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1
Wang, Wenhe y Kang Song. "Hybrid Active–Passive Reconfigurable Intelligent Surface for Cooperative Transmission Systems". Applied Sciences 14, n.º 1 (27 de diciembre de 2023): 231. http://dx.doi.org/10.3390/app14010231.
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Reconfigurable intelligent surfaces (RISs) are acknowledged as one of the key technologies for the next-generation communications systems due to their low cost, high-energy efficiency, and the ability to intelligently control the wireless propagation environment. In this paper, we present a hybrid active–passive reconfigurable intelligent surface (HAPR) for cooperative transmission system, where HAPR can intelligently change its operating mode according to the channel environment, eliminating the “multiplicative fading” effect of traditional passive RIS (P-RIS) and higher power consumption of active RIS (A-RIS), and combining the advantages of both to effectively improve the system performance. First, we investigate the ideal reflection coefficient of RIS reflecting elements (REs) under the condition of a limited power budget. Using the compound Simpson formula, the closed-form approximation expression for the system outage probability (OP) has been derived. Finally, Monte Carlo simulation is used to confirm the accuracy of the expression. The simulation results demonstrate that HAPR has a better performance than both A-RIS and P-RIS, which can achieve a lower OP.
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Widodo, Agung Mulyo, Heri Wijayanto, I. Gede Pasek Suta Wijaya, Andika Wisnujati y Ahmad Musnansyah. "Analyzing Coverage Probability of Reconfigurable Intelligence Surface-aided NOMA". JOIV : International Journal on Informatics Visualization 7, n.º 3 (10 de septiembre de 2023): 839. http://dx.doi.org/10.30630/joiv.7.3.2054.
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Along with the explosive growth of wireless communication network users who require large frequency bands and low latency, it is a challenge to create a new wireless communication network beyond 5G. This is because installing a massive 5G network requires a large investment by network providers. For this reason, the authors propose an alternative beyond 5G that has better quality than 5G and a relatively lower investment value than 5G networks. This study aims to analyze the downlink of the cooperative non-orthogonal multiple access (NOMA) network, which is usually used in 5G, combined with the use of a reconfigurable intelligence surface (RIS) antenna with decode and forward relay mechanisms. RIS is processed with a limited number of objects utilizing Rayleigh fading channels. The scenario is created by a user who relays without a direct link for users near the base station and with a direct link for users far from the base station. Under the Nakagami-m fading channel, the authors carefully evaluated the probability of loss for various users as a function of perfect channel statistical information (p-CSI) utilizing simply a single input-output (SISO) system with a finite number of RIS elements. As a key success metric, the efficiency of the proposed RIS-assisted NOMA transmission mechanism is evaluated through numerical data on the outage probability for each user. The modeling outcomes demonstrate that the RIS-aided NOMA network outperforms the traditional NOMA network
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Rana, Biswarup, Sung-Sil Cho y Ic-Pyo Hong. "Passive Type Reconfigurable Intelligent Surface: Measurement of Radiation Patterns". Micromachines 14, n.º 4 (5 de abril de 2023): 818. http://dx.doi.org/10.3390/mi14040818.
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The demand for unprecedented data and ubiquitous wireless connections have led to the adoption of new types of transmitters and receivers. Additionally, different new types of devices and technologies need to be proposed for such demand. Reconfigurable intelligent surface (RIS) is going to play a very significant role in the upcoming beyond-5G/6G communications. It is envisioned that not only the RIS will be deployed to assist and create a smart wireless environment for the upcoming communications, but also the receiver and transmitter can be fabricated using RIS to make a smart and intelligent transmitter and receiver. Thus, the latency of upcoming communications can be reduced very significantly using RIS, which is a very important factor. Artificial intelligence assists communications and shall be adopted widely for the next generation networks. In this paper, radiation pattern measurement results of our previously published RIS have been provided. This work is the extension work of our previously proposed RIS. The polarization-independent passive type of RIS working in the sub-6 GHz frequency band using low-cost FR4-substrate was designed. Each unit cell with dimensions of 42 mm × 42 mm had a single-layer substrate backed by a copper plate. A 10 × 10-unit cell array was fabricated to check the performance of the RIS. Such types of unit cells and RIS were designed to set up initial measurement facilities in our laboratory for any kinds of RIS measurements.
