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Abstract

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 $\log \,_{2} N$ for both non-colluding and colluding Eves. Numerical results are provided to verify the analytical results and the obtained scaling laws.

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... Unlike the system model in [10], they assume that the direct link between the source and the destination is in a permanent outage. Such Gaussian approximations are also used to characterize metrics like ergodic capacity, secrecy outage probability in many other works including [12]- [15]. Similarly, Gamma approximations (using moment matching) are used for deriving approximate OP by the authors of [16]- [19]. ...
... As mentioned by the authors of [19], the Gamma distribution is a Type-III Pearson distribution and is widely used in fitting distributions for positive random variables (RVs) [20], [21]. The authors of [12], [15], [17], [22] consider more practical IRS models, where due to hardware constraints the possible phase shifts at the IRS elements are restricted to a finite set of discrete values. the corresponding OP. ...
... Note that the expression in (10) is very easy to evaluate when compared to the OP approximations proposed in a few of the recent literature including [22], [24], [32]. Also, the proposed approximations hold well both for the cases of small and large values of N, unlike the Gaussian approximations using CLT [12]- [14], [19], [23] which holds only for large N. Furthermore, the proposed CDF of γ IRS can be easily used for deriving the expressions of other metrics of interest like the rate [33]. Since we have considered a very general scenario in Theorem 3, we present certain special cases of interest in the following corollaries. ...
Preprint
In this work, we study the outage probability (OP) at the destination of an intelligent reflecting surface (IRS) assisted communication system in the presence of phase error due to quantization at the IRS when a) source-destination (SD) link is present and b) SD link is absent. First,an exact expression is derived and then we derive three simple approximations for the OP using the following approaches: (i) uni-variate dimension reduction, (ii) moment matching and,(iii) Kullback-Leibler divergence minimization. The resulting expressions for OP are simple to evaluate and quite tight even in the tail region. The validity of these approximations is demonstrated using extensive Monte Carlo simulations.
... However, regarding the secure performance, the existing theoretical analysis focus on terrestrial IRS scenarios, and the research on the synergy of IRS and UAV technologies remains an open issue. Specifically, [11] provided analytical expressions for the secrecy outage probability (SOP) of an IRS-assisted terrestrial system in the presence of an Eve, while the authors in [12] and [13] extended the analysis to systems with multiple Eves. ...
... Besides, these studies restricted to single-input settings and overlooked the randomness of the distribution of Eves in reality. Furthermore, to simplify analysis, the derivations in [11]- [13] are based on the assumption that all links follow Rayleigh channels. Thus these derived results can not be directly applied to the UAV-enabled systems which are dominated by LoS paths. ...
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In this letter, we study the secrecy performance of an intelligent reflecting surface (IRS)-aided unmanned aerial vehicle (UAV) relay communication system in the presence of multiple ground eavesdroppers (Eves). Specifically, a UAV equipped with an IRS is deployed as a passive relay to forward the signals transmitted from the base station to users. By modeling the distribution of Eves with stochastic geometry theory and taking the estimation errors into account, we extract the novel expressions for the statistical characterizations of the signal-to-noise ratio, for both legitimate receiver and Eves. For completeness, different eavesdropping channels are investigated, namely, the cooperative and independent Eve cases. The secrecy outage probability (SOP) is analytically evaluated to unveil the impact of the number of reflecting elements and the location of UAV on SOP performance. Finally, numerical results corroborate the theoretical analysis.
... Maximizing the secrecy rate in the presence of a transmitter, receiver, eavesdropper and an IRS is studied in the literature, with the knowledge of perfect channel state information (CSI) [5], [6]. Extensions to multiple eavesdroppers [7], [13], and optimization based on the knowledge of statistical CSI of the eavesdropper [13] are also available. However, all these works consider PHY security for one-way communications. ...
... Maximizing the secrecy rate in the presence of a transmitter, receiver, eavesdropper and an IRS is studied in the literature, with the knowledge of perfect channel state information (CSI) [5], [6]. Extensions to multiple eavesdroppers [7], [13], and optimization based on the knowledge of statistical CSI of the eavesdropper [13] are also available. However, all these works consider PHY security for one-way communications. ...
