Relay Receiver Research Articles

Energy Signal-Aided Secure Beamforming and Self-Energy Recycling in Full-Duplex Wireless-Powered Relay Networks

In this paper, the object of study is secure transmission and green energy transfer in full-duplex (FD) wireless-powered relay (WPR) secure systems, where an FD relay collects the power from radio-frequency signs and transmits the information in the face of multiple eavesdroppers. In order to improve the efficiency and safety of the contemporaneous wireless energy and information delivery, we propose a joint energy-signal- (ES-) aided secure beamforming and time-switch scheme under the self-power circulation protocol at the relay. The question formulated in this paper is to maximize the confidentiality rate according to energy restrictions at both the relay and energy receiver. As the question is non-salient and hard to resolve directly, we transform it into two sub-problems. For the first sub-problem, a two-level optimization technique is suggested to separately gain the optimal beamforming as well as the ES covariance. The extrinsic rank is a single-variable majorization question, which can be solved by single-dimensional (1D) examination. We attain an optimal solution to the inner level by a semi-definite relaxation (SDR) technique. For the second sub-problem, we again use 1D search to solve this problem. Moreover, we prove that SDR always exists as a level-1 optimal resolution. Mathematical outcomes show that the suggested plan can achieve a considerable gain of confidentiality rate by comparison with other benchmark plans.

Performance analysis of two‐way AF relaying system with the presence of hardware impairments over Nakagami‐ m fading channels

The authors evaluate theoutage probability, ergodic capacity, and symbol error rate (SER) performances of an amplify-and-forward relaying system equipped with a non-ideal variable gain single relay with hardware (HW) distortions at both the transmitter and receiver sides with the derivations of the instantaneous end-to-end signal-to-noise-and-distortion ratios. More specifically, they analytically derive new algebraic expressions for the outage probability and ergodic capacity in the two-way relaying system over the Nakagami-m fading environments. They further derive new closed-form expressions for the asymptotic outage probability to analyse the performance in the high signal-to-noise regime. The derived statistics, along with the transmitter–relay–receiver channels are then used to obtain a closed-form expression of the approximate and upper bound ergodic capacity. Finally, they investigate the generic mathematical expressions utilising the average and asymptotic SER, valid for several types of modulation schemes operating over the Nakagami-m fading. Monte Carlo simulations and numerical examples are provided to quantify the validity of the derived analytical expressions. The authors' results highlight the effect of HW impairments in the two-way relaying system over the Nakagami-m fading channels and reveal the impact of the level of HW impairments, data rates, modulation types, and shaping parameters on the overall system performance.

A methodology to achieve the maximum transfer efficiency for magnetic coupling wireless power transfer systems

Transfer efficiency is one of the most significant indexes of magnetic coupling wireless power transfer (MC-WPT) systems, which is severely affected by frequency splitting. In this paper, a novel method is proposed for MC-WPT systems to achieve the maximum transfer efficiency by introducing and controlling the circuit detuning factors while maintaining the operating frequency at constant. Firstly, the circuit model of tri-coil MC-WPT systems is established along with the derivation of some key concepts, including the transfer efficiency and circuit detuning factors. Then the analytical expressions of the optimal circuit detuning factors, maximum transfer efficiency and a comprehensive discriminant which could quickly and accurately determine the critical value for every system parameters are derived. Further, the physical interpretation of the maximum transfer efficiency is firstly elucidated from the perspective of energy flow: (1) when the system is in non-splitting region, the energy flow path of the maximum transfer efficiency is transmitter–relay–receiver; (2) when system is in splitting region, the energy flow path of the maximum transfer efficiency is directly from the transmitter to the receiver. Finally, simulation models and practical prototypes are designed to verify the theoretical results. The simulation and experimental results show that the proposed system can maintain an almost constant maximum transfer efficiency over a wide range of transfer distance. The derived discriminant is very useful for guiding the system design in the future, and the energy flow analysis method will be beneficial for maximizing the efficiency for multi-coil MC-WPT systems.

