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.
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.
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.
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.
In this paper, we investigate opportunistic secure multiuser scheduling in energy harvesting untrusted relay networks, where an energy-constrained amplify-and-forward (AF) relay harvests energy from the received radio frequency signal via using the power splitting protocol. To exploit the potential advantages (e.g., multiuser diversity and direct links) for secrecy improvement, we examine three opportunistic user scheduling schemes, i.e., optimal scheduling scheme, maximum scheduling scheme, and minimum scheduling scheme. Specifically, the optimal scheduling scheme performs user selection by maximizing the ratio between the signal-to-noise-ratio (SNR) at the destination and the corresponding SNR at the untrusted relay. The maximum scheduling scheme is conventional user selection that maximizes the channel gain of the direct links. For the minimum scheduling scheme, we try to reduce the overheard information at the untrusted relay by selecting the user with the lowest channel gain of the relay links. For these three schemes, we comprehensively examine the achievable secrecy performance including probability of positive secrecy rate, secrecy outage probability (SOP), asymptotic SOP, secrecy throughput (ST), as well as secure energy efficiency (SEE) to help facilitate an energy-efficient secure transmission design. Simulation results demonstrate that the maximum scheduling scheme outperforms the minimum scheduling scheme in terms of SOP at relatively low SNRs and target secrecy rates.
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.
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.
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.