Article
This letter investigates the exploitation of an intelligent reflecting surface (IRS) to communicate securely in a two-way network consisting of an untrusted user. In particular, the transmit powers and the phase shift at each element of the IRS are optimized to maximize the sum-secrecy rate, such that the IRS-reflected and non-IRS-reflected signals are added destructively at the untrusted user. The proposed iterative algorithm converges rapidly to a feasible solution of high accuracy with a few iterations. Numerical results demonstrate sum-secrecy rate gains up to 120% compared to naive or partially optimized schemes.
... For example, with the help of an IRS equipped relaying node, a novel user scheduler is proposed in [5] for multiuser two-way networks, which can achieve a remarkable secrecy improvement. Furthermore, the detailed performance analysis for the IRS-assisted networks is conducted for different application scenarios in [6][7][8][9]. ...
Article
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Covert communications is critical in many application scenarios for ensuring transmission security and privacy. Two-way protocols are widely adopted in intelligent reflecting surface (IRS) assisted relaying networks to enable covert communications and prevent wireless signals from being overheard. To quantify the performance of covert communications in this special scenario, we derive the closed-form expression of outage probability and its asymptote in this paper. Considering the worst-case of covert communications, the optimal normalized power threshold of warden's detector is analyzed under a complex Gaussian distribution approximation. To meet the requirement of the detection error probability, the ratio of the transmission power between the covert nodes is investigated. Simulation results are provided to validate the theoretical expressions as well as the asymptotic analysis with a small number of reflecting elements.
... The authors in [33] demonstrated that transmission under imperfect reflectors is equivalent to a point-to-point communication over a Nakagami fading channel. For the IRS-aided physical layer security networks with phase errors, secrecy outage probability and the average secrecy rate was studied in [34] for a single eavesdropper case and in [35] for the case with multiple eavesdroppers. ...
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Different from conventional wired line connections, industrial control through wireless transmission is widely regarded as a promising solution due to its reduced cost, increased long-term reliability, and enhanced reliability. However, mission-critical applications impose stringent quality of service (QoS) requirements that entail ultra-reliability low-latency communications (URLLC). The primary feature of URLLC is that the blocklength of channel codes is short, and the conventional Shannon’s Capacity is not applicable. In this paper, we consider the URLLC in a factory automation (FA) scenario. Due to densely deployed equipment in FA, wireless signal are easily blocked by the obstacles. To address this issue, we propose to deploy intelligent reflecting surface (IRS) to create an alternative transmission link, which can enhance the transmission reliability. In this paper, we focus on the performance analysis for IRS-aided URLLC-enabled communications in a FA scenario. Both the average data rate (ADR) and the average decoding error probability (ADEP) are derived under finite channel blocklength for seven cases: 1) Rayleigh fading channel; 2) With direct channel link; 3) Nakagami-m fading channel; 4) Imperfect phase alignment; 5) Multiple-IRS case; 6) Rician fading channel; 7) Correlated channels. Extensive numerical results are provided to verify the accuracy of our derived results.
... The authors maximized the SR under hardware impairments by jointly optimizing the discrete RIS phase shifts and the transmit beamforming. In the work of [101], the Ergodic Secrecy Rate (ESR) of RIS-aided communication systems was considered in the presence of discrete phase shifts and multiple eavesdroppers. ...
Article
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Reconfigurable intelligent surface (RIS)-aided communication is considered as an exciting research topic in academic and industrial communities since it provides an emerging affordable solution to achieve high quality and secure next-generation wireless systems. Especially, the deployment of RIS in multi-user wireless networks promises to reduce system hardware costs, signal processing complexity, as well as energy consumption due to small size, lightweight and ability to actively shape the wireless propagation environment. Further, by realizing a cost-effective radio environment, RIS-aided communication can be implemented to be an appealing technology for future integration with other emerging wireless applications and communication systems. Despite the positive appeal, RISs face new challenges that hinder integrating efficiently into wireless networks, such as network secrecy performance and system sum-rates, as well as achieving efficient deployment design in highly dynamic and time-varying wireless environments. To this end, we overview recent state-of-the-art techniques to address the above issues faced in the integration of RISs with various emerging multi-user communication techniques, such as Unmanned Aerial Vehicles (UAVs), Non-Orthogonal Multiple Access (NOMA), Millimeter Wave (mmWave) and Terahertz (THz) communications, Physical Layer Security (PLS), massive antennas, and Simultaneous Wireless Information and Power Transfer (SWIPT). Finally, we highlight promising future research directions of RIS-aided communication in Cell-Free Massive Multiple-Input-Multiple-Output (MIMO) systems, Rate-Splitting Multiple Access (RSMA), Light Fidelity (LiFi), and Cognitive Radio (CR) systems.