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Yu Lu, Hao Jiang y Linglong Dai. "Artificial intelligence for RIS-aided wireless communications". ITU Journal on Future and Evolving Technologies 4, n.º 1 (6 de marzo de 2023): 70–77. http://dx.doi.org/10.52953/hymy1464.
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The recently proposed Reconfigurable Intelligent Surface (RIS) can reconstruct the wireless channels between the transceivers, thus it is regarded as a promising technology for future 6G wireless networks to enlarge their coverage and improve the capacity. However, RISs also impose some new challenges, such as an unaffordable overhead for channel estimation and high complexity for real-time beam-forming. Fortunately, the impressive success of Artificial Intelligence (AI) in various fields has inspired its application in RIS-aided communications to address these challenges. In this paper, two pairs of dominant methodologies of using AI for RIS-aided wireless communications are discussed. The first one is the AI-based algorithm design, which is illustrated by some examples of typical transmission techniques. The second one is the AI-based architecture design, which breaks the classical block-based design rule of wireless communications in the past few decades. The interplay between AI and RIS is also highlighted. Finally, key challenges and future opportunities in this emerging area are pointed out. We expect that this paper will stimulate more promising AI-based investigations for RIS-aided wireless communications.
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Goh, Chi Yen, Chee Yen Leow y Rosdiadee Nordin. "Energy Efficiency of Unmanned Aerial Vehicle with Reconfigurable Intelligent Surfaces: A Comparative Study". Drones 7, n.º 2 (31 de enero de 2023): 98. http://dx.doi.org/10.3390/drones7020098.
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Unmanned aerial vehicles (UAVs) and reconfigurable intelligent surfaces (RIS) are the promising emerging technologies proposed for the 6th-Generation (6G) network to improve the capacity, reliability, and coverage of wireless communications. By integrating the UAV with RIS (RIS-UAV), the three-dimensional (3D) mobility of the UAV can be leveraged to establish strong line-of-sight links with the ground nodes, while the RIS intelligently reflect the signals toward the desired directions. However, the existing literature on RIS-UAV systems mainly assumes the use of passive elements, which suffers from the double path-loss problem. The use of active elements in RIS, which could improve the reflected link performance at the cost of increased energy consumption, has not been considered for the RIS-UAV system. Further, the energy efficiency of a RIS-UAV with active elements remains as an open direction because there is a need to investigate the feasibility of either an active or hybrid RIS-UAV implementation. This paper proposes active and hybrid RIS-UAVs and investigates the energy efficiencies of active and hybrid RIS-UAVs in comparison with existing passive RIS-UAVs and conventional UAV relays. The numerical results reveal that the proposed hybrid and active RIS-UAV relaying schemes can provide up to 14 times and 26 times improvement as compared to the passive RIS-UAV, respectively. As opposed to the active RIS-UAV that requires a larger power budget, half-duplex UAV relays that have a lower spectral efficiency, and full-duplex UAV relays that suffer from self-interference, the hybrid RIS-UAV emerges as a promising option to assist the ground communication system.
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Martín-Martín, Alberto, Rubén Padial-Allué, Encarnación Castillo, Luis Parrilla, Ignacio Parellada-Serrano, Alejandro Morán y Antonio García. "Hardware Implementations of a Deep Learning Approach to Optimal Configuration of Reconfigurable Intelligence Surfaces". Sensors 24, n.º 3 (30 de enero de 2024): 899. http://dx.doi.org/10.3390/s24030899.
