Ahmed H. Abd El-Malek

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.

Outage Analysis of Mixed Underlay Cognitive RF MIMO and FSO Relaying With Interference Reduction

In this paper, we study the outage performance of multiuser mixed underlay radio frequency (RF)/multidestinations free-space optical (FSO) links. For RF links, we consider a secondary network with multiple users that can communicate with multiple destinations through a relaying node. The relay is equipped with an antenna array at the RF side, and it uses the amplify-and-forward (AF) protocol. The primary users (PUs) are equipped with multiple antennas at transmit and receive nodes. The RF link is subjected to the aggregate PUs interference effect on the secondary network. To reduce the effect of PUs interference on secondary network at the relay node, two interference cancellation (IC) schemes are adopted, which vary in terms of complexity and achieved performance. On the other hand, the multidestination FSO links can be exploited to further enhance the quality of the second hop, and their associated channel models account for pointing errors, intensity modulation/direct detection, and heterodyne detection. For the aforementioned system model, we obtain exact and asymptotic closed-form expressions for the end-to-end outage probability. To further enhance system performance, optimal power allocation between the two hops is obtained based on the derived asymptotic outage probability expressions.

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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Security and reliability analysis of diversity combining techniques in SIMO mixed RF/FSO with multiple users

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.

MIMO Cognitive Relay Networks With Correlated Antennas Over Rayleigh Fading Channels

In this paper, the impact of co-channel interference (CCI) on the secrecy performance of the dual-hop decode-and-forward relaying network is investigated. First, the security-reliability trade-off (SRT) analysis is studied for conventional single-hop networks under a single passive eavesdropper attack. Then, the SRT analysis is investigated to the opportunistic relay selection (ORS) model in the presence of independent and identically distributed (i.i.d.) interfering signals. Moreover, the proposed work enhances physical layer (PHY) security performance of ORS model using cooperative jamming techniques (CJ-ORS). For this purpose, new closed-form expressions are derived for intercept probability and outage probability of CJ-ORS model in the presence of interference over Rayleigh fading channels. A power allocation optimization problem is formulated and solved for enhancing the system security. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions of the paper.

MIMO multiuser cognitive relay network in spectrum sharing environment with antenna correlation over Rayleigh fading channels

In this paper, we investigate the impact of different diversity combining techniques on the security and reliability analysis of a single-input-multiple-output (SIMO) mixed radio frequency (RF)/free space optical (FSO) relay network with opportunistic multiuser scheduling. In this model, the user of the best channel among multiple users communicates with a multiple antennas relay node over an RF link, and then, the relay node employs amplify-and-forward (AF) protocol in retransmitting the user data to the destination over an FSO link. Moreover, the authorized transmission is assumed to be attacked by a single passive RF eavesdropper equipped with multiple antennas. Therefore, the system security reliability trade-off analysis is investigated. Closed-form expressions for the system outage probability and the system intercept probability are derived. Then, the newly derived expressions are simplified to their asymptotic formulas at the high signal-to-noise- ratio (SNR) region. Numerical results are presented to validate the achieved exact and asymptotic results and to illustrate the impact of various system parameters on the system performance.

A Cooperative Model for Enhancing Spectral Efficiency in Two-Way Amplify-and-Forward Relaying Networks

In this paper, we examine orthogonal space-time block coding with receiver maximal ratio combining (OSTBC/MRC) and selection combining (OSTBC/SC) in multiple-input-multiple-output (MIMO) decode-and-forward (DF) relay networks with underlay spectrum sharing, considering optimal and suboptimal cases. The secondary network under consideration is equipped with multiple correlated antennas at the source, the relay, and the destination. On the other hand, the primary network is composed of L primary users (PUs), each of which is equipped with multiple correlated antennas. For the considered underlay spectrum sharing, the transmit power condition is related by an interference limit on the primary network and the maximum transmission power in the secondary network. In particular, new exact expressions for the outage probability of the adopted system models are obtained. Moreover, simple asymptotic expressions for the outage probability are provided to enable the characterization of the achievable diversity orders and coding gains. To enhance the secondary network performance, optimal power allocation (PA) between the secondary source and the secondary relay is obtained based on the asymptotic outage probability under the constraints of total allowable transmit power at the secondary user (SU) and maximum allowable interference power limit at the PU. The derived analytical formulas herein are supported by numerical results to clarify the main contributions.

A Bandwidth-Efficient Cognitive Radio With Two-Path Amplify-and-Forward Relaying

In this paper, we examine the impact of antenna correlation on transmit antenna selection with maximal ratio combining (TAS/MRC)in multiple-input-multiple-output multiuser cognitive relay networks (MIMO-MCRNs). A single secondary user (SU) source communicates with M SU destinations via SU decode-and-forward (DF) relay over Rayleigh fading channels and in the presence of L PU destinations. Each node in the considered SU network is equipped with multiple correlated antennas as well as the L PU destinations. The SU network employs underlay spectrum sharing paradigm in which the SU transmission power is limited by peak interference temperature limit on the PU network and the maximum allowable transmission power at each node of the SU network. As a measure of performance, we derived an exact expression for the outage probability of the proposed SU network. To gain further insights, a simple asymptotic expression for the outage probability is provided to obtain the achievable diversity order and coding gain.

Physical Layer Security Enhancement in Multiuser Mixed RF#x002F;FSO Relay Networks under RF Interference

In this work, a new cooperative two-way relaying (TWR) model with amplify-and-forward (AF) protocol is proposed in which a primary user (PU) network consisting of two PU sources communicate with each other via a single relay. In addition, a secondary user (SU) source transmits its data to its SU destination via the same PU relay node. In order to mitigate SU interference caused to the PU network, the PU network considers the SU network pairs (i.e., source and destination) as two additional relay nodes helping the original PU relay node in improving the PU network performance via orthogonal space-time block code (OSTBC) technique. As a reward, the PU network allows the SU network to communicate simultaneously via the PU relay node using the decode-and-forward (DF) protocol. A power allocation optimization problem is formulated to minimize the weighted sum of the average symbol error probability of both PU and SU systems. Results show that the error performance of the proposed model outperforms the conventional TWR-AF model.