• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.17-23
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• 2012

Recently, for spectral efficiency and power saving, an incremental best relay selection of a cooperative diversity scheme is proposed. However during the best relay selection process, there may exist a delay between channel estimation and actual data transmission. Consequently, this delay causes outdated channel state information (CSI). We analytically derive the effect of the outdated CSI to an incremental best relay selection diversity scheme. It is noted that the system performance deteriorates with decreasing the value of the correlation coefficient sensitively. When the correlation coefficient reduces from 1 to 0.9, the most performance degradation is denoted. However, the performance degradation is diminished with decreasing the correlation coefficient.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.3
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• pp.1016-1033
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• 2016

In this paper, we present a joint relay-and-antenna selection and power allocation strategy for multiple-input multi-output (MIMO) amplify-and-forward (AF) two-way relay networks (TWRNs). In our approach, we select the best transmit and receive antennas at the two sources, a best relay and a best transmit and receive antenna at the selected relay based on maximizing the minimum of the end-to-end received signal-to-noise-ratios (SNRs) under a total transmit power constraints. We obtained the closed-form solution for the optimal power allocation firstly. Then with the optimal allocation solution we found, we can reduce the joint relay-and-antenna selection to a simpler problem. Besides, the overall outage probability is investigated and a tight closed-form approximation is derived, which provides a method to evaluate the outage performance easily and fast. Simulation results are presented to verify the analysis.

• Journal of Communications and Networks
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• v.17 no.2
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• pp.162-171
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• 2015

This paper provides an analytic performance evaluation of the bit error rate (BER) of underlay decode-and-forward cognitive networks with best relay selection over Rayleigh multipath fading channels. A generalized BER expression valid for arbitrary operational parameters is firstly presented in the form of a single integral, which is then employed for determining the diversity order and coding gain for different best relay selection scenarios. Furthermore, a novel and highly accurate closed-form approximate BER expression is derived for the specific case where relays are located relatively close to each other. The presented results are rather convenient to handle both analytically and numerically, while they are shown to be in good agreement with results from respective computer simulations. In addition, it is shown that as in the case of conventional relaying networks, the behaviour of underlay relaying cognitive networks with best relay selection depends significantly on the number of involved relays.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.1
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• pp.81-108
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• 2018

In this paper, we derive the theoretical Symbol Error Probability (SEP) of cooperative systems with best relay selection for Nakagami-m fading channels. For Amplify and Forward (AF) relaying, the selected relay offers the best instantaneous Signal to Noise Ratio (SNR) of the relaying link (source-relay-destination). In cooperative networks using Decode and Forward (DF), the selected relay offers the best instantaneous SNR of the link between the relay and the destination among the relays that have correctly decoded the transmitted information by the source. In the second part of the paper, we derive the SEP when all participating AF and DF relaying is performed. In the last part of the paper, we extend our results to cognitive radio networks where there is interference constraints : only relays that generate interference to primary receiver lower than a predefined threshold T can transmit. Both AF and DF relaying with and without relay selection are considered.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7A
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• pp.530-539
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• 2009

Wireless Relaying is a promising solutions to overcome the channel impairments and provides high data rate coverage that appear for beyond 3G mobile communications. In this paper we present end to end BER performance of dual hop wireless communication systems equipped with multiple Decode and Forward relays over Rayleigh fading channel with the best relay selection. We compare the BER performance of the best relay with the BER performance of single relay. We select the best relay based on the end to end channel conditions. We further calculate the outage probability of the best relay. It is shown that the outage probability of the best relay is equivalent to the outage probability when all relays take part in the transmission. We apply Orthogonal Space Time Block coding(OSTBC) at the source terminal. Numerical and simulation results are presented to verify our analysis.

• Journal of electromagnetic engineering and science
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• v.12 no.1
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• pp.8-12
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• 2012

In this paper, we evaluate performances of dual-hop decode-and-forward relaying systems with the $N^{th}$ best-relay selection scheme. In some schemes, such as scheduling or load balancing schemes, the best relay is unavailable and hence the system must resort the second best, third best, or generally the $N^{th}$ best relay. We derive the expressions of the outage probability and symbol error rate (SER) for this scenario over Rayleigh fading channels. Monte-Carlo simulations are presented to verify the analytical results.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.2
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• pp.389-405
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• 2014

Outdated Channel State Information (CSI) was proved to have negative effect on performance in two-way relay networks. The diversity order of widely used opportunistic relay selection (ORS) was degraded to unity in networks with outdated CSI. This paper proposed a multiple relay selection scheme for amplify-and-forward (AF) based two-way relay networks (TWRN) with outdated CSI. In this scheme, two sources exchange information through more than one relays. We firstly select N best relays out of all candidate relays with respect to signal-noise ratio (SNR). Then, the ratios of the SNRs on the rest of the candidate relays to that of the Nth highest SNR are tested against a normalized threshold ${\mu}{\in}[0,1]$, and only those relays passing this test are selected in addition to the N best relays. Expressions of outage probability, average bit error rate (BER) and ergodic channel capacity were obtained in closed-form for the proposed scheme. Numerical results and Simulations verified our theoretical analyses, and showed that the proposed scheme had significant gains comparing with conventional ORS.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.10
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• pp.3409-3422
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• 2014

The frequency spectrum available for the wireless communication is extremely crowded. In order to improve the spectral efficiency, the two-way relay networks have aroused great attention. A simple $N^{th}$ best-relay selection criterion for the opportunistic two-way relay networks is proposed, which can be implemented easily by extending the distributed timer technique in practice, since the proposed criterion is mainly based on the channel gains. The outage performance of the proposed relay selection scheme is analyzed under the outdated channel state information (CSI), and a tight closed-form lower bound and asymptotic value of the outage probability over Rayleigh fading channels are obtained. Simulation results demonstrate that the tight closed-form lower bound of the outage probability very closely matches with simulated ones in the whole SNR region, and the asymptotic results provide good tight approximations to the simulation ones, especially in the high SNR region.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.2
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• pp.13-18
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• 2008

In this paper, we consider an amplifying-and-forward(AF) dual-hop relaying system where the source node transmits to a destination node with the help of R relay nodes. We assume that the source node equips M transmit antennas, but only one antenna is equipped at the each node of relay and destination. The outage probabilities are presented when the transmit maximum-ratio-combining(MRC) is used at the source-relay(S-R) links, and the best relay selection, which selects only one relay that contributes the most to the received signal-to-noise ratio(SNR) as active relay, is combined. Simulation results validate these analytical results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.12
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• pp.2812-2817
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• 2013

In this paper, an outage probability for the best relay selection in decode-and-forward relaying systems in the presence of interference is analyzed over Rayleigh fading channels. Based on the outage performance results, we propose a method to determine effective relay candidates for the best relay selection, where the effective relay candidates represent the relays except for relays that make no contribution to improving the performance. in all possible relays given in the system. By determining the effective relay candidates, the feedback overhead of channel state information and the energy consumption of relays can be significantly reduced while minimizing the performance degradation. In this paper, we provide important parameters that affect the determination of the effective relay candidates.