Evaluating secrecy performance of cooperative NOMA networks under existence of relay link and direct link

The secrecy performance of a nonorthogonal multiple access (NOMA) system is examined in this study by employment of a dual‐hop decode‐and‐forward (DF) relay under existence of eavesdropper. Due to the fact that the relay is trusted or untrusted device and thus eavesdropper may wiretap information from the base station or the relay. In this regard, three scenarios related to trusted and untrusted relays are proposed, with different assumptions on the information overhearing ability of the eavesdropper; ie, the first scenario is that an eavesdropper overhears signal from the relay while the BS is overheard by eavesdropper in the second scenarios. More specifically, we derive closed‐form expressions for the secure probability metrics when the direct and relay links experience independent Rayleigh fading. There metrics include strictly positive secrecy capacity (SPSC) and the secure outage probability (SOP). Furthermore, secure performance of traditional orthogonal multiple access (OMA) is also provided as further comparison with NOMA counterpart. We analyze the influence of main coefficients such as the target rates and the transmit SNR factors on the secrecy performance. Our results specify that for reasonable selection of such parameters, secrecy performance can be enhanced remarkably. Numerical results are delivered to corroborate the derived results.     

Secure AF relaying with efficient partial relay selection scheme

This paper evaluates the secrecy performance for the amplify‐and‐forward (AF) protocol with partial relay selection (PRS) schemes in the scenario of multiple independent but not necessarily identically distributed eavesdroppers. The secrecy performances of the first‐hop and second‐hop PRS schemes are revisited. Given the secrecy data rate, an efficient PRS scheme is presented, which selects the relay based on the instantaneous channel state information (CSI) of either the first or second hop according to the statistical CSI of two hops. The proposed PRS scheme provides the trade‐off between the two‐hop and one‐hop PRS criteria. Results show that the secrecy outage probability (SOP) performance of the proposed scheme is close to that of the conventional opportunistic relaying in the medium main‐to‐eavesdropper ratio (MER) regions. As for the intercept probability, the second‐hop scheme achieves the highest diversity order among PRS schemes and its performance depends on the overall eavesdroppers' behavior not on individual effects of the specific relay. The proposed criterion also outperforms the first‐hop PRS scheme. Simulation results finally substantiate the accuracy of the theoretical analysis.     

Analysis of secrecy outage performance for full duplex NOMA relay systems with appearance of multiple eavesdroppers

Full-duplex (FD) relay systems including a transmit antenna selection and a non-orthogonal multiple access (NOMA) methods are analyzed under presence of multiple eavesdroppers. A channel state information of both the considered system and eavesdroppers is assumed to be outdated and eavesdroppers eavesdrop information signals independently. A closed-form of secure outage probability (SOP), secrecy throughput of every user is derived to evaluate the secrecy performance, and the mathematical analysis approach is verified by the Monte-Carlo simulation. Furthermore, the Golden-Section Search algorithm is proposed to find the maximum of the secrecy throughput of the considered FD-NOMA system. Numerical results indicate that there exists the SOP floor in the considered system and it is constrained by the channel gain of near user. Moreover, there is the optimal signal to interference plus noise ratio value which minimizes the SOP of the system regardless of the number of eavesdroppers. In comparison with half-duplex NOMA model, the SOP of FD-NOMA model is better.

     

NOMA-D2D协作无线系统的物理层安全

针对未来海量用户设备接入的物理层安全（physical layer security，PLS）应用需求，提出了一种组合非正交多址接入（non-orthogonal multiple access，NOMA）、终端直通（device-to-device，D2D）与中继协作的NOMA-D2D协作无线系统PLS模型。该模型由采用发射天线选择（transmit antenna selection，TAS）的基站、分别作为基站和D2D发射端的NOMA远端蜂窝用户、D2D接收端以及被动窃听者组成，其中的D2D发射端承担基站的 NOMA 近端用户和解码转发中继两种角色。利用高斯—切比雪夫正交定理推导两种 TAS 方案下NOMA-D2D协作无线系统的安全中断概率、非零安全容量概率以及渐近安全中断概率的近似表达式。数值计算和仿真实验验证了NOMA-D2D协作无线系统PLS性能分析的准确性；在基站总功率恒定时增大分配给远端蜂窝用户的功率能有效提升NOMA-D2D协作无线系统的PLS性能。     

