Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE  

In this article, we investigate the performance of the newly designed 4 × 4 optical wireless multiple-input-multiple-output (MIMO-OWC) system based on a linearly-shaped arrangement of transmitters and receivers, to achieve long-distance and high data rate transmission. To highlight the importance of selecting an appropriate arrangement for the optical elements, we carried on a comparative study, considering both the conventional square and the proposed horizontal linear constellation of optical modems. The performance of the bit error rate (BER) is experimentally evaluated at distances up to 65 m, using two important metrics inherent to the MIMO transmission channel matrix, i.e., the Frobenius norm and the condition number. The results show that the channel matrix shape characterized by the condition number dominates the BER if the Frobenius norm is smaller than 1. Furthermore, the proposed MIMO-OWC system employing a linearly-shaped arrangement of transmitters and receivers, shows to be more immune to the calibration error rather than the conventional square constellation optical modems. Moreover, the transmission of 100 Mbps data-rate and a BER lower than 10 -4 could be successfully achieved at a 65 m communication range.

DOI： 10.1109/JPHOT.2021.3050499

Web of Science

Language：Japanese  

We consider a system using an unmanned aerial vehicle (UAV) equipped with a self-owned wireless transceiver for inspection of power transmission lines, in which control information for the flight is transmitted by a base station (BS) placed on a power plant or substation. In order to realize reliable communication between the BS and UAV, we consider relay stations on the power transmission towers or UAVs and propose a network configuration method using geographic information system (GIS).

DOI： 10.14923/transcomj.2022gwl0001

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

<p>This paper considers an emergency communication system controlling multiple unmanned aerial vehicles (UAVs) in the sky over a large-scale disaster-affected area. This system is based on delay-tolerant networking, and information from ground users is relayed by the UAVs through wireless transmission and the movement of UAVs in a store-and-forward manner. Each UAV moves autonomously according to a predetermined flight method, which uses the positions of other UAVs through communication. In this paper, we propose a new method for UAV flight considering the non-uniformity of user distributions. The method is based on the Voronoi cell using the predicted locations of other UAVs. We evaluate the performance of the proposed method through computer simulations with a non-uniform user distribution generated by a general cluster point process. The simulation results demonstrate the effectiveness of the proposed method.</p>

DOI： 10.1587/transcom.2022EBP3017

Web of Science

Scopus

CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper investigates underwater optical wireless communication (UOWC) systems. We introduce a system model including the main factors impairing the optical signal intensity, i.e., light absorption, scattering, together with water turbulence, which have not been thoroughly investigated in other UOWC studies. The optimal receiver design is based on maximum a posteriori (MAP) estimation while considering not only thermal noise but also shot noise. In addition to the MAP-based receiver, a simplified configuration of the receiver is also examined. The symbol error rate (SER) is analytically calculated for 3 different modulation schemes, i.e., pulse-position modulation (PPM), pulse- amplitude modulation (PAM), and pulse-amplitude-and-position modulation (PAPM). The obtained results show that a SER of 10−3 is achieved at a distance of 20 m for all the modulation schemes. The superiority of PPM over PAM and PAPM in terms of the SER is also shown. We demonstrate that the simplified receiver obtains almost the same SER performance as the MAP receiver.

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Lead author   Language：English   Publishing type：Research paper (conference, symposium, etc.)  

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： doi.org/10.1109/CCNC49033.2022.9700578

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： doi.org/10.1109/CCNC49033.2022.9700615

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

A wireless relay network using unmanned aerial vehicles (UAVs) to deliver messages, such as damage reports and safety confirmation, in wide areas affected by large-scale disasters is proposed. In this system, UAVs move autonomously following a predetermined flight method and deliver a message in a delay-tolerant manner by transmitting it hop by hop to other UAVs within the communication range. In this study, we propose a UAV flight method for non-uniform-user-distribution environments. The proposed method is based on coverage control and utilizes the Voronoi cell with a density function. We considered cases where the user distribution was available in advance and also where it was not. Simulation results showed that the proposed method could improve effectiveness in terms of average message delivery delay, especially when the user distribution was considerably non-uniform.

