Multi-relay Selection Research Articles

An Energy-Efficiency Multi-Relay Selection and Power Allocation Based on Deep Neural Network for Amplify-and-Forward Cooperative Transmission

In this letter, an energy-efficiency (EE) resource allocation strategy is investigated for the amplify-and-forward (AF) protocol used to forward data to the destination. First, we formulate an EE optimization problem of multi-relay AF system, which correlates the power of source with the power of each relay. Then, a deep neural network (DNN)-based model is constructed to implement the joint power allocation of source and multiple relays. In particular, we adopt the modified rectified linear unit (ReLU) as the activation function in the output layer of the DNN model to hinder relays’ negative output power weightings, thereby to simultaneously realize the selection of relays and their power allocation. The simulation results show that our scheme enables better performance in term of the EE of system compared with the conventional strategies and convolutional neural network (CNN).

Joint User Scheduling, Relay Selection, and Power Allocation for Multi-Antenna Opportunistic Beamforming Systems.

Opportunistic beamforming (OBF) is a potential technique in the fifth generation (5G) and beyond 5G (B5G) that can boost the performance of communication systems and encourage high user quality of service (QoS) through multi-user selection gain. However, the achievable rate tends to be saturated with the increased number of users, when the number of users is large. To further improve the achievable rate, we proposed a multi-antenna opportunistic beamforming-based relay (MOBR) system, which can achieve both multi-user and multi-relay selection gains. Then, an optimization problem is formulated to maximize the achievable rate. Nevertheless, the optimization problem is a non-deterministic polynomial (NP)-hard problem, and it is difficult to obtain an optimal solution. In order to solve the proposed optimization problem, we divide it into two suboptimal issues and apply a joint iterative algorithm to consider both the suboptimal issues. Our simulation results indicate that the proposed system achieved a higher achievable rate than the conventional OBF systems and outperformed other beamforming schemes with low feedback information.

Multi-relay selection scheme for cooperative QAM-FBMC based broadband PLC systems

Selecting the appropriate modulation technique is a major concern in designing reliable broadband power line communication (BPLC) systems. Orthogonal Frequency Division Multiplexing (OFDM) was gaining more attention as a multi-carrier modulation (MCM) technique for cooperative BPLC. Nevertheless, OFDM has some drawbacks that degrade the BPLC performance. Here, the author first proposes a new Quadrature Amplitude Modulation-Filter-Bank Multicarrier (QAM-FBMC) transceiver to improve the bit error rate (BER) performance and to achieve higher throughput in BPLC-based systems. Furthermore, an opportunistic multi-parameter-based multi-relay selection (OMP-MRS) scheme is proposed to future improve the performance of cooperative BPLC-based systems. In this regard, the analytical expressions for outage probability and system throughput are derived and validated with Monte Carlo simulations. The optimal parameters that maximise the BPLC performance are obtained via exhaustive search. The proposed scheme harvesting the high amount of noise exists in PLC, especially impulsive noise to further improve the energy efficiency. Numerical and simulation results validate the consistency of the analytical model and its derivations. Results reveal that the proposed OMP-MRS scheme outperforms the existing multi-relay selection schemes presented in literature with an acceptable computational complexity.

Multi-relay selection strategy in two-hop amplify-and-forward relay network based on deep learning

Multi-relay selection strategy in two-hop amplify-and-forward relay network based on deep learning

Throughput and Energy Efficiency of Cooperative ARQ Strategies for VANETs Based on Hybrid Vehicle Communication Mode

Vehicular ad-hoc networks (VANETs) are promising research areas which mainly include three communication modes: vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and hybrid vehicle communication (HVC). But most of the current research on HVC mode in which vehicle nodes and infrastructures coexist only focuses on the analysis of the optimal single-type relay selection schemes. Inspired by this, in order to design an optimal multi-relay selection scheme which can select different types of relays simultaneously, and to compare it with single-type schemes, this paper firstly introduces a more practical network scenario by proposing a four-node system model which considers communication links between relays and building different channel models for different types of links. Four optimal relay selection protocols, which are named as Non-OR, SOR-AP, SOR-V and DOR-APV respectively, are then designed from the perspective of the different types and numbers of selected relays. The exact expressions of outage probability for each protocol are calculated based on the automatic repeat request (ARQ) protocol to evaluate the link interruption of the four protocols. Furthermore, this paper establishes a generalized 2-dimensional discrete time Markov chain (DTMC) model and analyzes the one-step state transition probability for each protocol. The closed-form expressions of system throughput and energy efficiency are derived by calculating the steady state distribution of the DTMC. Finally, the simulation results summarize the suitable network scenarios for which the four proposed protocols are recommended by comparing their system performance, so as to provide some suggestions for the future design and optimization of vehicle mobile networks.

