Decode-and-forward Relay Research Articles

Vehicle-to-Vehicle Relay-Assisted VLC With Misalignment Induced Azimuth or Elevation Offset Angles

This letter investigates a vehicle-to-vehicle relay-assisted visible light communications link with amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes and analyze the effect of the relay vehicle's orientation with respect to the source vehicle. Results show up to 150 % increase in the link span under emulated sunlight for the DF relay link compared with AF at the end of the second hop using the same system parameters at the forward error correction bit error rate limit of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . A method to mitigate the effect of system performance degradation due to misalignment between communicating vehicles is also proposed.

Performance Analysis of UAV-Based Mixed RF-UWOC Transmission Systems

In this paper, we investigate the performance of a mixed radio-frequency-underwater wireless optical communication (RF-UWOC) system where an unmanned aerial vehicle (UAV), as a low-altitude mobile aerial base station, transmits information to an autonomous underwater vehicle (AUV) through a fixed-gain amplify-and-forward (AF) or decode-and-forward (DF) relay. The analysis accounts for the main factors that affect the system performance, such as the UAV height, air bubbles, temperature gradient, water salinity variations, detection techniques, and pointing errors. Employing the fixed-gain AF and DF relays, expressions for some key performance metrics are derived, e.g., outage probability (OP), average bit error rate (ABER), and average channel capacity. Moreover, in order to get further insights, asymptotic analyses for the OP and ABER are also carried out. Additionally, for the two relaying systems, we derive analytical expressions for the optimal UAV altitude that minimizes the OP. Simulation results show that the UAV altitude influences the system performance and there is an optimal altitude which ensures a minimum OP. Furthermore, it is demonstrated that the diversity order of the fixed-gain AF relaying depends on the RF link and pointing errors, while the diversity order of the DF relaying depends on the detection techniques and pointing errors.

Outage of NOMA-Based Hybrid Satellite-Terrestrial Multi-antenna DF Relay Networks

This letter analyzes the outage performance of a novel two-user non-orthogonal multiple access (NOMA)-based hybrid satellite-terrestrial relay network (HSTRN), in which one user can directly receive the signals from the satellite while the other user can only acquire its desired signal through a multiple-antenna decode-and-forward (DF) relay. In particular, a novel DF relaying protocol is designed to deal with the unbalanced channel condition and improve the performance for both users. Numerical results are provided to validate our analyses, unveil the impacts of key parameters on the system performance, and demonstrate the advantages of our proposed scheme over other benchmarks.

On the Performance of Cooperative Relaying with Maximum-Ratio Combination (MRC) for mmWave Systems

In this paper, cooperative communication using a two-way relaying network (TWRN) is considered for millimeter-wave (mmWave) communications. Two schemes of TWRN are employed for cooperation and performance evaluation, which are amplify-and-forward (AF) and decode-and-forward (DF) relays. Furthermore, maximum-ratio combination (MRC) is utilized in each node in the proposed systems. It is noteworthy that MRC is exploited in this paper as a channel equalization and also to maximize the strength of the received signals at each node. The performance is evaluated for the proposed systems over 28 and 73 GHz using one and two parallel AF and DF relays in the presence of the direct path. Moreover, compassion between the two frequencies is achieved, via obtaining the bit-error-rate (BER) against different values of signal-to-noise ratios (SNR)’s, by assuming the same distances between the source, relay/relays, and the destination. The results show the outperforming of 28 GHz in this performance metric, i.e. BER-SNR, by using AF relaying, due to the amplification factor added to the signal to compensate for the inherent attenuation in this frequency band. Moreover, the proposed DF relay schemes have limited compensation to the attenuated signals comparing to the AF relay.

Evaluation and Analysis for Maximum Lifespan of Wireless Sensor Networks by Energy-Efficient Design

Wireless Sensor Networks (WSNs) have used worldwide in the past few years and are now being used in health monitoring ,disaster management, defense, telecommunications, etc. Such networks are used in many industrial and consumer applications such as industrial process and environment monitoring, among others. A WSN network is a collection of specialized transducers known as sensor nodes with a communication link distributed randomly in any locations to monitor environmental parameters such as water level, and temperature. Each sensor node is equipped with a transducer, a signal processor, a power unit, and a transceiver. WSNs are now being widely used to monitor environmental parameters, including the amount of gas, water, temperature, humidity, oxygen level, dust, etc. The WSN for environment monitoring can be equivalently replaced by a multiple-input multiple-output (MIMO) relay network. Multi-hop relay networks have attracted significant research interest in recent years for their capability in increasing the coverage range. The network communication link from a source to a destination is implemented using the amplify-and-forward (AF) or decode-and-forward (DF) schemes. The AF relay receives information from the previous relay and simply amplifies the received signal and then forwards it to the next relay. On the other hand, the DF relay first decodes the received signal and then forwards it to the next relay in the second stage if it can perfectly decode the incoming signal. For analytical simplicity, in this thesis, we consider the AF relaying scheme and the results of this work can also be developed for the DF relay.

