Full-duplex Relay Networks Research Articles

Dual-hop full duplex relay networks over composite fading channels: Power and location optimization

This paper investigates schemes for improving the outage performance of dual-hop full duplex (FD) and half duplex (HD) decode and forward (DF) based relay networks over composite Nakagami-m/log-normal fading channels. First of all, we derive new analytical expression for the outage probability of dual-hop FDR network considering the effects of interference caused by direct link from source-to-destination and the residual self-interference (RSI) at the full duplex relay (FDR). We also provide the asymptotic outage probability expression. We then investigate optimal power allocation (OPA); optimal relay location (ORL) and joint optimization of transmit power and relay location that minimizes the outage probability. We show that the first two problems are convex and devise modified Polak–Ribiere Conjugate Gradient Method to determine the OPA and ORL. Since the joint optimization problem is non convex, we devise an efficient, low complex and fast converging iterative algorithm based on alternating optimization technique. We repeat the investigations for dual-hop HDR networks as well assuming composite fading model. The results demonstrate that both OPA and ORL can improve the outage probability; however joint optimization leads to superior performance as compared to OPA, ORL and un-optimized cases.

Performance of Transceiver Antenna Selection in Two Way Full-Duplex Relay Networks Over Rayleigh Fading Channels

A novel transceiver antenna selection (TRAS) strategy selecting a pair of antennas for transmission and reception at terminal sources for full-duplex amplify-forward multi-input multi-output two way relay networks is proposed. Antenna pair is selected in accordance with maximum and second maximum signal to self-interference-plus-noise ratio between the sources and relay, where the terminal sources and relay are full-duplex. Unlike reciprocal channel gains, forward and backward paths between the sources and relay are taken to be different. With four different antenna selection (AS) scenarios, the exact sum outage probability (SOP) for fading self-interference (SI) and the exact, approximated, and asymptotic SOP expressions for nonfading SI over Rayleigh fading channels are derived and validated via Monte Carlo simulation technique. The proposed AS strategy uses all antenna space for either transmission or reception which results in a reduction in total number of antennas at each terminal node. It is shown that performance can be significantly improved by usage of offered TRAS strategy at terminal sources. For example, up to 25 dB gain is obtained for five antennas at the sources with respect to no selection case of two antennas. In addition, it outperforms the selection strategy using maximum paths from two divided antenna sets at each source, where one set is only used for transmission and the other one for reception. The diversity order of the system is proven to be dependent on SI and varies between zero and minimum of the total number of antennas of two sources minus 1. For different SI values, optimum power allocations are demonstrated and factors affecting optimum relay location are also elaborated. Each AS scenario produces the lowest SOP for different combinations of SI occurrences, power allocations, and relay locations.

Joint relay-user selection in energy harvesting relay network with direct link

In this paper, a joint relay-user selection (JRUS) scheme is proposed for an amplify-and-forward full-duplex (FD) relay network which includes one source node, multi-relay node and multi-user node, and the direct link between the source node and the user node is considered to convey information. Each FD relay node is energy-constrained and the simultaneous wireless information and power transfer technology is employed to harvest energy. A power splitter at each FD relay node splits the received signals into two components for energy harvesting and information processing. The implementation of the proposed JRUS scheme includes two steps: (1) the optimal user node is selected according to signal-to-noise ratio of the direct link between the source node and the user nodes; (2) the optimal energy harvesting relay node with optimal power splitting (PS) factor is picked out based on signal-to-interference-plus-noise ratio of the relaying link. The outage probability of the investigated relay network with the JRUS scheme is derived. In order to characterize the diversity order, we further present the asymptotic outage probability at high SNR. Moreover, the optimal PS factor of each relay node is calculated by minimizing the outage probability of the reconstructed relay network. Finally, numerical results demonstrate the accuracy of our performance analysis and the efficiency of the proposed scheme.

Power allocation under global and individual power constraints for full‐duplex relay networks

In this study, the authors propose a power allocation strategy for full-duplex relay (FDR) networks, where two cases are considered according to whether the direct link is desired or not. The power allocation is studied in two scenes under the amplify-and-forward and decode-and-forward protocols, respectively. Aiming at maximising the system capacity, the authors derive the optimal power allocation strategy under the condition that the source and relay have the same maximum power constraint and the total power is limited. The effects of global and individual power constraints for FDR on system capacity are analysed. Simulations verify the theoretical analysis and indicate that the proposed power allocation strategy enhances the system performance greatly compared with uniform power allocation.