... Importantly, Sánchez et al. assessed the secrecy performance analysis of a RIS-based network subject to the presence of phase estimation and quantization errors [24]. Furthermore, the work in [25], [26] extended the secrecy analysis of such a WCS by considering phase estimation and quantization errors along with multiple eavesdroppers under the presence and absence of a direct link, respectively. On the other hand, a limited number of work in the literature analyzed the interplay between conventional dual/multi-hop relaying techniques and RIS when incorporated together on a transmission system. ...
Preprint
In this paper, we quantify the physical layer security of a dual-hop regenerative relaying-based wireless communication system assisted by reconfigurable intelligent surfaces (RISs). In particular, the setup consists of a source node communicating with a destination node via a regenerative relay. In this setup, a RIS is installed in each hop to increase the source-relay and relay-destination communications reliability, where the RISs' phase shifts are subject to quantization errors. The legitimate transmission is performed under the presence of a malicious eavesdropper attempting to compromise the legitimate transmissions by overhearing the broadcasted signal from the relay. To overcome this problem, we incorporate a jammer to increase the system's secrecy by disrupting the eavesdropper through a broadcasted jamming signal. Leveraging the well-adopted Gamma and Exponential distributions approximations, the system's secrecy level is quantified by deriving approximate and asymptotic expressions of the secrecy intercept probability (IP) metric in terms of the main network parameters. The results show that the secrecy is enhanced significantly by increasing the jamming power and/or the number of reflective elements (REs). In particular, an IP of approximately $10^{-4}$ can be reached with $40$ REs and $10$ dB of jamming power-to-noise ratio even when the legitimate links' average signal-to-noise ratios are $10$-dB less than the eavesdropper's one. We show that cooperative jamming is very helpful in strong eavesdropping scenarios with a fixed number of REs, and the number of quantization bits does not influence the secrecy when exceeding $3$ bits. All the analytical results are endorsed by Monte Carlo simulations.
... Meanwhile, IRS also can be configured to steer signals towards required directions or locations not only for enhancing the signal quality but also for suppressing unwanted signals that interfere with the wireless network [76] . Besides, IRS can be configured to worsen the signal towards malicious users either by creating destructive interference or by changing the reflection of signals off the locations occupied by malicious users [77]− [79] . Moreover, IRS can be intelligently configured to shape the wireless environment whose channel matrix has a high rank and a good condition number, to increase the channel capacity [80] . ...
Preprint
The intelligent information society, which is highly digitized, intelligence inspired and globally data driven, will be deployed in the next decade. The next 6G wireless communication networks are the key to achieve this grand blueprint, which is expected to connect everything, provide full dimensional wireless coverage and integrate all functions to support full-vertical applications. Recent research reveals that intelligent reflecting surface (IRS) with wireless environment control capability is a promising technology for 6G networks. Specifically, IRS can intelligently control the wavefront, e.g., the phase, amplitude, frequency, and even polarization by massive tunable elements, thus achieving fine-grained 3-D passive beamforming. In this paper, we first give a blueprint of the next 6G networks including the vision, typical scenarios and key performance indicators (KPIs). Then, we provide an overview of IRS including the new signal model, hardware architecture and competitive advantages in 6G networks. Besides, we discuss the potential application of IRS in the connectivity of 6G networks in detail, including intelligent and controllable wireless environment, ubiquitous connectivity, deep connectivity and holographic connectivity. At last, we summarize the challenges of IRS application and deployment in 6G networks. As a timely review of IRS, our summary will be of interest to both researchers and practitioners engaging in IRS for 6G networks.