RIS source decode-and-forward relaying network with interference

We consider in this paper the scenario of reconfigurable intelligent surface (RIS) source decode-and-forward (DF) relaying network with interference. The system includes single source of multiple reflecting elements, multiple DF relays, and single destination with interference at the relays and destination. Assuming Rayleigh fading channels, we obtain closed-form accurate approximations for the outage probability. Additionally, we investigate the behavior at high signal-to-noise ratio (SNR) values where the diversity order and the coding gain are obtained. Findings illustrate that the number of reflecting elements N at the source has a small impact on the system coding gain and not on the diversity gain. Furthermore, results show that the number of relays K is affecting the diversity order and is more impactful on the behavior than N. Findings demonstrate that when N=1, the interference value at the relays and destination is determining, which hop dominates the behavior, whereas when N>1 the behavior is always dominated by the second hop regardless of the interference value.

Spatially Correlated Dual Hop RIS Aided Next Generation Wireless Systems: An Outage Perspective

Design and analysis of Reconfigurable Intelligent Surfaces (RIS) assisted new wireless communication systems have attracted much attention among the 6G technology researchers. Recently, studies were made to compare the use of RIS and Decode and Forward (DF) relaying when a weak direct path exists between the transmitter and receiver. Amalgamating the merits of both RIS and DF relay technologies, an RIS assisted DF relay-based cooperative wireless system with energy harvesting is proposed in this paper. A Lambertian model of reflectance is employed in the analysis of the reflecting nature of RIS. Further, the impact of spatial correlation which arises due to the tightly-packed planar RIS array geometry is also considered for performance analysis. By varying inter-element distances and transmit power, the performance of the proposed system is analyzed in terms of outage probability and energy harvesting capability. Numerical expressions are derived for the outage probability of the proposed system and verified using Monte-Carlo simulations. Based on the high performance, the concept of joint use of RIS and DF Relay is extended to the Index Modulation (IM) based wireless system.

Impairments-Aware Resource Allocation for FD Massive MIMO Relay Networks: Sum Rate and Delivery-Time Optimization Perspectives

In this paper, we investigate the resource allocation problem for a full-duplex (FD) massive multiple-input-multiple-output (mMIMO) multi-carrier (MC) decode and forward (DF) relay system which serves multiple MC single-antenna half-duplex (HD) nodes. In addition to the prior studies focusing on maximizing the sum-rate and energy efficiency, we focus on minimizing the overall delivery time for a given set of communication tasks to the user terminals. As our system is an FD MC system, we consider the impact of hardware distortions resulting in residual self-interference and inter-carrier leakage. We also consider that only limited channel state information is available. A joint power and sub-carrier allocation problem to maximize the sum-rate of the system is then formulated. Due to the intractable nature of the underlying problem, an iterative solution is proposed, employing the successive inner approximation (SIA) framework, with guaranteed convergence to the point that satisfies the Karush-Kuhn-Tucker (KKT) conditions. For the energy efficiency maximization problem, a two-stage iterative algorithm which follows the SIA and Dinkelbach algorithm is proposed. The operation of an FD mMIMO MC DF relay system is evaluated for different system parameters using numerical simulations. We also show the importance of considering delivery time minimization rather than sum-rate maximization, i.e., maximizing the sum-rate of the system does not necessarily minimize the overall delivery time. Numerical results show the significance of distortion-aware design for such systems and also the significant gain in terms of different objectives such as sum-rate, energy efficiency, and delivery time compared to its HD counterpart.

