Optimal Relay Selection Scheme Research Articles

Optimal Relay Selection for Secure NOMA Systems Under Untrusted Users

The key idea of non-orthogonal multiple access (NOMA) is to serve multiple users in the same frequency band to improve the spectral efficiency. Whereas a security flaw emerges in the presence of untrusted users or low security clearance users who can access the messages of trusted users due to the spectrum sharing and may work as eavesdroppers. To achieve reliable and secure communications of NOMA systems under untrusted users, we in this paper propose two relay selection (RS) schemes termed decode-and-forward (DF) and amplify-and-forward (AF) protocols based optimal relay selection (i.e., DORS and AORS) schemes, respectively. To explicitly reveal the benefits of the DORS and AORS schemes, we derive the exact and asymptotic closed-form expressions of the secrecy outage probability (SOP) and positive secrecy capacity probability (PSCP) achieved by the two schemes, and analyze the optimality of the two schemes. Analysis and simulation results indicate that both the DORS and AORS schemes significantly outperform the benchmark schemes, in addition to achieving the same SOP and desirable PSCP at high SNR.

Relay selection algorithm based on social network combined with Q‐learning for vehicle D2D communication

A relay selection algorithm was proposed to improve a communication rate of D2D (device-to-device) users in-vehicle networking communication systems based on social network combined with Q-learning. The scheme was divided into two steps. Firstly, a social threshold was introduced to filter the potential relay nodes to reduce the number of probing times based on the user's interest similarity in D2D communication network. Then, an optimal relay selection algorithm was proposed to maximise the total rate of D2D links based on a Q-learning algorithm. This method can provide the optimal relay selection scheme to meet the requirements of vehicle networking communication. The simulation results showed that the proposed scheme could reduce the number of probing relays and improve the communication speed of the system on the basis of ensuring communication security.

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

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

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

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

Security Optimization of Two-Hop AF Cooperative Relay Network

In a two-hop cooperative relay network under eavesdropping environment, selecting the appropriate relay node forwarding information can improve the security performance of the system. Traditional relay selection depends on the channel condition of the two-hop link acquired through feedback to select the optimal relay node, ignoring the possible feedback delay of the system during relay selection moment and data transmission moment and inevitably causing the system security performance decline. With this in mind, this paper aims at improving the security transmission performance of the system, considering the condition of two-hop link channel of AF secure cooperative network combined with the maximum posterior probability criterion to weaken the influence of feedback delay to the relay selection, thus improving the security performance of the system. The simulation results shows that, with the improved optimal relay selection strategy based on the maximum posterior probability criterion, the reliability of relay selection is improved, and the system security performance is better.

An Optimal Relay Scheme for Outage Minimization in Fog-Based Internet-of-Things (IoT) Networks

Fog devices are beginning to play a key role in relaying data and services within the Internet-of-Things (IoT) ecosystem. These relays may be static or mobile, with the latter offering a new degree of freedom for performance improvement via careful relay mobility design. Besides that, power conservation has been a prevalent issue in IoT networks with devices being power-constrained, requiring optimal power-control mechanisms. In this paper, we consider a multitier fog-based IoT architecture where a mobile/static fog node acts as an amplify and forward relay that transmits received information from a sensor node to a higher hierarchically placed static fog device, which offers some localized services. The outage probability of the presented scenario was efficiently minimized by jointly optimizing the mobility pattern and the transmit power of the fog relay. A closed-form analytical expression for the outage probability was derived. Furthermore, due to the intractability and nonconvexity of the formulated problem, we applied an iterative algorithm based on the steepest descent method to arrive at a desirable objective. Simulations reveal that the outage probability was improved by 62.7% in the optimized-location fixed-power scheme, 79.3% in the optimized-power fixed-location scheme, and 94.2% in the optimized-location optimized-power scheme, as against the fixed-location and fixed-power scheme (i.e., without optimization). Lastly, we present an optimal relay selection strategy that chooses an appropriate relay node from randomly distributed relaying candidates.

