Full-Duplex Two-Way Relay Research Articles

Energy-efficient two-way full-duplex relay transmission strategy with SWIPT and direct links

In this paper, we improve networks’ spectral efficiency (SE), extend networks’ lifetime, and maximize networks’ energy efficiency (EE) of two-way full-duplex (FD) relay networks. Firstly, to improve networks’ SE and to extend networks’ lifetime simultaneously, we design a two-way FD relay transmission strategy with simultaneous wireless information and power transfer and direct links (DLs). The designed transmission strategy can complete a bidirectional communication in only one time slot with the exists of DLs and the energy-constrained relay node. With the designed transmission strategy, we further give the characteristics of relay amplification factor, the analysis of the designed transmission strategy, and the EE analysis of traditional half-duplex two-way amplify-and-forward relaying. Secondly, to maximize networks’ EE, we present both the EE maximization problems and analyses of the designed transmission strategy with equal power allocation and optimal power allocation. To solve the EE maximization problems, we further propose the alternating optimal algorithm and give complexity analysis of the algorithm. Simulations show that our designed transmission strategy can improve the SE and EE of the networks.

System Outage Performance of SWIPT Enabled Full-Duplex Two-Way Relaying With Residual Hardware Impairments and Self-Interference

This article investigates the joint impact of residual hardware impairments (RHIs) and residual self-interference (RSI) at all transceivers on the system outage performance for a simultaneous wireless information and power transfer (SWIPT) enabled full-duplex two-way decode-and-forward (DF) relay network. Considering a time switching scheme at the relay node, we derive the system outage probability in a closed-form, and further identify the overall system ceiling (OSC) effect caused by only RHIs. More specifically, when the data rate exceeds the OSC threshold determined by the RHIs level, the communication of the entire network ceases no matter what the signal-to-noise ratio is. In addition, we derive the achievable diversity gain of the considered network, and demonstrate that the diversity gain always equals zero due to the existence of RHIs and RSI. Finally, numerical simulations are provided to study the influence of multifarious network parameters on the system outage performance and the performance gap between the DF and amplify-and-forward strategies.

Throughput Maximization for the Full-Duplex Two-Way Relay System with Energy Harvesting

The full-duplex technique can improve the transmission capacity of the communication systems, and energy harvesting (EH) is a promising operation to prolong the lifespan of a wireless node by utilizing the radio-frequency signals. In this paper, the throughput performance of a full-duplex two-way energy EH capable relay system is investigated. In particular, a practical EH protocol, named the time-switching-based relaying (TSR) protocol, is used for EH and the decode-and-forward (DF) policy for information transmission. The outage probability is successfully obtained, and the corresponding system throughput for TSR protocol can be derived by it. The derived throughput is a function of different system parameters, including the time-switching (TS) ratio, power allocation ratio, and the length of the communication time slot. Meanwhile, the throughput is used to characterize a joint time and power allocation scheme for the system, and we aim to find the optimal time and power allocation to achieve the optimal throughput. Due to the existence of three variables and the integral form of throughput expression, an optimization for the throughput is difficult. However, a modified simulated annealing-based search (SABS) algorithm can be used to optimize the throughput. The modified SABS algorithm overcomes being highly impacted by the initial point, and derives the optimal solution fast. Simulation results show that the analytical throughput expression is related with the TS ratio, power allocation ratio, and the length of the communication time slot. The analytical curve of the throughput matches with the simulated one well, which shows that the obtained analytical system throughput for the TSR protocol is valid. Meanwhile, the proposed modified SABS algorithm could be used to derive accurate throughput when SNR is higher than 10 dB.

Generalized Spatial Modulation in Full-Duplex Two-Way Relay Channel

In this letter, we propose generalized spatial modulation (GSM) in full duplex system equipped with two way relay channel (FD-GSM-TWRC). We propose a couple of receiver algorithms, structured complex orthogonal matching pursuit (S-COMP) and structured ordered block OMP (S-OBOMP) by casting the observation model suitably to apply compressive sensing framework. We substantiate that FD-GSM-TWRC with the proposed receiver algorithms, offer an optimal trade-off among bit-error rate (BER) performance, throughput and complexity.

