Decode-forward Research Articles

Fuzzified power allocation scheme for relay network

This paper presents a new fuzzified power allocation strategy that maximizes achievable secrecy rates while limiting overall transmit power. The fuzzy weight value obtained by determining the rules based on the weights obtained through the sequential update process. Also, it considers the outage probability of multi-source network-coded Device-2-Device (D2D) multicast with predetermined relays in the proposed fuzzified power allocation strategy. Multiple cooperative relays on each hop are also considered, to perform cooperative beamforming in the presence of multiple eavesdroppers. Enhancement in the secrecy rate us also assured along with power allocation. Numerical outcomes are presented to investigate the secrecy capacity obtained by the fuzzy based power allocation in multi-hop Decode & Forward (DF) relay networks and to confirm the enhancement of the proposed power allocation scheme by yielding the secrecy rate as 0.148. From the results, the energy efficiency of the proposed method based on Rayleigh h=1 is 5.74, and it is 4.18%, and 1.92% better than the extant ICBD and NCDMC methods. In addition, the proposed work initially had a very low energy efficiency of 2.6864 (at the ns=8) but eventually reached the highest energy efficiency of 7.194 as it approached the ns=2.

Secrecy Performance by Power Splitting in Cooperative Dual-Hop Relay Wireless Energy Harvesting

In wireless communication systems, for secure communication between a transmitter and receiver over the communication channel, the physical layer security is widely utilized. The paper presents a dual-hop wireless full-duplex relay (FDR) network with a source relay and destination relay between two nodes and listening devices. The relay and source use energy harvesting to gain energy from power beacon. Two cooperative techniques are utilized to investigate the amplify-forward (AF) and decode-forward (DF) secrecy capacity in the energy harvesting power splitting system. It is shown that the secrecy performance of an AF relay is better than the secrecy performance of a DF relay in the given form. At 40-meter distance between the relay and the eavesdropper in an energy harvesting system, the AF relay outperforms the DF relay. The simulation is performed using the Monte-Carlo method in MATLAB.

Cooperative SWIPT MIMO-NOMA for Reliable THz 6G Communications

In this paper, cooperative simultaneous wireless information and power transfer (SWIPT) terahertz (THz) multiple-input multiple-output (MIMO) nonorthogonal multiple access (NOMA) are considered. The aim is to improve wireless connectivity, resource management, scalability, and user fairness, as well as to enhance the overall performance of wireless communications and reliability. We optimized the current wireless communication systems by utilizing MIMO-NOMA technology and THz frequencies, exploring the performance and gains obtained. Hence, we developed a path-selection mechanism for the far user to enhance the system performance. The EH SWIPT approach used to improve THz communications performance was investigated. Moreover, we proposed a reliable transmission mechanism with a non-LoS (NLoS) line of THz communications for open areas or any location where the intelligent reflecting surface (IRS) cannot be deployed, in addition to using the cheap decode-forward (DF) relaying instead of IRS. The performance and scalability of the upgradeable system were examined, using adjustable parameters and the simplest modulation scheme. The system presents a noticeable improvement in energy efficiency (EE) and spectral efficiency (SE), in addition to reliability. Accordingly, the outcome showed an improvement in the overall reliability, SE, EE, and outage probability as compared to the conventional cooperative networks of the recent related work (e.g., cooperative MIMO-NOMA with THz) by multiple times with a simpler design, whereas it outperformed our previous work, i.e., cooperative SWIPT SISO-NOMA with THz, by more than 50%, with a doubled individual user gain. This system reduces the transceiver hardware and improves reliability with increasing transmission rates.

Performance Analysis of Intelligent Reflecting Surfaces in Multi-Input-Single-Output Indoor Hotspot Environment

The evolution of 5G and beyond is boosting the development of telecommunication technology. In the future communication system, achievable rate and energy efficiency become the main aspects due to highly reliable and low latency requirements. Applying multiple antennas and applying cooperative communication scenarios to the system may enhance the network's performance. Intelligent reflecting surfaces (IRS) and relaying protocols are some examples of cooperative communication applications. IRS is multiple two-dimensional meta-surface elements that can reflect the incoming signal to get the desirable beam-forming based on its phase. While the relay is a device that can be used to enhance the performance of the networks based on its protocols such as amplify forward (AF) and decode forward (DF). Accordingly, this paper studies an IRS supporting MISO transmission and compares it with the relay deployment scenario. As a result, IRS has higher performance compared with any other scenario, and adding more IRS elements may enhance the achievable rate.