Energy efficiency and throughput maximization scheme based on joint antenna selection and beamforming optimization in FD-SWIPT bidirectional relay systems

FD-SWIPT two-way relay is used to provide cell coverage in mobile cellular networks and improve the throughput and energy efficiency of the system. To address the problem in FD-SWIPT bidirectional relay research, an efficient and throughput maximization scheme based on joint optimization antenna selection and beamforming in the FD-SWIPT bidirectional relay system is proposed in this study. First, a sub-optimal antenna grouping algorithm with low complexity is presented. The strategy of antenna grouping is used at the relay receiver to transmit the received signal with great channel CSI to the destination node, and then the remaining signal is used for energy harvest. Second, the beamforming scheme is designed at the relay transmitter, and the maximum generalized eigenvalue method is used to optimize the beamforming vector and enhance the signal-to-interference-plus-noise ratio of the system. The simulation results show that the proposed joint optimization scheme can effectively improve the throughput and energy efficiency of the system, and the antenna selection scheme plays an important role in the system.

Asymptotic Performance Analysis of Massive MIMO Relay Systems With Multi-Pair Devices Over Correlated Fading Channels

In this paper, we investigate a relay system with multi-pair single-antenna devices, where massive antenna array (also known as massive multiple-input-multiple-output (MIMO) technology) is deployed at the relay with low-complexity maximum-ratio combining/maximum-ratio transmission precoding scheme. By combining massive MIMO and relay cooperation, the performance of relay-assisted communication systems is predicted to be dramatically improved in many areas, e.g., spectral efficiency, energy efficiency, inter-user interference cancelation, and so on, by exploring the abundant spatial degree of freedom of massive MIMO. However, a large number of antennas employed at relay node inevitably leads to antenna correlation because of small antenna spacing subjected to the limited size of the relay node, which may affect the system performance and has not yet been compressively studied. Thus, we focus on analyzing the effect of antenna correlation on the asymptotic performance of system ergodic rate by using a general channel correlation model. First, by means of the deterministic equivalent technology, the analytical expression of the ergodic rate with arbitrary channel correlations is derived, which presents the quantitative relations among system parameters, i.e., the numbers of relay antennas and device-pairs, the channel spatial correlations at the relay's receiver side and the transmitter side, and the transmit powers of the source devices and the relay. By using a general scaling model for system parameters with respect to the relay antenna number, the asymptotic performance of the ergodic rate under spatially correlated channel and the corresponding scaling laws of the system parameters are obtained, which provides useful guidelines to trade off the transmit power and the ergodic rate as well as the number of the served device-pairs. It is further revealed that the influence degrees of the antenna correlations at the relay's receiver and the transmitter on the ergodic rate is nearly the same. Finally, the analytical conclusions are justified through the numerical simulations.

High-performance beamformer and low-complexity detector for DF-based full-duplex mimo relaying networks

In this paper, we consider a full-duplex multiple-input multiple-output (MIMO) relaying network with the decode-and-forward (DF) protocol. Due to the full-duplex transmissions, the self-interference from the relay transmitter to the relay receiver degrades the system performance. We thus propose an iterative beamforming structure (IBS) to mitigate the self-interference. In this method, the receive beamforming at the relay is optimized to maximize the signal-to-interference- plus-noise-ratio (Max-SINR), while the transmit beamforming at the relay is optimized to maximize the signal-to-leakage-plusnoise- ratio (Max-SLNR). To further improve the performance, the receive and transmit beamforming matrices are optimized between Max-SINR and Max-SLNR in an iterative manner. Furthermore, in the presence of the residual self-interference, a low-complexity whitening-filter (WF) maximum likelihood (ML) detector is proposed. In this detector, a WF is designed to transform a colored interference- plus-noise to a white noise, while the singular value decomposition is used to convert coupled spatial subchannels to parallel independent ones. From simulations, we find that the proposed IBS performs much better than the existing schemes. Also, the proposed low-complexity detector significantly reduces the complexity of the conventional ML (CML) detector from exponential time (an exponential function of the number of the source transmit antennas) to polynomial one while achieving a slightly better BER performance than the CML due to interference whitening.

