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This paper investigates an integrated wireless communication system including non-orthogonal multiple access, full-duplex relaying, and energy harvesting techniques (named as EH-FD-NOMA). In this scheme, an energy-limited full-duplex relay harvests energy from a source at the first stage. Then, the relay detects the superimposed signal from the source and transmits the decoded signal to destination. Closed-form outage probabilities and ergodic rates at the relay and destination are derived. Numerical results verify the analytical results and show the superior performance of the EH-FD-NOMA if compared to its counterparts. [ABSTRACT FROM AUTHOR]

To improve the secrecy performance of the untrusted relay system with a multiple-antenna destination, a novel full-duplex destination jamming scheme with optimal antenna selection (FDJ-OAS) is proposed in this paper. The approximate closed-form expressions of the average achievable secrecy rate are derived for the proposed scheme. To attain more insightful results, the approximated closed-form expressions for the average achievable secrecy rate and the optimal power allocation factor for FDJ-OAS are derived in the case with a large-scale antenna array, and simple power allocation solutions are also provided in the high and low SNR regimes, respectively. Furthermore, we derive the asymptotic expressions for the secrecy outage probability under different asymptotic conditions for the proposed scheme, and the analysis results indicate that the secrecy diversity order of FDJ-OAS is significantly superior to that of the comparable schemes. Simulation results show that the analytical curves match well with the simulation results, and the advantage of FDJ-OAS is also clearly demonstrated through performance comparison. [ABSTRACT FROM AUTHOR]

We design, for the first time, novel successive interference cancellation (SIC) schemes for a two-user nonorthogonal multiple access system using low-density parity-check codes. We first develop a low-complexity SIC scheme treating interference as noise, referred to as the N-SIC scheme, and a SIC with joint detection scheme treating the modulation of interference signal at the near user as side information, referred to as the J-SIC scheme. We then propose a new extrinsic information assisted SIC scheme, referred to as the E-SIC scheme, which exchanges the extrinsic decoding information of the signals for two users and thus incurs an increase complexity. With simulations, we demonstrate that the error performance advantage of the E-SIC scheme over the N-SIC and J-SIC schemes is more significant when the power allocated to the near user is larger, e.g., higher than 45%. When this power becomes smaller, e.g., less than 10%, the low-complexity N-SIC scheme can achieve the best error performance. In addition, we have an important finding that when the two users adopt different order modulation, the decoding convergence speed of the E-SIC scheme improves when the difference between the constellation sizes of two users is larger. [ABSTRACT FROM AUTHOR]

In this paper, an efficient transmission scheme, termed the joint antenna selection and data exchange (AS-DE) scheme, is proposed for a two-way amplify-and-forward relaying network, where two single-antenna source terminals exchange information via a multiantenna relay station. For the proposed scheme, the best antenna at the relay for each source terminal is first selected separately, following the max–max scheme. Then, from the set of the previously selected antennas, either one antenna is selected, in a similar fashion as well-known max–min and max–sum schemes, or two antennas exchange their respective received signals, which are then coded, amplified, and broadcasted to the source and destination terminals. Tight lower and upper bounds on the outage probability (OP) for the proposed scheme have been derived assuming independent and identically distributed Rayleigh fading channels. Furthermore, our analysis reveals that the proposed joint AS-DE scheme can achieve full diversity. Finally, it is shown that under the same resource constraints, i.e., in terms of the number of the utilized time slots and transmit power, the proposed joint AS-DE scheme outperforms the max–min, the max–sum, and the max–max schemes. Extensive numerical results accompanied with computer simulations, are further provided to validate the developed analytical results. [ABSTRACT FROM PUBLISHER]

This paper considers the performance analysis of sparse code multiple access (SCMA) with receive diversity arrays and randomly deployed users in a cellular uplink scenario. The impact of path loss on the performance of SCMA is characterized, by assuming independent Rayleigh fading and joint maximum likelihood (ML) receivers. A tight upper bound on the probability of symbol detection error is derived, and the achievable diversity and coding gains are investigated. The analytical results are validated by using simulations, and show that a diversity order which is equal to the product of the number of receive antennas and the signal-space diversity can be achieved, and the large-scale path-loss decreases only the coding gain. [ABSTRACT FROM AUTHOR]

Interrelay interference (IRI) is known to degrade the performance of virtual full-duplex (FD) relaying schemes. Although interference avoidance and cancelation strategies have been proposed in the existing literature, most studies reflect the traditional information theoretical viewpoint of interference as a degrading factor on information decoding (ID). However, from energy harvesting (EH) perspective, the IRI could be beneficial. This motivates the study of simultaneous wireless information and power transfer in decode-and-forward multiple input multiple output virtual FD relaying system, where the IRI serves as an additional source of energy to the relay. To manage the degrading effect of the IRI on the ID receiver, transmit antenna selection is proposed at the relay. In addition, precoding matrices that optimize the ID and EH receivers are jointly designed. The simulated results show that although IRI could be a degrading factor from the information viewpoint, it can be properly managed and exploited for EH at the relay while maintaining the end-to-end data rate. In addition, the results show that the end-to-end information rate and harvested energy can be simultaneously achieved using the proposed precoders. [ABSTRACT FROM AUTHOR]

