Journal of Information and Intelligence最新文献

Reconfigurable intelligent surfaces (RISs) are lately being attractive for their great potential in future sixth generation wireless communications (6G), which is attributed to their affordable energy consumption and easy integration. However, the large numbers of low-cost reflecting elements comprising RISs impose challenges for channel acquisition in various RIS-based wireless applications, such as RIS-enhanced orthogonal frequency-division multiplexing and multi-user multiple-input multiple-output systems. In this article, we first overview the state-of-the-art RIS hardware architectures designed to assist channel estimation for RIS-empowered wireless communication systems. We also overview existing channel estimation approaches, which are categorized into model-based and model-free techniques, and discuss their advantages and limitations depending on the RIS deployment. Design challenges with RIS-empowered systems in terms of hardware and other parameter limitations are presented, together with future research directions for channel estimation in RIS-based wireless systems, such as RISs with extremely large numbers of elements, multi-hop communications with RISs, and frequency division duplexing for high mobility systems.

In this paper, we investigate a reconfigurable intelligent surface (RIS) assisted downlink orthogonal frequency division multiplexing (OFDM) transmission system. Taking into account hardware constraint, the RIS is considered to be organized into several blocks, and each block of RIS share the same phase shift, which has only 1-bit resolution. With multiple antennas at the base station (BS) serving multiple single-antenna users, we try to design the BS precoder and the RIS reflection phase shifts to maximize the minimum user spectral efficiency, so as to ensure fairness. A deep reinforcement learning (DRL) based algorithm is proposed, in which maximum ratio transmission (MRT) precoding is utilized at the BS and the dueling deep Q-network (DQN) framework is utilized for RIS phase shift optimization. Simulation results demonstrate that the proposed DRL-based algorithm can achieve almost optimal performance, while has much less computation consumption.

Reconfigurable intelligent surfaces (RISs) have aroused extensive attentions from academic and wireless communication communities due to their abilities to customize the electromagnetic (EM) characteristics of the propagation channels flexibly and rapidly. Recent advances in theoretical innovations and prototype systems have demonstrated the advantages of RISs in terms of low cost, low power consumption, and easy deployment. Meanwhile, the optically transparent RISs are demanded in some application scenarios. In this paper, we propose a 2-bit metalmesh-based RIS with high optical-transparency. By analyzing the surface current distributions on the element, we employ the metalmesh-grid patterns and metalmesh-stripe patterns on the top and ground layers respectively. The metalmesh patterns can help improve the optical transparency of RISs, while maintaining similar microwave characteristics. The RIS can reach the optical transparency of 79%, and the reflection amplitude is greater than −3.2 ​dB within the operating band. Finally, to verify the capability of the proposed RIS in wavefront controls, the far-field scattering patterns of the RIS with different coding sequences are investigated and the simulation results are in good agreement with the theoretical results.

In this paper, we proposed an active metasurface in reflection manner that can generate reconfigurable OAM vortex beams with high purity in the X-band. The metasurface has a high reflectance of 0.94 and achieves a phase coverage of 320° between 9.8 ​GHz and 11 ​GHz. Then, by encoding the phase distribution of the meta-atoms, various OAM vortex beams including ±1, ±2, ±3, and ±4 orders are generated, where the purity of all modes can be above 70%. Moreover, the metasurface can also deflect the OAM beam with a certain angle while maintaining high purity, which can be applied to reduce the influence of the alignment deviation between transmitting and receiving antennas during the communication processes. As a validation, the metasurface composed of 30 ​× ​30 meta-atoms is fabricated and measured. Both simulation and measurement results demonstrate the capability of the proposed metasurface to generate reconfigurable OAM beams with high purity, indicating the application potentials of proposed meta-devices in future OAM communications.

This paper proposes a new method to generate a two-dimensional (2D) Airy beam and Airy autofocusing beam by using the scalar holographic metasurface with amplitude-phase modulation in the microwave band. The proposed holographic metasurface comprises subwavelength patch unit cells with a period of fewer than 1/8 wavelengths, which means that it has the finer sampling for electromagnetic waves and can simultaneously achieve precise modulations for the amplitude and phase of electromagnetic waves. Firstly, the 2D-Airy beam with quasi-non-diffraction and self-bending characteristics is generated, from which the holographic metasurface is designed to realize four different 2D-Airy beams with the same focus, achieving the 2D-Airy autofocusing beam in the microwave frequency. The holographic metasurface for Airy beam generation has high efficiency and an ultra-lower profile. Meanwhile, for applying the Airy beam in wireless power transfer (WPT), the efficiency of the generated Airy beam and Airy autofocusing beam is calculated for the first time in the microwave field. The simulation results show that the efficiency of the 2D-Airy beam can reach 66% at 150 ​mm away from the metasurface, while the efficiency of the 2D-Airy autofocusing beam at the focus, which is 280 ​mm from the metasurface, can reach 35%. The theoretical, simulated, and measured results show that the proposed method and holographic metasurfaces can flexibly achieve the special characteristics of self-autofocusing and self-bending Airy beams in the microwave domain, providing an effective path for wireless power transfer (WPT) scenario with radial obstructions.

