• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1513-1527
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• 2011

This paper investigates the capacity rate problems for a joint decode-and-forward (JDF) based two-way relaying with network coding. We first characterize the achievable rate region for a conventional three-node network scenario along with the calculation of the corresponding maximal sum-rate. Then, for the goal of maximizing the system sum-rate, opportunistic relay selection is examined for multi-relay networks. As a result, a novel strategy for the implementation of relay selection is proposed, which depends on the instantaneous channel state and allows a single best relay to help the two-way information exchange. The JDF scheme and the scheme using relay selection are analyzed in terms of outage probability, after which the corresponding exact expressions are developed over Rayleigh fading channels. For the purpose of comparison, outage probabilities of the amplify-and-forward (AF) scheme and those of the scheme using relay selection are also derived. Finally, simulation experiments are done and performance comparisons are conducted. The results verify that the proposed strategy is an appropriate method for the implementation of relay selection and can achieve significant performance gains in terms of outage probability regardless of the symmetry or asymmetry of the channels. Compared with the AF scheme and the scheme using relay selection, the conventional JDF scheme and that using relay selection perform well at low signal-to-noise ratios (SNRs).

• Korea Multimedia Society
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• v.19 no.2
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• pp.26-34
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• 2015

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.6
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• pp.1238-1240
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• 2009

In the wireless sensor network, cooperative transmission is an effective technique to combat multi-path fading and reduce transmitted power. Relay selection and power allocation are important technical issues to determine the performance of cooperative transmission. In this paper, we proposed a new multi-relay selection and power allocation algorithm to increase network lifetime. The proposed relay selection scheme minimizes the transmitted power and increase the network lifetime by considering residual power as well as channel conditions. Simulation results show that proposed algorithm obtains much longer network lifetime than the conventional algorithm.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.9-11
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• 2010

Multiple-input multiple-output (MIMO) systems assisted by multi-relays with single antenna are considered. Signal transmission consists of two hops. In the first hop, the source node broadcasts the vector symbols to all relays, then all relays forward the received signals multiplied by each power gain to the destination simultaneously. Unlike the case of full cooperation between relays such as single relay with multiple antennas, in our case there is no closed form solution for optimal relay power gain with respect to minimum mean square error (MMSE). Thus we propose an alternative approach in which we use an approximation of the cost function based on rank-one matrix decomposition. As a cost function, we choose the trace of MSE matrix. We give several simulation results to validate that our proposed method obtains a negligible performance loss compared to optimal solution obtained by exhaustive search.

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.3-5
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• 2009

In this paper, we exploit the cooperative diversity relay protocol to compensate for defects of wireless communication in 60 GHz. We derive and proof results of the numerical expressions versus various scenarios using the computer simulations. Optimal location and scaling factor of relay are presented through analysis of performances and compared between direct-path and time diversity transmission. Consequently, our results confirm that cooperative diversity relay protocol is an effective mean of enhancing the performance of wireless communication systems in 60 GHz.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.219-220
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• 2008

We proposes an adaptive relay selection scheme for a regenerative (OFDMA) relay network with fairness constrains. The proposed scheme selects the best relays out of a set of potential relays to maximize system capacity. Among these selected relays, subcarriers are reallocated to satisfy fairness constraints as well as to minimize the decrease of the system capacity. The simulation results show that the proposed scheme achieves significant performance improvement over direct transmission and opportunistic relaying with OFDM (OR-OFDM).

• Journal of Communications and Networks
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• v.13 no.3
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• pp.250-256
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• 2011

A two-way relaying (TWR) system is analyzed, where two source terminals with unequal numbers of antennas exchange data via an amplify-and-forward relay terminal with a single antenna. In the system considered herein, the link quality between the sources and relay can generally be asymmetric due to the nonidentical antenna configuration, power allocation, and relay location. In such a general setup, accurate bounds on the average sum rate (ASR) are derived when beamforming or orthogonal space time block coding is employed at the sources. We show that the proposed bounds are almost indistinguishable from the exact ASR under various system configurations. It is also observed that the ASR performance of the TWR system with unequal numbers of source antennas is more sensitive to the relay location than to the power allocation.

• Journal of Internet Computing and Services
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• v.12 no.6
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• pp.35-42
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• 2011

Cooperative relay communication for wireless networks has been extensively studied due to its ability to mitigate fading effectively via spatial diversity. In this paper, we propose a balanced transmit scheme in cooperative relay communication with decode-and-forward DF) scheme. The proposed scheme selects the feedback bits to obtain the maximum cooperative diversity gain. The simulation results show that the proposed scheme improves the bit error rate BER) performance as compare with a conventional scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.12
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• pp.5361-5374
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• 2016

Combining channel coding and network coding in a physical layer in a fading channel, generalized joint channel-network coding (G-JCNC) is proved to highly perform in a two-way relay channel (TWRC). However, most relevant discussions are restricted to symmetric networks. This paper investigates the G-JCNC protocols in an asymmetric TWRC (A-TWRC). A newly designed encoder used by source nodes that is dedicated to correlate codewords with different orders is presented. Moreover, the capability of a simple common non-binary decoder at a relay node is verified. The effects of a power match under various numbers of iteration and code lengths are also analyzed. The simulation results give the optimum power match ratio and demonstrate that the designed scheme based on G-JCNC in an A-TWRC has excellent bit error rate performance under an appropriate power match ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4A
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• pp.345-355
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• 2011

This paper introduces the coded cooperation protocol in wireless relay network. We propose a two relay based coded cooperation protocol with RCPC codes for wireless networks. The proposed two-relay based system can achieve a diversity of order 4 under slow fading environment. Under fast fading, the diversity order is 2 times of the free distance of the convolutional code. We develop upper bounds on BER and FER for the system under both slow and fast fading with Rayleigh distribution. The effect of various channel conditions on the cooperation is also examined in this work.