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In this letter, we investigate the use of active elements in reconfigurable intelligent surfaces (RIS) to overcome the double-fading problem introduced in the RIS-aided link in a wireless communications system. Towards this end, each active RIS element amplifies the reflected incident signal rather than only reflecting it has done in passive RIS modules. As revealed in our analysis and simulation, the use of active elements leads to a drastic reduction in the size of RIS to achieve a given performance level. Furthermore, a practical design for active RIS is proposed.

In this letter, we consider a secure underlay cognitive radio network consisting of a secondary source-destination pair and a primary transmitter-receiver pair in the presence of a primary passive eavesdropper. Herein, a secondary multi-antenna full-duplex destination node acts as a jammer to the primary eavesdropper in an effort to improve the physical layer security of the primary network. In return for this favor, the energy constrained secondary source gets access to the primary network to transmit its own information so long as the interference to the latter is below a certain level. In light of the aforementioned, we evaluate the system performance in terms of the outage probability for the secondary network, the secrecy outage probability, and the probability of non-zero secrecy capacity for the primary network. Numerical results are provided to verify the correctness of the proposed analytical framework.

This letter investigates a reconfigurable intelligent surfaces (RIS)-aided wireless communication system in an inband underlay Device-to-Device (D2D) communication, where the direct link between D2D users is unavailable. An RIS is used to adjust its reflecting elements to enhance the D2D communication data transmission while improving the cellular network’s secrecy performance concurrently. Specifically, analytical results for the secrecy outage probability and the probability of non-zero secrecy capacity are derived for the cellular network. Moreover, the D2D outage probability is also provided. Simulation and analytical results are presented to verify the derived expressions’ correctness and the effectiveness of the proposed scenario. Moreover, the asymptotic results are presented.

This letter examines the physical layer security of a cellular network with inband underlay relay-aided Device-to-Device (D2D) communication, considering the scenario where the channel state information is outdated. The relay node, which operates in a full-duplex mode, can concurrently serve as a friendly jammer to enhance the cellular network secrecy performance while increasing the D2D communication data transmission. A passive eavesdropper utilizes combining approaches to combine the eavesdropping signals. Closed-form expressions for the D2D outage probability and the secrecy outage probability are derived. Furthermore, the asymptotic results are also provided.

In this paper, we study the underlay relay-aided Device-to-Device (D2D) communications to improve the physical layer (PHY) security of the cellular network. We propose a cooperative scheme, whereby the D2D pair, in return of being allowed to share the spectrum band of the cellular network, serves as a friendly jammer, through its multiple-input multiple-output relay, to degrade the wiretapped signal at an eavesdropper. This paper aims to show that spectrum sharing is advantageous for both D2D communications and cellular networks with respect to reliability and robustness for the former, and the physical layer security enhancement for the latter. To assess the proposed cooperative system model, closed-form expressions for the D2D outage probability, the secrecy outage probability, and the probability of non-zero secrecy capacity are derived. More importantly, the benefits due to the cooperation scheme are verified through numerical and simulation results.

This paper investigates the physical layer security of inband underlay Device-to-Device (D2D) communication, where there is no direct link between D2D users. In this respect, optimal relay selection is utilized to secure the D2D transmission. The eavesdropper uses either maximal-ratio combining or selection combining to improve the wiretapped signals. The D2D secrecy performance analysis is performed regarding the secrecy out-age probability (SOP) and the probability of non-zero secrecy capacity, and closed-form expressions are provided. To validate the correctness of our analysis, numerical and simulation results are presented. Furthermore, the asymptotic analysis of the SOP is provided, where new insights into the system parameters are revealed.

This paper investigates physical layer security and data transmission in cellular networks with inband underlay Device-to-Device (D2D) communication, where there is no direct links between D2D users. We propose the use of full-duplex (FD) transmission and dual antenna selection at the relay node. Thanks to the FD transmission, the relay node can simultaneously act as a jammer to enhance the cellular network secrecy performance, while improving the D2D communication data transmission. This describes a practical attractive scheme, where spectrum sharing is beneficial for both the D2D and cellular networks in terms of throughput enhancement and security provisioning, respectively. We analyze the secrecy performance of the cellular network and derive closed-form expressions for the secrecy outage probability (SOP) and the probability of non-zero secrecy capacity. We also derive a closed-form expression of the D2D outage probability. Furthermore, asymptotic analysis for SOP is performed. Simulation and numerical results are provided to verify the efficiency of the proposed scheme and to validate the accuracy of the derived expressions.

Cognitive radio is of great interest for current and future wireless communications. In this paper, the capacity of underlay cognitive radio networks is studied where closed-form expressions for both the ergodic capacity and the outage capacity of the secondary user (SU) are derived. The obtained results reveal new details on the joint effect of multipath fading and shadowing on the capacity of the SU where the increase of the ergodic capacity and degradation of the outage capacity due to heavy shadowing are demonstrated and quantified. Furthermore, the analytical results are verified by Monte-Carlo simulations for different fading scenarios.

This paper studies the physical layer security (PLS) of underlay multihop device-to-device (D2D) relaying. New closed-form expressions on the lower bound of the outage probability, the secrecy outage probability (SOP), and the probability of non-zero secrecy capacity are derived. Hence, new insights into the secrecy performance of the underlay multihop D2D relaying are revealed. The obtained analysis is validated through Mont-Carlo simulations.