Hybrid Relay Research Articles

Charge-Then-Cooperate: Secure Resource Allocation for Wireless-Powered Relay Networks With Wireless Energy Transfer

This correspondence studies resource allocation for a wireless-powered relay network, where a hybrid relay with constant energy supply assists an energy-constrained source to send confidential information to a destination in the presence of an eavesdropper. We propose a novel transmission protocol termed charge-then-cooperate to support secure communications in this network. Specifically, the hybrid relay charges the source in the energy transfer phase; then it forwards the confidential information from the source to the destination and concurrently injects jamming signals to combat eavesdropping. We aim to maximize the secrecy rate of the system via a joint optimization of power allocation and time assignment. To solve the formulated highly non-convex problem, we develop an efficient two-layer optimization algorithm that involves the one-dimensional search, the alternating optimization method, the successive convex approximation technique, and the Lagrange duality method. Simulation results demonstrate that the proposed scheme can guarantee a satisfactory secrecy rate.

Discrete Phase Shifters-Based Hybrid Precoding for Full-Duplex mmWave Relaying Systems

This paper considers the hybrid precoding design with quantized phase shifters (PSs) for full-duplex millimeter-wave relaying systems, in which the relay node is equipped with PSs of different resolution levels. The joint optimization of relay hybrid precoding and discrete PSs is a high-dimensional non-convex problem with both higher-order polynomial and modulus constraints. To solve this challenging problem, the optimization function under the imperfect channel state information (CSI) is reformulated into a low-complexity norm-minimization form equation. Then, a relaxed algorithm based on the alternating direction method of multipliers and quantization steps is proposed to obtain the coupling approximate solutions for the above optimized equation. And the optimality of analytical solutions is guaranteed based on the imposed termination criterion and necessary conditions. Furthermore, given the requirement of arbitrary quantization, the trade-off between spectral efficiency (SE) and energy efficiency (EE) is investigated under the imperfect CSI. Numerical results verify that the hybrid precoding with low-resolution PSs can achieve excellent SE close to the full-resolution one but with a considerably lighter burden of energy consumption. Moreover, the transmission power plays a positive role in compensating quantization loss, but the excessive value will bring the reduction of EE.

Secure Multiuser Scheduling for Hybrid Relay-Assisted Wireless Powered Cooperative Communication Networks With Full-Duplex Destination-Based Jamming

In this paper, we investigate secure communication in a hybrid relay (HR)-assisted wireless powered cooperative communication network (WPCCN), where an eavesdropper tries to intercept the data transmitted by a source user and the HR simultaneously. The HR has the ability to wireless powered the energy-constrained multiple users in the downlink and to relay the received confidential information in the uplink. In particular, the full-duplex destination-based jamming (FD-DBJ) strategy is exploited to improve the secrecy performance. Moreover, in order to conduct effective secure communications, we design two multiuser scheduling schemes, i.e., random user selection (RUS), and best user selection (BUS) based on the main channel quality. In order to evaluate the secrecy performance, we analytically derive the energy outage probability (EOP), the secrecy outage probability (SOP), and the hybrid outage probability (HOP), respectively. As such, we formulate the secrecy throughput (ST) maximization problem to optimize the predetermined transmission rate. Our analysis and numerical results reveal that: 1) The BUS scheme has better security performance. 2) Both of the energy conversion efficiency and the number of users have a positive effect on secrecy performance. 3) The FD-DBJ scheme is an effective method to achieve secure communications. 4) The time-switching factor and predetermined transmission rate have a crucial influence on the secrecy performance, which should be considered carefully in system design.