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Reconfigurable intelligent surfaces (RIS) offer the potential to customize the radio propagation environment for wireless networks, and will be a key element for 6G communications. However, due to the unique constraints in these systems, the optimization problems associated to RIS configuration are challenging to solve. This paper illustrates a new approach to the RIS configuration problem, based on the use of artificial intelligence (AI) and deep learning (DL) algorithms. Concretely, a custom convolutional neural network (CNN) intended for edge computing is presented, and implementations on different representative edge devices are compared, including the use of commercial AI-oriented devices and a field-programmable gate array (FPGA) platform. This FPGA option provides the best performance, with ×20 performance increase over the closest FP32, GPU-accelerated option, and almost ×3 performance advantage when compared with the INT8-quantized, TPU-accelerated implementation. More noticeably, this is achieved even when high-level synthesis (HLS) tools are used and no custom accelerators are developed. At the same time, the inherent reconfigurability of FPGAs opens a new field for their use as enabler hardware in RIS applications.
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Hong, Ic-Pyo. "Reviews Based on the Reconfigurable Intelligent Surface Technical Issues". Electronics 12, n.º 21 (1 de noviembre de 2023): 4489. http://dx.doi.org/10.3390/electronics12214489.
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Reconfigurable intelligent surfaces (RISs) are programmable metasurface structures that can control the propagation of electromagnetic waves by changing the electrical and magnetic properties of the surface. They can be used to intelligently reconfigure the wireless environment to improve the capacity and coverage of wireless networks. In recent years, numerous theoretical innovations and prototype tests have demonstrated that the RIS has the advantages of low cost, low power consumption, and easy deployment, and creates many potential opportunities and broad application prospects in 5G and future 6G networks. In this paper, starting from the technological development of RISs, we discussed the technical issues of RISs. The standardization of RISs, types of RISs according to operation modes, channel modeling, considerations for hardware implementation, differences from existing communication modules and the need for active RIS implementation, noise and power characteristics to ensure the efficiency of RISs, and performance parameters of RISs and field test results of RISs in indoor and outdoor environments were reviewed. By resolving the current technical issues of RISs, it is expected that RISs will be successfully used for B5G/6G communication through commercialization.
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Wang, Yi, Haibo Wang y XueWen Jiang. "Performance of Reconfigurable-Intelligent-Surface-Assisted Satellite Quasi-Stationary Aircraft–Terrestrial Laser Communication System". Drones 6, n.º 12 (8 de diciembre de 2022): 405. http://dx.doi.org/10.3390/drones6120405.
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This paper proposes the use of quasi-stationary aircraft and reconfigurable intelligent surfaces (RIS) to improve the system performance in satellite–terrestrial laser communication downlink. Single-input multiple-output (SIMO) technology is applied to the relay node of a quasi-stationary aircraft. The closed expression of the bit error rate (BER) of an RIS-assisted satellite quasi-stationary aircraft–terrestrial laser communication system (RIS-SHTLC) is derived under the M-distributed atmospheric turbulence model while considering the influence of atmospheric turbulence and pointing errors caused by RIS jitter. The effects of coherent binary frequency shift keying (CBFSK), coherent binary phase-shift keying (CBPSK), non-coherent binary frequency shift keying (NBFSK), and differential binary phase-shift keying (DBPSK) on the performance of an RIS-SHTLC system are simulated and analyzed under weak turbulence. The results show that the RIS-SHTLC system with CBPSK modulation has the best communication performance. Simultaneously, the relationships between the average signal-to-noise ratio (SNR) and BER of the RIS-SHTLC system under different RIS elements are simulated and analyzed, and compared with the traditional SHTLC system. In addition, the influence of the zenith angle, receiving aperture and divergence angle on the performance of the system is studied. Finally, Monte Carlo simulations are used to validate the analytical results.
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Li, Zongze, Shuai Wang, Qingfeng Lin, Yang Li, Miaowen Wen, Yik-Chung Wu y H. Vincent Poor. "Phase Shift Design in RIS Empowered Wireless Networks: From Optimization to AI-Based Methods". Network 2, n.º 3 (11 de julio de 2022): 398–418. http://dx.doi.org/10.3390/network2030025.
