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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we propose an uplink multiuser-multiple input multiple output (MU-MIMO) cooperative retransmission control scheme for the reliable and efficient communication of autonomous unmanned aerial vehicles (i.e., flight communication and drone-to-drone communication). This scheme is a key element in the design of a drone-based ad-hoc network. Because drone relay transmission operates in the air, flexible wireless relay networks over large areas can be achieved without interference from multipath signals caused by buildings and obstacles in ground-based communication. However, two main challenges exist. First, the relay transmission system occupies bandwidth every time the drone relays information. Therefore, because the radio channel is shared by multiple relay stations, the throughput is greatly reduced. To improve throughput, it is better to transmit using the minimum number of relay stations. Ultimately, long-distance direct transmission is the best. The other issue is a direct result of the first issues solution: the propagation loss increase when relaying information directly over a long distance. Moreover, because the frequency of interference waves from the ground increases, transmission signal errors are an important issue. To solve this issue, a transmission scheme to reduce errors is required. The scheme proposed in this study achieves high transmission reliability and efficiency even under high transmission error conditions. The results of a computer simulation reveal that the proposed method achieves a direct transmission throughput that is 1.5 times better than that of a conventional scheme. It is also shown that the proposed scheme requires only about three stations to achieve acceptable results.

DOI： 10.1109/TVT.2020.2965597

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

Uplink MU-MIMO techniques achieve the high frequency efficiency. However, it is known that the frequency efficiency depends on the arrangement of antennas of the access point. Moreover, we have proposed the distributed antenna system (DAS) which selects the high density arranged antennas according to user distribution and shown its effectiveness using narrow band signals in an actual indoor environment. For the actual implementation, this paper proposes an antenna selection methods that selects the antenna in a limited area and selects the antenna in a non-limited area. We compare the basic characteristics of the DAS when applied the uplink MU-MIMO by broadband OFDM signals in an indoor environment for each selection method, and demonstrate the effectiveness of DAS with the proposed antenna selection methods.

DOI： 10.1109/ISANP.2017.8228847

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

The multiple input multiple output (MIMO) sensor utilized for human detection by channel state information in a MIMO propagation channel has been proposed. In this paper, we evaluate the estimation of the detection of the person and the approximate direction of arrival (DoA) of the person using a correlation function with only 2 by 2 MEMO configuration. We focus on the DoA estimation of the human in an indoor scenario by applying MEMO sensor with the time correlation for wide and narrow element spacings in the horizontal place at the transmit and receive array antennas. The measurement results show that the narrow element spacing was effective for the broadside direction estimation, whereas the wider element spacing was effective for the end-fire direction estimation considering the approximate DoA estimation using the time correlation even if high-resolution techniques, such as the MUSIC algorithm, is not used.

DOI： 10.1109/ISANP.2017.8229031

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

Massive MIMO transmission has been attracted much attention as one of key technologies in next-generation mobile communication system, because it enables improvement in service area and interference mitigation by simple signal processing. Multi-beam massive MIMO configuration has proposed that utilizes the beam selection in analog part and blind algorithm such as constant modulus algorithm (CMA) which does not need channel sate information (CSI) is applied in digital part. In this paper, to achieve the further higher transmission rate, we propose beam selection method with only amplitude information regarding the multi-beams.

DOI： 10.1109/ISANP.2017.8228844

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

In the 5G system, high frequency bands over 6 GHz (6-100 GHz) will be a key factor in providing a very wide bandwidth. Because of high path losses, these bands are considered to use for small cells. To design radio links with high accuracy and evaluate 5G system performances for various scenarios, channel characteristics must be clarified. In this paper, we clarify channel characteristics in an outdoor small cell environment at the 20 GHz band based on the measurement using a channel sounder.

DOI： 10.1109/ISANP.2017.8228839

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

Multi-beam massive MIMO configuration has been proposed that utilizes the beam selection with high power in an analog part and blind algorithm such as constant modulus algorithm (CMA) which does not need channel state information (CSI) in a digital part. In this paper, we evaluate the transmission performance in the downlink with a simple control at the user terminal by the massive MIMO transmission. By the computer simulation, it is shown that the multi-beam selection at the base station and CMA at the user terminal with two antennas can effectively realize the transmission with high order modulation scheme.

DOI： 10.1109/ISANP.2017.8228845

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper presents multiple-input multiple-output (MIMO) measurements in the 20-GHz band, and evaluates the basic performance of massive MIMO systems when considering 100 elements at a base station (BS) and seven user equipment units. First, it is shown that zero forcing (ZF) is essential as a transmission scheme in massive MIMO systems, whereas the maximum-ratio combining method cannot reduce interference effectively in such systems. In addition, it is shown that analog-digital hybrid beamforming can be used to reduce the calculation complexity and improve hardware implementation. Next, we compared the Shannon capacity with the achievable bit rate (ABR), using ZF for seven-user MIMO transmissions with 100 elements at the BS. When the number of degrees of freedom in the array antenna is guaranteed, the ABR is almost the same as the Shannon capacity. Moreover, multiuser transmission is realized by linear decoding. Thus, decoding methods such as ZF are effective in massive MIMO systems.

DOI： 10.1109/TAP.2017.2754441

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper proposes an analog eigenmode transmission technique suitable for a short-range multiple-input multiple-output (SR-MIMO) system consisting of arbitrary power-of-two number of antennas utilizing the idea of orbital angular momentum. In the proposed technique, uniform circular arrays that are coaxially arranged are used at both the transmitting (Tx) and receiving (Rx) sides. With this array configuration, the channel matrix is always a circulant matrix regardless of antenna type, array radius, Tx-Rx distance, and rotation about the coaxis. Due to the characteristics of a circulant matrix, the channel matrix can be diagonalized independently of the above-mentioned factors by fixed-weight beamforming based on a discrete Fourier transform (DFT) matrix uniquely determined by just the number of antennas. In this paper, the operating principle of the proposed technique is discussed from the viewpoints of linear algebra, and some example network configurations are presented with the determination of the DFT-matrix weight. Numerical analyses confirm the two important features of the proposed technique: 1) support of more than 4x4 SR-MIMO and 2) independence with regard to rotation about the coaxis. Furthermore, an experiment on a fabricated DFT circuit confirmed the feasibility of the proposed technique in realizing practical short-range communication.

DOI： 10.1109/TAP.2017.2742582

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we introduce an interference suppression technique that combines a multiple-input multipleoutput antenna arrangement with eigen-beamforming suitable for space division duplex relay that uses separate transmitter (Tx) and receiver (Rx) in relay stations (RSs) to realize full-duplex communication. The proposed technique degenerates the rank of the interference channel matrix to basically one at the RSs by careful arrangement of the antenna, which allows the Tx and Rx arrays to use nearly zero space weights. This scheme offers significant interference suppression while consuming only one degree of spatial division multiplexing freedom. To implement this scheme, we adopt the end-fire arrangement, where all antenna elements are arranged in line. In line-of-sight environments, this arrangement degenerates the rank of the interference channel matrix. The results of a numerical analysis and an experiment show that the proposed method can reduce the interference by up to 75.2 and 36.5 dB, respectively. The simulation using measured data clarifies that the proposed system attains 1.81 times higher capacity (12.1 b/s/Hz) than the conventional system.

DOI： 10.1109/TAP.2017.2688798

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Massive MIMO transmission, whose number of antennas is much larger than the number of user terminals, has been attracted much attention as one of key technologies in next-generation mobile communication system because it enables improvement in service area and interference mitigation by simple signal processing. Multi-beam massive MIMO has proposed that utilizes the beam selection with high power in analog part and blind algorithm such as constant modulus algorithm (CMA) which does not need channel state information (CSI) is applied in digital part. Proposed configuration obtains high transmission efficiency. We have evaluated QPSK signals because the CMA basically focuses on the constant amplitude modulation. In this paper, in order to achieve the further higher transmission rate, the amplitude and phase compensation scheme is proposed when using the CMA with amplitude and phase modulation scheme such as QAM. The effectiveness of proposed method is verified by the computer simulation.

DOI： 10.1587/transcom.2016WSP0006

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In IEEE 802.11 wireless local area networks (WLANs), contention window (CW) in carrier sense multiple access with collision avoidance (CSMA/CA) is one of the most important techniques determining throughput performance. In this paper, we propose a novel CW control scheme to achieve high transmission efficiency in dense user environments. Whereas the standard CSMA/CA mechanism. Employs an adaptive CW control scheme that responds to the number of retransmissions, the proposed scheme uses the optimum CW size, which is shown to be a function of the number of terminal stations. In the proposed scheme, the number of terminal stations are estimated from the probability of packet collision measured at an access point (AP). The optimum CW size is then derived from a theoretical analysis based on a Markov chain model. We evaluate the performance of the proposed scheme with simulation experiments and show that it significantly improves the throughput performance.

