Abstract Here, the issue of physical layer security in a two‐way multi‐antenna relay network) is studied. In such a network, two multi‐antenna transceivers attempt to exchange their secret messages via a multi‐antenna relay node in the presence of an eavesdropper. Throughout the first hop, two sources send their messages to the relay node, while an eavesdropper tries to overhear these messages. Then, in the second hop, the relay attempts to send its signal in the null‐space direction of relay‐to‐eavesdropper channel to prevent eavesdropping. The main goal is to obtain effective receive and transmit beamforming vectors at transceivers as well as the beamforming matrix at the relay node to address the secrecy rate balancing problem. The underlying problem is not convex in general. To overcome this issue, the original problem is divided into three subproblems. In the first subproblem the beamforming design at the relay is optimized while in the second subproblem the receive beamforming in a closed form solution is obtained. Finally, in the last subproblem the transmit beamforming is solved using the semi‐definite relaxation and Taylor series expansion. Numerical results represent the effectiveness of the proposed method compared to the previous works in the literature.

Abstract This paper investigates the resource allocation design in device‐to‐device (D2D) communication underlying cellular networks, which is assisted by multiple intelligent reflecting surfaces (IRSs) deployed at the cell boundary to enhance desired signals and mitigate interference between D2D pairs and CUs. In this regard, a multi‐objective optimization problem (MOOP) framework is formulated to jointly maximize the downlink sum‐rate of the D2D pairs and cellular users (CUs). To doing so, the MOOP is first converted into a single‐objective optimization problem (SOOP) by invoking the weighted sum method. Next, to facilitate the high‐coupled non‐convex SOOP formulation, it is decomposed into two sub‐problems through the alternative optimization method. For the first sub‐problem, the inner approximation and successive convex approximations are adopted for jointly allocating D2D transmission power, subcarrier assignment, and transmit beamforming matrix at the BS. For the second sub‐problem, an iterative algorithm based on the penalty‐based method as well as Fenchel's duality approach is adopted to design the passive beamforming matrices at IRSs, which is guaranteed to rapidly converge to a stationary point. Simulation results reveal that a non‐trivial trade‐off between the total throughput of CUs and D2D pairs exist. Furthermore, the proposed framework significantly outperforms existing works addressed in the literature.

This paper aims at exploring the achievable distortion of a Gaussian source over a point-to-point Rayleigh channel exploiting one-bit feedback information. It is assumed that the channel gain is constant for each block and varies independently for next blocks. Incorporating one-bit feedback information, a scalable source coding together with a multi-layer channel coding approach is employed at the transmitter to effectively improve the achievable distortion under mean square measure. Accordingly, the optimal power allocation policy across code layers is derived to minimize the average distortion.

This study investigates the achievable secrecy rate of two‐way relay‐assisted networks. It is assumed that there is no direct link between transceiver ends and the communication is carried out in two hops through the use of multi‐antenna relays in the middle of transmission, where the relays employ amplify‐and‐forward strategies. To increase the bandwidth efficiency, intending nodes exchange their confidential messages in two hops. First, both nodes simultaneously send their messages to the relay nodes. Then, throughout the second hop, the relays make use of cooperative beamforming to send their incoming information in such a way that the achievable secrecy sum rate is maximised, considering each node is subject to a minimum secrecy rate constraint. Accordingly, two beamforming strategies, named as null‐space beamforming and information leakage alignment beamforming are proposed, where their achievable secrecy sum rates are investigated and compared to existing works addressed in the literature.

This study investigates the average achievable rate of a two‐hop block‐fading communication channel, where some single antenna relays are situated in the middle of the transmission and make the destination accessible to the transmitter. It is assumed that the transmitter as well as the relays are not aware of their corresponding instantaneous channel state information (CSI). However, a central node has the corresponding CSI of all links and selects the proper relay that best fits the provided selection criteria. By incorporating a multi‐layer coding approach, which is well known to be a state‐of‐the‐art option to deal with the lack of CSI at the transmitter, the power allocation among the code layers are derived at the transmitter as well as the selected relay node, and the effect of incorporating the aforementioned coding approach in conjunction with the provided relay selection strategies are studied. The results are also compared with that of the single‐layer coding which is being served as a benchmark in this study.

