Decode-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.

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.

Security Performance Analysis for Best Relay Selection in Energy-Harvesting Cooperative Communication Networks

In this paper, we investigate an energy-harvesting cooperative communication network, which comprises of a source, a destination, and multiple decode-and-forward (DF) relays in the presence of multiple passive eavesdropper (Es). Es attempt to intercept confidential information transmissions from the source to destination via DF relays. In this network, all the DF relays harvest energy from radio-frequency (RF) signals of a source through time-switching receivers. In order to improve the physical layer security of energy-harvesting cooperative communication networks, we propose a best relay selection (BRS) scheme, where the “best” relay is chosen to assist the source-destination transmission. For the purpose of comparison, we consider the classic direct transmission (DT) and equal relay selection (ERS) as benchmark schemes. We derive the exact closed-form expressions of outage probability (OP) and intercept probability (IP) for the ERS and BRS schemes over Rayleigh fading channels. Besides, the security-reliability tradeoff (SRT) is analyzed as a metric to evaluate the tradeoff performance of the proposed BRS scheme. Numerical results show that the SRT of the BRS scheme consistently outperforms that of the ERS scheme, which demonstrates the advantage of our proposed scheme against eavesdroppers. Besides, it is verified that total error rate (TER) defined as the sum of OP and IP can be minimized for both the ERS and BRS schemes through changing the time allocation factor between information transmission and energy harvesting phases. Moreover, there is a best energy conversation efficiency to obtain a maximal SRT value of the ERS and BRS schemes. In addition, as the number of DF relays increases, the SRT of BRS scheme improves notably, while that of ERS scheme remains unchanged. And as the number of Es increases, the SRT of both the ERS and BRS schemes become worse.

Performance analysis of a cognitive radio network with adaptive RF energy harvesting

ABSTRACT In this paper, we proposed an adaptive energy harvesting scheme and evaluated the performance of a dual hop cognitive radio network (CRN) under the proposed scheme. We considered a simultaneous wireless information and power transfer (SWIPT) protocol-based transmission of data from a secondary source (SS) to a secondary destination (SD) via a decode and forward (DF) relay. A time switching relay (TSR)-based energy harvesting is used to supply power to the DF relay. The secondary relay (SR) extracts energy from RF signal of SS to derive the transmit power at SR to a level of maximum allowable transmit power satisfying an interference constraint at the primary receiver (PR). To achieve a transmit power to a level of maximum allowable transmit power, the harvesting time duration or time fraction is dynamically adapted for each data frame. Outage probability with proposed adaptive harvesting scheme is derived analytically. A comparative study of the outage and throughput of our proposed adaptive harvesting scheme with a conventional fixed time based harvesting is presented. Finally, the proposed adaptive harvesting scheme is shown to outperform a fixed time-based harvesting scheme.

Buffer-aided relay selection for secure two-hop wireless networks with decode-and-forward relays and a diversity-combining eavesdropper

This paper investigates the buffer-aided relay selection issue for achieving physical layer security (PLS) in two-hop wireless networks with Decode-and-Forward (DF) relays. Available works mainly focus on scenarios with independent-decoding eavesdroppers. However, the more hazardous scenarios with diversity-combining eavesdroppers that combine the signals in two hops to decode the packets are largely ignored. This paper considers a two-hop wireless network with multiple DF relays and one diversity-combining eavesdropper under two cases with perfect and partial eavesdropper channel state information (CSI) respectively. We first propose two secure buffer-aided relay selection schemes to suppress the eavesdropper for both eavesdropper CSI cases respectively. We then derive analytical expressions for the end-to-end (E2E) secure transmission probability (STP) and E2E delay of the network. Finally, we provide extensive simulation and numerical results to validate the correctness of the expressions and also to investigate the E2E STP and E2E delay performances. The results showed that the proposed schemes can achieve better E2E STP performance than the well-known Max-ratio buffer-aided relay selection scheme but at the cost of an increased E2E delay.

Energy Efficiency of a Decode-and-Forward Multiple-Relay Network with Rate Adaptive LDPC Codes.