Spectral and Energy Efficiency for Large-Scale Multiple-Input-Multiple-Output Two-Way Hybrid Relaying With Multi-Pair Users Under Imperfect Channel State Information

Herein, we investigate the system spectral efficiency (SSE) and system energy efficiency (SEE) for massive two-way multiple-input-multiple-output (MIMO) relaying networks while considering imperfect channel state information (CSI) with $K$ -pair users in the presence of the hybrid relaying processing. First, we obtain the general expression of the signal-to-interference-and-noise-ratio (SINR) for the considered system when the antenna number of the relay station (RS) $M$ tends to be significantly large. Next, we consider the power scaling scheme (PSS) and achieve asymptotic SSE and SEE. We set the pilot sequence transmit power $P_{P}$ to be fixed $P_{P}$ and variable $P_{P}$ . For a nonvanishing SINR, we achieve different power scaling cases under fixed and variable $P_{P}$ . For a fixed $P_{P}$ value, the optimal PSS of the SSE can be obtained when the transmit power of each user can be scaled by $M$ , whereas that of the SEE can be achieved when the transmit power of both the RS and each user terminal can be reduced by $M$ . Based on the variable value of $P_{P}$ , the optimal PSS’ of both the SSE and the SEE can be used when the transmit power of both RS and each user can be scaled by $M^{1/3}$ . Thus, we conclude that the required SSE and SEE performances can be attained in multi-pair massive MIMO two-way relaying networks with a considerably low transmit power at RS and/or the transmit power of each user. The analytical results for the same are validated via simulation.

LoLa4SOR: Leveraging Successive Transmissions for Low-Latency Buffer-Aided Opportunistic Relay Networks

Buffer-aided (BA) relaying improves the diversity of cooperative networks often at the cost of increasing end-to-end packet delays. This characteristic renders BA relaying unsuitable for delay-sensitive applications. However, the increased diversity makes BA relaying appealing for ultra-reliable communications. Towards enabling ultra-reliable low-latency communication (URLLC), we aim at enhancing BA relaying for supporting delay-sensitive applications. In this paper, reliable full-duplex (FD) network operation is targeted and for this purpose, hybrid relay selection algorithms are formulated, combining BA successive relaying (SuR) and delay- and diversity-aware (DDA) half-duplex (HD) algorithms. In this context, a hybrid FD DDA algorithm is presented, namely LoLa4SOR, switching between SuR and HD operation. Additionally, a low-complexity distributed version is given, namely d-LoLa4SOR, providing a trade-off among channel state information requirements and performance. The theoretical analysis shows that the diversity of LoLa4SOR equals to two times the number of available relays $K$ , i.e., $2K$ , when the buffer size $L$ is greater than or equal to 3. Comparisons with other HD, SuR and hybrid algorithms reveal that LoLa4SOR offers superior outage and throughput performance while, the average delay is reduced due to SuR-based FD operation and the consideration of buffer state information for relay-pair selection. d-LoLa4SOR, as one of the few distributed algorithms in the literature, has a reasonable performance that makes it a more practical approach.

Midpoint Relay Selection Using Social Trust and Battery Level to Enhance Throughput in Cooperative Device-to-Device Communications.

Device-to-device communications in underlay mode has emerged as a promising way to enhance spectrum efficiency in cellular networks. Recently, relay selection in D2D communications underlaying cellular networks is gaining more research interest. In this paper, we propose two relay selection schemes for D2D communications underlaying cellular networks, Midpoint Relay Selection using Social Trust and Battery Level (MRS-ST-BL) and Midpoint Relay Selection using Social Distance and Battery Level (MRS-SD-BL). These proposed schemes utilize battery power level information of devices together with social trust information of users in the network for relay selection. For performance evaluation, initially we show that the throughput of state-of-the-art schemes Hybrid Relay Selection (HRS) and our previously proposed schemes Midpoint Relay Selection using Social Trust (MRS-ST) and Midpoint Relay Selection Using Social Distance (MRS-SD) decrease, when relays have varying battery power. Then, we compare the performance of our proposed schemes against existing schemes including HRS, MRS-ST and MRS-SD. The performance comparison is done at various social trust scenarios and device densities. We show that our proposed schemes can significantly improve the throughput of D2D communications, particularly when relays have different battery power levels in weak social trust scenarios. Finally, we show that the performance of our proposed scheme MRS-ST-BL varies with the change in battery power threshold.