Combining Power Allocation and Superposition Coding for an Underlay Two-way Decode-and-forward Scheme

Combining Power Allocation and Superposition Coding for an Underlay Two-way Decode-and-forward Scheme

Performance Analysis of Two-Way Full-Duplex Relay Mixed RF/FSO System With Self-Interference

In this letter, a two-way full-duplex (FD) relay mixed radio frequency/free space optical (RF/FSO) system corrupted by self-interference is proposed and investigated. The RF/FSO channels employ Nakagami-m distribution and pointing errors combined Gamma-Gamma turbulence model, respectively. Relay selection strategies based on channel state information (CSI) are applied. Considering the effect of self-interference, the exact outage probability (OP) and upper bound achievable sum-rate (ASR) are presented and evaluated. To make the research more comprehensive, the analysis further covers the effect of residual self-interference on the considered system as well as compares the performance difference of FD relay and half-duplex (HD) relay. To get more insight, asymptotic OP is further presented.

Throughput Maximization for full-duplex two-way relay with finite buffers

<div>Optimal queueing control of multi-hop networks remains a challenging problem, e</div><div>specially in two-way relaying systems, even in the most straightforward scenarios.</div><div>In this paper, we explore two-way relaying having a full-duplex decode-and-forward</div><div>relay with two fifinite buffers. Principally, we propose a novel concept based on the</div><div>multi-agent reinforcement learning (that maximizes the cumulative network through</div><div>put) based on the combination of the buffer states and the lossy links; a decision is</div><div>generated as to whether it can transmit, receive or even simultaneously receive and</div><div>transmit information. Towards this objective, chieflfly, based on the queue state transi</div><div>tion and the lossy links, an analytic Markov decision process is proposed to analyze</div><div>this scheme, and the throughput and queueing delay are derived. Our numerical results</div><div>reveal exciting insights. First, artifificial intelligence based on reinforcement learning</div><div>is optimal when the length of the buffer is superior to a certain threshold. Second, we</div><div>demonstrate that reinforcement learning can boost transmission effificiency and prevent</div><div>buffer overflflow.</div>

Throughput maximization for full-duplex two-way relay with finite buffers

Throughput maximization for full-duplex two-way relay with finite buffers

Large-System Analysis of AF Full-Duplex Massive MIMO Two-Way MRC/MRT Relaying

The massive multiple-input multiple-output (MIMO) full-duplex two-way relaying (FD-TWR) literature has extensively investigated power scaling for rate guarantees by considering a fixed number of users. We investigate the pairwise error probability (PEP) and the per-user rate of a FD-TWR with $N_{r}$ relay antennas that employs maximal ratio combining/transmission to enable two-way communication between $K$ FD users. We propose novel relay and user powers scalings, with both $N_{r}$ and $K$ tending to infinity, and show that the PEP of each user converges almost surely to its AWGN counterpart. These power scalings are different from the existing ones, which are derived by fixing $K$ and by assuming that only $N_{r}$ tends to large values. We show that the analysis developed herein applies to both Gaussian and non-Gaussian complex channels with finite number of moments. We numerically show that when both $K$ and $N_{r}$ increase concurrently to large values, the proposed power scaling schemes not only have better per-user PEP and rate than the existing schemes, but they are also robust to the FD self loop-interference power.

Design and Optimization for Energy-Efficient Full-Duplex Transmission With Direct Links

Full-duplex (FD) technique has been extensively studied recently, due to its effective improvement in spectral efficiency (SE) and significant advance on self-interference cancellation (SIC). Relay technique can expand network coverage, reduce power consumption and improve energy efficiency (EE) under bad direct links situation. Combining the FD technique with the relay technique can further improve the system’s SE and EE. In this paper, both bidirectional direct and relay FD transmission strategies for transmitting the signal as much as possible with fewer antennas and less self-interference are designed first. At the same time, the SE analysis of the designed transmission strategies under the existence of residual self-interference (RSI) is given. In addition, minimum total energy consumption (TEC) problems and their solutions of the designed transmission strategies with joint optimization of transmit power (TP) and transmit time (TT) are given. The minimum TEC problems consider non-ideal power amplifiers (PAs) efficiency and non-negligible circuit powers (CPs) consumption. Furthermore, a simple EE analysis of the designed transmission strategies with symmetric and asymmetric transmission tasks in two directions is given. Simulations reveal that when RSI coefficients are below 0.2, our two-way FD relay transmission (TWFDT) strategy can improve the system’s SE and EE.

