• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.499-500
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• 2007

The existing digital protection relay is continuously growing with an improvement in technology. In this paper, we propose the development of the digital protection relay which displays the trip area in real time. In most of the digital protection relays monitor whether analog signal enters into the pre-determined trip area, but those aren't provide the trip area information for a operator in real time. Therefore, if the digital protection relay continuously displays the trip area in real time, the operator analysis power system status easily. This paper particularly introduces selective ground protective relay and differential protective relay with trip area and presents a method of providing the trip area information to operator in real time.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.2
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• pp.77-86
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• 2005

The DC protection and control device for the feeding system of a Light Rail Transit(LRT) system is developed. For the development, the short circuit characteristics in the system are analyzed. As a result a protection algorithm for the DC fault selective relay (50F) is newly proposed, and principles of the DC fault selective relay, Line Test Device (LTD), DC Over Current Relay (DC OCR) are introduced From the development, the specifications and codes used to be unclear have become clarified and summarized. Moreover, the methods to examine the protective characteristics and Electromagnetic Compatibility (EMC) are established Finally, the performance and the effectiveness of the developed protective relay have been verified with the test based on IEC. For the reliability of the system, the relay has been installed and is being operated at the test track of the LRT system at Gyeong-San.

• Journal of IKEEE
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• v.15 no.1
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• pp.64-69
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• 2011

In this paper, a semi-analytical approach is proposed for decode-and-forward(DF) relay systems over rayleigh fading channels. At first, we derive the general form of the averaged bit error rate(BER) based on error-events at relay nodes in which a selection scheme is not used. It is confirmed that an erroneous detection and transmission at relay nodes can cause the degradation of the received signal-to-noise ratio (SNR) and the averaged BER performance. Furthermore, the proposed method can be extended to selective-DF(SDF) relay schemes so that it is verified to be another general solution for DF relay systems. Also, proposed semi-analytical expressions have been verified by comparing with simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3524-3542
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• 2017

In a single-source and multi-relay amplify-forward (AF) cooperative network, the outage probability and the power allocation are two key factors to influence the performance of an entire system. In this paper, an optimized AF relay selection by an exclusive method and near optimal power allocation (NOPA) is proposed for both good outage probability and power efficiency. Given the same power at the source and the relay nodes, a threshold for selecting the relay nodes is deduced and employed to minimize the average outage probability. It mainly excludes the relay nodes with much higher thresholds over the aforementioned threshold and thus the remainders of the relay nodes participate in cooperative forwarding efficiently. So the proposed scheme can improve the utility of the resources in the cooperative multi-relay system, as well as reduce the computational complexity. In addition, based on the proposed scheme, a NOPA is also suggested to approach sub-optimal power efficiency with low complexity. Simulation results show that the proposed scheme obtains about 2.1dB and 5.8dB performance gain at outage probability of $10^{-4}$, when compared with the all-relay-forward (6 participated relays) and the single-relay-forward schemes. Furthermore, it obtains the minimum outage probability among all selective relay schemes with the same number of the relays. Meanwhile, it approaches closely to the optimal exhaustive scheme, thus reduce much complexity. Moreover, the proposed NOPA scheme achieves better outage probability than those of the equal power allocation schemes. Therefore, the proposed scheme can obtain good outage probability, low computational complexity and high power efficiency, which makes it pragmatic efficiently in the single-source and multi-relay AF based cooperative networks.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.451-465
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• 2008

The DC over current relay(76i) and the DC under voltage relay(mid-point relay, 80A) used mainly with DC protective relay system of DC electric railway in Korea, But the DC fault selective relay(50F) is applying to recently mainly. In this study, simulation to compare 76i/80A and 50F in the methods of protection and the operational characteristics were executed through verifying a calculation of short circuit current and using PSCAD/EMTDC transition program. As a result of this study, it was proved that while 80A runs in relation to the scale of fault resistance, 50F runs regardless of the scale of fault resistance or the length of rail.

