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物理層におけるセキュリティ技術の一つとして，空間選択性変調方式(SSM: Spatially selective Modulation)が提案されている．この方式では，チャネルの場所依存性を活用し適切に送信位相の設定を行うことで，所定位置に存在する正規受信局でのみ，所望の変調信号を受信することができる．本稿では，実際の室内環境における伝搬特性を，決定論的チャネルモデルであるレイトレーシングにより求める．解析により得られた特性から，計算機上でSSMを構築することで，室内環境における秘密伝送性能の評価を行い，想定環境下でのSSMの有効性を検証する．, As a physical layer security technique, we have proposed spatially selective modulation (SSM). In the method, properly controlling the phase of the transmitted signals allows only at the location of the legitimate receiver to receive the desired modulated signal. In this paper, the propagation characteristics in an indoor environment are calculated by the ray-tracing by which the performance of SSM for spatial geometry and the distribution of the transmitter and the receiver can be evaluated. Based on the characteristics obtained from the analysis, the secret transmission performance was evaluated, and the effectiveness of SSM was verified in the assumed environment.

本論文では，移動通信環境における偏波特性を議論する．偏波特性は，XPDや偏波方向などによって定量化される．商用セルラ通信の電波を受信することにより，実環境におけるこれらの特性を明らかにした．さらに，レイトレーシングに基づく解析を行って測定結果と比較することにより，偏波特性の物理的メカニズムを確認した．, In this paper, we discuss polarization characteristics in a cellular communication environment. The polarization characteristics are quantified by the cross-polarization discrimination (XPD) and the polarization direction. These characteristics in an actual environment are clarified by receiving radio waves of a commercial cellular system. Furthermore, the physical mechanism of the polarization characteristics is discussed by comparing the measured results with those obtained through ray-tracing based analysis.

3種のアンテナ設置位置にて偏波特性を測定した．この測定により，XPD特性の車載受信アンテナの設置状況への依存性を明らかにした．また，2つの偏波を理想的に受信して利用できると仮定した利得を評価した．これは，最大比合成のダイバーシチ利得に相当する．そのため，実測データを用いて，空間ダイバーシチと偏波ダイバーシチの利得を評価した．これらを踏まえて，アンテナ設置状況に着目した水平偏波の有効性について考察する．, We carried out measurements of the received power at three different antenna positions. By the measurement, we clarified the dependency of the XPD characteristics on the installation situation of a receiving antenna in a vehicle. We also evaluate the gain where the dual polarizations are ideally received and utilized. It is equivalent to the diversity gain of the maximal ratio combing. Therefore, using the measured data, we evaluated the gain of the space diversity and the polarization diversity. Based on these considerations, we discuss the effectiveness of the horizontal polarization focusing on the antenna installation situation.

In this paper, we propose a learning program for “Energy Conversion” in “Technology and Home Economics (Technology)” at Junior high school. As an important subject, this program features a power flow between radio transmitter and radio receiver in Wireless LAN (WLAN) system, i.e. the conversion from electric power to radio wave, radio wave propagation in the space considered, and the conversion from radio wave to electric power. Students study all of the energy conversions within limited range of time, by using computer simulation tools for electromagnetic wave analyses (ray tracing analysis tool, FD-TD analysis tool, and so forth) for getting beautiful color image of electric field distribution in their school WLAN environment. By reading the image obtained, the students can easily understand whether or not they are in good positions for reception of the radio wave. This learning procedure is based on an application of the computer simulation technologies, so this can also be applicable to a program (algorithm and programing education) for “Information Study by Scientific Approach” in “Information” at High School. In the program, next, to validate the simulation results and detect insensitive zones of their school WLAN, actual electric field distribution (signal strength) in the school is simply measured by using ICT device as tablet PC, in which the FREE app with simplified field strength measurement function is installed. At the end of the program, a collaborative learning practice is carried out for the purpose to discuss a common problem among the students and evaluate it quantitatively. The collaborative group working may also be extended to a subject for “the Period for Integrated Studies”.

Car crushes at intersections of residential area are one of the serious problems. Therefore, the inter-vehicle communication system using 700MHz band to prevent car crush at an intersection has been proposed. It is important to know propagation characteristics at intersections. In this paper, propagation analyses of 700MHz band at an intersection of residential area consisting of concrete block walls are studied using the FDTD method. Propagation characteristics for various locations of wave source and wall structures were investigated. These characteristics considering uniform concrete and concrete block walls are compared. The power azimuth delay profiles were obtained by using the direction of arrival estimation method.

近年,交差点における自動車衝突事故防止のため,車車間通信を用いた衝突防止システムの研究が進められている.特に家屋塀で囲まれた道幅の狭い住宅地交差点では,その効果が期待されている.現在,車車間通信用の周波数帯として720MHz帯及び5.8GHz帯の利用が検討されている.本研究では軽量コンクリート家屋塀で囲まれた住宅地交差点における720MHz帯及び5.8GHz帯での電波伝搬特性解析を行った.種々の塀厚み及び送信側自動車位置に対する伝搬損失特性を明らかにした.また,電波の伝搬メカニズムを明らかにするため電力遅延プロファイル特性解析を行った.尚,電磁界解析手法としてFDTD法を用いた. Recently, inter-vehicle communication system to prevent car crush at an intersection has been proposed. In the system, the use of 720MHz and 5.8GHz bands have been considered. In Japan, there are many intersections surrounded by light-weight concrete walls at residential area, which have poor visibility. It is important to know the propagation characteristics at these intersections in each frequency band. In this paper, the propagation analyses of 720MHz and 5.8GHz bands at an intersection in residential area are carried out using the FDTD method. The propagation characteristics for both various locations of wave source and wall thickness were investigated. The azimuthal power delay profiles were obtained by using the direction of arrival estimation method.

近年,交差点における自動車衝突事故防止のために700MHz帯車車間通信を用いた衝突防止技術に関する研究が行われている.衝突事故の中でも特に出会い頭衝突事故が問題となっている.出会い頭衝突事故は市街地交差点,住宅地交差点等,様々な環境において発生しており,交差点における電波伝搬特性の把握は重要である.本研究では住宅地交差点における700MHz帯電波伝搬特性解析を行った.具体的には,送信側自動車位置及び家屋塀の違いによる伝搬特性比較,電力角度遅延プロファイル解析を行った.尚,電磁界解析手法としてはFDTD法を用いた., Recently, inter-vehicle communication system at an intersection to prevent car crush using 700MHz band has been proposed. Especially, car crush at an intersection is a serious problem. Car crush is occurred at various intersections. It is important to know propagation characteristics of each intersection. In this paper, propagation analyses of 700MHz band at an intersection of residential area are studied using the FDTD method. Propagation characteristics for various locations of wave source and wall structures were investigated. The power azimuth delay profiles were obtained by using the direction of arrival estimation method.