DOI： 10.1109/CCNC49033.2022.9700615

Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

This paper investigates underwater optical wireless communication (UOWC) systems. We introduce a system model including the main factors impairing the optical signal intensity, i.e., light absorption, scattering, together with water turbulence, which have not been thoroughly investigated in other UOWC studies. The optimal receiver design is based on maximum a posteriori (MAP) estimation while considering not only thermal noise but also shot noise. In addition to the MAP-based receiver, a simplified configuration of the receiver is also examined. The symbol error rate (SER) is analytically calculated for 3 different modulation schemes, i.e., pulse-position modulation (PPM), pulse-amplitude modulation (PAM), and pulse-amplitude-and-position modulation (PAPM). The obtained results show that a SER of 10−3 is achieved at a distance of 20 m for all the modulation schemes. The superiority of PPM over PAM and PAPM in terms of the SER is also shown. We demonstrate that the simplified receiver obtains almost the same SER performance as the MAP receiver.

DOI： 10.1109/VTC2022-Spring54318.2022.9860647

Web of Science

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Lead author   Language：English   Publishing type：Research paper (conference, symposium, etc.)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE Access  

In this article, we consider a wireless relay network using drones as a temporary communication system in a large-scale disaster area. We assume that insufficient drones are present to maintain a wireless connection, and we apply a delay-tolerant network to this system. In this system, information is transmitted by wireless transmission between drones and their movement, and as the delivery delay mainly depends on the latter, the movement pattern of the drones, which we call a flight model, is of great importance. We utilize coverage control to handle the deployment of multiple drones and propose a novel flight model of drones using Voronoi tessellation. In the proposed model, we calculate the Voronoi cell using the predicted positions of some drones, and we associate weights with those positions to utilize the weighted Voronoi cell. Through simulation, we evaluate the relationship among the weight decay method, distribution and movement of drones, and delay characteristics. Simulation results demonstrate that the proposed flight model achieves better delay characteristics by setting appropriate weights compared to a previous flight model.

DOI： 10.1109/ACCESS.2021.3051913

Web of Science

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

In a large-scale indoor environment such as an industrial one, a multiple-input-multiple-output optical wireless communication (MIMO-OWC) system represents a flexible and easy-to-deploy solution to achieve point-to-point long-distance and high-speed data transmission. The majority of imaging MIMO-OWC systems have mainly targeted high data rate communication over short distances, not exceeding 10 m. In this work, on the contrary, we focus on longer-distance links providing high- speed transmission data rate. For this purpose, we propose an imaging MIMO-OWC system that features an improved optical modulator array with a one-dimensional element arrangement, and a new imaging receiver using long focal length lenses placed in front of the receiving photo-detector array. The performance of the proposed system is then experimentally evaluated. The obtained results show that the measured MIMO channel matrices have sparse patterns, which means that the elements not corresponding to the emitted beams are nearly zero. We successfully demonstrate the transmission at a high data rate of 100 Mbps over a long distance of 50 m. This result surpasses the achieved distance corresponding to the conventional MIMO-OWC system using an independent optical system for each light-receiving element. Consequently, the experimental results confirm that our proposed system has the potential for higher speed with longer distances.

DOI： 10.1109/GLOBECOM42002.2020.9322574

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：電子情報通信学会  

広域災害被災地における臨時通信システムとして，ドローンを用いた無線リレーネットワークを考える．ドローンの飛行モデルである反発飛行について，どの程度離れた位置を目的地とするかを決める反発率を導入し，反発率を変化させた場合の遅延特性を評価する．

DOI： 10.14923/transcomj.2020JBL4004

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

IEEE802.11 には変調方式，符号化率の組み合わせをインデックス化したModulation and Coding Scheme (MCS) により，多段階で送信レートが規定されている．通信環境に対して適切な送信レートを選択することがスルー プット最大化のために必要である．しかし，実際の通信環境はフェージングの影響や他の通信による競合・隠れ端末 問題など，複雑な要因が絡み合っており，従来手法では適切な送信レートを選択することは難しい．先行研究では， 機械学習を適用することで複雑な通信環境に対応した送信レート選択手法を検討した．しかし，1 対1 の通信実験の みで，従来手法との比較が十分になされていない．本研究では，LightGBM を適用した送信レート選択と従来手法を， 競合する通信の存在下にて比較検証を行うことで提案手法の優位性を示す．