Quantum evolutionary algorithm hybridized with Enhanced colliding bodies for optimization

New methods based on meta-heuristic approaches for solving hard problems have become efficient tools in many disciplines such as engineering, computer science, mathematics, and some other fields. Quantum-inspired evolutionary algorithms, one of the three main research areas related to the complex interaction between quantum computing and evolutionary algorithms, are receiving renewed attention. The original version of the quantum evolutionary algorithm (QEA) uses Q-bit individuals in binary code analogous to genes in the conventional genetic algorithm and the concept of quantum computing. Getting stuck in local optimum in some case studies is considered a weakness of primary QEA and makes access to the high standard deviation in statistical analysis. The idea of a combination of two or more methods can create a new approach with augmented features of all the combined methods. QECBO, as a high-level relay hybrid technique, is a new quantum version of the ECBO, which combines ECBO with the property of the quantum particle. QECBO gives quantum particle properties to colliding bodies of solution. The main idea of QECBO originates from the concept of quantum particle behavior in delta potential well and Schrödinger's uncertainty principle addition to Newtonian collision laws. It seems that the QECBO utilizes the rules of uncertainty inside classical mechanics. This paper is devoted to the assessment of the QECBO using some well-known benchmark optimization problems. In addition to less sensitive to population size, the quality of obtained results implies that QECBO utilizes an advanced approach to search solution space based on ECBO and balances exploration and exploitation concepts by using uncertainty laws. The inclination of the agents to the best solution in each iteration could provide a better chance to find an optimal solution. Also, efficient randomization due to uncertainty laws helps the algorithm to escape from the local optimum. Attained statistical results show the QECBO could be a new advanced method that would avoid local optimum and provide an excellent balance between intensification and diversification.

A Bandit Approach for Mode Selection in Ambient Backscatter-Assisted Wireless-Powered Relaying

Backscattering assisted wireless-powered communication combines ultralow-power backscatter transmitters with energy harvesting devices. This paper investigates the transmission mode selection problem of a hybrid relay that forwards data by switching between the active wireless-powered transmission and the passive ambient backscattering. It first presents a hybrid relay system model and derives its end-to-end success probability under theoretically optimal, but practically unrealistic, conditions. The transmission mode selection is then formulated as a stochastic two-armed bandit problem in a varying environment where the distributions of rewards are nonstationary. The proposed model selection scheme does not assume to have access to any channel states or network conditions, but merely relies on learning from past transmission records. Numerical analyses are performed to validate the proposed bandit-based mode selection approach.

On the Capacity Regions of Degraded Relay Broadcast Channels with and without Feedback.

The four-node relay broadcast channel (RBC) is considered, in which a transmitter communicates with two receivers with the assistance of a relay node. We first investigate three types of physically degraded RBCs (PDRBCs) based on different degradation orders among the relay and the receivers’ observed signals. For the discrete memoryless (DM) case, only the capacity region of the second type of PDRBC is already known, while for the Gaussian case, only the capacity region of the first type of PDRBC is already known. In this paper, we step forward and make the following progress: (1) for the first type of DM-PDRBC, a new outer bound is established, which has the same rate expression as an existing inner bound, with only a slight difference on the input distributions; (2) for the second type of Gaussian PDRBC, the capacity region is established; (3) for the third type of PDRBC, the capacity regions are established both for DM and Gaussian cases. Besides, we also consider the RBC with relay feedback where the relay node can send the feedback signal to the transmitter. A new coding scheme based on a hybrid relay strategy and a layered Marton’s coding is proposed. It is shown that our scheme can strictly enlarge Behboodi and Piantanida’s rate region, which is tight for the second type of DM-PDRBC. Moreover, we show that capacity regions of the second and third types of PDRBCs are exactly the same as that without feedback, which means feedback cannot enlarge capacity regions for these types of RBCs.

A Hybrid Relay and Intelligent Reflecting Surface Network and Its Ergodic Performance Analysis

This letter proposes a novel hybrid relay and Intelligent Reflecting Surface (IRS) assisted system for future wireless networks. We demonstrate that for practical scenarios where the amount of radiated power and/or the number of reflecting elements are/is limited, the performance of an IRS-supported system can be significantly enhanced by utilizing a simple Decode-and-Forward (DF) relay. Tight upper bounds for the ergodic capacity are derived for the proposed scheme under different channel environments, and shown to closely match Monte-Carlo simulations.