Physical Layer Secrecy Analysis of Multihop Hybrid Satellite‐Terrestrial Relay Networks with Jamming

This paper explores the secrecy analysis of a multihop hybrid satellite‐terrestrial relay network (HSTRN) with jamming, where one satellite source is aimed at communicating with destination users via multihop decode‐and‐forward (DF) terrestrial relays, in the existence of an eavesdropper. All the destination users are deployed randomly following a homogeneous Poisson point process (PPP) based on stochastic geometry. Each relay operates not only as a conventional DF relay to forward the received signal but also as a jammer to generate intentional interference to degrade the eavesdropper link, considering shadowed‐Rician fading for legitimate link and wiretap link while Rayleigh fading for jamming link. To characterize the secrecy performance of the considered network, the accurate analytical expression for the secrecy outage probability (SOP) is derived. In order to reveal further insights on the achievable diversity order of the network, the asymptotic behavior of SOP expression at high signal‐to‐noise ratio (SNR) region is deduced. Moreover, the throughput of the system is discussed to characterize the secrecy performance. Finally, the theoretical results are validated through comparison with simulation results and show that (1) the secrecy performance of the considered network gets better with the decreasing of the hops and with the decreasing severity of the channel fading scenario, (2) the relay of the network operating as a jammer can provide better secrecy performance without extra network resources, and (3) small hops and high SNR can yield to high throughput of the system.

Efficient Hybrid Beamforming Design in mmWave Massive MU-MIMO DF Relay Systems With the Mixed-Structure

In this paper, we consider the decode-and-forward (DF) relay system in millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems, and propose a hybrid beamforming design method for the mixed structure, which contains the fully-connected and sub-connected structures. To satisfy constant-modulus and block-diagonalization (BD) constraints, the analog beamforming is designed by the idea of sorted successive interference cancellation (SSIC). More specifically, the proposed method first sorts the capacities of different analog sub-channels in descending order, and then designs the analog beamforming serially according to the order of the capacities. To efficiently mitigate the inner-user and inter-user interference, we propose a modified baseband BD technology to reduce the information loss in digital beamforming design, thereby improving the system capacity. In addition, the proposed hybrid beamforming algorithm is designed by considering both uniform linear arrays (ULAs) and uniform planar arrays (UPAs). Simulation results demonstrate that the proposed hybrid beamforming design scheme can obtain good performance in terms of the achievable sum-rate and power efficiency in ULAs and UPAs.

Performance of Hybrid RF/FSO Cooperative Systems Based on Quasicyclic LDPC Codes and Space-Coupled LDPC Codes

Free space optical (FSO) communication systems provide wireless line of sight connectivity in the unlicensed spectrum, and wireless optical communication achieves higher data rates compared to their radio frequency (RF) counterparts. FSO systems are particularly attractive for last mile access problem by bridging fiber optic backbone connectivity to RF access networks. To cope with this practical deployment scenario, there has been increasing attention to the so-called dual-hop (RF/FSO) systems where RF transmission is used at a hop followed by FSO transmission to another. In this article, we study the performance of cooperative transmission systems using a mixed RF-FSO DF (decode and forward) relay using error-correcting codes including QC-LDPC codes at the relay level. The FSO link is modeled by the gamma-gamma distribution, and the RF link is modeled by the Additive White Gaussian Noise (AWGN) model. Another innovation in this article is the use of cooperative systems using a mixed FSO/RF DF relay using quasicyclic low-density parity check (QC-LDPC) codes at the relay level. We also use the space-coupled low-density parity check (SC-LDPC) codes on the same scheme to show its importance in cooperative optical transmission but also in hybrid RF/FSO transmission. The latter will be compared with QC-LDPC codes. The use of mixed RF/FSO cooperative transmission systems can improve the reliability and transmission of information in networks. The results demonstrate an improvement in the performance of the cooperative RF/FSO DF system based on QC-LDPC and SC-LDPC codes compared to RF/FSO systems without the use of codes, but also to the DF systems proposed in the existing literature.

Performance analysis of diffusion-based decode-and-forward relay with depleted molecule shift keying

The distance-decay effect of molecular signals makes communication range a major challenge for diffusion-based Molecular Communication (MC). To solve this problem, the intermediate nano-machine is deployed as a relay between the transmitter and its intended receiver nano-machines. In this work, we employ the Depleted Molecule Shift Keying (D-MoSK) to model a Decode-and-Forward (DF) relay communication scheme. The closed-form expression of Bit Error Rate (BER) for the concerned DF relay with D-MoSK is derived. Meanwhile, the maximum a posteriori probability, minimum error probability, and maximum likelihood schemes are formulated for data detection. The relationships between BER and other key parameters, including the number of released molecules, receiving radius, and relay position, are investigated in detail. Simulation results show that the proposed scheme can improve communication reliability significantly. Moreover, the performance gain can be maximized by optimizing the position of the relay and the receiving radius.

