Amplify-and-forward Scheme Research Articles

System outage probability and diversity analysis of a SWIPT based two-way DF relay network under transceiver hardware impairments

This paper investigates the system outage performance of a simultaneous wireless information and power transfer (SWIPT) based two-way decode-and-forward (DF) relay network, where potential hardware impairments (HIs) in all transceivers are considered. After harvesting energy and decoding messages simultaneously via a power splitting scheme, the energy-limited relay node forwards the decoded information to both terminals. Each terminal combines the signals from the direct and relaying links via selection combining. We derive the system outage probability under independent but non-identically distributed Nakagami-m fading channels. It reveals an overall system ceiling (OSC) effect, i.e., the system falls in outage if the target rate exceeds an OSC threshold that is determined by the levels of HIs. Furthermore, we derive the diversity gain of the considered network. The result reveals that when the transmission rate is below the OSC threshold, the achieved diversity gain equals the sum of the shape parameter of the direct link and the smaller shape parameter of the terminal-to-relay links; otherwise, the diversity gain is zero. This is different from the amplify-and-forward (AF) strategy, under which the relaying links have no contribution to the diversity gain. Simulation results validate the analytical results and reveal that compared with the AF strategy, the SWIPT based two-way relaying links under the DF strategy are more robust to HIs and achieve a lower system outage probability.

On the Study of Multiuser Mixed Dual-Hop RF/THz Systems

A multiuser mixed radio frequency/terahertz (MRFTHz) system is studied, where the multiple RF channels experience <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\eta$</tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> fading and the THz channel obeys <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu _{1}$</tex-math></inline-formula> fading with pointing errors (PEs). Both fixed-gain (FG) amplify-and-forward (AF) and decode-and-forward (DF) protocols are considered in the relay. Firstly, the exact expressions of the cumulative distribution functions of the overall signal-to-noise ratio under AF and DF schemes are derived. On this basis, the Fox's H-function (FHF) and bivariate FHF are used to obtain exact analytical expressions of the outage probability (OP), average bit error rate, and average channel capacity. Additionally, the asymptotic results at high signal-to-noise ratios (SNRs) are provided to gain the system's diversity order (DO). Results show that the DOs of the AF and DF relaying systems are decided by the PEs and channel fading parameters (FPs). In addition, considering the FG AF relaying and multi-antenna scenarios, the asymptotic OP at high SNRs is derived, which obtaining the DO is determined by the numbers of the antenna, PEs, and FPs. Finally, we apply the Monte Carlo simulations to verify numerical results. Results show that the path loss, PEs, FPs, and the number of users can significantly affect the proposed multiuser MRFTHz system.

CSIN-assisted AF dual-hop relaying communication systems over imperfect Nagakami-[formula omitted] fading channels: Exact error performance

Relaying-based communication techniques are promising for current and future wireless systems. Amplify-and-forward (AF) relaying is more attractive due to the low cost and simplicity in its relay implementation. As compared to other AF schemes, the channel-state-information (CSI)-and-noise (CSIN)-assisted one is optimal and practically recommended. However, up to this moment, the exact symbol error rate (SER) performance of CSIN-assisted AF dual-hop relaying systems has been analytically derived only for Rayleigh fading environments, while for other more generic fading models, including Nakagami-m, it has been computed either approximately or via long-running time computer simulations. Thus, in this paper, we consider a CSIN-assisted AF dual-hop relaying system with independent and non-identical Nakagami-m fading channels and derive a new expression for its exact SER performance under the effect of imperfect channel estimation. The derived expression includes infinite series that can truncate quickly using a few terms, requires short computational time as compare to simulation, shows perfect matching with the simulation results, and offers remarkable accuracy enhancement over its approximate peer derived in literature. In addition, it helps in demonstrating some useful insights into the system’s realistic error performance considering different system and fading severity conditions. For example, results show that the system’s exact SER performance is dominated by the worse fading hop, does not change when the system’s two fading hops exchange their fading conditions, and improves faster with the per symbol average SNR when the fading severity conditions are better.

Mobile Two-Way Molecular Communication via Diffusion Using Amplify-and-Forward and Analog Network Coding.