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Reconfigurable intelligent surfaces (RISs) offer the potential to customize the radio propagation environment for wireless networks. To fully exploit the advantages of RISs in wireless systems, the phases of the reflecting elements must be jointly designed with conventional communication resources, such as beamformers, the transmit power, and computation time. However, due to the unique constraints on the phase shifts and the massive numbers of reflecting units and users in large-scale networks, the resulting optimization problems are challenging to solve. This paper provides a review of the current optimization methods and artificial-intelligence-based methods for handling the constraints imposed by RISs and compares them in terms of the solution quality and computational complexity. Future challenges in phase-shift optimization involving RISs are also described, and potential solutions are discussed.
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Shi, Baihua, Yang Wang, Danqi Li, Wenlong Cai, Jinyong Lin, Shuo Zhang, Weiping Shi, Shihao Yan y Feng Shu. "STAR-RIS-UAV-Aided Coordinated Multipoint Cellular System for Multi-User Networks". Drones 7, n.º 6 (17 de junio de 2023): 403. http://dx.doi.org/10.3390/drones7060403.
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Different from conventional reconfigurable intelligent surfaces (RIS), simultaneous transmitting and reflecting RIS (STAR-RIS) can reflect and transmit signals to the receiver. In this paper, to serve more ground users and increase deployment flexibility, we investigate an unmanned aerial vehicle (UAV) equipped with STAR-RIS (STAR-RIS-UAV)-aided wireless communications for multi-user networks. Energy splitting (ES) and mode switching (MS) protocols are considered to control the reflection and transmission coefficients of STAR-RIS elements. To maximize the sum rate of the STAR-RIS-UAV-aided coordinated multipoint (CoMP) cellular system for multi-user networks, the corresponding beamforming vectors as well as transmitted and reflected coefficient matrices are optimized. Specifically, instead of adopting the alternating optimization, we design an iteration method to optimize all variables for both the ES and MS protocols at the same time. Simulation results reveal that the STAR-RIS-UAV-aided CoMP system has a much higher sum rate than systems with conventional RIS or without RIS. Furthermore, the proposed structure is more flexible than fixed STAR-RIS and could greatly promote the sum rate.
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Naaz, Farheen, Ali Nauman, Tahir Khurshaid y Sung-Won Kim. "Empowering the Vehicular Network with RIS Technology: A State-of-the-Art Review". Sensors 24, n.º 2 (5 de enero de 2024): 337. http://dx.doi.org/10.3390/s24020337.
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Reconfigurable intelligent surfaces (RIS) are expected to bring about a revolutionary transformation in vehicular networks, thus paving the way for a future characterized by connected and automated vehicles (CAV). An RIS is a planar structure comprising many passive elements that can dynamically manipulate electromagnetic waves to enhance wireless communication by reflecting, refracting, and focusing signals in a programmable manner. RIS exhibits substantial potential for improving vehicle-to-everything (V2X) communication through various means, including coverage enhancement, interference mitigation, improving signal strength, and providing additional layers of privacy and security. This article presents a comprehensive survey that explores the emerging opportunities arising from the integration of RIS into vehicular networks. To examine the convergence of RIS and V2X communications, the survey adopted a holistic approach, thus highlighting the potential benefits and challenges of this combination. In this study, we examined several applications of RIS-aided V2X communication. Subsequently, we delve into the fundamental emerging technologies that are expected to empower vehicular networks, encompassing mobile edge computing (MEC), non-orthogonal multiple access (NOMA), millimeter-wave communication (mmWave), Artificial Intelligence (AI), and visible light communication (VLC). Finally, to stimulate further research in this domain, we emphasize noteworthy research challenges and potential avenues for future exploration.
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Kim, Jihyung, Eunhye Hong, Jaemin Jung, Jinkyu Kang y Seongah Jeong. "Energy Minimization in Reconfigurable Intelligent Surface-Assisted Unmanned Aerial Vehicle-Enabled Wireless Powered Mobile Edge Computing Systems with Rate-Splitting Multiple Access". Drones 7, n.º 12 (25 de noviembre de 2023): 688. http://dx.doi.org/10.3390/drones7120688.