DOI： 10.1587/transcom.2016EBP3056

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper presents a novel simultaneous decoupling and matching technique for transmitting (Tx) and receiving (Rx) ports in short-range multiple-input multiple-output (SR-MIMO) systems. The principal difference with conventional decoupling and matching network (DMN) approaches is that the proposed technique considers strong mutual coupling between closely-positioned Tx/Rx arrays, and the S-parameter variation due to the presence of each other's array. This technique has two stages; first, 180-degree hybrid couplers are connected to both Tx/Rx ports of a plane-symmetrical MIMO system. This decouples both Tx/Rx ports, and moreover, channels between them are orthogonalized. That is, the MIMO system is transformed into multi orthogonalized single-input single-output (SISO) systems. Second, Tx/Rx ports of each orthogonalized SISO system are simultaneously matched based on conjugate matching theory. Consequently, the transmission power of the short-range MIMO system is maximized. Numerical results show that the proposed technique realizes higher channel capacity than the conventional DMN; indeed it achieves the theoretically possible capacity. In addition to theoretical analyses, we provide an example for microstrip line (MSL) circuit implementation. This MSL model offers good simultaneous decoupling and matching performance yielding channel capacity comparable to that of an ideally-designed circuit model. This validates the implementation feasibility of the proposed technique.

DOI： 10.1587/transcom.2015EBP3463

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

This paper proposes a method of implementing analog eigenmode transmission for a short-range multiple-input-multiple-output (SR-MIMO) system that uses only 180° hybrid couplers. If the short-range MIMO system places transmitting and receiving arrays in line-of-sight (LOS) and symmetrically with respect to specific reference planes, the channel matrix in the system also becomes symmetrical. This allows the channel matrix to be diagonalized by connecting 180° hybrid couplers to both ports at the transmitter and receiver sides, i.e., eigenmode transmission can be realized. In this paper, first, the theory of the proposed technique is explained by taking a 2 × 2 MIMO as an example, based on the characteristics of 180° hybrid coupler and the theory of the cascade-connected network. Moreover, an extension to the method that offers 4 × 4 MIMO is also proposed. This paper clarifies that this proposed technique can diagonalize the channel matrix, regardless of array configuration, such as type of antennas and antenna spacing, as long as the symmetry of the system configuration is assured. Furthermore, numerical results verify that the distance between the transmitter and the receiver has no effect on channel orthogonality. As a result, this technique partially avoids the performance degradation caused by array displacement, which is a major disadvantage of the conventional analog-beamforming-based decoding technique for short-range MIMO systems. Thus, the superiority of the proposed technique is clear.

DOI： 10.1109/TVT.2015.2397194

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

An analog-beamforming-based eigenmode transmission technique is proposed that employs a network of interconnected 180-degree hybrid couplers at both transmitting and receiving sides of a plane-symmetrically configured short-range MIMO system. This technique can orthogonalize MIMO channels regardless of array parameters such as antenna spacing and Tx-Rx distance, provided the MIMO array is symmetric. For verifying the effectiveness of the proposed technique in channel orthogonalization, an experiment is conducted using a 4x4 MIMO array consisting of microstrip antennas and cascade-connected rat-race hybrid couplers. The results indicate a reduction in interference by approximately -28.3dB on average compared to desired signal power, and the ability to realize four-stream parallel MIMO transmission by using only analog passive networks. The proposed technique can achieve channel capacity almost equivalent to that of eigenbeam space division multiplexing with ideal digital beamforming.

DOI： 10.1587/transcom.2015ISP0028

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes Fast Fourier Transform (FFT) based orthogonal beam selection method at the user terminals (UTs) to reduce the number of nulls for the other users except an intended user by the Block Diagonalization (BD) algorithm in multiuser MIMO (MU-MIMO) sytems. The BD algorithm has been proposed in order to realize MU-MIMO broadcast transmission with a realistic signal processing burden. The BD algorithm cancels inter-user interference by creating the weights so that the channel matrixes for the other users are set to be zero matrixes. However, when the number of transmit antennas is equals to the total number of received antennas, the transmission rate by the BD algorithm is decreased. The proposed method realizes the performance improvement compared to the conventional BD algorithm without the burden on the UTs. It is verified via bit error rate (BER) evaluation that the proposed method is effective compared to the conventional BD algorithm and antenna selection method. Moreover, the effectiveness of proposed method is verified by the performance evaluation considering medium access control (MAC) layer in a comparison with the conventional BD algorithm which needs the channel state information (CSI) feedback. Because the proposed method can be easily applied to beamforming without the CSI feedback (implicit beamforming), it is shown that the propose method is effective from a point of view on the transmission efficiency in MU-MIMO system.

DOI： 10.1587/transcom.2015ISP0019

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, we propose multi-input multi-output (MIMO) transmission using human bodies. The proposed scheme is experimentally evaluated using test subjects, whose bodies are located at different positions. A high channel capacity was achieved by using MIMO transmission. The channel capacity obtained for 2 x 2 MIMO in body-to-body communication is approximately 1.6 times higher than that obtained when using single-input single-output transmission. The experimental results indicate the success of the proposed method in increasing channel capacity using MIMO. The presented research is relatively unique, and the results would therefore be a valuable contribution to this field of research.

DOI： 10.1587/comex.2016XBL0096

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Multi-user MIMO (MU-MIMO) realizes a high channel capacity with a little limited number of antennas at user terminals. On the other hand, MU-MIMO needs a channel state information to obtain the transmit weight of beam forming. The distributed antenna system (DAS), which switches the high density arranged antennas according to user distribution in indoor environment, has been proposed. In this paper, we obtain the channel state information in an actual indoor environment. The paper shows that the SNR, eigenvalues and channel capacity can be improved compared to centralized antenna system by selecting antenna with highest SNR from limited area. We verify that the proposed antenna selection is effective from points of view on both the simplification of antenna selection and improvement on channel capacity.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes a collision detection scheme in asynchronous multiuser-multiple input multiple-output (MU-MIMO) transmission and self-interference cancellation. We assume that asynchronous MU-MIMO which realizes the efficient transmission and other antennas can receive preamble signals while the transmission is employed with antennas which are used in asynchronous MU-MIMO. The self-interference can be cancelled by subtracting the short preamble signal which is multiplied by the estimated channel response using the received signal after FFT processing. The effectiveness of proposed method is shown by computer simulation. In addition, interfering power from the interfering user terminal (IT) at the access point (AP) and desired user terminal (DT) is verified in an actual indoor environment.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Multiuser multiple-input multiple-output (MU-MIMO) has been much attracted much attention for improving the spectral efficiency within a limited frequency band. However, it is not possible to communicate with the users that exceed the number of base station (BS) antennas in the MU-MIMO transmission. We have proposed a method by using non orthogonal multiple access (NOMA) and Zero Forcing (ZF) at the BS and Minimum Mean Square Error (MMSE) at user terminals (UTs). Furthermore, user selection algorithm for the proposed system by utilizing channel capacity equation of ZF algorithm has been proposed. By the proposed system, it was shown that the proposed method realizes the transmission with four users with only two antennas at the BS. In this paper, the effectiveness of proposed method is evaluated when considering a large number of multiple users in order to show validity of proposed system in more realistic environment.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In this paper, we discuss the inter-array decoupling technique suitable for MIMO full-duplex, which uses a combination of the end-fire antenna arrangement and eigen-beamforming. An experimental evaluation clarifies that the end-fire antenna arrangement contributes to the reduction of the inter-array coupling by 18.7 dB compared with the facing antenna arrangement, and that the small antenna aperture of the array brings the significant interference reduction by the beamforming.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

The Multiuser Multiple-Input Multiple-Output (MU-MIMO) has been much attracted much attention for improving the spectral efficiency within a limited frequency band. The MU-MIMO techniques have been introduced in the standardization of IEEE802.11ac and LTE-advanced. However, it is not possible to communicate with the users that exceed the number of base station (BS) antennas in the MU-MIMO transmission. In this paper, we propose a new transmission method by using non orthogonal multiple access (NOMA) and Zero Forcing (ZF) at the BS and Minimum Mean Square Error (MMSE) at user terminals (UTs). Furthermore, we propose user selection algorithm for the proposed system by utilizing channel capacity equation of ZF algorithm. By the computer simulation, it is shown that the proposed method realizes the transmission with four users with only two antennas at the BS and the transmission rate by the proposed method is improved compared to that by conventional ZF algorithm.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In this paper, we propose the new scheme, multi-user full-duplex MIMO (Multiple-Input and Multiple-Output) system, which performs uplink and downlink signal transmissions at the same frequency and time between the base station and multiple terminals. We show the characteristics of the transmission capacity of the proposed full duplex MIMO system by use of the channel information measured in an actual outdoor environment.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Multiple Input Multiple Output (MIMO) sensor, which is utilized for intruder detection by channel state information (CSI) in MIMO propagation channel, has been proposed. We have focused on wide range human detection in indoor scenario by applying array antenna with wide element spacing in the horizontal place at transmit and receive antennas. On the other hand, human detection with limited range such as a gate might be needed when considering MIMO sensor application. In this paper, basic performance on the human detection by the MIMO sensor with antennas arranged at ceil and floor is evaluated. The time correlation function is used as the measure on the MIMO sensor. In this paper, the human detection performance when considering multiple users and their waking is evaluated, although only one person is considered in the previous studies.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper demonstrates the measurement results showing the effectiveness of a fast human localization and tracking method suitable for multi-path environment. In this method, a time-differential channel is calculated by taking difference among the observed channels corresponding to biological activity. The human locations are estimated by two-dimensional MUSIC (MUltiple SIgnal Classification) correlation matrix calculated from the time-differential channels. The experiments were carried out in an indoor environment, and the results show that the target locations and trajectories can be estimated by the temporal-subtracting technique. The averaged tracking error is 0.29 m in this experiment.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Massive MIMO transmission has been attracted much attention as one of key technologies in next-generation mobile communication system, because it enables improvement in service area and interference mitigation by simple signal processing. Multi-beam massive MIMO configuration has proposed that utilizes the beam selection with high power in analog part and blind algorithm such as constant modulus algorithm (CMA) which does not need channel sate information (CSI) is applied in digital part. In this paper, in order to achieve the further higher transmission rate, the amplitude and phase compensation scheme is proposed when using the CMA with amplitude and phase modulation scheme.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

Recently, the next generation (5G) mobile communication system has been actively investigated all over the world, in order to satisfy the strong demand for the faster and larger data communication. not only UHF band but also SHF/EHF bands have been much attracted much attention. Therefore, frequency characteristic of radio propagation loss must be studied. We previously investigated the outdoor to indoor (O2I) propagation characteristics in the 2.2 GHz band, and have proposed a modified path loss model instead of 3 GPP model. In this paper, in order to develop more advanced model, we show measurement results of 0.8, 2.2 and 4.7 GHz bands. Moreover, we consider an indoor penetration loss factor which is calculated by the least square approximation.