Secrecy analysis of a cooperative NOMA network using an EH untrusted relay

In this paper, a down-link non-orthogonal multiple access (NOMA) system with imperfect successive interference cancellation (SIC) using Energy-Harvesting untrusted relays is investigated. These relaying nodes use in this study use a power-switching architecture to harvest energy from the sources signals and apply an amplify-and-forward protocol to forward the signals. In addition, transmit jamming or artificial noise, is generated by a source node to improve the security of the system and protect confidential source information from untrusted relays. Likewise, three relaying selection strategies are employed to examine the secrecy performance of the proposed system. In order to evaluate the performance evaluation of the proposed system, closed-form expressions of the Secrecy Outage Probability (SOP) are studied over Rayleigh fading channels and a Monte Carlo simulation is used to confirm the analytical results. Furthermore, we study the effects of various parameters, such as power allocation factors, relay node selection, the number of relays, energy harvesting efficiency and the location of relay nodes on the secure outage performances for two users of NOMA system and conventional orthogonal multiple access (OMA). These results show that NOMA offers the better security performance with multiple users.     

Physical layer security for dual‐hop FSO/RF system using generalized ΓΓ/η−μ fading channels

We investigate the physical layer security of decode‐and‐forward–relayed free space optics (FSO)/radio frequency (RF) communication system. In this network, the eavesdropper exists after relay node and overhears RF transmission. Further, FSO being a line‐of‐sight transmission is assumed to be secure from eavesdroppers. Here, we have the Gamma‐Gamma (ΓΓ) distribution for FSO link and generalized η?μ distribution for RF link. The security for information transmission to the legitimate user in the presence of an eavesdropper is measured in terms of secrecy capacity and secrecy outage probability. Deriving the probability density function and cumulative distribution function of end‐to‐end signal‐to‐noise ratio, the closed‐form expressions for security parameters are achieved. The numerical analysis of the proposed system is done under the influence of atmospheric turbulence effects and various fading conditions. The results have been verified through simulation.     

Secrecy performance analysis of AF relaying with relay selection scheme over Nakagami‐m fading channels

This paper investigates the secrecy outage probability (SOP) and intercept behavior for the amplify‐and‐forward network over Nakagami‐m fading channels. Relay selection schemes are evaluated. The optimal and suboptimal criterions require the instantaneous and statistical channel state information of the eavesdroppers' channels, respectively. The enhanced 2‐hop criterion needs the additional information of the target secrecy rate for relay selection. Theoretical analysis reveals that the diversity order of the SOP is dominated by the minimum fading figures of the source‐relay and relay‐destination channels, while that of the intercept probability depends on the fading figure of the relay‐destination channel. In the multirelay scenario, the optimal, suboptimal, and enhanced 2‐hop scheme achieve the same diversity orders of the SOP. For the intercept probability, the optimal and second‐hop relay selection schemes provide the same diversity order, while the diversity orders of the suboptimal and enhanced 2‐hop schemes are the same. Simulation results finally substantiate the accuracy of the theoretical analysis.     

On the secrecy performance of integrated satellite‐aerial‐terrestrial networks

This paper investigates secure transmission of an integrated satellite‐aerial‐terrestrial network (ISATN), where multiple eavesdroppers (Eves) attempt to overhear the satellite signals cooperatively. The ISATN adopts an unmanned aerial vehicle (UAV) equipped with multiple antennas as a relay with threshold‐based decode‐and‐forward (DF) protocol. By assuming that perfect instantaneous channel state information (CSI) of the satellite‐UAV link and the statistical CSI of the UAV‐user link are available, we first propose a beamforming (BF) scheme for maximizing the achievable secrecy rate (ASR) of the considered network. Then, we derive the analytical expressions of the secrecy outage probability (SOP) and ergodic secrecy rate (ESR) of the considered system with the BF strategy under an assumption that the satellite‐UAV link undergoes the shadowed‐Rician fading, while the UAV‐user link experiences the correlated Rayleigh fading. Finally, numerical results are given to demonstrate the superiority of the proposed BF scheme against zero forcing (ZF) and maximal ratio transmission (MRT) schemes and the validity of the secrecy performance analysis.     

