Conventional Relay Selection Scheme Research Articles

Relay Selection Scheme Enhancing Reliability Based on MIMO-OFDM System

In this paper, a relay selection scheme is proposed in the Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. The conventional relay selection schemes in the wireless cooperative communication system have high implementation complexity and overhead. The proposed scheme is an adaptive relay selection scheme using Singular Value Decomposition (SVD) to select a relay with channel coefficients that maximize channel capacity. Proposed scheme uses combining factor with singular value in order to combine received signal. Simulation result shows that the proposed scheme improves the Bit Error Rate (BER) performance, compared with the conventional schemes. The proposed scheme with combining factors has enhanced BER performance than the conventional schemes.

Short-Packet Communications in Wireless-Powered Cognitive IoT Networks: Performance Analysis and Deep Learning Evaluation

In this paper, we study short-packet communications in wireless-powered cognitive Internet-of-Things (IoT) networks with multiple primary receivers (PRs). The considered system can be applied for small factory automations, where a source and multiple relays harvest energy from a multi-antenna dedicated power beacon (PB) to send short packets to a robot destination for controlling purposes under cognitive radio constraint imposed by PRs. We propose an opportunistic relay selection (ORS) scheme to maximize the end-to-end signal-to-noise ratio in cognitive IoT systems. Closed-form expressions for the average block error rate (BLER) of the proposed system are obtained, based on which the performance floor analysis, goodput, and energy efficiency (EE) are also carried out. Relying on analytical results, we develop a deep learning framework for the BLER prediction with high accuracy and short execution time. Simulation results show the BLER, goodput, and EE improvements of the ORS scheme over conventional relay selection schemes. Moreover, the developed deep learning-based evaluation model achieves the equivalent performance as the ORS scheme in terms of BLER, goodput, and EE, while remarkably reducing the execution time in cognitive IoT systems.

Secrecy Outage Probability of Energy-Harvesting Cooperative NOMA Transmissions With Relay Selection

Three relay selection techniques, aiming at achieving secure non-orthogonal multiple access in cooperative energy-harvesting (EH) communications, are proposed and compared. In the cooperative relaying system, the source node communicates with multiple users through amplify-and-forward EH relays in the presence of a passive eavesdropper. The relay selection is a two-stage strategy, where the first stage aims at achieving the users’ target data rate, and the second aims at optimizing the secrecy outage probability. New explicit analytical expressions for the secrecy outage probability are derived for three operating scenarios: i) when the channel state information (CSI) of the eavesdropper is unknown, and a two-stage conventional relay selection scheme is considered, ii) when CSI of the eavesdropper is known, and a two-stage optimal relay selection scheme is used, and iii) when multiple relays participate in forwarding the signal to the end users. Monte-Carlo simulations are provided to confirm the derivations, and the effects of the main system parameters on its secrecy are investigated. In particular, it is shown that the optimal relay selection scheme outperforms the conventional and the multiple-relays schemes in terms of secrecy outage probability, and that this superiority becomes more obvious when the number of the relays increases.

A Novel Relay Selection Scheme Based on Q-Learning in Multi-Hop Wireless Networks

In wireless communication systems, reliability, low latency and power are essential in large scale multi-hop environment. Multi-hop based cooperative communication is an efficient way to achieve goals of wireless networks. This paper proposes a relay selection scheme for reliable transmission by selecting an optimal relay. The proposed scheme uses a signal-to-noise ratio (SNR) based Q-learning relay selection scheme to select an optimal relay in multi-hop transmission. Q-learning consists of an agent, environment, state, action and reward. When the learning is converged, the agent learns the optimal policy which is a rule of the actions that maximize the reward. In other words, the base station (BS) knows the optimal relay to select and transmit the signal. At this time, the cooperative communication scheme used in this paper is a decode-and-forward (DF) scheme in orthogonal frequency division multiplexing (OFDM) system. The Q-learning in the proposed scheme defines an environment to maximize a reward which is defined as SNR. After the learning process, the proposed scheme finds an optimal policy. Furthermore, this paper defines a reward which is based on the SNR. The simulation results show that the proposed scheme has the same bit error rate (BER) performance as the conventional relay selection scheme. However, this paper proposes an advantage of selecting fewer relays than conventional scheme when the target BER is satisfied. This can reduce the latency and the waste of resources. Therefore, the performance of the multi-hop transmission in wireless networks is enhanced.

