This paper investigates the physical layer security for a cooperative cognitive radio (CCR) system with energy-harvesting (EH) techniques, which is made up of a cognitive source (CS), multiple cognitive relays (CRs) and a cognitive destination (CD) as well as multiple eavesdroppers (Es) who may overhear the confidential information. Both CS and CRs are equipped with energy-harvesters to harvest energy from the surrounding radio frequency environment. Additionally, in order to guarantee the quality-of-service of primary communications, the cognitive transmit power of CS and CRs are limited by the maximum tolerant power at primary destination. Depending on the channel state information (CSI) of wireless energy links from primary transmitter (PT) to CRs is unavailable or available for CRs, we respectively propose non-energy aware relay selection (NEARS) and energy aware relay selection (EARS) schemes for protecting private transmission between CS and CD aided with CRs from leaking to Es. We take use of security-reliability tradeoff (SRT) into account to measure the performance of NEARS and EARS schemes. To achieve the purpose of comparison, we also carry out the analysis of SRT for conventional direct communication (DC). Furthermore, the closed-form expressions of outage probability and intercept probability for all DC, and EARS schemes are derived and the numerical results indicate that the performance of EARS performs better than that of DC and NEARS schemes in terms of SRT.

This paper investigates the physical layer security for a distributed antenna system, where a base station (BS) equipped with multiple distributed antennas transmits signals to a legitimate user (U) through an opportunistic antenna. Meanwhile, multiple non-colluding eavesdroppers (Es) attempt to tap the information transmission between the BS and U. To enhance the physical layer security, a friendly jammer (J) is employed to create a potential interference to Es by emitting artificial noise. However, since U is not aware of the information sent by J, it can be affected by the interference. In this context, this paper proposes adaptive jamming (AJ) scheme and interference cancellation (IC) scheme to mitigate the interference’s impact on U and consequently improve secrecy performance. Specifically, the AJ scheme avoids interference from having a negative effect on the system security by setting an interference threshold, activating the jammer only when the interference to U is below the threshold value. By contrast, the IC scheme designs an advanced special signal to eliminate the interference from J to U. For comparison, we present conventional non-jammer (NJ) scheme as a benchmark. Exact and asymptotic secrecy outage probability expressions for NJ, AJ, and IC schemes are derived over Nakagami- m fading channels. Numerical results show that the proposed AJ and IC schemes perform better than NJ scheme in terms of secrecy outage probability. Additionally, the physical layer security of all schemes can be improved by increasing the number of distributed antennas.

rgb0,0,0For an unmanned aerial vehicle (UAV)-aided energy-harvesting non-orthogonal multiple access (EH-NOMA) network, where an untrusted far user (UFU) overhears the confidential transmissions from base station (BS) to the trusted near user (TNU), how to ensure the security of TNU and achieve the reliability of UFU becomes an open issue. The traditional artificial noise (TAN) scheme just guarantees the security of TNU without focusing on the reliability of UFU, while the non-artificial noise (NAN) scheme only ensures the reliability of UFU but sacrifices the security of TNU. Thus, the TAN and NAN schemes are unable to guarantee the fairness between TNU and UFU. To this end, we employ digital network coding to encrypt confidential signals with artificial noise signals, and the proposed artificial noise (PAN) scheme not only protects the confidential transmissions of TNU but also guarantees the reliability of UFU. We use security-reliability tradeoff (SRT) and interference-reliability tradeoff (IRT) to evaluate the performance of TNU and UFU, respectively. Additionally, we derive the exact and asymptotic expressions of outage probabilities for both TNU and UFU, and the intercept probability for TNU. Numerical results verify the accuracy of our theoretical results and demonstrate that: 1) the SRT and IRT performance of the PAN scheme is better than that of the TAN and NAN schemes; 2) the PAN scheme achieves better secrecy for TNU compared to the TAN scheme. Meanwhile, the reliability of UFU in the PAN scheme is almost the same as the NAN scheme, indicating the PAN scheme simultaneously realizes the security of TNU and the reliability of UFU and the fairness of NOMA users is achieved by the PAN scheme.

This article investigates physical-layer security (PLS) for an energy-harvesting cognitive network with nonorthogonal multiple access (EHCN-NOMA), where a cognitive base station (CBS) communicates with two cognitive users named cognitive near user (CNU) and cognitive far user (CFU) by adopting the NOMA principle under an active or passive eavesdropper (Eve) attack. By means of energy harvesters, the CBS collects the radio frequency energy from the primary source (PS) by a time-switching protocol; meanwhile, the cognitive transmit power is limited by the interference threshold of primary destination (PD) to guarantee the Quality of Service (QoS) of primary transmissions. To evaluate the impact of active and/or passive eavesdroppings on system performance, we derive closed-form expressions in terms of outage probabilities (OPs), intercept probabilities (IPs), as well as effective secrecy throughputs (ESTs). The numerical results verify the correctness of our theoretical derivations and confirm that there exists a tradeoff between security and reliability for the EHCN-NOMA transmissions. Moreover, the EST improvement depends on the competition between security and reliability. Furthermore, the maximum EST performance can be achieved for both eavesdropping scenarios by adjusting the time allocation between that of the energy transfer phase and the information transmission phase.

This paper considers a multiple-input-multiple-output (MIMO) energy-harvesting (ER) system, which is made up of a source (S) and a destination (D) as well as an eavesdropper (E). In this system, S, D and E are equipped with multiple antennas and S can be charged by a power beacon (PB) in the energy-harvesting phase of the total communication process. To enhance the physical-layer security, we propose optimal antenna selection (OAS) and suboptimal antenna selection (SAS) schemes, relying on whether the global channel state information is available or unavailable to S. Moreover, the analysis of the conventional space-time transmission (STT) is carried out as a baseline. In order to intuitively show the effect of the number of antennas on secrecy outage performance, the secrecy diversity analysis for RRS, SAS and OAS schemes is carried out through the asymptotic secrecy outage probability as the MER (the average gains between main channel from S to D and wiretap channel from S to E) intends infinity. Additionally, the results show that the secrecy diversities of STT, SAS and OAS are the product of the number of antennas at S and D, which has no relation to E. Furthermore, the research findings indicate that our proposed OAS scheme performs the best in terms of secrecy outage probability and STT scheme achieves the worst secrecy performance.

This article studies the secrecy performance for a dual-hop nonorthogonal multiple access (NOMA)-aided unmanned aerial vehicle (UAV) network in the face of a passive untrusted far user (UFU). A new artificial noise (AN) scheme is proposed, where AN generated in the first hop can be used to encrypt confidential signals by XOR operation in the second hop. Based on the proposed AN (PAN) scheme, we analyze the exact and asymptotic outage probabilities (OPs) for both NOMA users and intercept probability (IP) for trusted near user (TNU). Simulation results verify the correctness of our theoretical analysis and demonstrate that the PAN scheme significantly improves the security for TNU at the cost of negligible reliability of UFU compared to the benchmark schemes.