Performance analysis of RF-FSO communication systems over the Málaga distribution channel with pointing error

Free Space Optical (FSO) communication systems are used for high speed, secure and cheaper optical connectivity between users. It can transport the data from a suitable relay which is multiplexing many RF users to the receiver. These kind of networks are known as dual hop and asymmetric RF-FSO links. In this work, such an RF-FSO cooperative system is studied which is based on the Decode-Forward (DF) relaying method. For the analysis, the generalized channel models are considered such that the existing results can be expressed under more generic performance expressions. The outage probability is initially derived for this system and subsequently the average bit error rate (ABER) is derived using it. The cooperative diversity performance is also investigated by deriving the asymptotic expressions for these metrics at high received signal-to-noise ratio (SNR).

Secrecy Analysis in NOMA Full-Duplex Relaying Networks With Artificial Jamming

Non-orthogonal multiple access (NOMA) is an important technology for the forthcoming 5 G and beyond. However, its privacy often suffers from adversarial eavesdropping, especially for the users with higher transmit power. In this paper, we propose a jamming-aided secure transmission scheme for cooperative NOMA networks with a full-duplex (FD) relay. In this scheme, two pairs of users perform secure transmission with the help of a decode-forward (DF) relay, which forwards information and generates artificial jamming to counteract eavesdropping. The precoding vectors are designed to zero-force the artificial jamming at legal receivers. Then, the channel statistics are calculated, based on which the secrecy rates of legitimate signals are analyzed and the expressions of secrecy outage probability (SOP) are derived. Furthermore, three benchmark schemes are also presented with their performance analyzed to verify the advantage of the proposed scheme. Simulation results show the accuracy of our analysis, and demonstrate that the proposed scheme can effectively reduce the SOP and improve the effective secrecy throughput via artificial jamming and FD relaying.

On the Capacity Regions of Cloud Radio Access Networks With Limited Orthogonal Fronthaul

Uplink and downlink cloud radio access networks are modeled as two-hop ${K}$ -user ${L}$ -relay networks, whereby small base-stations act as relays for end-to-end communications and are connected to a central processor via orthogonal fronthaul links of finite capacities. Simplified versions of network compress–forward (or noisy network coding) and distributed decode–forward are presented to establish inner bounds on the capacity region for uplink and downlink communications, that match the respective cutset bounds to within a finite gap independent of the channel gains and signal to noise ratios. These approximate capacity regions are then compared with the capacity regions for networks with no capacity limit on the fronthaul. Although it takes infinite fronthaul link capacities to achieve these “fronthaul-unlimited” capacity regions exactly, these capacity regions can be approached approximately with finite-capacity fronthaul. The total fronthaul link capacities required to approach the fronthaul-unlimited sum-rates (for uplink and downlink) are characterized. Based on these results, the capacity scaling law in the large network size limit is established under certain uplink and downlink network models, both theoretically and via simulations.

Broadcast Approach for the Information Bottleneck Channel

This work considers a layered coding approach for efficient transmission of data over a wireless block fading channel without transmitter channel state information (CSI), which is connected to a limited capacity reliable link, known as the bottleneck channel. Two main approaches are considered, the first is an oblivious approach, where the sampled noisy observations are compressed and transmitted over the bottleneck channel without having any knowledge of the original information codebook. The second approach is a non-oblivious decode-forward (DF) relay where the sampled noisy data is decoded, and whatever is successfully decoded is reliably transmitted over the bottleneck channel. The bottleneck channel from relay to destination has a fixed capacity $C$ . We examine also the case where the channel capacity can dynamically change due to variable loads on the backhaul link. The broadcast approach is analyzed for cases that only the relay knows the available capacity for next block, and for the case that neither source nor relay know the capacity per block, only its capacity distribution. Fortunately, it is possible to analytically describe in closed form expressions, the optimal continuous layering power distribution which maximizes the average achievable rate. Numerical results demonstrate the achievable broadcast rates.