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In this study, a reconfigurable intelligent surface (RIS)-assisted wireless-powered mobile edge computing (WP-MEC) system is proposed, where a single-antenna unmanned aerial vehicle (UAV)-mounted cloudlet provides offloading opportunities to K user equipments (UEs) with a single antenna, and the K UEs can harvest the energy from the broadcast radio-frequency signals of the UAV. In addition, rate-splitting multiple access is used to provide offloading opportunities to multiple UEs for effective power control and high spectral efficiency. The aim of this paper is to minimize the total energy consumption by jointly optimizing the resource allocation in terms of time, power, computing frequency, and task load, along with the UAV trajectory and RIS phase-shift matrix. Since coupling issues between optimization variable designs are caused, however, an alternating optimization-based algorithm is developed. The performance of the proposed algorithm is verified via simulations and compared with the benchmark schemes of partial optimizations of resource allocation, path planning, and RIS phase design. The proposed algorithm exhibits high performance in WP-MEC systems with insufficient resources, e.g., achieving up to 40% energy reduction for a UAV with eight elements of RIS.
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Sarker, Md Abdul Latif, Woosung Son y Dong Seog Han. "RIS-Assisted Hybrid Beamforming and Connected User Vehicle Localization for Millimeter Wave MIMO Systems". Sensors 23, n.º 7 (3 de abril de 2023): 3713. http://dx.doi.org/10.3390/s23073713.
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A reconfigurable intelligent surface (RIS) is a type of metasurface that can dynamically control the reflection and transmission of electromagnetic waves, such as radio waves, by changing its physical properties. Recently, RISs have played an important role in intelligently reshaping wireless propagation environments to improve the received signal gain as well as spectral efficiency performance. In this paper, we consider a millimeter wave (mmWave) vehicle-to-vehicle (V2V) multiple-input multiple-output (MIMO) system in which, an RIS is deployed to aid downlink V2V data transmission. In particular, the line-of-sight path of the mmWave system is affected by blockages, resulting in higher signaling overhead. Thus, the system performance may suffer due to interruptions caused by static or mobile blockers, such as buildings, trees, vehicles, and pedestrians. In this paper, we propose an RIS-assisted hybrid beamforming scheme for blockage-aware mmWave V2V MIMO systems to increase communication service coverage. First, we propose a conjugate gradient and location-based hybrid beamforming (CG-LHB) algorithm to solve the user sub-rate maximization problem. We then propose a double-step iterative algorithm that utilizes an error covariance matrix splitting method to minimize the effect of location error on the passive beamforming. The proposed algorithms perform quite well when the channel uncertainty is smaller than 10%. Finally, the simulation results validate the proposed CG-LHB algorithm in terms of the RIS-assisted equivalent channel for mmWave V2V MIMO communications.
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Yao, Yuanyuan, Ke Lv, Sai Huang, Xuehua Li y Wei Xiang. "UAV Trajectory and Energy Efficiency Optimization in RIS-Assisted Multi-User Air-to-Ground Communications Networks". Drones 7, n.º 4 (15 de abril de 2023): 272. http://dx.doi.org/10.3390/drones7040272.
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An air-to-ground downlink communication network consisting of a reconfigurable intelligent surface (RIS) and unmanned aerial vehicle (UAV) is proposed. In conjunction with a resource allocation strategy, the system’s energy efficiency is improved. Specifically, the UAV equipped with a RIS starts from an initial location, and an energy-efficient unmanned aerial vehicle deployment (EEUD) algorithm is deployed to jointly optimize the UAV trajectory, RIS phase shifts, and BS transmit power, so as to obtain a quasi-optimal deployment location and hence improve the energy efficiency. First, the RIS phase shifts are optimized by using the block coordinate descent (BCD) algorithm to deal with the nonconvex inequality constraint, and then integrated with the Dinkelbach algorithm to address the resource allocation problem of the BS transmit power. Finally, for solving the UAV trajectory optimization problem, the complex objective function is transformed into a convex function, and the optimal UAV flight trajectory is obtained. Our simulation results show that the quasi-optimal deployment location obtained by the EEUD algorithm is superior to other deployment strategies in energy efficiency. Moreover, the instantaneous energy efficiency of the UAVs along the trajectory of searching the deployment location is better than other comparison trajectories. Furthermore, the RIS-assisted multi-user air-to-ground communication network can offer up to 145% improvement in energy efficiency over the traditional amplify-and-forward (AF) relay.