This paper presents cooperative transmission (CT), where multiple relays are used to achieve array and diversity gains, as an enabling technology for Internet of Things (IoT) networks with hardware-limited devices. We investigate a channel coding aided decode-and-forward (DF) relaying network, considering a two-hop multiple-relay network, where the data transmission between the source and the destination is realized with the help of DF relays. Low density parity check (LDPC) codes are adopted as forward error correction (FEC) codes to encode and decode the data both at the source and relays. We consider both fixed and variable code rates depending upon the quality-of-service (QoS) provisioning such as spectral efficiency and maximum energy efficiency. Furthermore, an optimal power allocation scheme is studied for the cooperative system under the energy efficiency constraint. We present the simulation results of our proposed scheme, compared with conventional methods, which show that if decoupled code rates are used on both hops then a trade-off has to be maintained between system complexity, transmission delay, and bit error rate (BER).

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.

Optimum Design of Energy Harvesting Relay for Two-Way Decode-and-Forward Relay Networks Under Max–Min and Max-Sum Criterions

We study the optimum design of an energy harvesting relay for two-way decode-and-forward (DF) relay networks. In the networks, the relay harvests energy as well as decodes information using the received signal from two sources with power splitting relaying (PSR) and time switching relaying (TSR) strategies. Since the two-way relay network has two opposite traffic flows, it can be considered as a special case of multi-user systems. Applying the max–min criterion for fairness and max-sum criterion for maximum resource utilization, we optimize the operations of the energy harvesting relay. Specifically, considering the transmission rate constraints of individual hops, we derive optimum power splitting coefficients and optimum time switching coefficients, respectively, for PSR-based and TSR-based networks under both criterions, and analytically calculate the resulting maximum transmission rates. Numerical results confirm that our analyses exactly match with exhaustive search simulations. The obtained optimum coefficients are given in closed-form, therefore, they can be easily adopted in simple two-way relay networks with limited computational power such as sensor/Internet of Things (IoT) networks and can help two-way DF relay networks.

Machine Learning-Based Relay Selection for Secure Transmission in Multi-Hop DF Relay Networks

A relay selection method is proposed for physical-layer security in multi-hop decode-and-forward (DF) relaying systems. In the proposed method, cooperative relays are selected to maximize the achievable secrecy rates under DF-relaying constraints by the classification method. Artificial neural networks (ANNs), which are used for machine learning, are applied to classify the set of cooperative relays based on the channel state information of all nodes. Simulation results show that the proposed method can achieve near-optimal performance for an exhaustive search method for all combinations of relay selection, while computation time are reduced significantly. Furthermore, the proposed method outperforms the best relay selection method, in which the best relay in terms of secrecy performance is selected among active ones.

Performance Analysis of FSO DF Relays with Log-Normal Fading Channel

Abstract This paper studies the bit error performance analysis of decode-and-forward (DF) relays-based free-space optical (FSO) communication systems using avalanche photodiode (APD). The system uses subcarrier intensity binary phase shift keying (BPSK) modulated signals and subjects to scintillation due to optical turbulence. A log-normal random process is considered to model the received signal intensity fluctuation for a clear-air condition (weak atmospheric turbulence) scenario. Mathematical expressions of the average bit error probability and bit error rate (BER) are derived by taking into account the impact of atmospheric loss, thermal-noise and shot-noise limited conditions. It can be inferred from the numerical results that using DF relay nodes can extend the transmission distance and minimize BER performance of FSO system significantly compared with the direct transmission. Moreover, the selection of APD’s gain values is essential to minimize the system’s error rate performance. Therefore, the system could achieve the minimal BER by selecting an optimal average APD gain value appropriately. Moreover, the optimal average gain values of APD significantly depend on various conditions, such as the bit rate, total transmitted power, and the number of relay nodes.