Joint relay and jammer selection for secure cooperative networks with a full‐duplex active eavesdropper

In this study, the authors investigate the secure transmission of a cooperative network, in which a source communicates with a destination via multiple cooperative nodes in the presence of a full-duplex active eavesdropper, which can intercept the confidential signals and transmit jamming signals simultaneously. To safeguard the security of legitimate communication, two joint relay and jammer selection schemes are proposed according to the availability of the eavesdropper's channel state information, namely, optimal relay and random jammer selection scheme and optimal relay and optimal jammer selection scheme. The authors first derive the exact closed-form expressions of the secrecy outage probability (SOP) for different selection schemes. Aiming at minimising SOP, they then adopt the deep feedforward neural network to determine the optimal power allocation between the selected relay and jammer. Further, the asymptotic expressions for SOP in the high signal-to-noise ratio regime are derived. Numerical results verify the analysis and demonstrate the performance advantage of the proposed scheme over conventional relay selection scheme with optimal power allocation.

Millimeter-Wave-Based Cooperative Backhaul for a Mobile Station in an X-Haul Network

In this paper, we propose a millimeter-wave-based cooperative backhaul scheme for a mobile X-haul distributed unit (XDU), whose line of sight for backhaul data reception is not always guaranteed in an X-haul network. Since the received signal at the mobile XDU experiences severe path loss than other stationary XDUs, the proposed scheme selects one of stationary wireless XDUs as a relay for assisting the mobile XDU. The relaying XDU selection takes into account not only the location information, but also the load information of wireless XDUs. We derive the outage probability of the mobile XDU and show that the proposed scheme outperforms the conventional relay selection scheme without taking account of the traffic load on relaying nodes.

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.

Relay Selection for Improved Physical Layer Security in Cognitive Relay Networks Using Artificial Noise

In this paper, the physical layer security of underlay cognitive decode-and-forward (DF) relay networks is investigated, wherein one secondary transmitter (ST) exchanges confidential information with one secondary destination with the assistance of multiple cognitive DF relays by sharing the licensed spectrum of an primary user, and the relayed transmission is intercepted by multiple passive eavesdroppers. To provide security guarantee for secondary transmission, we propose a novel cooperative scheme aided by artificial noise. In the absence of the eavesdroppers’ channel state information (CSI), two opportunistic relay selection schemes, namely best relay selection (BRS) and conventional relay selection (CRS), are proposed as an incentive to further enhance the physical layer security. To be specific, only the CSI of the main channel is employed in the CRS scheme, whereas the BRS scheme invokes both the CSI of the main channel and interference channel. We address the secrecy performance in terms of secrecy outage probability, for which the closed-form expressions for both the relay selection schemes are derived. Simulation results are provided to verify our analysis and show that the proposed BRS scheme significantly achieves a better secrecy outage performance compared with the CRS scheme as well as the conventional scheme without jamming.

A reliable relay selection scheme for SSK modulation in cooperative communication systems

Space shift keying (SSK) modulation is a scheme in which the indices of active transmit antennas play an essential role in carrying information bits. In SSK modulation, the communication channel acts as modulating unit. Therefore, using the conventional relay selection schemes based on channel coefficients are impossible in cooperative systems using SSK modulation. In this paper, we propose a novel relay selection scheme that is applicable in cooperative systems using SSK modulation. The proposed scheme is based on calculating and measuring the Euclidean distances between received signal and all active or inactive channel coefficients. The proposed relay selection scheme is applied for a cooperative communication system with multiple relay nodes and a direct link between source and destination. The analytical expressions are derived to calculate the average bit error rate over Rayleigh fading channels. The analytical and simulation results show that this relay selection scheme can provide a full cooperative diversity order, for SSK modulation. In addition, we show that this scheme can be used at destination as a signal selection method, to select the best received signal from different paths. The analytical results are validated using Monte Carlo simulation studies.

Adjustable Multiple Relay Selection Based on Steady-State Mean Square Joint Error for Cooperative Communication

In this paper, an adjustable multiple relay selection (MRS) scheme for cooperative communication with amplify-and-forward (AF) relay under frequency selective channels is proposed. In the proposed scheme, the relays are ordered firstly by the steady-state mean square error (MSE), then the relays are sequentially selected out from N relays and the number of cooperating relays is adjusted dynamically according to the steady-state mean square joint error (MSJE). The aim of this work is to dynamically estimate the optimum number N o of cooperating relays. Optimum means the minimum number of cooperating relays, N o , achieving the minimum level of steady-state MSJE. Numerical results verify the analyses and show that the scheme can adaptively adjust the number of cooperating relays, and outperform conventional relay selection schemes. Hence, the proposed scheme provides better tradeoff between BER performance and spectral efficiency and to save more energy in cooperative wireless networks.