Capacity Analysis of an AF Relay Cooperative NOMA System Using MRC

Non-orthogonal multiple access (NOMA) is widely studied in both academia and industry due to its high spectral efficiency over orthogonal multiple access (OMA). To effectively improve spectrum efficiency, an amplify-and-forward (AF) cooperative NOMA system is proposed as well as a novel detection scheme is proposed, in which we first perform successive interference cancellation (SIC) twice at U1 for the two signals received from two time slots to remove interference from symbol 2, then two new signals apply max ratio combining (MRC). In addition, a closed-form upper bound approximation for the ergodic capacity of our proposed system is derived. Monte-Carlo simulations and numerical analysis illustrate that our proposed system has better ergodic capacity performance than the conventional cooperative NOMA system with decode-forward (DF) relay, the conventional cooperative NOMA system with AF relay and the proposed AF cooperative NOMA system in [16]. In addition, we can see that ergodic capacity of all NOMA cooperative systems increase with the increase of transmit SNR. Finally, simulations display that power allocation coefficients have little effect on ergodic capacity of all NOMA cooperative systems. This is due to this fact that ergodic capacity of two symbols can be complementary with changing of power allocation coefficients.

On Cooperative Achievable Rates of UAV Assisted Cellular Networks

In this paper, we study an UAV base station (UBS) assisted cellular network that consists of a single ground macro base station (MBS), multiple UBSs, and multiple ground terminals. We assume that the MBS transmits to the UBSs and the terminals in the licensed band while the UBSs use a separate unlicensed band (e.g., Wi-Fi) to transmit to the terminals. For the utilization of the UBSs, we propose a cooperative decode-forward (DF) protocol in which multiple UBSs assist the terminals simultaneously while maintaining a predetermined interference level on the coexisting unlicensed band users. For our network setup, we formulate a joint optimization problem for minimizing the aggregate gap between the target rates and the throughputs of terminals by optimizing over the 3D positions of the UBSs and the resources (power, time, bandwidth) of the network. To solve the optimization problem, we propose an efficient nested structured algorithm based on particle swarm optimization and convex optimization methods. Extensive numerical evaluations of the proposed algorithm is performed considering various aspects to demonstrate the performance of our algorithm and the gain for utilizing UBSs.

A Unified Framework for HS-UAV NOMA Networks: Performance Analysis and Location Optimization

In this paper, we propose a unified framework for hybrid satellite/unmanned aerial vehicle (HSUAV) terrestrial non-orthogonal multiple access (NOMA) networks, where satellite aims to communicate with ground users with the aid of a decode-forward (DF) UAV relay by using NOMA protocol. All users are randomly deployed to follow a homogeneous Poisson point process (PPP), which is modeled by the stochastic geometry approach. To reap the benefits of satellite and UAV, the links of both satellite-to-UAV and UAV-to-ground user are assumed to experience Rician fading. More practically, we assume that perfect channel state information (CSI) is infeasible at the receiver, as well as the distance-determined path-loss. To characterize the performance of the proposed framework, we derive analytical approximate closed-form expressions of the outage probability (OP) for the far user and the near user under the condition of imperfect CSI. Also, the system throughput under delay-limited transmission mode is evaluated and discussed. In order to obtain more insights, the asymptotic behavior is explored in the high signal-to-noise ratio (SNR) region and the diversity orders are obtained and discussed. To further improve the system performance, based on the derived approximations, we optimize the location of the UAV to maximize the sum rate by minimizing the average distance between the UAV and users. The simulated numerical results show that: i) there are error floors for the far and the near users due to the channel estimation error; ii) the outage probability decreases as the Rician factor K increasing, and iii) the outage performance and system throughput performance can be further improved considerably by carefully selecting the location of the UAV.

On Residual Energy Maximization in DF Cognitive Radio Networks With Multiple Eavesdroppers

This paper explores the issues of energy harvesting (EH) and multiple eavesdropping in an underlay cognitive radio network (CRN) that comprises of a secondary transmitter ( $SU_{\mathcal {T}}$ ) and destination ( $SU_{\mathcal {D}}$ ) node connected through a decode-forward (DF) relay ( $S_{\mathcal {R}}$ ). CRN is operated following a frame structure that includes three non-overlapping slots where in the first one, the relay harvests energy from the information signal of $SU_{\mathcal {T}}$ and the interference signal of primary user (PU). During the second slot, $SU_{\mathcal {T}}$ transmits data to the relay node. In the last slot, $S_{\mathcal {R}}$ forwards the same to $SU_{\mathcal {D}}$ and $SU_{\mathcal {T}}$ does EH from PU signal. Residual energy maximization is done under the constraints of energy causality for $SU_{\mathcal {T}}$ and $S_{\mathcal {R}}$ , interference to PU, secondary outage probability and secrecy outage probability. Analytical expressions of ergodic secrecy capacity and secrecy outage probability are derived for non-colluding (NCE) and colluding eavesdropping (CE) scenarios. Closed form expressions for the optimal transmit power of $SU_{\mathcal {T}}$ and $S_{\mathcal {R}}$ along with the time slot for EH are derived and their impacts on the residual energy, secondary outage probability and secrecy outage probability are analysed. Simulation results show a gain on the maximum value of the residual energy by ~8.13% for CE and ~4.72% for NCE over the existing works.

