16 bit, 250 MS/s data acquisition system was used to analyze PD patterns. To simulate insulation defects in a power cable, a needle with the curvature radius of $10{\mu}m$ was inserted into the insulation part. We measured phase ($\Phi$), magnitude (q), and counts (n) of PD pulse for the defects, and classified PD patterns using the PRPD (phase Resolved Partial Discharge) method. From the analysis of acquired PD signals, we could find that a unique PD pattern is formed according to the types of defect.

• Journal of Communications and Networks
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• 제8권3호
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• pp.313-322
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• 2006

We consider a power controlled code division multiple access (CDMA) system with multiple flow types. At each of the N nodes, there are F flow types with different signal-to-interference-and-noise-ratio (SINR) requirements. To keep the complexity of the transmitter low, we assume that each node uses the same power level for all its flows. The single flow case has been fully solved and is well-understood. We concentrate on the multiple flow case, and use a novel and different approach. For the uplink problem with N = 2 and F arbitrary, the necessary and sufficient conditions to have a solution are found and proved. For the general N > 1 uplink problem, we provide a necessary condition for the problem to have a solution and an iterative algorithm to find the optimum solution. For the downlink case with F > 1 some properties of the optimal sequences are obtained.

• Smart Structures and Systems
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• 제14권4호
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• pp.699-718
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• 2014

The indirect displacement estimation using acceleration and strain (IDEAS) method is extended to various types of beam structures beyond the previous validation on the prismatic or near-prismatic beams. By fusing different types of responses, the IDEAS method is able to estimate displacements containing pseudo-static components with high frequency noise to be significantly reduced. However, the concerns to the IDEAS method come from possible disagreement of the assumed sinusoidal mode shapes to the actual mode shapes, which allows the IDEAS method to be valid only for simply-supported prismatic beams and limits its applicability to real world problems. In this paper, the extension of the IDEAS method to the general types of beams is investigated by the mathematical formulation of the modal mapping matrix only for the monitored substructure, so-called monitoring span. The formulation particularly considers continuous and wide beams to extend the IDEAS method to general beam structures that reflect many real bridges. Numerical simulations using four types of beams with various irregularities are presented to show the effectiveness and accuracy of the IDEAS method in estimating displacements.

• 한국항행학회논문지
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• 제6권1호
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• pp.52-62
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• 2002

본 논문에서는 출력단에 Wilkinson 전력결합기 또는 T 접합 전력결합기를 사용한 20 GHz Push-Push FET 유전체 공진기 발진기를 설계 제작하고 그 특성을 조사 연구하였다. 기본 주파수 10 GHz를 억제하고 제 2 고조파 주파수를 이용하는 20 GHz Push-Push 발진기를 $TE_{01{\delta}}$ 모드의 유전체 공진기와 GaAs MESFET를 두께 H = 20 mil(${\varepsilon}_r$=2.52) 테프론기판 위에 장착하는 구조로 설계하고 제작하였다. Wilkinson 전력결합기를 이용하여 제작된 발진기는 20 GHz에서 출력 전력이 5.67 dBm, 기본 주파수 억압특성은 -29.33 dBc, 위상 잡음은 100 kHz offset에서 -105.5 dBc/Hz 특성을 나타내었으며, T 접합 전력결합기 이용하여 제작된 발진기는 20 GHz에서 출력 전력이 -1.17 dBm, 기본 주파수 억압특성은 -17.84 dBc, 위상 잡음은 100 kHz offset에서 -102.2 dBc/Hz 특성을 나타내었다.

• Journal of Multimedia Information System
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• 제4권4호
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• pp.163-170
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• 2017