DOI： 10.1109/iWEM.2015.7365087

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes a method that uses bistatic Multiple-Input Multiple-Output (MIMO) radar to locate living-bodies. In this method, directions of living-bodies are estimated by the MUltiple SIgnal Classification (MUSIC) method at the transmitter and receiver, where the Fourier transformed virtual Single-Input Multiple-Output (SIMO) channel matrix is used. Body location is taken as the intersection of the two directions. The proposal uses a single frequency and so has a great advantage over conventional methods that need a wide frequency band. Also, this method can be used in multipath-rich environments such as indoors. An experiment is performed in an indoor environment, and the MIMO channels yielded by various subject numbers and positions are measured. The result indicates that the proposed method can estimate multiple living-body locations with high accuracy, even in multipath environments.

DOI： 10.1587/transcom.E98.B.2314

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The concept of massive multiple input multiple output (MIMO) has recently been proposed. It has been reported that using linear or planar arrays to implement massive MIMO yields narrow beams that can mitigate the interference signal even if interference cancellation techniques such as zero forcing (ZF) are not employed. In this work, we investigate the interference reduction performance achieved by circular array implemented massive MIMO in a real micro cell environment. The channel state information (CSI) is obtained by using a wideband channel sounder with cylindrical 96-element array in the 2-GHz band in an urban area. Circular arrays have much larger beamwidth and sidelobe level than linear arrays. In this paper, when considering the cylindrical array, the interference reduction performance between ZF and maximum ratio combining is compared when one desired user exists in the micro cell while the interference user moves around the adjacent cell. We show that ZF is essential for reducing the interference from the adjacent cell in the circular array based massive MIMO. The required number of antennas in the vertical and horizontal planes for the interference reduction is evaluated, in order to simplify the burden of signal processing for the ZF algorithm in massive MIMO. Because there are elements with low signal to noise power ratio (SNR) when considering cylindrical 96-element array, it is shown that the degradation of the signal to noise plus interference power ratio (SINR) when the number of antennas is reduced is smaller than that by ideal antenna gain reduction with a linear array. Moreover, we show that the appropriate antennas should be selected when a limited number of antennas is assumed, because the dominant waves arrive from certain specific directions.

DOI： 10.1587/transcom.E98.B.1447

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記述言語：英語  

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記述言語：英語  

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Controlling interference from the secondary system (SS) to the receiver of the primary system (PS) is an important issue when the SS uses the same frequency band as the television broadcast system. The reason includes that the SS is unaware of the interference imposed on the primary receiver (PS-Rx), which does not have a transmitter. In this paper, we propose an interference control method between PS-Rx and SS, where a load modulation scheme is introduced to the PS-Rx. In this method, the signal from the PS transmitting station is scattered by switching its load impedance. The SS observes the scattered channel and calculates the interference suppression weights for transmitting, and controls interference by transmit beamforming. A simulation shows that the Signal-to-Interference Ratio (SIR) with interference control is improved by up to 41.5 dB compared to that without interference control at short distances; the results confirm that the proposed method is effective in controlling interference between PS-Rx and SS. Furthermore, we evaluate the Signal-to-Noise Ratio (SNR) and channel capacity at SS.

DOI： 10.1587/transcom.E98.B.861

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Mobile terminal stations utilizing wireless local area network (WLAN) devices have recently increased. Hence, packet collisions due to interfering signals have become an important issue. WLANs detect collisions when the acknowledgment (ACK) frame is not returned. This considerably reduces the WLAN transmission efficiency. This paper proposes a retransmission control scheme utilizing multiple input multiple output (MIMO) transmission, in which collisions may be detected during signal transmission. We evaluated and analyzed the effectiveness of the proposed scheme through computer simulations and theoretical analysis. The theoretical analysis agree with the computer simulation results, indicating the efficiency and reliability of our proposed scheme.

DOI： 10.1587/comex.4.61

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

The authors have proposed a non-contact vital sign detection method using a microwave. In general, the body surface movement due to respiration is significantly larger than that of heartbeat, and this obstructs heartbeat detection. In this paper, we propose the microwave heartbeat detection method by suppressing the respiration component. Measurements were carried out in a multi-path environment, and the experimental results showed that the proposed method works well in detecting heartbeat.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Massive MIMO enables the improvement on the transmission rate without increasing the burden on the signal processing by employing a large number of antennas at a base station (BS). Channel state information (CSI) feedback scheme from terminal stations to BS gives a very large overhead when considering massive MIMO and implicit beamforming (IBF) with the calibration technique as the countermeasures are introduced. However, it is reported that CSI estimation itself has a large overhead when considering massive MIMO. In this paper, we propose analog-digital hybrid configuration using analog multi-beams with dielectric line array and lens and blind algorithm called Constant Modulus Algorithm (CMA) which does not need the CSI estimation. Via a computer simulation, the effectiveness of proposed configuration is verified.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Massive MIMO enables the improvement on the transmission rate without increasing the burden on the signal processing by employing a large number of antennas at a base station. However, the interference cancellation with maximum ratio combining (MRC) does not sufficiently work when the circular array is used for the purpose on the circular cell, because the sidelobe level in the circular array is increased compared to the linear array. In this paper, an actual propagation channel was measured by using a wideband channel sounder with cylindrical array in 2 GHz band at a microcell environment. Moreover, we verify the effectiveness of the interference rejection when using the hybrid algorithm which employs the MRC on the analog part and zero forcing (ZF) in the digital processing part.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper investigates an indoor penetration loss between measured result and the result by a hybrid method of ray-tracing (RT) and physical optics (PO) (PT-PO method), when considering heterogeneous networks. In heterogeneous networks, interference from/to macrocell to/from small cell in indoor arrives with each other. Therefore, exact interference power estimation is essential in heterogeneous networks. From the comparison of indoor penetration loss among measured result, 3GPP model and result by RT-PO method, it is shown that the path loss between the measured result and RT-PO method agree well with each other when considering the severe interference environment.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes a self-interference reduction method exploiting antenna arrangement and beamforming for space division duplex (SDD) relay station. When transmitting (Tx) and receiving (Rx) linear array antennas are placed in end-fire arrangement, spatial correlation between Tx and Rx increases. This causes rank degeneracy of the channel matrix between Tx and Rx. With this channel, almost all the self-interference inside SDD relay station can be reduced by forming beam to the nearly-zero space at Tx. Simulation results show that there is the optimum element spacing of linear array, and that the proposed method greatly improves channel capacity of SDD relay system, which is higher than that of the time division duplex (TDD) system.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Massive MIMO enables automatic interference cancellation by a high beamforming resolution when using a linear and planer arrays. This paper investigates the interference reduction performance when considering the cylindrical array based massive MIMO in a real micro cell environment. The channel state information is obtained by using a wideband channel sounder in a 2 GHz band at an urban area. In this paper, the interference reduction performance between zero forcing (ZF) and maximum ratio combining is compared. Moreover, we clarify the characteristics with the smaller number of antennas at the base station, in order to simplify the burden of signal processing on the ZF algorithm.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In this paper, the frequency sharing technique between existing TV and new wireless communication systems are discussed. By adding a load modulation function to TV receiver antenna, the secondary system, i.e. new wireless communication system, can identify the interference channel between secondary system and primary TV receiver. The simulation has been carried out and it is found that the fairly high capacity is obtained even though the secondary system needs to suppress the interference to primary TV receiver.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Massive multiple input multiple output (MIMO) enables the improvement on the transmission rate without increasing the burden on the signal processing by employing a large number of antennas at a base station. It was reported an effect of applying a massive MIMO to small cell at the 2-GHz band. However, main target of the massive MIMO will be the small cells at the high-frequency band, because the antenna size is very large when considering the massive MIMO in macro frequency band. In this paper, real propagation channels are measured by using a wideband channel sounder with horn antenna in 20-GHz band in an actual indoor propagation environment. Moreover, the performance of the interference rejection is evaluated when virtual circular array antenna with 24 elements is assumed.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE Computer Society  

In this paper, we analyze by theoretical calculation of the proposed scheme for collision detection in wireless local area networks (WLANs). The proposed scheme utilizes the medium access control (MAC) procedure of multiple input multiple output (MIMO) transmission technology, which is used to achieve high-speed transmission in WLANs in recent years
however, the transmission efficiency degrades at the MAC layer level, although a high transmission link rate is achieved at the physical (PHY) layer. The proposed scheme were performed high transmission efficiency of approximately 90% by the computer simulation in our previous work. In this paper, the results of our theoretical calculations correspond with the computer simulation results, indicating that the proposed scheme is indeed efficient and reliable.

