Cooperative Relay Networks Research Articles

A New Energy Efficiency/Spectrum Efficiency Model for Cooperative Cognitive Radio Network

In this paper we study the resources access problem in cognitive radio networks, especially we are interested in the large number of secondary users (SUs). We establish a model based on channel access process when the PU (Primary User) is active, respecting the level of interference authorized by the operator. We study a system of cooperation between the SUs and the PUs to increase the performance of the system. SUs pass through an negotiation phase with the PUs for the acquisition of the underutilized channels with exceeded interference caused to the PU. The PU will support additional interference Δ but will benefit from the cooperation of SUs to relay its data. We model this cooperation as coalitional game.The utility function depends on two main parameters which are: transmission power and noise level. A distributed coalition formation algorithm is also proposed, which can be used by SUs to decide whether to join or leave a coalition. Such a decision is based on whether it can increase the maximal coalition utility value. We consider also the trade off between energy efficiency and the target throughput in the proposed cooperative relay network. The objective of this work is to validate the expected enhancement of the overall throughput of the network and also the energy efficiency while increasing the opportunity for SUs to access the licensed spectrum owned by PUs.

Stackelberg game for price and power control in secure cooperative relay network

In this study, the authors propose a scheme based on Stackelberg game for price and power control in threshold-based relay network, where the source transmits message to destination with the cooperation of a relay, in the presence of an eavesdropper. The relay gets revenue for transmitting the source information and the source profits from the cooperation secrecy rate. The source needs to pay for the amount of power allocated by the relay for transmission of source data to destination. Threshold-based relaying is considered, where the relay can correctly decode the message, only if the received signal satisfies the predetermined threshold. Maximal ratio combining scheme is employed at destination and eavesdropper to maximise the probability of secure transmission and successful eavesdropping, respectively. Unlike other works to date, the authors have maximised the utility of relay and source, with allocated maximum power constraints at the relay node, using Stackelberg security game scheme. The closed-form optimal solution for price and power control is obtained, for this leader-follower security equilibrium game model, with the help of convex optimisation.

Lyapunov-Optimized Two-Way Relay Networks With Stochastic Energy Harvesting

Energy harvesting wireless cooperative communications have become more and more popular in recent years. In this paper, we consider a two-way relay cooperative network, where the relay is an energy harvesting node and uses decode-and-forward (DF) or amplify-and-forward (AF) cooperation protocol. We formulate the energy management problem in such a network as an optimization problem, which minimizes the long-term average outages with a long-term average battery constraint. We then apply Lyapunov optimization to transform the long-term optimization problem into the drift-plus-penalty. We also conduct theoretic analysis of the proposed energy management strategy. Specifically, we prove that the long-term average battery constraint can be guaranteed with the proposed strategy and derive an upper bound of the average outages with the proposed strategy. Furthermore, we analyze theoretically the diversity order and energy harvesting gain of the proposed strategy with the DF and AF protocols. Finally, simulation results using real-solar irradiance data measured by the solar site in Elizabeth City University show that the outage performance and the diversity order of our algorithms are better than the existing MDP-based method.

On the performance of an enhanced transmission scheme for cooperative relay networks with NOMA

In this paper, an enhanced transmission scheme for cooperative relaying networks with non-orthogonal multiple access (ECRN-NOMA) is proposed. In the proposed scheme, two different kinds of transmission schemes are investigated which are the single signal transmission and the enhanced superposition transmission schemes. Particularly, for the single transmission scheme, a successive interference cancellation (SIC) is utilized to decode the received signal, sent by the relay, at the destination. On the other hand, for the enhanced superposition coded signal transmission scheme, a maximum ratio combining (MRC) is utilized at the destination to improve the ergodic sum-rate (SR) of the proposed system. Specifically, two power allocation (PA) strategies are comprehensively discussed to characterize the performance of our proposed scheme. The achievable average SR of the proposed systems are analyzed for independent Rayleigh fading channels, and also their asymptotic expressions are also provided. Qualitative numerical results corroborating our theoretical analysis show that the enhanced superposition coded signal transmission scheme applied to the proposed ECRN-NOMA improves the SR performance significantly in comparison to the others.

Modified genetic algorithm based power allocation scheme for amplify-and-forward cooperative relay network

Cooperative relay (CR) is a favorable technique to provide better spectral efficiency and enhance the cell coverage area in a cost-effective manner. However, several undesired issues, such as high-power consumption, arise due to use of a high number of relay nodes (RNs) in the network, Moreover, in a dynamic environment, full channel state information (CSI) is not always available. Therefore, all RNs need to calculate the abrupt changes in the channel; otherwise, the overhead delay will increase and the RNs will consume higher network power. To address this, an optimized modified genetic algorithm (Modified GA) based scheme is proposed that utilizes probabilistic selection rules and fitness scores. The results are presented in terms of symbol error rate (SER), network capacity, power consumption, and power improvement in order to analyze the performance of the proposed scheme. The results show that the proposed scheme provides better overall performance as compared to conventional optimization approaches.