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.

Adaptive Relay Selection and Data Transmission Scheme for Cooperative Communication

In this paper, an adaptive relay selection and transmission scheme are proposed for cooperative communication. As the conventional relay selection schemes, the best harmonic mean and the threshold-based relay selection scheme require channel state information (CSI) in advance at the source. By using CSI, they can select the optimal or the sub-optimal relay. But, the source does not know CSI as a priori information in general environment. Additionally, the conventional system uses the fixed maximum throughput regardless of channel state. The proposed relay selection scheme does not require a priori information at the source. It uses a characteristic of Reed---Solomon codes. By using it, the source can select the optimal relay for cooperative communication. Additionally, the proposed adaptive transmission scheme can change the maximum throughput according to the result of optimal relay selection. By using the proposed relay selection and adaptive transmission scheme, the proposed system is more reliable and adaptable according to selected relay.

Performance Analysis for Opportunistic Full-Duplex Relay Selection in Underlay Cognitive Networks

The performance analysis of optimal decode-and-forward (DF) relay selection for the full-duplex (FD) mode in underlay cognitive radio (CR) networks is studied, with the impact of critical parameters such as the residual self-interference, the distributions of the received signal-to-noise ratio (SNR), and the outage probability, being analyzed. Different from the conventional relay selection schemes with half-duplex (HD) mode, the FD relay suffers from the impact of residual self-interference due to its simultaneous transmission and reception using the same channel. Furthermore, the exact closed-form expressions for the outage probabilities of the proposed FD relay-selection scheme over both independent Nakagami- m and Rayleigh fading channels are derived, with the validity of the proposed analysis being proven by using simulation. Numerical results show that, in the presence of multiple candidate relays, an optimum relay-selection solution in terms of outage probability can always be achievable within the SNR range of (10 dB, 15 dB).

Efficient Full-Duplex Relaying With Joint Antenna-Relay Selection and Self-Interference Suppression

In this paper, we propose a joint relay and transmit/ receive (Tx/Rx) antenna mode selection scheme (RAMS) in the general full-duplex (FD) relay networks consisting of one source, one destination, and N FD amplify-and-forward (AF) relays. Each FD relay is equipped with two antennas, one for receiving and the other for transmitting. In the proposed scheme, each antenna of the FD relay is able to transmit/receive the signal. Each relay adaptively selects its Tx antenna and Rx antenna based on the instantaneous channel conditions, and the optimal single relay with the optimal Tx/Rx antenna configuration is selected to maximize the end-to-end signal to interference and noise ratio (SINR) of the FD relay system. The performance of the proposed scheme is analyzed. The closed-form expressions of the outage probability, average symbol error rate, and the ergodic capacity are derived. The analytical results are verified by the simulations. To reduce the error floor and capacity ceiling caused by the self-loop interference in FD relay, we propose a RAMS scheme with adaptive power allocation (RAMS-PA). We provide an upper bound and a lower bound of the end-to-end SINR for RAMS-PA scheme, and prove that the error floor can be removed in the RAMS-PA scheme. Results show that the proposed scheme achieves an extra spatial diversity in the medium SNR region due to the FD antenna selection at the relay nodes and considerably improve the system performance compared to the conventional FD relay selection scheme with fixed relay Tx and Rx antennas.

ORS-FA: An Opportunistic Relay Selection Scheme for Frame-Aggregated Environments

In conventional opportunistic relay selection schemes, one or multiple relays with better channel condition are selected. However, if frame aggregation is supported for improving MAC throughput, each relay can have different amounts of data and thus conventional selection schemes may choose a worse relay node only with good channel condition but little data. In this paper, we propose a novel opportunistic relay selection scheme when frame aggregation is adopted. In the proposed scheme, a relay node is selected in a distributed manner by considering the amount of data as well as channel condition, and therefore the most appropriate relay node can be chosen. Simulation results demonstrate that the proposed scheme outperforms other relay selection schemes, especially when the number of relay nodes is large.