Multipair Two-Way Full-Duplex Relaying With Massive Array and Power Allocation

We consider a multipair two-way full-duplex relay network, where multiple pairs of full-duplex users can exchange information through a common relay station with a single massive array. Each user has one shared-antenna and the relay station has $M$ shared-antennas. The relay adopts amplify-and-forward protocol, and the beamforming is performed using maximal-ratio combining/transmission or zero-forcing reception/transmission method. When the number of relay antennas grows to infinity or large enough, we derive the asymptotic transmit power of relay and the asymptotic/approximate spectral efficiency with/without power-scaling. The users’ transmit powers are optimally allocated to maximize the spectral efficiency under the users’ total transmit power constraint. Simulations verify our asymptotic and approximate results with large-scale antenna array, and demonstrate the spectral and energy efficiency with optimal power allocation.

Relay selection in two-way full-duplex relay networks over Nakagami-m fading channels

We analyze the outage performance of relay selection in two-way full-duplex amplify-and-forward cooperative systems in the presence of residual loop-interference (LI) over Nakagami-m fading channels. In the proposed system, a relay node is selected according to max-min policy and the physical-layer-network-coding technique is applied for two-way transmission. By using end-to-end signal-to-interference-plus-noise-ratio, a new exact outage probability expression is derived in a single-integral form. The numerical and Monte-Carlo simulation results verify the analysis. Moreover, lower-bound and asymptotic expressions for the outage probability are obtained in closed-form. The numerical results reveal that the max-min selection policy provides a significant performance improvement for two-way full-duplex relaying. We observe that the outage performance can be enhanced as long as either the number of relay nodes, the transmit power, or the efficiency of the LI cancellation process increases.

Performance Analysis with Wireless Power Transfer Constraint Policies in Full-Duplex Relaying Networks

In practice, full-duplex (FD) transmission mode not only helps extend the coverage but also lengthen network lifetime. In this paper, we develop wireless power supply policies, namely separated power (SP) and harvested power (HP) to propose a flexible architecture at the relay node in FD decode-and-forward (DF) relaying networks considering time switching-based relaying protocol (TSR) to achieve optimal time used for a communication process. This transmission mode requires more processing procedure at the relay, i.e. antenna installations and radio frequency (RF) self-interference cancellation. We evaluate the optimal power constraints in case of SP and HP to achieve better power consumption efficiency at the relay node. More importantly, closed-form expressions for outage probability and throughput are provided, and we also use numerical and simulation results to compare SP with HP.DOI: http://dx.doi.org/10.5755/j01.eie.23.4.18725

SC-FDE Based Full-Duplex Relay Communication Robust to Residual Loop Interference

In this letter, we consider a full-duplex (FD) relay communication network on flat fading Rayleigh channels, where the relay is allowed to receive and transmit at the same time and over the same frequency band. Based on single carrier frequency domain equalization, we propose an amplify-and-forward protocol FD relaying scheme, which is robust to the residual loop interference. In this scheme, the relay only needs to amplify and forward the received signal by controlling the amplifying factor and as a result the processing at the relay is simple. The amplifying factor is optimized in terms of system parameters such as the length of cyclic prefix, noise power, and estimated channel state information. Simulation results are presented to evaluate the performance of the proposed scheme and verify the theoretical analysis.

Capacity-Enhancing Full-Duplex Relay Networks based on Power-Splitting (PS-)SWIPT

In this paper, we investigate the application of simultaneous wireless information and power transfer (SWIPT) in a full-duplex relay network, where the relay node is wirelessly powered by harvesting a portion of the received signal power from the source node. Different from existing work that has employed time-switching-SWIPT, we propose to use power-splitting-SWIPT. As a result, our proposed approach gives rise to a truly full-duplex relay network, where the information reception and transmission take place simultaneously at the relay node all the time. This more thorough exploitation of the full-duplex feature consequently leads to a significant capacity improvement, compared with existing alternatives in the literature.

On the Performance of Spatial Modulation MIMO for Full-Duplex Relay Networks

In this paper, we investigate, for the first time, the performance of a full-duplex (FD) relaying protocol, where a single-RF spatial modulation (SM) multiple-input multiple-output (MIMO) system is employed at the relay node. We refer to this protocol as SM-aided FD relaying (SM-FDR). At the destination, a demodulator that takes advantage of the direct connectivity between the source and destination is developed in order to maximize its performance. Based on this demodulator, we introduce a mathematical framework for computing the average error-probability of SM-FDR in the presence of residual self-interference (SI). Furthermore, we derive mathematical expressions for computing the achievable rate of SM-FDR. With the aid of these achievable rate expressions, we provide an estimate on the quality of SI cancellation required for the suitability of FD transmission. In addition, we develop and evaluate three relay selection policies specifically designed for the SM-FDR protocol. The mathematical analysis is substantiated with the aid of extensive Monte Carlo simulations. Finally, we also assess the performance of SM-FDR against traditional FD relaying protocols.