Power allocation-Assisted secrecy analysis for NOMA enabled cooperative network under multiple eavesdroppers

In this work, the secrecy of a typical wireless cooperative dual-hop non-orthogonal multiple access (NOMA)-enabled decode-and-forward (DF) relay network is investigated with the impact of collaborative and non-collaborative eavesdropping. The system model consists of a source that broadcasts the multiplexed signal to two NOMA users via a DF relay, and information security against the eavesdropper nodes is provided by a helpful jammer. The performance metric is secrecy rate and ergodic secrecy capacity is approximated analytically. In addition, a differential evolution algorithm-based power allocation scheme is proposed to find the optimal power allocation factors for relay, jammer, and NOMA users by employing different jamming schemes. Furthermore, the secrecy rate analysis is validated at the NOMA users by adopting different jamming schemes such as without jamming (WJ) or conventional relaying, jamming (J), and with control jamming (CJ). Simulation results demonstrate the superiority of CJ over the J and WJ schemes. Finally, the proposed power allocation outperforms the fixed power allocation under all conditions considered in this work.     

Secrecy performance analysis on cooperative CR-NOMA network

In order to improve the secrecy performance of communication system and make efficient use of limited spectrum,overlay cognitive radio (OCR) technology was combined with non-orthogonal multiple access (NOMA) technology and the communication model was proposed,in which secondary network realized dynamic switching between assisting primary network communication and secondary network communication by sensing whether the primary user occupied the spectrum or not.Artificial noise (AN) aided technology was used in primary and secondary networks respectively to further improve the secrecy performance of the system.The secrecy performance of the system was studied by deducing the expressions of the primary and secondary network secrecy outage probability and secrecy throughput respectively.The simulation results show that the proposed cognitive cooperative NOMA communication scheme is beneficial in reducing secrecy outage probability and increasing secrecy throughput.Furthermore,the influence of AN power allocation factor on system performance is given.     

Performance analysis of nonorthogonal multiple access‐based underlay cognitive relay network

This paper considers cooperative non‐orthogonal multiple access (NOMA) scheme in an underlay cognitive radio (CR) network. A single‐cell downlink cooperative NOMA system has been considered for the secondary network, consisting of a base station (BS) and two secondary users, ie, a far user and a near user. The BS employs NOMA signaling to send messages for the two secondary users where the near user is enabled to act as a half‐duplex decode‐and‐forward (DF) relay for the far user. We derive exact expressions for the outage probability experienced by both the users and the outage probability of the secondary system assuming the links to experience independent, nonidentically distributed Rayleigh fading. Further, we analyze the ergodic rates of both the users and the ergodic sum rate of the secondary network. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. Further, the interference caused by the primary transmitter (PT) on the secondary network is also considered for the analysis. The performance of the proposed CR NOMA network has been observed to be significantly better than a CR network that uses conventional orthogonal multiple access (OMA) scheme. The analytical results are validated by extensive simulation studies.     

基于安全中断概率的D2D安全接入策略

针对D2D蜂窝系统通信安全性受资源限制的问题,考虑到蜂窝链路和D2D链路的同频干扰能够为两者带来安全增益,基于此,提出一种基于安全中断概率的D2D用户接入策略。首先理论分析了蜂窝用户和D2D用户的安全中断概率,并给出了基于安全中断概率最小化的D2D用户功率优化算法。在上述分析的基础上,选择安全中断概率最小的D2D用户接入复用蜂窝用户的无线资源,同时提高D2D通信链路和蜂窝上行链路的安全性。最后,仿真结果证明了所提算法的有效性。     

