• International Journal of Contents
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• v.14 no.1
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• pp.18-27
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• 2018

The objective of this study was to derive approximate closed-form error rates for M-ary burst symbol transmission (MBST) of dual-hop adaptive decode-and-forward (ADF) cooperative relay systems over quasi-static Rayleigh fading channels. Within a burst, there are pilot symbols and data symbols. Pilot symbols are used for channel estimation schemes and each relay node's transmission mode selection schemes. At first, our focus was on ADF relay systems' error-events at relay nodes. Each event's occurrence probability and probability density function (PDF) were then derived. With error-event based approach, we derived a tractable form of PDF for combined signal-to-noise ratio (SNR). Averaged error rates were then derived as approximate expressions for arbitrary link SNR with different modulation orders and numbers of relays. Its accuracy was verified by comparison with simulation results.

• Journal of Communications and Networks
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• v.13 no.6
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• pp.633-638
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• 2011

In this paper, we consider resource allocation with proportional fairness in the downlink orthogonal frequency division multiple access relay networks, in which relay nodes operate in decode-and-forward mode. A joint optimization problem is formulated for relay selection, subcarrier assignment and power allocation. Since the formulated primal problem is nondeterministic polynomial time-complete, we make continuous relaxation and solve the dual problem by Lagrangian dual decomposition method. A near-optimal solution is obtained using Karush-Kuhn-Tucker conditions. Simulation results show that the proposed algorithm provides superior system throughput and much better fairness among users comparing with a heuristic algorithm.

• Journal of electromagnetic engineering and science
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• v.11 no.1
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• pp.5-10
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• 2011

We propose an adaptive cooperative scheme with a multi-relay node that achieves high bandwidth efficiency and achieves better SEP performance. In the proposed protocol, if the quality of the direct channel is better than that of the all channels from relays to destination, the source will transmit directly to the destination. Otherwise, the source broadcasts the signal and then a potential relay will be chosen to help the source. A re-transmission will also occur if the potential relay cannot be detected. The spectral efficiency is first derived by calculating the probability of each mode, i.e., direct and cooperation transmission. Subsequently, the SEP performance of M-PSK modulation for the scheme is analyzed by considering each event where the source transmits data to the destination. Finally, the obtained analytical results are verified through computer simulations.

• Journal of Satellite, Information and Communications
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• v.7 no.2
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• pp.30-35
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• 2012

In this paper, we proposed spectrum sensing using cooperative relay to solve problem of sensing performance degradation due to CPE (Customer-Primise equipments) which causes low SNR (signal-to-noise ratio) problem. This system model is expected that cooperative relay scheme guarantees the high sensing performance by its diversity gain. Based on these backgrounds, in this paper, we apply to cooperative relay scheme to the CR (cognitive radio) system, and simulation results show comparison of the sensing performance combining method EGC and MRC.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.2
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• pp.275-280
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• 2016

In this paper, we propose a novel relay selection technique which utilizes a priori decoding information at relays for buffer-aided successive relaying networks. In the conventional relaying schemes, a single relay pair is selected for receiving data from the source and transmitting data to the destination. In the proposed technique, however, all relays except the relay selected for transmitting data to the destination try to decode the received signal from the source, and they store the data if they succeed decoding. The proposed technique selects the relay such that it can succeed its own transmission and it maximizes the number of relays successfully decoding the data from the source at the same time. It is shown that the proposed relaying technique significantly outperforms the conventional buffer-aided relaying schemes in terms of outage probability through extensive computer simulations.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.6
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• pp.39-47
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• 2012