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

広域災害被災地における臨時通信システムとしてドローンを用いた無線リレーネットワークを考える．マルチエージェントの配置を扱う被覆制御に注目し，ボロノイ分割を利用した新たなドローンの飛行モデルを提案する．提案飛行モデルでは通常の被覆制御の拡張として，通信範囲外となったドローンの位置を通信時の目的地から予測してボロノイ領域を計算する．また，通信外のドローンの予測位置に重みを設定することで，通常のボロノイ領域の代わりに重み付きボロノイ領域を用いる．シミュレーション結果から，提案飛行モデルは予測位置の重みを適切に設定することでネットワークの遅延特性を改善できることを示す．

Event date： 2020.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

IEEE 802.11無線LANを用いた分散ネットワークでは，各ノードは，変調方式と符号化率の組み合わせにより定められた，複数の送信レートを利用することができる．スループットを最大化するためには，通信環境の変化に合わせた適切な送信レートを選択する必要がある．従来のアルゴリズムでは，Received Signal Strength Indication(RSSI)や通信成功率，確認応答フレームを参照することでスループットの最大化を目指している．しかし，RSSIとスループットが1対1対応しないことや，隠れ端末問題による不必要な送信レート制御，さらには，複数のアンテナが存在する場合，RSSIも複数取得できることなど，様々な要因により実環境におけるスループットの最大化は実現することが難しい．そこで本研究では，実験により収集されたRSSI等の通信品質情報やスループットをデータセットとした教師あり学習を行い，通信品質情報を入力とし，送信レートを出力とするモデルを作成する．提案手法としてGradient boosting regressorを使用したレート選択モデルを作成し，従来手法とスループットの比較実験を行った結果．一部従来手法を上回る結果を達成出来たことを報告する．

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

広域災害被災地における臨時通信システムとして，ドローンが移動しながら情報を中継するリレーネットワークを考える．本研究では，情報が送信元から宛先に伝達するまでにかかる遅延時間を短縮することを目指す．その実現のため，マルチエージェントシステムの被覆制御に注目し，それを利用した新たな飛行モデルとして，被覆飛行，目的地維持型被覆飛行を提案，及びシミュレーションにより性能を評価する．シミュレーションから得られた遅延時間とドローンの飛行軌跡を考察し，ドローンの台数が多い場合に目的地維持型被覆飛行が既存の飛行モデルより低遅延なリレーネットワークを構築できることを示す．

Event date： 2020.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

高速通信用の4×4 光無線MIMO(Multiple-Input Multiple-Output) 通信システムの送受信光アレイにおいて，線形の素子配置の適用を考える．さらに実験により従来の正方形光アレイとの通信性能の比較・検討を行った．具体的には，距離65m までの範囲通信を行い，伝搬路行列のフロベニウスノルムおよび条件数とビット誤り率との関係を評価した．その結果，BER は，フロベニウスノルムが１以下となるような領域では，伝搬路行列の条件数がビット誤り率を支配することを示した．さらに，従来の正方形アレイと比べ，線形アレイを用いる方が，通信性能に与える設置誤差の影響が小さいことなどを明らかにした．また，通信距離速度の点では，65m・100Mpbs において10^−4以下の誤り率を実現した．

-I was in charge of the following practice Lab: 「C2A8 Microcomputer」.
In this Lab, the students could learn about the following concepts, i) monitor signals over the bus during the microprocessor's operation, ii) understand the signal flow and timings, and iii) configure a simple output interface circuit based on this. Therefore, thanks to this Lab, they were able to build a clearer fundamental understanding of the microcomputer hardware.
-After the practice Lab, the students were required to submit a report summarizing their findings and addressing the corresponding technical points.