DOI： 10.1109/WiMOB.2014.6962145

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

We have proposed an intruder detection method by using multiple-input multiple-output (MIMO) channels. Although the channel capacity for MIMO transmission is severely degraded in time-variant channels, we can take advantage of this feature in MIMO sensor applications. For MIMO sensors, the accurate estimation of channel state information (CSI) is essential. Moreover, the transceiver should be simplified from the viewpoint of saving power. Narrowband signals such as minimum shift keying (MSK) and offset quaternary phase shift keying signals are effective and are used in sensor network systems. However, because the timing and carrier offsets between the transmitter and receiver are relatively large compared to the symbol rate, accurate CSI estimation is impossible given the severe constraints imposed by the timing and carrier offsets. To solve this issue, a signal synchronization method for the CSI estimation using a narrowband MSK signal has been proposed. In this paper, we propose a new CSI estimation method for arbitrary amplitude and phase modulation schemes for the MIMO sensor. The key point of the proposed method is that control signals (unique words) are mapped so as not to pass through the origin of the complex I/Q plane. The estimation accuracy of the proposed method is evaluated via a computer simulation. Moreover, the basic performance by the proposed CSI estimation method is verified when considering intruder detection by MIMO sensor.

DOI： 10.1587/transcom.E97.B.2102

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Multi-user MIMO (MU-MIMO) improves the system channel capacity by employing the transmission between a base station and multiple user terminals (UTs). Block Diagonalization (BD) has been proposed in order to realize MU-MIMO broadcast transmission. The BD algorithm cancels inter-user interference by creating the weights so that the channel matrixes for the other users are set to be zero matrixes. However, when the number of transmit antennas is equals to the total number of received antennas, the transmission rate by the BD algorithm is decreased. This paper proposes a new antenna selection method at the UTs to reduce the number of nulls for the other users except an intended user by the BD algorithm. It is verified via bit error rate (BER) evaluation that the proposed method is effective compared to the conventional BD algorithm, especially, when the number of users is increased with a low bit rate. Moreover, this paper evaluates the transmission rate based on IEEE802.11ac standard when considering BD algorithm with ideal user scheduling. Although the number of equivalent receive antenna is only one by the proposed method when the number of antennas at the the UT is two, it is shown that the transmission rate by the proposed method is higher than that by the conventional BD algorithm when the SNR is low even in the condition on user scheduling.

DOI： 10.1587/transcom.E97.B.2118

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記述言語：日本語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

A novel analog decoding method using only 90-degree phase shifters is proposed to simplify the decoding method for short-range multiple-input multiple-output (MIMO) transmission. In a short-range MIMO transmission, an optimal element spacing that maximizes the channel capacity exists for a given transmit distance between the transmitter and receiver. We focus on the fact that the weight matrix by zero forcing (ZF) at the optimal element spacing can be obtained by using dividers and 90-degree phase shifters because it can be expressed by a unitary matrix. The channel capacity by the proposed method is next derived for the evaluation of the exact limitation of the channel capacity. Moreover, it is shown that an optimal weight when using directional antennas can be expressed by using only dividers, 90-degree phase shifters, and attenuators, regardless of the beam width of the directional antenna. Finally, bit error rate and channel capacity evaluations by both simulation and measurement confirm the effectiveness of the proposed method.

DOI： 10.1587/transcom.E97.B.620

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

One of the procedures for increasing the number of multi-input and multi-output (MIMO) branches without increasing the computational cost for MIMO detection or multiplexing is to exploit parallel transmissions by using polarization multiplexing. In this paper the effectiveness of using polarization multiplexing is confirmed under the existence of polarization rotation, which is inevitably present in short-range multi-input and multi-output (SR-MIMO) channels with planar array antennas. It is confirmed that 8 x 8 SR-MIMO transmission system with polarization multiplexing has 60 bit/s/Hz of channel capacity. This paper also shows a model for theoretical cross polarization discrimination (XPD) degradation, which is useful to calculate XPD degradations on diagonal paths.

DOI： 10.1587/transcom.E97.B.459

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記述言語：日本語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this letter, we introduce a method that uses the radar system to observe the waves reflected from the target with the single-input-multiple-output (SIMO) array configuration to estimate living-body directions in a multipath environment for applications such as elderly monitoring. Directions of living body are estimated by the MUltiple SIgnal Classification (MUSIC) method, where the Fourier transformed channel matrix is used. Our use of the 2.4-GHz band allows greater miniaturization of the antenna than is possible with the low-frequency band used by conventional systems. Also, this method can be used in multipath-rich environments such as indoors. The experiments are carried out in a specific indoor environment as a demonstration, and the SIMO channel is measured with various subject numbers and positions. The results indicate that the proposed method can estimate living-body directions with high accuracy even in multipath environments.

DOI： 10.1109/LAWP.2014.2315671

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

We are focusing our research on indoor positioning technology; specifically, a type that uses Visible Light Communication (VLC); modulatable LED lights transmit data at 9600 bps, using 4 Pulse Position Modulation (4PPM), while a fish-eye lens-equipped camera receives the light signal over a 160-degree field-of-view. This type of lighting requires neither additional space nor -power. We assigned a unique ID to each LED, in order to recognize its position. Self-location is calculated from the relationship between the LED positions and coordinates on the image plane. In our previous research, we confirmed that self-location can be determined within 10 cm, using our system. However, we needed to attach dedicated transmitters to each LED used for positioning, especially in large buildings such as hospitals and shopping malls. So, in this paper, we propose LED-tracking and ID-estimation using LEDs with known IDs; doing so will significantly reduce the cost of installing-and running transmitters. Additionally, with the increased use of LEDs for positioning, accuracy naturally improves. We conducted experiments with the camera moving in 2 different environments: a) a small area, with just 4 LEDs; b) the VLC platform with a total of 24 LEDs, to demonstrate that as many as 13 LEDs can be identified. With 2 or more IDs detected beforehand, unidentified LEDs, as well as some that failed to be tracked, could be estimated, while the camera was in motion. Average positioning error in the smaller environment and the VLC platform were 3.78 cm and 6.96 cm, respectively. From this, location can be determined, even when some LEDs are offline.

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記述言語：日本語   出版者・発行元：電気関係学会東北支部連合大会実行委員会  

DOI： 10.11528/tsjc.2014.0_11

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

The authors have proposed a direction estimation method of the living-body using array antenna in multi-path environment. However, this method has a problem that takes time as several tens of seconds. In this paper, we present a fast algorithm for estimating living-body direction. The experiment showed that the proposed method works well in estimating living-body direction with high accuracy in multi-path environment even when the observation time is less than conventional method.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Massive MIMO enables the improvement on the transmission rate without increasing the burden on the signal processing by employing a large number of antennas at a base station. Even if the interference cancellation techniques are not employed, the interference signal can be mitigated thanks to a narrow beam by the massive MIMO transmission. In this paper, an actual propagation channel was measured by using a wideband channel sounder with 96 elements in 2 GHz band at small cell environment. Moreover, we verify the effectiveness of the interference rejection when using antenna sector selection.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes a bidirectional matching technique for Tx and Rx ports in a short-range MIMO system. First, by connecting 180-degree hybrid couplers to a plane symmetrically configured MIMO system, both Tx and Rx ports are decoupled, and channels between them are orthogonalized, that is, the MIMO system is converted into multi orthogonalized SISO systems. Next, matching is done at both Tx and Rx ports of each SISO system based on the theory of conjugate-image impedance. As a result, the transmission power of the short-range MIMO is maximized. Numerical results show that the proposed technique realizes the higher channel capacity than that of conventional eigenbeam-space division multiplexing.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

An intruder detection method by using Multiple Input Multiple Output (MIMO) channels was proposed (MIMO sensor). Although the channel capacity on the MIMO transmission is severely degraded in time variant channels, we can take advantage of this feature in MIMO sensor applications. For the MIMO sensor, the accurate estimation of channel state information (CSI) is essential. Moreover, the transceiver should be simplified from the viewpoint of power saving, and narrowband signals are effective and are used in sensor network systems. In this paper, we propose a new CSI estimation method for arbitrary amplitude and phase modulation schemes for the MIMO sensor. The experimental results using 16 quadrature amplitude modulation (QAM) are shown when considering the intruder detection by the MIMO sensor.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In massive MIMO transmission, implicit beam forming was studied to eliminate channel state information (CSI) feedback. However, it is essential to introduce the calibration circuit which compensates the difference of complex amplitudes between the transmitters and receivers. This paper presents the effectiveness of calibration circuit for massive MIMO transmission by the testbed which implements the calibration circuit, when considering the interference signal.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

