In this paper, we study the secrecy outage probability (SOP) of an opportunistic relay selection scheme where an optimal relay is selected based on the delayed feedback from the multi-antenna destination. We present a new exact closed-form expression of the SOP, and two kinds of asymptotic form of SOP are further derived to explicitly show secrecy performance. In addition, we show that the SOP can be reduced by increasing the number of relays through analysis and simulation results. An important result show that the secrecy diversity order of the system has nothing to do with the number of relays with outdated CSI.
In this paper, we study the secrecy outage probability (SOP) of an opportunistic relay selection scheme where an optimal relay is selected based on the delayed feedback from the multi-antenna destination. We present a new exact closed-form expression of the SOP, and two kinds of asymptotic form of SOP are further derived to explicitly show secrecy performance. In addition, we show that the SOP can be reduced by increasing the number of relays through analysis and simulation results. An important result show that the secrecy diversity order of the system has nothing to do with the number of relays with outdated CSI.
Opportunistic relay selection is an important approach to enhance physical layer secrecy of relaying networks, but that severely depends on the obtained CSIs. In this letter, we study the impact of limited CSI feedback on the secrecy performance of cooperative decode-and-forward (DF) relay networks with opportunistic relay selection. We first derive the exact closed-form expression for the secrecy outage probability (SOP), and the asymptotic expression for SOP in the high signal-to-noise ratio (SNR) region. Then, based on the derived expressions, we evaluate the impact of limited CSI feeback on secrecy outage probability and secrecy diversity order. Numerical results show that the secrecy diversity order is 2, regardless of the number of feedback bits. However, increasing the number of feedback bits can improve the secrecy outage performance.
In this paper, we present a comprehensive investigation on the secrecy performance of opportunistic relay selection systems employing the decode-and-forward protocol over Rayleigh fading channels. Considering a practical setting where direct link between the source node (Alice) and the destination node (Bob) is available, we study the secrecy performance of three different diversity combining schemes, namely, maximum ratio combining (MRC), distributed selection combining (DSC), and distributed switch-and-stay combining (DSSC). Throughout the analysis, we consider two different scenarios based on the availability of the eavesdropper's channel state information (CSI), i.e., Scenario A, where the eavesdropper's CSI is not available at Alice and the relay, and Scenario B, where Alice and the relay have knowledge about the eavesdropper's CSI. For Scenario A, we derive exact closed-form expressions for secrecy outage probability and simple asymptotic approximations for the secrecy outage probability, which enable the characterization of the achievable secrecy diversity order and coding gains. For Scenario B, we derive closed-form expressions for the achievable secrecy rates. For both scenarios, we investigate the impact of feedback delay (outdated CSI) on the secrecy performance wherein exact and asymptotic secrecy outage probability and closed-form expressions of the secrecy achievable rates are obtained. Our analytical findings suggest that both the MRC and DSC schemes achieve the maximum diversity order of K+1 where K is the number of relays. In addition, the feedback delay has a significant impact on the achievable secrecy performance by reducing the achievable diversity order to two.
This paper investigates secure cooperative transmissions in a dual-hop MIMO relay system using a combined transmit antenna selection (TAS) and maximal-ratio combining (MRC) scheme over the Nakagami-m fading channels, where an adaptive decode-and-forward relaying protocol and an multi-antenna eavesdropper are considered. Due to the feedback delay, channel state information (CSI) for TAS might be outdated at both the source and the relay. To evaluate the secrecy performance of the TAS/MRC scheme and the impacts of outdated CSI, the closed-form expressions for the metrics of exact ergodic secrecy rate and exact secrecy outage probability are derived under both perfect and outdated CSI conditions in a channel feedback error model. In order to explicitly reveal the behaviors of the secrecy performance in high signal-to-noise ratio regime, asymptotic expressions for both the metrics are further derived. As validated by simulation results, analytically numerical results demonstrate that outdated the CSI always results in a loss in the secrecy performance, but the loss can be recovered by increasing the number of antennas at legitimate receivers. Furthermore, the outdated CSI yields a reduced secrecy diversity order, whereas only the perfect CSI leads to the full secrecy diversity order.
This paper studies cooperative transmission for securing a two‐hop network where the eavesdropper can wiretap the relay channels. With outdated channel state information (CSI), we propose an opportunistic relaying with destination‐based jamming scheme, where one relay is chosen to forward the confidential signal and the destination sends jamming signal to confuse the eavesdropper. To reveal the capability of the proposed scheme in improving the system secrecy, we investigate the two common performance metrics under different assumptions on the eavesdropper CSI. First, lower bound on the ergodic secrecy capacity (ESC) is derived assuming perfect knowledge of the eavesdropper channel gains. We, then, extend our results to the scenario where only the legitimate channel gain is known. Here, lower bound on the secrecy outage probability (SOP) is obtained. To further improve the utility of the destination, under total power constraint, a power allocation between data signal and jamming noise is considered. Both the analysis and simulation results indicate that the system performance is significantly improved in terms of both ESC and SOP when the jamming power at the destination is adjusted according to the selected relay position. We verify that, with outdated CSI, the secrecy performance of opportunistic relaying is severely degraded.
In this letter, we analyze the impacts of outdated channel state information (CSI) on the secrecy performance for multiple-input single-output multiple-eavesdropper (MISOME) systems using transmit antenna selection (TAS) scheme and derive the exact closed-form expressions for the secrecy outage probability and the probability of non-zero secrecy capacity. Then, we present the asymptotic secrecy outage probability which reveals the secrecy diversity order and the secrecy array gain. The analysis and simulation results show that the security performance of TAS scheme is quite sensitive to outdated CSI and the achievable secrecy diversity order is only one under the effect of outdated CSI.
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.