• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.260-279
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• 2015

In this paper, we investigate physical layer security for multiple decode-and-forward (DF) relaying underlay cognitive radio networks (CRNs) with fixed transmit power at the secondary network against passive eavesdropping attacks. We propose a simple relay selection scheme to improve wireless transmission security based on the instantaneous channel information of all legitimate users and the statistical information about the eavesdropper channels. The closed-form expressions of the probability of non-zero secrecy capacity and the secrecy outage probability (SOP) are derived over independent and non-identically distributed Rayleigh fading environments. Furthermore, we conduct the asymptotic analysis to evaluate the secrecy diversity order performance and prove that full diversity is achieved by using the proposed relay selection. Finally, numerical results are presented to verify the theoretical analysis and depict that primary interference constrain has a significant impact on the secure performance and a proper transmit power for the second transmitters is preferred to be energy-efficient and improve the secure performance.

• ETRI Journal
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• v.43 no.4
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• pp.758-768
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• 2021

In this work, the secrecy of a typical wireless cooperative dual-hop non-orthogonal multiple access (NOMA)-enabled decode-and-forward (DF) relay network is investigated with the impact of collaborative and non-collaborative eavesdropping. The system model consists of a source that broadcasts the multiplexed signal to two NOMA users via a DF relay, and information security against the eavesdropper nodes is provided by a helpful jammer. The performance metric is secrecy rate and ergodic secrecy capacity is approximated analytically. In addition, a differential evolution algorithm-based power allocation scheme is proposed to find the optimal power allocation factors for relay, jammer, and NOMA users by employing different jamming schemes. Furthermore, the secrecy rate analysis is validated at the NOMA users by adopting different jamming schemes such as without jamming (WJ) or conventional relaying, jamming (J), and with control jamming (CJ). Simulation results demonstrate the superiority of CJ over the J and WJ schemes. Finally, the proposed power allocation outperforms the fixed power allocation under all conditions considered in this work.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.5
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• pp.2416-2432
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• 2017

In this paper, we investigate the security performance for cooperative networks over Nakagami-m fading channels. Based on whether the channel state information (CSI) of wiretap link is available or not, optimal relay selection (ORS) and suboptimal relay selection (SRS) schemes are considered. Also, multiple relays combining (MRC) scheme is considered for comparison purpose. The exact and asymptotic closed-form expressions for secrecy outage probability (SOP) are derived and simulations are presented to validate the accuracy of our proposed analytical results. The numerical results illustrate that the ORS is the best scheme and SRS scheme is better than MRC scheme in some special scenarios such as when the destination is far away from the relays. Furthermore, through asymptotic analysis, we obtain the closed-form expressions for the secrecy diversity order and secrecy array gain for the three different selection schemes. The secrecy diversity order is closely related to the number of relays and fading parameter between relay and destination.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6A
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• pp.468-475
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• 2009

In OFDM-based Full Duplex Relays (FDR) with Decode and Forward (DF) scheme, an interference cancellation technique in the frequency domain is more efficient than the one in the time domain. However, an Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) may occur due to the timing mismatch between the feedback interference signal and the desired signal from Base Station (BS) when the feedback interference cancellation and demodulation are performed in the frequency domain. In this paper, the effects of timing mismatch on the synchronous type and asynchronous type of OFDM-based FDR are analyzed for uplink and downlink cases. Then, synchronization procedure and methods for reducing ISI and ICI in OFDM-based FDR with frequency-domain feedback interference canceller are proposed and verified by computer simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.12
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• pp.82-88
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• 2009

An adaptive cooperation system is considered with the cooperation decision strategy based on the differences between instantaneous signal-to-noise ratio (SNR) S-D and R-D channels. Specifically, if the quality of the direct link (S-D) is better than that of the link from the relay to the destination (R-D), the source will transmit to destination directly with all scheme's transmitted power. Otherwise, the source broadcasts the signal with a lower power in the first time slot. Then, in the second time slot, if the relay decodes its received signal correctly, it re-transmits the re-encoded signal to the destination else the source will transmit again with the remaining power. Firstly, the spectral efficiency is derived by calculating the probabilities of direct transmission and cooperation mode. Subsequently, the BER performance for the adaptive cooperation schemes is analyzed by considering the BER routine of each mode. Finally, the Monte-Carlo simulation results are presented to confirm the performance enhancement offered by the proposed schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.12
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• pp.5943-5962
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• 2017

A resource allocation algorithm based on simultaneous wireless information and power transfer (SWIPT) to maximize the system throughput is proposed in orthogonal frequency division multiplexing (OFDM) relay networks. The algorithm formulates the problem under the peak power constraints of the source and each subcarrier (SC), and the energy causality constraint of the relay. With the given SC allocation of the source, we give and prove the optimal propositions of the formulated problem. Then, the formulated problem could be decomposed into two separate throughput maximization sub-problems by setting the total power to transfer energy. Finally, several SC allocation schemes are proposed, which are energy priority scheme, information priority scheme, balanced allocation scheme and exhaustive scheme. The simulation results reveal that the energy priority scheme can significantly reduce computational complexity and achieve approximate performance with the exhaustive scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.11
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• pp.5370-5393
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• 2019

In this paper, we consider a two-way relay non-orthogonal multiple access (TWR-NOMA) system with residual hardware impairments (RHIs) and channel estimation errors (CEEs), where two group users exchange their information via the decode-and-forward (DF) relay by using NOMA protocol. To evaluate the performance of the considered system, exact analytical expressions for the outage probability of the two groups users are derived in closed-form. Moreover, the asymptotic outage behavior in the high signal-to-noise ratio (SNR) regime is examined and the diversity order is derived and discussed. Numerical simulation results verify the accuracy of theoretical analyses, and show that: i) RHIs and CEEs have a deleterious effects on the outage probabilities; ii) CEEs have significant effects on the performance of the near user; iii) Due to the RHIs, CEEs, inter-group interference and intra-group interference, there exists error floors for the outage probability.

• Journal of electromagnetic engineering and science
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• v.11 no.4
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• pp.262-268
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• 2011

In this paper, we evaluate the outage performance of cooperative transmission in two-dimensional random networks. Firstly, we derive the joint distributions of the source-relay and the relay-destination links. Secondly, the outage probability for the decode-and-forward relaying system is derived when selection combining (SC) is employed at the destination. Finally, we calculate the average outage probability of the system and then attempt to express it by a simple approximate expression. The simulation results are presented to verify the accuracy of the derivations. Similar to deterministic networks, the cooperative transmission in random networks outperforms direct transmission at a high signal-to-noise ratio (SNR).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.5
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• pp.1-7
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• 2011

In this paper, CDD(Cyclic Delay Diversity)-DF(Decode-and-Forward)-Relay scheme is proposed for MC-CDMA(Multicarrier-Code Division Multiple Access) systems over multipath Rayleigh fading channels. The advantages of general DF schemes come at the expense of the spectral efficiency since the source and all the relays must transmit on orthogonal channels. In order to mitigate this disadvantage of general DF schemes, we have applied CDD techniques to each relays so that all the relays can transmit on single channel. It means that all R-D link channels can be considered as a single channel which is widely delay spread. Namely, it causes the increasing the number of multipath so that the frequency diversity gain can be achieved in MC-CDMA systems. By simulations, we have compared proposed one with general DF scheme. Therefore, it is confirmed that the proposed one can be a possible solution to achieve cooperative diversity gain without a reduction of spectral efficiency.