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Dai, Gaoyuan, Ronglan Huang, Jing Yuan, Zeng Hu, Longru Chen, Jianxian Lu, Tianrui Fan et al. "Towards Flawless Designs: Recent Progresses in Non-Orthogonal Multiple Access Technology". Electronics 12, n.º 22 (9 de noviembre de 2023): 4577. http://dx.doi.org/10.3390/electronics12224577.
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High effectiveness and high reliability are two fundamental concerns in data transmission. Non-orthogonal multiple-access (NOMA) technology presents a promising solution for high-speed data transmission, which has long been pursued by academia and industry. However, there is still a significant road ahead for it to effectively support a wide range of applications. This paper provides a comprehensive study, comparison, and classification of the current advanced NOMA schemes from the perspectives of single-carrier (SC) systems, multicarrier (MC) systems, reconfigurable-intelligent-surface (RIS)-assisted systems, and deep-learning (DL)-assisted systems. Specifically, system implementation issues such as the transition from SC-NOMA to MC-NOMA, the relaxation of distinct channel gains, the consideration of imperfect channel knowledge, and the mitigation of error propagation/intra-group interference are involved. To begin with, we present an overview of the state-of-the-art developments related to the advanced design of SC-NOMA. Subsequently, a generalized MC-NOMA framework that provides the diversity–multiplexing gain by enhancing users’ signal-to-interference-plus-noise ratio (SINR) is proposed for better system performance. Moreover, we delve into discussions on RIS-assisted NOMA systems, where the receiver’s SINR can be enhanced by intelligently reconfiguring the reflected signal propagations. Finally, we analyze designs that combine NOMA/RIS-NOMA with DL to achieve highly efficient data transmission. We also identify key trends and future directions in deep-learning-based NOMA frameworks, providing valuable insights for researchers in this field.
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Lai, Huan, Dongfen Li, Fang Xu, Xiao Wang, Jin Ning, Yanmei Hu y Bin Duo. "Optimization of Full-Duplex UAV Secure Communication with the Aid of RIS". Drones 7, n.º 9 (20 de septiembre de 2023): 591. http://dx.doi.org/10.3390/drones7090591.
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Recently, unmanned aerial vehicles (UAVs) have gained significant popularity and have been extensively utilized in wireless communications. Due to the susceptibility of wireless channels to eavesdropping, interference and other security attacks, UAV communication security faces serious challenges. Therefore, novel solutions need to be investigated for handling corresponding issues. Note that the UAV with full-duplex (FD) mode can actively improve spectral efficiency, and reconfigurable intelligent surface (RIS) can enable the intelligent control of signal reflection for improving transmission quality. Accordingly, the security of UAV communications may be considerably improved by combining the two techniques mentioned above. In this paper, we investigate the performance of secure communication in urban areas, assisted by a FD UAV and an RIS, where the UAV receives sensitive information from the ground users and sends jamming signals to the ground eavesdroppers. Particularly, we propose an approach to jointly optimize the user scheduling, user transmit power, UAV jamming power, RIS phase shift, and UAV trajectory for maximizing the worst-case secrecy rate. However, the non-convexity of the problem makes it difficult to solve. Combining alternating optimization (AO), slack variable techniques, successive convex approximation (SCA), and semi-definite relaxation (SDR), we propose an effective algorithm to obtain a suboptimal solution. According to the simulation results, in contrast to other benchmark schemes, we show that our proposed algorithm can significantly improve the overall secrecy rate.