Capitalizing Backscatter-Aided Hybrid Relay Communications With Wireless Energy Harvesting

In this work, we employ multiple energy harvesting relays to assist information transmission from a multi-antenna hybrid access point (HAP) to a receiver. All the relays are wirelessly powered by the HAP in the power-splitting (PS) protocol. We introduce the novel concept of hybrid relay communications, which allows each relay to switch between two radio modes, i.e., the active RF communications and the passive backscatter communications, according to its channel and energy conditions. We envision that the complement transmissions in two radio modes can be exploited to improve the overall relay performance. As such, we aim to jointly optimize the HAP's beamforming, individual relays' radio mode, the PS ratio, and the relays' collaborative beamforming to enhance the throughput performance at the receiver. The resulting formulation becomes a combinatorial and non-convex problem. Thus, we firstly propose a convex approximation to the original problem, which serves as a lower bound of the relay performance. Then, we design an iterative algorithm that decomposes the binary relay mode optimization from the other operating parameters. In the inner loop of the algorithm, we exploit the structural properties to optimize the relay performance with the fixed relay mode in the alternating optimization framework. In the outer loop, different performance metrics are derived to guide the search for a set of passive relays to further improve the relay performance. Simulation results verify that the hybrid relaying communications can achieve 20% performance improvement compared to the conventional relay communications with all active relays.

Hybrid Massive MIMO Two-Way Relaying With Users and Relay Hardware Impairments

Most of the existing spectral efficiency (SE) investigations for massive multi-input multi-output (MIMO) relaying assume that each antenna has a dedicated radio-frequency (RF) chain with high-quality user and relay hardware. We consider a hybrid massive MIMO multi-pair two-way half-duplex relay, wherein each RF chain steers multiple antennas and assume that both users and relay have hardware impairments. We derive i) a novel closed-form SE expression using large-scale approximation; and ii) asymptotic SE expressions for two different power scaling schemes. We numerically demonstrate that i) a hardware-impaired hybrid relay has measurably degraded SE than a hardware-impaired conventional full-RF chain relay; and ii) the impact of hardware impairments do not vanish asymptotically as $N\rightarrow \infty$ , mainly due to users hardware impairments.

Hybrid Precoding Design for Two-Way Relay-Assisted Terahertz Massive MIMO Systems

Hybrid precoding has emerged as a promising technique to reduce the hardware cost and complexity in millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems. However, due to the drastic increase in the number of user devices and higher data rate demand, new frequency bands (i.e., terahertz (THz) communications) are needed to explore. At THz frequencies, the precoding technique can provide a large beamforming gain, but still, the blockage and high path-loss remain a significant problem. To overcome the blockage problem, in this paper, we introduce the two-way relay design where the well-known two-way amplify-and-forward (AF) relay in THz-MIMO orthogonal frequency-division multiplexing (OFDM) systems is employed. The optimal two-way relay hybrid precoding problem is non-convex due to the practical hardware constraints (i.e., unit-modulus and block-diagonal constraints). To solve this problem, we first propose to use mathematical manipulations to remove the block-diagonal constraints from its analog part and then reformulate the original two-way relay hybrid precoding problem into a quadratic-convex problem with only power constraint. Finally, we obtain the closed-form solution for the two-way relay hybrid precoding problem. Simulation results reveal that our proposed solution can achieve better sum-rate and energy efficiency than existing hybrid schemes.

Outage and Throughput Analysis of Spectrum Sharing Cognitive Radio Network Incorporating Energy Harvesting Hybrid Relay

In this paper, cooperative spectrum sharing in cognitive radio (CR) network is incorporated with multi-antenna based RF energy harvesting relays (EH). The performance has been analyzed in the presence of multiple primary users. The relays can harvest energy from source signal and interference from primary transmitter. The relays follow adaptive hybrid protocol (AHR) for forwarding the received signal from source to destination. Outage probability and achievable throughput have been analyzed using a time-splitting relaying (TSR) scheme at the destination where best relay selection (BRS) strategy is used. The outage performances of energy harvesting and non-energy harvesting model have been compared. Throughput and outage performance comparison for AF, DF and AHR have been analyzed. The effect of the number of primary users is also investigated. A trade-off is shown between the number of relays and the number of antennas to achieve the desired throughput. The results depict that the use of energy harvesting strategy in cognitive radio network can result in an energy-efficient solution for future wireless communication.