... In [23], a beamforming and jamming technique were presented jointly to analyze the secrecy performance without any eavesdropper's channel state information (CSI). The impacts of colluding and non-colluding eavesdroppers assuming a discrete phase shift at the RIS was shown in [24] in terms of ergodic secrecy rate. The PLS in vehicular network was described in [4], where the transmission is dependent on RIS, source power, eavesdroppers' position, and distance. ...
Preprint
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Since security has been one of the crucial issues for high-yield communications such as 5G and 6G, the researchers continuously come up with newer techniques to enhance the security and performance of these progressive wireless communications. Reconfigurable intelligent surface (RIS) is one of those techniques that artificially rearrange and optimize the propagation environment of electromagnetic waves to improve both spectrum and energy efficiency of wireless networks. Besides, in underwater communication, underwater optical wireless communication (UOWC) is a better alternative/replacement for conventional acoustic and radio frequency (RF) technologies. Hence, mixed RIS-aided RF-UOWC can be treated as a promising technology for future wireless networks. This work focuses on the secrecy performance of mixed dual-hop RIS-aided RF-UOWC networks under the intercepting effort of a probable eavesdropper. The RF link operates under generalized Gamma fading distribution; likewise, the UOWC link experiences the mixture exponential generalized Gamma distribution. The secrecy analysis subsumes the derivations of closed-form expressions for average secrecy capacity, exact and lower bound of secrecy outage probability, and strictly positive secrecy capacity, all in terms of Meijer G functions. Capitalizing on these derivations, the effects of heterodyne and intensity modulation/direct detection systems, underwater turbulence resulting from air bubble levels, temperature gradients, and salinity gradients, are measured. Unlike conventional models that merely deal with thermally uniform scenarios, this proposed model is likely to be unique in terms of dealing with secrecy analysis of a temperature gradient RIS-aided RF-UOWC network. Lastly, the derivations are validated via Monte-Carlo simulations.
... However, we consider S D a general scenario considering fading coefficients h i and g i to be independent but non-identical distributed (i.ni.d). Note that several publications employ the assumption of independent channels as a first approximation to analyze RIS-assisted systems [15], [16], [41], [42]. ...
Article
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Reconfigurable intelligent surface (RIS) is an excellent use case for line-of-sight (LOS) based technologies such as free-space optical (FSO) communications. In this paper, we analyze the performance of RIS-empowered FSO (RISE-FSO) systems by unifying Fisher–Snedecor (F), Gamma-Gamma (GG), and Malága (M) distributions for atmospheric turbulence with zero-boresight pointing errors over deterministic as well as random path-loss in foggy conditions with heterodyne detection (HD) and intensity modulation/direct detection (IM/DD) methods. By deriving the probability density function (PDF) and cumulative distribution function (CDF) of the direct-link (DL) with the statistical effect of atmospheric turbulence, pointing errors and random fog, we develop exact expressions of PDF and CDF of the resultant channel for the RISE-FSO system. Using the derived statistical results, we present exact expressions of outage probability, average bit-error-rate (BER), ergodic capacity, and moments of signal-to-noise ratio (SNR) for both DL-FSO and RISE-FSO systems. We also develop an asymptotic analysis of the outage probability and average BER and derive the diversity order of the considered systems. We validate the analytical expressions using Monte-Carlo simulations and demonstrate the performance scaling of the FSO system with the number of RIS elements for various turbulence channels, detection techniques, and weather conditions.
... Considering that IRS can enhance the legitimate signal while impairing the receiving power of the Eve via adjusting the reflection signal in real time, the authors in [27,28] researched the issue where IRS enhances the PLS of MISO wireless communication networks, revealing that IRS has great potentiality in improving system security. In [29], the authors explored the system ergodic secrecy rate of IRS with discrete phase shifters. As a further development, authors of [30,31] maximized the security rate through joint optimization of TPC matrix at the base station (BS), covariance matrix of artificial noise (AN) and phase shifters at IRS. ...
