• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.6
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• pp.19-25
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• 2009

The performance of a cognitive radio system with cooperative diversity which includes the direct and indirect path is analysed. The selection relay cooperation which selects the best relay, the relay with the best received signal-to-noise ratio(SNR) in destination node, is considered and derived the performance degradation caused by the CSI(Channel State Information) delay analytically. Numerical examples show that the cooperative diversity which have the direct and the indirect paths effectively improves the system performance in Rayleigh fading; the performance improves 4.4 dB with 1/10 of SNR of the indirect path. And the system performance is more degraded with the less frequency acquisition probability and with the high CSI delay.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.102-122
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• 2017

Nanotechnology has provided a set of tools that the engineers can use to design and manufacture integrated nano devices, which are capable of performing sensing, computing, data storing and actuation. One of the main hurdles for nano devices has been the amount of power that it can generate for transmission of data. In this paper, we proposed cooperative nano communication in the Terahertz (THz) Gap frequency band to increase the range of transmission. Outage probability (OP) performances for the proposed cooperative nano communication networks in the THz band (0.1 - 10THz) have been evaluated for the following scenarios; A) A single decode-and-forward (DF) relay over independent identically distributed (i.i.d.) Rayleigh fading channels, B) DF multi-relay network with best relay selection (BRS) over i.i.d. Rayleigh fading channels, and C) DF multi-relay network with multiple hops with BRS over i.i.d. Rayleigh fading channels. The results show that the transmission distance can be improved significantly by employing DF relays. Also, it is shown that by increasing the number of hops in a relay the OP performance is marginally degraded. The analytical results have been verified by Monte-Carlo simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.9
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• pp.4180-4196
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• 2017

In this paper, we analyze average capacity of an amplify-and-forward (AF) cooperative communication system model in multi-relay multiuser networks. In contrast to conventional cooperative networks, relays in the considered network have no embedded energy supply. They need to rely on the energy harvested from the signals broadcasted by the source for their cooperative information transmission. Based on this structure, a two-step selection scheme is proposed considering both channel state information (CSI) and battery status of relays. Assuming each relay has infinite or finite energy storage for accumulating the energy, we use the infinite or finite Markov chain to capture the evolution of relay batteries and certain simplified assumptions to reduce computational complexity of the Markov chain analysis. The approximate closed-form expressions for the average capacity of the proposed scheme are derived. All theoretical results are validated by numerical simulations. The impacts of the system parameters, such as relay or user number, energy harvesting threshold and battery size, on the capacity performance are extensively investigated. Results show that although the performance of our scheme is inferior to the optimal joint selection scheme, it is still a practical scheme because its complexity is much lower than that of the optimal scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.12
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• pp.2317-2323
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• 2015

In this paper, we analyze the performance of dual-hop amplify-and-forward (AF) relaying in cooperative networks with partial relay selection. An AF relay gain considered in this paper includes channel-noise-assisted relay gain. Leveraging a received signal-to-noise ratio (SNR) model, we derive exact closed-form expressions for the probability density function (pdf) and cumulative distribution function (cdf) of the end-to-end SNR. Moreover, an exact closed-form expression of the ergodic capacity for dual-hop AF relaying with channel-noise-assisted relay gain and partial relay selection is investigated. The analytical results shown in this paper are confirmed by Monte-Carlo simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.9
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• pp.4357-4378
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• 2017

In cooperative multi-relay networks, the relay nodes which are selected are very important to the system performance. How to choose the best cooperative relay nodes is an optimization problem. In this paper, multi-relay selection schemes which consider either single objective or multi-objective are proposed based on evolutionary algorithms. Firstly, the single objective optimization problems of multi-relay selection considering signal to noise ratio (SNR) or power efficiency maximization are solved based on the quantum bee colony optimization (QBCO). Then the multi-objective optimization problems of multi-relay selection considering SNR maximization and power consumption minimization (two contradictive objectives) or SNR maximization and power efficiency maximization (also two contradictive objectives) are solved based on non-dominated sorting quantum bee colony optimization (NSQBCO), which can obtain the Pareto front solutions considering two contradictive objectives simultaneously. Simulation results show that QBCO based multi-relay selection schemes have the ability to search global optimal solution compared with other multi-relay selection schemes in literature, while NSQBCO based multi-relay selection schemes can obtain the same Pareto front solutions as exhaustive search when the number of relays is not very large. When the number of relays is very large, exhaustive search cannot be used due to complexity but NSQBCO based multi-relay selection schemes can still be used to solve the problems. All simulation results demonstrate the effectiveness of the proposed schemes.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.5
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• pp.66-71
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• 2012