Efficient Resource Allocation for Relay-Assisted Computation Offloading in Mobile-Edge Computing

In this article, we consider the problem of relay assisted computation offloading (RACO), in which user A aims to share the results of computational tasks with another user B through wireless exchange over a relay platform equipped with mobile edge computing capabilities, referred to as a mobile edge relay server (MERS). To support the computation offloading, we propose a hybrid relaying (HR) approach employing two orthogonal frequency bands, where the amplify-and-forward scheme is used in one band to exchange computational results, while the decode-and-forward scheme is used in the other band to transfer the unprocessed tasks. The motivation behind the proposed HR scheme for RACO is to adapt the allocation of computing and communication resources both to dynamic user requirements and to diverse computational tasks. Within this framework, we seek to minimize the weighted sum of the execution delay and the energy consumption in the RACO system by jointly optimizing the computation offloading ratio, the bandwidth allocation, the processor speeds, as well as the transmit power levels of both user $A$ and the MERS, under practical constraints on the available computing and communication resources. The resultant problem is formulated as a non-differentiable and nonconvex optimization program with highly coupled constraints. By adopting a series of transformations and introducing auxiliary variables, we first convert this problem into a more tractable yet equivalent form. We then develop an efficient iterative algorithm for its solution based on the concave-convex procedure. By exploiting the special structure of this problem, we also propose a simplified algorithm based on the inexact block coordinate descent method, with reduced computational complexity. Finally, we present numerical results that illustrate the advantages of the proposed algorithms over state-of-the-art benchmark schemes.

Ambient Backscatter-Assisted Wireless-Powered Relaying

Internet-of-Things (IoT) features with low-power communications among a massive number of ubiquitously-deployed and energy-constrained electronics, e.g., sensors and actuators. To cope with the demand, wireless-powered cooperative relaying emerges as a promising communication paradigm to extend data transmission coverage and solve energy scarcity for the IoT devices. In this paper, we propose a novel hybrid relaying strategy by combining wireless-powered communication and ambient backscattering functions to improve the applicability and performance of data transfer. In particular, the hybrid relay can harvest energy from radio frequency (RF) signals and use the energy for active transmission. Alternatively, the hybrid relay can choose to perform ambient backscattering of incident RF signals for passive transmission. For the operation of the hybrid relaying, selecting a proper mode based on the network environment is the key to better relaying performance. To address this issue, we design mode selection protocols to coordinate between the active and passive relaying in the cases with and without instantaneous channel state information (CSI) of active transmission, respectively. In the former case, since the hybrid relay is aware of whether the two relaying modes are applicable for the current time slot based on the CSI, it selects active relaying if applicable due to higher capacity and selects passive relaying otherwise. In the latter case, the hybrid relay first explores the two relaying modes and commits to the mode that achieves more successful transmissions during the exploration period. With different mode selection protocols, we characterize the success probability and ergodic capacity of a dual-hop relaying system with the hybrid relay in the field of randomly located ambient transmitters. The analytical and the numerical results demonstrate the effectiveness of the mode selection protocols in adapting the hybrid relaying into the network environment and reveal the impacts of system parameters on the performance of the hybrid relaying. As applications of our analytical framework which is computationally tractable, we formulate optimization problems based on the derived expressions to optimize the system parameters with different objectives. The optimal solutions exhibit a tradeoff between the maximum energy efficiency and target success probability.