End-to-End Performance Analysis of Underwater Optical Wireless Relaying and Routing Techniques Under Location Uncertainty

On the contrary of low speed and high delay acoustic systems, underwater optical wireless communication (UOWC) can deliver a high speed and low latency service at the expense of short communication ranges. Therefore, multihop communication is of utmost importance to extend the range, improve degree of connectivity, and overall performance of underwater optical wireless networks (UOWNs). In this regard, this paper investigates relaying and routing techniques and provides their end-to-end (E2E) performance analysis under the location uncertainty. To achieve robust and reliable links, we first consider adaptive beamwidths and derive the divergence angles under the absence and presence of a pointing-acquisitioning-and-tracking (PAT) mechanism. Thereafter, important E2E performance metrics (e.g., data rate, bit error rate, transmission power, amplifier gain, etc.) are obtained for two potential relaying techniques; decode & forward (DF) and optical amplify & forward (AF). We develop centralized routing schemes for both relaying techniques to optimize E2E rate, bit error rate, and power consumption. Alternatively, a distributed routing protocol, namely Light Path Routing (LiPaR), is proposed by leveraging the range-beamwidth tradeoff of UOWCs. LiPaR is especially shown to be favorable when there is no PAT mechanism and available network information. In order to show the benefits of multihop communications, extensive simulations are conducted to compare different routing and relaying schemes under different network parameters and underwater environments.

A Deep Study on Layered Multi-Relay Non-Orthogonal Amplify-Forward Networks

The paper introduces a cross-layer design for transmission of Successive Refinement (SR) source code interplayed with non-orthogonal layered code, deployed over a half-duplex multi-relay Non-orthogonal Amplify-Forward (NAF) network. Assuming the Channel State Information (CSI) is not available at the source node, firstly the achievable layered Diversity-Multiplexing Tradeoff (DMT) curve is derived. Then, by taking Distortion Exponent (DE) as the figure of merit, several achievable lower bounds are proved and the optimal expected distortion performance under high Signal to Noise Ratio (SNR) approximation is explicitly obtained. It is shown that the proposed coding can achieve the Multi-Input Single-Output (MISO) upper bound under certain regions of bandwidth ratios, by which the optimal performance in these regions can be explicitly characterized. Further the non-orthogonal layered coding scheme is extended to a multi-hop MIMO Decode-Forward (DF) relay network and set of DE lower bounds is derived. Simulation results confirm the effectiveness of the proposed scheme under general SNR values and compared with its counterparts.

Multi-relay Antennas for Energy Harvesting Cognitive Radio Networks using Energy-Assisted Decode Forward Method

The single antenna relay energy-assisted decode forward (EDF) was not applicable for multi cognitive users that has less data rates. In order to achieve higher data rates with increased user demands energy harvesting or Simultaneous Wireless Information and Power Transfer (SWIPT) enabled networks with multi antenna relays are highly recommended. The proposed work considers multi relay EDFSWIPT for 5G systems with presence of transmitter and an antenna array. The transmitter affords data and power towards various numerous single-antenna secondary receivers (SR). The SR outfitted with a power splitter receiving system where multiple primary relays are introduced. The goal of proposed work is to amplify weighted sum rate harvested energy for SR using multi relay EDF. The simulation considers the capacity, outage probability, and throughput for both primary and secondary networks with respect to both single multi relay EDF. The simulation results afford that multi relay EDF has better performance than single antenna array EDF.

Optimal Transmitted Molecules and Decision Threshold for Drift-Induced Diffusive Molecular Channel With Mobile Nanomachines.