Article
This paper investigates the physical layer security of an intelligent reflecting surface (IRS) aided non-orthogonal multiple access (NOMA) networks, where a remote user is regarded as an eavesdropper to intercept the information of nearby user. To evaluate the security performance of IRS-aided NOMA networks, a problem of maximizing achievable secrecy rate is formulated via jointly optimizing the beamforming and phase shifting. More specifically, we aim to tackle the non-convex problem by optimizing beamforming vector as well as phase shifting matrix with the assistance of block coordinate descent (BCD) and minorization maximization (MM) algorithms. Numerical results illustrate that: 1) The secrecy rates of IRS-aided NOMA with BCD and MM algorithms are superior to that of orthogonal multiple access schemes; 2) With increasing the number of reflecting elements, the secrecy rates of IRS-aided NOMA networks are achieved carefully; and 3) The IRS-aided NOMA networks are capable of relieving the transmission pressure of base station.
... Substituting (38) into (37), we havē ...
Preprint
p>We focus on the secure performance metrics at the legitimate users, i.e. secure outage probability (SOP) and secrecy capacity, to quantify the secrecy performance of NOMA-RIS-aided IoT systems. We assume the RIS is placed between the access point and the legitimate devices, and is expected to enhance the link security through the smart phase shift mechanism of metasurface elements in RIS. We first present analytical results for the SOP and secrecy capacity. Next, an iterative search algorithm is adopted to exhibit optimal SOP for further insights and analysis. In order to help the base station allocate power coefficients to NOMA users properly, an efficient deep-neural network (DNN)-based secure metric prediction scheme is adopted to achieve the secure performance. Our derivations and simulations indicate that the number of meta-surface elements of the RIS and the average signal-to-noise ratio at the base station contribute the most to the system performance enhancement. </p
... It is worth mentioning that RIS-assisted system outperforms the AF-relaying system. To show the performance loss caused by discrete phase shifts, we provide simulation results with the phase error of each reflector uniformly distributed in − π 2 2 , π 2 2 [25]. Furthermore, the simulation and numerical results agree perfectly, confirming the accuracy of our results. ...
Article
This letter investigates a reconfigurable intelligent surfaces (RIS)-aided wireless communication system in an inband underlay Device-to-Device (D2D) communication, where the direct link between D2D users is unavailable. An RIS is used to adjust its reflecting elements to enhance the D2D communication data transmission while improving the cellular network’s secrecy performance concurrently. Specifically, analytical results for the secrecy outage probability and the probability of non-zero secrecy capacity are derived for the cellular network. Moreover, the D2D outage probability is also provided. Simulation and analytical results are presented to verify the derived expressions’ correctness and the effectiveness of the proposed scenario. Moreover, the asymptotic results are presented.
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In the past as well as present wireless communication systems, the wireless propagation environment is regarded as an uncontrollable black box that impairs the received signal quality, and its negative impacts are compensated for by relying on the design of various sophisticated transmission/reception schemes. However, the improvements through applying such schemes operating at two endpoints (i.e., transmitter and receiver) only are limited even after five generations of wireless systems. Reconfigurable intelligent surface (RIS) or intelligent reflecting surface (IRS) have emerged as a new and revolutionary technology that can configure the wireless environment in a favorable manner by properly tuning the phase shifts of a large number of passive and low-cost reflecting elements, thus standing out as a promising candidate technology for the next-/sixth-generation (6G) wireless system. However, to reap the performance benefits promised by RIS/IRS, efficient signal processing techniques are crucial, for a variety of purposes such as channel estimation, transmission design, radio localization, and so on. In this paper, we provide a comprehensive overview of recent advances on RIS/IRS-aided wireless systems from the signal processing perspective. We also highlight promising research directions that are worthy of investigation in the future.
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This work investigates the following question: subject to strictly limited (finite-rate) feedback in a multi-user multi-antenna system, what channel state information (CSI) should we send back to the transmitter, and how should it be used? Considering the class of single-beam systems, we suggest a combination of beamforming (array gain) and multi-user diversity. It has been shown that in single antenna systems, one bit of feedback per user can capture almost all gains available due to multi-user diversity, therefore we propose and analyze a compound strategy that uses one bit for multi-user diversity and any further feedback bits for beamforming. We obtain the scaling laws of this compound strategy, showing that it scales as well as any single-beam system with full transmit-CSI.
