This work aims to enhance the physical layer security (PLS) of non-orthogonal multiple access (NOMA) aided indoor visible light communication (VLC) system with semi-grant-free (SGF) transmission scheme, in which a grant-free (GF) user shares the same resource block with a grant-based (GB) user whose quality of service (QoS) must be strictly guaranteed. Besides, the GF user is also provided with an acceptable QoS experience, which is closely aligned with the practical application. Both active and passive eavesdropping attacks are discussed in this work, where users' random distributions are taken into account. Specifically, to maximize the secrecy rate of the GB user in the presence of an active eavesdropper, the optimal power allocation policy is obtained in exact closed-form and the user fairness is then assessed by Jain's fairness index. Moreover, the secrecy outage performance of the GB user is analyzed in the presence of the passive eavesdropping attack. Both exact and asymptotic theoretical expressions for the secrecy outage probability (SOP) of the GB user are derived, respectively. Furthermore, the effective secrecy throughput (EST) is investigated on the basis of the derived SOP expression. Through simulations, it is found that the PLS of this VLC system can be significantly improved by the proposed optimal power allocation scheme. The radius of the protected zone, the outage target rate for the GF user, and the secrecy target rate for the GB user would have pronounced impacts on the PLS and user fairness performance of this SGF-NOMA assisted indoor VLC system. The maximum EST will increase with the increasing transmit power and it is hardly influenced by the target rate for the GF user. This work will benefit the design of indoor VLC system.
This work aims to enhance the physical layer security (PLS) of non-orthogonal multiple access (NOMA) aided indoor visible light communication (VLC) system with semi-grant-free (SGF) transmission scheme, in which a grant-free (GF) user shares the same resource block with a grant-based (GB) user whose quality of service (QoS) must be strictly guaranteed. Besides, the GF user is also provided with an acceptable QoS experience, which is closely aligned with the practical application. Both active and passive eavesdropping attacks are discussed in this work, where users' random distributions are taken into account. Specifically, to maximize the secrecy rate of the GB user in the presence of an active eavesdropper, the optimal power allocation policy is obtained in exact closed-form and the user fairness is then assessed by Jain's fairness index. Moreover, the secrecy outage performance of the GB user is analyzed in the presence of the passive eavesdropping attack. Both exact and asymptotic theoretical expressions for the secrecy outage probability (SOP) of the GB user are derived, respectively. Furthermore, the effective secrecy throughput (EST) is investigated on the basis of the derived SOP expression. Through simulations, it is found that the PLS of this VLC system can be significantly improved by the proposed optimal power allocation scheme. The radius of the protected zone, the outage target rate for the GF user, and the secrecy target rate for the GB user would have pronounced impacts on the PLS and user fairness performance of this SGF-NOMA assisted indoor VLC system. The maximum EST will increase with the increasing transmit power and it is hardly influenced by the target rate for the GF user. This work will benefit the design of indoor VLC system.
In order to improve the security performance of multiuser visible light communication (VLC) and facilitate the secure application of optical wireless communication technology in Internet-of-Things, we investigate the physical-layer security in a multiuser VLC system with non-orthogonal multiple access (NOMA). When the light-emitting diode (LED) transmitter communicates with multiple legitimate users by downlink NOMA, both single eavesdropper and multi-eavesdropper scenarios are considered. In the presence of single eavesdropper, based on transmission characteristics of the optical wireless channel, with known instantaneous channel state information (CSI) of the NOMA legitimate channels and statistical CSI of the eavesdropper channel, an exact expression of secrecy outage probability (SOP) is derived, which acts as a benchmark of the security performance to guide selecting or optimizing parameters of the LED transmitter and the photodiode receiver of NOMA legitimate users. In the multi-eavesdropper case, based on the spatial distribution of legitimate users and eavesdroppers, the SOP is obtained via a stochastic geometry theory, so as to guide the NOMA legitimate users to keep away from the area with high eavesdropper density. For typical parameters of the indoor LED transmitter and the PD receiver, simulation results show that the SOP performance improves with the increasing of LED transmission power or transmission signal-to-noise ratio (SNR) in both scenarios. Specifically, in the single eavesdropper case, enlarging the channel condition difference of user groups or deviating the eavesdropper from the given user group can improve the SOP performance, and for a given NOMA legitimate user, the SOP eventually settles around 0.2 while the semiangle at half illuminance of the LED varies between 15° to 60°. In the multi-eavesdropper case, we can get a better SOP performance when reducing the eavesdropper density or the semi-angle at half illuminance of the LED for a given eavesdropper density.