Mobile molecular communication via diffusion (MCvD) has attracted lots of attentions due to its time-varying channels. In this paper, we investigate a mobile two-way MCvD model, which consists of two mobile source nanomachines and a mobile relay nanomachine. The amplify-and-forward (AF) relaying and analog network coding (ANC) are utilized to implement the exchange of information between two source nanomachines in this model. To explore the performance of the mobile two-way MCvD system, we first adopt the depleted molecule shift keying (D-MoSK) modulation, and then the mathematical expressions of symbol error probability (SEP) and mutual information are derived by using AF and ANC scheme on the basis of maximum a posteriori (MAP) probability detection. Finally, we present the numerical and simulation results. Compared with the AF-No-ANC scheme which is without use of ANC scheme, the scheme of combining AF and ANC can significantly improve the performance of SEP and mutual information. Moreover, the D-MoSK modulation outperforms the molecule shift keying (MoSK) modulation for this mobile two-way MCvD system. In addition, we propose the evaluation and discussion about the impacts of several important parameters on the performance of this system. These results can be used to design mobile two-way MCvD system with lower SEP and higher mutual information.

Physical Layer Secrecy by Power Splitting and Jamming in Cooperative Multiple Relay Based on Energy Harvesting in Full-Duplex Network

In this article, we investigated the secrecy performance of a three-hop relay network system with Power Splitting (PS) and Energy Harvesting (EH). In the presence of one eavesdropper, a signal is transferred from source to destination with the help of a relay. The source signal transmits in full-duplex (FD) mood, jamming the relay transfer signals to the destination. The relay and source employ Time Switching (TS) and Energy Harvesting (EH) techniques to obtain the power from the power beacon. In this study, we compared the Secrecy Rate of two Cooperative Schemes, Amplify and Forward (AF) and Decode and Forward (DF), for both designed systems with the established EH and PS system. The Secrecy Rate was improved by 50.5% in the AF scheme and by 44.2% in the DF scheme between the relay and eavesdropper at 40 m apart for the proposed system in EH and PS. This simulation was performed using the Monto Carlo method in MATLAB.

Secure transmission for wireless collaborative systems based on second‐order channel statistics

AbstractIn this article, we investigate the maximum secrecy rates (SRs) and the optimal beamforming schemes for a collaborative wireless network under uncertain channel levels of available second‐order statistics. Both decode‐and‐forward (DF) and amplify‐and‐forward (AF) strategies under the aggregate and individual power constraints are considered. We have derived the maximum SRs and the optimal beamforming vectors under aforementioned conditions and an efficient cooperation paradigm to provide secrecy in a multirelay environment. A closed‐form maximum SR in the DF scheme under aggregate power constraint is presented. Next, the upper and lower bounds for the maximum SR under aggregate power constraint in the AF scheme is derived. The optimization problem in the AF scheme can be converted into a convex semidefinite programming problem, which is efficiently solved by the bisection method. Moreover, the optimal beamforming weights are also obtained to maximize the SRs under both aggregate and individual relay power constraints. Numerical results are provided to demonstrate the effectiveness of proposed algorithms.

A Novel Adaptive and Cooperative Scheme to Save Energy for Wireless Sensor Network

In this paper, we evaluate the performance of a novel cooperative adaptive relaying scheme called ISDF (Incremental Selective Decode and Forward). We compare the energy efficiency of this underlying scheme with direct transmission (DT), Fixed and adaptive relaying schemes in Wireless Sensor Network (WSN). The system is constrained by a minimum value of Signal-to- Noise Ratio (SNR) and the end-to-end throughput. We consider a three-node cooperative system. The relay is equidistant to the source and destination, and then we study different positions of the latter. The destination receives two copies of the message: one from the source and the other from the relay. Then it combines them by using maximal ratio combining (MRC). The proposed scheme differs from other schemes by the combination of the selective decode and forward scheme with the incremental scheme which requires the presence of a feed-back from the destination. The analysis reveals that the proposed ISDF provides good energy efficiency compared to DT and other cooperative schemes. It also shows that DF cooperative scheme (decode and forward , either with feedback or no, is outperformed by AF (amplify and forward) scheme especially when the relay is placed near the destination.

Performance Analysis of Dual-Hop Relaying With I/Q Imbalance and Additive Hardware Impairment

Hardware impairment is common in practical transceivers. This work analyzes the impact of hardware impairment on the performance of dual-hop relaying. In the analysis, both multiplicative I/Q imbalance and additive hardware impairment are considered at all nodes. The outage probabilities of amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes are derived. The AF scheme includes both fixed-gain AF and variable-gain AF. Optimum maximum likelihood detectors are obtained. Numerical results are presented to show the effects of hardware impairment on relaying performances.