Secrecy Performance Analysis of Relay Selection in Cooperative NOMA Systems

This paper investigates the security performance of two relay selection schemes for cooperative non-orthogonal multiple access (NOMA) systems, where $K$ randomly distributed relays are employed with either decode-and-forward (DF) or amplify-and-forward (AF) protocols. More particularly, two-stage relay selection (TRS) and optimal relay selection (ORS) schemes are taken into consideration. To characterize the secrecy behaviors of these RS schemes, new closed-form expressions of both exact and asymptotic secrecy outage probability (SOP) are derived. We confirm that the SOP of the TRS scheme is equal to that of the ORS scheme for DF/AF-based NOMA systems. Based on the analytical results, the secrecy diversity orders achieved by the pair of RS schemes for the DF/AF-based NOMA systems are $K$ , which are equal to the number of relays. It is shown that the secrecy diversity orders for the cooperative NOMA systems are determined by the number of the relays. The numerical results are presented to demonstrate that: 1) the secrecy performance of the AF-based NOMA system outperforms that of the DF-based NOMA system, when not all DF relays successfully decode the received information; 2) with the number of relays increasing, the SOP of these RS schemes for the DF-/AF-based NOMA systems becomes lower, and; 3) the TRS/ORS schemes are capable of achieving better secrecy outage behaviors compared with random RS and orthogonal multiple access-based RS schemes.

On Secure Wireless Sensor Networks With Cooperative Energy Harvesting Relaying

In this paper, we investigate the physical layer security (PLS) of a wireless sensor network (WSN) that consists of a base station (BS), multiple sensor nodes (SNs), and multiple energy-limited relays (ERs) in the presence of a passive eavesdropper (EAV). We adopt a time-switching/power-splitting (TSPS) mechanism for information transmission. The communication protocol is divided into two phases. The purpose of the first phase is to decode information, and energy harvesting (EH) is performed in accordance with the TSPS protocol. The purpose of the second phase is to transmit information to multiple destinations using the amplify-and-forward (AF) technique. In this study, we introduce a multirelay cooperative scheme (MRCS) to improve the secrecy performance. We derive analytical expressions for the secrecy outage probability (SOP) of the MRCS and that of the noncooperative relay scheme (NCRS) by using the statistical characteristics of the signal-to-noise ratio (SNR). Specifically, we propose an optimal relay selection scheme to guarantee the security of the system for the MRCS. In addition, Monte Carlo simulation results are presented to confirm the accuracy of our analysis based on simulations of the secrecy performance under various system parameters, such as the positions and number of ERs, the EH time, and the EH efficiency coefficients. Finally, the simulation results show that the secrecy performance of our MRCS is higher than that of the NCRS and the traditional cooperative relay scheme (TCRS).

Optimal Relay Selection Schemes for Cooperative NOMA

This correspondence paper investigates relay selection (RS) schemes for cooperative downlink nonorthogonal multiple access (NOMA) networks with multiple relays. Two optimal RS schemes, termed as the two-stage weighted-max-min (WMM) and max-weighted-harmonic-mean (MWHM) schemes, are proposed for cooperative NOMA with fixed and adaptive power allocations (PAs) at the relays, respectively. Then, the outage probabilities of the two proposed RS schemes are analyzed, and their diversity gains are also determined. The provided simulation results show that the proposed optimal two-stage WMM and MWHM schemes outperform the existing suboptimal RS schemes for cooperative NOMA networks with fixed and adaptive PAs at the relays, respectively.

Analog network coding using differential and double-differential modulation with relay selection

Abstract A simple relay selection scheme is proposed for analog network coding using differential modulation (ANC-DM). We propose a relay selection scheme based solely on the received signal power in which their own information is canceled out at each source node. The proposed power-based relay selection scheme is further applied to analog network coding using double-differential modulation (ANC-DDM), which is suitable for channels with carrier offset. Simulation results show that our proposed simple power-based criterion for relay selection in ANC-DM system has little loss compared to the optimal relay selection scheme using ideal BER.

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.

Cross-layer Joint Relay Selection and Power Allocation Scheme for Cooperative Relaying System

A novel cross-layer joint relay selection and power allocation (CL-JRSPA) scheme over physical layer and data-link layer is proposed for cooperative relaying system in this paper. Our goal is finding the optimal relay selection and power allocation scheme to maximize system achievable rate when satisfying total transmit power constraint in physical layer and statistical delay quality-of-service (QoS) demand in data-link layer. Using the concept of effective capacity (EC), our goal can be formulated into an optimal joint relay selection and power allocation (JRSPA) problem to maximize the EC when satisfying total transmit power limitation. We first solving optimal power allocation (PA) problem with Lagrange multiplier approach, and then solving optimal relay selection (RS) problem. Simulation results demonstrate that CL-JRSPA scheme gets larger EC than other schemes when satisfying delay QoS demand. In addition, the proposed CL-JRSPA scheme achieves the maximal EC when relay located approximately halfway between source and destination, and EC becomes smaller when the QoS exponent becomes larger.

