Abstract We investigate the secrecy performance of cellular multiuser two‐way relay networks, where the bidirectional information exchange between a multiantenna base station (BS), and several users can be accomplished with the assistance of decode‐and‐forward relay(s) in the presence of a multiantenna passive eavesdropper. We employ low‐complexity antenna selection strategy at the BS coupled with user scheduling for maximizing the end‐to‐end signal‐to‐noise ratios (SNRs). To enhance the wiretap probability, the eavesdropper applies a maximal ratio combining technique to combine the received signals. Under such considerations, in the single‐relay scenario, we deduce the exact closed‐form secrecy outage probability (SOP) expression under Rayleigh fading channels. For more insights into the system secrecy diversity order, we derive the closed‐form asymptotic SOP expressions at high SNR based on the quality of the main and wiretap links. In the multirelay scenario, we formulate an opportunistic relay selection strategy, followed by its impact on the SOP performance in the presence of Rayleigh channels. To show the impact of multiple relays on the secrecy diversity order, we derive the asymptotic SOP expressions in the high SNR regime depending on the quality of the main and wiretap links. It is shown from the asymptotic SOP expressions under both single‐relay and multirelay scenarios that the secrecy diversity order reduces to zero in the high SNR regime, regardless of number of antennas, number of users, and number of relays. Our results also reveal that the SOP performance diminishes with an increased number of eavesdropper antennas. Numerical and simulation results verify our derived analytical findings.
Abstract We investigate the secrecy performance of cellular multiuser two‐way relay networks, where the bidirectional information exchange between a multiantenna base station (BS), and several users can be accomplished with the assistance of decode‐and‐forward relay(s) in the presence of a multiantenna passive eavesdropper. We employ low‐complexity antenna selection strategy at the BS coupled with user scheduling for maximizing the end‐to‐end signal‐to‐noise ratios (SNRs). To enhance the wiretap probability, the eavesdropper applies a maximal ratio combining technique to combine the received signals. Under such considerations, in the single‐relay scenario, we deduce the exact closed‐form secrecy outage probability (SOP) expression under Rayleigh fading channels. For more insights into the system secrecy diversity order, we derive the closed‐form asymptotic SOP expressions at high SNR based on the quality of the main and wiretap links. In the multirelay scenario, we formulate an opportunistic relay selection strategy, followed by its impact on the SOP performance in the presence of Rayleigh channels. To show the impact of multiple relays on the secrecy diversity order, we derive the asymptotic SOP expressions in the high SNR regime depending on the quality of the main and wiretap links. It is shown from the asymptotic SOP expressions under both single‐relay and multirelay scenarios that the secrecy diversity order reduces to zero in the high SNR regime, regardless of number of antennas, number of users, and number of relays. Our results also reveal that the SOP performance diminishes with an increased number of eavesdropper antennas. Numerical and simulation results verify our derived analytical findings.
In this paper, we investigate the secrecy performance of cellular multiuser two-way decode-and-forward (DF) relay networks with physical-layer security constraints, wherein a multiantenna base station (BS) communicates bidirectionally with several single-antenna mobile stations (MSs) via single-antenna DF relay in the presence of a single-antenna eavesdropper. We employ antenna selection (AS) transmission scheme at the BS with MS scheduling. Specifically, we derive the closed-form expression for the secrecy outage probability (SOP) of the considered system under independent and identically distributed (i.i.d.) Rayleigh fading channels. To gain more insights into the system secrecy diversity order, we analyze the asymptotic secrecy outage behavior in the high signal-to-noise ratio (SNR) regime. Our results reveal that the SOP saturates in the medium-to-high SNR regime, and reduces the secrecy diversity order to zero. Finally, the numerical and simulation corroborate our theoretical and analytical findings.
In this paper, we investigate the performance of secure cellular multiuser two-way amplify-and-forward relay networks, wherein one Na-antenna base station (BS) exchanges information bidirectionally with K single-antenna users (USs) by the assistance of a single-antenna relay node in the presence of a singleantenna passive eavesdropper. We employ user selection coupled with antenna selection (AS) scheme at the BS so as to maximize the end-to-end signal-to-noise ratios. In the considered system, by employing two possible combining techniques at the eavesdropper, viz., maximum ratio combining (MRC) and selection combining (SC), we derive the novel tight closed-form expressions for the secrecy outage probability (SOP) under Rayleigh fading channels. We present an asymptotic secrecy diversity order analysis of the considered system for the large transmit power, and demonstrate that the eavesdropping reduces the secrecy diversity order from min(Na, K) to 1. Further, we present some useful insights into the impact of eavesdropper and number of antennas and users on the SOP performance. It is shown that the eavesdropper has a severe impact on the SOP performance, regardless of number of antennas and users. The numerical and simulation results corroborate our theoretical findings, and demonstrate the influence of eavesdropper and relay positions on the SOP performance. We show that the SOP performance improves significantly when the eavesdropper is far away from the BS and USs. It is also shown that the SOP performance enhances noticeably if the relay location is chosen optimally, for different eavesdropper positions and/or different values of antennas and users. Moreover, our results also reveal that only coding gain rather than diversity gain is achieved by increasing Naand K, because of the dominance of information leakage by the first time phase. Furthermore, results illustrate that the SOP performance under SC technique employed at the eavesdropper outperforms the MRC-based technique for the broad range of transmit power.