Erratum to: Chaotic masking of communication in an emitter–relay–receiver electronic setup

Erratum to: Chaotic masking of communication in an emitter–relay–receiver electronic setup

A Random Channel Sounding Decision Feedback Receiver for Two-Way Relay Communication With Pilotless Orthogonal Signaling and Physical-Layer Network Coding

We propose a decision feedback (DFB) receiver at the relay of a two-phase (2P) two-way relay (TWR) communication system that employs pilotless orthogonal modulation (such as frequency-shift keying) in the uplink and physical-layer network coding over finite field in the downlink. The proposed relay receiver is able to attain a performance very close to that of an ideal coherent detector in the presence of time-selective Rayleigh fading and additive white Gaussian noise in the uplinks. It exploits the fact that when the uplink symbols from the users are different, then the fading gains affecting these symbols can be separated and individually tracked at the relay. In essence, the proposed receiver performs random channel sounding although no actual pilots are transmitted. The channel estimates obtained this way can then be subsequently used in a coherent detector to improve the reliability of the relay detected data. To ensure fast convergence, we propose to kick start the DFB receiver using a partial-coherent detector developed earlier by the authors. We compare the performance of the proposed system against a similar 2P-TWR system that employs differential phase-shift keying (DPSK) in the uplink and DFB multiple-symbol differential detection at the relay. We found that the proposed pilotless orthogonal modulation system can actually attain a significantly lower bit error rate (BER) than its DPSK counterpart. For static fading and a BER of $\mbox{10}^{-3}$ , the signal-to-noise ratio (SNR) gap between the two approaches is 1 dB in the binary case and 8 dB in the quaternary case. These gaps increase further with time-selective fading.

Wireless Information and Power Transfer in Multiway Massive MIMO Relay Networks

Simultaneous wireless information and power transfer techniques for multiway massive multiple-input multiple-output (MIMO) relay networks are investigated. By using two practically viable relay receiver designs, namely 1) the power splitting receiver and 2) the time switching receiver, asymptotic signal-to-interference-plus-noise ratio (SINR) expressions are derived for an unlimited number of antennas at the relay. These asymptotic SINRs are then used to derive asymptotic symmetric sum rate expressions in closed form. Notably, these asymptotic SINRs and sum rates become independent of radio frequency-to-direct current (RF-to-DC) conversion efficiency in the limit of infinitely many relay antennas. Moreover, tight average sum rate approximations are derived in closed form for finitely many relay antennas. The fundamental tradeoff between the harvested energy and the sum rate is quantified for both relay receiver structures. Notably, the detrimental impact of imperfect channel state information (CSI) on the MIMO detector/precoder is investigated, and thereby, the performance degradation caused by pilot contamination, which is the residual interference due to nonorthogonal pilot sequence usage in adjacent/cochannel systems, is quantified. The presence of cochannel interference (CCI) can be exploited to be beneficial for energy harvesting at the relay, and consequently, the asymptotic harvested energy is an increasing function of the number of cochannel interferers. Notably, in the genie-aided perfect CSI case, the detrimental impact of CCI for signal decoding can be cancelled completely whenever the number of relay antennas grows without bound. Nevertheless, the pilot contamination severely degrades the sum rate performance even for infinitely many relay antennas.

Chaotic masking of communication in an emitter–relay–receiver electronic setup

In this paper, an experimental study of practical realization for the transmission of information using chaotic oscillators is presented. We use a ring of three coupled oscillators (emitter–relay–receiver) to demonstrate some views of chaotic masking. Furthermore, several secure communication lines are discussed in this paper. We take into account the parameters mismatch, and the experimental results are in close accordance with the theoretical ones.

Achievable rate regions for many‐to‐one Gaussian interference channel with a fusion centre

This paper considers a many-to-one Gaussian interference channel with a fusion centre (FC) where there is a K -user interference channel in which only one relay (receiver) faces interference while the remaining K-1 receivers are interference free. All the relays communicate information about their observed sequence to the FC through noiseless links at communication rate R 0. First, by analysing traditional relaying schemes, i.e., Decode and Forward, Compress and Forward and Compute and Forward, three rate-regions for this setting are derived. Then, based on nested lattice codes, a new achievable rate-region is provided. Based on the proposed scheme, one can design a transmission scheme that can recover both integer and non-integer linear combination of messages. Numerical examples show that if channel gains are integer, the proposed scheme performs similarly to the compute-and-forward scheme. In the case of non-integer channel gains, the proposed scheme outperforms other relaying schemes at high signal-to-noise ratios. Finally, it is shown that if the channel gains are larger than one and if the rate of each relay-to-FC link equals to the capacity of an AWGN channel, then the proposed scheme can achieve the capacity region in high SNR regime.