In this paper, we consider a cooperative simultaneous wireless information and power transfer (SWIPT) network with one source–destination pair and multiple energy harvesting relays. How to efficiently use these relays has been addressed in conventional cooperative networks, and this paper investigates the impact of SWIPT on the performance of such multirelay cooperative networks. In particular, the main contribution of this paper is that a closed-form expression of the outage probability achieved by the multirelay cooperative protocol is obtained, as well as its approximation at high SNR. In addition, the performance of the cooperative network with the SWIPT relays is compared with that in conventional systems with self-powered relays. [ABSTRACT FROM PUBLISHER]

This paper investigates the buffer-aided relay selection problem for a decode-and-forward cooperative wireless network with K relays. We propose a new relay selection scheme that incorporates the status of the relay buffers and the instantaneous strength of the wireless links. Specifically, each link is assigned with a weight related to the buffer status; then, the best relay is selected with the largest weight among all the qualified source–relay and relay–destination links. We derive the closed-form expression for the outage probability and the diversity gain by introducing several Markov chains (MCs) to model the evolution of the buffer status. The analysis shows that the proposed scheme can achieve the optimal diversity gain \mbox{2}K for a small L (i.e., L\ge \mbox3), an improvement in comparison with the existing max-link scheme that achieves the optimal diversity gain only when L is sufficiently large, where $L$ denotes the buffer size of each relay. The provided theoretical and numerical results confirm the performance gain of the proposed relay selection scheme over the existing max-link scheme. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate physical-layer security in a random wireless network where both legitimate and eavesdropping nodes are randomly deployed. In the first scenario, we study the basic random network without a protected zone around the source node. The probability density functions (pdfs) for the composite channel gain with both fading and path loss is derived and used to calculate the probability of secure connection and ergodic secrecy capacity. In the second scenario, we consider the use of secrecy protected zone around the source node to enhance the security in a noise-limited network. Here, we study the following two cases: 1) The eavesdroppers are aware of the secrecy protected zone, and 2) the eavesdroppers are unaware of the secrecy protected zone. Moreover, the distribution of the distances between the origin and random nodes outside the secrecy protected zone is derived. In the final scenario, the interferer protected zones around the legitimate receivers are used to improve the physical-layer security by restructuring the interference. The derived analytical results are verified by the Monte Carlo simulations. It is shown that the application of secrecy and interferer protected zones lead to significant improvement in security, depending on different system parameters. [ABSTRACT FROM AUTHOR]

In this paper, we study different secrecy rate optimization techniques for a multiple-input–multiple-output (MIMO) secrecy channel, where a multiantenna cooperative jammer is employed to improve secret communication in the presence of a multiantenna eavesdropper. Specifically, we consider two optimization problems, namely, power minimization and secrecy rate maximization. These problems are not jointly convex in terms of the transmit covariance matrices of the legitimate transmitter and the cooperative jammer. To circumvent these nonconvexity issues, we alternatively design the transmit covariance matrix of the legitimate transmitter and the cooperative jammer. For a given transmit covariance matrix at the cooperative jammer, we solve the power minimization and secrecy rate maximization problems based on a Taylor series expansion. Then, we propose two iterative algorithms to solve these approximated problems. In addition, we develop a robust scheme by incorporating channel uncertainties associated with the eavesdropper. By exploiting S-Procedure, we show that these robust optimization problems can be formulated into semidefinite programming. Moreover, we consider the secrecy rate maximization problem based on game theory, where the jammer introduces charges for its jamming service based on the amount of the interference caused to the eavesdropper. This secrecy rate maximization problem is formulated into a Stackelberg game where the jammer and the transmitter are the leader and the follower of the game, respectively. For the proposed game, Stackelberg equilibrium is analytically derived. Simulation results have been provided to validate the convergence and performance of the proposed algorithms. In addition, it is shown that the proposed robust scheme outperforms the nonrobust scheme in terms of the achieved secrecy rate and the worst-case secrecy rate. Finally, the Stackelberg equilibrium solution has been validated through numerical results. [ABSTRACT FROM PUBLISHER]