In this paper, we study a downlink multiuser network in which one base station sends its message to one of multiple users, assisted by one of multiple intermediate decode-and-forward (DF) relays. Multiple eavesdroppers exist at the receiver side, and they can overhear the message from the base station, which brings out the issue of information security. We consider moderate shadowing environments so that direct links from the base station to the users and eavesdroppers exist. Maximal ratio combing (MRC) technique is employed at the receivers to combine the signals from the relaying and direct links. We select the best user and relay pair by maximizing the received signal-to-noise ratio (SNR) at the user. We study the effects of the selection on the system secrecy performance by deriving the closed-form expression of secrecy outage probability. We also provide the asymptotic secrecy outage probability with high transmit power and high main-to-eavesdropper ratio (MER). From the asymptotic expression, we can find that the system can achieve the diversity of the total number of users and relays, irrespective of the number of eavesdroppers. Simulation and numerical results are finally demonstrated to verify the proposed studies.
We present two physical layer secure transmission schemes for multiuser multirelay networks, where the communication from M users to the base station is assisted by direct links and by N decode-and-forward relays. In this network, we consider that a passive eavesdropper exists to overhear the transmitted information, which entails exploiting the advantages of both direct and relay links for physical layer security enhancement. To fulfill this requirement, we investigate two criteria for user and relay selection and examine the achievable secrecy performance. Criterion I performs a joint user and relay selection, while Criterion II performs separate user and relay selections, with a lower implementation complexity. We derive a tight lower bound on the secrecy outage probability for Criterion I and an accurate analytical expression for the secrecy outage probability for Criterion II. We further derive the asymptotic secrecy outage probabilities at high transmit signal-to-noise ratios and high main-to-eavesdropper ratios for both criteria. We demonstrate that the secrecy diversity order is min (MN, M + N) for Criterion I, and N for Criterion II. Finally, we present numerical and simulation results to validate the proposed analysis, and show the occurrence condition of the secrecy outage probability floor.
The authors investigate the secrecy performance of a cooperative relaying network, wherein a fixed source communicates with a fixed destination via an amplify‐and‐forward mobile relay in the presence of a passive mobile eavesdropper. They assume that the source‐to‐relay channel and relay‐to‐destination channel experience Nakagami‐ m fading, whereas relay‐to‐eavesdropper link follows double Nakagami‐ m fading. Under such a mixed fading environment, they derive the novel tight closed‐form expressions for the secrecy outage probability (SOP), probability of non‐zero secrecy capacity, and intercept probability of the considered system. They also deduce the asymptotic secrecy outage and intercept probability expressions in the high signal‐to‐noise ratio regime to highlight the impact of fading parameters and channel conditions on the secrecy diversity order. It is shown that the system can achieve secrecy diversity order of min( ) in terms of SOP, and in terms of intercept probability, where and represent the fading severity parameters between source and relay and between relay and destination, respectively. They also formulate and investigate analytically two optimisation problems, namely, optimal relay location with fixed power allocation and optimal power allocation with fixed relay location, to minimise the system SOP. They verify analytical findings via numerical and simulation results.
This paper proposes relay selection to increase the physical layer security in multiuser cooperative relay networks with multiple amplify-and-forward relays, in the presence of multiple eavesdroppers. To strengthen the network security against eavesdropping attack, we present three criteria to select the best relay and user pair. Specifically, criteria I and II study the received signal-to-noise ratio (SNR) at the receivers, and perform the selection by maximizing the SNR ratio of the user to the eavesdroppers. To this end, criterion I relies on both the main and eavesdropper links, while criterion II relies on the main links only. Criterion III is the standard max-min selection criterion, which maximizes the minimum of the dual-hop channel gains of main links. For the three selection criteria, we examine the system secrecy performance by deriving the analytical expressions for the secrecy outage probability. We also derive the asymptotic analysis for the secrecy outage probability with high main-to-eavesdropper ratio. From the asymptotic analysis, an interesting observation is reached: for each criterion, the system diversity order is equivalent to the number of relays regardless of the number of users and eavesdroppers.