• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1260-1266
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• 2007

Error propagation of source-relay (S-R) link limits the performance of decode-and-forward (DF) relay and prohibits DF relay from achieving full diversity gain. In order to solve this problem, the proposed deployment strategy focuses on two objectives. One is to achieve full diversity gain, and the other is to minimize the used power of the DF relay system. In order to achieve full diversity, the error probability of S-R link should be lower than that of maximal ratio combining (MRC) at destination without error propagation since the error probability of the weaker link dominates the total error probability. The proposed strategy of relay positioning points out the range of the relay position for achieving full diversity, and the used power of the relay is minimized by this range. Analysis of error probability and simulation results prove that the two objectives are achieved by the proposed strategy of the relay position.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.2
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• pp.49-54
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• 2018

In this paper, we study the secrecy outage probability when using cooperative diversity and jammer in a relay system based on decode-and-forward. MRC method is used in receiver and eavesdroppers to obtain cooperative diversity. To use the MRC technique, direct links between the sender and receiver, and between the sender and the eavesdropper are used, respectively. Jammers are used to generate intentional noise siganls to increase security capacity. Jammers generate intentional noise, degrading the channel quality of the eavesdropper and helping physical layer security be realized. The secrecy outage probability is used to evaluate security performance. Assume that the system is under the Rayleigh fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5C
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• pp.487-494
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• 2010

This paper presents an OFDM-based dual-hop multi-relay system with best relay selection maximizing the mutual information. For the system either with decode-and-forward (DF) relays or with amplify-and-forward (AF) relays, we derive a lower-bound on the outage probability and the diversity order achievable in frequency selective fading channels and provide the outage capacity from simulation. Performance evaluation shows that both DF and AF provide the same diversity order as in the lower-bound but DF of which the outage probability is much closer to the lower-bound provides a better outage capacity than AF. It is also observed that the SNR gain of DF over AF gets larger as either the number of resolvable multipaths or the number of relay candidates increases, which makes DF relaying more favorable to the OFDM-based multi-relay system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.136-143
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• 2010

In this paper, we investigate decode-and-forward (DF) relaying systems with a direct link between the source and the destination node. The objective of this paper is to determine the better relaying strategy between 3-hop DF relaying and dual-hop DF relaying with the best relay selection. Assuming Rayleigh fading channels, we present closed-form outage probability of the 3-hop relaying and the dual-hop relaying, respectively, and compare the performances by numerical investigation. Numerical results show that if the channel is poor, the outage performance of the 3-hop relaying is better than the dual-hop relaying.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.4
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• pp.87-92
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• 2015

In this Paper, we proposed optimization of system performance, optimal splitting factor ${\alpha}$ applied to power splitting protocol with relay protocol with decode and forward undergo co-channel interference. We can possible to optimize and maximize the channel capacity of the receive performance and the efficiency of the network through optimal factor of splitting protocol. We verified BER performance and Channel capacity and Outage probability for the proposed scheme over Rayleigh fading through Monte-Carlo simulation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.3
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• pp.71-75
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• 2018

In this paper, we study the secrecy outage probability when using jammer in a relay system based on decode-and-forward. The jammer may be selected among the relays not selected to increase the security capacity in the physical layer so as to generate intentional noise. Jammer noise can equally interfere with the receiver and eavesdropper but can enhance the physical layer security by selecting an optimal jammer that makes the channel quality between the sender-eavesdropper links worse than the channel of the sender-receiver link. In this paper, we compute the theoretical formula of the secrecy outage probability with and without jammers, and compare the theoretical value with the simulation value to prove that the equation is valid.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1244-1250
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• 2007

User cooperation provides high reliability in wireless communication systems by employing relay nodes to transmit the same information. In this paper, a bit error rate (BER) study is presented for decode-and-forward (DF) relaying for user cooperation in independent and identically distributed Rayleigh fading channels. For an arbitrary number of relays, exact and closed-form expressions of the BER are proposed for M-ary PAM (Pulse Amplitude Modulation), QAM (Quadrature Amplitude Modulation) and PSK (Phase Shift Keying), respectively. It is also shown that the analytic results are perfectly matched with the simulated ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1A
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• pp.1-9
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• 2010

This paper offers performance analysis of selection decode and forward (DF) networks with differential modulation/demodulation for an arbitrary number of relays in independent but not identically distributed Rayleigh fading channels. We have shown that the selection DF protocol with differential modulation can achieve full diversity in both independent identically distributed (i.i.d.) and independent but not identically distributed (i.n.d.) Rayleigh fading channels, and the performance loss due to using non-coherent detection is not substantial. Furthermore, we study the impact of combining techniques on the performance of the system by comparing a system that uses selection combining (SC) to one that uses maximum ratio combining (MRC). Simulations are performed and show that they match exactly with analytic ones in high SNR regime.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6A
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• pp.568-576
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• 2010

In this paper, we analyze the outage probability of full duplex relay (FDR) with decode-and-forward (DF) protocol is derived under fading channels. The fading channel for source-relay link is assumed to be Rician fading to consider the infrastructured fixed relay with line of sight (LOS) propagation, and the other fading channels are assumed to be Rayleigh fading. Based on this analytical result, we provide the criterion that FDR shows a lower outage probability than HDR to consider the interference problem and the resource efficiency improvement by full duplex (FD) operation. The accuracy of the analysis is confirmed throughout the simulation results.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.12 no.3
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• pp.87-95
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• 2013

In this paper, the outage probability of efficient partial relay selection(EPRS) using only one-hop channel information in multi-hop systems is analyzed in Rayleigh fading channels. In particular, we derive an exact and closed-form expression for the outage probability of decode-and-forward relaying based EPRS. In order to prove the usefulness of EPRS in multi-hop systems, we also analyze the correlation between the end-to-end signal-to-noise ratio(SNR) and the SNR for each hop at an arbitrary relaying path. Furthermore, through numerical investigation, we compare the outage performances for EPRS and the best relay selection using all channel information.