On Secrecy Outage of Relay Selection in Underlay Cognitive Radio Networks Over Nakagami- $m$ Fading Channels

In this paper, the secrecy outage performance of an underlay cognitive decode-and-forward relay network over independent but not necessarily identical distributed Nakagami-m fading channels is investigated, in which the secondary user transmitter communicates with the secondary destination via relays, and an eavesdropper attempts to overhear the information. Based on whether the channel state information of the wiretap links is available or not, we analyze the secrecy outage performance with optimal relay selection (ORS) and suboptimal relay selection (SRS) schemes, and multiple relays combining scheme (MRC) scheme is considered for comparison purpose. The exact and asymptotic closed-form expressions for the secrecy outage probability with three different relay selection schemes are derived and verified by Monte-Carlo simulations. The numerical results illustrate that ORS scheme always outperforms SRS and MRC schemes, and SRS scheme is better than MRC scheme in the lower fading parameters scenario. Furthermore, through asymptotic analysis, we find that these three different schemes achieve the same secrecy diversity order, which is determined by the number of the relays, and the fading parameters of the links among the relays and the destination.

Cognitive Bidirectional Buffer-Aided DF Relay Networks: Protocol design and Power Allocation

In this paper, we consider bidirectional decode-and-forward buffer-aided relay selection and transmission power allocation schemes for underlay cognitive radio relay networks. First, a low complexity delay-constrained bidirectional relaying protocol is proposed. The proposed protocol maximizes the single-hop normalized sum of the primary network (PN) and secondary network (SN) rates and controls the maximum packet delay caused by physical layer buffering at relays. Second, optimal transmission power expressions that maximize the single-hop normalized sum rate are derived for each possible transmission mode. Simulation results are provided to evaluate the performance of the proposed relaying protocol and transmission power allocation scheme and compare their performance with that of the optimal scenario. Additionally, the impacts of several system parameters including maximum buffer size, interference threshold, maximum packet delay and number of relays on the network performance are also investigated. The results reveal that the proposed bidirectional relaying protocol and antenna transmission power allocation schemes introduce a satisfactory performance with much lower complexity compared to the optimal relay selection and power allocation schemes and provide an application dependent delay-controlling mechanism. It is also found that the network performance degrades as the delay constraint is more restricted until it matches the performance of conventional unbuffered relaying with delay constraints of three. Additionally, findings show that using buffer-aided relaying significantly enhances the SN performance while slightly weakens the performance of the PN.

Analysis of transmission capacity for multi-mode D2D communication in mobile networks

Device-to-device (D2D) communication is one of the promising technologies in the 5th generation of wireless communication (5G). This paper investigates the achievable transmission capacity for multi-mode D2D communication. By utilizing stochastic geometry tools, we first provide the system model and derive the transmission capacity for two different sharing schemes of underlaying D2D mode. The first one is that each cellular spectrum can be reused by single D2D pair and the other one considers the multiple sharing among several D2D pairs with the same spectrum. In addition, we analyze the strategy for the optimal selection between both different sharing scenarios. Secondly, we analyze the transmission capacity for overlay D2D mode. Finally, with the optimal relay selection strategy, the maximization of transmission capacity for relay-assisted D2D communication is obtained under the constraint of minimum energy consumption. Furthermore, simulations are carried out and the results demonstrate the effectiveness and validity of our analysis.

Maximum harvested energy policy in full‐duplex relaying networks with SWIPT

SummaryIt is considered that energy scavenging is a promising way for source node transfer energy to powered constraint relay in cooperative networks with advantage of cost‐effective maintenance and flexible deployment, which so‐called simultaneous wireless information and power transfer. In this paper, relay selection for optimal wireless energy is investigated. In terms of time switching–based relaying, this paper considers the performance comparison of 3 proposed relay selection schemes, namely, (1) optimal relay selection scheme, (2) maximum harvested energy relay selection scheme, and (3) minimum self‐interference relay selection. In particular, the system performance is studied intensively with regard to outage probability and throughput over Rayleigh fading channels. We also achieve the integral form for accurate expressions and closed form for approximate expressions. Finally, these analytical expressions are proved exactness according to Monte Carlo simulation.