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Reconfigurable intelligent surfaces (RISs), also known as intelligent reflecting surfaces (IRSs), or large intelligent surfaces (LISs), <sup>1</sup> have received significant attention for their potential to enhance the capacity and coverage of wireless networks by smartly reconfiguring the wireless propagation environment. Therefore, RISs are considered a promising technology for the sixth-generation (6G) of communication networks. In this context, we provide a comprehensive overview of the state-of-the-art on RISs, with focus on their operating principles, performance evaluation, beamforming design and resource management, applications of machine learning to RIS-enhanced wireless networks, as well as the integration of RISs with other emerging technologies. We describe the basic principles of RISs both from physics and communications perspectives, based on which we present performance evaluation of multiantenna assisted RIS systems. In addition, we systematically survey existing designs for RIS-enhanced wireless networks encompassing performance analysis, information theory, and performance optimization perspectives. Furthermore, we survey existing research contributions that apply machine learning for tackling challenges in dynamic scenarios, such as random fluctuations of wireless channels and user mobility in RIS-enhanced wireless networks. Last but not least, we identify major issues and research opportunities associated with the integration of RISs and other emerging technologies for applications to next-generation networks. <sup>1</sup> Without loss of generality, we use the name of RIS in the remainder of this paper. </fn
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Due to hardware limitations, the phase shifts of the reflecting elements of reconfigurable intelligent surfaces (RISs) need to be quantized into discrete values. This letter aims to unveil the minimum required number of phase quantization levels L in order to achieve the full diversity order in RIS-assisted wireless communication systems. With the aid of an upper bound of the outage probability, we first prove that the full diversity order is achievable provided that L is not less than three. If L=2, on the other hand, we prove that the achievable diversity order cannot exceed (N+1)/2, where N is the number of reflecting elements. This is obtained with the aid of a lower bound of the outage probability. Therefore, we prove that the minimum required value of L for achieving the full diversity order is L=3. Simulation results verify the theoretical analysis and the impact of phase quantization levels on RIS-assisted communication systems.
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Reconfigurable intelligent surfaces have emerged as a promising technology for future wireless networks. Given that a large number of reflecting elements is typically used and that the surface has no signal processing capabilities, a major challenge is to cope with the overhead that is required to estimate the channel state information and to report the optimized phase shifts to the surface. This issue has not been addressed by previous works, which do not explicitly consider the overhead during the resource allocation phase. This work aims at filling this gap, by developing an overhead-aware resource allocation framework for wireless networks where reconfigurable intelligent surfaces are used to improve the communication performance. An overhead model is proposed and incorporated in the expressions of the system rate and energy efficiency, which are then optimized with respect to the phase shifts of the reconfigurable intelligent surface, the transmit and receive filters, the power and bandwidth used for the communication and feedback phases. The bi-objective maximization of the rate and energy efficiency is investigated, too. The proposed framework characterizes the trade-off between optimized radio resource allocation policies and the related overhead in networks with reconfigurable intelligent surfaces.
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We consider a fading channel in which a multi-antenna transmitter communicates with a multi-antenna receiver through a reconfigurable intelligent surface (RIS) that is made of N reconfigurable passive scatterers impaired by phase noise. The beamforming vector at the transmitter, the combining vector at the receiver, and the phase shifts of the N scatterers are optimized in order to maximize the signal-to-noise-ratio (SNR) at the receiver. By assuming Rayleigh fading (or line-of-sight propagation) on the transmitter-RIS link and Rayleigh fading on the RIS-receiver link, we prove that the SNR is a random variable that is equivalent in distribution to the product of three (or two) independent random variables whose distributions are approximated by two (or one) gamma random variables and the sum of two scaled non-central chi-square random variables. The proposed analytical framework allows us to quantify the robustness of RIS-aided transmission to fading channels. For example, we prove that the amount of fading experienced on the transmitter-RIS-receiver channel linearly decreases with N1. This proves that RISs of large size can be effectively employed to make fading less severe and wireless channels more reliable.