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Lv, Chaoluo y Zhongqiang Luo. "Deep Learning for Channel Estimation in Physical Layer Wireless Communications: Fundamental, Methods, and Challenges". Electronics 12, n.º 24 (11 de diciembre de 2023): 4965. http://dx.doi.org/10.3390/electronics12244965.
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With the rapid development of wireless communication technology, intelligent communication has become one of the mainstream research directions after the fifth generation (5G). In particular, deep learning has emerged as a significant artificial intelligence technology widely applied in the physical layer of wireless communication for achieving intelligent receiving processing. Channel estimation, a crucial component of physical layer communication, is essential for further information recovery. As a motivation, this paper aims to review the relevant research on applying deep learning methods in channel estimation. Firstly, this paper briefly introduces the conventional channel estimation methods and then analyzes their respective merits and drawbacks. Subsequently, this paper introduces several common types of neural networks and describes the application of deep learning in channel estimation according to data-driven and model-driven approaches, respectively. Then, this paper extends to emerging communication scenarios and discusses the existing research on channel estimation based on deep learning for reconfigurable intelligent surface (RIS)-aided communication systems. Finally, to meet the demands of next-generation wireless communication, challenges and future research trends in deep-learning-based channel estimation are discussed.
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Elamassie, Mohammed y Murat Uysal. "Free Space Optical Communication: An Enabling Backhaul Technology for 6G Non-Terrestrial Networks". Photonics 10, n.º 11 (30 de octubre de 2023): 1210. http://dx.doi.org/10.3390/photonics10111210.
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The deployment of non-terrestrial networks (NTNs) is envisioned to achieve global coverage for 6G and beyond. In addition to space nodes, aerial NTN nodes such as high-altitude platform stations (HAPSs) and rotary-wing unmanned aerial vehicles (UAVs) could be deployed, based on the intended coverage and operational altitude requirements. NTN nodes have the potential to support both wireless access and backhauling. While the onboard base station provides wireless access for the end users, the backhauling link connects the airborne/space-borne base station to the core network. With its high data transmission capability comparable to fiber optics and its ability to operate in the interference-free optical spectrum, free space optical (FSO) communication is ideally suited to backhauling requirements in NTNs. In this paper, we present a comprehensive tutorial on airborne FSO backhauling. We first delve into the fundamentals of FSO signal transmission and discuss aspects such as geometrical loss, atmospheric attenuation, turbulence-induced fading, and pointing errors, all of which are critical for determining received signal levels and related link budget calculations. Then, we discuss the requirements of airborne backhaul system architectures, based on use cases. While single-layer backhaul systems are sufficient for providing coverage in rural areas, multi-layer designs are typically required to establish connectivity in urban areas, where line of sight (LoS) links are harder to maintain. We review physical layer design principles for FSO-based airborne links, discussing both intensity modulation/direct detection (IM/DD) and coherent modulation/coherent demodulation (CM/CD). Another critical design criteria for airborne backhauling is self-sustainability, which is further discussed in our paper. We conclude the paper by discussing current challenges and future research directions. In this context, we discuss reconfigurable intelligent surfaces (RIS) and spatial division multiplexing (SDM), for improved performance and an extended transmission range. We emphasize the importance of advanced handover techniques and scalability issues for practical implementation. We also highlight the growing role of artificial intelligence/machine learning (AI/ML) and their potential applications in the design and optimization of future FSO-based NTNs.
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YILANKIRKAN, Melike y Mehmet BİLİM. "RIS destekli iki atlamalı DF kablosuz haberleşme sistemlerinin α-λ-η-μ/Rayleigh sönümlenmesi durumunda performans analizi". Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi, 25 de abril de 2023. http://dx.doi.org/10.28948/ngumuh.1268618.
