In 3.0-T magnetic resonance imaging (MRI), shortened radio frequency (RF) wavelengths cause B₁ inhomogeneity. Multi (MT) has been reported as a method of solving this problem. We compared MT with single (ST) and ST body-tuned CLEAR (BTC) in terms of basic performance because we got an opportunity to use MT. A phantom was used to evaluate the uniformity of the flip angles (FAs) of images, the phantom’s diameter, and the specific electric conductivity. To evaluate contrast, volunteers performed the significant difference test, and the changes in the FA of the phantom were measured. MT and BTC were better than ST in terms of the uniformity of the images. MT had the best contrast. The results showed that the uniformity of the images and the contrast were improved using MT compared with ST because MT can be uniformly irradiated to an object using two individual RF transmitters.

抄録全体を表示

Reducing the

power of mobile phones is effective in preventing electromagnetic interference (EMI) with medical devices in hospitals. However, to our best knowledge, no study has shown power measurement results of mobile phones for which the configured-maximum--power was controlled by specific base station (BS) parameters. This letter shows power measurement results from a mobile phone for which the configured-maximum--power is experimentally controlled by indoor BSs in a hospital. Reduction in the mobile phone power and the issue of preventing EMI with medical devices are discussed based on the measurement results.

抄録全体を表示

Square-root Nyquist filtering is typically used in single-carrier (SC) transmission. By changing the filter roll-off factor, the bit-error rate (BER), peak-to-average power ratio (PAPR), and spectrum efficiency (SE) changes, resulting in a tradeoff among these performance indicators. In this paper, assuming SC with frequency-domain equalization (SC-FDE), we design a new filtering based on the minimum variance of instantaneous power (VIP) criterion in order to reduce the PAPR of the signal of SC-FDE. Performance evaluation of SC-FDE using the proposed filtering is done by computer simulation, and shows that the proposed filtering contributes lower PAPR, while there exists only a small degradation in BER performance compared to SC-FDE using square-root Nyquist filtering.

抄録全体を表示

Diffusion kurtosis imaging (DKI) is a method of analyzing restricted diffusion. Mean kurtosis (MK) is obtained from DKI. It is not known how different MRI scanners and coil systems will change MK when the same imaging parameters are used. The purpose of this study is to identify tendencies in MK when using various MRI scanners and coil systems. A total of 27 healthy volunteers were enrolled in this study. DKI was performed on the brain for each volunteer on five MRI scanner/coil system combinations using the same scan parameters. MK of 10 anatomical areas of the brain were compared, and the signal-noise ratios (SNRs) of b-2000 s/mm² images were measured in identical areas. There were no significant differences among MKs from multi

(MT) MRI systems, but MK was significantly lower on the single MRI system because of pepper artifact caused by low SNR. In conclusion, we found no significant differences in MK among MT systems, and MK was significantly lower without MT.

抄録全体を表示

目的：血流の評価は，超音波画像診断で重要な役割を果たす．カラーフローイメージング法は，臨床で幅広く使用されている方法の1つである．自己相関はエイリアシングの影響を受けるため，超音波パルスの送信間隔は可能な限り短くする必要がある．そのため，カラーフローイメージング法では特定の送受信シーケンス，すなわちパケット送信が広く使用されている．さらに，近年導入された平面波イメージング法は，時間分解能の改善に大きく貢献する．また，特異値分解（singular value decomposition: SVD）クラッタフィルタは，従来型のクラッタフィルタよりも優れていることが示されている．本研究では，パケット送信シーケンスを使用した平面波イメージング法でのSDVクラッタフィルタの実現可能性を検討した．方法：本研究では，ステアリング角を変更する前に，平面波を複数回同一方向に送信することで，平面波イメージング法でパケット送信シーケンスを実現した．1番目の方法では，集束送信ビームを使用して走査線単位で受信信号を取得する従来のカラーフローイメージング法のように，各パケットの超音波RF（radio-frequency: RF）信号にクラッタフィルタを適用した．2番目の方法では，パケットごとの送信回数は2に設定され，クラッタフィルタは，異なるパケットでの1回目または2回目の送信から取得したRF信号群に適用された．結果：ヒト頸動脈でのin vivo計測結果では，SVDフィルタを使用した2番目の方法が，従来型フィルタとして多項式回帰フィルタを使用した1番目の方法に比べて，優れていることを示した．結論：SVDクラッタフィルタは，パケット送信シーケンスを使用した平面波イメージング法に適用可能であり，パケットごとの送信回数を2回に制限することで性能が向上した．

抄録全体を表示

In this paper, we propose a multi-block frequency-domain equalization (MB-FDE) for frequency-domain space-time block coded joint /receive diversity (FD-STBC-JTRD). Noting that a STBC codeword consists of multiple coded blocks, the MB-FDE uses the multiple FDE weight matrices, each associated with each coded block. Both single-carrier (SC) transmission and orthogonal frequency-division multiplexing (OFDM) transmission are considered. For SC transmission, the MB-FDE weight matrices are jointly optimized so as to minimize the mean square error (MSE) between the signal before STBC encoding and the received signal after STBC decoding. For OFDM transmission, they are jointly optimized so as to maximize the received signal-to-noise power ratio (SNR) after STBC decoding. We show by theoretical analysis that the proposed MB-FDE can achieve 1/R_STBC times higher received SNR than the conventional single-block FDE (SB-FDE), where R_STBC represents the code rate of STBC. It is confirmed by computer simulation that, when more than 2 receive antennas are used, MB-FDE can always achieve better BER performance than SB-FDE irrespective of the number of antennas, and the channel frequency-selectivity.