Integrating visible light communication (VLC) and radio-frequency (RF) networks can improve the performance of communication systems in terms of coverage and data rates. However, adding RF links to VLC networks weakens the secrecy performance due to the broadcast and ubiquitous nature of RF links. This paper studies the physical layer security (PLS) in cooperative non-orthogonal multiple access (CoNOMA) hybrid VLC/RF systems. Consider a VLC system, where two entrusted users close to a VLC access point (AP) help an out-of-coverage legitimate user using RF signals in the presence of an eavesdropper. The AP transmits data to both entrusted users and the legitimate user using the principle of NOMA, where the entrusted users harvest energy from the received light intensity, decode the legitimate user's message, forward it using a RF link, and then decode their messages. It is required to maximize the secrecy rate at the legitimate user under quality-of-service (QoS) constraints using beamforming and DC-bias and power allocation. Different solutions are proposed for both active and passive eavesdropper cases, using semidefinite relaxation, zero-forcing, beamforming, and jamming. Numerical results compare between the different proposed approaches and show how the proposed approaches contribute in improving the secrecy performance of the proposed model.
Observing the significance of spectrally-efficient secure non-orthogonal multiple access (NOMA), this paper proposes a novel quality of service (QoS) aware secure NOMA protocol that maximizes secrecy fairness among untrusted users. Considering a base station (BS) and two users, a novel decoding order is designed that provides security to both users. With the objective of ensuring secrecy fairness between users, while satisfying their QoS requirements under BS transmit power budget constraint, we explore the problem of minimizing the maximum secrecy outage probability (SOP). Closed-form expression of pair outage probability (POP) and optimal power allocation (PA) minimizing POP are obtained. To analyze secrecy performance, analytical expressions of SOP for both users are derived, and individual SOP minimization problems are solved using concept of generalized-convexity. High signal-to-noise ratio approximation of SOP and asymptotically optimized solution minimizing this approximation is also found. Furthermore, global-optimal solution from secrecy fairness standpoint is obtained at low computational complexity, and tight approximation is derived to get analytical insights. Numerical results present useful insights on globally optimized PA which ensure secrecy fairness and provide performance gain of about 55.12%, 69.30%, and 19.11%, respectively, compared to fixed PA and individual users' optimal PAs. Finally, a tradeoff between secrecy fairness performance and QoS demands is presented.
This paper investigates the physical-layer data secure transmission for indoor visible light communications (VLC) with simultaneous lightwave information and power transfer (SLIPT) and random terminals. A typical indoor VLC system including one transmitter, one desired information receiver and one energy receiver is considered. The two receivers are randomly deployed on the floor, and the random channel characteristics is analyzed. Based on the possibility that the energy receiver is a passive information eavesdropper, the secrecy outage probability (SOP) and the average secrecy capacity (ASC) are employed to evaluate the system performance. A closed-form expression for the lower bound of the SOP and an exact closed-form expression for the ASC are derived, respectively. To further improve the physical-layer security, a protected zone based scheme is proposed, and then the SOP and the ASC are re-derived. By using Monte-Carlo simulations, the accuracy of the derived lower bound of SOP and the exact ASC are verified. Moreover, numerical results show that the security of the VLC system significantly improves by employing the protected zone.
This paper investigates physical layer security (PLS) in hybrid automatic repeat request (HARQ)-assisted non-orthogonal multiple access (NOMA) networks, where a security-required user is paired with a quality of service (QoS)-required user to perform NOMA in presence of an eavesdropper (Eve). We derive the closed-form expressions for connection outage probability (COP) of security-required and QoS-required users. In addition, the closed-form expressions for secrecy outage probability (SOP) secrecy transmission probability (RSP), and effective secrecy throughput (EST) of security-required user are also derived. Although the expression of SOP demonstrates that HARQ increases the risk of leaking confidential message to eavesdropper (Eve), however, from the perspective of Eve and security-required user, secrecy performance improves significantly, in terms of EST and RSP, when applying HARQ.
Since successive interference cancellation in non-orthogonal multiple access (NOMA) is enabled at the strong user to remove the signal of the weak user, if the information safety of the strong user cannot be ensured, neither can the weak user. The physical-layer security of the strong user in a two-user multiple-input single-output (MISO)-NOMA visible light communication (VLC) system in the presence of a passive eavesdropper was studied, with multiple light-emitting diodes (LEDs) transmitting and a photodiode (PD) receiver receiving. To demonstrate the superiority of the MISO-NOMA VLC system over the SISO-NOMA VLC system, numerical simulations were made, and results show that the secrecy outage probability (SOP) performance of the strong user in the MISO-NOMA VLC system is superior to that in the SISO-NOMA VLC system. Furthermore, the SOP of the strong user depends highly on the room arrangement, the difference between the legitimate channel and eavesdropper channel, and the properties of the LEDs and PD.