The authors study the optimal design of simultaneous wireless information and power transfer relaying in bidirectional non‐regenerative relay networks. They consider both power splitting relaying and time switching relaying. Since there are two opposite traffic flows between two sources, they characterise the transmission rate performance by the minimum rate of two opposite traffic flows. Specifically, they first obtain closed‐form expressions for the optimum power splitting and time switching coefficients to maximise the minimum transmission rate of bidirectional non‐regenerative relaying. They also derive the resulting maximum transmission rate expressions. Furthermore, they consider a minimum input radio frequency (RF) power level to turn on diodes, and derive the turn‐on probability of the RF energy harvesting circuit when two channels experience independent Rayleigh fading. Numerical results confirm that the authors' analyses exactly match with simulation results and that the two relaying strategies with optimum coefficients give almost the same transmission rate performance.

We study the optimum design of an energy harvesting relay for two-way decode-and-forward (DF) relay networks. In the networks, the relay harvests energy as well as decodes information using the received signal from two sources with power splitting relaying (PSR) and time switching relaying (TSR) strategies. Since the two-way relay network has two opposite traffic flows, it can be considered as a special case of multi-user systems. Applying the max-min criterion for fairness and max-sum criterion for maximum resource utilization, we optimize the operations of the energy harvesting relay. Specifically, considering the transmission rate constraints of individual hops, we derive optimum power splitting coefficients and optimum time switching coefficients, respectively, for PSR-based and TSR-based networks under both criterions, and analytically calculate the resulting maximum transmission rates. Numerical results confirm that our analyses exactly match with exhaustive search simulations. The obtained optimum coefficients are given in closed-form, therefore, they can be easily adopted in simple two-way relay networks with limited computational power such as sensor/Internet of Things (IoT) networks and can help two-way DF relay networks.

In this paper, we consider the power splitting relaying (PSR) and time switching relaying (TSR) protocols for decode-and-forward (DF)-based relay networks consisting of a source, a relay, and a destination. For the networks, the relay is assumed to have a rechargeable battery with a certain amount of remaining energy for energy harvesting through the received signal transmitted from the source. Specifically, for the PSR protocol with and without the direct-path, we present the outage probability expression with a given power splitting coefficient, and we obtain the optimum power splitting coefficient to maximize the transmission rate and derive its transmission rate and outage probability, where the optimum coefficient depends on channel conditions and remaining energy. For the TSR protocol with and without the direct-path, we present the outage probability expression with a given time switching coefficient, and we obtain the optimum time switching coefficient to maximize the transmission rate and derive its transmission rate, where the optimum coefficient also depends on channel conditions and remaining energy.

In this paper, we investigate two different relay selection schemes, opportunistic relaying (OR) and selection cooperation (SC), for decode-and-forward (DF)-based relay networks consisting of a source, multiple relays, and a destination in the presence of multiple co-channel interferers, where each terminal has a single antenna and operates in a half-duplex mode. For the network, we first extend the conventional OR and SC to relay networks with the direct-path and multiple co-channel interferers, and obtain the exact and closed-form outage probability of the OR. Then, we show that the SC is equivalent to the OR in terms of outage performance for relay networks with the direct-path and multiple co-channel interferers. Finally, we show that the SC and OR are outage-optimal under the aggregate power consumption constraint at the relays for relay networks with the direct-path and multiple co-channel interferers.

In this letter, we offer the secrecy outage probability of the amplify-and-forward (AF) transmission, which consists of one source, one destination, one relay, and one passive eavesdropper. Particularly, we consider that the relay is equipped with multiple antennas while other terminals is utilized with single antenna and apply some diversity techniques (for both the reception and the transmission) in the relay to achieve gains in a secrecy outage performance. Additionally, we analyze the exact secrecy outage probability of the proposed systems in a one-integral form. Finally, some numerical examples are given to verify our provided analytical results for different system conditions.

We study a new relay selection scheme in nonregenerative relay networks consisting of a source, a destination, an eavesdropper, and multiple relays, where each terminal has a single antenna and operates in a half duplex mode. In these networks, it is desirable to protect the confidential message from the source to the destination against the eavesdropper with the help of a single selected relay. Specifically, we begin by investigating one scenario: instantaneous signal to noise ratios (SNRs) related to the eavesdropper are available. For the scenario, we propose relay selection to maximize the secrecy capacity of nonregenerative networks with and without direct paths. For networks with direct-paths, we derive a closed-form approximation of the secrecy outage probability. As a special case, for networks without direct-paths, we derive the exact secrecy outage probability expression in integral form and offer as well a closed-form approximation.

Two-way relaying (TWR) has recently received a great deal of attention since it can recover the loss in spectral efficiency that characterizes conventional half-duplex transmission systems operating within cooperative networks. Additionally, when relay selection is considered in multiple relay network, outdated channel state information (CSI) due to feedback delays can create important challenges from a practical point of view. In this paper, we study the outage performance of an amplify-and-forward (AF)-based TWR system with multiple relays where a single relay selection is performed based on outdated CSI. Specifically, we consider a single relay selection scheme in AF-based TWR system under outdated CSI conditions and offer a statistical analysis of the signal-to-noise ratio per hop with the given policy. For the analysis of the outage probability with asymmetric outage thresholds, we offer an accurate closed-form approximation based on the provided statistical/joint statistical analyses of a dual-hop AF transmission. Finally, we verify our analytical results with some selected computer-based simulation results.

In this paper, we study the outage performance of an amplify-and-forward (AF)-based two-way relaying (TWR) system with multiple relays where a single relay selection is performed based on outdated channel state information (CSI). Specifically, we propose a single relay selection scheme in AF-based TWR system under outdated CSI conditions. With this policy, we offer a statistical analysis of the signal-to-noise ratio per hop and analyze the outage probability with asymmetric outage thresholds based on CSI-assisted AF protocol. Additionally, we provide the exact and asymptotic expressions based on the provided statistical/joint statistical analyses of a dual-hop AF transmission. Finally, we verify our analytical results with some selected computer-based simulation results.