The downlink non orthogonal multiple access (NOMA) was proposed by using successive interference cancellation (SIC) at the receiver that enables communication with the terminal over the number of base station antennas. Furthermore, technique using both random beamforming and SIC was proposed. In this paper, we propose the spatial multiplexing for multiple users exceeding degree of freedom at the base station antennas by SIC and zero forcing (ZF). By computer simulation, the proposed method improves the transmission rate compared to the conventional ZF scheme.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

this paper proposes an analog-digital hybrid eigenmode transmission technique for massive short-range MIMO, which utilizes both analog and digital beamformings. In this method, first, a channel matrix in a plane-symmetrically configured MIMO array is block-diagonalized by analog beamforming with hybrid couplers. Then, eigenmode transmission is virtually realized by digital beamforming toward each block-diagonalized sub channel matrix. This approach is geometrically realizable and results in a reduction in the required number of calculations.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper presents a localization method of multiple living-bodies suitable for multi-path environments. The time-variant Multiple-Input Multiple-Output (MIMO) channel is measured and the bistatic MIMO radar estimates multiple target locations from Fourier-transformed channel information. Measurements are carried out in an indoor environment, and it is shown the proposed method can estimate multiple target locations with fairly good accuracy.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Intruder detection method by using time variant Multiple Input Multiple Output (MIMO) channels was proposed (MIMO sensor). It was verified that the antenna height and element spacing suitable for the MIMO sensor by the measurement. It was also shown that 2 x 2 MIMO sensor obtains the higher detection performance compared to 1 x 4 SIMO sensor. However, we conducted only the measurement when considering a person inside the room. In this paper, the performance by 2 x 2 MIMO sensor is evaluated when a person moves near the window. It is shown that distributed antenna arrangement is effective for the high detection performance in indoor and low detection performance in outdoor when considering the person near the window.

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記述言語：日本語   出版者・発行元：電気関係学会東北支部連合大会実行委員会  

DOI： 10.11528/tsjc.2014.0_148

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Intruder detection method by utilizing a time variation of Multiple Input Multiple Output (MIMO) channel (MIMO Sensor) has been proposed. Although the channel capacity on the MIMO transmission is severely degraded in time variant channels, we can take advantage of this feature in MIMO Sensor applications. We have already demonstrated the effectiveness of 2x2 MIMO sensor using 2.4 GHz band at a small room (Size is 50 m(2)). In this paper, we compare the detection probability of SIMO/MIMO sensors when the number of channel responses are same between SIMO/MIMO sensors: The numbers of transmit and receive antennas are 1 and 4 (SIMO), it is clarified that 2 and 2 (MIMO). The measurement was carried out at the room with the size of 140 m(2). From the measured results, 2x2 MIMO sensor obtains the same or higher detection probability compared to 4x1 SIMO sensor regardless of the measured location.

DOI： 10.1587/transcom.E96.B.2499

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes the antenna arrangement for 2 x 2 MEMO (Multiple-Input Multiple-Output) sensor and evaluates the detection performance based on raytracing simulation. In this arrangement, the transmitting and receiving antennas are placed closely. Two types of the arrangement are considered. In the first method, all of the transmitting and receiving antennas are located closely. In the second method, two sets of the antennas are placed separately, and each set has one transmitting and one receiving antennas. The numerical analysis of the indoor propagation based on the raytracing method is carried out. The path distribution and intrusion detection performance with the various antenna arrangements are evaluated for the human positions all over the room. The numerical analysis results show that the proposed antenna arrangements achieve the compact configuration of the sensor antenna system as well as high detection performance.

DOI： 10.1587/transcom.E96.B.2491

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記述言語：英語  

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記述言語：日本語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Parasitic antenna elements with tunable terminations can be used for interference suppression in multi-antenna systems without using the degrees of freedom. The authors have proposed a fast non-iterative algorithm for optimizing the termination conditions. However, this method cannot be used for suppressing the interference from unknown systems since it requires the channel state information. In this paper, a fast non-iterative algorithm based on the correlation matrix, which can be obtained even from unknown interference sources, is proposed for the multi-antenna system with parasitic antenna elements. The correlation matrix including both receiving and parasitic antennas can be estimated from a few observations of the signals even without receiving signals at the parasitic antenna. By using this correlation matrix, the power of the interference with the arbitrary termination conditions can be easily estimated. Therefore, the termination condition, which minimizes the interference power, can be calculated without knowledge of the channel state information or additional estimations. The results of a numerical analysis indicate that proposed method works well in suppressing the interference without the perfect channel state information.

DOI： 10.1587/transcom.E96.B.1945

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In LTE-Advanced heterogeneous networks, a typical cell layout to enhance frequency utilization is to incorporate picocells and femtocells in a macrocell. However, the co-channel interference between the marcocell and picocell/femtocell is an important issue when the same frequency band is used between these systems. We have already clarified how the interference from the femto(macro) cell affects on the macro(femto) cell. In this paper, we evaluate the interference rejection characteristics by an adaptive array with user equipment (UE). The characteristics are evaluated based on the K-factor used in the Nakagami-Race Fading model and the spatial correlation that is obtained in an actual outdoor environment. It is shown that a two-element adaptive array at the macro UE (M-UE) can sufficiently reduce the interference from the femto base station (F-BS) to the M-UE even if the number of total signals exceeds the degrees of freedom of the array.

DOI： 10.1587/transcom.E96.B.1256

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記述言語：英語  

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記述言語：英語  

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記述言語：英語  

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The IEEE 802.11 distributed coordinated function (DCF) adopts carrier sense multiple access with collision avoidance (CSMA/CA) as its medium access control (MAC) protocol. CSMA/CA is designed such that the transmission from any one station does not have priority over any other. In a congested environment with many DCF stations, this design makes it difficult to protect channel resources for certain stations such as when products are used for presentation at exhibitions, which should be protected based on priority. On the other hand, The IEEE 802.11 enhanced distributed channel access (EDCA) provides a quality-of-service (QoS) mechanism for DCF. However in EDCA, transmission opportunities are allocated based on not individual stations but on the defined traffic type of applications. This paper proposes a distributed dynamic resource allocation method that enables control of flexible bandwidth allocation to each specific station. The proposed method controls the priority level and can coexist with conventional CSMA/CA. Moreover, the proposed method improves the system throughput. Specifically, under the coexistence environment with DCF stations, the proposed method is able to obtain up to over 300% higher user throughput characteristic compared to the case in which the proposed method is not introduced. In addition, under non-coexistence environment, all the proposed stations achieve 70% higher throughput than DCF stations when the number of stations in a network is 50.

DOI： 10.1587/transcom.E96.B.419

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Concept of very large MIMO (VL-MIMO) has recently been proposed. In this paper, basic performance of VL-MIMO is investigated when considering the small cell such as phantomcell. An optimal radio frequency which is suitable VL-MIMO is evaluated when changing the cell size in the phantomcell. Moreover, it is shown that the channel capacity by Maximum Ratio Combining is compared with that by Zero Forcing algorithm when changing the number of interfering signals.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

A spatial division multiplexing (SDM) transmission method utilizing the characteristics of two-ray fading without relying on narrow beam of the antennas is introduced. This letter formulates the optimized array antenna arrangements and channel capacity as functions of the transmission distance and shows achievable channel capacity for two-and three-element antenna arrays. The letter also describes bandwidth dependency up to 15% bandwidth based on an assumed application to 60-GHz-band gigabit wireless systems. The proposed method provides increased capacity comparable to multiple-input-multiple-output (MIMO) transmission without the extra signal processing cost incurred when using conventional MIMO.

DOI： 10.1109/LAWP.2013.2294454

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In LTE-Advanced heterogeneous networks, a typical cell layout to enhance frequency utilization is to incorporate picocells and femtocells in a macrocell. However, the co-channel interference between the marcocell and picocell/femtocell is an important issue when the same frequency band is used between these systems. In this paper, we evaluate the interference rejection characteristics by an adaptive array for user equipment (UE) with Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) algorithms. The characteristics are evaluated based on the K-factor used in the Nakagami-Race Fading model and the spatial correlation that is obtained in an actual outdoor environment. It is shown that a two-element adaptive array at the macro UE (M-UE) can sufficiently reduce the interference from the femto base station (F-BS) to the M-UE even if the number of total signals exceeds the degrees of freedom of the array. Moreover, 1.5 dB SINR difference is observed when comparing ZF and MMSE algorithms when the number of interfering signals is two.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes a wireless sensor network system in a rocket and describes the architecture of sensor tags. The proposed health monitoring system based on the wireless sensor network employs MIMO communication systems, dual-band; 5GHz for downlink and 24GHz for uplink, and dual power sources; vibration and electromagnetic. The paper also demonstrates a GaAs pHEMT 20-30 GHz band low-power consumption amplifier MMIC for the sensor system. At 1V supply voltage, the amplifier achieves a gain of 11.4dB at 24.5GHz. The power consumption and the output 1-dB compression point are 6.16mW and -0.8dBm, respectively. The MMIC achieves the highest performances of reported 24-GHz amplifier ICs.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Multi-user MIMO (MU-MIMO) improves the system channel capacity by employing the transmission between a base station and multiple user terminals (UT). Block Diagonalization (BD) has been proposed in order to realize MU-MIMO broadcast. The BD algorithm cancels inter-user interference by creating the weights so that the channel matrixes for the other users are set to be zero matrixes. However, when the number of transmit antennas is equals to the total number of received antennas, the transmission rate by the BD algorithm is decreased. In this paper, we propose the antenna selection method to reduce the number of nulls for the other users except an intended user by the BD algorithm. It is verified that the proposed method is effective compared to the conventional BD algorithm, especially, when the number of users is increased with a low bit rate.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