Multicast Transmissions With Full-Duplex Amplify-and-Forward User Cooperation

In order to improve the multicast transmissions, a full-duplex (FD) user cooperation scheme is proposed. In this paper, the transmitter sends the common messages to two FD users, and each user forwards its received signals to its counterpart by amplify-and-forward (AF) scheme. Considering the imperfect self-interference (SI) cancellation at the users and the AF scheme, the residual self-interference and the additive noise (RIAN) is shown to be accumulated over time. This paper first analyzes the equivalent channel model of the considered system, as well as the asymptotic statistics of the accumulated RIAN. Then, with the forward and backward decoding schemes, the corresponding achievable rates are derived, and the optimal power allocation is obtained via solving a max-min problem. In particular, one-side cooperation scheme (i.e., only one user forwards its received signal to its counterpart) is shown to be optimal to achieve the best system performance.

Interference Channels With Full-Duplex Amplify-and-Forward Receiver Cooperations

This paper considers a two-transmitter and two-receiver interference channel (IC), where each transmitter sends a message to its desired receiver. In particular, the full-duplex (FD) amplify-and-forward (AF) protocol is adopted to build up the receiver cooperations: each receiver can receive the signals from the two transmitters and two receivers, and after self-interference (SI) cancellation and message decoding, it forwards them to its counterpart. With the above scheme, the equivalent channel model is analyzed, and the statistics of the accumulated residual interference and noise (ARIN), generated by the imperfect SI cancellation and the AF scheme at the receivers, is calculated by mathematical induction. Then, the achievable rate regions of both the single-user and joint decoding schemes are derived. It is proved that one-side cooperation, i.e., only one of the two receivers forwards its counterpart’s signal, is optimal to achieve the best system performance. Next, to characterize the obtained rate regions, the rate maximization problems are formulated and approximately solved by a sequential parametric convex approximation (SPCA) method. Simulation results show that the proposed scheme can improve the achievable rate compared to the conventional non-cooperative scheme in several typical scenarios.

Exploiting hybrid decode-and-forward – amplify-and-forward in NOMA: an application to device-to-device networks

A novel model regarding downlink cooperative non-orthogonal multiple access (NOMA) in device-to-device network will be investigated in this paper, especially combining amplify-and-forward (AF) and decode-and-forward (DF) to achieve a hybrid scheme. We consider a remarkable trade-off between outage performances and power allocation factors. Especially, we study a hybrid AF and DF scheme, namely HDAF scheme for NOMA as follows: 1) The proposed scheme applies the AF scheme when the signal-to-interference-plus-noise ratio (SINR) at the relay is below a predefined threshold such that the relay cannot successfully decode the signal; 2) On the other hand, when the SINR at the relay is greater than the predefined threshold, the system will be applied the DF scheme to decode the signal and then forwards it to the destination, i.e., avoids noise and interference amplification at the relay. An analytical expression of the outage probability of the hybrid HDAF NOMA is derived based on the outage probability function in AF and DF mode. Numerical results are provided to illustrate the influence of network parameters such as transmit power, power constraint, and link distances on the outage probability.

Performance Characterization of Relaying Using Backscatter Devices

In this paper, we examine the error performance of backscatter communication in the presence of ambient interference, where the backscatter device acts as a relay. Specifically, the performance comparison of amplify-and-forward (AF) and decode-and-forward (DF) backscatter relaying is considered for the first time. Considering energy-based detection for on-off keying (OOK) modulation, we derive the statistics of the received signal power, from which the detection thresholds and corresponding bit error rates (BER) are obtained analytically. For the DF scheme, we allow the source node to transmit continuous-wave signals during the relay-to-destination transmission phase to power the backscatter relay. Under a total power budget constraint at the source, we optimize the power allocation for the transmissions in the source-to-relay and relay-to-destination phases. Numerical analysis shows that the DF scheme with optimal power allocation performs similarly compared to the AF scheme, despite the added complexity of the decoding operation. On the other hand, the AF scheme significantly outperforms the DF scheme when the reflection coefficients at the backscatter device do not correspond to perfect OOK. These results provide valuable insights into the design and deployment of backscatter nodes with the goal of improving coverage.

