• 생태와환경
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• 제40권2호
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• pp.327-336
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• 2007

본 연구는 1999년 6월과 8월에 남한강 상류수계의 15개 조사지점으로부터 어류의 다변수 모델을 이용하여 생태건강성을 평가하였고, 전통적인 군집분석에 의한 지수와 서로 비교 평가하였다. 본 연구를 위해 우리나라의 생태적 특성에 맞게 보완된 10-메트릭 건강성 평가 모델을 적용하였다. 어류조사에 따르면, 총 6과 24종이 출현하였고, 생태적인 교란정도와 하천차수에 따라 일부 변이를 보였다. 생태길드분석에 따르면, 민감종과 충식종은 각각 91%, 56%로서 생태적으로 수환경이 건강한 상태로 나타났다. 그러나 S1과 S2의 2차 하천에서는 내성종이 66%, 잡식종이 76%가 채집되어 물리적 서식지의 질적 저하가 영향을 나타낸 것으로 판단되었다. 본 수계에서 생태건강도의 평균 모델값은 38로서 양호상태를 보였고, 개별적 IBI 값의 패턴은 다른 산간계류형 하천들과 유사하여 비교적 이화학적 오염에 의한 영향이 적은 것으로 사료되었다. 하천차수에 따른 IBI 값과 종다양성 지수와의 비교에 따르면, 두 변수 값은 분명한 차이가 있음을 보여주었다 Shannon-Weaver의 종다양성 지수는 실제 군집상태를 잘 반영하지 못했으며, 특히 2차 하천에서의 종다양성 지수 변이의 폭은 IBI 값으로 산정한 생태 건강도에 비해 훨씬 크게 나타났다. 본 연구결과는 다변수 메트릭에 의한 연구 접근방식은 수생태계 관리에 유용한 도구로 사용될 수 있으나, 기존의 종 다양도 지수와 같은 군집 분석법은 하천차수를 고려하지 않을 경우 비효율적인 것으로 사료되었다.

• 전자공학회논문지S
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• 제35S권6호
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• pp.19-24
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• 1998

본 논문에서는 동일한 평균 전력을 가지며 주파수 비선택적 느린 나카가미 m-분포의 페이딩을 겪는 MPSK 신호들에 대한 다수의 다이버시티 가지 중 크기가 센 두세개의 신호를 순서대로 선택하고 합성하는 일반화된 선택성 합성 기법에 대한 평균 심벌 오류 확률식을 유도한다. 오류 확률식을 유도하기 위해 순서 통계량(Order Statistics)의 개념을 적용한다. 유도 과정에서 수신 신호의 확률 밀도 함수에 대한 새로운 전개가 소개되고 있으며, 다양한 수학적 기법들을 사용한다. 기존의 선택적 합성과 최대비 함성 기법과의 성능을 비교하여 적절한 다이버시티 가짓수를 찾는다.

• 한국통신학회논문지
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• 제34권1C호
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• pp.1-8
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• 2009

Cooperative diversity is a novel technique to improve diversity gains, capacity gains, and energy saving. This technique involves multiple terminals sharing resources in order to build a virtual antenna array in a distributed fashion. In this paper, we propose a multi-user cooperative diversity protocol called Relay-assisted Multiple Access Channel(R-MAC) that allows multiple source terminals to transmit their signals simultaneously and the relay terminal forwards the aggregated signal received from the source terminals to the destination terminal. The proposed protocol converts the distributed antenna channels into an effective MIMO channel by exploiting a relay, increasing both diversity gain and system throughput. We investigate the performance of the proposed protocol in terms of outage probability and diversity-multiplexing tradeoff where we assume block fading channel environment. Our simulation results show that the proposed protocol outperforms direct transmission in the high spectral efficiency regime where the conventional cooperative diversity protocols cannot outperform direct transmission.

• International Journal of Computer Science & Network Security
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• 제24권2호
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• pp.95-100
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• 2024

Cyclic Delay Diversity (CDD) is a diversity scheme used in OFDM-based telecommunication systems, transforming spatial diversity into frequency diversity and thus avoiding intersymbol interference without entailing the receiver to be aware of the transmission strategy making the signal more reliable achieving full diversity gain in cooperative systems. Here the analyzation of the influence of CDD-SC scheme in Cognitive Radio Network (CRN) is done with the challenge of overcoming the complication called channel estimation along with overhead in CNR. More specifically, the closed-form expressions for outage probability and symbol error rate are divided under different frequencies among independent and identically distributed (i.i.d.) frequency selective fading channel model i.e., the signal is divided into different frequencies and transmitted among several narrow band channels of different characteristics. It is useful in the reduction of interference and crosstalk. The results reveal the diversity order of the proposed system to be mainly affected by the number of multipath components that are available in the CNR.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2006년도 학술대회
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• pp.175-177
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• 2006