Security Performance Analysis of DF Cooperative Relay Networks over Nakagami-m Fading Channels

In this paper, we investigate the security performance for cooperative networks over Nakagami-m fading channels. Based on whether the channel state information (CSI) of wiretap link is available or not, optimal relay selection (ORS) and suboptimal relay selection (SRS) schemes are considered. Also, multiple relays combining (MRC) scheme is considered for comparison purpose. The exact and asymptotic closed-form expressions for secrecy outage probability (SOP) are derived and simulations are presented to validate the accuracy of our proposed analytical results. The numerical results illustrate that the ORS is the best scheme and SRS scheme is better than MRC scheme in some special scenarios such as when the destination is far away from the relays. Furthermore, through asymptotic analysis, we obtain the closed-form expressions for the secrecy diversity order and secrecy array gain for the three different selection schemes. The secrecy diversity order is closely related to the number of relays and fading parameter between relay and destination.

Secure full-duplex two-way relaying networks with optimal relay selection

The secrecy outage probability (SOP) of cooperative communication systems with optimal relay selection (ORS) scheme in the presence of an eavesdropper is investigated by implementing decode-and-forward-based full-duplex (FD) two-way relayingmode. Under Rayleigh fading assumptions, the closed-form expressions for the distributions of end-to-end signal-to-interference-plus-noise ratio in each wireless link are derived. Furthermore, the closed-form expression for the exact SOP of the proposed ORS scheme is given out. Numerical results show that the SOP of the proposed system can be substantially impacted by several parameters involved, including the number of relays, the average signal-to-noise ratio (SNR) of eavesdropper links, and the average residual self-interference (SI) imposed on the FD relays. In particular, the impact of residual SI is shown to be more obvious in terms of eroding the system’s secrecy performance in a low-to-medium SNR regime than in a high-SNR regime. As long as the residual SI power is not beyond the background noise level, the proposed FD-TWC scheme can always outperform the conventional half-duplex mode in terms of SOP.

Enhancing physical-layer security via big-data-aided hybrid relay selection

The explosive growth in data traffic presents new challenges to the new generation of wireless communication systems, such as computing capabilities, spectrum efficiency and security. In this paper, we use the network structure, which is adaptable for the big data traffic, to improve the security of wireless networks. Specifically, a big-data aided hybrid relay selection scheme is designed and analyzed to enhance physical layer security. First, considering the ideal situation that an eavesdropper’s CSI (Channel State Information) is known to the legal nodes, we propose an optimal hybrid relay selection scheme consisting of the optimal mode selection scheme and the optimal relay selection scheme. In this case, we analyze the upper bound of an eavesdropper’s capacity in FD (Full-Duplex) mode and the secrecy outage probabilities of the optimal HD (Half-Duplex), FD, and hybrid relay selection schemes. Through the analysis of data, it is clear that the mode selection is decided by the self-interference of the FD technique. However, the instantaneous CSI of an eavesdropper is difficult to obtain due to the passive characteristic of eavesdroppers in practice. Therefore, a more practical hybrid relay selection scheme with only the channel distribution information of an eavesdropper is further studied, where a weighting factor is employed to guarantee that the hybrid mode is no worse than either the FD mode or HD mode when the self-interference grows. Finally, the simulation results show the improved security of our proposed scheme.

Quantum flower pollination algorithm for optimal multiple relay selection scheme

In order to obtain optimal selection scheme with multiple source-destination pairs and multiple potential relays in cooperative relay networks, an optimal relay selection scheme is designed in cooperative relay networks considering co-channel interference (CCI). It is an integer optimisation problem for selecting suitable relay nodes to obtain optimal system performance. To get the optimal estimation performance with low computing complexity, quantum flower pollination algorithm (QFPA) is proposed to resolve the difficulties of optimal relay selection, and the proposed optimal relay selection scheme is called as quantum flower pollination algorithm based optimal relay selection (QFPA-ORS). The proposed QFPA combines the advantages of quantum evolutionary theory and flower pollination algorithm (FPA). So QFPA has the capability to search the optimal solution. Simulation results show that QFPA based relay selection scheme has the ability to search global optimal solution compared with other relay selection schemes based on classical algorithm and performs better than three other previous intelligent algorithms.