A Device-to-Device Communication-Based Disaster Response Network

Device-to-Device (D2D) communication and cognitive radio are among the key technologies that can help to solve the bandwidth bottleneck problem of cellular networks. Such technologies help to maintain the necessary communication between user devices in case of natural disasters and traffic hotspot situations. In this paper, we efficiently exploit the relay selection and cooperative beamforming (CBF) strategies for D2D communication and show that user devices can securely communicate with each other without infrastructure support. We propose a cluster-based hierarchical topology for a multi-hop cooperative relay network, to cover the potentially long distance between the source and the destination. The cluster heads in the proposal act as primary users (PUs) and the cluster members are regarded as secondary users (SUs) or relay nodes. A system model is presented to analyze the problems of relay selection and power allocation in SUs located in different clusters and hierarchical levels. To investigate the efficiency of our proposed model, we define the utilities of PUs employing relay selection and CBF, considering received signal power and latency. We optimize relay selection and beamforming vector by solving a mixed integer non-linear problem. Numerical results demonstrate the efficiency and robustness of our approach.

Secrecy outage of threshold-based cooperative relay network with and without direct links

In this paper, we investigate the secrecy outage performance of a dual-hop decode-and-forward (DF) threshold-based cooperative relay network, both with and without the direct links between source-eavesdropper and source-destination. Without assuming that all the relays can always perfectly decode, here we consider that only those relays who satisfy predetermined threshold can correctly decode the message. We have investigated the outage probability of optimal relay selection scheme, when either full instantaneous channel state information (ICSI) or statistical channel state information (SCSI) of all the links is available. We have shown that CSI knowledge at the transmitter can improve secrecy, and the amount of improvement for the outage probability is more when the required rate is low and for low operating SNR. Asymptotic and diversity gain analysis of the secrecy outage for both the single relay and multi-relay system is obtained, when average SNRs of source-relay and relay-destination links are equal or unequal. We have shown that the improvement in predetermined threshold, eavesdropper channel quality, direct links, and required secrecy rate significantly affects the secrecy performance of the system.

Auction-Based Fair Partner Selection for Decode-and-Forward Cooperative Relay Networks

In this paper, we propose a fair partner selection scheme for decode-and-forward cooperative relay networks based on auction theory. Modelling a single relay node as an auctioneer and multiple source nodes as bidders, the source nodes compete with each other by offering competitive prices to determine the recipient of the cooperative resources. To maximize the expected payoff, a closed-form Nash equilibrium strategy for each source node is derived over independent and identically distributed Rayleigh fading channels. Finally, numerical results and analysis verify the effectiveness of the proposed schemes.

Non-Orthogonal Multiple Access for Cooperative Communications: Challenges, Opportunities, and Trends

NOMA is a promising radio access technique for next-generation wireless networks. In this article, we investigate the NOMA-based cooperative relay network. We begin with an introduction of the existing relay-assisted NOMA systems by classifying them into three categories: uplink, downlink, and composite architectures. Then we discuss their principles and key features, and provide a comprehensive comparison from the perspective of spectral efficiency, energy efficiency, and total transmit power. A novel strategy called hybrid power allocation is further discussed for the composite architecture, which can reduce the computational complexity and signaling overhead at the expense of marginal sum rate degradation. Finally, major challenges, opportunities, and future research trends for the design of NOMA-based cooperative relay systems with other techniques are also highlighted to provide insights for researchers in this field.

Secure cognitive radio networks with source selection and unreliable backhaul connections

In this study, the secrecy performance of cooperative half-duplex cognitive relay networks (CRNs) comprised of multiple primary users (PUs) and multiple eavesdroppers under the effect of unreliable wireless backhauls is studied. The authors consider relay networks with single relay assisting multiple sources under power constraints at PUs and secondary transmitters, and based on the availability of channel-state information at the sources, they propose two best source selection schemes, namely: (i) optimal source selection (OSS) and (ii) sub-optimal source selection (SoSS). For both scenarios, they obtain exact closed-form and asymptotic expressions for the system's outage probability and carry out numerical simulations to justify their analyses. From the results, source selection is proven to be capable of counteracting the negative impact of unreliable backhaul on CRNs. The secrecy performance limitations are also verified to be influenced by the backhaul reliability. Furthermore, OSS is more desirable compared to SoSS in low signal-to-noise ratio (SNR) regime, while the secrecy performance for both schemes converge to an asymptotic limit in high-SNR ranges.