Outage Analysis of Cooperative Transmission with Energy Harvesting Relay: Time Switching versus Power Splitting

This paper investigates the multiuser transmission network with an energy harvesting (EH) cooperative relay, where a source transmits independent information to multiple destinations with the help of an energy constrained relay. The relay can harvest energy from the radio frequency (RF) signals transmitted from the source, and it helps the multiuser transmission only by consuming the harvested energy. By adopting the time switching and the power splitting relay receiver architectures, we firstly propose two protocols, the time switching cooperative multiuser transmission (TSCMT) protocol and the power splitting cooperative multiuser transmission (PSCMT) protocol, to enable the simultaneous information processing and EH at the relay for the system. To evaluate the system performance, we theoretically analyze the system outage probability for the two proposed protocols and then derive explicit expressions for each of them, respectively. Numerical results are provided to demonstrate the accuracy of our analytical results and reveal that compared with traditional noncooperative scheme our proposed protocols are green solutions to offer reliable communication and lower system outage probability without consuming additional energy. In particular, for the same transmit power at the source, the PSCMT protocol is superior to the TSCMT protocol to obtain lower system outage probability.

An Optimal Full-Duplex AF Relay for Joint Analog and Digital Domain Self-Interference Cancellation

In this paper, a full-duplex (FD) amplify-and-forward (AF) relay is designed to compensate for the duplexing loss of the half-duplex (HD) AF relay. In particular, when there is no direct link between a source and a destination, joint analog domain self-interference suppression and digital domain residual self-interference cancellation is considered with an FD-AF relay having single receive antenna but multiple transmit antennas. Unlike previous approaches, a nonconvex quadratically constrained quadratic programming problem is formulated to find the optimal solution. The end-to-end spectral efficiency or, equivalently, the end-to-end signal-to-interference-plus-noise ratio from the source to the destination is chosen as the objective function to be maximized subject to the average transmit power constraint at the relay. In addition, an average power constraint is imposed on the output of the relay's receive antenna to avoid the nonlinear distortion in the low noise amplifier and the excessive quantization noise in the analog-to-digital converter. Through the systematic reduction and the partitioning of the constraint set, the optimal solution is derived in a closed algorithmic expression and shows how it allocates the transmission power not only in the direction of maximal performance improvement but also in the orthogonal direction in order to balance the system performance and the amount of self interference. It is shown that the optimal FD-AF relay significantly outperforms the optimal HD-AF relay even with the hardware limitations in the RF chain of the relay's receiver being well taken into account.

Performance analysis of multiple-input multiple-output relay networks based impulse radio ultra-wideband

In this paper, we study the performance of time hopping pulse position modulation for impulse radio ultra-wideband. We consider relay network applying decode-and-forward protocol. The channels between nodes adopt the IEEE 802.15.4a norms. The bit error rate performance is analyzed considering the effect of interference. Our results show significant improvement due to the diversity gain provided by the relay nodes. However, the performance is limited when multiple access interference MAI is present. To combat the MAI effect and further improve the detection reliability, we propose to use antenna selection at the relay. The relay receiver is assumed to be equipped with multiple antennas, and only the best antenna is selected. This is shown to improve the performance in the presence of MAI and improve the diversity gain.Copyright © 2013 John Wiley & Sons, Ltd.

Joint Tomlinson-Harashima source and linear relay precoder design in amplify-and-forward multiple-input multiple-output two-way relay systems

Existing minimum-mean-squared-error (MMSE) transceiver designs in amplified-and-forward (AF) multiple-input multiple-output (MIMO) two-way relay systems all assume a linear precoder at the sources. Nonlinear source precoders in such a system have not been considered yet. In this paper, we study the joint design of source Tomlinson-Harashima precoders (THPs), relay linear precoder and MMSE receivers in two-way relay systems. This joint design problem is a highly nonconvex optimization problem. By dividing the original problem into three sub-problems, we propose an iterative algorithm to optimize precoders and receivers. The convergence of the algorithm is ensured since the updated solution is optimal to each sub-problem. Numerical simulation results show that the proposed iterative algorithm outperforms other algorithms in the high signal-to-noise ratio (SNR) region.