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In this letter, improving the security of an intelligent reflecting surface (IRS) assisted multiple-input single-output (MISO) communication system is studied. Different from the ideal assumption in existing literatures that full eavesdropper's (Eve's) channel state information (CSI) is available, we consider a more practical scenario that no Eve's CSI is available. To enhance the security of this system given a total transmit power at transmitter (Alice), we propose a joint beamforming and jamming approach, in which a minimum transmit power is firstly optimized at Alice so as to meet the quality of service (QoS) at legitimate user (Bob), and then artificial noise (AN) is applied to jam the eavesdropper by using the residual power at Alice. Two efficient algorithms exploiting oblique manifold (OM) and minorization-maximization (MM) algorithms, respectively, are developed for solving the resulting non-convex optimization problem. Simulation results have been provided to validate the performance and convergence of the proposed algorithms.
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Reconfigurable intelligent surfaces (RISs) are an emerging transmission technology for application to wireless communications. RISs can be realized in different ways, which include (i) large arrays of inexpensive antennas that are usually spaced half of the wavelength apart; and (ii) metamaterial-based planar or conformal large surfaces whose scattering elements have sizes and inter-distances much smaller than the wavelength. Compared with other transmission technologies, e.g., phased arrays, multi-antenna transmitters, and relays, RISs require the largest number of scattering elements, but each of them needs to be backed by the fewest and least costly components. Also, no power amplifiers are usually needed. For these reasons, RISs constitute a promising software-defined architecture that can be realized at reduced cost, size, weight, and power (C-SWaP design), and are regarded as an enabling technology for realizing the emerging concept of smart radio environments (SREs). In this paper, we (i) introduce the emerging research field of RIS-empowered SREs; (ii) overview the most suitable applications of RISs in wireless networks; (iii) present an electromagnetic-based communication-theoretic framework for analyzing and optimizing metamaterial-based RISs; (iv) provide a comprehensive overview of the current state of research; and (v) discuss the most important research issues to tackle. Owing to the interdisciplinary essence of RIS-empowered SREs, finally, we put forth the need of reconciling and reuniting C. E. Shannon’s mathematical theory of communication with G. Green’s and J. C. Maxwell’s mathematical theories of electromagnetism for appropriately modeling, analyzing, optimizing, and deploying future wireless networks empowered by RISs.
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In this work, we study the secrecy performance of a reconfigurable intelligent surfaces (RIS)-aided wireless communication system in the presence of an eavesdropping user. Specifically, we assume that the RIS is placed between the source and the legitimate user to create a smart environment and used to improve the link security. In particular, analytical results for the secrecy outage probability (SOP) is derived. We also provide an asymptotic analysis to investigate the effect of the main parameters on the secrecy performance of our proposed system, such as the number of the reflectors in the RIS and the average signal-to-noise ratios. Finally, we verify our analytical results via simulations. Results show the positive effect of utilizing the RIS for enhancing wireless systems secrecy performance.
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In this paper, intelligent reflecting surfaces (IRSs) are employed to enhance the physical layer security in a challenging radio environment. In particular, a multi-antenna access point (AP) has to serve multiple single-antenna legitimate users, which do not have line-of-sight communication links, in the presence of multiple multi-antenna potential eavesdroppers whose channel state information (CSI) is not perfectly known. Artificial noise (AN) is transmitted from the AP to deliberately impair the eavesdropping channels for security provisioning. We investigate the joint design of the beamformers and AN covariance matrix at the AP and the phase shifters at the IRSs for maximization of the system sum-rate while limiting the maximum information leakage to the potential eavesdroppers. To this end, we formulate a robust non-convex optimization problem taking into account the impact of the imperfect CSI of the eavesdropping channels. To address the non-convexity of the optimization problem, an efficient algorithm is developed by capitalizing on alternating optimization, a penalty-based approach, successive convex approximation, and semidefinite relaxation. Simulation results show that IRSs can significantly improve the system secrecy performance compared to conventional architectures without IRS. Furthermore, our results unveil that, for physical layer security, uniformly distributing the reflecting elements among multiple IRSs is preferable over deploying them at a single IRS.