Security Performance Analysis of Joint Multi-Relay and Jammer Selection for Physical-Layer Security under Nakagami-m Fading Channel

Security Performance Analysis of Joint Multi-Relay and Jammer Selection for Physical-Layer Security under Nakagami-m Fading Channel

Multi-relay selection in energy-harvesting cooperative wireless networks: game-theoretic modeling and analysis

This paper studies distributed multi-relay selection in energy-harvesting cooperative wireless networks and models it as an Indian Buffet Game (IBG). Particularly, the IBG is utilized to model the multi-relay selection decisions of network source nodes, while accounting for negative network externality. Two scenarios are considered: (1) constrained selections (CS), and (2) unconstrained selections (US). In the former scenario, each source is constrained to a maximum number of relay selections; while in the latter scenario, the source nodes can select as many relays as possible. Since the relays are energy-harvesting—and thus intermittently harvest random amounts of energy—the accumulated energy at each relay is unknown to the source nodes, leading to uncertain relays’ energy states. In turn, a non-Bayesian learning (NBL) algorithm is devised for the source nodes to learn the relays’ energy states. After that, two distributed best-response (BR) recursive algorithms, namely BR-CS and BR-US, are proposed to allow the source nodes to make multi-relay selection decisions, while guaranteeing subgame perfect Nash equilibrium. Simulation results are presented to verify the efficacy of the proposed distributed NBL and multi-relay selection algorithms. Specifically, the NBL is shown to efficiently learn the true relays’ energy states. More importantly, the BR-CS algorithm is shown to be comparable to the centralized multi-relay selection—and superior to other relay selection schemes—in terms of network sum-rate improvement (and utility). Lastly, the number of relay selections of the BR-CS algorithm must be constrained to the minimum so as to reduce complexity and fully exploit diversity gains.

Learning-based multi-relay selection for cooperative networks based on compressed sensing

Cooperative relaying is an effective technology to improve the secrecy capacity of physical-layer (PHY) security. Multiple relays can help further exploit the spatial diversity of cooperative networks. In power-limited networks, relay selection scheme is crucial important for it determines whether the optimal relay combination can be selected. This paper studies the problem of multi-relay selection in amplify-and-forward compressed sensing (AF-CS) networks, in which relays help all sources amplify and forward the signal, and the transmission matrix is used as the measurement matrix to encrypt the information. A self-organizing algorithm based on stochastic learning automata (SLA) is proposed for the AF-CS network to look for the best relay combination in a self-learning and self-optimizing way, and named “learning-based multi-relay selection algorithm” (L-MRS). In L-MRS, the destination node is self-optimizing to select the best state autonomously, and relays are self-organizing to decide whether to join the cooperation or not according to the environment feedback. Simulation studies verify the L-MRS’s is able to select the optimal relay-combination in a very stable way, and can get higher secrecy capacity compared with the coalition formation game method.

Time-Switching EH-Based Joint Relay Selection and Resource Allocation Algorithms for Multi-User Multi-Carrier AF Relay Networks

In this paper, an energy efficiency maximization (EEM) optimization problem for the multi-user multi-carrier energy-constrained amplify-and-forward (AF) multi-relay network is formulated under the total source transmit power budget and energy-causality constraints. We consider that each relay node is solely powered by the source nodes, employing energy harvesting time-switching (EHTS) protocol to harvest the energy through the ambient radio-frequency (RF) signal transmitted from the source nodes under the simultaneous wireless information and power transfer (SWIPT) paradigm. First, we propose a subcarrier and energy causality-based multi-relay selection policy. Second, we jointly optimize the parameters that control the energy efficiency (EE) of the system namely multi-relay selection, subcarrier pairing, user allocation, power allocation, and RF EHTS time block, that renders the problem to be a mixed integer non-linear programming problem (MINLP) which remains NP-hard to solve. Hence, we remodel the problem to a tractable quasi-concave form by applying a string of convex transformations. Later, we propose an iterative EEM algorithm to optimize the multi-parameter problem. Further, a suboptimal and best relay selection algorithm is studied by trading-off between complexity and performance. The effectiveness of the proposed algorithms is demonstrated by simulation results.

