Amplify-and-forward Relay Research Articles

Energy-Efficient Resource Allocation in SWIPT Cooperative Wireless Networks

In this article, energy-efficient resource allocation in simultaneous wireless information and power transfer (SWIPT) cooperative wireless networks is studied. With the transferred power, the SWIPT relays are adopted to improve the energy efficiency at the destination node. Two typical relay structures, decode-and-forward (DF) and amplify-and-forward (AF), are exploited for the optimal relay selection and power allocation with a power splitting SWIPT architecture. Nonconvex energy efficiency optimization problems are formulated for both DF and AF relay types. Based on the SNRs at the destination node, closed-form expressions of the optimal power splitting ratios are provided for DF and AF relays, respectively. With the optimal power splitting ratio, relay selection schemes based on full and partial knowledge of the channel state information are derived. Moreover, a novel power allocation scheme is proposed and illustrated based on the property of the simplified optimization problem with the power and quality of service constraints. Simulation results demonstrate that the proposed resource allocation scheme achieves the maximum energy efficiency with low computational complexity, in which the proposed relay selection outperforms the typical relay selection schemes in terms of energy efficiency.

Higher order statistics of cooperative mobile-to-mobile relay communications over composite fading channels

The paper investigates mobile-to-mobile (M2M) dual-hop amplify-and-forward relay (AFR) communications in composite fading environments. We model composite fading signal as the product of Nakagami-m (Nm) and Gamma (G) random processes (RPs) in order to address multipath-shadowing scenario and derive novel, fast computing, closed form mathematical formulas for: 1) probability density function; 2) cumulative distribution function; 3) outage probability; 4) average level crossing rate; 5) average fade duration. The integral form statistical expressions are directly approximated by Laplace approximation (LA) method and exponential LA method. Moreover, we extended the model to cooperative M2M relay communications with n parallel independent dual-hop AFR links with selection combining scheme (SCS) at reception. The obtained results are numerically presented in order to show the impact of multipath-shadowing severity sets of parameters on the proposed M2M system. The detailed comparison of exact and approximated numerical results is provided for all considered statistical measures.

Sum-Rate Maximization for UAV Aided Wireless Power Transfer in Space-Air-Ground Networks

The Internet of things (IoT) has become a prominent platform which bridges diverse technologies in order to meet the ever-increasing application requirements of various industries. However, the IoT devices, especially in remote areas that lack infrastructures, are featured by the restricted energy and pose great challenges on network access and sustainable communication. In this paper, we investigate the unmanned aerial vehicle (UAV) aided wireless power transfer under a space-air-ground (SAG) network, where the UAV is exploited as an aerial relay to assist in uploading information generated by ground nodes (GNs), and mounted with energy transmitter to deliver wireless energy for GNs. The goal is to maximize the system sum rate while satisfying the proportional rate for GNs and the sustainability of the ground network. To this end, by adopting decode and forward (DF) and amplify and forward (AF) protocols, two sum rate maximization problems are formulated via jointly optimizing power control, time allocation as well as UAV trajectory. The resource allocation problems are both nonconvex, which are difficult to solve directly. To tackle them, two near-optimal iterative algorithms are proposed by leveraging the successive convex approximation technology and the alternating optimization method. Extensive simulations are provided to demonstrate the effectiveness of the proposed algorithms and evaluate the impacts of various parameters on DF and AF relays.

First order outage statistics of asymmetrical RF-OW dual-hop relay communications

This paper addresses the first-order outage statistics of asymmetrical radio frequency (RF)-optical wireless (OW) relay systems over non turbulent-induced-fading (nTIF) and turbulent-induced-fading (TIF) channels. We rely on dual-hop amplify-and-forward relay (AFR) scheme and provide detailed mathematical development for derivation of novel exact analytical as well as novel closed form approximative expressions for: i). cumulative distribution function, II.) outage probability, and III.) average bit-error-rate. The system under consideration is modeled as the product of independent Nakagmi-m and double squared Nakagami-m (also known as Gamma-Gamma) random processes. The obtained results of the proposed system are graphically presented for RF-OW TIF and nTIF channel sets of parameters. Moreover, the detailed comparisons of exact and approximated numerical results whose derivation resorts on exponential Laplace approximation method (LAM) are provided and thoroughly examined for the considered RF-OW statistical measures.