This paper is a study of the Gaussian weak interference channel in which two single-antenna sources aim to send their messages to legitimate destinations such that all messages are kept confidential from non-intended receivers. Under the Gaussian codebook assumption, the problem of secrecy rate balancing with the objective of exploring the optimal power allocation policy at the sources in an attempt to maximize the minimum achievable secrecy rate is investigated, assuming each source is subject to a transmit power constraint. It is shown that at the optimal point, the two secrecy rates are equal; hence, the problem is abstracted to maximize the secrecy rate associated with one destination, while the other is restricted to having the same secrecy rate. The optimum secrecy rate associated with the investigated max-min problem is analytically derived, leading to the solution of the secrecy rate balancing problem. An additional scenario is considered in which sources can transmit artificial noise in addition to their signals. In this case, the max-min problem is solved and a suboptimal solution is provided. Numerical results show that the proposed solution is near-optimal and can be used as a suitable alternative.

This study investigates multi‐layer coding over a dirty‐paper channel. First, it is demonstrated that superposition coding in such channel still achieves the capacity of interference‐free additive white Gaussian noise channel when the transmitter is non‐causally aware of interference signal. Then, the problem is extended to the dirty‐paper block fading channel, where it is shown that in the lack of channel information at the transmitter, the so‐called broadcast approach maximises the average achievable rate of such channel.

This study concerns maximising the minimum achievable secrecy rate (ASR) of a two‐way relay network in the presence of an eavesdropper, in which two nodes aim to exchange messages in two hops, using a multi‐antenna relay. Throughout the first hop, the two nodes simultaneously transmit their messages to the relay. In the second hop, the relay broadcasts a combination of the received information to the users such that the transmitted signal lies in the null space of the eavesdropper's channel; this is called null space beamforming (NSBF). The best NSBF matrix for maximising the minimum ASR is studied, showing that the problem is not convex in general. To address this issue, the problem is divided into three sub‐problems: a close‐to‐optimal solution is derived by using the semi‐definite relaxation technique. Simulation results demonstrate the superiority of the proposed method w.r.t. the most well‐known method addressed in the literature.

This study concerns two‐hop transmission over relay‐assisted block fading channels, assuming there is no direct link between transmission ends and the communication is carried out through using a relay. It is assumed that the channel gains from source‐to‐relay and relay‐to‐destination are known at the relay, while the source is unaware of channel gains. In this case, it is demonstrated that the best signalling method is using a multi‐layer code at the first hop, while using a single‐layer code at the second hop. Accordingly, the decode‐and‐forward (DF) and amplify‐and‐forward (AF) strategies at the relay are investigated, where for DF strategy under two special cases of peak power and average power constraints, the optimal power allocation policy across coding blocks are devised. Moreover, for AF strategy the optimal weight function maximising the average signal‐to‐noise ratio at the destination is derived. The simulation results for Rayleigh fading environment demonstrate the superiority of DF over AF in terms of the average achievable rate. More specifically, it is demonstrated that the broadcast approach in DF strategy under average power constraint closely follows the so‐called broadcast cutset upper bound, thereby providing favourable results in such network.

This study discusses the secrecy rate of two‐hop relay‐assisted cooperative wiretap channels, incorporating multi‐antenna amplify and forward relaying in the middle of transmission. In this regard, under the Gaussian code book assumption, three main scenarios including null‐space beamforming (NSBF), rank‐1 beamforming (RBF), and the so‐called general rank beamforming (GRBF) are proposed to be employed at the relay where their achievable secrecy rates are studied. Accordingly, for NSBF, a closed‐form solution is derived, whereas the corresponding optimisation problems are formulated for the remaining cases as a standard semi‐definite programming problem. Though GRBF ranks the first in terms of the achievable secrecy rate, RBF exhibits favourable results with a much lower complexity, as the corresponding optimisation problem runs over a reduced dimension. Moreover, NSBF has a much lower complexity, as it provides an analytical solution at the expense of a decrease in the secrecy rate, and interestingly, it performs quite well when the number of eavesdroppers is less than that of the relay antennas.