We study a drift-induced diffusive mobile molecular communication system where source, destination and cooperative nanomachines follow the one-dimensional Brownian motion. For information exchange from source nanomachine to receiver nanomachine, both direct and decode-forward (DF) relay-assisted cooperative paths are considered. The closed-form expressions for the probabilities of detection and false alarm are derived at the cooperative and destination nanomachines considering the multiple-source interference (MSI) and the inter-symbol-interference (ISI). The closed-form expressions for end-to-end average probability of error, and maximum achievable rate are also obtained. Moreover, to achieve minimum expected probability of error the optimum number of molecules to be transmitted from transmitter and optimal detection threshold in receiver nanomachine are found. The analytical expressions are validated through particle-based and Monte-Carlo simulation methods.

Quasi-Concavity for Gaussian Multicast Relay Channels.

Standard upper and lower bounds on the capacity of relay channels are cut-set (CS), decode-forward (DF), and quantize-forward (QF) rates. For real additive white Gaussian noise (AWGN) multicast relay channels with one source node and one relay node, these bounds are shown to be quasi-concave in the receiver signal-to-noise ratios and the squared source-relay correlation coefficient. Furthermore, the CS rates are shown to be quasi-concave in the relay position for a fixed correlation coefficient, and the DF rates are shown to be quasi-concave in the relay position. The latter property characterizes the optimal relay position when using DF. The results extend to complex AWGN channels with random phase variations.

Deep Learning Detection in MIMO Decode-Forward Relay Channels

We consider a signal detection problem by using deep learning techniques in a multiple-input multiple-output (MIMO) decode-forward (DF) relay channel. There exist some suboptimal detectors such as the near maximum likelihood (NML) detector and the NML with two-level pair-wise error probability (NMLw2PEP) detector in the channel. However, the NML detectors require an exponentially increasing complexity as the number of transmit antennas increases. More seriously, without the channel state information (CSI) of the source-relay (SR) link, there is no detector that can achieve good performance even at high complexity. In this paper, we propose a deep learning approach to the NML (DL-NML) detector that achieves good performance with low complexity regardless of whether the CSI of the SR link is known or not at the destination. The DL-NML detector can detect signals in changing channels after a single training by using randomly generated channels. Furthermore, we propose a linear detector and a semidefinite relaxation approach to the NML detector to compare with the DL-NML detector in performance and complexity. The complexity analysis and simulation results validate the superiority of the proposed DL-NML detector.

Cooperative Hybrid VLC-RF Systems With Spatially Random Terminals

In this paper, a cooperative hybrid visible light communication (VLC)-radio frequency (RF) relay system, which includes a transmitter (S) with a cluster of light emitting diodes (LED) lamps, a relay (R), and a destination (D), is taken into consideration. Moreover, decode-forward (DF) and amplify-forward (AF) schemes are considered at R to aid the data transmissions between S and D. Specially, R is randomly located in the coverage of the LED lamps, D is randomly distributed out of the coverage of the LED lamps. Then, VLC is employed for S-R link, and a traditional RF communication technology is adopted over the R-D link. Considering Nakagami- $m$ fading over the R-D link, and the randomness of the locations of R and D, the statistical characteristics of the received signal-to-noise ratio at D under AF scheme, and the ones at R and D under the DF scheme are characterized, respectively. Subsequently, approximated analytical and asymptotic expressions for the outage probability of the considered system are derived, as well as the approximated expression for the average symbol error rate of M-ary quadrature amplitude modulation scheme under the DF scheme. Finally, simulation and numerical analysis are conducted to verify the correctness of our proposed models.

A Hybrid Adaptive Relay Technique for Cooperative Communication System

Cooperative communication will increase the channel capacity, when the communicating terminals exceed more than two. Therefore, a relay is termed, as three-terminal unit is a fundamental for user cooperation. The cooperation provides throughput enhancement, reliability, and coverage improvement for wireless communication. Relay technique plays a vital role in cooperative communication in terms of increasing coverage range as well as spectral efficiency. In existing techniques Amplify Forward increase the noise and Decode Forward increase the computational cost of the receiver. In order to overcome the above limitation, a hybrid adaptive relay technique is proposed for cooperative communication system, which will initially check the channel quality of the end user received SNR. When the receiver does not able to decode the message, then the user will choose relay signal. We derived a closed form expression to find the outage probability and channel capacity for the Rayleigh fading channel. Finally, simulation results show the performance of proposed adaptive relay technique in comparison with traditional relay technique by considering both perfect and imperfect CSI.