抄録全体を表示

In this paper, space-time block coding (STBC) is applied to single-carrier distributed antenna network (SC-DAN). By using the frequency-domain STBC coded joint /receive diversity (FD-STBC-JTRD) for the downlink while using the well-known frequency-domain space-time diversity (FD-STTD) for the uplink, the diversity order is given by the product of the number of distributed antennas and that of mobile terminal (MT) antennas. It is shown by computer simulation that the downlink and uplink can achieve almost the same bit error rate (BER) performance and that by increasing the number of distributed antennas, the BER performance can be significantly improved while keeping the MT complexity low.

抄録全体を表示

Complex interleaved orthogonal design (CIOD) can offers diversity gain to the part of the source in spatial modulation which has single radio frequency (RF) front-end at the transmitter despite multiple-input multiple-output, but emits the undesired component out-of-band. For the reducing out-of-band emission, we give up indicating the information source by the antenna switching and increase both the interleaver size and the antenna switching interval. The increase reduces the discontinuities in the waveform and out-of-band emission. We propose such a scheme as diversity with single RF front-end using CIOD. The diversity gain of the proposed scheme is equivalent to the case for CIOD. Moreover, we evaluate the increase of out-of-band emission and confirm that of the proposed scheme compared to the ideal case is only 3 dB.

抄録全体を表示

Geared transmissions are used in a variety of mechanical devices to realize a wide range of speeds or torques. However, the transmission of power and motion in a geared transmission is interrupted when the working gear pairs are changed to vary the velocity ratio. In order to solve this problem, an uninterrupted transmission system was proposed in the previous report that can change the velocity ratio while transmitting power and rotation from the input shaft to the output shaft. However, in the uninterrupted transmission system, there are some cases in which it is difficult to design a suitable noncircular gear based on the combination of angular velocity ratios. In addition, since there is a design constraint that must be satisfied between the angular velocity ratio and the number of teeth on the clutch, the gears and clutches cannot be designed independently. To solve this problem, a new type of uninterrupted transmission system that enables the design of a suitable noncircular gear for various combinations of angular velocity ratios is proposed in this report. Furthermore, in order to avoid the constraint between the angular velocity ratio and the number of teeth on the clutch, a new transition method is proposed. An experimental device using the novel uninterrupted transmission system is constructed, and the effectiveness of the proposed system is verified by experiment.

抄録全体を表示

This paper proposes a demodulation scheme based on channel prediction for differential multiple-input multiple-output (MIMO) spatial multiplexing employing per- antenna differential mapping (PADM). As PADM is one of the differential space-time trellis codings (DSTTCs), it requires per-survivor processing (PSP) based on the Viterbi algorithm (VA) for its demodulation. Therefore, PADM has excellent tracking performance on fast time-varying channels. However, aiming at higher frequency efficiency, PADM for a higher modulation index suffers from the following two disadvantages: (1) poor receiver sensitivity; (2) high computational complexity. In order to solve the items (1) and (2), this paper employs a spatial multiplexing structure and a state reduction algorithm for the VA, i.e., decision-feedback sequence estimation (DFSE), respectively. Finally, for a frequency efficiency of 4bps/Hz with two receive antennas, computer simulation results confirm that the proposed scheme has excellent bit error rate (BER) performance on fast time-varying channels in the case of the maximum Doppler frequency normalized by a symbol rate of 4%.

抄録全体を表示

　In medical institutions, wandering elderly patients have become a problem, and the introduction of wandering sensing systems is underway. However, wandering sensing systems are known to affect wireless medical telemetry systems. In this research, we aimed to clarify the following two points. The first point is to visualize the signal of the wandering sensing equipment and the medical telemeter which influence by using the real time USB spectrum analyzer and to clarify the cause of the electromagnetic interference. The second point is to focus on the medical telemeter channel and to investigate how the wandering sensing system affects to which channel of the medical telemeter. With DPX real time display, we could observe three signals of wandering sensing system, main signal, out of band emission, instantaneous signal. Furthermore, the center frequency in the main signal of the wandering sensing system corresponds to 3000 series of wireless medical telemetry system. Those experiments suggested the possibility of electromagnetic interference when using the wandering sensing system and the wireless medical telemetry system (the channel numbers of 3000 series) simultaneously at relatively short distances (10 cm, 1 m, and 3 m). In addition to being the frequency band allocated for wireless medical telemetry systems, these channels are used in the wandering sensing system. Hence, it is necessary to consider possible electromagnetic interference problems.