Physical layer security has received considerable attentions in recent years. Moreover, cooperative communications using some nodes of network as relays make use of the benefit of multi‐antenna systems such as increasing the secrecy capacity. This study studies a communication network incorporating some multi‐input–multi‐output amplify and forward relays in the presence of some eavesdroppers. The objective persuaded in the current work is to find the beamforming matrices at the relays to maximise the achievable secrecy rate under either individual or total power constraint at these nodes. Accordingly, three main approaches including general rank beamforming (GRBF), rank‐1 beamforming (RBF) and null‐space beamforming (NSBF) are developed. For the NSBF under the total power constraint, a closed‐form solution is obtained, while for the remaining scenarios the corresponding optimisation problem is expressed as a semi‐definite programming problem. Numerical results indicate that the RBF and NSBF methods follow GRBF in some cases and degraded from GRBF in the others. However, it is shown that these two methods have much lower complexity than GRBF.

This study concerns two-hop communication over a relay-assisted wireless network, including L point-to-point communication links and a multi-antenna relaying node. It is assumed the relay is equipped with Nr antennas and the amplify-and-forward strategy is employed at this node, considering the second-order statistics of channel coefficients are merely available at the relay. To this end, each source sends its desired signal to the relay during the first hop. Thus, the relay simultaneously receives a faded version of L transmitted signals corrupted with an additive white Gaussian noise in a vector form. Then, the relay applies a weight matrix of dimension Nr×Nr to the received vector and transmits the resulting vector to the destinations throughout the second hop. In this regard, the task of finding the best weight matrix at the relaying node under two different criteria, that is, minimising the relay's transmit power to have a minimum signal-to-interference noise ratio (SINR) at destinations and maximising the worst-case SINR for a given relay's transmit power, is investigated. Accordingly, it is demonstrated that the corresponding problems can be formulated as optimisation problems which are not convex in general. This motivated the authors to propose suboptimal solutions through using the so-called semidefinite relaxation method to translate original problems into semidefinite programming problems. Numerical results are provided, showing the superiority of the proposed methods as compared to the best known method.

To ensure that a modified software system has not regressed, one approach is to rerun existing test cases. However, this is a potentially costly task. To mitigate the costs, the testing effort can be optimized by executing only a selected subset of the test cases that are believed to have a better chance of revealing faults. This paper proposes a novel approach for selecting and ordering a predetermined number of test cases from an existing test suite. Our approach forms an Integer Linear Programming problem using two different coverage-based criteria, and uses constraint relaxation to find many close-to-optimal solution points. These points are then combined to obtain a final solution using a voting mechanism. The selected subset of test cases is then prioritized using a greedy algorithm that maximizes minimum coverage in an iterative manner. The proposed approach has been empirically evaluated and the results show significant improvements over existing approaches for some cases and comparable results for the rest. Moreover, our approach provides more consistency compared to existing approaches.

This paper aims at investigating the required feedback to achieve the Degrees of freedom (DoF) of X channel. Accordingly, a fixed precoding approach is proposed and is argued can achieve the DoF of such channel, assuming the channel state information is partially available at each transmitter through a feedback mechanism. This is achieved through using the notion of ergodic interference alignment technique. Accordingly, in a Rayleigh fading environment, it is shown a feedback rate of 2 log(p) + Θ(log log(p)) can achieve this DoF, where p is the total transmit power.

Density evolution (DE) is a technique for tracking the distribution of the log likelihood ratio (LLR) messages exchanged between the variable nodes and the check nodes in a bipartite graph. It is widely assumed that these distributions are close to Gaussian. However, in many scenarios, this assumption is not valid, for example, the case that the signal to noise ratio is low, or the degree of variable nodes exceeds a certain threshold. A new (suboptimal) method for DE algorithm in low-density parity-check codes is introduced. We provide a more accurate model for the distribution of message bits (as compared to Gaussian) through matching the first n statistical moments. An iterative message passing algorithm is proposed to compute these moments from the graphical representation of the underlying code. It shown that the proposed algorithm results in an improved estimate of the underlying EXIT chart as compared to using a Gaussian assumption. In this respect, the proposed method achieves a performance very close to that of the best earlier methods, while it offers a much lower complexity.