A joint cooperative jamming and opportunistic scheduling (CJOS) scheme is proposed for a downlink multiuser relay network (MRN) with an untrusted fixed‐gain amplify‐and‐forward relay. Specifically, the source's confident message is protected by employing CJ at the destinations and multiuser diversity is harvested via OS. Unified tight approximation and asymptotic expressions for the system secrecy outage probability with perfect/outdated channel state information (CSI) are derived. Our results explicitly show that with perfect CSI, CJOS scheme can improve the secrecy diversity order from 1/2 in single‐user networks up to full diversity of 1 in MRNs. However, the outdated CSI degrades the secrecy diversity order from 1 to 1/2.
A joint cooperative jamming and opportunistic scheduling (CJOS) scheme is proposed for a downlink multiuser relay network (MRN) with an untrusted fixed‐gain amplify‐and‐forward relay. Specifically, the source's confident message is protected by employing CJ at the destinations and multiuser diversity is harvested via OS. Unified tight approximation and asymptotic expressions for the system secrecy outage probability with perfect/outdated channel state information (CSI) are derived. Our results explicitly show that with perfect CSI, CJOS scheme can improve the secrecy diversity order from 1/2 in single‐user networks up to full diversity of 1 in MRNs. However, the outdated CSI degrades the secrecy diversity order from 1 to 1/2.
In this paper, we investigate secure communication for a dual-hop multiuser relay network, where a source communication with N ( N ≥ 1 ) destinations via an untrusted variable gains relay. To exploit multiuser diversity while protecting source’s confidential message, we first propose a joint destination-based jamming and opportunistic scheduling (DJOS) scheme. Then, we derive closed-form approximated and asymptotic expressions of the secrecy outage probability (SOP) for the considered system with DJOS. Furthermore, we determine an asymptotical optimal power allocation (OPA), which minimizes the asymptotic SOP, to further improve the secrecy performance. Our analytical results show that the achievable secrecy diversity order in terms of SOP with fixed power allocation is min ( 1 , N 2 ) , whereas, with OPA, the achievable secrecy diversity order can be improved up to min ( 1 , 2 N N + 2 ) . This interesting result reveals that OPA can improve the secrecy diversity order of the single-user network. This is intuitive since full diversity order of 1 cannot be achieved when N = 1 , thus leaving some space for OPA to improve the diversity order. Nevertheless, for N ≥ 2 , the effect of OPA is to increase the secrecy array gain rather than the secrecy diversity order since full diversity order 1 has been achieved by the OS scheme. Finally, simulation results are presented to validate our analysis.
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.
To improve the physical-layer security performance in the multiuser untrusted relay networks,we propose an opportunistic scheduling combined with cooperative jamming(OSCJ)scheme.We derive the analytical expression of the ergodic secrecy capacity(ESC)lower bound for the OSCJ scheme and the closed-form expression of the lower bound of the secrecy outage probability(SOP).Furthermore,we conduct an asymptotic analysis for ESC.The numerical simulations validate the accuracy of our analysis and show that the proposed OSCJ scheme outperforms the random scheduling and jamming scheme in terms of both ESC and SOP performance.
This paper investigates the physical-layer security of an amplify-and-forward wireless cooperative network, where N source nodes communicate with their corresponding destination nodes under the help of an untrusted relay. In each slot, only one user-pair is scheduled to transmit the information, and the destination-aided cooperative jamming is adopted to protect information from being intercepted by the untrusted relay. Three user-pair selection schemes have been proposed for the considered system, namely opportunistic user-pair selection (OUS) scheme, greedy user-pair selection (GUS) scheme, and genie-aided user-pair selection scheme. Both the secrecy outage probability and the average secrecy rate have been studied to evaluate the performance of the OUS and GUS schemes, and the asymptotic analysis has also been obtained. It reveals that the proposed schemes can improve the secrecy performance for the cooperative multiuser networks as the number of user-pairs increases. We also prove that the achievable diversity order of both OUS and GUS schemes is N/2. Finally, numerical and simulation results are presented to validate the accuracy of the developed analytical results.
This paper studies the secrecy performance of an untrusted amplify-and-forward relaying network where both the relaying and the direct links are used to convey the source's information. Since relays act as eavesdroppers, a source-based jamming technique is proposed to keep the source's message secret from these helper nodes. We analyze the secrecy capacity of partial relay selection based on outdated channel state information. The study is conducted analytically by deriving the lower-bound expression for the ergodic secrecy capacity (ESC). We demonstrate through the simulation results the tightness of the derived bound. The use of the direct link is shown to improve the secrecy performance of the proposed scheme. In this case, we found that ESC performance with maximum ratio combining at the destination is better than that with selection combining. The system performance worsens as the correlation coefficient decreases. Furthermore, the maximum of ESC is achieved when relays are in the middle between the source and the destination with equal power allocation between the information and the jamming signals at the source.
In this paper, we study the physical layer security (PLS) of opportunistic scheduling for uplink scenarios of multiuser multirelay cooperative networks. To this end, we propose a low-complexity, yet comparable secrecy performance source relay selection scheme, called the proposed source relay selection (PSRS) scheme. Specifically, the PSRS scheme first selects the least vulnerable source and then selects the relay that maximizes the system secrecy capacity for the given selected source. Additionally, the maximal ratio combining (MRC) technique and the selection combining (SC) technique are considered at the eavesdropper, respectively. Investigating the system performance in terms of secrecy outage probability (SOP), closed-form expressions of the SOP are derived. The developed analysis is corroborated through Monte Carlo simulation. Numerical results show that the PSRS scheme significantly improves the secure ability of the system compared to that of the random source relay selection scheme, but does not outperform the optimal joint source relay selection (OJSRS) scheme. However, the PSRS scheme drastically reduces the required amount of channel state information (CSI) estimations compared to that required by the OJSRS scheme, specially in dense cooperative networks.