• Journal of Communications and Networks
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• v.13 no.1
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• pp.56-62
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• 2011

In this paper, we propose a block-based selective orthogonal frequency division multiplexing (OFDM) decode-and-forward relaying scheme for 4G mobile communication systems. In the scheme, an OFDM symbol is divided into blocks and one relay is selected for each block. Theoretical outage performance and error performance are analyzed and evaluated. A unified outage expression is given for our scheme and the other two schemes and the lower bound of the bit error rate of the three schemes is also obtained. The effect of the coherence bandwidth on the proposed scheme is also investigated. Monte Carlo simulations are carried out to validate our analysis. The scheme can obtain a good tradeoff between complexity and performance and can be used in future 4G mobile communication systems.

• Journal of electromagnetic engineering and science
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• v.11 no.4
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• pp.239-249
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• 2011

In this paper, we propose a reliable $8{\times}8$ up-down switching polar relay code based on 3GPP LTE standard, motivated by 3GPP LTE down link, which is 30 bps/Hz for $8{\times}8$ MIMO antennas, and by Arikan's channel polarization for the frequency selective fading (FSF) channels with the generator matrix $Q_8$. In this scheme, a polar encoder and OFDM modulator are implemented sequentially at both the source node and relay nodes, the time reversion and complex conjugation operations are separately implemented at each relay node, and the successive interference cancellation (SIC) decoder, together with the cyclic prefix (CP) removal, is performed at the destination node. Use of the scheme shows that decoding at the relay without any delay is not required, which results in a lower complexity. The numerical result shows that the system coded by polar codes has better performance than currently used designs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7B
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• pp.517-527
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• 2012

This paper considers a cooperative communication system with a single relay node, where two-layer superposition coding and successive decoding is employed to reduce the expected distortion of a Gaussian source delivered. For the system, we propose a relay scheme which forwards an appropriate relay signal at the relay node, based on the local decoding result of layers and the decoding result of layers at the destination node fed back to the relay node. In the scheme, the relay signal is designed not only by applying decode-and-forward but also by applying amplify-and-forward to reduce the outage probability in final decoding of each layer. The performance of the proposed scheme is evaluated numerically in terms of the expected distortion at various relay locations using outage probabilities derived. The results show that the proposed scheme outperforms the conventional schemes in most cases of the relay location and the gain gets larger when the relay node is closer to the source node in particular.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4326-4341
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• 2016

In this paper, an adjustable multiple relay selection (MRS) scheme for cooperative communication with amplify-and-forward (AF) relay under frequency selective channels is proposed. In the proposed scheme, the relays are ordered firstly by the steady-state mean square error (MSE), then the relays are sequentially selected out from N relays and the number of cooperating relays is adjusted dynamically according to the steady-state mean square joint error (MSJE). The aim of this work is to dynamically estimate the optimum number N_o of cooperating relays. Optimum means the minimum number of cooperating relays, N_o, achieving the minimum level of steady-state MSJE. Numerical results verify the analyses and show that the scheme can adaptively adjust the number of cooperating relays, and outperform conventional relay selection schemes. Hence, the proposed scheme provides better tradeoff between BER performance and spectral efficiency and to save more energy in cooperative wireless networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.10
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• pp.593-600
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• 2014

OFDMA systems solves frequency selective fading problem and provides improved performance by optimal allocation of subcarriers and transmit power. Two-way relay systems provide improved spectral efficiency compared to that of the conventional half-duplex relay using bidirectional communications. In legacy OFDMA system such as WiBro, two-way DF relay utilization causes pilot re-assignment and impossibility of channel estimation and decoding at relay nodes by self-interference. In this paper, resource allocation schemes for legacy OFDMA systems with two-way DF relay are proposed. The proposed schemes allocate subcarriers considering destinations nodes which are connected to relay nodes as individual nodes which are directly connected to a base station. Subsequently, the proposed schemes compensate bandwidth loss due to orthogonal allocations by overlapped allocating unused subcarriers at other noes. Numerical simulations show that the proposed resource allocation schemes provide improved performance compared with orthogonal allocation.