We investigated the antenna arrangement suitable for outdoor MIMO (Multiple-Input Multiple-Output) sensor which is used for intruder surveillance application. Detection rate characteristics are evaluated as functions of the height of antenna array in several environments. A channel correlation that compares the MIMO channels with and without a person is used in the intrusion detection algorithm. The experimental results indicated the intruder detection performance is improved by lowering the height of antenna than the height of targets in outdoor environment.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes novel antenna arrangements which improve the channel capacity for 4x4 multiple-input multiple-output (MIMO) system in line-of-sight (LOS) environment. It is shown that the channel matrix is unitary matrix by the proposed antenna arrangement and the high channel capacity is obtained by the proposed antenna arrangement with directional antennas even if the multipath signals in indoor scenario are considered.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Controlling interference from the secondary system to the receiver of the primary system is important issues when the secondary system uses the same frequency band in the area of television broadcast system. The reason includes that the secondary system cannot know the interference channel to the primary receiver, which does not have a transmitter. In this paper, we propose the interference control method between primary receiver and secondary system, where a load modulation scheme is introduced to the primary receiver. In this method, the signal from the transmitter station is scattered by switching load impedance at the primary receiver. Also, the secondary system estimates the reflected wave from receiver and estimates the interference suppression weights. Based on the simulation, it is shown that the proposed method is effective in controlling interference between primary receiver and secondary system. © 2013 IEEE.

DOI： 10.1109/APMC.2013.6694873

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

This paper presents the experimental evaluation results of antenna arrangement method for 2×2 MIMO sensor. In the proposed arrangement, all of the transmitting and receiving antennas are located closely. The measurement campaign of MIMO channel in the indoor environment is carried out. The intrusion detection performance with the various antenna arrangements are evaluated for the human positions all over the room. It is found that the proposed antenna arrangement achieves the compact configuration of the sensor antenna system as well as high detection performance. © 2013 IEEE.

DOI： 10.1109/ATC.2013.6698082

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記述言語：日本語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

A fast control method for parasitic antennas based on a noniterative measurement is proposed in this paper. This method uses the channel state information at the receivers and predicts the channel even at the parasitic antennas that have tunable reactances instead of receivers. The channel prediction accuracy is investigated by considering the effect of the noise, and it is found that the channel at the parasitic antennas is well predicted from a few trials without recourse to iterated measurements when the signal to noise ratio is higher than 20 dB. The results of the simulation and measurement show that the interference can be suppressed even when the estimation accuracy is affected by the noise if the number of trials is sufficient. The experimental results demonstrate that the proposed methods achieve a fourfold channel capacity improvement and 10 dB improvement in signal-to-interference-plus-noise ratio (SINR) compared to two antennas without the parasitic antennas.

DOI： 10.1109/TAP.2012.2186217

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper investigates the effectiveness of the multiple input multiple output (MIMO) transmission with the aid of relay nodes by using measured outdoor channel state information (CSI) for the source, relay, and destination which are used in cooperative transmission. Single/multi-user MIMO (SU/MU-MIMO) systems have attracted much attention as the technology enhances the channel capacity with a limited frequency band. In this paper, cooperative transmission using the relay station is applied to SU/MU-MIMO systems: Relay MIMO transmission. Although the performance of relay MIMO transmission is affected by the actual propagation environment, the performance has not yet been investigated using measured propagation channel data in outdoor scenarios. In this paper, we demonstrate that the channel capacity with the relay MIMO transmission can be improved compared to the conventional MIMO transmission without the relay nodes, especially in multi-user scenarios. Moreover, orthogonal polarization is introduced and its effectiveness is shown in further improving the channel capacity of relay MIMO transmission.

DOI： 10.1109/TAP.2011.2173434

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Short-range Multiple-Input-Multiple-Output (SR-MIMO) transmission is an effective technique for achieving high-speed and short-range wireless communication. With this technique, however, the optimum aperture size of array antennas grows when the transmission distance is increased. Thus, antenna miniaturization is an important issue in SR-MIMO. In this paper, we clarify the effectiveness of using dual-polarized planar antennas as a means of miniaturizing SR-MIMO array antennas by measurements and analysis of MIMO transmission characteristics. We found that even in SR-MIMO transmission, the use of dual-polarized transmission enables higher channel capacity. Dual-polarized antennas can reduce by two thirds the array area that is needed to obtain the same channel capacity. For a transmission distance of two wavelengths, the use of a dual-polarized antenna improved the channel capacity by 26 bit/s/Hz while maintaining the same number of transmitters and receivers and the same antenna aperture size. Moreover, dual-polarized SR-MIMO has a further benefit when zero-forcing (ZF) reception without transmit beamforming is adopted, i.e., it effectively simplifies hardware configuration because it can reduce spatial correlation even in narrow element spacing. In this work, we confirmed that the application of dual-polarization to SR-MIMO is an effective way to both increase channel capacity and enhance transceiver simplification.

DOI： 10.1587/transcom.E95.B.87

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

This paper proposes an intruder detection method using Multiple Input Multiple Output channel, MIMO Sensor. Although the channel capacity on the MIMO transmission is severely degraded in time variant channels, we can take advantage of this feature MIMO Sensor applications. We have already demonstrated the effectiveness of 2×2 MIMO sensor using 2.4GHz band at a small room (Size is 50m 2). In this paper, we compare the detection probability of SIMO/MIMO sensors using the measured propagation channels at the room with the size of 140m 2. From the measured results, It is confirmed that 400MHz band is appropriate compared to 2.4 GHz band due to its lower propagation path loss. Moreover, 2×2 MIMO sensor obtains the higher detection probability compared to 4×1 SIMO sensor regardless of the measured location. © 2012 IEEE.

DOI： 10.1109/EuCAP.2012.6206250

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In emergency situations, first responders must possess the means to communicate vital information, such as the number of patients requiring immediate medical attention, -and their precise locations, as quickly and efficiently as possible, to fire and rescue-, and police departments, as well as city officials. For these situations, we developed a mobile terminal incorporating a GPS, as well as an RFID reader. The objectives of our current research are to develop; 1) -a mobile terminal for use in disaster areas; 2) a robust "Web-GIS" platform to disseminate patient information to medical teams, during a disaster.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In the short range MIMO transmission, an optimal element spacing, which maximizes the channel capacity, exists, when the transmit distance between the transmitter and receiver is given. We focus on that the weight by a zero forcing (ZF) at the optimal element spacing can be realized by using 90-degree phase shifters and dividers because the matrix of weight by the ZF at the optimal element spacing can be expressed as the unitary matrix. In this paper, we propose the simple decoding method for short range MIMO transmission by using analog devices. Moreover, it is shown that the proposed method is effective by the evaluation via Bit Error Rate.

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Short-range multiple-input and multiple-output (SR-MIMO) has attracted much attention, because the technique makes it possible to raise channel capacity to several hundred Gbit/s by utilizing the millimeter-wave band (e.g., 60 GHz band). Although the opposed transceiving antennas are assumed to be accurately positioned in previous studies regarding SR-MIMO, a very important issue is to evaluate the performance degradation due to displacement between MIMO transceivers. In SR-MIMO over the millimeter-wave band, any displacement is perceived as significant because the wavelength is small. This paper evaluates the influence on SR-MIMO transmission performance over millimeter-wave caused by displacement between the transmitting and receiving antennas. The channel capacity is found to degrade by 5% when the horizontal displacement is 1 mm and by 2.7% when the rotational displacement is 10 degrees. In addition, comparing performances obtained with a number of antenna array arrangements clarifies that a square pattern arrangement is suitable for short-range wireless transmission.

DOI： 10.1587/transcom.E94.B.2891

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper discusses the possibility of deploying a short-range cognitive radio (secondary communication system) within the service area of a primary system. Although the secondary system interferes with the primary system, there are certain locations in the service area of the primary system where the cognitive radio can reuse the frequency of the primary system without causing harmful interference to it and being disturbed by the primary system. These locations are referred to as having a spatial opportunity for communications in the secondary system, since it can reuse the frequency of the primary system. Simulation results indicate that the antenna gain, beamwidth, and propagation path loss greatly affect the spatial opportunity of frequency reuse for the secondary users. The results show that spatial spectrum reuse can be significantly increased when the primary system users are equipped with directional antennas. An important component in this study is the heterogeneous path loss model, i.e., the path loss model within the primary system is different from the model used to calculate the interference between the primary and the secondary systems. Our results show that the propagation models corresponding to the actual antenna heights in the primary/secondary system can largely impact the possibilities for spectrum reuse by the cognitive radios.