Joint Relay Selection and Destination Assisted Cooperative Jamming with Power Allocation for Secure DF Relay Network

To enhance the physical-layer security of a decode-and-forward (DF) cooperative relay network in the presence of a potential eavesdropper, a joint relay selection and destination assisted cooperative jamming (CJ) scheme is proposed. In phase I, the source transmits its confidential signal, and concurrently, it cooperates with the friendly jammers and the destination to send jamming signals to confuse the eavesdropper without affecting the forwarding relay which is preselected. In phase II, the forwarding relay retransmits the decoded signal, and simultaneously, the particular relay cooperates with the friendly jammers to send jamming signal to confuse the eavesdropper without affecting the destination. The achievable secrecy rate maximization (SRM) problem is investigated by optimally allocating the power between the data signal and jamming signals. Although SRM problem is non-convex, the power allocation problem can be solved by a bisection method together with a one-dimensional search. Optimal relay selection and suboptimal relay selection schemes are also proposed to further improve the secrecy rate. Simulation results are presented to show that the joint scheme can attain higher achievable secrecy rates than some existing works.

Intercept Probability Analysis of Cognitive Radio Threshold-Based System With Diversity Reception

The intercept probability performance of decode-and-forward (DF) underlay cognitive radio threshold-based network is investigated in this paper. Here, a secondary source is transferring data to secondary destination via secondary relay cooperation. There are interference limitations on secondary user of cognitive system from the primary licensed users. The DF relays are not assumed to correctly decode the message always and only those relays which can satisfy the predetermined threshold are successful in decoding the source message. The worst case scenario has been studied, where Maximal Ratio Combining (MRC) and Selection Combining (SC) diversity reception schemes have been applied only at eavesdropper. We have obtained asymptotic and diversity analysis for balanced and unbalanced system. The secrecy of the system is shown to be significantly affected by eavesdropper link quality, predetermined threshold and interference power limitations. Furthermore, the optimal relay selection scheme (OS) is presented and the improvement in secrecy performance is shown with the increase in relay number.

Switching-Based Cooperative Decode-and-Forward Relaying for Hybrid FSO/RF Networks

In this paper, we propose a switching scheme for a hybrid free-space optical (FSO)/radio frequency (RF) system with a selective decode-and-forward (DF) relay network. Specifically, the system transmits over FSO channels when the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is greater than the threshold SNR. If the SNR drops below the threshold, the system switches and transmits over RF channels. The exact outage probability and average symbol error rate (SER) expressions are derived for a selective DF relay network with maximal ratio combining (MRC) assumed at the destination. In addition, the asymptotic outage and SER expressions with a lower computational complexity are derived and the diversity order is determined. The optimum value of the threshold SNR, which satisfies the target SER, has been calculated numerically for the proposed switching scheme. The theoretical results, which are validated by Monte Carlo simulations, show that the proposed switching scheme for a cooperative hybrid FSO/RF system drastically improves the performance compared to that of a single-hop (SH) switching-based hybrid FSO/RF and cooperative FSO systems.

Power Splitting-Based SWIPT Systems With Decoding Cost

We study optimal power splitting-based simultaneous wireless information and power transfer (PS-SWIPT) for two communication systems wherein all receiving nodes are subject to a decoding cost. First, for a point-to-point (PtP) channel, the optimal achievable rate is obtained, and then, for a two-hop half-duplex (HD) decode-and-forward (DF) relay channel, the achievable data rate is maximized. Finally, performances of the PtP system and the relay channel with DF and amplify-and-forward (AF) relaying schemes are discussed where we observe performance superiority of the DF relay channel over AF relaying and the PtP channel for sufficiently less decoding cost at the relay than the destination.

Energy Efficiency Maximization for SWIPT Enabled Two-Way DF Relaying

This paper focuses on the design of an optimal resource allocation scheme to maximize the energy efficiency (EE) in a simultaneous wireless information and power transfer (SWIPT) enabled two-way decode-and-forward (DF) relay network under a non-linear energy harvesting model. In particular, we formulate an optimization problem by jointly optimizing the transmit powers of two source nodes, the power-splitting (PS) ratios of the relay, and the time for the source-relay transmission, under multiple constraints including the transmit power constraints at sources and the minimum rate requirement. Although the formulated problem is non-convex, an iterative algorithm is developed to obtain the optimal resource allocation. Simulation results verify the proposed algorithm and show that the designed resource allocation scheme is superior to other benchmark schemes in terms of EE.

