• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.509-516
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• 2006

Satellite-Digital Multimedia Broadcasting(S-DMB) systems are single frequency networks which consist of a satellite and gap fillers. Though gap fillers are required to extend the coverage to NLOS(Non Line-of-Sight) area, the receiver performance can be degraded with a limited number of fingers due to the increased number of multi-paths. The paper proposes to use frequency domain equalizer(FDE) instead of conventional Rake receiver, where the guard interval is not considered in order to minimize the impact on the current S-DMB systems. Through a campaign of simulations, it is found that the proposed FDE is less sensitive to the number of gap fillers compared to the conventional Rake receiver, and can achieve a greater channel capacity in most channel environments.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2006.11a
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• pp.223-227
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• 2006

본 논문에서는 이동 환경에서 지상파DTV의 Delay Profile의 도출을 위하여 이동 상태에서 필드테스트로 측정된 수신데이터에 포함되어 있는 PN 511(Psuedo Noise)코드를 이용하여 다양한 이동환경에서의 ACF(Auto Correlation Function)값을 도출하였다. 또한, 지역별 대표적인 LOS지역, NLOS지역, 중간지역으로 구분되는 대표적인 세 곳을 선정하여 다양한 이동속도에서의 도출된 ACF값을 통해 최대지연, 평균지연, RMS 지연을 도출하여 이동환경에서의 지상파 DTV의 Delay Profile을 제시하였다.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.283-287
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• 2001

본 논문에서는 3D Ray Tracing 편파특성 예측 시뮬레이터를 개발하고 초고속 옥내 무선환경에서의 원형편파 우수성을 시뮬레이션을 통하여 확인하였다. 제안된 3D Ray Tracing 기법을 이용하여 시뮬레이션 한 결과 기수회의 반사파가 수신기에서 수신되지 않는 원형판파의 특성 때문에 다중경로 페이딩을 현저히 감소시킬 수 있음을 확인하였다. 또한, 옥내 가시거리(LOS) 및 비가시거리(NLOS) 환경에서의 원형편파를 이용한 페이딩 경감효과는 수직 및 수평견파나 편파다이버시티보다 우수함을 알 수 있었고, DS-CDMA 시스템을 이용한 경우에 있어서도 원형편파가 보다 우수한 BER 성능을 나타냄을 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.1014-1019
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• 2006

The research deals with the measurement of electromagnetic wave propagation in subway tunnels at 2.65GHz. Measurements have been conducted in 4 different types of tunnel courses, a straight tunnel, two curved tunnels, with 245m and 500m radius of curvature, and a tunnel that has both straight and curved sections. we found that the path loss exponent for the line-of-sight(LOS) region inside all the tunnels is $1.31{\sim}2.19$. The path loss exponents for LOS regions in the tunnel is lower than $(3{\sim}4)$, which corresponds to the path loss exponent factor for outdoor cellular environments. The path loss exponents of the straight tunnel, two curved tunnels with 245m and 500m radius of curvature are 1.94, 2.92, and 4.34, respectively. This indicates that a smaller radius of curvature in tunnel results in a higher path loss exponent for nonline-of-sight(NLOS) region. The path loss exponents for the NLOS region in the combined and curved tunnel, which have the same radii of cuvature, are 5.88 and 4.34, respectively. Therefore, it can be concluded that the path loss characteristics in tunnel environments are infulenced by the radii of curvature as well as the LOS distance.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.5 no.2 s.10
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• pp.19-28
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• 2006

In the IEEE 802.15.4a system, they require simple, economical and low power consumption transmitter and receiver to transmit low rate data and to identify distance and location. To meet these requirements, LR-WPAN system use transmitter and receiver with simple modulation and demodulation scheme. In this paper, use PPM+BPSK modulation and windowing scheme to overcome multipath fading effect. Then we apply this channel estimation scheme to LR-WPAN system and compare performance depends on transmitter scheme. Proposed method using preamble to find channel characteristic out and we compensate distorted data with that information. Therefore we can detect signal easily at the demodulation part. Simulation result shows that performance evaluation is greater at the NLOS channel than LOS channel no matter what the receiver scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2B
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• pp.287-295
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• 2010

RTLS used to track the location of object or person in real time. However, if there are a lot of tags and readers, the conventional single RTLS server may fail to estimate location of tags. And if the server cannot receive the tags signal due to pass-loss or NLOS from more than three readers, the server fail to estimate location of tags. In this paper, we propose a special reader which embeds RTLS location engine for distributed RTLS. And by using multi-directional antenna, alleviating multi-path effect and allowing estimate tag's location only using two readers. We also implement the system, we can reduce server packet 16times and get the all results of location estimate in single second. We achieved the location error within 1m.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.5
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• pp.578-588
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• 1998

In this paper, we analyzed the propagation characteristics of polarization diversity in the view of diversity gain, cross correlation coefficient and average received signal strength, and compared it with those of space diversity. From the results, we could confirm that in the care of line of sight(LOS), space diversity gain is bigger than polarization diversity gain by 2 dB and the diversity gain of mobile transmitting with 90 degree is bigger than that of mobile transmitting with 45 degree by 1 dB. However, in the area of non-line of sight(NLOS), the diversity gains were all most the same in two diversity schemes and in specular cases, polarization diversity showed better performances. Also it was verified that under the NLOS conditions, diversity gain of mobile transmitting with 45 degree was at least 1 dB bigger than that of mobile transmitting with 90 degree.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.91-97
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• 2018

This paper presents implementation possibilities of digital IoT doorlock systems via VLC(Visible Light Communication)'s color grid. The color grid-based VLC modulation scheme which are discussed in this paper utilize the straightness of light and abundant frequency resources which are the properties of the light. Performance results in this paper are compared to that of conventional modulations with Bit Error Rate (BER) and Signal to Noise Ratio (SNR) simulations. With respect to a channel model, the proposed modulation schemes select the nearest Line Of Sight (LOS) except Non Line Of Sight (NLOS). Experiments in this paper show error rates of received symbols by changing power dB at a distance of 3m between Tx and Rx in an indoor environment. Through performance results and experiments, this paper demonstrates superiority of the proposed color grid-based modulation schemes.

• Journal of Internet Computing and Services
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• v.6 no.5
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• pp.167-175
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• 2005

In the microcell or picocell-based system the frequent movements of mobiles bring about excessive traffics Into the networks. A mobile location estimation mechanism can facilitate both efficient resource allocation and better QoS provisioning through handoff optimization. Existing location estimation schemes consider only LOS model and have poor performance in presence of multi-path and shadowing. In this paper we study multi-criteria decision making which can increase estimation accuracy by considering other multiple decision parameters than the received signal strength.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.298-301
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• 2003

본 논문에서는 2.4 [GHz] 대역에서 1(equation omitted)2 마이크로스트림 배열 안테나를 이용한 지하철 터널내의 전파특성을 고찰하였다. 445 [m]의 터널구간에서 협대역 측정결과 LOS (Line-of-Sight)구간에 비하여 NLOS(Non-Line-of-Sight)구간에서는 수신 전력 레벨이 급격히 감소 하였으며, 10단 길이의 PN Sequence를 이용한 광대역 채널 측정에서는 Fan Beam의 평균과도지연과 RMS 지연확산이 각각 3.5736 [ns]과 11.7327 [ns]로서 원편파와 지향성 빔에 비하여 우수함을 확인하였다. 또한 전체 측정구간에 대한 평균과도지연과 RMS 지연확산의 중간값과 표준편차를 구하였고 각각의 빔에 대하여 비교하였다.