DOI： 10.1587/transcom.E94.B.1243

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes a power saving control method for battery-powered portable wireless LAN (WLAN) access points (APs) in an overlapping basic service set (OBSS) environment. The IEEE802.11 standard does not support power saving control for APs. Some conventional power saving control methods for APs have been proposed that use the network allocation vector (NAV) to inhibit transmission at stations (STAs) while the AP is sleeping. However, since with these approaches the actual beacon interval in the OBSS environment may be extended due to the NAV as compared to the beacon interval which is set at the AP, the power consumption and delay may be increased as compared to a single BSS unaffected by interference from neighboring APs. To overcome this problem, this paper introduces a new action frame named power saving access point (PSAP) action frame which the AP uses to inform STAs within its BSS about the AP's sleep length. In addition, a function of the PSAP action frame is that STAs enter the sleep state after receiving the PSAP action frame. The proposed control method avoids the postponement of beacon transmission and reduces the power consumption in an OBSS environment, as compared to the conventional control method. Numerical analysis and computer simulation reveal that the newly proposed control method conserves power as compared to the conventional control method. The proposed control method achieves the minimum consumed power ratio at the AP, which is 44% as compared to the standard, when the beacon interval is 100 ms and the sleep length is 60 ms, even if the number of neighboring APs in an OBSS environment is increased.

DOI： 10.1587/transcom.E94.B.658

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper investigates a transmission scheme that is suitable for short-range multiple-input-multiple-output (MIMO) transmission. Since the distance between two array antennas that face each other is comparable with the size of the array antenna aperture in short-range MIMO, the propagation characteristics are greatly different from those in conventional MIMO. Unlike conventional MIMO, the optimal element spacing, which maximizes channel capacity, exists in short-range MIMO. Moreover, the channel capacity with optimal antenna spacing exceeds the ergodic capacity of independent identically distributed (i.i.d.) channels since optimal eigenvalue distribution, which can maximize channel capacity, is obtained in the short-range MIMO. In this paper, we focus on the actual transmission methods, because complex transmission schemes such as eigenmode transmission or maximum-likelihood detection are required to obtain ideal channel capacity. We clarify that the channel capacity obtained by zero forcing (ZF) at the receiver without beamforming at the transmitter is almost the same as that using eigenmode transmission when considering the optimal element spacing. The effectiveness of short-range MIMO communication is also clarified using a 4 x 4 MIMO testbed with actual signals based on the IEEE 802.11n standard. Simulated and measured results show that optimal element spacing is a key parameter in the short-range MIMO communication. We found that designing antenna arrays with optimal element spacing is a very effective approach to achieving a simple hardware configuration.

DOI： 10.1109/TVT.2011.2113196

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

In this paper, a novel decoupling technique suitable for a compact array antenna is proposed. In this technique, an orthogonal excitation weight in MISO channel between 2 x 1 antennas are utilized. The simulation results demonstrate the excellent isolation and matching characteristics can be obtained when the proposed decoupling technique is applied to a compact three inverted-F array. Also, the proposed technique offers high radiation efficiency over the broad bandwidth. © 2011 IEEE.

DOI： 10.1109/URSIGASS.2011.6050541

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes interference cancellation that utilizes relay stations (RSs). In Long Term Evolution (LTE)-Advanced, heterogeneous networks in which femto and picocells are overlaid onto macrocells are extensively discussed. However, interference between macro and pico(femto) cells arises due to their different transmit power levels. Unlike conventional cooperative transmission schemes, the RS decodes interference in the first transmit timing period and forwards it to the user equipment (UE) in the second period. Moreover, cooperative transmission can be achieved without stopping the transmission from the base station (BS) to UE when forwarding the interference from the RS to the UE by utilizing the fact that signal to noise power ratio (SNR) between the RS and UE is much greater than that between the BS and UE. The effectiveness of the proposed method and the optimal relay arrangement are shown based on computer simulation when considering heterogeneous pathloss models.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes a channel capacity maximization method for Multiple-Input Multiple-Output (MIMO) antennas with parasitic elements. Reactive terminations are connected to the parasitic elements, and the reactance values are determined to achieve stochastically high channel capacity for the environment targeted. This method treats the S-parameter and propagation channel of the antenna, including the parasitic elements, as a combined circuit. The idea of the 'parasitic channel,' which is observed at the parasitic antenna, is introduced to simplify the optimization procedure. This method can significantly reduce the number of necessary measurements of the channel for designing the antenna. As a design example, a bidirectional Yagi-Uda array, which has two driven antennas at both ends of the linear array, is measured in an indoor environment. The resulting design offers enhanced channel capacity mainly due to its improved signal-to-noise ratio compared to the antenna without the parasitic antennas.

DOI： 10.1587/transcom.E93.B.2578

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記述言語：日本語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes an interference avoidance technique that allows wireless device with similar frequency bands to be operated adjacent to each other for compact mobile wireless routers (MWRs). This MWR implements two devices of Wireless LAN (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX). The MWR connects WLAN terminals to the backbone network by using WiMAX-WLAN relay. Generally, different frequency channels are assigned for the wireless systems assign in order not to interfere among multiple systems. However, mutual system interference is generated if the space between each device is very close and if the frequency using each system is adjacent. To suppress this interference, this paper proposes a novel interference avoidance technique that leverages IEEE802.1 In Power Save Multi-Poll (PSMP). First, we clarify the conditions that raise the issues of mutual interference by experiment. Simulations are conducted to show that the proposed scheme outperforms the conventional schemes. Finally, the effectiveness of the proposed scheme is shown by the computer simulation.

DOI： 10.1587/transcom.E93.B.2053

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Multi-user multiple input multiple output (MU-MIMO) systems have attracted much attention as a technology that enhances the total system capacity by generating a virtual MIMO channel between a base station and multiple terminal stations. Extensive evaluations are still needed because there are many more system parameters in MU-MIMO than in single user (SU)-MIMO and the MU-MIMO performance in actual environments is still not well understood. This paper describes the features and effectiveness of a 16 x 16 MU-MIMO testbed in an actual indoor environment. Moreover, we propose a simple adaptive modulation scheme for MU-MIMO-OFDM transmission that employs a bit interleaver in the frequency and space domains, We evaluate the frequency efficiency by obtaining the bit error rate of this testbed in an actual indoor environment. We show that 16x4x4-user MU-MIMO transmission using the proposed modulation scheme achieves the frequency utilization of 870 Mbps and I Gbps (respective SNRs: 31 and 36 dB) with a 20-MHz bandwidth.

DOI： 10.1587/transcom.E93.B.345

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Multiple-Input Multiple-Output (MIMO) wireless communication technology has been expected to improve the channel capacity with a limited bandwidth for the future networks. Since the propagation environment or the propagation channel becomes very complex, it is difficult to simply estimate the channel capacity in urban MIMO systems. Hence, we introduce the characteristics of channel capacity in urban MIMO system by using a ray-tracing method. The simulation by this method with variable parameters can estimate various urban propagation characteristics and discriminate the effects of the urban model and antenna configurations. Moreover, we introduce path visibility, which is defined as the probability that at least one of the antenna elements of the mobile terminal (MT) can receive the direct wave when considering the downlink scenario, in order to make a measure in urban MIMO systems. It is represented in this study that the characteristics of the channel capacity can be figured out directly from the path visibility by the ray-tracing simulation. It also gives the guidance that the appropriate range of the base station (BS) antenna height can be determined from the path visibility. © 2010 IEEE.

DOI： 10.1109/RWS.2010.5434149

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

In microwave frequency bands, we have found that the application of spatial division multiplexing (SDM) using a number of antenna arrays is particularly effective for short transmission distances. We were also able to raise channel capacity in short-distance communication to several hundred Gbit/s by utilizing parallel transmission over a 60-GHz band with its wide bandwidth. When utilizing this technology, displacement of TX and RX antennas occurs because of the need to adjust the position of antennas manually by users. Antenna displacement causes deterioration in channel capacity. Electromagnetic field analysis results clarified the impact on channel capacity of antenna displacement that occurs in short-range transmission applications. Our results showed that channel capacity degradation is 10% when the horizontal antenna displacement is 1.5 mm and channel capacity degradation is only 2.7% when the rotational antenna displacement is 10°. The channel capacity degradation is smaller with longer transmission distances. © 2010 IEEE.

DOI： 10.1109/RWS.2010.5434243

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

System studies are being conducted at millimeter-wave frequency for high-speed wireless communications such as several Gbit/s. However, the highly rectilinear propagation characteristics of these systems, created by the millimeter-wave frequencies, place significant limitations on the applications and the usage environments. To address this problem, we already proposed the adoption of a high data-rate relay system using short range multi input multi output (MIMO) transmission technology. This paper reports the results of experiments conducted to verify the simulation method. We evaluate 4x4 MIMO transmission, using the signal specified by IEEE 802.11n, and confirm that the optimal array spacing. The measured and simulated frequency utilization rates of 4x4 MIMO transmission are in good agreement. Frequency utilization of over 20 bits/s/Hz can be achieved: 800Mbps/1.6Gbps transmission can be realized when the bandwidth of 40/80 MHz is assumed. Moreover, the measured and simulated results indicate higher frequency utilization rates than found in the i.i.d. channel. © 2010 IEEE.