Adaptive Relay Selection Strategies for Cooperative NOMA Networks With User and Relay Cooperation

This paper studies a two-user cooperative non-orthogonal multiple access network with a novel cooperation scheme, where the source communicates with the near user directly or through the help of $K$ relays, while the communication to the far user relies on the help of the near user or the $K$ relays. For cases with decode-and-forward (DF) relays and amplify-and-forward (AF) relays, we propose two different two-phase transmission protocols. In each protocol, the near user sends a two-bit feedback (in DF-relay case) or a one-bit feedback (in AF-relay case) to inform relays of its detection results in the first phase. Then based on the limited feedback and the available channel state information at each relay, a relay selection strategy with adaptive selection criteria is proposed for each transmission protocol to minimize the system outage probability (SOP). Tight-approximated as well as asymptotic closed-form expressions of the SOP for both transmission protocols are derived. Asymptotic results illustrate that our proposed adaptive relay selection strategies have the full diversity order of $K+1$ . Furthermore, we analytically prove that when DF relays are used, SOP is smaller than that when AF relays are used.

Joint Time Allocation for Wireless Energy Harvesting Decode-and-Forward Relay-Based IoT Networks With Rechargeable and Nonrechargeable Batteries

This article considers a one-way decode-and-forward (DF) relay-based Internet-of-Things (IoT) network consisting of a source, a relay, and a destination in wireless energy harvesting (EH) and information transmission (IT) using the time switching-based relaying (TSR) protocol. The one-way DF relay network using the TSR protocol consists of some time slots. This article proposes the time allocation scheme for maximizing the achievable data rate under the total block time constraint. It is assumed that the relay is considered the IoT device used for long periods of time without battery replacement and it is equipped with both nonrechargeable and rechargeable batteries. Based on the supplied power by the nonrechargeable battery, the proposed scheme determines whether or not to harvest energy and operates two alternate time allocation schemes. Since the proposed scheme is based on the closed-form expressions, it provides low complexity. Numerical results show that the achievable data rate of the proposed time allocation scheme is greater than that of the fixed time allocation scheme.

Pointing errors influence at the performance of a multi-hop terrestrial FSO link emulated by a dual-hop scheme

The last years, FSO technologies raised interest from both scientific and commercial point of view. However, due to the optical beam propagation through the atmosphere, the signal is impaired by several phenomena like the scintillation effect, mainly because of atmospheric turbulence and imperfect misalignment between optical beam and destination terminal. In order to mitigate their negative influence, various countermeasures have been proposed. A well-known technique to preserve their performance over long distances is the employment of decode-and-forward (DF) relay nodes. Nevertheless, when the signal propagates over composite channels, characterized by atmospheric turbulence along with pointing errors effects, the employment of several DF relays increases significantly the complexity of the mathematical models used for performance evaluation. Motivated by this, we are trying to reduce the complexity of these expressions in the current work by replacing the multi-hop relay configuration via an equivalent dual-hop scheme. For first time, to the best of our knowledge, we are trying to emulate such an FSO system taking into account the simultaneous influence of both, atmospheric turbulence and pointing errors effects, in order to derive closed form mathematical expressions, which can be used in practice for the design of very fast optical wireless communication systems which can be used in the 5G/5G+ networks, mainly as backhaul communication links and support reliable their operation.

VCSEL and LED Based Visible Light Communication System by Applying Decode-and-Forward Relay Transmission

In this investigation, we propose and demonstrate an integrated vertical-cavity surface-emitting laser (VCSEL) and blue light emitting diode (LED) based visible light communication (VLC) system by using the decode-and-forward (DF) relay scheme indoors. The 682 nm visible VCSEL can reach 3 Gbit/s on-off keying (OOK) modulation rate for 4 m free space transmission by applying 1.25 GHz bandwidth PIN photodiode (PD). Then, the VLCVCSEL signal connects to multiple blue LEDs for broadcasting VLCLED traffic in parallel. Therefore, the maximum VLCLED rates of 775, 700, and 600 Mbit/s are obtained at the free space transmission lengths of 2, 3, and 4 m, respectively within the forward error correction (FEC) target under 4 m VLC transmission at the low detected power of 15 μW. In addition, the number of LEDs used in the DF relay VLC system depends on the practical requirement of VLCLED rate and traffic length indoors.