Analysis of channel uncertainty in ARQ relay networks.

Several power allocation algorithms for cooperative relay networks are presented in the literature. These contributions assume perfect channel knowledge and capacity achieving codes. However in practice, obtaining the channel state information at a relay or at the destination is an estimation problem and can generally not be error free. The investigation of the power allocation mechanism in a wireless network due to channel imperfections is important because it can severely degrade its performance regarding throughput and bit error rate. In this paper, the impact of imperfect channel state information on the power allocation of an adaptive relay network is investigated. Moreover, a framework including Automatic Repeat reQuest (ARQ) mechanism is provided to make the power allocation mechanism robust against these channel imperfections. For this framework, the end-to-end SNR is calculated considering imperfect channel knowledge using ARQ analytically. The goal is to emphasize the impact of imperfect channel knowledge on the power allocation mechanism. In this paper, the simulation results illustrate the impact of channel uncertainties on the average outage probability, throughput, and consumed sum power for different qualities of channel estimation. It is shown that the presented framework with ARQ is extremely robust against the channel imperfections.

Performance Analysis of FD MIMO DF Cooperative Relaying Networks Using ZFBF

In this paper, we statistically analyze the performance of full-duplex (FD) MIMO decode-&-forward (DF) cooperative relaying networks. More specifically, we evaluate the end-to-end statistics under assumed system and channel models. Then, based on these results, we derive accurate closed-form expressions of the outage probability and the average bit error rate for both the transmit and the receive zero-forcing beamforming schemes in Rayleigh fading environments. Some selected results are presented to show some interesting observations useful for system designers. For instance, we find that the increased hardware complexity of DF relays is generally worth the high cost in FD relay scenarios, but not in half-duplex cases.

Performance Analysis of Energy Harvesting Multi-Antenna Relay Networks With Different Antenna Selection Schemes

In this paper, we investigate the performance of three transmit antenna selection (TAS) schemes for an energy harvesting decode-and-forward relay cooperative network. In the network, the energy-limited relay first harvests the energy from the received signal with the power-splitting scheme, and then utilizes the harvested energy to forward the received signal to the destination. Specifically, exact analytical expressions for the outage probability of the considered network with three TAS schemes are derived for evaluating the impact of key parameters on the outage performance. In order to deeply extract insights, we further present tractable asymptotic outage probabilities for three TAS schemes to characterize the diversity order and coding gain in high signal-to-noise ratio regimes, respectively. In addition, we also analyze the impact of feedback delays on the performance of the optimal TAS scheme, which is quantified by the reduction of diversity order and coding gain. Numerical results sustained by Monte Carlo simulations demonstrate that: 1) the second suboptimal TAS schemes achieve a comparable performance as the optimal TAS scheme with the reduced implementation cost; 2) the relay location has a great impact on the outage performance and the optimal power-splitting ratio; and 3) the feedback delay plays a critical role in determining the diversity order achieved by the considered system.

Physical-Layer Network Coding Based Multi-User Cooperative Relay Transmission With Multi-Antennas in Cognitive Wireless Networks

A promising way to improve the performance and guarantee the quality of service (QoS) of cognitive wireless cooperative relay networks is to jointly employ physical-layer network coding (PNC) and multi-antenna space–time block coding. This paper proposes a new multi-user transmission coding scheme, cooperative quadrature PNC (CQPNC), for cognitive wireless networks. In CQPNC scheme, two source nodes (users) first use quadrature carriers to transmit signals simultaneously, which are received and processed by a cooperative relay node using the PNC method. The processed signal is then transmitted to the destination node, which makes a combination of the signals from the direct path and relay path to obtain the information transmitted by the source node. Simulation results in difference cases of cognitive wireless networks show that the CQPNC scheme outperforms the traditional cooperation and cooperative network coding transmission schemes on the performance of anti-noise and throughput.

Virtual-Link Relay Selection Scheme for Buffer-Aided IoT Based Cooperative Relay Networks

This paper investigates the performance of a buffer-aided cooperative relay network. In the proposed design, each location in a buffer is assumed to act independently called the virtual relay having a buffer of size 1. The relay selection is based on the instantaneous strength of the wireless link and status of the virtual relay buffer. The proposed scheme is analyzed for symmetric and asymmetric channel conditions and also for symmetric and asymmetric buffer sizes at the relay. Markov chain is used to model the evolution of buffer status and to derive the closed-form expressions for outage probability, diversity gain, delay, and throughput. The proposed design achieves the diversity gain of $(L_{1}+L_{2}+ \cdots +L_{K})$ , where $L_{i}$ is the buffer size of the $i$ -th relay and $K$ is the total number of relays.