Second-Order Statistics of MRC Reception With a Transparent Amplify-and-Forward Relay

Achievable spatial diversity supported by a single transparent amplify-and-forward (AF) relay relies on disintegrated channel state information (CSI) that can be acquired at the destination. This paper studies the impact of the quantization of the source-relay (SR) CSI in terms of the first- and second-order statistics of maximal-ratio combining (MRC) reception with the incomplete SR CSI at the destination. Probability density functions (PDFs) of the upper and lower bounds of the signal-to-noise ratio (SNR) achieved at the destination are derived. Corresponding level-crossing rate (LCR) and average fade-duration (AFD), which are undoubtedly required to choose parameters of forward error correcting (FEC) mechanisms across the transparent AF relay network, are evaluated via Monte Carlo simulations. The simulations show that the SNR PDF, LCR and AFD highly depends not only on the accuracy of SR CSI at the destination but also on the location of the AF relay.

Pattern Division Multiple Access Featuring Amplify-and-Forward Relaying in an Uplink Network

NOMA is one of key enabling technologies for prosumer energy management. We studied co-operative techniques useful for establishing pattern division multiple access (PDMA) in an uplink network. In particular, we examined amplify-and-forward (AF) relaying with PDMA (AF-PDMA) over Rayleigh channels. To characterize the performance of AF-PDMA, we derived outage probability and system throughput data, and performed diversity analysis. To verify the performance advantages afforded by the AF-PDMA scheme, we allocated fixed power values to users when comparing the performance to that of a non-cooperative PDMA scheme, an AF relay with orthogonal multiple access (AF-OMA) scheme, and an OMA scheme. Monte Carlo simulation revealed that AF-PDMA outperformed the other three schemes in terms of outage probability and system throughput.

Secure Beamforming in Full-Duplex Two-Way Relay Networks With SWIPT for Multimedia Transmission

With the advent of 5G, multimedia services in wireless communication networks will grow dramatically. So far, many researches have focused on improving security, throughput and channel capacity to support multimedia services. In this paper, a new system model of full-duplex (FD) two-way amplify-and-forward (AF) relay network with simultaneous wireless information and power transfer is presented, where two FD legitimate nodes with two single-antenna communicate with each other via energy-constrained AF relay with multiple antennas, and there is a half-duplex node with single antenna who intends to eavesdrop. This paper targets to maximize the secrecy sum rate of the system by designing the transmit beamforming vector of relay under power constraint and zero-forcing constraint, where two energy harvesting protocols, namely, power splitting and time switching are considered. However the maximization problem is a non-convex optimization, and it is very complex to solve. Therefore a linear method is used to find the lower bound of the secrecy sum rate and the non-convex problem is transformed into a convex optimization problem. After that, an iterative algorithm based on difference-of-convex programming is proposed to solve this convex optimization problem. The simulation results show the good convergence of the proposed iterative algorithm and also the superiority of secrecy sum rate of our proposed scheme compared with two traditional schemes.

Power Control for Two-Way AF Relay Assisted D2D Communications Underlaying Cellular Networks

As a key technology of the 5G communication system, device-to-device (D2D) communications have drawn significant research interests. However, the advantage of D2D communications may be limited when D2D users are far away from each other or the communication environments are harsh. In order to extend the range of D2D communications, a promising way is to use relaying technique to assist the communications. In this paper, we use a two-way amplify-and-forward (AF) relay to assist the underlay D2D communications and investigate the power control problem. Specifically, we formulate the power control problem as the optimization of the performance of the D2D link while fulfilling the quality-of-service (QoS) requirement of the cellular link. Two optimization objectives are considered for the D2D link, i.e., maximization of the minimum SINR at D2D users and maximization of the sum-rate of D2D users. For the first optimization objective, we can compare the possible optimal solutions for the three boundary conditions and obtain the optimal solutions. For the second optimization objective, we can convert the objective function into a concave function based on difference of convex (D. C.) structure, and use an iterative algorithm to solve the optimization problem. The simulation results show that the proposed power control scheme can improve the performance of the D2D link.