Joint design of beamforming and time switching/power splitting for wireless-powered multi-antenna dual-relay network

In this paper, we consider a wireless-powered dual-relay network consisting of one multi-antenna source, two single-antenna energy-constrained relays and one single-antenna destination without direct source to destination link. In order to establish the communication flow, the energy-constrained relays harvest energy from the radio frequency transmitted by the source firstly, then exploit the harvested energy to forward the source information to the destination based on distributed space time coding (DSTC). Under this network architecture, three decode-and-forward (DF) technique-based relaying protocols, i.e., time switching-based relaying (TSR) protocol, power splitting-based relaying (PSR) protocol, and hybrid relaying (HR) protocol, are considered to drive the energy transfer and information transmission. To maximize the network throughput, the joint design for the optimal energy and information beamforming vectors employed at the source, the optimal time switching, and power splitting ratios under these three protocols are investigated and solved efficiently by employing simple sequential optimization approach or alternating optimization approach. Simulations are conducted to show the superior performance achieved by our proposed scheme. Moreover, we find that the TSR protocol outperforms the PSR protocol in the low signal-to-noise ratio (SNR) region, while the latter outperforms the former in the high SNR region. And the HR protocol achieves the best performance in any SNR region. At the same time, the effect of the relays’ locations on the throughput performance of these three protocols is also investigated.

Transceiver Design for Massive MIMO Two-Way Half-Duplex AF Hybrid Relay With MIMO Users

We consider a multi-pair two-way amplify-and-forward massive multi-input multi-output (MIMO) hybrid relay with MIMO user-pairs. We employ block-diagonalization-based digital baseband processing at the hybrid relay to cancel the inter user-pair interference, and equal-gain-combining-based radio-frequency (RF) processing to maximize the beamforming gain. We then construct digital relay precoder and the user precoder/decoders using generalized singular value decomposition (GSVD). We also optimize the following for the proposed GSVD transceiver. First, the network transmit power subject to per-stream quality-of-service (QoS) constraints. Second, rate of the transmit stream with the worst signal-to-noise ratio. Finally, sum-rate subject to the per-stream QoS constraints. We numerically show that the proposed hybrid relay has only marginally inferior performance than a full RF chain relay for the three optimization metrics. We also demonstrate the efficacy of the proposed GSVD design over another state-of-the-art transceiver design.

A Novel Approach of Cooperative Sharing Based On Hybrid Relaying Scheme of Chase Algo and Decode and Forward Using Fuzzy Logic in Cognitive Radio

International Journal of Computer Sciences and Engineering (A UGC Approved and indexed with DOI, ICI and Approved, DPI Digital Library) is one of the leading and growing open access, peer-reviewed, monthly, and scientific research journal for scientists, engineers, research scholars, and academicians, which gains a foothold in Asia and opens to the world, aims to publish original, theoretical and practical advances in Computer Science,Information Technology, Engineering (Software, Mechanical, Civil, Electronics & Electrical), and all interdisciplinary streams of Computing Sciences. It intends to disseminate original, scientific, theoretical or applied research in the field of Computer Sciences and allied fields. It provides a platform for publishing results and research with a strong empirical component. It aims to bridge the significant gap between research and practice by promoting the publication of original, novel, industry-relevant research.

Sampling of feces during daytime is sufficient when titanium dioxide is used to estimate organic matter digestibility in equine

Hybrid metaheuristics have proven to be effective at solving complex real-world problems. However, designing hybrid metaheuristics is extremely time consuming and requires expert knowledge of the different metaheuristics that are hybridized. In previous work, the effectiveness of automating the design of relay hybrid metaheuristics has been established. A genetic algorithm was used to determine the sequence of hybridized metaheuristics and the parameters of the metaheuristics in the hybrid. This study extends this idea by automating the design of each metaheuristic involved in the hybridization in addition to automating the design of the hybridization. A template is specified for each metaheuristic, defining the metaheuristic in terms of components. Manual design of metaheuristics usually involves determining the components of the metaheuristic. In this study, a genetic algorithm is employed to determine the components and parameters for each metaheuristic as well as the sequence of hybridized metaheuristics. The proposed genetic algorithm approach was evaluated by using it to automatically design hybrid metaheuristics for two problem domains, namely, the aircraft landing problem and the two-dimensional bin packing problem. The automatically designed hybrid metaheuristics were found to perform competitively to state-of-the-art hybridized metaheuristics for both problems. Future research will extend these ideas by looking at automating the derivation of metaheuristic algorithms without predefined structures specified by the templates.