The capacity criteria have been proposed in order to select a cooperative relay node in WSNs, under the environment where direct path has a poor link gain. This process may ensure the efficiency improvement of signal transfer between source and destination and reduction of energy consumption as well. Two criteria are incorporated to select a cooperative relay node. Firstly, calculate the energy gain ratio between the relay path and the direct path. These are defined as the ratio between the energy factors of 1/g and 1/B. Each stands for an inverse of direct path gain and relay path gain. Secondly, investigate the effects of relay node's usage in WSNs through the simulation in terms of energy consumption. In conclusion, using a selected cooperative relay node based on the selected criteria is effective in terms of both energy efficiency and capacity of WSNs especially when direct path gain is relatively low.

• Journal of Broadcast Engineering
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• v.15 no.2
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• pp.157-162
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• 2010

In this paper, We propose that the adaptive cooperative relay transmission technique using closed-loop MIMO scheme for duplex communication system. As the mobility between relay and base station is little, closed-loop MIMO is better diversity gain than open-loop MIMO. At this time, more than one relaying terminals are included in one cooperative group to share their transmission and take precoding weight feedback. For minimization of throughput reduction caused by increasing feedback bits, we use codebook-based MRT that limit the number of feedback bits. Among the cooperative relay group, the best relays are selected from the base stataion and get the feedback. A protocol senarios are also proposed for this relay system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.10
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• pp.4231-4245
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• 2020

Non-orthogonal multiple access (NOMA) is widely studied in both academia and industry due to its high spectral efficiency over orthogonal multiple access (OMA). To effectively improve spectrum efficiency, an amplify-and-forward (AF) cooperative NOMA system is proposed as well as a novel detection scheme is proposed, in which we first perform successive interference cancellation (SIC) twice at U1 for the two signals received from two time slots to remove interference from symbol 2, then two new signals apply max ratio combining (MRC). In addition, a closed-form upper bound approximation for the ergodic capacity of our proposed system is derived. Monte-Carlo simulations and numerical analysis illustrate that our proposed system has better ergodic capacity performance than the conventional cooperative NOMA system with decode-forward (DF) relay, the conventional cooperative NOMA system with AF relay and the proposed AF cooperative NOMA system in [16]. In addition, we can see that ergodic capacity of all NOMA cooperative systems increase with the increase of transmit SNR. Finally, simulations display that power allocation coefficients have little effect on ergodic capacity of all NOMA cooperative systems. This is due to this fact that ergodic capacity of two symbols can be complementary with changing of power allocation coefficients.

• Journal of information and communication convergence engineering
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• v.15 no.1
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• pp.21-27
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• 2017

In this research, we study the outage probability for distributed space-time coding-based cooperative (DSTC) systems with amplify-and-forward relaying over Rayleigh fading channels with a high temporal correlation where the direct link between the source and the destination is available. In particular, we derive the upper and lower bounds of the outage probability as well as their corresponding asymptotic expressions. In addition, using only the average channel powers for the source-to-relay and relay-to-destination links, we propose an efficient power allocation scheme between the source and the relay to minimize the asymptotic upper bound of the outage probability. Through a numerical investigation, we verify the analytical expressions as well as the effectiveness of the proposed efficient power allocation. The numerical results show that the lower and upper bounds tightly correspond to the exact outage probability, and the proposed efficient power allocation scheme provides an outage probability similar to that of the optimal power allocation scheme that minimizes the exact outage probability.