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Bu çalışmada, yeniden uyarlanabilir akıllı yüzey (reconfigurable intelligence surface, RIS) destekli sistemlerin α-λ-η-μ/Rayleigh sönümlenmesi altında servis-dışı kalma olasılığı (outage probability, OP) ve hata olasılığı (error probability, Pe) analizleri sunulmuştur. Ele alınan sistemde bir adet RIS’a sahip röle düğümü, bir adet verici ve bir adet alıcı bulunmaktadır. Burada verici ile RIS düğümü arasındaki kanal ortamının α-λ-η-μ sönümlenmeli olduğu kabul edilirken, RIS düğümü ile hedef arasındaki kanalın ise Rayleigh sönümlenmesine sahip olduğu varsayılmıştır. İlgili sönümlü kanallara ait olasılık yoğunluk fonksiyonlarından yararlanarak sisteme ait birikimli dağılım fonksiyonu tabanlı analizler ve türetimler gerçekleştirilmiştir. Yapılan analizler sonucunda elde edilen OP ve Pe ifadelerinin doğruluğu çeşitli senaryolarla gösterilmiş ve tam nümerik simülasyonlarla kıyaslanarak verilmiştir.
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Singh, Ashish K., Ajay K. Maurya, Ravi Prakash, Prabhat Thakur y Brij Bihari Tiwari. "Reconfigurable intelligent surface with 6G for industrial revolution: Potential applications and research challenges". Paladyn, Journal of Behavioral Robotics 14, n.º 1 (1 de enero de 2023). http://dx.doi.org/10.1515/pjbr-2022-0114.
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Abstract With proper tuning in the phase shift of reconfigurable intelligent surfaces (RISs) or intelligent reflecting surfaces (IRSs), which consist of huge number of passive reflecting elements, are the most promising and transforming technology to reconfigure the wireless propagation ecosystems to improve the “spectral-and energy-efficiency” for the future generation wireless communication system. This article presents a systematic review of RIS/IRS technology and conceptualizes the prospective requirement, operations, and application. Further, we have presented its capability for execution in a forthcoming smart industrial ecosystem to assist the development of Industry 5.0 with a series of emerging applications. Finally, we discuss the potential, open research challenges, and prospects of RIS technology in the emerging intelligent manufacturing industry to encourage future research in this area.
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Min, Kyungsik y Minchae Jung. "A power method based user selection for reconfigurable intelligent surface (RIS) assisted multiuser massive MISO systems". ICT Express, agosto de 2022. http://dx.doi.org/10.1016/j.icte.2022.08.002.
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Zhou, Xiaoping, Xinyue Chen, Le Tong y Yang Wang. "Attention-deep reinforcement learning jointly beamforming based on tensor decomposition for RIS-assisted V2X mmWave massive MIMO system". Complex & Intelligent Systems, 17 de julio de 2023. http://dx.doi.org/10.1007/s40747-023-01148-7.
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AbstractTo achieve a green and sustainable wireless communication network, the reconfigurable intelligent surface (RIS) technology has emerged as an emerging technology. The RIS-assisted mmWave massive MIMO vehicle-to-everything (V2X) communications can support enhanced V2X applications for connected and automated vehicles. The design of RIS-assisted mmWave V2X communications is though not exempt of challenges as a result of fast time-varying propagation and highly dynamic vehicular networks and topologies. To address some of these challenges, we propose an attention-deep reinforcement learning jointly beamforming based on tensor decomposition for RIS-assisted mmWave massive MIMO system to improving the safety and traffic efficiency of cooperative automated driving. The received signal of the vehicle is decomposed into four-dimensional tensors and study the channel, frequency and time attention (CFTA) algorithm using the low order tensor characteristics of mmWave channels. This algorithm can extract the frequency and time characteristics of the channel, and obtain the millimeter wave characteristic channel between the corresponding base station (BS) and the vehicles. The problem of jointly optimization of beamforming matrix at the BS and the phase shift matrix on the RIS is constructed and solved using deep reinforcement learning (DRL). Unlike traditional alternating optimization methods, the integration of DRL techniques into the optimal design of the system enables the observation of immediate rewards, learning from the environment and improving it to obtain optimal solutions to high-dimensional jointly beamforming optimization problems ultimately. The simulation results show that the proposed algorithm has meaningful performance compared with other methods.