A Triple-Parameter Based Multi-Relay Selection Strategy for Wireless-Powered Cooperative Network

This paper studies a wireless-powered cooperative network consisting of a single source, multiple wireless-powered relays, and a single destination. The relays harvest radio frequency energy from the source, decode the information, and use beamforming to forward the information to the destination. We develop a triple-parameter-based multi-relay selection (TPMRS) strategy to determine how to assign the energy harvesting and information decoding tasks to different relays. By modeling the TPMRS strategy as a finite state Markov chain, we derive the stationary distribution of each state and obtain an analytical expression of the system throughput. The optimal parameters that maximize the system throughput are obtained via exhaustive search. The numerical and simulation results validate the correctness of the model and derivations. In addition, our proposed TPMRS strategy outperforms the existing multi-relay selection scheme.

Impact of Hardware Impairments on Outage Performance of Hybrid Satellite-Terrestrial Relay Systems

The hardware impairments of transceiver nodes that generate signal distortions degrade the reliability performance of communication systems. This paper investigates the impact of hardware imperfections on the outage performance of hybrid satellite-terrestrial relay systems (HSTRS), where a geosynchronous earth orbit (GEO) satellite transmits its data to the terrestrial destination with the help of decode-and-forward (DF) terrestrial relays. We consider that all network nodes are subjected to hardware impairments and propose a multi-relay selection (MRS) scheme to enhance the outage performance of the HSTRS. The traditional single-relay selection (SRS) scheme is also considered for comparison purposes. We derive closed-form outage probability expressions for both the SRS and MRS schemes. Moreover, an asymptotic outage probability analysis is carried for both the SRS and MRS schemes in the high signal-to-noise-ratio (SNR) region. The simulation results show that the outage performance of the HSTRS can be enhanced under the MRS scheme with a certain level of hardware impairments at the HSTRS. Compared to the condition of ideal hardware, the outage probability of HSTRS increases for both the SRS and MRS schemes if the hardware is not ideal. When the amplify-and-forward (AF) protocol is employed at relays, the outage performance of HSTRS degrades compared to that of DF for both the SRS and MRS schemes.

Joint Relay Selection and Power Allocation through a Genetic Algorithm for Secure Cooperative Cognitive Radio Networks

In cooperative cognitive radio networks (CCRNs), there has been growing demand of transmitting secondary user (SU) source information secretly to the corresponding SU destination with the aid of cooperative SU relays. Efficient power allocation (PA) among SU relays and multi-relay selection (MRS) are a critical problem for operating such networks whereas the interference to the primary user receiver is being kept below a tolerable level and the transmission power requirements of the secondary users are being satisfied. Subsequently, in the paper, we develop the problem to solve the optimal solution for PA and MRS in a collaborative amplify-and-forward-based CCRNs, in terms of maximizing the secrecy rate (SR) of the networks. It is found that the problem is a mixed integer programming problem and difficult to be solved. To cope with this difficulty, we propose a meta-heuristic genetic algorithm-based MRS and PA scheme to maximize the SR of the networks while satisfying transmission power and the interference requirements of the networks. Our simulation results reveal that the proposed scheme achieves near-optimal SR performance, compared to the exhaustive search scheme, and provides a significant SR improvement when compared with some conventional relay selection schemes with equal power allocation.

Distributed Multi-Relay Selection in Accumulate-Then-Forward Energy Harvesting Relay Networks

This paper investigates a wireless-powered cooperative network (WPCN) consisting of one source-destination pair and multiple decode-and-forward relays. We develop an energy threshold based multi-relay selection (ETMRS) scheme for the considered WPCN. The proposed ETMRS scheme can be implemented in a fully distributed manner as the relays only need local information to switch between energy harvesting and information forwarding modes. By modeling the charging/discharging behaviors of the finite-capacity battery at each relay as a finite-state Markov chain, we derive an analytical expression for the system outage probability of the proposed ETMRS scheme over mixed Nakagami- ${m}$ and Rayleigh fading channels. Based on the derived expression, the optimal energy thresholds for all the relays corresponding to the minimum system outage probability can be obtained via an exhaustive search. However, this approach becomes computationally prohibitive when the number of relays and the associated number of battery energy levels are large. To resolve this issue, we propose a heuristic approach to optimize the energy threshold for each relay. To gain some useful insights for practical relay design, we also derive the upper bound for system outage probability corresponding to the case that all relays are equipped with infinite-capacity batteries. Numerical results validate our theoretical analysis. It is shown that the proposed heuristic approach can achieve a near-optimal system performance and our ETMRS scheme outperforms the existing single-relay selection scheme and common energy threshold scheme.