Reconfigurable intelligent surface (RIS) is emerged as a promising technique to solve the challenges faced by future wireless communication networks. Although the most commonly used electrically-controlled RISs can achieve millisecond-scale speed of dynamic switch, they have a large number of microwave circuit elements (such as PIN diodes or varactors) which will bring non-negligible insertion loss, and the complicity of the bias network to electrically addressing each element will increase with the expansion of the RIS aperture. Aiming at further reducing the fabrication cost and power consumption, herein an electromechanical RIS used for sub-6G wireless communication is proposed. The electromechanical RIS is designed with a passive metasurface and step-motor driver modules, providing simultaneous high-efficiency reflection (over 80%) and continuous reflection phase coverage of 360°. Through electromechanical control, the RIS system can realize different reflective wavefront shaping, and has been employed in the indoor sub-6G wireless environment demonstrating a maximum signal improvement of 8.3 ​dB. The proposed electromechanical RIS is particularly useful for wireless signal enhancement in static blind area, and has the obvious advantage of not requiring continuous power supply after the RIS being regulated. Therefore, it greatly reduces the overall cost and power consumption which may have potentials in indoor application scenarios for improving wireless communication performance.

With the help of a developing technology called reconfigurable intelligent surfaces (RISs), it is possible to modify the propagation environment and boost the data rates of wireless communication networks. In this article, we optimized the phases of the RIS elements and performed a fair power allocation for each subcarrier over the full bandwidth in a single-input-single-output (SISO) wideband system where the user and the access point (AP) are provided with a single antenna. The data rate or its equivalent channel power is maximized by proposing different low-complex algorithms. The strongest tap maximization (STM) and power methods are compared with the semidefinite relaxation (SDR) method in terms of computational complexity and data rate performance. Runtime and complexity analysis of the suggested methods are computed and compared to reveal the actual time consumption and the required number of operations for each method. Simulation results show that with an optimized RIS, the sum rate is 2.5 times higher than with an unconfigured surface, demonstrating the RIS's tremendous advantages even in complex configurations. The data rate performance of the SDR method is higher than the power method and less than the STM method but with higher computational complexity, more than 6 million complex operations, and 50 ​min of runtime calculations compared with the other STM and power optimization methods.

It is of great importance to control flexibly wireless links in the modern society, especially with the advent of the Internet of Things (IoT), fifth-generation communication (5G), and beyond. Recently, we have witnessed that programmable metasurface (PM) or reconfigurable intelligent surface (RIS) has become a key enabling technology for manipulating flexibly the wireless link; however, one fundamental but challenging issue is to online design the PM's control sequence in a complicated wireless environment, such as the real-world indoor environment. Here, we propose a reinforcement learning (RL) approach to online control of the PM and thus in-situ improve the quality of the underline wireless link. We designed an inexpensive one-bit PM working at around 2.442 ​GHz and developed associated RL algorithms, and demonstrated experimentally that it is capable of enhancing the quality of commodity wireless link by a factor of about 10 ​dB and beyond in multiple scenarios, even if the wireless transmitter is in the glancing angle of the PM in the real-world indoor environment. Moreover, we also prove that our RL algorithm can be extended to improve the wireless signals of receivers in dual-receiver scenario. We faithfully expect that the presented technique could hold important potentials in future wireless communication, smart homes, and many other fields.

Reconfigurable intelligent surfaces (RISs) are a promising technology for wireless communication applications, but their performance is often optimized using simplified electromagnetic reradiation models. In this study, we explore the impact on the RIS performance of more realistic assumptions, including the (possibly imperfect) quantization of the reflection coefficients, sub-wavelength inter-element spacing, near-field location, and presence of electromagnetic interference. We find that design constraints can cause an RIS to reradiate power in unwanted directions. Therefore, it is important to optimize an RIS by considering the entire reradiation pattern. Overall, our study indicates that a 2-bit digitally controllable RIS with a nearly constant reflection amplitude and RIS elements with a size and inter-element spacing between (1/8)th and (1/4)th of the signal wavelength may offer a reasonable tradeoff between performance, complexity, and cost.