Performance of Joint Relay and Antenna Selection in the Full-Duplex Amplify-and-Forward Relay Networks

This paper focuses on the joint relay and antenna selection problem in dual hop full-duplex (FD) relay network with one source, one destination and N FD amplify-and-forward relays in flat Rayleigh ...

QoS-Constrained Relay Control for Full-Duplex Relaying With SWIPT

This study investigates relay control for simultaneous wireless information and power transfer in full-duplex relay networks under Nakagami- $m$ fading channels. Unlike previous work, harvest-transmit (HT) and general harvest-transmit-store (HTS) models are respectively considered to maximize average throughput subject to quality of service (QoS) constraints. The end-to-end outage probability of the network in an HT model is presented in an exact integral-form. To prevent outage performance degradation in an HT model, time switching (TS) is designed to maximize average throughput subject to QoS constraints of minimizing outage probability and maintaining a target outage probability, respectively. The optimal TS factors subject to QoS constraints are presented for an HT model. In general, in an HTS model, energy scheduling is performed across different transmission blocks and TS is performed within each block. Compared with the block-based HTS model without TS, the proposed general HTS model can greatly improve outage performance via greedy search (GS). By modeling the relay’s energy levels as a Markov chain with a two-stage state transition, the outage probability for the GS implementation of the general HTS model is derived. To demonstrate the practical significance of QoS-constrained relay control, numerical results are presented showing that the proposed relay control achieves substantial improvement of outage performance and successful rate.

An Optimal Analysis in Wireless Powered Full-duplex Relaying Network

An Optimal Analysis in Wireless Powered Full-duplex Relaying Network

A novel forwarding method for full-duplex two-way relay networks

An estimate-and-forward (EF) scheme for single-input single-output (SISO) and multiple-input multiple-output (MIMO) full-duplex two-way relay networks is proposed and analyzed. The relay estimates the received signal from two terminal nodes by a minimum mean squared error (MMSE) estimation and forwards a scaled version of the MMSE estimate to the destination. The proposed EF outperforms conventional amplify- and-forward (AF) and decode-and-forward (DF) across all signal-to-noise ratio (SNR) region. Because its computational complexity is high for relays with a large number of antennas (large MIMO) and/or high order constellations, an approximate EF scheme, called list EF, are thus proposed to reduce the computational complexity. The proposed list EF computes a candidate list for the MMSE estimate by using a sphere decoder, and it approaches the performance of the exact EF relay at a negligible performance loss. The proposed forwarding approach also could be used to other relay networks, such as half-duplex, one-way or massive MIMO relay networks.

Joint optimization of spectral and energy efficiency for multi-pair full-duplex two-way relay networks with imperfect channel state information

An iterative algorithm is proposed for jointly optimizing spectral and energy efficiency in a multipair full-duplex (FD) two-way relaying (TWR) system with imperfect channel state information (CSI). Based on Dinkelbach method, a Taylor expansion based approximation method and the Generalized Lagrange Multiplier Method have been applied iteratively to obtain the near optimal relay amplified matrix and power allocation, respectively. And the simulation results illustrate the effectiveness of the proposed algorithm and the algorithm can converge quickly.

QoS-Driven Energy-Efficient Resource Allocation in Multiuser Amplify-and-Forward Relay Networks

In this paper, we investigate energy-efficient joint subcarrier pairing, subcarrier allocation, and power allocation algorithms for improving the network energy efficiency (EE) in multiuser amplify-and-forward (AF) relay networks while ensuring the desired quality-of-service (QoS) requirement for the users through the concept of “network price.” Further, we introduce a network price paid for the consumed power as a penalty for the achievable sum rate and formulate a resource allocation problem subject to limited transmit power budget and QoS constraints. The formulated problem is a nonconvex binary mixed-integer nonlinear programming (MINLP) problem and it is hard to solve the problem. We then apply a concave lower bound on the pricing-based network utility to transform the problem into a convex one. The dual decomposition method is adopted to propose a $\pounds $ -price resource allocation algorithm to find the near-optimal solution. Next, we discuss the optimal utility-price from an EE perspective. Moreover, we rigorously analyze the behavior of the network pricing-based resource allocation in two-user case under different noise operating regimes, and discuss the corresponding strategies for achieving energy-efficient transmission, generating water-filling and channel-reversal approaches. To strike a balance between the computational complexity and the optimality, we propose a low-complexity suboptimal algorithm. Furthermore, we extend the proposed algorithm to maximize the EE of multiuser multirelay full-duplex (FD) relay networks and the relay networks with an eavesdropper. The performance gain of the proposed algorithms is validated through computer simulations.