Outage Capacity Analysis of Cooperative Relay Networks Using Statistic CSI with Smart Grid

Outage Capacity Analysis of Cooperative Relay Networks Using Statistic CSI with Smart Grid

On Linear Precoding of Nonregenerative MIMO Relay Networks for Finite-Alphabet Source

Multiple input and multiple output (MIMO) relay could provide broader wireless coverage, better diversity, and higher throughput. Most existing precoder designs for either source or relay node are based on the assumption of Gaussian input signals. However, recent works have revealed possible performance loss of MIMO systems originally optimized for Gaussian source signals when applied to practical finite-alphabet source signals. In this work, we investigate the design problem of joint MIMO precoding for wireless two-hop nonregenerative cooperative relay networks under finite-alphabet source signals. We identify several structural properties of optimal precoders. Specifically, we provided the optimal left singular vectors of the relay precoder, and proved the convexity of mutual information with respect to the square of relay precoder singular value. These results generalize the two-hop relay networks in Gaussian input assumption to the cooperative relay networks in arbitrary finite-alphabet input signals. Furthermore, we propose gradient-based numerical iterative optimization algorithms not only for arbitrary finite-alphabet source signal precoding but also for cooperative relay networks which may or may not have a direct source to destination link. Our results demonstrate substantial performance improvement over existing precoder designed traditionally under Gaussian input assumption, which indicates that the waterfilling based precoding strategy is not suitable for finite-alphabet constellation source inputs.

Buffer-Aided Relay Selection for Cooperative Relay Networks With Certain Information Rates and Delay Bounds

In this paper, we propose a relay selection scheme for cooperative buffer-aided relay networks with specific information rates and delay bounds. The proposed scheme differs from most of the well-known schemes in the literature that assume the source is saturated with data and/or without delay constraints. The proposed scheme is designed to encompass the delay-sensitive applications that are subject to delay limits and have certain rates. The proposed scheme exploits the channel state information, buffer state information, and delay state information to minimize the outage probability and achieve higher throughput. To achieve that, it uses these information to compromise between the selections of relays for reception and transmission. The proposed scheme is analyzed in the independent and identically distributed and independent and nonidentically distributed Rayleigh fading channels. The analysis is in terms of outage probability, packet dropping probability of the source node, packet dropping probability of the entire system, and throughput. For systems with high delay constraints, simulation results show that the proposed scheme offers lower packet dropping probability and higher throughput as compared to the renowned relay selection schemes.

Secure Massive MIMO Relaying Systems in a Poisson Field of Eavesdroppers

A cooperative relay network operating in the presence of eavesdroppers, whose locations are distributed according to a homogeneous Poisson point process, is considered. The relay is equipped with a very large antenna array and can exploit maximal ratio combing in the uplink and maximal ratio transmission in the downlink. A realistic model in which the channel state information of every eavesdropper is not known is considered, as eavesdroppers tend to hide themselves in practice. The destination is thus in a much weaker position than all the eavesdroppers because it only receives the retransmitted signal from the relay. Under this setting, the security performance is investigated for two relaying protocols: amplify-and-forward and decode-and-forward. The secrecy outage probability, the connection outage probability, and the tradeoff between them, which is controlled by the source power allocation, are examined. Finally, suitable solutions for the source power (such that once the transmission occurs with high reliability, the secure risk is below a given threshold) are proposed for a tradeoff between security and reliability.

Improving performance of the asynchronous cooperative relay networks with maximum ratio combining and transmit antenna selection technique

In this paper, a new amplify and forward (AF) asynchronous cooperative relay networks using maximum ratio combining (MRC) and transmit antenna selection (TAS) technique is considered. In order to obtain a maximal received diversity gain, the received signal vectors of all antennas of the each relay node are jointly combined by MRC technique in the first phase. Then, only one the selected antenna of each relay will amplify and retransmit the resulting MRC signal vectors to the destination node in the second transmission step of network. The proposed scheme not only offers to reduce the interference components induced by inter-symbol interference (ISI) among the relay nodes, but also can effectively remove them with employment near-optimum detection (NOD) at the destination node as compared with the previous distributed close loop extended-orthogonal space time block code (DCL EO-STBC) scheme. The analysis and simulation results confirm that the new scheme outperforms the previous cooperative relay networks in both synchronous and asynchronous conditions. Moreover, the proposed scheme allows to reduce the requirement of the Radio-Frequency (RF) chains at the relay nodes and is extended to general multi-antenna relay network without decreasing transmission rate.