Semi-Blind Data Detection and Non-Linear Equalization in Full-Duplex TWR-OFDM Systems With High Mobility

Full-duplex two-way relay (FD-TWR) system has potential to increase the spectral efficiency in the future 5G wireless system. Full-duplex transceiver suffers from inevitable self-interference (SI) which can be alleviated by active self-interference cancellation (SIC) method. However, the mitigation capability of SIC mechanism is limited specifically due to inherent non-linearities of transmitter and receiver front end. As a consequence, residual self-interference (RSI) will degrade the system’s signal-to-noise ratio (SNR) and throughput. Non-linearity in RF power amplifier in collusion with time-variant channel results is a great challenge in efficient signal detection and successful SI suppression. In contrast to classical schemes, which consider non-linear distortion at the transmitter, we present a semi-blind data detection and non-linear channel estimation in the presence of RSI at the receiver. Attributed to non-linearity, the target posterior probability density function is mathematically intractable. In this paper, a sequential importance sampling based particle filtering is used for joint data detection and estimation. Intractable distribution is approximated by using weighted random measures. A Taylor’s series expansion is used to locally linearize the non-analytic form of distribution. Numerical results validate the joint detection and channel estimation scheme. The robustness of the scheme is verified in presence of RSI under high mobility.

Feasibility and Optimization of 1-TTI-Based Full-Duplex Two-Way Relay System

Maximizing system capacity is one of the major concerns in inband full-duplex (IFD) two-way relay (TWR) system using analog network coding (ANC). This paper compares 1-transmission-time-interval (TTI)-based ANC (1TA) TWR, in which each node operates in IFD mode, with 2-TTI-based ANC (2TA) TWR operating in inband half-duplex mode. System capacity of the 1TA TWR is derived with adverse factor such as direct link interference (DLI). Also, this work proposes an iterative optimal power allocation (OPA) method to maximize the system capacity, which is based on golden section search under total power constraint. Numerical results elucidate that the 1TA TWR based on the OPA outperforms the 2TA TWR in all cases of relay position and DLI.

Relay selection based on energy harvesting in two-way full-duplex relay networks

In this paper, the time switching (TS) relay protocol and the self-energy recycling (SER) relay protocol are integrated into a two-way full-duplex (FD) relay network. For the proposed TS FD relay protocol, the joint optimization of the TS factor and the relay selection (RS) problem is proposed, where the relay nodes switch between energy harvesting (EH) and FD information relaying in different phases. To remove the self-interference (SI) operation at the relay nodes, a novel FD transmission protocol suitable for the two-way relay system is proposed, in which the relay nodes can recycle the SI as part of energy. Then two relay selection schemes are proposed to improve the outage probability and the sum rate of the two-way relay networks. Besides, the proposed RS schemes and two FD relay protocols can improve the performance metrics and solve the power constraint of the relay node. Simulation results show that the proposed two RS schemes for two-way FD relay networks can improve the output performance than traditional schemes.

Performance Evaluation of In-Band Full-Duplex System Using One-Time-Slot Two-Way Relay

In-band full-duplex (IFD) two-way relay (TWR) system becomes one among the major concern for maximizing system capacity in wireless network, where one relay node and two source nodes using analog network coding (ANC) are deployed. This paper compares one-time-slot ANC (1TA) TWR, in which each node operates in IFD mode, with two-time-slot ANC (2TA) TWR, where each node is in in-band half-duplex mode. In addition, achievable sum rate of the 1TA-TWR is derived with adverse factors such as direct link interference as well as self-interference (SI), which is induced by IFD signaling. This paper proposes an iterative optimal power allocation (OPA) method to maximize the derived end-to-end sum rate, which is based on Lagrangian and Newton–Raphson algorithm under total power constraint. Numerical results elucidate the efficiency of the 1TA-TWR over the 2TA-TWR as the following: the 1TA-TWR based on the OPA becomes more and more viable than the 2TA-TWR based on existing OPA, as the relay node goes into the center of two source nodes, the link channel gain of mutual source nodes increases, and the SI channel gain approaches noise floor level.

