• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.335-344
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• 2016

Scientific CubeSat with Instruments for Global Magnetic Fields and Radiations (SIGMA) is a 3-U size CubeSat that will be operated in low earth orbit (LEO). The SIGMA communication system uses a very high frequency (VHF) band for uplink and an ultra high frequency (UHF) band for downlink. Both frequencies belong to an amateur band. The ground station that communicates with SIGMA is located at Kyung Hee Astronomical Observatory (KHAO). For reliable communication, we carried out a laboratory (LAB) test and far-field tests between the CubeSat and a ground station. In the field test, we considered test parameters such as attenuation, antenna deployment, CubeSat body attitude, and Doppler frequency shift in transmitting commands and receiving data. In this paper, we present a communication performance test of SIGMA, a link budget analysis, and a field test process. We also compare the link budget with the field test results of transmitting commands and receiving data.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.5
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• pp.2400-2413
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• 2019

Doubly-selective (DS) fading channel is often occurred in many orthogonal frequency division multiplexing (OFDM) communication systems, such as high-speed rail communication systems and underwater acoustic (UWA) wireless networks. It is challenging to provide an accurate and fast estimation over the doubly-selective channel, due to the strong Doppler shift. This paper addresses the doubly selective channel estimation problem based on complex exponential basis expansion model (CE-BEM) in OFDM systems from the perspective of distributed compressive sensing (DCS). We propose a novel DCS-based improved sparsity adaptive matching pursuit (DCS-IMSAMP) algorithm. The advantage of the proposed algorithm is that it can exploit the joint channel sparsity information using dynamic threshold, variable step size and tailoring mechanism. Simulation results show that the proposed algorithm achieves 5dB performance gain with faster operation speed, in comparison with traditional DCS-based sparsity adaptive matching pursuit (DCS-SAMP) algorithm.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.3
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• pp.245-256
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• 2024

Following the introduction of civilian navigation, the commercial Global Navigation Satellite System (GNSS) receivers' market has been expanding in various fields such as autonomous driving and smart cities. With improved receiver performance and widespread use of GNSS, the configurations of base and rover receivers are becoming more complex. As a result, user must consider combinations of base stations with different qualities, costs, and performances. To address these issues, we conducted zero-baseline tests to analyze the double-differenced code-pseudorange noise of various receiver combinations, ranging from low- to high-cost. The results showed that the noise varied depending on the receiver combination. Notably, receivers from the same manufacturer exhibited similar noise and positioning errors despite significant price differences. We also found that the double-differenced noise of all receiver combinations was correlated with the Carrier-to-Noise Density Ratio (C/N0), the satellite elevation angle, and the Doppler shift, and it did not perfectly follow a normal distribution. Further analysis based on Modified Allan Deviation (MDEV) showed that different types of noise were observed for each receiver combination and the double-differenced noise and positioning errors have similar statistical characteristics. From this study, the importance of receiver combinations and their various characteristics can be better understood.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.185.1-185.1
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• 2010

원격탐사(remote sensing)란 관측 대상과의 접촉 없이 멀리서 정보를 얻어내는 기술을 말한다. 기상관측분야에는 이미 소다(SODAR) 장비가 폭넓게 사용되거 왔으나 최근 풍력자원평가(wind resource assessment)를 위한 풍황측정에 SODAR와 더불어 라이다(LIDAR)가 적극적으로 활용되기 시작하고 있다. 참고로 SODAR(SOnic Detection And Ranging)는 수직 및 동서 남북 방향으로 음파를 발생시키고 대기유동에 의해 산란 반사된 에코를 수신하여 진동수 변화와 반사에코 강도를 측정하여 각 방향의 에코자료를 벡터 합성함으로써 풍향 및 풍속을 산출하는 원리이다. 반면 LIDAR(Light Detection And Ranging)는 비교적 최근에 풍황측정 용도로 개발된 레이저 탐지에 바탕을 둔 원거리 센서로, 공기입자(먼지, 수증기, 구름, 안개, 오염물질 등)에 의해 산란된 레이저 발산의 도플러 쉬프트(Doppler shift)를 이용하여 풍향 및 풍속을 측정하는 원격탐사 장비이다. 풍력자원평가 측면에서 라이다는 그 정확도가 IEC61400-12에 의거한 풍황탑(met-mast) 측정자료 다수와의 비교검증 실측평가(Albers et al., 2009)를 통하여 입증된 바 있다. 한편 한국에너지기술연구원에서 운용 중인 라이다 시스템은 그림 1의 우측 그림과 같이 1초에 $360^{\circ}$를 스캔하여 50지점에서 반사되는 레이저를 스펙트럼으로 측정하되 설정된 관측높이에서 풍속은 샘플링 부피(sampling volume)의 평균값으로 정의된다. 그런데 샘플링 부피는 설정된 관측높이로부터 상하 12.5m, 총 25m의 높이구간에서 관측한 스펙트럼의 평균값을 그 중앙지점에서의 풍속으로 환산하는 알고리듬(algorithm)을 채택하고 있다. 따라서 비선형적으로 변화하는 풍속연직분포 관측 시 풍속환산 알고리듬에 의한 측정오차가 개입될 가능성이 존재하는 것이다. 이에 본 연구에서는 라이다에 의한 풍속연직분포 측정 시 샘플링 부피의 구간 평균화 과정에서 발생하는 불확도(uncertainty)를 정량적으로 분석함으로써 라이다에 의한 풍속연직분포 관측의 불확도를 정량평가하고자 한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.10
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• pp.966-980
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• 2011

