[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

The adoption of a reconfigurable intelligent surface (RIS) for downlink multi-user communication from a multi-antenna base station is investigated in this paper. We develop energy-efficient designs for both the transmit power allocation and the phase shifts of the surface reflecting elements subject to individual link budget guarantees for the mobile users. This leads to non-convex design optimization problems for which to tackle we propose two computationally affordable approaches, capitalizing on alternating maximization, gradient descent search, and sequential fractional programming. Specifically, one algorithm employs gradient descent for obtaining the RIS phase coefficients, and fractional programming for optimal transmit power allocation. Instead, the second algorithm employs sequential fractional programming for the optimization of the RIS phase shifts. In addition, a realistic power consumption model for RIS-based systems is presented, and the performance of the proposed methods is analyzed in a realistic outdoor environment. In particular, our results show that the proposed RIS-based resource allocation methods are able to provide up to 300% higher energy efficiency in comparison with the use of regular multi-antenna amplify-and-forward relaying.

Reconfigurable Intelligent Surfaces for Energy Efficiency in Wireless Communication

IRS is a new and revolutionizing technology that is able to significantly improve the performance of wireless communication networks, by smartly reconfiguring the wireless propagation environment with the use of massive low-cost passive reflecting elements integrated on a planar surface. Specifically, different elements of an IRS can independently reflect the incident signal by controlling its amplitude and/or phase and thereby collaboratively achieve fine-grained 3D passive beamforming for directional signal enhancement or nulling. In this article, we first provide an overview of the IRS technology, including its main applications in wireless communication, competitive advantages over existing technologies, hardware architecture as well as the corresponding new signal model. We then address the key challenges in designing and implementing the new IRS-aided hybrid (with both active and passive components) wireless network, as compared to the traditional network comprising active components only. Finally, numerical results are provided to show the great performance enhancement with the use of IRS in typical wireless networks.

Towards Smart and Reconfigurable Environment: Intelligent Reflecting Surface Aided Wireless Network

Intelligent reflecting surface (IRS) is an enabling technology to engineer the radio signal propagation in wireless networks. By smartly tuning the signal reflection via a large number of low-cost passive reflecting elements, IRS is capable of dynamically altering wireless channels to enhance the communication performance. It is thus expected that the new IRS-aided hybrid wireless network comprising both active and passive components will be highly promising to achieve a sustainable capacity growth cost-effectively in the future. Despite its great potential, IRS faces new challenges to be efficiently integrated into wireless networks, such as reflection optimization, channel estimation, and deployment from communication design perspectives. In this paper, we provide a tutorial overview of IRS-aided wireless communications to address the above issues, and elaborate its reflection and channel models, hardware architecture and practical constraints, as well as various appealing applications in wireless networks. Moreover, we highlight important directions worthy of further investigation in future work.

Intelligent Reflecting Surface-Aided Wireless Communications: A Tutorial

Metamaterial or Metastructural Thin Films for EM Wave Control

Method of moments (MoM) is an essential tool to model electromagnetic wave interactions with three-dimensional targets. Numerical integration is a key technique in MoM. Due to the singular nature of Green's function, MoM requires special treatment in the calculation of singular integration, which is usually timeconsuming. In this study, the barycentric subdivision method is investigated to compute numerical integration in three-dimensional surface integral equations. This method allows a uniform treatment for both singular and non-singular integrals. Numerical examples show that this method could reach the same level of accuracy as the singularity extraction method for RWG basis functions, and the computational time of setting up the matrix can be reduced by half.

Application of Barycentric Subdivision Method for Singularity Integration in Method of Moments

In this work, we study the application of the supervised descent method to two-dimensional electromagnetic inverse problems. The inversion process contains two stages: offline training and online prediction. In the offline stage, the average descent directions of cost functions are learned from a set of training data; and in the online stage, model reconstruction is achieved through iterative minimization based on learned descent directions. This scheme offers a new perspective to incorporate prior information into inversion, and reduce the computational complexity in the online inversion. Numerical examples validate the accuracy and efficiency of this method.

Imaging of Two Dimensional Scatterers using Descent Learning Technique

Intelligent metasurfaces to create smart electromagnetic environments have attracted a surge of interest. The multiscale property of metasurfaces results in a huge computational challenge, further hindering their engineering development. Our previous paper has developed a fast FDTD algorithm for patch-like metasurfaces analysis using the Surface Susceptibility Model (SSM). This study extends that to efficient fishnet-like metasurfaces analysis using the Surface Porosity Model (SPM), a useful complement to SSM. We introduce the SPM to FDTD, replacing brute force simulations, to accelerate fishnet-like metasurfaces analysis. At last, we conduct a series of numerical experiments, demonstrating that the proposed FDTD-SPM algorithm greatly reduces the number of computational meshing lattices and the consumed time.

Characteristic Model and Efficient FDTD-SPM Algorithm for Fishnet Metasurfaces Analysis

A method for calculating the Casimir force between large, complex 3D objects is presented. Difficulties have previously arisen in broadband multiscale calculation using CEM methods. To expand the range of problems that can be calculated, we use an integral equation, domain decomposition method (DDM) and argument principle to derive the Casimir force formula. The broadband integral equation DDM, which is the augmented equivalence principle algorithm (A-EPA), allows for an efficient broadband solution of large, complex objects. A-EPA subdivides a complex problem into separate smaller subproblems that are later recombined into a reduced matrix. This yields a reduced number of unknowns for complex structures making them feasible with modest computer resources. We demonstrate the advantages of the A-EPA by simulating large, finite, 3D, unaligned corrugated plates, which have previously only been modeled approximately as infinite plates using 2D techniques.

https://www.jpier.org/PIER/pier149/19.14102112.pdf

Maokun Li

Papers

Metamaterial or Metastructural Thin Films for EM Wave Control

Application of Barycentric Subdivision Method for Singularity Integration in Method of Moments

Imaging of Two Dimensional Scatterers using Descent Learning Technique

Characteristic Model and Efficient FDTD-SPM Algorithm for Fishnet Metasurfaces Analysis

Casimir Force for Complex Objects Using Domain Decomposition Techniques