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.
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 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important result show that the secrecy diversity order of the system has nothing to do with the number of relays with outdated CSI.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 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 considers secrecy of a three node cooperative wireless system in the presence of a passive eavesdropper. The threshold-selection decode-and-forward relay is considered, which can decode the source message correctly only if a predefined signal-to-noise ratio (SNR) is achieved. The effects of channel state information (CSI) availability on secrecy outage probability (SOP) and ergodic secrecy rate (ESR) are investigated, and closed-form expressions are derived. Diversity is achieved from the direct and relaying paths both at the destination and at the eavesdropper by combinations of maximal-ratio combining and selection combining schemes. An asymptotic analysis is provided when each hop SNR is the same in the balanced case and when it is different in the unbalanced case. The analysis shows that both hops can be a bottleneck for secure communication; however, they do not affect the secrecy identically. While it is observed that CSI knowledge can improve secrecy, the amount of improvement for SOP is more when the required rate is low and for ESR when the operating SNR is also low. It is also shown that the source to eavesdropper link SNR is more crucial for secure communication.
Considering existing eavesdroppers, this paper analyzes the secrecy outage probability (SOP) of the full-duplex (FD) relaying network with imperfect channel state information (CSI), where the decode-and-forward relay protocol is adopted. To enhance the physical-layer security, two relay selection schemes are proposed. The first scheme uses the maximum-minimum principle to select the optimal relay. The other selection scheme is based on partial signal-to-interference-plus-noise ratio. Then, the tight closed-form approximations of the SOP are obtained for three special CSI cases, respectively. Moreover, based on these approximated results, the effects of some system parameters are analyzed for the SOP of the relay system, including the CSI error, the number of relays, the signal-to-noise ratio (SNR) of the eavesdropper, and the residual self-interference caused by the FD model. The numerical results show that at low SNR of the eavesdropper, residual self-interference has a significantly impact on SOP, while at high SNR of the eavesdropper, this effect is negligible. In addition, the SOP of FD model is always superior to the half-duplex (HD) model when the number of relays changes.
This paper investigates the physical-layer security of the modify-and-forward (MF) protocol in multi-relay and multieavesdropper networks. Three relay selection critera are developed according to the channel state information (CSI) acquisition. CriterionI requires the CSI of all main channels for relay selection. Criteria II and III rely only on the CSI of the source-relay and relay-destination channels, respectively. We derive the exact secrecy outage probability (SOP), probability of nonzero secrecy capacity, and the ergodic secrecy rate in the closed forms. The €-outage secrecy capacity is also evaluated. Asymptotic analysis of the SOP explicitly reveals that the secrecy diversity order of criterionI depends on the total number of relays, whereas those of criteriaII and III are 2 and 1, respectively. The probability of nonzero secrecy capacity asymptotically decreases with the SNR of the wiretap channel as the eavesdropper is close to the source and relays. CriterionI is always superior to criteriaII and III in terms of the ergodic secrecy rate and €-outage secrecy capacity. Simulations results also demonstrated that the €-outage secrecy capacity deteriorates as the SNR of the eavesdropper's channel increases.
In this work, we investigate the security performance of adaptive decode-and-forward cooperative networks when the signals transmitted from source and relay would be wiretapped. Based on whether the channel state information (CSI) of the wiretap link is available or not, optimal relay selection (ORS), conventional relay selection (CRS), and multiple relays selection (MRS) schemes are considered, and the exact closed-form expressions for security outage probability (SOP) are derived. Besides, we obtain the closed-form expressions for the secrecy diversity order and secrecy array gain of the three different selection schemes through asymptotic analysis. Simulations are presented to validate the accuracy of our proposed analytical results and illustrate that ORS is the best scheme. Furthermore, asymptotic analysis reveals that the secrecy diversity order of each scheme is the same and closely related to the number of relays. The impact of the wiretap channels is only reflected in the secrecy array gain. Finally, we determine the optimal power allocation between the source and relay.