This letter investigates the ergodic secrecy rate (ESR) of a reconfigurable intelligent surface (RIS)-assisted communication system in the presence multiple eavesdroppers (Eves), and by assuming discrete phase shifts at the RIS. In particular, a closed-form approximation of the ESR is derived for both non-colluding and colluding Eves. The analytical results are shown to be accurate when the number of reflecting elements of the RIS N is large. Asymptotic analysis is provided to investigate the impact of N on the ESR, and it is proved that the ESR scales with log2N for both non-colluding and colluding Eves. Numerical results are provided to verify the analytical results and the obtained scaling laws.
This letter investigates the ergodic secrecy rate (ESR) of a reconfigurable intelligent surface (RIS)-assisted communication system in the presence multiple eavesdroppers (Eves), and by assuming discrete phase shifts at the RIS. In particular, a closed-form approximation of the ESR is derived for both non-colluding and colluding Eves. The analytical results are shown to be accurate when the number of reflecting elements of the RIS N is large. Asymptotic analysis is provided to investigate the impact of N on the ESR, and it is proved that the ESR scales with log2N for both non-colluding and colluding Eves. Numerical results are provided to verify the analytical results and the obtained scaling laws.
In this letter, we investigate the secrecy performance of a reconfigurable intelligent surface (RIS) assisted multiple-input multiple-output (MIMO) communication network in the presence of randomly positioned eavesdroppers. We derive closed form expressions for the beamforming vector of the base station (BS) and the phase shifts of the RIS. Considering the colluding wiretap strategy, the secrecy outage probability is obtained in closed form by using the theory of stochastic geometry. Numerical results confirm the effectiveness of our theoretical analysis, demonstrating that increasing the number of BS antennas and RIS elements can significantly enhance the secrecy performance of the system.
The full-space capability of the reconfigurable intelligent surface (RIS) provides an intelligent radio environment for information transmissions. This paper investigates the RIS-assisted secure transmissions in the presence of multiple eavesdroppers (Eves), where the colluding and the non-colluding behaviors of Eves are considered. We first propose a tractable Gamma distribution to characterize the distributions of the signal-to-noise ratio (SNR) under the Rayleigh, the Rice and the Nakagami-m channels. Then we derive the theoretical expressions of the average security capacity (ASC) for colluding and non-colluding eavesdroppers. Besides, the asymptotic expressions of the ASC are also obtained when the SNRs are large in practical scenarios. The simulation results demonstrate that the RIS is capable of reducing the negative impact of the increase in the number of eavesdroppers on the security performance by deploying more RIS elements in both colluding and non-colluding eavesdroppers.
In this paper, we investigate the secrecy performance of a secure wireless communication system configured with reconfigurable intelligent surfaces (RIS). In particular, a legitimate source sends its private message to a legitimate destination with the aid of an RIS, while a passive eavesdropper intercepts this private information from both source and RIS. Considering this system setup, we first study the statistical analysis of the instantaneous signal-to-noise ratios (SNRs) at the destination and eavesdropper by exploiting the method of moments. Then, we deduce the closed-form expression of the ergodic secrecy capacity (ESC) over independent and identically distributed Rayleigh fading channels. Further, we provide the asymptotic ESC analysis in the high SNR regime to reveal some insightful information. Using the asymptotic ESC analysis, we also analytically present the impact of number of RIS elements on the ESC performance. Lastly, the analytical findings are corroborated via numerical and simulation studies, and show the impact of various involved parameters on the ESC performance.
In this article, the physical layer security (PLS) is investigated for reconfigurable intelligent surface (RIS)-aided wireless communication systems, where one RIS is deployed to assist the communications between a pair of transmitter (Alice) and receiver (Bob), under a passive eavesdropper (Eve) attack. For the Eve, different from the bounded channel state information uncertainty model, the distribution of the Eve’s location is introduced into the wiretap link. In the proposed system, considering that the Eve can overhear signals transmitted from Alice or reflected by the RIS, two scenarios are studied for RIS-aided secure communication systems: one is that the Eve distributes close to Alice without the RIS orientation, and the other is that the Eve locates close to Bob and in the presence of the RIS. After investigating the probability distribution functions of the Eve’s location and the wiretap link, the novel cumulative density functions (CDFs) of the received signal-to-noise ratios (SNRs) at the Eves are, respectively, derived for the two considered scenarios, taking into account the effects of RIS reflection coefficients, pathloss, and Eve’s location distribution. The closed-form expressions for the probability of the nonzero secrecy capacity and the ergodic secrecy capacity are obtained, providing insights into the impact of the Eve’s location uncertainty and the RIS design on the secrecy performance. Moreover, based on the derived CDFs for received SNRs at Eves, the secrecy outage probabilities are, respectively, analyzed. Specifically, under the constraint of the secrecy outage probability, the closed forms of the minimum required SNRs at Bob and the number of RIS elements are also obtained. Simulation and analytical results corroborate the derived expressions and reveal the tradeoff between the system’s energy efficiency and the number of RIS elements.
In this letter, we analyze the secrecy performance of a reconfigurable intelligent surface (RIS)-aided communication system with spatially random unmanned aerial vehicles (UAVs) acting as eavesdroppers. We consider the scenarios where the base station (BS) is equipped with single and multiple antennas. The signal-to-noise ratios (SNRs) of the legitimate user and the eavesdroppers are derived analytically and approximated through a computationally effective method. The ergodic secrecy capacity is approximated and derived in closed-form expressions. Simulation results validate the accuracy of the analytical and approximate expressions and show the security-enhanced effect of the deployment of the RIS.
This paper investigates the integration of a reconfigurable intelligent surface (RIS) into a secure multiuser massive multiple-input multiple-output (MIMO) system in the presence of transceiver hardware impairments (HWI), imperfect channel state information (CSI), and spatially correlated channels. We first introduce a linear minimum-mean-square error estimation algorithm for the aggregate channel by considering the impact of transceiver HWI and RIS phase-shift errors. Then, we derive a lower bound for the achievable ergodic secrecy rate in the presence of a multi-antenna eavesdropper when artificial noise (AN) is employed at the base station (BS). In addition, the obtained expressions of the ergodic secrecy rate are further simplified in some noteworthy special cases to obtain valuable insights. To counteract the effects of HWI, we present a power allocation optimization strategy between the confidential signals and AN, which admits a fixed-point equation solution. Our analysis reveals that a non-zero ergodic secrecy rate is preserved if the total transmit power decreases no faster than 1/N, whereNis the number of RIS elements. Moreover, the ergodic secrecy rate grows logarithmically with the number of BS antennasMand approaches a certain limit in the asymptotic regimeN→ ∞. Simulation results are provided to verify the derived analytical results. They reveal the impact of key design parameters on the secrecy rate. It is shown that, with the proposed power allocation strategy, the secrecy rate loss due to HWI can be counteracted by increasing the number of low-cost RIS elements.