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In this letter, we investigate the ergodic capacity of the intelligent reflecting surface (IRS)-assisted communication system with quantization phase errors, which is different from existing works assuming ideal continuous or discrete phases. The ergodic capacity, however, does not admit an exact closed-form expression if not impossible. In order to gain insight into the capacity performance, the impact of phase errors on the capacity degradation is quantified, and the minimum number of the reflectors to achieve a given rate threshold is obtained. Simulation results verify the effectiveness of the IRS-assisted system and the capacity scaling law.
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Enabling vehicles to communicate with other vehicles, infrastructure, pedestrians, and everything for use cases such as road safety, automatic driving, and infotainment is important for the future cellular networks. However, some vehicle-to-everything (V2X) services need secure transmissions and should be prevented from eavesdropping. Physical layer security, an information- theoretical framework, utilizes the randomness of underlying channels to ensure secrecy in the physical layer. Different from ground communications, unmanned aerial vehicles (UAVs) create line-of-sight connections to vehicles and mobile users making them an ideal platform to conduct physical layer security strategies. In this article, we embrace UAV to V2X communications to enhance the V2X security from the physical layer security's perspective. To be specific, we present security problems in V2X systems, highlight security threats in V2X networks, and illustrate some potential applications of UAVs in V2X security. Open problems for UAV-assisted V2X secure communications are also discussed.
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Intelligent reflecting surface (IRS) is a revolutionary and transformative technology for achieving spectrum and energy efficient wireless communication cost-effectively in the future. Specifically, an IRS consists of a large number of low-cost passive elements each being able to reflect the incident signal independently with an adjustable phase shift so as to collaboratively achieve three-dimensional (3D) passive beamforming without the need of any transmit radio-frequency (RF) chains. In this paper, we study an IRS-aided single-cell wireless system where one IRS is deployed to assist in the communications between a multi-antenna access point (AP) and multiple single-antenna users. We formulate and solve new problems to minimize the total transmit power at the AP by jointly optimizing the transmit beamforming by active antenna array at the AP and reflect beamforming by passive phase shifters at the IRS, subject to users’ individual signal-to-interference-plus-noise ratio (SINR) constraints. Moreover, we analyze the asymptotic performance of IRS’s passive beamforming with infinitely large number of reflecting elements and compare it to that of the traditional active beamforming/relaying. Simulation results demonstrate that an IRS-aided MIMO system can achieve the same rate performance as a benchmark massive MIMO system without using IRS, but with significantly reduced active antennas/RF chains. We also draw useful insights into optimally deploying IRS in future wireless systems.
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An intelligent reflecting surface (IRS) can adaptively adjust the phase shifts of its reflecting units to strengthen the desired signal and/or suppress the undesired signal. In this letter, we investigate an IRS-aided secure wireless communication system where a multi-antenna access point (AP) sends confidential messages to a single-antenna user in the presence of a single-antenna eavesdropper. In particular, we consider the challenging scenario where the eavesdropping channel is stronger than the legitimate communication channel and they are also highly correlated in space. We maximize the secrecy rate of the legitimate communication link by jointly designing the AP’s transmit beamforming and the IRS’s reflect beamforming. While the resultant optimization problem is difficult to solve, we propose an efficient algorithm to obtain high-quality suboptimal solution for it by applying the alternating optimization and semidefinite relaxation methods. Simulation results show that the proposed design significantly improves the secrecy communication rate for the considered setup over the case without using the IRS, and outperforms a heuristic scheme.
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In Part I of this paper, we introduced the intrinsically secure communications graph (iS-graph)-a random graph which describes the connections that can be established with strong secrecy over a large-scale network, in the presence of eavesdroppers. We focused on the local connectivity of the iS-graph, and proposed techniques to improve it. In this second part, we characterize the maximum secrecy rate (MSR) that can be achieved between a node and its neighbors. We then consider the scenario where the eavesdroppers are allowed to collude, i.e., exchange and combine information. We quantify exactly how eavesdropper collusion degrades the secrecy properties of the network, in comparison to a noncolluding scenario. Our analysis helps clarify how the presence of eavesdroppers can jeopardize the success of wireless physical-layer security.