• Information and Communications Magazine
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• v.24 no.5
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• pp.84-97
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• 2007

MIMO 기술은 데이터 전송률을 증대시키고 수신 성능을 향상시킬 수 있는 다중 안테나 기술로써 각광받아왔다. 그러나 단말 크기의 제한으로 인하여 구현에 큰 어려움이 따르게 되었고 이를 해결하기 위해서 하나의 안테나를 갖고 있는 단말간 서로 협력(cooperation) 하여 데이터 전송률을 높이고 수신 성능을 향상시키기 위한 연구가 논의되고 있다. 특히 ad-hoc 이나 mesh 네트워크에서의 다중 홉 기술을 기반으로 단말간 서로 협력하여 채널 용량을 늘리고 수신 성능을 향상시키기 위한 다양한 연구가 진행 중이다. 본 고에서는 다중 홉 중계 기술에 대한 기본적인 개념과 협력 통신 기술, 그리고 IEEE 802.16j 표준화 동향에 대해 살펴본다. 이론적인 채널 용량 분석과 중계(relay)의 목적에 대해 알아보고 중계 기법에 따른 채널 용량을 분석한다. 더 나아가 다중 홉 중계 전송 기법의 성능을 분석하고 다중 홉 지원을 위한 표준화 동향 및 프레임 구조를 알아본다. 마지막으로 다이버시티 이득과 다중화 이득을 얻을 수 있는 협력통신 기술에 대해 살펴본다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1023-1030
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• 2012

The diversity techniques can benefit underwater acoustic communications when the distance between sensors is sufficiently apart, and this leads to the increases in the physical size of the communication system: thus it is very hard to practically use such systems in real-environments. Therefore, in this paper, we have collected data from real underwater cannel environments in order to analyze the usability of diversity combined with beamforming techniques. And we have estimated the fading characteristics from the measurement data, and analyzed the correlation coefficients using the estimated fading characteristics. After analyzing the estimated fading characteristics from the measurements data, we found out that by applying diversity techniques on the output signals from beamformers that perform beamforming from different multipath directions, we can reduce the distance between sensors and at the same time benefit from the diversity gain.

• The KIPS Transactions:PartC
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• v.11C no.6 s.95
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• pp.835-842
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• 2004

In this paper, we have analyzed the MC-DS/CDMA system with input signal synchronized completely through adjustment of the gain in the PLL loop, by using the hybrid SC/MRC-(2/3) technique, which is said to one of the optimal diversity techniques under the multi-path fading environment, assuming that phase error is defined to the phase difference between the received signal from the multi-path and the reference signal in the PLL of the receiver. Also, assuming that the regarded radio channel model for the mobile communication is subject to the Nakagami-m fading channel, we have developed the expressions and performed the simulation under the consideration of various factor, in the MC/DS-CDMA system with the hybrid SC.MRC-(2/3) diversity method, such as the Nakagami fading index(m), $the\;number\;of\;paths\;(L_p),$ the number of hybrid SC.MRC-(2/3) $diversity\;branches\;(L,\;L_c),$ the number of users (K), the number of subcarriers (U), and the gain in the PLL loop. As a result of the simulation, it has been confirmed that the performance improvement of the system can be achieved by adjusting properly the PLL loop in order for the MC/DS-CDMA system with the hybrid SC/MRC-(2/3) diversity method to receive a fully synchronized signal. And the value of the gain in the PLL loop should exceed 7dB in order for the system to receive the signal with prefect synchronization, even though there might be a slight difference according to the values of the fading index and the spread processing gain of the subcarrier.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3A
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• pp.197-204
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• 2009

Cyclic delay diversity (CDD) is considered a simple approach to exploit the frequency diversity, to improve the system performance in orthogonal frequency division multiplexing (OFDM) systems. Also, the linear preceding technique can significantly improve the performance of communication systems by exploiting the channel state in formation (CSI). In order to achieve enhanced performance, we propose applying linear preceding to the conventional CDD-OFDM transmit diversity schemes over Rayleigh fading channels. The proposed scheme works effectively with the accurate CSI in time-division-duplex (TDD) OFDM systems with CDD, where the reciprocity is ass umed instead of channel state feedback. For a BER of $10^{-4}$ and the mobility of 3 km/h, simulation results show that a gain of 6 dB is achieved by the proposed scheme over both flat fading and Pedestrian A (Ped A) channels, compared to the conventional CDD-OFDM system. On the other hand, for a mobility of 120 km/h, a gain of 2.7 dB and 3.8 dB is achieved in flat fading and Vehicular A (Veh A) channels, respectively.

