Anas M. Salhab

Outage Analysis of N^{th}-Best DF Relay Systems in the Presence of CCI over Rayleigh Fading Channels

This letter investigates the outage behavior of a dual-hop N^{th}-best decode-and-forward (DF) relay system in which the relay and the destination undergo independent sources of co-channel interference (CCI). The fading envelopes associated with the desired and interfering users are assumed to follow independent but non-identically distributed (i.n.d.) Rayleigh fading models. Through the analysis, exact and approximate outage probability are derived based on which the diversity order and coding gain are obtained. Our findings suggest that the diversity order linearly increases with the number of relays and decreases with the order of the relay. Furthermore, results reveal that the system is still able to achieve full diversity gain in the presence of finite number of interferers with finite powers. The analytical results are supported and validated by Monte-Carlo simulations.

A low-complexity relay selection scheme based on switch-and-examine diversity combining for AF relay systems

In this study, the authours present a low-complexity relay selection scheme for channel-state information (CSI)-assisted dual-hop amplify-and-forward cooperative systems. The scheme is mainly based on the switch-and-examine diversity combining (SEC) and SEC post-selection (SECps) techniques in which a relay out of multiple relays is selected to forward the source signal to destination. The selection process is performed such that the selected relay signal-to-noise ratio (SNR) satisfies a predetermined switching threshold instead of best relay. Such a relay that satisfies this threshold will be chosen instead of the best relay. In this study, the authorsuse an upper bound on the end-to-end (e2e) SNR of the selection scheme and derive the probability density function and the cumulative distribution function of this SNR assuming the Rayleigh fading channels. These statistics are then used to derive accurate approximations for both the e2e outage probability and bit error probability, where the direct link in considered. The authours assume that maximal-ratio combining is used at the destination to combine the signals through the relay and the direct link. To obtain more about system insights, the outage performance is studied at high SNR regime, where approximate expressions for the outage probability as well as the diversity order and coding gain are derived and analysed. The Monte-Carlo simulations are provided to illustrate the validity of the analytical results and to show the tightness of the used SNR bound. Results illustrate the effectiveness of the proposed relaying schemes in reducing the required number of channel estimations and hence, reducing the system complexity compared with the opportunistic relaying. Furthermore, results show the gain achieved in the system performance; especially, at low-to-medium SNR values when the SECps selection scheme is used compared with the conventional SEC relaying. Finally, findings show that the system with the SEC and the SECps relaying schemes has the same diversity order of two and the same coding gain.

Security-Reliability Trade-Off Analysis for Multiuser SIMO Mixed RF/FSO Relay Networks With Opportunistic User Scheduling

In this paper, we study the performance of multiuser single-input multiple-output mixed radio frequency (RF)/free space optical (FSO) relay network with opportunistic user scheduling. The considered system includes multiple users, one amplify-and-forward relay, one destination, and a multipleantenna eavesdropper. The users are connected with the relay node through RF links and the relay is connected with the destination through an FSO link. Both maximum ratio combining and selection combining schemes are used at the multipleantenna relay to combine the signal received from the best user on different antennas. The RF/FSO channels models are assumed to follow Nakagami-m/gamma-gamma fading models with pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability, and ergodic channel capacity. Then, the power of the selected best user is determined to minimize the system asymptotic outage probability under the dominant RF or FSO link. Then, the considered system secrecy performance is investigated, where the closedform expressions for the intercept probability are derived. Finally, we propose a new cooperative jamming model in which the worst user is selected by the authorized system to jam the existing eavesdropper. Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results.

Power Allocation and Performance of Multiuser Mixed RF/FSO Relay Networks With Opportunistic Scheduling and Outdated Channel Information

This paper studies the performance of a multiuser mixed radio frequency (RF)/free space optical (FSO) relay network with transmit opportunistic scheduling. The outdated channel information (OCI) on the first relaying hop and its effect on the system performance is also studied in this paper. Furthermore, a power allocation scheme is proposed for optimizing the overall system performance. The considered system includes K sources (users), one amplify-and-froward relay and one destination. The users are connected with the relay node through RF links and the relay is connected with the destination through an FSO link. In the analysis, the first hop channels are assumed to follow Rayleigh fading model and the second hop channel is assumed to follow Gamma-Gamma fading model with considering the effect of pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability, and ergodic channel capacity. Furthermore, the system performance is studied at high signal-to-noise ratio regime, where the diversity order and coding gain are derived and analyzed. Using the asymptotic results, the power of users and relay are determined to minimize the system outage probability under a total power constraint. Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results. Main results show that under weak atmospheric turbulence conditions, the system performance is dominated by the RF channels and a diversity order of K is achieved by the system, whereas under severe atmospheric turbulence conditions, the system is dominated by the FSO channel and the diversity order is determined by the minimum value of the turbulence fading and pointing error parameters.