A Two-Hop MIMO Relay Architecture Using LTE and Millimeter Wave Bands in High-Speed Trains

In this paper, a novel two-hop relay architecture using mobile relay nodes (MRN) technology for high-speed trains is presented. In this architecture, a long-term evolution advanced (LTE-A) link in sub-6 GHz bands is established between the Donor-eNB (DeNB) and the MRNs mounted on the roof of the train and another in millimeter Wave (mmWave) bands between the MRN and the user equipment (UE) terminals inside the train. Moreover, the multiple-input multiple-output (MIMO) channel is exploited between the DeNB and the UEs to enhance channel capacity. Different relay structures—several relays in a train carriage and a single relay with multiple antennas—and different types of relays—amplify-and-forward and decode-and-forward (DF)—are studied. Ultimately, performance analysis is studied and discussed by means of a downlink-level simulator with accurate channel models. Furthermore, multiuser transmission and conventional user scheduling algorithms are added to obtain a more realistic simulator. A new algorithm for one of the structures and the DF relay is proposed. This paper will examine how to provide broadband data access to train passengers in high-speed environments by validating a new architecture, which takes advantage of MIMO techniques, mobile relays, and millimeter bands.

System Outage Performance for Three-Step Two-Way Energy Harvesting DF Relaying

Wireless energy harvesting (WEH) has been recognized as a promising technique to prolong the lifetime of energy constrained relay nodes in wireless sensor networks. Its application and related performance study in three-step two-way decode-and-forward (DF) relay networks are of high interest but still lack sufficient study. In this paper we propose a dynamic power splitting (PS) scheme to minimize the system outage probability in a three-step two-way energy harvesting DF relay network and derive an analytical expression for the system outage probability with respect to the optimal dynamic PS ratios. In order to further improve the system outage performance, we propose an improved dynamic scheme where both the PS ratios and the power allocation ratio at the relay are dynamically adjusted according to instantaneous channel gains. The corresponding system performance with the improved dynamic scheme is also investigated. Simulation results show that our proposed schemes outperform the existing scheme in terms of the system outage performance and the improved dynamic scheme is superior to the dynamic PS scheme.

NOMA Inspired Cooperative Relaying System Using an AF Relay

In this letter, we propose a cooperative relaying system (CRS) based on non-orthogonal multiple access (NOMA) which uses an amplify-and-forward relay. This letter proposes a novel detection scheme in which the received signals of two consecutive time slots at destination is applied. We calculate asymptotic outage probability and derive diversity order of two for each symbol. Simulations show that our system has much better outage performance than NOMA-based CRS with decode-and-forward (DF) relay. Also, asymptotic ergodic sum rate increases log-linearly with transmit SNR and outperforms NOMA-based CRS with DF relay and conventional CRS. Finally, we verify analytical results by Monte-Carlo simulations.

Impact of Fast Fading CCI on Performance of Optimum Combining in DF Relaying

We present the effect of fast fading co-channel interference (CCI) on the performance of decode-and-forward (DF) relaying. This paper derives closed-form expressions for the average symbol error rate (SER) with optimum combining (OC) in the presence of fast fading CCI. It is shown that the average SER performance of fast fading CCI is worse than that of slow fading CCI, which is the previous research assumption. In result, DF relaying systems should be designed with consideration of fast fading CCI.

Outage Probability of Cognitive DF Relay Systems over Nakagami-m Fading

This paper aims to derive accurate outage probability expressions of a cognitive decode-and-forward (DF) relay system over the Nakagami-m fading channel. A secondary system and a primary system coexist in a spectrum sharing the environment. In order to protect the data transmission of the primary system, the transmission power of the secondary system cannot exceed the tolerable interference threshold of the primary system and its available peak power. In particular, we also consider the impact on the secondary system when the primary system turns on its transmitter. Simulation results align with our theoretical formulas very well.