Energy-Efficiency for IoT System With Cache-Enabled Fixed-Wing UAV Relay

This paper studies the energy efficiency (EE) maximization problem of fixed-wing Unmanned aerial vehicles (UAVs) enabled Internet of Things (IoT) system, where an UAV is employed as an aerial relay with enough cache capacity to amplify and forward (AF) received signals between narrow band (NB)-IoT device and eNodeB. This paper optimizes the unconstrained trajectory of the UAV to maximize the EE of UAV-enabled IoT system to achieve the green communication. Due to the objective function is a fraction and is non-convex, it's hard to solve the optimization problem. Therefore, this paper alternately optimizes trajectory in source subspace and destination subspace with the other fixed and comes up with an algorithm based on successive convex approximation (SCA) method and Dinkelbach method to obtain a local optimal solution. Numerical results show that the proposed UAV trajectory design method can obtain much bigger EE than the running track (RT) trajectory and circular trajectory. Besides, the proposed cache-enabled AF strategy can obtain much bigger EE than non cache-enabled AF strategy.

Green RF/FSO Communications in Cognitive Relay-Based Space Information Networks for Maritime Surveillance

In this paper, we provide an overview of a space-based network for the maritime surveillance information sharing and evaluate the coverage, the throughput and the real-time reception capacity of the presented systems. The focus is on the feeder link of a multi-hop geostationary satellite system. We propose a cognitive relay-based architecture for the inter-satellite and satellite-to-ground communication with a multi-band spectrum sensing operating on both free-space optical (FSO) and radio frequency (RF) bands. Furthermore, modeling the spectrum sensing energy as a Gamma distribution we derive the formula of the network energy consumption in presence of multipath fading and considering two different data relay schemes: amplify-and-forward (AF) and decode-and-forward (DF). We prove that the RF/FSO communication in the proposed relay-based architecture enhances the data transmission increasing the throughput and the real-time reception capacity and reducing the network energy consumption. The performance evaluation shows that the DF scheme overcomes the AF one in terms of energy consumption while the AF scheme overcomes the DF one in terms of probability detection, both experience the same throughput. Finally, the proposed novel architecture has been compared with existing ones showing that it enhances the current maritime surveillance systems by jointly optimizing communication functionalities.

Cooperative Non-Orthogonal Multiple Access over Log-Normal Power Line Communication Channels

In this paper, we analyze the performance of cooperative power domain non-orthogonal multiple access (NOMA) in power line communication (PLC) networks. Due to the high signal attenuation of the source to user links, a relay aids communication from the source to two users. With half-duplex transmission, the source transmits a superimposed symbol in the first phase. The relay utilizes amplify-and-forward (AF) and decode-and-forward (DF) protocol on the received superimposed signal and forwards it to the users in the second phase. We derive analytic expressions for the outage probability and the system throughput of the proposed system under a PLC log-normal channel with impulsive noise. Based on the results for AF NOMA relaying case, we analyze the system performance at high signal-to-noise ratio (SNR) and derive closed-form lower and upper bounds for the outage probability. Simulation results show an improvement in the outage probability and the system throughput performance of the AF and DF NOMA schemes compared to the NOMA without relaying transmission and conventional orthogonal multiple access scheme. Furthermore, the impact of the channel variance is highlighted in the results. It is shown that the DF NOMA has a better outage probability than the AF NOMA scheme for low channel variance scenarios (i.e., less branches and connected loads in the PLC network). However, as the channel variance increases, AF NOMA scheme has similar outage probability performance as the DF NOMA scheme. In addition, it is shown that the system throughput is enhanced when the relay employs DF relaying compared to AF relaying.

Exploiting Hybrid Decode-and-Forward - Amplify-and-Forward in NOMA: An application to Device-To-Device Networks

A novel model regarding downlink cooperative non-orthogonal multiple access (NOMA) in device-to-device network will be investigated in this paper, especially combining amplify-and-forward (AF) and decode-and-forward (DF) to achieve a hybrid scheme. We consider a remarkable trade-off between outage performances and power allocation factors. Especially, we study a hybrid AF and DF scheme, namely HDAF scheme for NOMA as follows: 1) The proposed scheme applies the AF scheme when the signal-to-interference-plus-noise ratio (SINR) at the relay is below a predefined threshold such that the relay cannot successfully decode the signal; 2) On the other hand, when the SINR at the relay is greater than the predefined threshold, the system will be applied the DF scheme to decode the signal and then forwards it to the destination, i.e., avoids noise and interference amplification at the relay. An analytical expression of the outage probability of the hybrid HDAF NOMA is derived based on the outage probability function in AF and DF mode. Numerical results are provided to illustrate the influence of network parameters such as transmit power, power constraint, and link distances on the outage probability.