Cooperative Transmission in Uplink NOMA Networks with Wireless Power Transfer

5G networks and wireless power transfer are the topics that have attracted both academic and industry communities in recent years. In this paper, we study the cooperative transmission of uplink non-orthogonal multiple access (NOMA) network with wireless power transfer in terms of performance analysis. Specifically, energy-constrained amplifyand-forward relay cooperates with two users that applying NOMA scheme to transmit the message to base station by using the energy harvested from base station. For performance analysis, we derive the closed-form expressions of outage probability and throughput for two users based on the statistical characteristics of signal-to-noise ratio (SNR) and signalto-interference-plus-noise ratio (SINR) by using the Gaussian-Chebyshev quadrature method. To understand more detail of the behaviour of this considered system, the numerical results are provided according to the system key parameters, e.g., transmit power, distances. Furthermore, the theoretical results are also verified by the Monte-Carlo simulation.

Performance Analysis of Signal Detection for Amplify-and-Forward Relay in Diffusion-Based Molecular Communication Systems

Molecular communication (MC) is a promising technique of using molecules to realize communication between nanomachines for Internet of Bio-Nano Things in the body area nanonetwork. Due to the properties of diffusion and the attenuation of molecular transmission, the diffusion-based MC confronts with challenges in terms of the communication range and the signal detection accuracy. To extend the coverage, the intermediate nanomachine is deployed as relay between transmitter and its intended receiver. In this article, amplify-and-forward (AF) relaying is researched, and the performance under diverse signal detection schemes is analyzed, including mean square error (MSE) detection, maximum a posteriori probability detection, minimum error probability (MEP) detection under stationary fluid environment, and the MEP detection with a drift velocity simulation. The key parameters, such as the number of released molecules, receiving radius, and the relay position, influencing on the AF relaying performance under different detection methods are explored. The simulation results show that the MEP detection can achieve the best performance gain for the AF relay with a drift velocity channel. In particular, when the number of released molecules is 500, the gain is up to 35 dB.

A Unified Performance Analysis of Relaying Communication System for IoT Application With Hybrid Fading

Power line and wireless hybrid communication address the problem that wireless and power line cannot communicate with each other in the Internet of Things (IoT). However, the theoretical performance of amplify-and-forward (AF) relay communication based on hybrid fading condition has no closed expression. This article takes a relay system model of wireless and power line hybrid media as a representative and investigates a unified performance analysis method for AF relay systems with hybrid fading. The mixture lognormal (LogN) approximate algorithm based on the moment-generating function (MGF) is applied to approximate a wireless fading coefficient to mixture LogN distribution. Moreover, we propose a joint optimization algorithm for determining the key parameters given that the adjustable variables in the MGF equations evidently affect the approximation accuracy. Importantly, this article is then extended to other fading models, taking general gamma (GG) as an example. The effectiveness and reliability of the algorithm are verified by the Monte Carlo simulation. Finally, closed analytic expressions of the system performance, such as bit error rate (BER), outage probability, and average channel capacity, are derived. The effects of hybrid fading factor, impulse noise parameter, and power allocation on system performance are analyzed using the theoretical formulas.

Joint Power Splitting and Relay Selection in Energy-Harvesting Communications for IoT Networks

In this paper, we consider an energy-harvesting (EH) relay system consisting of a source, a destination, and multiple EH decode-and-forward (DF) relays that can harvest the energy from their received radio signals. A power-splitting ratio is employed at an EH DF relay to characterize a trade-off between an energy used for decoding the source signal received at the relay and the remaining energy harvested for retransmitting the decode outcome. We propose an optimal power splitting and relay selection (OPS-RS) framework and also consider the conventional equal power splitting and relay selection (EPS-RS) for comparison purposes. We derive closed-form expressions of outage probability for both the OPS-RS and EPS-RS schemes and characterize their diversity gains through an asymptotic outage analysis in the high signal-to-noise ratio region. We further examine an extension of our OPS-RS framework to an energy-harvesting battery (EHB) enabled cooperative relay scenario, where the EH relays are equipped with batteries used to store their harvested energies. We propose an amplify-and-forward (AF) based EHB-OPS-RS and a DF based EHB-OPS-RS schemes for AF and DF relay networks, respectively. Numerical results show that the proposed OPS-RS always outperforms the EPS-RS in terms of outage probability. Moreover, the outage probabilities of AF and DF based EHB-OPS-RS schemes are much smaller than that of OPS-RS and EPS-RS methods, demonstrating the benefit of exploiting the batteries in EH relays. Additionally, the DF based EHB-OPS-RS substantially outperforms the AF based EHB-OPS-RS and such an outage advantage becomes more significant, as the number of EH relays increases.

