• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.483-487
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• 2003

본 논문에서는 부채널 상관 특성을 이용하여 상관도가 가장 낮은 두 개의 부채널로 정보를 전송함으로써 OFDM 시스템에서 주파수 다이버시티 이득을 얻는 방안을 제안하였다. 제안된 기법은 간단한 심볼 부호화 과정을 통해 상관도가 가장 낮은 두 부채널로 특정한 위상차를 갖는 심볼을 전송하며, 수신단에서는 두 부채널을 통해 수신된 심볼의 위상차를 검출, 조합함으로써 주파수 다이버시티 이득을 얻을 수 있다. 제안된 기법은 부호화 및 복호화 과정이 간단하기 때문에 시스템의 복잡도와 성능면에서 우수하며, 또한 기존의 다중 안테나 신호처리 기술과 결합시킴으로써 송신 및 수신 다이버시티 기법의 성능을 개선할 수 있다. 제안된 기법의 검증을 위해 채널 변화가 느린 레일리 페이딩 환경 하에서 컴퓨터 시뮬레이션을 통해 기존의 OFDM 및 2개의 수신 안테나를 가지는 OFDM 시스템과 성능을 비교, 분석하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.644-651
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• 2007

In multiple antenna systems, vertical Bell Labs Layered Space-Time (V-BLAST) systems enable very high throughput by nulling and cancelling at each layer detection. In this paper, we propose a V-BLAST system which combines with signal space diversity technique. The benefit of the signal space diversity is that we can obtain an additional gain without extra bandwidth and power expansion by applying inphase/quadrature interleaving and the constellation rotation. Through simulation results, it is shown that the performance of the proposed system is less than 0.5dB away from the ideal upper bound.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.85-91
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• 2007

In this paper, we introduce the amplify-and-forward (AF) cooperative diversity with multiple relays using phase feedback. Simulation results show that the AF cooperative diversity with multiple relays using phase feedback not only provide the better performance than the direct transmission, but also obtain the diversity gain according to the number of the cooperating terminals. The performance of proposed scheme using tolerable feedback is close to optimal performance.

• Journal of Navigation and Port Research
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• v.37 no.3
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• pp.269-273
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• 2013

Underwater acoustic channels are generally recognized as one of the most difficult communication media because of the multipath propagation, dispersion, and so on. MIMO (Multiple-input multiple-output) techniques have been actively pursued in underwater acoustic communications recently to increase the data rate over the bandwidth-limited channels. The transmit diversity techniques can be applied in this case, and one of them is Alamouti's scheme. In this paper the performances of the transmit diversity technique are evaluated via experiment. Two transmitters and two receivers were used in experiment, and the experiment was performed in indoor water tank. The error rate 5~8% was confirmed in experimental results, and these are the improved values than the error rate 14.8% for SISO(Single-input single-output) channel under same data rate condition.

• The Journal of the Korea Contents Association
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• v.9 no.4
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• pp.65-71
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• 2009

In this paper a new space-time diversity relaying strategy using cooperative communication technique is proposed. More than one relaying terminals are included in one cooperative group to share their state information, such as frame error rate and channel state information. The best terminals are selected to send bit information using space-time diversity relay system. An implementation for the proposed scheme is also presented using the TDMA cooperative protocol. The resulting receive signal to transmit signal ratio and computer simulation demonstrate that the proposed strategy outperforms the conventional cooperative system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7C
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• pp.954-961
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• 2004

In this paper, we propose a STF(Space-Time-Frequency) coded OFDM(Orthogonal Frequency Division Multiplexing) transmission scheme as an attractive solution for high bit rate data transmission in a multipath fading environment. The STF-OFDM transmission scheme that we propose in this paper is a simple transmission cheme for achieving frequency diversity gain with low complexity. Using preceding in frequency domain, we obtain frequency diversity gain and improve the SER performance of conventional ST-OFDM. The preceding scheme proposed in this paper is a very simple method that can be encoded and decoded with low complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.394-401
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• 2007

MIMO transmission systems can have various transmission modes, which result from the various combinations of the antenna diversity with spatial multiplexing. In this paper, we find the optimal mode to maximize the capacity with the BER constraint and the optimal selection (diversity transmission or spatial multiplexing transmission) for transmission of each transmission antenna, if necessary. The computer simulation results show that the proposed scheme has more capacity than the conventional scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.817-823
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• 2010

MC-DS-CDMA is technique where a single data symbol is transmitted at multiple subcarriers which are orthogonal to each other. With this technique, frequency diversity can be achieved. The performance of PSAM MC-DS-CDMA system with the application of MRRC antenna diversity is analyzed. The BER performance of this system over multipath fading environment is evaluated, considering the channel estimation error, carrier frequency offset, and the nonlinear high power amplifier.

• The KIPS Transactions:PartC
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• v.14C no.7
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• pp.597-602
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• 2007

In conventional cooperative communication data rate is 1/2 than non cooperative protocols. In this paper, we propose a full data rate DF (Decode and Forward) cooperative transmission scheme. Proposed scheme is based on time division multiplexing (TDM) channel access. When DF protocol has full data rate, it can not obtain diversity gain under the pairwise error probability (PEP) view point. If it increases time slot to obtain diversity gain, then data rate is reduced. The proposed algorithm uses orthogonal frequency and constellation rotation to obtain both full data rate and diversity order 2. Moreover, performance is analyzed according to distance and optimized components that affect the system performance by using computer simulation. The simulation results revealed that the cooperation can save the network power up to 7dB over direct transmission and 5dB over multi-hop transmission at BER of $10^{-2}$. Besides, it can improve date rate of system compared with the conventional DF protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.72-78
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• 2006

It is impossible to provide full diversity and full rate simultaneously using more than two transmit antennas in transmit diversity system. To do this, simple interference cancellation scheme and transmit power allocation scheme have been proposed, recently. But the former has increased noise power and the latter has increased interference which is induced by other channel in fading channel. In this paper, we propose an adaptive transmit power allocation algorithm to minimize the estimation error in the channel environments which have different fading levels each other and to improve the system performance.