Radar receiving echo signal provides target information - range, velocity and position by signal magnitude and Doppler shift, which are determined by target reflection characteristics and target maneuver. Target angle error is extracted from the magnitude ratio of difference channel to sum channel. In this paper, we introduce a radar Return Signal Simulation Equipment(RSSE) which is implemented for the purpose of performance analysis and evaluation of phased array multi-function radar(MFR). It generates multi-target environment with jamming signals using MC-DDS (Multi-Channel Direct Digital Synthesis), and has scalability by using the efficient hardware configuration. The performance of the developed RSSE has been evaluated under various test environments. Especially, we proved that required target detection performance is achieved by RSP(Radar Signal Processor) interfaced RSSE configuration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7B
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• pp.1351-1360
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• 1999

In frequency selective channels, conventional PN code acquisition schemes are not ideal candidates. This is because they are primarily designed for the AWGN channel. In this paper, a direct-sequence spread-spectrum(DSSS) PN code acquisition system based on digital matched filtering (DMF) with automatic threshold control(ATC) algorithm is presented and analyzed with regards to probability of detection and probability of false alarm. These two important probabilities, the probability of detection ($P_D$) and the probability of false alarm ($P_{FA}$) are derived and analyzed in considering Doppler shift, sampling rate, mean acquisition time, and PN chip rate in frequency selective Rayleigh fading channel when using serial-search method as detection technique. From computer simulation results of a DMF acquisition system model, it is shown that the performance of the acquisition system using ATC algorithm is better than that of constant threshold system.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.4
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• pp.21-26
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• 2007

A study on analysis and application of ocean currents information extracted from SAR (Synthetic Aperture Radar) satellite image. The current information extracted from SAR satellite image is not real vector information but scalar information in normal direction of orbital path. To correct current information extracted from satellite image, observation of currents in the field is carried out at the same time and area as those of satellite image. In the analysis, current information extracted from satellite image is corrected by using observed ones. By this correction, the speed and the direction of current can be estimated. The extract current information seem to agree well with the observed ones.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.74-77
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• 2015

WiSee is by utilizing the frequency of Wi-Fi(802.11n/ac), a technique for performing the operation recognized by the user's gesture. Current motion recognition scheme are using a dedicated device (leaf motion, Kinekuto) and the recognition range is 30cm ~ 3.5m. also For recognition range increases the narrow recognition rate, there is inconvenience for maintaining a limited distance. But WiSee is used by Wi-Fi it is possible to anywhere motion recognition if available location. Permeability also has advantages as compared with the conventional recognition method. In this paper I take a look at the operation process and the recent trend of WiSee.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.5
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• pp.444-450
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• 2004

In mobile communications environment, STBC-OFDM(Space Time Block Code-Orthogonal Frequency Division Multiplexing) system with transmit diversity obtains the MRRC(Maximal Ratio Receiver Combining) diversity gain in time-invariant channel between two received symbols. But in time-variant channel, due to the interference between received symbols, MRRC diversity gain cant be obtained. So, when the mobile device with transmit diversity moves in high speed, the scheme to reduce the performance degradation due to the interference is needed. In this paper, we propose the receiver architecture with advanced transmit diversity, which improves the performance of STBC-OFDM system. The proposed architecture obtains the diversity gain without the change of transmit bandwidth at the receiver with the interference canceller using ZF(Zero Forcing) algorithm. Simulation results show performance improvement as doppler shift is increasing.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.1
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• pp.53-58
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• 2017

UFMC is known as the one among novel multi-carrier modulation techniques which are designed for replacing OFDM for 5G wireless communication systems. It is the generalized model of OFDM and FBMC, which combines the advantages of OFDM and FBMC and avoids their weak points. UFMC is more robust in synchronization condition like Time-frequency misalignment compared to CP-OFDM. Moreover UFMC is more proper to burst uplink transmission like M2M 5G Communications. In this paper we analyze the BER performance in various channels and speeds. The simulation result shows that the BER performance is lowered when mobile devices are moving fast and the BER performance is so sensitive for the good channel environment.