BER analysis of amplify-and-forward relaying FSO systems using APD receiver over strong atmospheric turbulence channels

<span lang="EN-US">In this paper, we theoretically analyze the performance of amplify-and-forward (AF) serial relaying free-space optical (FSO) systems using avalanche photodiodes (APD) and subcarrier quadrature amplitude modulation (SC-QAM) over strong atmospheric turbulence channels modelled by gamma-gamma distribution. Closed-form expression for average bit error rate (BER) of system is theoretically derived talking into account APD shot noise, thermal noise as well as the impact of atmospheric loss and turbulence. The numerical results show that using AF relay stations can extend the transmission distance and help to improve performance of FSO system significantly when compared with the direct transmission. Moreover, the selection of APD gain value is indispensable to the system performance. The proposed system could be achieved the best performance by selecting an optimal APD gain value. In addition, the optimal value of APD gain also significantly depends on various conditions, such as link distance, the number of relay stations and APD receiver noise.</span>

Physical layer security based on NOMA and AJ for MISOSE channels with an untrusted relay

Physical layer security based on non-orthogonal multiple access (NOMA) and artificial jamming (AJ) is considered in a one-way amplify-and-forward (AF) relay network with an untrusted relay. In the first phase of the two-phase operation of the untrusted AF relay network, a source node transmits the first information and AJ symbols, and the destination decodes the AJ symbol first and waits for the relayed replica of the first information symbol, which is forwarded by the untrusted relay. In the second phase, the source sends the second information symbol and the relay amplifies and forwards the received signal in the first phase with a fixed gain. In such an operation scenario, an untrusted relay tries to eavesdrop on the information signal while relaying the received signal properly. To decode the information symbol, the destination cancels out the AJ signal and then decodes the first information symbol by combining the signals received during the two phases. Finally, the second information symbol is decoded with the second-phase signal after cancelling out all the other symbols, i.e., the first information and AJ symbols. The eavesdropper and relay try to eavesdrop on the information signal with all possible orders of interference cancellation, i.e., NOMA receive processing. In this study, an ergodic secrecy rate is derived according to the operation scenario during the two phases. The behaviours of the ergodic secrecy rate with respect to power allocation to two information symbols as well as an AJ symbol are investigated. It is shown that the expected secrecy rate can be maximized by selecting the transmit power and rates for the three symbols properly. It is also demonstrated that the proposed physical layer security scheme achieves a higher secrecy rate than a secure beamformed transmission based on NOMA and artificial noise.

Secrecy Sum Rate Optimization in Nonorthogonal Multiple Access AF Relay Networks

In this paper, nonorthogonal multiple access (NOMA) technique is employed to an amplify-and-forward (AF) relay system, which consists of a source, a relay, several users, and an eavesdropper. We aim to maximize the achievable secrecy sum rate by jointly designing power allocation at the source and cooperative beamforming at the relay, under the achievable rate constraints at the weak users and the transmit power constraints at the source and the relay. The formulated optimization problem is nonconvex due to the coupled variables. We proposed to decouple the problem into two subproblems and solve power allocation and relay beamforming in an iterative manner. Simulation results demonstrate that the proposed NOMA AF network can achieve a higher achievable secrecy sum rate than the conventional orthogonal multiple access AF relay network.

Multi-User AF Relay Networks with Power Allocation and Transfer: A Joint Approach

The Internet-of-Things (IoT) framework has been considered as an enabler of the smart world where all devices will be deployed with extra-sensory power in order to sense the world as well as communicate with other sensor nodes. As a result, smart devices require more energy. Therefore, energy harvesting (EH) and wireless power transfer (WPT) emerge as a remedy for relieving the battery limitations of wireless devices. In this work, we consider a multi-user amplify-and-forward (AF)-assisted network, wherein multiple source nodes communicate with destination nodes with the help of a relay node. All the source nodes and the relay node have the capability of EH. In addition, to cope with a single point of failure i.e., failure of the relay node due to the lack of transmit power, we consider the WPT from the source nodes to the relay node. For WPT, a dedicated energy control channel is utilized by the source nodes. To maximize the sum rate using a deadline, we adopt a joint approach of power allocation and WPT and formulate an optimization problem under the constraints of the battery as well as energy causality. The formulated problem is non-convex and intractable. In order to make the problem solvable, we utilize a successive convex approximation method. Furthermore, an iterative algorithm based on the dual decomposition technique is investigated to get the optimal power allocation and transfer. Numerical examples are used to illustrate the performance of the proposed iterative algorithm.