As a scheme to efficiently reduce the effects of multipath fading in next generation wireless communication systems, cooperative communication systems have recently come into the spotlight. Since these cooperative communication systems use cooperative relays with diverse fading coefficients to transmit information, having all relays participate in cooperative communication may result in unnecessary waste of resources, and thus relay selection schemes are required to efficiently use wireless resources. In this paper, we propose an efficient relay selection scheme through self-learning in cooperative wireless networks using Q-learning algorithm. In this scheme, we define states, actions and two rewards to achieve good SER (Symbol Error Rate) performance, while selecting a small number of cooperative relays. When these parameters are well-defined, we can obtain good performance. For demonstrating the superiority of the proposed Q-learning, We compared the proposed scheme with Q-learning and a relay selection scheme with a mathematical analysis. The simulation results show that, compared to a scheme that obtains optimum relays through a mathematical analysis, the proposed scheme uses resources efficiently by using smaller numbers of relays with comparable SER performance. According to these simulation results, the proposed scheme can be considered as a good attempt for future wireless communication.

• ETRI Journal
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• v.34 no.2
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• pp.264-267
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• 2012

This letter analyzes the performance of a two-hop MIMO multiuser relay network with a fixed gain amplify-and-forward protocol and antenna selection at the transmitter and receiver. A new expression for the cumulative distribution function of the highest instantaneous end-to-end signal-to-noise ratio is derived. Based on the above result, closed-form expressions for outage probability and bit error rate are presented. Also, the diversity order of the system is determined. Finally, computer simulations are compared to the analytical results, and insights and observations are provided.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.39-44
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• 2010

In this paper, we analyze the performance of the cooperative cognitive radio relay system which is adapted the recently highly focused cognitive radio system. The performance comparison is made between the system with and that without the opportunistic transmission relay. Especially the selection combining is considered at the destination for simple implementation. In this case, the effect of the channel state information (CSI) delay, which is caused essentially by the process during the CSI delivery, to the system performance is considered. It is noticed that the performance of the system with the opportunistic relay degrades up to 0.6 dB at a given condition compared to the system without the opportunistic relay. And it is shown that the system performance is more sensitive to the CSI delay compared to the frequency acquisition probability of the cognitive radio relay.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.10
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• pp.5035-5057
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• 2019

Advancements in nanotechnology and novel nano materials in the past decade have provided a set of tools that can be used to design and manufacture integrated nano devices, which are capable of performing sensing, computing, data storing and actuation. In this paper, we have proposed cooperative nano communication using Power Switching Relay (PSR) Wireless Power Transfer (WPT) protocol and Time Switching Relay (TSR) WPT protocol over independent identically distributed (i.i.d.) Rayleigh fading channels in the Terahertz (THz) Gap frequency band to increase the range of transmission. Outage Probability (OP) performances for the proposed cooperative nano communication networks have been evaluated for the following scenarios: A) A single decode-and-forward (DF) relay for PSR protocol and TSR protocol, B) DF multi-relay network with best relay selection (BRS) for PSR protocol and TSR protocol, and C) DF multi-relay network with multiple DF hops with BRS for PSR protocol and TSR protocol. The results have shown that the transmission distance can be improved significantly by employing DF relays with WPT. They have also shown that by increasing the number of hops in a relay the OP performance is only marginally degraded. The analytical results have been verified by Monte-Carlo simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.12
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• pp.3275-3295
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• 2012

In this paper, we analyze the performance of an amplify-and-forward (AF) two-way relaying system, where two sources exchange information via the aid of an intermediate relay that is selected among multiple relays according to max-min criterion. We consider a practical scenario, where one source-relay link undergoes Rician fading, and the other source-relay link is subject to Rayleigh fading. To be specific, we derive a tight lower bound for the outage probability. From this lower bound, the asymptotic outage probability and average symbol error rate (SER) expressions are derived to gain insight into the system performance at high signal-to-noise ratio (SNR) region. Furthermore, we investigate the optimal power allocation (PA) with fixed relay location (RL), optimal RL with fixed PA and joint optimization of PA and RL to minimize the outage probability and average SER. The analytical expressions are verified through Monte Carlo simulations, where the positive impact of Rician factor on the system performance is also illustrated. Simulation results also validate the effectiveness of the proposed PA and relay positioning schemes.