• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.5
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• pp.874-887
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• 2011

Compared to nomadic and fixed relay stations, vehicle-mounted mobile relay stations show different characteristics caused by the time-variant topology, due to their mobility. Especially, a relay mounted in a vehicle is differentiated from nomadic or fixed relay by the restricted distance between the relay and associated mobile station and the variable density of relay deployment in a cell. In this paper, we identify the characteristics of vehicle-mounted mobile relay stations and provide some parameters that highly influence the performance of vehicle-mounted relay. Through simulation, we measure the effect of relay density, zone ratio, relay transmission power, and frame transmission mode on the performance of vehicle-mounted relay. The results show that the performance of vehicle-mounted relay is highly susceptible to the above vehicle-mounted relay-specific parameters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.558-567
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• 2011

In this paper, we propose a partial full duplex relay scheme for 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution)-Advanced system using a Type 1 relay. The Type 1 relay as inband relay is prohibited to transmit and receive simultaneously because of self-interference. Therefore, the Type 1 relay cannot receive synchronization signals which are transmitted to eNB. To overcoming this problem, we propose the partial full duplex relay scheme which transmits to R-UE (Relay-User Equipment) and receives from eNB (evolved NodeB) simultaneously when eNB and the Type 1 relay transmit subframes which have synchronization signals. Additionally, for solving self-interference, the Type 1 relay transmitter and receiver antennas are sufficiently sufficiently isolated and self-interference cancellation is applied for the self-interference signal from the relay transmitter. Thus, the partial full duplex relay scheme can receive synchronization signals from eNB and solve the problems of conventional solutions and we propose the partial channel estimation scheme for partial full duplex relay scheme using SCI. By extensive computer simulation, we verify that the partial full duplex relay scheme is attractive and suitable for the Type 1 relay system.

• Journal of Communications and Networks
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• v.15 no.1
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• pp.45-53
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• 2013

Multi-hop cellular networks (MCNs), which reduce the transmit power, mitigate the inter-cell interference, and improve the system performance, have been widely studied nowadays. The relay selection scheme is a key technique that achieves these advantages, and inappropriate relay selection causes frequent relay switchings, which deteriorates the overall performance. In this study, we analyze the conditions for relay switching in MCNs and obtain the expressions for the relay switching rate and relay activation time. Two mobile-based relay selection schemes are proposed on the basis of this analysis. These schemes select the relay node with the longest relay activation time and minimal relay switching rate through mobility prediction of the mobile node requiring relay and available relay nodes. We compare the system performances via simulation and analyze the impact of various parameters on the system performance. The results show that the two proposed schemes can obtain a lower relay switching rate and longer relay activation time when there is no reduction in the system throughput as compared with the existing schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3501-3523
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• 2017

It is a classical integer optimization difficulty to design an optimal selection scheme in cooperative relay networks considering co-channel interference (CCI). In this paper, we solve single-objective and multi-objective relay selection problem. For the single-objective relay selection problem, in order to attain optimal system performance of cooperative relay network, a novel quantum differential evolutionary algorithm (QDEA) is proposed to resolve the optimization difficulty of optimal relay selection, and the proposed optimal relay selection scheme is called as optimal relay selection based on quantum differential evolutionary algorithm (QDEA). The proposed QDEA combines the advantages of quantum computing theory and differential evolutionary algorithm (DEA) to improve exploring and exploiting potency of DEA. So QDEA has the capability to find the optimal relay selection scheme in cooperative relay networks. For the multi-objective relay selection problem, we propose a novel non-dominated sorting quantum differential evolutionary algorithm (NSQDEA) to solve the relay selection problem which considers two objectives. Simulation results indicate that the proposed relay selection scheme based on QDEA is superior to other intelligent relay selection schemes based on differential evolutionary algorithm, artificial bee colony optimization and quantum bee colony optimization in terms of convergence speed and accuracy for the single-objective relay selection problem. Meanwhile, the simulation results also show that the proposed relay selection scheme based on NSQDEA has a good performance on multi-objective relay selection.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.5
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• pp.7-13
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• 2009

