The secrecy outage probability (SOP) performance is investigated for a cooperative non-orthogonal multiple access system under eavesdropping attack, where a base station transmits signals to a far user via a full-duplex relay, and to a near user directly at the same time, in the presence of an eavesdropper. All nodes are configured with multiple antennas and antenna selection is adopted by the base station and relay to enhance the security performance. The exact and asymptotic closed-form SOP expressions are derived, which incorporate the impact of imperfect channel state information and apply to general cases considering the quality of service of the far and near users, whether or not the wiretap channel is known, and the location of the eavesdropper. Monte Carlo simulations corroborate the analysis and the superiority of the proposed system over the single-antenna system and the one without antenna selection. It is also revealed that the asymptotic SOP performance of the near user is nearly independent of the power allocation.
The secrecy outage probability (SOP) performance is investigated for a cooperative non-orthogonal multiple access system under eavesdropping attack, where a base station transmits signals to a far user via a full-duplex relay, and to a near user directly at the same time, in the presence of an eavesdropper. All nodes are configured with multiple antennas and antenna selection is adopted by the base station and relay to enhance the security performance. The exact and asymptotic closed-form SOP expressions are derived, which incorporate the impact of imperfect channel state information and apply to general cases considering the quality of service of the far and near users, whether or not the wiretap channel is known, and the location of the eavesdropper. Monte Carlo simulations corroborate the analysis and the superiority of the proposed system over the single-antenna system and the one without antenna selection. It is also revealed that the asymptotic SOP performance of the near user is nearly independent of the power allocation.
In a downlink non-orthogonal multiple access (NOMA) system, the reliable transmission of cell-edge users cannot be guaranteed due to severe channel fading. On the other hand, the presence of eavesdroppers can severely threaten the secure transmission due to the open nature of wireless channel. Thus, a two-user NOMA system assisted by a multi-antenna decode-and-forward relay is considered in this paper, and a two-stage jamming scheme, full-duplex-jamming (FDJam), is proposed to ensure the secure transmission of NOMA users. In the FDJam scheme, using full-duplex, the relay transmits the jamming signal to the eavesdropper while receiving confidential messages in the first stage, and the base station generates the jamming signal in the second stage. Furthermore, we eliminate the self-interference and the jamming signal at the relay and the legitimate node, respectively, through relay beamforming. To measure the secrecy performance, analytical expressions for secrecy outage probability (SOP) are derived for both the cell-center and cell-edge users, and the asymptotic SOP analysis at high transmit power is presented as well. Moreover, two benchmark schemes, half-duplex-jamming and full-duplex-no-jamming, are also considered. Simulation results are presented to show the accuracy of the analytical expressions and the effectiveness of the proposed scheme.
Abstract Secure transmission is essential for future non-orthogonal multiple access (NOMA) system. This paper investigates relay–antenna selection to enhance physical-layer security of cooperative NOMA system in the presence of an eavesdropper, where multiple antennas are deployed at the relays, the users, and the eavesdropper. In order to reduce expense on radio frequency chains, selection combining (SC) is employed at both the relays and the users, whilst the eavesdropper employs either maximal-ratio combining or SC to process the received signals. Under the condition that the channel state information of the eavesdropping channel is available or unavailable, two effective relay–antenna selection schemes are proposed. Additionally, the closed-form expressions of secrecy outage probability (SOP) are derived for the proposed relay–antenna selection schemes. In order to gain more deep insights on the derived results, the asymptotic performance of the derived SOP is analyzed. In simulations, it is demonstrated that the theoretical results match well with the simulation results and the SOP of the proposed schemes is less than that of the conventional orthogonal multiple access scheme obviously.
This paper studies the secure communications of a wireless-powered full-duplex cooperative non-orthogonal multiple access (CoNOMA) system with a source node, a group of near users, a far user and an external eavesdropper. In particular, the eavesdropper intends to wiretap the transmitted signals from the source. Two of the near users are picked up, served as a wireless-powered relay and a wireless friendly jammer, respectively. We propose a user selection and cooperative jamming based secure transmission scheme. Specifically, the source transmits a superimposed signal to the selected near user. The selected near user, who is employed as a relay, can harvest energy from the radio frequency signals and decode the information simultaneously. The harvested energy are then utilized to forward the signal to the far user. The jammer also collects energy from the source, and emits artificial noise by using the harvested energy to confuse the eavesdropper. Based on the proposed scheme, the closed-form expression for secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived. The correctness of our theoretical analysis is verified by Monte-Carlo simulations, and the superiority of the proposed scheme in improving the system secure performance is also validated.
Abstract Secure transmission is essential for future non-orthogonal multiple access (NOMA) system. This paper investigates relay-antenna selection (RAS) to enhance physical-layer security (PLS) of cooperative NOMA system in the presence of an eavesdropper, where multiple antennas are deployed at the relays, the users, and the eavesdropper. In order to reduce expense on radio frequency (RF) chains, selection combining (SC) is employed at both the relays and the users, whilst the eavesdropper employs either maximal-ratio combining (MRC) or selection combining (SC) to process the received signals. Under the condition that the channel state information (CSI) of the eavesdropping channel is available or unavailable, two effective relay-antenna selection schemes are proposed. Additionally, the closed-form expressions of secrecy outage probability (SOP) are derived for the proposed relay-antenna selection schemes. In order to gain more deep insights on the derived results, the asymptotic performance of the derived SOP is analyzed. In simulations, it is demonstrated that the theoretical results match well with the simulation results and the SOP of the proposed schemes is less than that of the conventional orthogonal multiple access (OMA) scheme obviously.
In non-orthogonal multiple access (NOMA) systems, serving multiple users in shared resource blocks can allow untrusted users to overhear the messages of other users. In this context, we study a network consisting of a base station (BS), a near user and a far user, where the latter attempts to overhear the message of the former. The near user is a full-duplex (FD) node that can also act as a relay. Two operating scenarios are considered: 1) friendly jammer (FJ), where the FD node broadcasts noise for degrading the channel between the BS and the far user, while receiving data from the BS; and 2) friendly jammer relay (FJR), where, in addition to degrading the channel between the BS and the far user, the FD node relays the message of the far user. We investigate the secrecy performance of the network by characterizing the secrecy outage probability (SOP) in both scenarios. We obtain the exact SOP of the FJ case, and an approximation for the SOP of the FJR scenario, both expressed in closed-form. Numerical results confirm the accuracy of the analytical results. For a given BS power budget and power allocation to the users, it is demonstrated that the jamming and relaying powers are prominent factors to make the NOMA-FJR scheme superior to NOMA-FJ, as well as to conventional and cooperative NOMA schemes.
This paper investigates the secrecy performance of a two-user downlink non-orthogonal multiple access systems. Both single-input and single-output and multiple-input and single-output systems with different transmit antenna selection (TAS) strategies are considered. Depending on whether the base station has the global channel state information of both the main and wiretap channels, the exact closed-form expressions for the secrecy outage probability (SOP) with suboptimal antenna selection and optimal antenna selection schemes are obtained and compared with the traditional space-time transmission scheme. To obtain further insights, the asymptotic analysis of the SOP in high average channel power gains regime is presented and it is found that the secrecy diversity order for all the TAS schemes with fixed power allocation is zero. Furthermore, an effective power allocation scheme is proposed to obtain the non-zero diversity order with all the TAS schemes. Monte Carlo simulations are performed to verify the proposed analytical results.