Power-Efficient Distributed Beamforming for Full-Duplex MIMO Relaying Networks

Multiple-input–multiple-output (MIMO) full-duplex relaying (FDR) has been considered an efficient technique to provide coverage to users where their direct links from the base station (BS) are too weak for reliable signal reception. However, when multiple MIMO full-duplex relays are deployed in a network, the signal reception quality relies on the effective suppression of multiple types of interference. In this paper, the distributed beamforming is studied for the MIMO FDR network by formulating a power minimization problem with a nonstrict convex objective function (total transmit power of both the BS and all the relays in the network) under individual user rate constraints. We come up with two iterative distributed beamforming algorithms, Algorithm 1 for relays equipped with single receive antenna and Algorithm 2 with multiple receive antennas. The former can yield a global optimal solution of the power minimization problem, whereas the latter can yield only a local optimal solution due to conservative successive convex approximations (SCAs) performed at each iteration, and a rigorous analysis on the upper bounds of step sizes is proposed to guarantee their convergence. The proposed two algorithms only require local information exchange between relays and hence are scalable for different network sizes and topologies. An “early termination” strategy in the operation of the proposed two algorithms is also presented to acquire an acceptable transmit power solution with less computation time consumption and thus suitable for realistic applications. Finally, some simulation results are provided to demonstrate that the proposed two algorithms perform well and significantly better than the existing state-of-the-art scheme reported in the work of Lee and Shin.

Cognitive full-duplex relay networks under the peak interference power constraint of multiple primary users

This paper investigates the outage performance of cognitive spectrum-sharing multi-relay networks in which the relays operate in a full-duplex (FD) mode and employ the decode-and-forward (DF) protocol. Two relay selection schemes, i.e., partial relay selection (PRS) and optimal relay selection (ORS), are considered to enhance the system performance. New exact expressions for the outage probability (OP) in both schemes are derived based on which an asymptotic analysis is carried out. The results show that the ORS strategy outperforms PRS in terms of OP, and increasing the number of FD relays can significantly improve the system performance. Moreover, novel analytical results provide additional insights for system design. In particular, from the viewpoint of FD concept, the primary network parameters (i.e., peak interference at the primary receivers, number of primary receivers, and their locations) should be carefully considered since they significantly affect the secondary network performance.

Pilot Optimization and Power Allocation for OFDM-Based Full-Duplex Relay Networks With IQ-Imbalances

In OFDM relay networks with IQ imbalances and full-duplex relay station (RS), how to optimize pilot pattern and power allocation using the criterion of minimizing the sum of mean square errors (Sum-MSE) for the frequency-domain least-squares channel estimator has a heavy impact on self-interference cancellation. Firstly, the design problem of pilot pattern is casted as a convex optimization. From the KKT conditions, the optimal analytical expression is derived given the fixed source power and RS power. Subsequently, an optimal power allocation (OPA) strategy is proposed and presented to further alleviate the effect of Sum-MSE under the total transmit power sum constraint of source node and RS. Simulation results show that the proposed OPA performs better than equal power allocation (EPA) in terms of Sum-MSE, and the Sum-MSE performance gain grows with deviating $\rho$ from the value of $\rho^o$ minimizing the Sum-MSE, where $\rho$ is defined as the average ratio of the residual SI channel at RS to the intended channel from source to RS. For example, the OPA achieves about 5dB SNR gain over EPA by shrinking or stretching $\rho$ with a factor $4$. More importantly, as $\rho$ decreases or increases more, the performance gain becomes more significant.

Buffer-Aided Relaying Improves Throughput of Full-Duplex Relay Networks With Fixed-Rate Transmissions

The concept of buffer-aided relaying has recently emerged as a viable solution for improving the performance of wireless networks with half-duplex relays. In this letter, we show that buffer-aided relaying is also beneficial to wireless networks with ideal full-duplex (FD) relays. To this end, we investigate the two-hop FD relay network, which is comprised of a source, an FD relay equipped with a buffer, and a destination where a direct source–destination link does not exist. For this network, we assume that the source and the relay select their transmission rates from discrete sets of available transmission rates, and propose a corresponding buffer-aided relaying scheme, which maximizes the throughput. Our numerical results show that the proposed buffer-aided relaying scheme provides the significant throughput gains compared with conventional FD relaying schemes, which do not employ buffers at the relays.