In this paper, a cognitive-radio-inspired asymmetric network coding (CR-AsNC) scheme is proposed for multiple-input–multiple-output (MIMO) cellular transmissions, where information exchange among users and base-station (BS) broadcasting can be accomplished simultaneously. The key idea is to apply the concept of cognitive radio (CR) in network coding transmissions, where the BS tries sending new information while helping users' transmissions as a relay. In particular, we design an asymmetric network coding method for information exchange between the BS and the users, although many existing works consider the design of network coding in symmetric scenarios. To approach the optimal performance, an iterative precoding design for CR-AsNC is first developed. Then, a channel-diagonalization-based precoding design with low complexity is proposed, to which power allocation can be optimized with a closed-form solution. The simulation results show that the proposed CR-AsNC scheme with precoding optimization can significantly improve system transmission performance. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a denoise-and-forward network coding (DNF-NC) transmission scheme for its applications in two-way relay multiple-input and multiple-output (MIMO) systems. We first consider a scenario with a single pair of source nodes, and minimum mean square error (MMSE) receiver is applied at each node. The global optimal precoding design based on the mean square error (MSE) criterion can be achieved by solving two independent convex optimization problems. To achieve a better tradeoff between performance and complexity, an alternative power optimization approach is proposed using a channel diagonalization technique. Then, we proceed to considering a more challenging bidirectional communication scenario with multiple pairs of source nodes. With intrapair coordination at the sources, we modify DNF-NC by employing a signal alignment technique to combat interpair interference. The numerical results demonstrate that the proposed DNF-NC schemes can significantly improve bit error rate (BER) performance in both two scenarios, and such performance gains can be achieved with relatively low computational complexity. [ABSTRACT FROM PUBLISHER]

In this paper, we study how to improve wireless security for bidirectional communications. For the scenario with single-antenna nodes, effective criteria for relay and jamming node selection are developed to ensure that the probability to have nonzero secrecy rates is approaching one, given sufficient relays. For the scenario with multiple-antenna nodes, effective precoding is proposed to ensure that the mutual information obtained at the eavesdropper decreases to zero when there is a sufficient number of relays. [ABSTRACT FROM PUBLISHER]

In this paper, we first study the design of network coding for the generalized multiple-input–multiple-output (MIMO) Y channels, where K users wish to exchange information with each other within two time slots. Precoding at each user and the relay is carefully constructed to ensure that the signals from the same user pair are grouped together and that cross-pair interference can be canceled. In addition, a simple mapping function is proposed to ensure low-complexity detection at the relay. Exact expressions of symbol error rate (SER) are then developed to establish the explicit relationship between the diversity gain and the number of node antennas. Monte Carlo simulation is also provided to demonstrate the performance of the proposed scheme. [ABSTRACT FROM PUBLISHER]

In multiple-input–single-output (MISO) broadcast channels, the achievable diversity gain is limited by the number of source transmitter antennas. Cooperative transmission is able to provide another dimension of diversity gain improvement. In this paper, we introduce a spectrally efficient cooperative transmission protocol in MISO broadcast channels using linear precoding and nonorthogonal relaying. The proposed protocol can achieve maximum diversity gain expressed as the sum of the number of source transmitter antennas and the number of available relays. The diversity and multiplexing tradeoff of the proposed protocol outperforms the noncooperative scheme, even when only a single relay is used. For a large number of relay candidates, the diversity and multiplexing tradeoff of the proposed protocol completely surpasses the existing noncooperative scheme. [ABSTRACT FROM PUBLISHER]

Cooperative diversity has been recognized as an effective and low-cost technique to combat multipath fading and enhance transmission reliability. Motivated by the fact that many existing cooperative protocols suffer some loss of ergodic capacity, network coding, which is a technique that is well known for its capability to increase system throughput, is proposed in this paper to be combined with cooperative diversity for uplink transmissions. Two kinds of information-theoretic metrics, i.e., outage and ergodic capacities, are developed for the proposed transmission scheme to assist with performance evaluation. The developed analytic results, which are shown to fit well with Monte Carlo simulation, demonstrate that the proposed protocol can achieve better system robustness and larger system throughput simultaneously than comparable schemes. The application of the proposed transmission protocol to scheduling is also studied to achieve better fairness–throughput tradeoff. [ABSTRACT FROM PUBLISHER]

Existing work has shown that random coding across multicast sessions can significantly reduce system delay. However, such a scheme requires the strong assumption that each source has priori information of other sources' messages. The broadcasting nature of radio propagation can provide an opportunity to realize collaboration across sessions without causing much system overhead. In this paper, we propose the application of network coding to multisource-multidestination (MSMD) scenarios and provide formal analysis for the improvement of system delay. In particular, two types of analytical results have been developed, with one based on the outage probability and the other based on the use of practical convolutional codes. Monte Carlo simulation results have also been provided to demonstrate the delay performance of the proposed network-coded protocol. [ABSTRACT FROM AUTHOR]

Orthogonal space-time block coding (OSTBC) in multiple-antenna wireless systems has recently emerged as one of the most promising reliability-enhancing technologies for high-speed, high-quality data services. In this paper, we propose a technique to achieve joint channel estimation and symbol detection for OSTBC in frequency-selective fading channels. The key observation is that a multiple-input-single-output system, which is using OSTBC, can be transformed into an equivalent single-input-multiple-output system using the implicit redundancy in OSTBC. This allows a probabilistic method, known as the Baum-Welch algorithm, to be applied at each output branch. As each output branch is a function of the same input, redundant information may be exchanged between the multiple branches to improve detection performance. The proposed technique does not require multiple antennas at the receiver and only has moderate computational complexity. Furthermore, the Cramer-Rao lower bound (CRB) is also developed to facilitate performance analysis. Simulation results are provided to demonstrate the performance of the proposed algorithm. [ABSTRACT FROM AUTHOR]