Relay Selection for Improving Physical-Layer Security in Hybrid Satellite-Terrestrial Relay Networks

In this paper, a hybrid satellite-terrestrial relay network (HSTRN) interconnecting a satellite and multiple terrestrial nodes is considered, where communication is achieved by the satellite transmitting information to a destination through multiple relays at the appearance of an eavesdropper attempting to intercept the transmissions from both the satellite and relays. We present the single-relay selection and multi-relay selection as well as round-robin scheduling schemes to investigate the physical-layer security of this considered HSTRN by adopting the decode-and-forward relay strategy. Specifically, in a single-relay selection scheme, a relay is chosen as the “best” relay which has the maximum instantaneous capacity of relay-destination channel out of the decoding relay set, which is composed of all the relays capable to decode the received signals from the satellite successfully. By contrast, in a multi-relay selection scheme, all relays of the decoding relay set are invoked simultaneously to aid the satellite communicating with the destination. Moreover, suppose that only the main channels’ state information is known while the wiretap channels’ state information is unavailable due to the passive eavesdropper, we analyze the secrecy performance in accordance with secrecy outage probability of the HSTRN by driving out the closed-form expressions for the single-relay selection and baseline round-robin scheduling schemes, as well as by computer simulations for multi-relay selection scheme. Numerical results show that the two relay selection schemes generally outperform the round-robin scheduling baseline scheme in the light of improving the secrecy performance of HSTRN even when the legitimate links are inferior to the wiretap links.

Quantum Bee Colony Optimization and Non-dominated Sorting Quantum Bee Colony Optimization Based Multi-relay Selection Scheme

In cooperative multi-relay networks, the relay nodes which are selected are very important to the system performance. How to choose the best cooperative relay nodes is an optimization problem. In this paper, multi-relay selection schemes which consider either single objective or multi-objective are proposed based on evolutionary algorithms. Firstly, the single objective optimization problems of multi-relay selection considering signal to noise ratio (SNR) or power efficiency maximization are solved based on the quantum bee colony optimization (QBCO). Then the multi-objective optimization problems of multi-relay selection considering SNR maximization and power consumption minimization (two contradictive objectives) or SNR maximization and power efficiency maximization (also two contradictive objectives) are solved based on non-dominated sorting quantum bee colony optimization (NSQBCO), which can obtain the Pareto front solutions considering two contradictive objectives simultaneously. Simulation results show that QBCO based multi-relay selection schemes have the ability to search global optimal solution compared with other multi-relay selection schemes in literature, while NSQBCO based multi-relay selection schemes can obtain the same Pareto front solutions as exhaustive search when the number of relays is not very large. When the number of relays is very large, exhaustive search cannot be used due to complexity but NSQBCO based multi-relay selection schemes can still be used to solve the problems. All simulation results demonstrate the effectiveness of the proposed schemes.

Power Allocation and Relay Selection in Relay Networks: A Perturbation-Based Approach

A perturbation-based power allocation and multirelay selection approach is proposed for multiple-input multiple-output relay networks in multipath fading channels. In this approach, the relays are partitioned into two groups according to Lagrangian multipliers of power constraints. The power allocation for the relays is perturbed by increasing the power for the potential relay's group, while decreasing the power of the relays in the other group. An optimization framework is then formulated as a tradeoff between the relay selection and the mean square error performance degradation. Computer simulations are used to demonstrate the performance.

Optimized Power Allocation and Relay Location Selection in Cooperative Relay Networks

An incremental selection hybrid decode-amplify forward (ISHDAF) scheme for the two-hop single relay systems and a relay selection strategy based on the hybrid decode-amplify-and-forward (HDAF) scheme for the multirelay systems are proposed along with an optimized power allocation for the Internet of Thing (IoT). Given total power as the constraint and outage probability as an objective function, the proposed scheme possesses good power efficiency better than the equal power allocation. By the ISHDAF scheme and HDAF relay selection strategy, an optimized power allocation for both the source and relay nodes is obtained, as well as an effective reduction of outage probability. In addition, the optimal relay location for maximizing the gain of the proposed algorithm is also investigated and designed. Simulation results show that, in both single relay and multirelay selection systems, some outage probability gains by the proposed scheme can be obtained. In the comparison of the optimized power allocation scheme with the equal power allocation one, nearly 0.1695 gains are obtained in the ISHDAF single relay network at a total power of 2 dB, and about 0.083 gains are obtained in the HDAF relay selection system with 2 relays at a total power of 2 dB.

