Energy-Efficient Cooperative Protocols for Full-Duplex Relay Channels

In this work, energy-efficient cooperative protocols are studied for full-duplex relaying (FDR) with loopback interference. In these protocols, relay assistance is only sought under certain conditions on the different link outages to ensure effective cooperation. Recently, an energy-efficient selective decode-and-forward protocol was proposed for FDR, and was shown to outperform existing schemes in terms of outage. Here, we propose an incremental selective decode-and-forward protocol that offers additional power savings, while keeping the same outage performance. We compare the performance of the two protocols in terms of the end-to-end signal-to-noise ratio cumulative distribution function via closed-form expressions. Finally, we corroborate our theoretical results with simulation, and show the relative relay power savings in comparison to non-selective cooperation in which the relay cooperates regardless of channel conditions

Two-way CSI-assisted AF relaying with HPA nonlinearity

In this paper, we investigate half-duplex two-way dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) relaying in the presence of high-power amplifier (HPA) nonlinearity at relays. The expression for the end-to-end signal-to-noise ratio (SNR) is derived as per the modified system model by taking into account the interference caused by relaying scheme and HPA nonlinearity. The system performance of the considered relaying network is evaluated in terms of average symbol error probability (SEP) in Nakagami-$m$ fading channels, by making use of the moment-generating function (MGF) approach. Numerical results are provided and show the effects of several parameters, such as quadrature amplitude modulation (QAM) order, number of relays, HPA parameters, and Nakagami parameter, on performance

Physical-Layer Secret Key Generation via CQI-Mapped Spatial Modulation in Multi-Hop Wiretap Ad-Hoc Networks

Providing security guarantee is a critical concern in the ad-hoc networks relying on multi-hop channels, since their flexible topology is vulnerable to security attacks. To enhance the security of a spatial modulation (SM) assisted wireless network, various SM mapping patterns are activated by random channel quality indicator (CQI) patterns over the legitimate link, as a physical-layer secret key. The SM signals are encrypted by random mapping patterns to prevent eavesdroppers from correctly demapping their detections. This secret key is developed for multi-hop wiretap ad-hoc networks, where eavesdroppers might monitor all the transmitting nodes of a legitimate link. We substantially characterise the multi-hop wiretap model with receiver diversity techniques adopted by eavesdroppers. The security performance of the conceived scheme is evaluated in the scenarios where eavesdroppers attempt to detect their received signals using maximal-ratio combining or maximum-gain selection. The achievable data rates of both legitimate and wiretapper links are formulated with the objective of quantifying the secrecy rates for both Gaussian-distributed and finite-alphabet inputs. Illustrative numerical results are provided for the metrics of ergodic secrecy rate and secrecy outage probability, which substantiate the compelling benefits of the physical-layer secret key generation via CQI-mapped SM

Secrecy Outage Probability of Energy-Harvesting Cooperative NOMA Transmissions with Relay Selection

Three relay selection techniques, aiming at achieving secure non-orthogonal multiple access in cooperative energy-harvesting (EH) communications, are proposed and compared. In the cooperative relaying system, the source node communicates with multiple users through amplify-and- forward EH relays in the presence of a passive eavesdropper. The relay selection is a two-stage strategy, where the first stage aims at achieving the users’ target data rate, and the second aims at optimizing the secrecy outage probability. New explicit analytical expressions for the secrecy outage probability are derived for three operating scenarios: i) when the channel state information (CSI) of the eavesdropper is unknown, and a two-stage conventional relay selection scheme is considered, ii) when CSI of the eavesdropper is known, and a two- stage optimal relay selection scheme is used, and iii) when multiple relays participate in forwarding the signal to the end users. Monte-Carlo simulations are provided to confirm the derivations, and the effects of the main system parameters on its secrecy are investigated. In particular, it is shown that the optimal relay selection scheme outperforms the conventional and the multiple-relays schemes in terms of secrecy outage probability, and that this superiority becomes more obvious when the number of the relays increases

Rate Splitting in the Presence of Untrusted Users: Outage and Secrecy Outage Performances

In this contribution, a thorough investigation of the performance of rate splitting is conducted in terms of outage and secrecy outage for the simultaneous service to a near user and far user, where the latter attempts to overhear the message of the former. The source transmits a linear combination of the users’ common stream and private streams. Once the common stream is retrieved, two decoding strategies can be adopted by each user. In the first strategy, the nodes (near or far) treat the far user’s private stream as noise to retrieve the private stream of the near user, then the far user decodes its own stream. In the second strategy, the nodes decode the far user’s private stream by treating the one of the near user as noise, then the near user retrieves its private stream while the far user decodes the stream of the near user in its attempt to overhear it. Considering the four decoding combinations, we obtain exact closed-form expressions for the outage probability, and provide tight approximations for the secrecy outage probability. Comparative results are also provided. In particular, it is shown that to achieve better outage probability, with no concern about secrecy, once the decoding of the common stream is completed, each user should first retrieve the private stream with lower target data rate by treating the other private stream as noise. To improve the secrecy outage probability, once the common stream is decoded, the near user must first decode the far user’s private stream, and the far user should first retrieve the private stream with lower target data rate