Noncoherent Physical-Layer Network Coding with FSK Modulation: Relay Receiver Design Issues

A channel-coded physical-layer network coding strategy is refined for practical operation. The system uses frequency-shift keying (FSK) modulation and operates noncoherently, providing advantages over coherent operation: there are no requirements for perfect power control, phase synchronism, or estimates of carrier-phase offset. In contrast with analog network coding, which relays received analog signals plus noise, the system relays digital network codewords, obtained by digital demodulation and channel decoding at the relay. The emphasis of this paper is on the relay receiver formulation. Closed-form expressions are derived that provide bitwise log-likelihood ratios, which may be passed through a standard error-correction decoder. The role of fading-amplitude estimates is investigated, and an effective fading-amplitude estimator is developed. Simulation results are presented for a Rayleigh block-fading channel, and the influence of block length is explored. An example realization of the proposed system demonstrates a 32.4% throughput improvement compared to a similar system that performs network coding at the link layer. By properly selecting the rates of the channel codes, this benefit may be achieved without requiring an increase in transmit power.

3GPP LTE-Advanced 시스템에서 Type 1 relay의 셀 ID 검출을 위한 부분 전이중 relay 기법

In this paper, we propose a partial full duplex relay scheme for 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution)-Advanced system using a Type 1 relay. The Type 1 relay as inband relay is prohibited to transmit and receive simultaneously because of self-interference. Therefore, the Type 1 relay cannot receive synchronization signals which are transmitted to eNB. To overcoming this problem, we propose the partial full duplex relay scheme which transmits to R-UE (Relay-User Equipment) and receives from eNB (evolved NodeB) simultaneously when eNB and the Type 1 relay transmit subframes which have synchronization signals. Additionally, for solving self-interference, the Type 1 relay transmitter and receiver antennas are sufficiently sufficiently isolated and self-interference cancellation is applied for the self-interference signal from the relay transmitter. Thus, the partial full duplex relay scheme can receive synchronization signals from eNB and solve the problems of conventional solutions and we propose the partial channel estimation scheme for partial full duplex relay scheme using SCI. By extensive computer simulation, we verify that the partial full duplex relay scheme is attractive and suitable for the Type 1 relay system.

Joint Receive-Transmit Beamforming for Multi-Antenna Relaying Schemes

In this correspondence, we study the problem of joint receive and transmit beamforming for a wireless network consisting of a transmitter, a receiver, and a relay node. The relay node is equipped with multiple antennas while the transmitter and the receiver each uses only one antenna. Our communication scheme consists of two phases: first the transmitter sends the information symbols to the relay. In the second phase, the relay re-transmits a linearly transformed version of the vector of the signals received at its multiple antennas. We introduce the novel concept of general rank beamforming which can be applied to our communication scheme. In our general rank beamforming approach, the relay multiplies the vector of its received signals by a general-rank complex matrix and re-transmits each entry of the output vector on the corresponding antenna. Through maximizing the signal-to-noise ratio (SNR), we obtain a closed-form solution to the general rank beamforming problem. We also prove that for the case of statistically independent transmitter-relay (TR) and relay-receiver (RR) channels, the general rank beamforming approach results in a rank-one solution for the beamforming matrix regardless of the rank of the channel correlation matrices. Simulation results show that when applied to the case of statistically dependent TR and RR channels, our general rank beamforming technique outperforms the separable receive and transmit beamforming method by a significant margin.

Joint linear transceiver design for non-regenerative MIMO relay systems

The problem of designing the linear transmitters and receiver jointly in a non-regenerative MIMO relay system is considered, where linear processing is applied at the source, relay and destination node, using the minimum mean square error criterion. Under average power constraint at both the source and the relay node, the transmitters and receiver could be realised through a joint iterative algorithm. Simulation results are also provided to demonstrate the performance of this new method.

Capacity of a Class of Relay Channels With Orthogonal Components

The capacity of a class of discrete-memoryless relay channels with orthogonal channels from the sender to the relay receiver and from the sender and relay to the receiver is shown to be equal to the max-flow min-cut upper bound. The result is extended to additive white Gaussian noise (AWGN) relay channels where the channel from the sender to the relay uses a different frequency band from the channel from the sender and the relay to the receiver.