• 대한전자공학회논문지TC
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• 제47권3호
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• pp.16-21
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• 2010

본 논문에서는 다중 안테나 기반 증폭 후 재전송 중계 시스템을 위한 선형 전처리 필터 설계를 다룬다. 수신 신호의 평균 제곱 오차를 최소화하기 위한 송신 및 중계 선형 전처리 필터가 제안되며, 수신 단말에서는 제안된 전처리 필터에 적합한 MMSE 기반 수신기가 사용된다. 최적의 송신 및 중계 전처리 필터는 수식적으로 표현하기 어렵고 반복 과정으로 통하여 유도되므로 이러한 연산을 단순화한 전처리 기법을 제안한다. 모의실험을 통하여 제안한 전처리 기법이 최적의 전처리 기법과 거의 유사한 성능을 보이면서도 기존의 중계 전처리 기법 보다 우수한 성능을 보임을 확인할 수 있다. 게다가, 신호 대 잡음비가 높은 영역에서 중계 수선 단말간 신호 대 잡음비에 비하여 송선 중계 단말간 신호 대 잡음비가 성능에 더 많은 영향을 미친다는 사실도 확인할 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권11호
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• pp.5410-5426
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• 2019

With the advent of the fifth-generation (5G) era, Massive multiple-input multiple-output (MIMO) relay systems have experienced the rapid development. Recently, the performance analysis models of Massive MIMO relay systems have been proposed, which are mostly based on Rayleigh fading channels. In order to create a more suitable model for 5G Internet of Things scenarios, our study is based on the Rician fading channels, where line-of-sight (LOS) path exists in the channels. In this paper, we assume the channel state information (CSI) is perfect. In this case, we use statistical information to derive the analytical exact closed-form expression for the achievable sum rate of the uplink for the Massive MIMO two-hop relay system over Rician fading channels. Moreover, considering the different communication scenarios, we derive the analytical exact closed-form expression for the achievable sum rates of the uplink for other three scenarios. Finally, based on these expressions, we make simulations and analyze the performance under different transmit powers and Rician-factors, which provides a theoretical basis and reference for further research.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권7호
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• pp.3010-3025
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• 2016

Lattice reduction (LR) has been used widely in conventional multiple-input multiple-output (MIMO) systems to enhance the performance. However, LR is hard to be applied to the relay systems which are important but more complicated in the wireless communication theory. This paper introduces a new viewpoint for utilizing LR in multiuser MIMO relay systems. The vector precoding (VP) is designed along with zero force (ZF) criterion and minimum mean square error (MMSE) criterion and enhanced by LR algorithm. This implementable precoder design combines nonlinear processing at the base station (BS) and linear processing at the relay. This precoder is capable of avoiding multiuser interference (MUI) at the mobile stations (MSs) and achieving excellent performance. Moreover, it is shown that the amount of feedback information is much less than that of the singular value decomposition (SVD) design. Simulation results show that the proposed scheme using the complex version of the Lenstra--Lenstra--Lovász (LLL) algorithm significantly improves system performance.

• 한국항행학회논문지
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• 제15권4호
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• pp.562-570
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• 2011

본 논문에서는 이동성을 갖춘 릴레이를 도입한 다중 셀 OFDM (Orthogonal Frequency Division Multiplexing)-TDD (Time Division Duplex) 시스템에서 각 셀의 수율을 개별적으로 최대화시키기 위한 분산형 이동 릴레이 전력 제어 방식 (Distributed Mobile Relay Power Control; DMRPC)을 제안한다. DMRPC 방식을 사용한 릴레이 시스템에서는 서로 다른 셀 간 협력과 그에 따른 시그널링 오버헤드 없이 각 셀에서 개별적으로 릴레이의 전력 레벨을 제어한다. DMRPC 방식을 사용한 시스템이 전력 제어 없이 릴레이를 사용한 최대 전력 릴레이 시스템과, 릴레이를 사용하지 않은 기존 시스템에 비하여 향상된 셀 수율 성능을 보이는 것을 모의 실험을 통하여 검증한다. 또한, 최대 전력 릴레이 시스템이 기존 시스템에 비해 셀 외곽 지역 평균 수율 성능이 떨어지는 반면, DMRPC 방식을 사용하면 기존 시스템에 거의 근접한 셀 외곽 지역 평균 수율 성능을 얻을 수 있는 것을 보인다.