An Optimal Tradeoff between Security and Reliability in systems of Cognitive Radio

Objectives: To propose relay selection plans for a CR network. A network of Cognitive Radio (CR) is considered. It comprises of one Secondary Transmitter (ST), a set of multiple Secondary Relays (SRs) and one Secondary Destination (SD) and an eavesdropper is also present. Here the ST is transmitting to SD assisted by SRs, while eavesdropper attempts interception of secondary transmission. Methods: Care is exercised in selecting relay to protect ST-SD transmission. Protection is against eavesdropper both single-relay as well as multi-relay aid that. In particular, possibly best SR gets chosen in a singlerelay type selection to assist transmission of secondary type. Multi-relay selections invoke multiple SRs for simultaneous forwarding of transmission of ST to SD. Findings: Both probabilities of intercept as well as outage are analyzed for the put forth single-relay as well as relay of multi type selecting methods meant for transmission of secondary type. This relies upon the realistic kind of sensing of spectrum. Evaluation of performance is done on the classic type transmission of direct kind and also the approaches of artificial noise based for comparing them with proposed schemes of relay selection. Improvements/Applications: It shows that relaxing intercept probability requirement improves performance of outage related to transmission of direct type, schemes for selection of relay and also-based on noise of artificial type-scheme and vice versa. This leads to the implication that a trade-off is done between reliability and security of secondary transmission when eavesdropping attacks are present. This implication is popularly coined as security to reliability - a trade-off (SRT). Also it is demonstrated that SRTs schemes of single-relay as well as multi-relay selection are normally better compared to classic direct transmission. It explicitly demonstrates the salient features of selection of relay scheme in question. This is related to offering protection to transmissions of secondary type from attacks of eavesdropping. Apart from this there is an increase in SRs’ count, obviously SRTs about relay of single type in question now as well as relay of multi type selection method improve substantially.

Low-complexity timer-based multi-relay selection and sequential power allocation of cooperative cognitive radio networks for future Internet of things

Cooperative cognitive radio networks use cooperative relays to forward signal from the source to the destination. In cooperative cognitive radio networks, the transmission power of each relay is limited by the interference constraint of the primary user receiver. Thus, it is essential to optimize power allocation and multi-relay selection jointly to maximize the secondary system throughput. Optimizing multi-relay selection and power allocation requires an exhaustive search for all possible relay combinations, since this approach uses a large amount of valuable resources and entails high computational complexity. A suboptimal solution for power allocation may reduce the computational complexity but still involves high implementation complexity. Thus, for an efficient utilization of resources to support the applicability of cognitive radio for the Internet of things, we propose a low-complexity timer-based multi-relay selection that determines a forwarding relay set before the source begins to transmit its data. This allows the source to know the instantaneous channel state information of the relays, which helps the source to assign appropriate transmission power to the relays. By simulation, we show that the proposed scheme achieves near-optimal secondary system throughput performance to the optimal multi-relay selection as well as provides a significant secondary system throughput gain when compared to conventional and random relay selection scheme with equal power allocation.

Security–Reliability Tradeoff Analysis of Multirelay-Aided Decode-and-Forward Cooperation Systems

We consider a cooperative wireless network comprised of a source, a destination, and multiple relays operating in the presence of an eavesdropper, which attempts to tap the source-destination transmission. We propose a multirelay selection scheme for protecting the source against eavesdropping. More specifically, multirelay selection allows multiple relays to simultaneously forward the source's transmission to the destination, differing from the conventional single-relay selection, where only the best relay is chosen to assist in the transmission from the source to the destination. For the purpose of comparison, we consider the classic direct transmission and single-relay selection as benchmark schemes. We derive closed-form expressions of the intercept probability and the outage probability for the direct transmission, as well as for the single-relay and multirelay selection schemes over Rayleigh fading channels. It is demonstrated that as the outage requirement is relaxed, the intercept performance of the three schemes improves, and vice versa, implying that there is a security-versus-reliability tradeoff (SRT). We also show that both the single-relay and multirelay selection schemes outperform the direct transmission in terms of SRT, demonstrating the advantage of the relay selection schemes for protecting the source's transmission against the eavesdropping attacks. Finally, upon increasing the number of relays, the SRTs of both the single-relay and multirelay selection schemes significantly improve, and as expected, multirelay selection outperforms single-relay selection.