In this paper, we study how to improve physical layer security capability of multiple near users and multiple far users non-orthogonal multiple access (NOMA) networks. To this end, we propose an opportunistic user scheduling scheme, named the best-secure-near-user best-secure-far-user (BSNBSF) scheme. The BSNBSF aims to select the best near-far user pair, whose data transmission is the most robust against the interception of an eavesdropper. In order to facilitate the performance analysis of the proposed user scheduling scheme in terms of secrecy outage probability (SOP), we derive an exact closed-form expression and a tight approximate closed-form expression for the SOP of the selected near and far users, respectively. Numerical results show that the BSNBSF scheme significantly improves the secrecy outage performance NOMA networks compared to that of the random near user and random far user selection scheme. Additionally, discussions on the complicate convex characteristic of the total SOP with respect to the power allocation coefficients and the impact the number of near and/or far users are provided.
In this paper, we study how to improve physical layer security capability of multiple near users and multiple far users non-orthogonal multiple access (NOMA) networks. To this end, we propose an opportunistic user scheduling scheme, named the best-secure-near-user best-secure-far-user (BSNBSF) scheme. The BSNBSF aims to select the best near-far user pair, whose data transmission is the most robust against the interception of an eavesdropper. In order to facilitate the performance analysis of the proposed user scheduling scheme in terms of secrecy outage probability (SOP), we derive an exact closed-form expression and a tight approximate closed-form expression for the SOP of the selected near and far users, respectively. Numerical results show that the BSNBSF scheme significantly improves the secrecy outage performance NOMA networks compared to that of the random near user and random far user selection scheme. Additionally, discussions on the complicate convex characteristic of the total SOP with respect to the power allocation coefficients and the impact the number of near and/or far users are provided.
In this paper, we address the opportunistic scheduling in multitwo user NOMA system consisting of one base station, multinear user, multifar user, and one eavesdropper. To improve the secrecy performance, we propose the users selection scheme, called best‐secure‐near‐user best‐secure‐far‐user (BSNBSF) scheme. The BSNBSF scheme aims to select the best near‐far user pair, whose data transmission is the most robust against the overhearing of an eavesdropper. In order to facilitate the performance analysis of the BSNBSF scheme in terms of secrecy outage performance, we derive the exact closed‐form expression for secrecy outage probability (SOP) of the selected near user and the tight approximated closed‐form expression for SOP of the selected far user, respectively. Additionally, we propose the descent‐based search method to find the optimal values of the power allocation coefficients that can minimize the total secrecy outage probability (TSOP). The developed analyses are corroborated through Monte Carlo simulation. Comparisons with the random‐near‐user random‐far‐user (RNRF) scheme are performed and show that the proposed scheme significantly improves the secrecy performance.
This paper studies opportunistic scheduling schemes to enhance the secrecy performance in multi-user multiple-input single-output (MU-MISO) non-orthogonal multiple access (NOMA) systems, in which a multiple antenna base station (BS) serves multiple single-antenna cell-center and cell-edge users in the presence of multiple single-antenna eavesdroppers. In order to improve the secrecy performance, we propose an opportunistic scheduling scheme, called the proposed antenna/users selection (PAUS) scheme. Additionally, we consider two practical eavesdropping scenarios, namely colluding and non-colluding eavesdroppers. We derive the exact closed-form expression for secrecy outage probability (SOP) and asymptotic SOP of the PAUS scheme under different eavesdropping scenarios. We provide the 2D golden section search-based algorithm to find the optimal values of the transmit power and power allocation coefficient that minimize the system secrecy outage performance. The developed analyses are verified by Monte Carlo simulations. The numerical results show that the PAUS scheme improves secrecy performances compared to the benchmark random antenna/users selection (RAUS) scheme. To provide further insights into the system secure performance, the effects of transmit signal-to-noise ratio (SNR), power allocation coefficient, the number of transmit antennas at the BS, number of cell-center and cell-edge users, and the eavesdropper placements are extensively evaluated and discussed.
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 investigate secure transmission in a cooperative non-orthogonal multiple access (NOMA) system in the presence of an active eavesdropper. To enhance secrecy performance, we propose two approaches. The first is a novel cooperative NOMA architecture, in which the cell-edge user generates a jamming signal to degrade the eavesdropper’s channel condition. The second is a novel opportunistic scheduling scheme, referred to as the minimum antenna selection (MAS) scheme, which selects the transmit antenna at the source node to minimize the maximum eavesdropper channel capacity between the cell-center and cell-edge users. We derive closed-form expressions for the secrecy outage probability (SOP) of both the cell-center and cell-edge users to characterize the impact of various network parameters on secrecy performance. Through numerical results, we analyze the impact of the source, cell-center, and cell-edge users’ transmit power on the SOP; the impact of the power allocation coefficient, target secrecy rate, and eavesdropper transmit power on the total SOP; and the impact of the distance between the source node and the eavesdropper, as well as the distance between the cell-center user and the eavesdropper, on the secrecy sum throughput (SST). These results demonstrate that the proposed cooperative NOMA architecture and the MAS scheme can effectively protect confidential messages against active eavesdropping attacks.
In order to improve the Physical Layer Security (PLS) perspective, this paper aims to empower function of PLS by considering a backhaul Non-Orthogonal Multiple Access (NOMA) system in two practical situations. In the proposed schemes, the untrusted user intercepts information transmitted to the far user, or the external eavesdropper overhears confidential information sent to the far user in the context of NOMA technique. Unlike the conventional NOMA systems, this paper emphasizes the actual situations of the existence of actual illegal users and legitimate users, especially the reasonable use of relay selection architecture to improve the confidentiality performance. To evaluate the security properties of the proposed scheme, a comprehensive analysis of the Security Outage Probability (SOP) performance is first performed, and then the corresponding SOP asymptotic expressions are derived for real scenarios related to eavesdroppers and untrusted users. Numerical results are performed to verify the analysis in terms of the secure performance metric.
In this article, we study the physical-layer security (PHY-security) improvement method for a downlink nonorthogonal multiple access (NOMA) system in the presence of an active eavesdropper. To this end, we propose a full-duplex (FD)-enabled NOMA system and a promising scheme, called the minimal transmitter selection (MTS) scheme, to support secure transmission. Specifically, the cell-center and cell-edge users act simultaneously as both receivers and jammers to degrade the eavesdropper channel condition. Additionally, the proposed MTS scheme opportunistically selects the transmitter to minimize the maximum eavesdropper channel capacity. To estimate the secrecy performance of the proposed methods, we derive an approximated closed-form expression for secrecy outage probability (SOP) and build a deep neural network (DNN) model for SOP evaluation. Numerical results reveal that the proposed NOMA system and MTS scheme improve not only the SOP but also the secrecy sum throughput. Furthermore, the estimated SOP through the DNN model is shown to be tightly close to other approaches, i.e., the Monte-Carlo method and analytical expressions. The advantages and drawbacks of the proposed transmitter selection scheme are highlighted, along with insightful discussions.