• 전기전자학회논문지
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• 제16권2호
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• pp.138-144
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• 2012

본 논문에서는 DSF 릴레이 MC-CDMA 시스템에 대한 의사 성능분석 기법을 다중경로 레일리 페이딩 채널에 대해 제안한다. 오류율 성능과 복잡도를 고려하여 MC-CDMA 시스템의 결합기법으로는 MMSE-C 방법을 사용한다. 평균 오류율 유도를 위하여 DSF-Relay 기법의 릴레이 노드들에서 발생할 수 있는 오류 사건에 기반한 분석 방법을 우선 채택한다. 그리고 발생가능한 모든 오류 사건들을 고려한 형태로 평균 오류율 표현한다. 또한 제안된 의사 분석적 성능분석 결과는 모의실험 결과와의 비교를 통하여 검증하도록 한다. 최종적으로 유도된 성능분석 결과가 다양한 다중경로 레일리 페이딩 채널 환경을 반영하면서 DSF 릴레이 MC-CDMA 시스템의 성능 상한 값을 측정할 수 있는 분석 툴이 될 수 있음을 확인한다.

• 산업경영시스템학회지
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• 제13권22호
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• pp.59-64
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• 1990

This paper is aimed to study the standby redundant system with the relay of parallel structure, by making use of the character of standby system, which reliability is higher than parallel system's if the relay has higher reliability than a certain level. By assigning the low-priced relay to the subsystem, this method increases the relay reliability, optimizes the standby redundant system reliability without violating the restrictions, and consequently reduces the cost.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권10호
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• pp.2587-2600
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• 2012

It has been demonstrated that choosing an appropriate relay node can improve the transmission rate for the system. However, such system improvement brought by the relay selection may be degraded with the presence of the malicious relay nodes, which are selected but refuse to cooperate for transmissions deliberately. In this paper, we formulate the relay selection issue as a restless bandit problem with the objective to maximize the average rate, while considering the credibility of each relay node, which may be different at each time instant. Then the optimization problem is solved by using the priority-index heuristic method effectively. Furthermore, a low complexity algorithm is offered in order to facilitate the practical implementations. Simulation results are conducted to demonstrate the effectiveness of the proposed trust-based relay selection scheme.

• 대한전기학회논문지:전력기술부문A
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• 제52권8호
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• pp.444-449
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• 2003

In this paper present Autonomous Adaptive Digital Over Current Relay for distribution networks which acts autonomous setting using the short circuit impedance measured by relay of power systems. Automation of relay setting is one of the basic requirements for distribution automation, although manual relay setting is used at present. The short circuit impedance from a power source in distribution networks essential for the Autonomous Relay Setting changes frequently in distribution networks. In this paper the short circuit impedance is calculated with voltage and current measured in real time operation of digital relay using the Recursive Least Squares. A new method of digital relay setting is introduced using the the short circuit impedance and load current.

• Journal of information and communication convergence engineering
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• 제15권1호
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• pp.21-27
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• 2017

In this research, we study the outage probability for distributed space-time coding-based cooperative (DSTC) systems with amplify-and-forward relaying over Rayleigh fading channels with a high temporal correlation where the direct link between the source and the destination is available. In particular, we derive the upper and lower bounds of the outage probability as well as their corresponding asymptotic expressions. In addition, using only the average channel powers for the source-to-relay and relay-to-destination links, we propose an efficient power allocation scheme between the source and the relay to minimize the asymptotic upper bound of the outage probability. Through a numerical investigation, we verify the analytical expressions as well as the effectiveness of the proposed efficient power allocation. The numerical results show that the lower and upper bounds tightly correspond to the exact outage probability, and the proposed efficient power allocation scheme provides an outage probability similar to that of the optimal power allocation scheme that minimizes the exact outage probability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권6호
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• pp.2649-2669
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• 2020

In this paper, we analyze the secrecy performance of single-input multiple-output (SIMO) relay systems over κ-μ shadowed fading channels. Based on considering relay model employing decode-and-forward (DF) protocol, two security evaluation metrics, namely, secure outage probability (SOP) and probability of strictly positive secrecy capacity (SPSC) are studied, for which closed-form analytical expressions are derived. In addition, Monte Carlo results prove the validity of the theoretical derivation. The simulation results confirm that the factors that enhance the security include large ratio of (μ_D, μ_E), (m_D, m_E), (L_D, L_E) and small ratio of (k_D, k_E) under the high signal-to-noise ratio regime.