Performance of Switch-and-Examine DF Relay Systems With CCI at the Relays and Destination Over Rayleigh Fading Channels

In this paper, we evaluate the outage performance of a decode-and-forward (DF) relay system with a low-complexity relay selection schemes in the presence of interference at the relays and destination. The schemes are mainly based on the switch-and-examine diversity combining (SEC) and SEC with post-examine selection (SECps) techniques in which a relay whose second hop signal-to-noise ratio (SNR) satisfies a predetermined switching threshold is selected instead of the best relay to forward the source message to destination. In this paper, we first derive the probability density function (PDF) of the SNR of the relay selection scheme and the conditional cumulative distribution function (CDF) of the end-to-end (e2e) signal-to-interference plus noise ratio (SINR) assuming Rayleigh fading channels. The derived statistics along with the statistics of first hop channels of the relays and the direct link are then used to derive a closed-form expression for the e2e outage probability. We assume that maximal-ratio combining (MRC) is used at the destination to combine the signals of relay and the direct link. Furthermore, to get more about system insights, the outage performance is studied at high SNR regime. Monte-Carlo simulations are provided to validate the derived analytical and asymptotic expressions. Main results illustrate that when the interference power does not scale with SNR, the system can still achieve diversity gain, especially, at SNR values that are comparable to the switching threshold. Asymptotic results show that at high SNR values, the system with the SEC and SECps relaying schemes has a diversity order of 2 and approximately the same coding gain.

A new low-complexity relay selection scheme based on switch-and-examine diversity combining for dual-hop relay networks

In this paper, we present a new low-complexity relay selection scheme for channel-state information (CSI)-assisted dual-hop amplify-and-forward (AF) cooperative networks. The scheme is mainly based on the switch-and-examine (SEC) diversity combining technique where a relay out of multiple relays is only used to forward the source signal to destination. The selection process is performed based on a predetermined switching threshold. In analyzing the scheme performance, a lower bound on end-to-end (e2e) SNR is first used. Then, the probability density function (PDF) and the cumulative distribution function (CDF) are derived in a Rayleigh fading environment. After that, accurate approximations for both the outage probability and the bit error rate (BER) are evaluated. The maximal-ratio combining (MRC) is used at the destination to combine the signal on the relay path with that on the direct link. The Monte Carlo simulations show the validity of the analytical results and the tightness of the used bound, specially, at the high SNR values. Finally, we provide some numerical results to illustrate the effectiveness of the proposed scheme in reducing the system complexity and to verify the effect of other system parameters as the switching threshold and the number of relays on system behavior.

Cognitive Amplify-and-Forward Relay Networks with Switch-and-Examine Relaying in Rayleigh Fading Channels

This letter introduces cognitive channel-state-information (CSI)-assisted amplify-and-forward (AF) relay networks employing the low-complexity switch-and-examine diversity combining (SEC) relaying scheme. The scheme is based on the SEC diversity combining technique in which a relay out of multiple relays is selected to forward the source message to destination. The selection process is performed such that the end-to-end (e2e) signal-to-noise ratio (SNR) of the selected relay satisfies a predetermined switching threshold. In addition, the letter derives closed-form expressions for the outage probability and symbol error probability (SEP) of the proposed system. The system is also studied at high SNR values where approximate expressions for the outage probability, diversity order, and coding gain are derived. Results show that the diversity order of the studied cognitive AF relaying with SEC selection is the same as its non-cognitive counterpart.

New Bandwidth Efficient Relaying Schemes in Cooperative Cognitive Two-Way Relay Networks With Physical Layer Security

In this paper, a new cooperative two-way cognitive relaying scheme is proposed. In this model, a primary user (PU) network consisting of two PU sources communicate with each other via a single amplify-and-forward (AF) relay. In addition, a secondary user (SU) source transmits its data to an SU destination via the same PU relay node. To mitigate the SU interference caused to the PU network, the PU network considers the SU network pairs as two additional relay nodes helping the original PU relay node in improving the PU network performance. As a reward for its cooperation, the PU network allows the SU network to communicate simultaneously via the PU relay node by using the decode-and-forward protocol. The proposed system allows the transmission of four PU symbols and one SU symbol in four/three time slots resulting in a bandwidth efficiency of

Optimal Power Allocation for Enhancing Physical Layer Security in Opportunistic Relay Networks in the Presence of Co-Channel Interference

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Multi-Destination Cognitive Radio Relay Network with SWIPT and Multiple Primary Receivers

based on the cooperative scheme, respectively. Two power allocation optimization problems are formulated: the first problem minimizes the weighted sum of the average symbol error probability of both PU and SU systems, whereas the second problem maximizes the total achievable sum rate of the PU and SU networks. Lagrangian multiplier method is used to find the optimal solutions for both problems under the constraint of maximum allowable power budget. In addition, the paper investigates how the proposed model improves the PU physical layer security performance against a single passive eavesdropper. The results show that the error performance of the proposed relay selection model outperforms the conventional two-way relaying networks with AF protocol. Moreover, findings illustrate that the total achievable sum rate of the proposed relay elimination model is higher than the total achievable rate of the conventional two-way relaying model. From secrecy point of view, the proposed model is shown to achieve a nonzero secrecy rate that improves the PU system security against eavesdropping attacks.