MF中继选择系统的物理层安全性能

针对合谋窃听场景下单天线多中继修改转发（MF）协作无线系统的安全性能较差问题,提出一种合谋窃听场景下联合源节点发送天线选择（TAS）和多中继选择的MF协作物理层安全系统,考虑最优的最大化主信道信噪比（SNR）和次优的最大化源节点-中继节点链路 SNR 两种中继选择方案,推导其安全中断概率（SOP）和遍历安全容量（ESC）的解析表达式。最优或次优中继选择的MF安全中继系统的SOP和ESC的数值计算结果与仿真结果相吻合,验证了上述理论分析的正确性;同时也表明源节点发射天线数和中继节点数越多、窃听节点数越少,最优或次优中继选择的MF安全中继系统的物理层安全性能越好。     

Joint optimization for secure ambient backscatter communication in NOMA-enabled IoT networks

Non-Orthogonal Multiple Access (NOMA) has emerged as a novel air interface technology for massive connectivity in Sixth-Generation (6G) era. The recent integration of NOMA in Backscatter Communication (BC) has triggered significant research interest due to its applications in low-powered Internet of Things (IoT) networks. However, the link security aspect of these networks has not been well investigated. This article provides a new optimization framework for improving the physical layer security of the NOMA ambient BC system. Our system model takes into account the simultaneous operation of NOMA IoT users and the Backscatter Node (BN) in the presence of multiple EavesDroppers (EDs). The EDs in the surrounding area can overhear the communication of Base Station (BS) and BN due to the wireless broadcast transmission. Thus, the chief aim is to enhance link security by optimizing the BN reflection coefficient and BS transmit power. To gauge the performance of the proposed scheme, we also present the suboptimal NOMA and conventional orthogonal multiple access as benchmark schemes. Monte Carlo simulation results demonstrate the superiority of the NOMA BC scheme over the pure NOMA scheme without the BC and conventional orthogonal multiple access schemes in terms of system secrecy rate.     

Secure opportunistic access control in D2D-enabled cellular network

The mutual interference between cellular links and D2D links can bring the secrecy gain to cellular users in D2D-enable cellular networks.To make full use of them,a cooperative secrecy transmission scheme was proposed based on wireless channels.The channel direction information and gains depict the interference from D2D links to cellular links and other D2D links in the proposed scheme.Firstly,only the D2D users which meet the limited interference conditions were accessed to cellular networks to ensure their reliable communications.It was assumed that legitimate users and eavesdroppers were independent two-dimensional homogeneous Poisson point processes (PPP) distribution.Then the security outage probability (SOP) was derived for cellular users and the connection outage probability (COP) for D2D users,and the impacts of interference thresholds were discussed on their performances.Next,an optimization model was given to minimize D2D users’ COP while ensuring the secrecy performance requirements of cellular users,thus achieving the optimal performance.Finally,simulation results verify the validity of the proposed scheme.     

AN-aided full-duplex secure transmissions under imperfect self-interference cancellation

This paper considers a full-duplex (FD) secure transmission scheme with aid of the artificial noise deployed at both transmitter and receiver under imperfect self-interference cancellation. The expressions of secrecy and connection outage probabilities are derived, and hence, the secrecy throughput of the proposed scheme is evaluated. The results show that the performance of the proposed FD scheme outperforms that of conventional half-duplex and FD receiver schemes in terms of the secrecy outage probability. In addition, the proposed FD scheme can achieve high secrecy throughput under various locations of the eavesdropper. Especially when the eavesdropper is located close to the transmitter, the secrecy throughput of the proposed FD scheme is nearly double that of the half-duplex scheme with artificial noise injection while that of the scheme with FD jamming receiver goes to zero.     

Impact of fixed power allocation in wireless energy harvesting NOMA networks

The time switching‐based relaying (TSR) scheme is considered in energy harvesting protocol to implement with its advantage to nonorthogonal multiple access (NOMA) system. In particular, decode‐and‐forward (DF) mode is proposed to employ in relay to forward signal to serve two far NOMA users. There are two main metrics including outage probability and ergodic rate, which are derived in exact expressions with respect to varying performance under impacts of energy harvesting fractions. To evaluate system performance, outage event and related capacity are illustrated, and we tailor performance gap among two NOMA users and such gap can be controlled by selecting of appropriate power allocation factors assigned for each user to obtain optimal performance. By examining node arrangement, target rates and varying transmit signal to noise ratio (SNR), it can be further achieved performance in several situations of such NOMA. As important result, the considered NOMA system outperforms than the conventional multiple access scheme, and this expected result is confirmed in numerical result and theoretical results. We also explore impacts of transmit power at source, noise power, the other key parameters of energy harvesting scheme to exhibit outage, and ergodic performance. Simulation results are presented to corroborate the proposed methodology.     