In This Paper, we propose relay schemes for network-coding based two-way relay communication in multi relay channel. Two-way relay channel communication is a bi-directional communication that two users exchange their data with the help of a relay. Network-coding based Two-way relay communication can achieve more throughput compared to conventional two-way relay communication. In this paper, we propose relay selection schemes to provide maximum performance considering instantaneous signal-to-noise in multi-relay channel. Simulation results show that the proposed relay selection schemes can provide diversity order according to the number of relays.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5343-5364
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• 2016

Considering the tradeoff between energy consumption and outage behavior in buffer-aided relay selection, a novel energy-efficient buffer-aided optimal relay selection scheme with power adaptation and Inter-Relay Interference (IRI) cancellation is proposed. In the proposed scheme, energy consumption minimization is the objective with the consideration of relay buffer state, outage probability and relay power control, in order to eliminate IRI. The proposed scheme selects a pair of optimal relays from multiple candidate relays, denoted as optimal receive relay and optimal transmit relay respectively. Source-relay and relay-destination communications can be performed within a time-slot, which performs as Full-Duplex (FD) relaying. Markov chain model is applied to analyze the evolution of relay buffer states. System steady state outage probability and achievable diversity order are derived respectively. In addition, packet transmission delay and power reduction performance are investigated with a specific analysis. Numerical results show that the proposed scheme outperforms other relay selection schemes in terms of outage behavior with power adaptation and IRI cancellation in the same relay number and buffer size scenario. Compared with Buffer State relay selection method, the proposed scheme reduces transmission delay significantly with the same amount of relays. Average transmit power reduction can be implemented to relays with the increasing of relay number and buffer size, which realizes the tradeoff between energy-efficiency, outage behavior and delay performance in green cooperative communications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3B
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• pp.304-310
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• 2009

In this paper, we evaluate the performance of VoIP in OFDMA-based relay systems with various capabilities of relays. We classify relays according to capability as "mid-capability (MC)" and "high-capability (HC)" relay. In system with HC relays, not only base station (BS) but also relay station (RS) performs scheduling at its ova whereas only BS performs scheduling in system with MC relays using the information reported by MS (i.e. the received signal-to-interference-plus-noise ratio (SINR) of mobile station (HS), the amount of MS traffic, etc). In system with MC relays, the controling overhead of BS is larger than that of system with HC relays. However, since BS has all MS information, efficient resource allocation and scheduling is possible. We derived the "average packet delay," "good packet ratio," and "cell goodput" in a VoIP environment. The simulation results demonstrate that the system with MC relays has better VoIP performance over that with HC relays.

• ETRI Journal
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• v.32 no.2
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• pp.230-240
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• 2010

The IEEE802.16j standard uses non-transparent relay stations to extend coverage. There are two types of non-transparent relay modes, that is, the time-division transmit and receive (TTR) relay mode which can operate with one of two types of frame structures, a single-frame and multiframe structure, and the simultaneous transmit and receive (STR) relay mode. In this paper, we analyze the relay performance of TTR and STR relay modes in IEEE 802.16j MMR system. We also propose a fair resource allocation scheme for the downlink relay frame. Numerical results show that relay performance of the TTR with a single-frame or a multiframe structure and that of the STR relay modes are almost the same in a two-hop system. However, in a three-hop system, the TTR mode with a single-frame structure outperforms other relay modes.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.9
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• pp.437-443
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• 2005

This paper deals with an experimental study for Klippon reiay in Cheju-Heanam HVDC system Klippon relay was troubled many times for years, and Klippon relay's fault caused the HVDC system trip. So for several years, these reasons of Klippon relay fault were investigated. The malfunction of Klippon relay in Cheju-Haenam HVDC system has been caused by the incoming of random surge(current source and voltage source). This paper has stu야ed the theoretic리 analysis and experimental study of Klippon relay, and the solutions against the problems were suggested according to their causes. Among the problems, grounding problem was removed by one-point earth connection and by modification of grounding circuit. The effects of inrush current was removed by inserting the blocking diodes by series in Klippon relay circuits. Finally, The over-voltage induced on Klippon relay, by a relay excitation coil, was removed by inserting a free-wheeling diode in Parallel with the excitation coil.

• 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.