Internet of things (IoT) is a new paradigm for collecting, processing and analyzing various contents in order to detect anomalies and to monitor particular patterns in a specific environment. The collected data can be used to discover new patterns and to offer new insights. IoT-enabled data mashup is a new technology to combine various types of information from multiple sources into a single web service. Mashup services create a new horizon for different applications. Environmental monitoring is a serious tool for the state and private organizations, which are located in regions with environmental hazards and seek to gain insights to detect hazards and locate them clearly. These organizations may utilize IoT - enabled data mashup service to merge different types of datasets from different IoT sensor networks in order to leverage their data analytics performance and the accuracy of the predictions. This paper presents an IoT - enabled data mashup service, where the multimedia data is collected from the various IoT platforms, then fed into an environmental cognition service which executes different image processing techniques such as noise removal, segmentation, and feature extraction, in order to detect interesting patterns in hazardous areas. The noise present in the captured images is eliminated with the help of a noise removal and background subtraction processes. Markov based approach was utilized to segment the possible regions of interest. The viable features within each region were extracted using a multiresolution wavelet transform, then fed into a discriminative classifier to extract various patterns. Experimental results have shown an accurate detection performance and adequate processing time for the proposed approach. We also provide a data mashup scenario for an IoT-enabled environmental hazard detection service and experimentation results.

• 한국소음진동공학회논문집
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• 제24권12호
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• pp.985-991
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• 2014

The combined method utilizing airborne LiDAR and GIS data is suggested to extract 3-dimensional hybrid city model including roads and buildings. Combining the two types of data is more efficient to estimate the elevations of various types of roads and buildings than using either LiDAR or GIS data only. This method is particularly useful to model the overlapped roads around the so called spaghetti junction. The preliminary model is constructed from the LiDAR data, which can give wrong information around the overlapped parts. And then, the erratic vertex points are detected by imposing maximum vertical grade allowable on the elevated roads. For the purpose of efficiency, the erratic vertex points are corrected through linear interpolation method. To avoid the erratic treatment of the LiDAR data on the facades of buildings 2 meter inner-buffer zone is proposed to efficiently estimate the height of a building. It is validated by the mean value(=5.26 %) of differences between estimated elevations on 2 m inner buffer zone and randomly observed building elevations.

• 한국재난정보학회 논문집
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• 제10권2호
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• pp.274-281
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• 2014

선하역사는 역사 건물의 상부에 위치한 노반구조물을 통하여 열차 운행으로 인한 진동이 직접 역사 구조물로 전달되므로 소음 진동에 취약한 구조이다. 선하역사 내부의 소음은 주로 구조물의 진동으로 인하여 발생하는 고체소음이므로 보다 효율적인 진동 저감 대책의 수립을 위해서는 역사의 구조 형식, 부재 및 재료 등의 구성 요소에 따른 구조적 거동 및 감쇠 특성의 파악이 중요하다. 이 논문에서는 선하역사와 인접 교량과의 접속부의 역학적 특성에 따른 진동 특성 변화에 대한 검토 결과를 제시하였다. 해석 대상 역사는 대천역이며, ABAQUS로 유한요소해석을 수행하였다. 접속부 특성은 접속 교량이 있는 경우와 없는 경우, 그리고 있는 경우 라멘식과 받침형식으로 구분하여 검토를 수행하였다.

• 한국초등과학교육학회지:초등과학교육
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• 제43권1호
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• pp.81-94
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• 2024

이 연구에서는 생활 속 위험 문제 중 하나인 '소음'에 대해 예비교사들이 수행한 과학탐구 사례를 중심으로 서로 다른 유형의 데이터 활용에서 나타나는 인식적 특징을 탐색하고 비교하였다. 이를 위해, 소음에 대한 탐구 보고서를 수집하고, 탐구 보고서에서 1차 데이터와 2차 데이터가 어떻게 과학탐구에 활용되는지, 데이터의 유형에 따라 탐구 설계, 자료 수집 및 분석 과정이 어떻게 달라지는지를 분석하였다. 연구 결과, 센서 기반의 1차 데이터는 핵심 현상을 측정하고 관찰하는 주체가 탐구자 자신이지만, 2차 데이터는 공공 기관에서 이미 측정 대상과 방법을 결정하여 데이터로 제시하였기 때문에 예비교사들은 공공 데이터의 특징을 먼저 조사하고 탐구 목적에 맞게 선별적으로 활용하였다. 이러한 차이로 인해 탐구 과정에서 요구되는 인식적 고려 사항과 방식이 서로 달랐다. 끝으로 이러한 연구 결과가 과학탐구 교수학습 및 탐구 지도를 위한 교사교육, 그리고 변동성과 불확실성이 극대화될 VUCA 시대를 대비한 위험 대응 역량 교육의 측면에서 갖는 교육적 시사점을 논의하였다.