This letter deals with non-pilot-aided symbol timing estimation methods in an orthogonal frequency division multiplexing (OFDM) system. To do this, OFDM system uses a frequency diversity scheme over two consecutive data symbols. Our approach can be viewed as an expansion of Schmidl's and Minn's correlation methods. Using the OFDM signal equipped with frequency diversity, however, symbol timing is accurately estimated without additional training symbol and a second-order diversity gain is achieved.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2012년도 추계학술대회
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• pp.626-628
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• 2012

본 논문에서는 부사용자들의 공간 다이버시티를 이용한 협력 스펙트럼 센싱 기법을 제안한다. 우리의 기법에서는 부사용자가 다른 부사용자들로부터 신호를 받아 주사용자의 존재 여부에 대한 측정을 한다. 우리는 모의 실험 결과를 통해 부사용자의 수가 증가할수록 발견 실패 확률의 다이버시티 오더가 증가함을 알 수 있다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -2
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• pp.973-976
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• 2000

This paper proposes a new polarization diversity scheme for OPFDM (Orthogonal Polarization and Frequency Division Multiplexing). OPFDM is an extension of OFDM (Orthogonal Frequency Division Multiplexing) in conjunction with polarization multiplexing in order to ensure the orthogonality amongst subcarriers. Since OPFDM uses two orthogonally polarized channels, it can easily employ the polarization diversity. In order to get the diversity gain effectively in a frequency selective fading channel, the proposed scheme combines the signals in subcarrier-by-subcarrier basis. The computer simulation results confirm that the proposed scheme is superior to conventional one in the two orthogonally polarized two-ray Rayleigh fading channels with cross-talk between the two channels.

• 전기학회논문지P
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• 제62권4호
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• pp.216-222
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• 2013

Handover is a technical methodology to support mobility of wireless communication users, which mainly affects the capacity of wireless communication systems and the quality of service (QoS) of link level signal. However, in OFDMA-based cellular systems, there are few published technical reports investigating handovers with respect to diversity gains and resource consumption depending on what handover technique is adopted. In this paper, we propose handover schemes exploiting transmit diversity and macro-diversity in order to increase capacity of OFDMA-based wireless communication systems, and analyze their performance. In cellular environments, depending on what handover scheme is selected, average signal-to-interference-and-noise ratio is calculated first for a handover user in order to evaluate the link level QoS. Through this technical evaluation for handover schemes, we conclude what handover scheme is suitable for OFDMA-based cellular systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권3호
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• pp.1156-1173
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• 2021

In this paper, we propose a new joint precoder and postcoder design strategy to support multiple streams per user in multiuser multiple-input multiple-output (MIMO) systems. We propose two step precoding strategies using equal channel gain decomposition and block diagonalization at the transmitter. With the proposed precoder, the multiuser MIMO channel can be decomposed into multiple parallel channels with equal channel gain per user. After applying receive postcoder which is generated and sent by the transmitter, we can use ML based decoder per stream to achieve full receive diversity. Achievable sum rate bound and diversity performance of the proposed algorithm are presented with feedback signaling design and quantitative complexity analysis. Simulation results show that the proposed algorithm asymptotically approaches to the sum rate capacity of the MIMO broadcast channel while maintaining full diversity order.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권6호
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• pp.989-1005
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• 2010

Cooperative diversity is a technique with which a virtual multiple antenna array is established among the single antenna users of the wireless network to realize space diversity. Signal space diversity (SSD) is a bandwidth-efficient diversity technique, which uses constellation rotation and interleaving techniques to achieve diversity gain. A new cooperative diversity scheme with rotated constellations (RCCD) is proposed in this paper. In this scheme, data are modulated by using a rotated constellation, and the source and the relays transmit different components of the modulated symbols. Since any one of the components contains full information of the symbols, the destination can obtain multiple signals conveying the same information from different users. In this way, space diversity is achieved. The RCCD scheme inherits the advantage of SSD - being bandwidth-efficient but without the delay problem of SSD brought by interleaving. The symbol error rate of the RCCD scheme is analyzed and simulated. The analysis and simulation results show that the RCCD scheme can achieve full diversity order of two when the inter-user channel is good enough, and, with the same bandwidth efficiency, has a better performance than amplify-and-forward and detect-and-forward methods.