Analysis of DF Relay Selection in Massive MIMO Systems With Hardware Impairments

We consider a massive multiple-input multiple-output (m-MIMO) system in which a source communicates with a destination with the help of multiple single-antenna decode-and-forward (DF) relays. Employing optimal relay selection, we analyze the system performance in presence of hardware impairments (HWI) for two m-MIMO scenarios: massive-antenna source and single-antenna destination (m-MIMO I), and massive-antenna source and destination (m-MIMO II). We obtain lower bounds on the average signal-to-noise plus distortion ratio (SNDR) of the system and show that in the m-MIMO II regime, the HWI levels at the relays become the only limiting factors. Employing extreme value theory, we demonstrate that as the number of relays increases the end-to-end SNDR of the system tends to Gumbel and Weibull distributions for the m-MIMO I and m-MIMO II systems, respectively. In addition, for both arbitrary numbers of source and destination antennas and m-MIMO scenarios, we provide closed form expressions for optimal power allocation between the source and the selected relay, and the effects of HWI level distributions between the receiving and the transmitting parts of the relay (which can be exploited for optimal system design under cost constraints).

Relay selection schemes in threshold DF cooperative systems with wireless power transfer

In this work, a dual-hop cooperative wireless energy harvesting system, in which there are a Source-Destination (S−D) pair and several relay candidates is considered. all relay candidates adopt threshold decode-and-forward (DF) relaying scheme to decide whether to aid S−D pair information transmission or not. We assumed that these relay candidates and S are all equipped with single receiving antenna while D is equipped multiple receiving antenna and adopts generalized selection combining scheme to achieve receiving diversity gain. We also consider that relay candidates and S can harvest energy from D with finite energy storage capacity under time switching scheme. Three kinds of best relay selection (RS) schemes based threshold (TH) DF relay scheme, that is, the TH optimal source-relay link, the TH optimal relay-destination link, and the TH optimal source-relay-destination link, are proposed and studied. Closed-form analytical expressions for the outage probability over the three proposed RS schemes are derived and verified by Monte-Carol simulations.

On the Performance of Battery-Assisted PS-SWIPT Enabled DF Relaying

Compared with the conventional simultaneous wireless information and power transfer (SWIPT) based relaying with “harvest-then-forward” protocol, the battery-assisted SWIPT relaying is more practical and powerful due to the joint use of the harvested energy and supplementary battery. However, to the best of our knowledge, the performance of a battery-assisted power splitting (PS)-SWIPT decode-and-forward (DF) relay system has not been studied. In this paper, for a given amount of energy from the relay’s battery, we propose to maximize the outage and ergodic capacities by optimizing the static and dynamic PS ratios that rely on statistical and instantaneous channel state information (CSI), respectively, and derive their corresponding outage and ergodic capacities. Computer simulations validate our analytical results and demonstrate the advantages of the dynamic PS over the static PS in terms of the outage and ergodic capacities, as well as the energy efficiency.

Optimal power adaptive decode‐and‐forward cooperative device‐to‐device communication policies

Cooperative device-to-device (D2D) wireless systems use relays such as amplify-and-forward (AaF) and decode-and-forward (DaF). The AaF relay is simple to implement but amplifies noise as well. Conventional DaF relay does decoding and acts as a regenerative relay, hence deliver better noise performance. In this study, the authors generalise the cooperative D2D model by designing power adaptive decode-and-forward relays. In it, the probabilistically selected relay subject to an average relay transmit power constraint does decoding and jointly adapt its gain and transmit power as a function of the channel gains to the destination link. For the proposed cooperative D2D system model, the authors derive the optimal relaying policies which set relay gains to (i) minimise the fading averaged symbol error rate; (ii) maximise fading averaged spectral efficiency and (iii) maximise fading averaged energy efficiency. Then they present a comprehensive performance analysis of the optimal policies. The mathematical analysis includes derivations of exact expressions and their upper bound expressions. To further extend the FAvSER analysis, they investigate diversity order in an insightful scaling regime. Then they present extensive numerical results to validate the derived analytical expressions and to show that the proposed optimal relaying policies outperform the benchmark policies.