• The Journal of the Acoustical Society of Korea
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• v.31 no.2
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• pp.107-113
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• 2012

In this paper, we have analyzed the performance of space diversity technologies using experimental data in order to analyze the usability of space diversity techniques in underwater channel environments. After analyzing the experimental data we found out that high diversity gain should not be expected when using a stationary transmitter with a stationary receivers in swallow underwater channel. And we also find out that the distance between sensors should be at least 8 wavelengths apart to take advantage of diversity gain in underwater moving channel environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.233-238
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• 2013

In this paper, a novel diversity and directivity mode-switchable planar antenna array is proposed. For the diversity mode, four elements are unfolded on the plane and high isolation can be achieved. On the other hand, the antenna function is changed to the directivity mode when they are folded and stacked. Each element works such as a stacked Yagi-Uda antenna with high directivity. Especially, the curved feed line as well as the hybrid feeding method is used to improve performances. The simulation results agree well with measurement results and it is successfully demonstrated that two modes are properly working at 2.4 GHz.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.607-609
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• 2019

The split-channel two-tone OOK method proposed in this paper can improve the communication performance of IoT in fading channel environment. The frequency diversity effect can be obtained by separating the interval of the two tone signals, and a performance gain of 8 dB can be obtained in the fading channel. In addition, by using split-channel, the problem of degradation of the channel bandwidth efficiency caused by the frequency diversity technique can be prevented, thereby reducing the bandwidth efficiency by allocating the remaining frequency channels to other users.

• Journal of Digital Convergence
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• v.13 no.10
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• pp.319-325
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• 2015

We proposed the blocking channel to reduce the performance decrease using the low correlation with cyclic delay scheme in LED-ID system. LED-ID is based on the visible light to transmit the data. However, It is occurred the block channel by structure or environment of indoor for light of straightness. LED-ID system is degraded the performance by the block channel as loss of data, and burst error. To solve the block channel, the proposed system is overcome the burst error by low correlation among data, which is able to obtain the maximize time diversity gain to improve the performance of BER by cyclic delay scheme. The BER performance is evaluated by computer simulation according to channel parameter. The simulation results shows that proposed system gives much better performance than conventional system and constant cyclic delay scheme system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2B
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• pp.176-183
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• 2011

In this paper, we propose the implementation and performance analysis of power line communication based on SISO/MIMO-OFDM which focuses on high speed data transmission in smart grid and future power line grid. We employ Zimmermann frequency model and Middleton Class A model as the multipath power line fading channel and impulse noise channel, respectively. In this paper, in order to improve the three-phase or single-phase PLC performance, we introduce a new MRC (called a&f-MRC) which effectively sums up multiple antenna diversity gain and multipath fading diversity gain. Via simulation, we prove the performance advantage over existing SISO/MIMO systems. In addition, we offer the tradeoff on system design through comparing with MRC, EGC and SC.

• Information and Communications Magazine
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• v.24 no.5
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• pp.47-62
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• 2007

본 고에서는 셀룰러 이동망에서 다중 홉 릴레이를 도입할 때 셀 경계 및 릴레이 노드의 서비스 영역 경계에서의 서비스 불능 성능을 향상시키기 위한 방안으로서 다이버시티 이득을 제공할 수 있는 협력 통신 방식에 대해서 살펴본다. 협력 통신의 기본 개념과 관련 요소 기술들을 살펴보고, 특히 협력 통신을 고려한 다양한 전송 프로토콜들의 특성을 분석한다. 또한, IEEE 802.16e 규격의 IP-OFDMA기반 광대역 이동 액세스 망에서 이와 같은 협력 통신을 적용할 때 시스템 레벨의 성능 분석 결과를 고찰하고, 실제 시스템에서의 고려 사항에 대해서 살펴본다.