Nelder‐Mead–based power optimization for secrecy enhancement in amplify‐and‐forward cooperative relay networks

SummaryCooperative communication based on relaying nodes has been considered as a promising technique to increase the physical layer security (PLS) performance in wireless communications. In this paper, an optimal power allocation (OPA) scheme based on Nelder‐Mead (NM) algorithm is proposed for improving the secrecy rate of amplify‐and‐forward (AF) cooperative relay networks employing cooperative jamming (CJ) scheme. The proposed hybrid jamming scheme allows the source and selected relay to transmit the jamming signal along with the information to confound the eavesdropper. The path selection probability of ant colony optimization (ACO) algorithm is used for selecting the relay for transmission. The performance based on secrecy rate is evaluated for “n” trusted relays distributed dispersedly between the source and destination. Gradient‐based optimization and three‐dimensional exhaustive search methods are used as benchmark schemes for comparison of the proposed power optimization algorithm. The secrecy performance is also compared with conventional AF scheme and CJ scheme without power optimization (EPA). The impact of single and multiple relays on secrecy performance is also evaluated. Numerical results reveal that, compared with the gradient method and exhaustive search algorithm, the proposed power allocation strategy achieves optimal performance. Also, the derived OPA results show a significantly higher secrecy rate than the EPA strategy for both CJ and AF schemes.

Superposition coded OFDM transmissions in a downlink cooperative relay network based on statistical channel state information

Non-orthogonal multiple access has recently emerged as a promising multiple access technique for future wireless technology. In this study, the authors investigate superposition coding in a downlink cooperative cellular system based on the orthogonal frequency division multiplexing (OFDM) modulation in the presence of frequency selective multipath fading channels, a setup that has not been studied before. Specifically, the base station communicates with two paired mobile users simultaneously via the OFDM modulation with the help of a half-duplex relay under either the decode-and-forward (DF) or amplify-and-forward (AF) scheme, where the power allocation between two mobile users depends on the statistical channel state information (CSI) rather than perfect CSI. They derive the ergodic rate regions under Rayleigh fading channels and present an ad-hoc approach to determine the power splitting parameters when the target data rates are given. Simulation results based on the outage probabilities show that superposition coding consistently outperforms frequency division, however, the relative advantage of the DF and AF schemes in a superposition-coded OFDM relay system depends on the system geometry.

Optimum beam forming in selective-relay cooperative communication using effective capacity approach

Cooperative communication is a precious approach to overcome the interference of multiuser communication and increase data rate of communication system. Many papers are focused on this issue to achieve more efficiency of relay-based communication in view of QoS parameters. Effective capacity is a desired quality parameter that allows maximum constant data rate with guaranteeing delay. Beam forming coefficients are the main factors of transmitted power from relays and the purpose of the paper is to find maximum effective capacity due to the optimum beam forming coefficients allocated to the best-selected relays in Amplify and Forward (AF) strategy. Minimization of outage probability and transmitted power are the constraints of optimization process to keep the quality requirements. After considering effective capacity maximization and generating optimization problem, Lagrange multipliers are used to gain the optimum answer. Simulation results show that optimal power allocation is achievable using the proposed scheme which causes effective capacity maximization in cooperative communication system. Quantitatively stating, using the proposed method, BER is less than other similar AF or DF (Decode and Forward) cooperative strategies in similar systems. Moreover, the transmitted power is at least 1 dBw less than other efficient methods in larger SNR as shown in simulation results.

Individual Channel Estimation Based on Blind Interference Cancellation for Two-Way MIMO Relay Networks

In this paper, we investigate an individual channel estimation problem for multiple-input multiple-output (MIMO) two-way amplify-and-forward (AF) relay networks. To avoid self-interference during the estimation of the individual MIMO channels, a novel blind interference cancellation (BIC) approach is proposed based on an orthogonal preceding framework, where a pair of orthogonal precoding matrices is utilized at the source nodes. By designing an optimal decoding scheme, we propose to decompose the bidirectional transmission into a pair of unidirectional transmissions. Unlike most existing approaches, we make the practical assumption that the nonreciprocal MIMO channel and the mutual interference of multiple antennas are both taken into consideration. Under the precoding framework, we employ an orthogonal superimposed training strategy to obtain the individual MIMO channels. However, the AF strategy causes the noise at the terminal to be the sum of the local noise and the relay-propagated noise. To remove the relay-propagated noise during the estimation of the second-hop channel, a partial noise-nulling method is designed. We also derive a closed-form expression for the total mean square error (MSE) of the MIMO channel from which we compute the optimal power allocation. The simulation results demonstrate that the analytical and simulated curves match fully.