Partial Relay Selection in Decode and Forward Cooperative Cognitive Radio Networks over Rayleigh Fading Channels

The performance of an partial relay selection on the decode-and-forward (DF) mode cognitive radio (CR) relay networks is studied, with some important factors, including the outage probability, the bit error ratio (BER), and the average channel capacity being analyzed. Different from the conventional relay selection schemes, the impact of spectrum sensing process as well as the spectrum utilization efficiency of primary users on the performance of DF-based CR relaying networks has been taken into consideration. In particular, the exact closed-form expressions for the figures of merit such as outage probability, BER, and average channel capacity over independent and identically distributed (i.i.d.) Rayleigh fading channels, have been derived in this paper. The validity of the proposed analysis is proven by simulation, which showed that the numerical results are consistent with the theoretical analysis in terms of the outage probability, the BER and the average channel capacity. It is also shown that the full spatial diversity order can always be obtained at the signal-to-noise ratio (SNR) range of [0dB, 15dB] in the presence of multiple potential relays.

Decode-and-Forward Buffer-Aided Relay Selection in Cognitive Relay Networks

This paper investigates decode-and-forward (DF) buffer-aided relay selection for underlay cognitive relay networks (CRNs) in the presence of both primary transmitter and receiver. We propose a novel buffer-aided relay selection scheme for the CRN, where the best relay is selected with the highest signal-to-interference ratio (SIR) among all available source-to-relay and relay-to-destination links while keeping the interference to the primary destination within a certain level. A new closed-form expression for the outage probability of the proposed relay selection scheme is obtained. Both simulation and theoretical results are shown to confirm performance advantage over the conventional max-min relay selection scheme, making the proposed scheme attractive for CRNs.

Cooperative beamforming and relay selection in cognitive radio systems

SUMMARYIn this paper, a new scheme is suggested for cooperative beamforming (BF) and relay selection in CR networks, where a pair of secondary users communicates with each other assisted by some multiple antenna relay nodes. The goal of the algorithm is to maximize signal to interference plus noise ratio of secondary user receiver subject to limited interference caused for primary user receiver and power constraints of relay nodes. The relay selection and BF optimization problem is solved separately by employing convex semidefinite programming through rank‐one relaxation. It is shown that our proposed algorithm outperforms conventional relay selection and BF schemes. Copyright © 2014 John Wiley & Sons, Ltd.

Partial Relay Selection With Fixed-Gain Relays and Outdated CSI in Underlay Cognitive Networks

The impact of an imperfect channel estimation on the amplify-and-forward (AF) mode cooperative communications systems is studied, with some important factors, including the probability characteristic of the secondary user's end-to-end signal-to-noise ratio (SNR), the outage probability, the symbol error probability (SEP), and the channel capacity, being analyzed. Different from the conventional relay selection schemes, we assume that the primary users share their bandwidth with the secondary users to enable a secondary relay-aided communication if the interference added to the primary users is kept below a certain threshold in an underlay cognitive network. In particular, both the feedback delay and Doppler frequency shift are assumed to be within a tolerable range, and as compared with the conventional methods, less channel state information (CSI) feedback is required in the proposed method due to partial relay selection being performed in the latter. The proposed scheme is validated by carrying out both theoretical analysis and numerical simulation, and the theoretical approximations of closed-form expressions for some figures of merit, e.g., the outage probability, the SEP, and the channel capacity, are all consistent with the numerical results. The simulations also prove that the performance of the proposed scheme is considerably affected by some other critical parameters, such as the number of relays, the channel correlation coefficient, and the interference threshold. In the presence of multiple candidate relays, an optimum solution in terms of either the outage probability or the SEP performance can always be found within the SNR range of (0, 10 dB).

Effect of Feedback Delay on Secure Cooperative Networks with Joint Relay and Jammer Selection

Physical layer security is a promising technique to realize secure wireless communications without relying on conventional cryptographic methods. In cooperative networks with secrecy constraints, joint relay and jammer selection (JRJS) is an efficient approach to improving the security performance. However, due to feedback delay, the channel state information (CSI) used in the selection process may become outdated and differ from the CSI during the actual transmission of data and jamming. In this work, we study the effect of feedback delay on the JRJS scheme with decode-and-forward relaying strategy. We provide a lower bound for the ergodic secrecy capacity (ESC) and approximate closed-form expressions for the secrecy outage probability (SOP). Monte Carlo simulations are performed to verify the analytical results. The simulation results show that feedback delay decreases the ESC and increases the SOP floor of JRJS. However, in spite of the performance degradation, JRJS outperforms the conventional relay selection scheme without jamming.