Secrecy Performance of CCRN with an EHAF Relay under Source and Destination Jamming

In this paper, we investigate the secrecy performance of a cooperative cognitive radio network (CCRN) considering a single energy harvesting (EH) half‐duplex amplify and forward (AF) relay and an eavesdropper (EAV). Power is allocated to each node under cognitive constraints. Because of the absence of a direct wireless link, secondary source (SS) communicates with secondary destination (SD) in two time slots. The SD and the SS broadcast jamming signal to confuse the EAV in the first and in the second time slots, respectively. The relay harvests energy in the first time slot and amplifies and forwards the signal to SD in the second time slot. The EAV employs maximal ratio combining scheme to extract the information. We evaluate the performance in terms of secrecy outage probability (SOP) of the proposed CCRN. The approximate expression of SOP is obtained in integration form. Improvement in SOP is expected for the proposed CCRN because of the use of jamming signals. The secrecy performance of CCRN improves with increase in primary transmit power, peak transmit power of secondary nodes, channel mean power, and energy conversion efficiency but degrades with increase in threshold outage rate of primary receiver and threshold secrecy rate. A MATLAB‐based simulation framework has been developed to validate the analytical work.     

Secure communication in cognitive radio networks with untrusted AF relays

In this paper, two underlay based cognitive cooperative radio networks, each with one secondary source (SS), one secondary destination (SD), N untrusted secondary amplify and forward relays (USAFRs), one primary transmitter, and one primary receiver (PU‐RX), are considered for evaluating the secrecy performance. The SS sends the information to the SD in two time slots via multiple USAFRs in the absence of direct link between SS and SD. In the first time slot, SS and SD transmit the message and jamming signal to multiple USAFRs, respectively. In the second slot, a selected USAFR amplifies and forwards the combined received signals to the SD. The transmit powers of the secondary nodes are chosen so as to maintain the overall interference at PU‐RX below a specified limit. The transmit power of a selected USAFR is derived using the harvested energy from the RF signals of SS and SD. Two network scenarios of eavesdropping by USAFRs are studied: in one case, all USAFRs eavesdrop; while in the second case, only the selected USAFR eavesdrops the message during forwarding of the signal and power is allocated to secondary nodes on the basis of outage threshold of primary network. We investigate the secrecy outage probability (SOP) in both of the networks under several physical parameters. Analytical framework for evaluating SOP for both the cases are given while SOP in single integration form is given for the second case. MATLAB simulation results are presented for both the cases.     

Enhanced Physical Layer Security for Cooperative NOMA Network with Hybrid-Decode-Amplify-Forward Relaying via Power Allocation Assisted Control Jamming

This paper introduces the hybrid-decode-amplify-forward (HDAF) cooperative relaying into a control jamming aided NOMA network under Rayleigh-flat-fading channel conditions. In HDAF, the relay switches between AF and DF modes based on SNR threshold to forward the information signal to the corresponding NOMA users in the existence of an eavesdropper. We first characterize the secrecy performance of the considered network in terms of secrecy rate at both NOMA users analytically under different jamming scenarios. Further, to improve the secrecy rate, Differential Evolution (DE) algorithm-based power allocation is adopted to optimize the powers of jammer, relay, and NOMA users for which maximization of secrecy rate is chosen as the cost function. Moreover, the impact of different numerical parameters such as signal-to-noise ratio (SNR), jammer-to-eavesdropper distance, and relay-to-eavesdropper distance on the secrecy rate is investigated at both NOMA users by employing different jamming schemes. The MATLAB based simulation results validate the efficacy of proposed power allocation over fixed power allocation, CJ over other jamming schemes, and application of HDAF relaying for physical layer security enhancement of NOMA enabled cooperative network.