C-RECS （Creative Repository of Electro-Communications)
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Composition Engineering and Interface Optimization of Tin-based Perovskite Solar cells
Get PDF電気通信大学博士（工学）2022doctoral thesi
Spectrum Sharing for LPWA Under Intra-system and Inter-system Interference Constraints
Get PDF電気通信大学修士2022近年，省電力長距離通信を可能とするLPWA (Low Power Wide Area)端末数が急増しており，周波数資源の枯渇が懸念されている．一方，利用用途に応じて通信プロトコルの異なるLPWAシステムが数多く開発されており，これらは免許不要な同一のSub-GHz帯(日本では920[MHz]帯)を利用している．加えて，LPWA端末の多くは観測情報をゲートウェイ (GW:Gateway)に上り通信する際，周波数資源の混雑度を鑑みずに送信時刻や周波数チャネル(以下，チャネルと呼称)を無作為に決定する．故に，任意システムのGWには同一帯域で重畳された自他システムの信号が広範囲から到来(以下，システム内外干渉と呼称)し，自システムの復調性能が著しく劣化する恐れがある．
そこで，本研究では，システム内外干渉制約下における通信品質の担保を目的として，LPWA向け周波数共用手法を検討する．まず1つ目に，スペクトラムデータベースに基づくチャネル割当手法を提案する．本手法では，GWでシステム外干渉電力をチャネル毎に一定時間観測後，経験累積分布関数を事前推定することでチャネル利用状況を可視化する．これより，各自端末の信号が許容できない当該電力の時間占有率をチャネル毎に推定できる．その後，立式したシステム内干渉確率式も用いて，両確率の論理和が小さくなるチャネル組を組み合わせ最適化問題として算出後，各自端末に割り振る．結果より，チャネルをランダム選択する従来手法と比較してパケットロス率が低減することを示す．
一方，空きチャネルの枯渇に伴う多干渉状況下では，チャネル割当による干渉抑制に限界が生じる．そこで2つ目に，LPWAマルチシステム間逐次干渉除去(SIC: Successive Interference Cancellation)を提案する．本手法では，各システムの変復調器を搭載したGWが受信した重畳信号を一時的に蓄積し，復調可能なシステムの信号から順に(i)復調，(ii) 再変調，(iii)蓄積信号からの減算除去，を実行する．結果より，複数システムの重畳信号を一括復調でき，システム全体でパケット誤り率が低減することを示す．
一方，重畳された信号間に十分な電力差がない場合，相互干渉の影響を無視できず復調自体が困難となる．そこで3つ目に，複数GW間連携に基づくSICを提案する．本手法では，復調成功したGWが復調失敗したGWに取得したバイナリや受信波形を共有し，後者GWでは適応フィルタリングや高速フーリエ変換を活用して信号除去を試みる．結果より，単一GWによるSIC手法と比較しパケット誤り率が低減することを示す．thesi
Implementation and Evaluation of a Tool to Support the Development of a Domain-Specific Modeling Environment for Enumeration Based on View Patterns
Get PDF電気通信大学2023thesi
Multi-Objective Design for EMC Solutions by Using Preference Set-Based Design Method
Get PDF電気通信大学博士（工学）2023doctoral thesi
Polygonal obstacle avoidance method for swarm robots via fluid dynamics
Get PDFSwarm robots in obstacle environments perform search tasks efficiently while avoiding obstacles. Obstacle avoidance methods are classified by the way obstacles are represented. Potential functions are typical for circular obstacles, while collision cones and polygonal regions are used for non-circular obstacles. The shape of the obstacle this paper considers is angular. When swarm robots try to avoid angular obstacles with potential functions, they require information such as the relative angle between the robot and the obstacle and the size of the obstacle. This paper focuses on the shape parameters of angular obstacles and proposes an easier way to avoid angular obstacles in column formation. The key idea is fluid dynamics. The proposed method is based on a Polygon-Wall expression of MPS (Moving Particle Semi-implicit) method, a fluid dynamics method. The Polygon-Wall expression allows robots to measure the distance from the obstacle wall and avoid the obstacle without using the relative angles and the obstacle sizes. Usual MPS methods have the challenge of requiring centralized computation, while typical swarm robots are based on distributed computation. Therefore, this paper addresses this challenge by introducing potential functions into MPS method. The contribution of this paper is to propose a distributed obstacle avoidance method for angular obstacles with a small number of parameter designs for swarm robots. The results of numerical experiments reflecting these ideas show the effectiveness of the proposed method.journal articl
Theoretical prediction of two-dimensional II-V compounds
Get PDFGraphene has attracted significant attention as a pioneer of two-dimensional zero gap semiconductors, but the development of new two-dimensional materials with a finite band gap has been actively pursued. In this study, the structural stability of double bilayers (DBs) of group II-V compounds (II: Be, Zn, and Cd; V: P, As, and Sb) has been systematically investigated using first-principles calculations based on density functional theory. The thermodynamic calculations have confirmed that BeP, BeAs, ZnP, and ZnAs can be produced through exothermic reactions from their constituent bulk systems. It has also been confirmed that all the compounds have phonon dynamical stabilities. Only CdP and CdAs have been found to have an AB-stacked DB structure with threefold symmetry, while the other compounds have AB′-stacked DB structure with broken symmetry. The difference in atomic radii between group II and group V results in the so-called size effect, which determines the stacking pattern. The structural stability of II-V DB thin films is explained by analogy with the surface structural stability of compound semiconductors: The change in the atomic arrangement of the DB structure alters the electronegativity of the surface orbitals of the II-V thin film, which does not result in any unsaturated bonds, i.e., no metallic bands across the Fermi level appear. The various DB II-V compounds proposed in this study will join the ranks of atomic-level 2D semiconductor materials.journal articl
Chiral metamaterial showing one-sided circular polarized light transmission and another-sided circular polarized light absorption in optical region
Get PDF電気通信大学2022thesi
Spherical structured type deep learning based algorithms for 3D Direction-of-arrival estimation
Get PDF電気通信大学博士（工学）2022doctoral thesi
