In this paper, we propose a novel transmit antenna selection (TAS) scheme to improve the physical layer security of two-user non-orthogonal multiple access (NOMA) systems. Specifically, the proposed TAS scheme aims to select an antenna that is the most robust against the interception of an eavesdropper, in particular, the antenna that minimizes the maximum capacity of the eavesdropper channels. To evaluate the performance of the proposed scheme, we derive an exact closed-form expression for the secrecy outage probability (SOP) of the near user and a tight approximated closed-form expression for the SOP of the far user. Numerical results reveals that the proposed TAS scheme improves the total secrecy outage probability compared to that of some existing schemes. We also provide some insightful discussions on the impact of the number of antenna and the location of the eavesdropper on the security capability of the considered system.
In this paper, we propose a novel transmit antenna selection (TAS) scheme to improve the physical layer security of two-user non-orthogonal multiple access (NOMA) systems. Specifically, the proposed TAS scheme aims to select an antenna that is the most robust against the interception of an eavesdropper, in particular, the antenna that minimizes the maximum capacity of the eavesdropper channels. To evaluate the performance of the proposed scheme, we derive an exact closed-form expression for the secrecy outage probability (SOP) of the near user and a tight approximated closed-form expression for the SOP of the far user. Numerical results reveals that the proposed TAS scheme improves the total secrecy outage probability compared to that of some existing schemes. We also provide some insightful discussions on the impact of the number of antenna and the location of the eavesdropper on the security capability of the considered system.
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.
This paper investigates the physical layer security of downlink nonorthogonal multiple access (NOMA) systems operating over a degenerate keyhole channel in the presence of a multi-antenna eavesdropper. We propose a joint antenna selection framework with transmit antenna selection at the source and receive antenna selection at both legitimate users and eavesdroppers, thus striving to reduce hardware complexity while maximizing secrecy performance. In this framework, the efficacy of confidentiality is assessed for a specific user allocation methodology by deriving the closed-form approximate expression of secrecy outage probability (SOP). Extensive Monte Carlo simulations validate analytical results and reveal that increasing the number of antennas at the source and legitimate users dramatically lowers SOP, whereas a more capable eavesdropper raises the risk of secrecy. Our findings demonstrate that strategic antenna deployment and non-orthogonal access can effectively safeguard communications even through severely scattering environments.
In this paper, we studied a multi-input multi-output (MIMO) non-orthogonal multiple access (NOMA) network consisting of one source and two legitimate users (LUs), so-called near and far users according to their distances to the source, and one passive eavesdropper, over Nakagami-\textit{m} fading channel. Specifically, we investigated the scenario that the signals of the far user might or might not be decoded successfully at the eavesdropper and the near user. Thus, we aimed at designing a transmit antenna selection (TAS) secure communication protocol for the network. Then, two TAS solutions, namely Solutions I and II, were proposed. Specifically, solutions I and II focus on maximizing the received signal power between the source and the near user, and between the source and the far user, respectively. Accordingly, the exact and asymptotic closed-form expressions of the secrecy outage probability for the LUs and the overall system were derived. Our analytical results corroborated by Monte Carlo simulation indicate that the secrecy performance could be significantly improved by properly selecting power allocation coefficients and increasing the number of antennas at the source and the LUs. Interestingly, solution II could provide a better overall secrecy performance over solution I.
In this paper, we consider a multi-input multioutput (MIMO) nonorthogonal multiple access (NOMA) network consisting of one source and two legitimate users (LUs), so-called near and far users according to their distances to the source, and one passive eavesdropper, over Nakagami-m fading channels. Specifically, we investigate the cases where the signals of the far user might or might not be successfully decoded at the eavesdropper and the near user. Thus, we aim to design a transmit antenna selection (TAS) secure communication protocol for the network; where, two TAS solutions, namely Solutions I and II, are proposed. Specifically, Solutions I and II focus on maximizing the received signal power between the source and the near user, and between the source and the far user, respectively. Accordingly, exact and asymptotic closed-form expressions for the secrecy outage probability of the LUs and the overall system are derived. Our analytical results corroborated by the Monte Carlo simulation indicate that the secrecy performance could be significantly improved by properly selecting the power allocation coefficients and increasing the number of antennas at the source and the LUs. Interestingly, solution II is shown to provide a better overall secrecy performance over solution I.
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.
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.