• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.3
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• pp.16-21
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• 2010

In this paper, the linear source and relay precoders are designed for AF MIMO relay systems. In order to minimize mean squared error (MSE) of received symbol vector, the source and relay precoders are proposed, and MMSE receiver which is suitable to those precoders is utilized at the destination node. As the optimal precoders for source and relay nodes are not represented in closed form and induced by iterative method, we suggest a simple precoder design scheme. Simulation results show that the performance of the proposed precoding scheme is comparable with that of optimal scheme and outperforms other relay precoding schemes. Moreover, in high SNR region, it is revealed that SNR between source and relay node is more influential than SNR between relay and destination node in terms of bit error rate.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.145-146
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• 2006

In this paper, when concurrent transmission and diversity reception at each relay are assumed to increase bandwidth efficiency in linear multihop system, we analyze interference due to concurrent transmission and verify it. In the interference-free environment, more diversity sources at each relay result in better performance [1][2]. However, interference degrades BER performance because accumulated and propagated interference power surpasses original data power. Therefore, if we use the result of this paper, we can make bandwidth efficiency increase as well as BER performance good in linear multihop system by considering concurrent transmission with reuse factor and developing the algorithm which determines the number of diversity source.

• Journal of electromagnetic engineering and science
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• v.13 no.3
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• pp.173-177
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• 2013

This paper presents a new method for analyzing the maximum efficiency of a wireless power transfer (WPT) system with multiple n resonators. The method is based on ABCD matrices and allows transformation of the WPT system with multiple n resonators into a single two-port network system. The general maximum efficiency equation of a WPT system with multiple n resonators is derived using the ABCD matrix. Use of this equation allows placement of the relay resonators for maximum efficiency even though they are asymmetrical. The general maximum efficiency equation and the method of the optimum placement are verified by a full wave simulation. The results show that the method is useful for the analysis of a WPT system with relay resonators.

• Journal of Communications and Networks
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• v.15 no.2
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• pp.191-197
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• 2013

In this paper, a mobile relay station (MRS) for vehicles with a beamforming antenna is considered to increase the reliability of the transmission link, particularly for the MRS at the cell boundary. A cell searching and direction-of-arrival estimation method for an MRS with a uniform linear array is proposed for OFDM-based cellular systems in a multipath environment, even with the existence of the symbol timing offsets and carrier frequency offsets. The performance of the proposed method is evaluated by computer simulation using the standard profile of IEEE 802.16e.

• KIEE International Transactions on Power Engineering
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• v.4A no.1
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• pp.26-32
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• 2004

Digital technology has advanced significantly over the years both in terms of software tools and hardware availability. It is now applied extensively throughout many area of electrical engineering including protective relaying in power systems. Digital relays have numerous advantages over traditional analog relays, such as the ability to accomplish what is difficult or impossible using analog relays. Although non real-time simulators like PSCAD/EMTDC are employed to test the algorithms, such simulations are disadvantaged in that they cannot test the relay dynamically. Hence, real-time simulators like RTDS are used. However, the latter requires large space and is very expensive. This paper uses EMTP MODELS to simulate the power system and the distance relay. The distance relay algorithm is implemented and the distance relay is interfaced with a test power system. The distance relay's performance is then assessed interactively under various fault types, fault distances and fault inception angles. The test results show that we can simulate the distance relay effectively and we can examine the operation of the distance relay very closely including its drawbacks/limitations by using EMTP MODELS. Equally important, this approach facilitates any changes that need to be carried out in order to enhance the Distance Relay under test/examination.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.6
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• pp.13-19
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• 2008

In this paper, the new cooperative communication techniques is proposed for multi-input multi-output(MIMO)-orthogonal frequency division multiplexing (OFDM) system using the relay with multiple antenna. As the MIMO channel is formed by space time coding at the MS(mobile station)-RS(relay station) and RS-BS(base station), we can get the cooperative diversity and MIMO diversity gain simultaneously. Therefore, the performance of MIMO-OFDM system using the relay with multiple-antennas is very improved. And the simple power allocation technique is Proposed for the transmitting power of the mobile station and the relay.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.5
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• pp.25-32
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• 2010

This paper evaluates the outage probability of cognitive relay networks with cooperation between secondary users based on the underlay approach, when multiple primary receivers coexist with secondary users. Using an appropriate relay selection criterion in cognitive radio networks, we derive the outage probability of secondary user. It is shown that the outage probability increases as the number of primary receivers increases and we quantify the increase. Through the simulation results, we verify that the performance of relaying transmission is varied more sensitively compared to that of direct transmission as the number of primary receivers increases. In addition, the relaying transmission can be less efficient than the direct transmission when multiple primary receiver exist but it can be more efficient than the direct transmission by increasing the relay selection diversity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.6
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• pp.2889-2909
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• 2017

Wireless sensor networks (WSNs) have attracted lots of attention in recent years due to their potential for various applications. In this paper, we seek how to efficiently deploy relay nodes into traditional static WSNs with constrained locations, aiming to satisfy specific requirements of the industry, such as average energy consumption and average network reliability. This constrained relay node deployment problem (CRNDP) is known as NP-hard optimization problem in the literature. We consider addressing this multi-objective (MO) optimization problem with an improved Artificial Bee Colony (ABC) algorithm with a linear local search (MOABCLLS), which is an extension of an improved ABC and applies two strategies of MO optimization. In order to verify the effectiveness of the MOABCLLS, two versions of MO ABC, two additional standard genetic algorithms, NSGA-II and SPEA2, and two different MO trajectory algorithms are included for comparison. We employ these metaheuristics on a test data set obtained from the literature. For an in-depth analysis of the behavior of the MOABCLLS compared to traditional methodologies, a statistical procedure is utilized to analyze the results. After studying the results, it is concluded that constrained relay node deployment using the MOABCLLS outperforms the performance of the other algorithms, based on two MO quality metrics: hypervolume and coverage of two sets.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.11
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• pp.5370-5393
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• 2019

In this paper, we consider a two-way relay non-orthogonal multiple access (TWR-NOMA) system with residual hardware impairments (RHIs) and channel estimation errors (CEEs), where two group users exchange their information via the decode-and-forward (DF) relay by using NOMA protocol. To evaluate the performance of the considered system, exact analytical expressions for the outage probability of the two groups users are derived in closed-form. Moreover, the asymptotic outage behavior in the high signal-to-noise ratio (SNR) regime is examined and the diversity order is derived and discussed. Numerical simulation results verify the accuracy of theoretical analyses, and show that: i) RHIs and CEEs have a deleterious effects on the outage probabilities; ii) CEEs have significant effects on the performance of the near user; iii) Due to the RHIs, CEEs, inter-group interference and intra-group interference, there exists error floors for the outage probability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.58-67
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• 2013

In this paper, a mobile relay station(MRS) for vehicles with a beamforming antenna is considered to increase the reliability of a transmission link, especially for the MRS at cell boundary. Cell searching and direction-of-arrival(DoA) estimation methods for an MRS with a uniform linear array(ULA) are proposed for a multipath environment in OFDM-based cellular systems. Performances of the proposed methods(Method1 and Method2) are evaluated by computer simulation with the standard profile of IEEE 802.16e.