抄録全体を表示

This paper proposes an adaptive modulation (AM) and a

power control (TPC) on frequency symbol spreading (FSS) based orthogonal frequency division multiplexing (OFDM) relay system with considering the mobility of relay node. Wireless communications often suffer from large propagation loss due to shadowing and multipath fading. As a solution to this problem, relay communications, which forward data messages from a source to a destination via intermediate station(s), have been focused on. It can obtain the space diversity and expand the area coverage. In the situation where relay node has mobility, propagation channel fluctuates and communication quality is deteriorated. This paper presents a whole system design of FSS-OFDM employing AM and TPC. Exploiting a good match of AM and FSS, throughput performance can be significantly improved even in high mobility environment. In addition to this, utilizing TPC, the most suitable AM is enabled and leads to a further performance enhancement. Computer simulation verifies its effectiveness and reveals the proposed system is the most valuable means which realizes the flexible relay node deployment.

抄録全体を表示

情報の望ましさと伝達のメディアが, 伝達される内容の歪みに及ぼす効果と, 付加的に, 両変数が伝達時の音声反応や対人印象に及ぼす影響が検討された.
被検者は56名の男子大学生で, 実験者1 (E₁) から, 実験者2 (E₂) への伝言を依頼された. 伝言はE₂にとって悪い内容 (E₂のデータ分析が大失敗であった) か良い内容 (E₂のデータ分析が大成功であった) だった. もう1つの独立変数として, 被験者が伝言をE₂に伝えるメディア: 対面-電話が導入された.
仮説は次のとおりである: 1) 悪い知らせは良い知らせより, 内容が弱めて伝えられるだろう. 2) 対面条件では電話条件より, 悪い知らせの内容が弱めて伝えられるだろう.
実験の結果, 仮説1) は, 文節数, 述語数, 強め語句, 弱め語句および忠実度の全指標で支持された. 仮説2) はどの指標でも支持されず, 特に弱め語句と忠実度は, 仮説と逆の傾向を示していた.
音声反応に関しては, 対面条件のほうが電話条件より伝達速度が遅く, 伝達時に笑った被験者が多かった. また, 対面条件の被験者は, E₂をより暖かく, より好感がもてると評定し, 被験者自身がE₂に対して与えた印象も, より暖く, より好感がもてるものであると評定していた.

抄録全体を表示

In this letter, we analyze the impacts of outdated channel state information (CSI) on the secrecy performance for multiple-input single-output multiple-eavesdropper (MISOME) systems using antenna selection (TAS) scheme and derive the exact closed-form expressions for the secrecy outage probability and the probability of non-zero secrecy capacity. Then, we present the asymptotic secrecy outage probability which reveals the secrecy diversity order and the secrecy array gain. The analysis and simulation results show that the security performance of TAS scheme is quite sensitive to outdated CSI and the achievable secrecy diversity order is only one under the effect of outdated CSI.

抄録全体を表示

In multiple-input multiple-output (MIMO) cellular networks, certain schedulers have two independent phases: the first selects a group of users based on the scheduler criterion, and the second assigns the selected users to the antennas by using an assignment scheme taking into consideration capacity maximization. Other schedulers directly select among the available channels between users and the base station in a centralized way. The schedulers of the first category can be implemented with lower complexity compared with the schedulers of the second category. For the first category, we propose three near-optimal assignment schemes with low complexities. We conducted a simulation in which the mobility of users was considered that demonstrated the superior performance of our assignment schemes. Furthermore, we analytically demonstrate their efficiency.

抄録全体を表示

Partial sequence (PTS) is a well known technique used to reduce the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. However, it has relatively high complexity due to the computation of multiple inverse fast Fourier transforms (IFFTs). To reduce this complexity, we use intermediate signals within a decimation in frequency (DIF) radix IFFT and propose a new PTS subblocking technique which requires the computation of only partial IFFTs. Performance results are presented which show a PAPR reduction similar to that with other techniques such as original PTS (O-PTS). Further, we show that complexity reduction can be achieved with either low or high radix IFFT algorithms.

抄録全体を表示

This paper discusses an imaging of eddy current testing (ECT) data for surface breaking evaluation. The multicoil ECT probe utilized in this paper consists of -receive (TR) type sensors as array elements to obtain the information on crack directions and deep situation. Switching two direction scan modes gives two-dimensional vector mapping as ECT images. The ECT signals of the TR type sensor also give the information on crack directions from their variation displayed on the complex number plane. Extracting a complex number component of the signals makes it possible to visualize directions of proximate EDM notches.

抄録全体を表示

The blood pressure is earned recognition as a barometer of the health condition. Many blood pressure monitors use a cuff for measuring the pressure. These monitors are easy-to-use except for attaching the cuff. This paper proposes an estimation method of the diastolic blood pressure without a use of the cuff. The blood pressure is estimated by a pulse time which is measured by a Doppler sensor and a pulse wave sensor. An experiment shows that the proposed method can estimate a diastolic blood pressure.

抄録全体を表示