Secrecy Analysis in Wireless Network With Passive Eavesdroppers by Using Partial Cooperation

This paper proposes a new location-based multicasting technique, for dual phase amplify-and-forward (AF) large networks, aiming to improve the security in the presence of non-colluding passive eavesdroppers. These eavesdroppers could also be part of this cooperative network as relays. In order to reduce the impact of these eavesdroppers on the network security, we propose a new transmission strategy where, for the first hop of each transmission time, while the destination is jamming, the source randomly chooses a different subset $K$ of the total $T$ relays, to transmit its message toward the destination. For practical implementation, sectoral transmission can be achieved with analog beamforming at the source's side. In the second hop, using the distributed beamforming technique, the $K$ AF relays retransmit the received signal to the destination. We analytically demonstrated that the proposed technique decreases the probability of choosing the same sector that has certain eavesdroppers again, for each transmission time, to $K/T$ . Moreover, we also show that the secrecy capacity scaling of our technique is still the same as for broadcasting. Hereafter, the lower and upper bounds of the secrecy outage probability are calculated, and it is shown that the security performance is remarkably enhanced, compared to conventional multicasting technique.

Time-Switching EH-Based Joint Relay Selection and Resource Allocation Algorithms for Multi-User Multi-Carrier AF Relay Networks

In this paper, an energy efficiency maximization (EEM) optimization problem for the multi-user multi-carrier energy-constrained amplify-and-forward (AF) multi-relay network is formulated under the total source transmit power budget and energy-causality constraints. We consider that each relay node is solely powered by the source nodes, employing energy harvesting time-switching (EHTS) protocol to harvest the energy through the ambient radio-frequency (RF) signal transmitted from the source nodes under the simultaneous wireless information and power transfer (SWIPT) paradigm. First, we propose a subcarrier and energy causality-based multi-relay selection policy. Second, we jointly optimize the parameters that control the energy efficiency (EE) of the system namely multi-relay selection, subcarrier pairing, user allocation, power allocation, and RF EHTS time block, that renders the problem to be a mixed integer non-linear programming problem (MINLP) which remains NP-hard to solve. Hence, we remodel the problem to a tractable quasi-concave form by applying a string of convex transformations. Later, we propose an iterative EEM algorithm to optimize the multi-parameter problem. Further, a suboptimal and best relay selection algorithm is studied by trading-off between complexity and performance. The effectiveness of the proposed algorithms is demonstrated by simulation results.

On the Accumulated Loopback Self-Interference of Two-Way Full-Duplex AF Relaying Systems

Two-way full-duplex (TWFD) transmissions in cooperative amplify-and-forward (AF) relaying systems provide a promising way of communications with the improved spectral efficiency by concurrently transmitting/receiving data in the same frequency band and by the two-way transmission protocol. However, the loopback self-interference, caused by the imperfect channel estimation in the loopback link, at the AF relay accumulates and is forwarded to the end users recurrently, which substantially degrades the end users’ error performance if this accumulated loopback self-interference (ALSI) does not converge. It is therefore of critical importance to analyze the convergence behavior of the ALSI in the TWFD systems with AF relaying. In this paper, we establish sufficient conditions on the relay power to ensure the convergence of the ALSI, with which the average limiting signal-to-interference-plus-noise ratio at the infinite time horizon is derived. In addition, we specify the relay power at which the signal-to-noise ratio reaches the maximal value under different scenarios and obtain an upper bound to the symbol error rate. Finally, extensive computer simulations results are provided to corroborate the analytic derivations.

Delay constrained throughput optimization in multi-hop AF relay networks, using limited quantized CSI

In this paper, we analyze the throughput of multi-hop amplify and forward (AF) relay networks in delay-constrained scenario. Using quantized channel state information (CSI), the transmission rates and powers are discretely adapted with individual average power constraint on each node. A sub-gradient projection-based algorithm is utilized, by which there is no need for probability density functions (PDFs) to solve the optimization problem. Our numerical evaluations show that the sub-gradient projection-based algorithm results in a comparable performance with an analytical approach using PDFs. As shown, a considerably better performance obtained by the designed scheme compared to previous schemes with constant power transmission. More than 70% throughput improvement is achieved by our scheme compared to constant power transmission with just two more feedback bits and a short training time required at the beginning of the transmission.