Successive Two-Way Relaying for Full-Duplex Users With Generalized Self-Interference Mitigation

In this paper, we propose a novel successive two-way relaying (STWR) system that uses a pair of conventional half-duplex (HD) relays to mimic a full-duplex two-way relay (FD-TWR). Although classical FD-TWR is spectral efficient and expands cell coverage, the proposed STWR utilizes the existing HD infrastructure to boost the FD implementation and offers bi-directional data exchange and low-complexity residual self-interference (RSI) mitigation. To formulate STWR, we develop a unified signal model to facilitate the mitigation of the generalized self-interference (GSI). GSI consists of back-propagating interference due to two-way relaying, RSI of FD sources and inter-relay interference caused by the pairs of HD relays. Because the GSI channel matrix has a distinct row linearity, we propose an efficient digital approach to remove the GSI and design two low-complexity algorithms. These algorithms avoid RSI channel estimation, full-rank matrix, and complex matrix computation. Our analysis and simulations show that: 1) the proposed STWR achieves the multiplexing gain of the true FD-TWR; 2) the distance between the two HD relays should be optimized to achieve the highest spectral efficiency; and 3) the STWR system with two algorithms can achieve a diversity order of one or two, respectively. Therefore, the STWR concept achieves a flexible tradeoff between performance and complexity, potentially enabling large-scale relay deployments.

Performance analysis of two-way full-duplex relay with antenna selection under Nakagami channels

This paper focuses on a full-duplex (FD) two-way relay network with one base station (BS), one FD amplify-and-forward (AF) relay, and one user, and the BS is equipped with massive multiple-input multiple-output (MIMO) antennas. To reduce the complexity and cost of BS, the paper proposes a practical antenna selection way in BS to complete transmission in two-way FD relay networks to optimize the system performance of outage probability or bit error ratio (BER). In the proposed scheme, BS can implement transmit antenna selection (AS) based on the instantaneous channel state information (CSI), thereby improving the system performance compared to the traditional FD relay networks. Furthermore, closed-form expressions for the outage probability and average BER are derived under Nakagami-m channels. The analytical results show that the superiority of proposed scheme compared with the conventional AF relay scheme and the correctness of the theoretical analysis verified by the Monte Carlo simulations.

Transceiver Design for MIMO Full-Duplex Two-Way Relay Network

Mitigation of loopback self-interference (LSI) is one of the main challenges in full-duplex (FD) wireless communication systems. In this letter, we present the design of optimal transceiver and relay processing algorithms for an FD two-way amplify-and-forward (AF) multiple-input multiple-output relaying system. We consider a realistic scenario where the available channel state information of the LSI channels is imperfect. The resultant residual LSI is suppressed by the suitable design of precoders and receive filters. All the precoders and receive filters are updated in each time slot in order to combat the cumulative interference effect caused by AF operation of the FD relay. We derive a simple recursive equation to keep track of this cumulative interference. The performance of the proposed design is demonstrated via the simulation results.

Near-Maximum-Likelihood Decoding for Convolutionally Coded Physical-Layer Network Coding Over the Full-Duplex Two-Way Relay Channel

The full duplex (FD) two-way relay channel (TWRC) has recently been shown to be a feasible way to improve the network throughput in practical communications. In this correspondence, we consider the convolutionally coded physical-layer network coding over the TWRC in which two sources work in the FD mode and there exists a direct link between them. Every source receives two packets, one packet from the other source and one network coded packet from the relay. A near-maximum-likelihood decoding algorithm for the sources is proposed. A salient feature of the proposed algorithm is that it exploits the code structure to mitigate the error propagation induced by the relay. Furthermore, we derive the near maximum-likelihood decoding bound on end-to-end BER for the system. Simulation results indicate that the performance of the proposed algorithm matches well the bound.

Max–min fair beamforming designs of SWIPT-aided full-duplex two-way relay systems

A full-duplex two-way relaying (FD-TWR) system with an energy-constrained relay is studied with simultaneous wireless information and power transfer (SWIPT). In this network, the sources have a reliable power supply, whereas the relay has to harvest energy from the source-emitted radio-frequency signal via time switching (TS) operation. Our aim is to maximize the minimum achievable rate of the two sources by jointly optimizing the relay beamforming vector and TS ratio under the energy-harvesting-then-transmitting mode, i.e., the relay harvested energy need to meet the consumed energy. Specifically, the max–min fairness beamforming design problems are formulated for both the perfect channel state information (CSI) model and imperfect CSI model. A one-dimensional search algorithm and the semidefinite relaxation technique are proposed to solve these complex non-convex problems. It is shown that the optimal beamforming vectors and the TS ratio can always be found under the two considered CSI model. Numerical results show that the proposed two FD schemes achieve significant performance improvement compared to the traditional half-duplex (HD) scheme. Moreover, the robust scheme can get most of the performance gain of the perfect scheme. Some tradeoffs are elucidated among the achievable rate and the TS ratio, the system performance and the self-interference cancellation (SIC) level under a max–min fairness criterion.

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.