DOI： 10.1109/RWS.2010.5434178

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Multiuser-Multiple Input Multiple Output (MU-MIMO) techniques were proposed to increase spectrum efficiency; a key assumption was that the Mobile Terminals (MTs) were simple with only a few antennas. This paper focuses on the Block Diagonalization algorithm (BD) based on the equal power allocation strategy as a practical MU-MIMO technique. When there are many MTs inside the service area of the access point (AP), the AP must determine, at each time slot, the subset of the MTs to be spatially multiplexed. Since the transmission performance depends on the subsets of MTs, the user selection method needs to use the Channel State Information (CSI) obtained in the physical layer to maximize the Achievable Transmission Rate (ATR). In this paper, we clarify the relationship between ATR with SU-MIMO and that with MU-MIMO in a high eigenvalue channel. Based on the derived relationship, we propose a new measure for user selection. The new measure, the eigenvalue decay factor, represents the degradation of the eigenvalues in null space compared to those in SU-MIMO; it is obtained from the signal space vectors of the MTs. A user selection method based on the proposed measure identifies the combination of MTs that yields the highest ATR; our approach also reduces the computational load of user selection. We evaluate the effectiveness of user selection with the new measure using numerical formulations and computer simulations.

DOI： 10.1587/transcom.E92.B.3206

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper. we propose a novel multiuser detection (MUD) method that is robust against timing offset between wireless terminals (WTs) for the multiuser multiple-input multiple-output (MU-MIMO) orthogonal frequency division multiplexing (OFDM) uplink. In the proposed method, MUD is carried out in the frequency-domain using overlapping fast Fourier transform (FFT) windows. After the inverse FIT (IFFT) operation, the samples obtained at both ends of each FFT window are discarded to suppress the effect of inter-block interference (IBI). Thus, it realizes an MUD regardless of the arrival timing differences of the signals from the WTs. The achievable bit error rate (BER) performance of the proposed MUD method is evaluated by computer simulations in a frequency selective fading channel.

DOI： 10.1587/transcom.E92.B.1582

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Multiple-Input Multiple-Output (MIMO) system has been actively investigated to enhance wireless data transmission in outdoor environments. Micro/Macro-cell services such as WLAN/WiMAX have been much attention because they achieve a high throughput. Since proliferation of these services are expected, base stations (BSs) need to be located at various heights and locations in outdoor environments. Although many publications have reported measurements of the channel state information (CSI) in outdoor environments, the relationship between the BS heights or locations and the transmission performance in MIMO systems has not yet been fully investigated. Moreover, when the number of BSs increases per area, inter-cell interference problem occurs. Such an interference deteriorates the communication quality. In this paper, the experiment is conducted in urban area, in Japan, and the CSI was obtained using 4x4 MIMO-OFDM signals. We present signal to noise ratio (SNR), channel capacity and eigenvalues in MIMO channels, when the BS heights and locations are changed. We clarify that eigenvalues are one of important parameters for not only the channel capacity in MIMO channels but also inter-cell interference by the analysis using the measured MIMO channels.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Various technologies have been put to practical use for high-speed wireless communications systems. For short transmission distances, we have found that the application of spatial parallel transmission using a number of antenna arrays is particularly effective in microwave frequency bands. This report describes how we were able to raise channel capacity in short distance communication considerably by utilizing parallel transmission over a 60-GHz band with its wide bandwidth on the basis of electromagnetic field analysis results. We also clarified the impact on channel capacity of antenna displacement that occurs when placing the antennas. Our results showed that the channel capacity obtained using 20 mm x 20 mm antenna arrays is more than 1,000 Gbit/s when the transmission distance is 1 mm and that channel capacity degradation is 5% when the antenna displacement is 1 mm. The degradation becomes smaller with longer transmission distances.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In this paper, a novel communication scheme, which uses short range MIMO transmission, is introduced and evaluated. In this scheme, two facing array antennas are placed closely within the severalfold distance of the aperture width. When the distance between the transmitting and receiving array antennas is short enough, the array antenna with the optimally narrow element spacing can give high signal-to-noise ratio, and fairly low spatial correlation. It is found that the channel capacity with the optimal antenna spacing is higher than the ergodic capacity of the i.i.d. channel since the near-field MIMO scheme has a high similarity with a parallel data transmission.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Recently, the Multiuser Multiple input Multiple Output (MU-MIMO) System has attracted much attention as a technology that enhances the total system capacity by generating a virtual MIMO channel between a base station and multiple terminal stations. Although extensive evaluations are needed because the number of system parameters in MU-MIMO is much larger compared to the Single User (SU)-MIMO, the performance of MU-MIMO in actual environments is still not well understood. This paper describes the features and effectiveness of a 16 x 16 Multi-user (MU)-MIMO testbed in an actual indoor environment. Moreover, we propose a simple adaptive modulation scheme for MU-MIMO-OFDM transmission that employs a bit interleaver for the frequency and space domains. Finally, we evaluate the frequency efficiency by obtaining the bit error rate of this testbed in an actual indoor environment. We clarity that 16 x 4 x 4-user MU-MIMO transmission using the proposed modulation scheme achieves the frequency utilization of 870 Mbps and 1Gbps (SNR: 31 and 36 dB) with 20MHz bandwidth, respectively.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes an antenna selection method for terminal antennas employing orthogonal polarizations and patterns, which is suitable for outdoor MultiUser Multi-Input Multi-Output (MU-MIMO) systems. In addition, this paper introduces and verifies two other antenna selection methods for comparison. For the sake of simplicity, three orthogonal dipoles are considered, and this antenna configuration using the proposed selection method is compared to an antenna configuration with three vertical or horizontal dipoles. In the proposed antenna selection method, we always choose the vertical dipole, and choose one of two horizontal dipoles, which are orthogonal to each other, based on the Signal-to-Noise Ratio (SNR). We measured the MU-MIMO transmission properties and found that the proposed selection method employing the antenna with orthogonal polarizations and patterns can offer fairly high channel capacity in a multiuser scenario.

DOI： 10.1093/ietcom/e91-b.6.1752

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

This paper proposes a new interference cancellation/avoidance scheme for secondary spectrum usage, which takes advantage of the features of Time Division Duplex (TDD) based primary systems. We focus on the co-existence between the heterogeneous systems, where the primary and the secondary are using the same spectrum simultaneously. The secondary systems have to accurately find the possible interference from/to the primary systems for discreet and efficient secondary transmission. In order to judge the arrival of interference from/to the primary system, the secondary access point (AP) compares the difference in power between the up and downlink signals in TDD-based primary systems. This scheme enables the secondary AP to know the level of interference from the primary systems that arrives at the AP without employing complex signal detection. The proposed scheme also determines the level of interference induced to the primary system by measuring the difference in power. To cancel and avoid interference in the proposed scheme, we introduce an adaptive array at only the AP that creates a null toward the interference with a higher power level between the up and downlink signals. Moreover, new algorithms by using scheduling information of the multiple primary nodes are introduced in the proposed method, in order to enhance the transmission quality of a secondary mobile station (MS) while maintaining a simple control scheme for the MS. Finally, we verify the effectiveness of the proposed method based on computer simulations.

DOI： 10.1007/s11277-008-9472-7

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

This paper proposes a novel interference cancellation technique using the concept of a distributed array, for the secondary use of the frequency resources in frequency division duplexing (FDD)-based cellular systems. In order to achieve efficient distributed interference cancellation, the secondary system exploit intervals for periodic training signals transmitted by FDD-time division multiple access (TDMA)-based cellular systems. We show that an efficient interference cancellation can be achieved by introducing helpers that decode the interference and transfer it to the secondary nodes. We take advantage of the high-speed links within the secondary system and devise a data compressing scheme that reduces time for transferring the decoded interference. We clarify the effectiveness of the proposed scheme by using computer simulation. As a parameter, the transmission quality between the helper and secondary nodes is varied. The results indicate that the proposed distributed interference cancellation is effective compared to a conventional adaptive array using a zero forcing algorithm, when the signal to noise ratio between the helper and the target secondary node is greater than 20 dB. ©2008 IEEE.

DOI： 10.1109/ICC.2008.573

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

The application of the multiuser multiple-input multiple-output (MIMO) technique with orthogonal frequency division multiplexing (OFDM) signal transmission to future wireless communications systems has attracted much attention. In the uplink, the difference in the arrival timings among the signals from multiple wireless terminals (WTs) causes significant transmission quality degradation. In this paper, we propose a novel multiuser detection (MUD) technique that overcomes this problem. The proposed method discards the samples at both ends of each fast Fourier transform (FFT) window. In addition, it overlaps the FFT windows to recover all consecutive samples. Thus, it enables a signal separation regardless of the difference in the arrival times among WTs with an acceptable level of calculation complexity. The achievable bit error rate (BER) performance of the proposed MUD method is evaluated by computer simulation in a frequency selective fading channel. The results show that compared to the conventional method the proposed MUD method reduces the required Eb/N0 by 2.6 dB to achieve the BER of 10-4, when 16QAM and rate 2/3 convolutional codes are used. © 2008 IEEE.

DOI： 10.1109/VETECS.2008.344

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

The application of the multiuser multiple-input multiple-output (MIMO) technique with orthogonal frequency division multiplexing (OFDM) signal transmission to future wireless communications systems has attracted much attention. In the uplink, the difference in the arrival timings among the signals from multiple wireless terminals (WTs) causes significant transmission quality degradation. In this paper, we propose a novel multiuser detection (MUD) technique that overcomes this problem. The proposed method discards the samples at both ends of each fast Fourier transform (FFT) window. In addition, it overlaps the FFT windows to recover all consecutive samples. Thus, it enables a signal separation regardless of the difference in the arrival times among WTs with an acceptable level of calculation complexity. The achievable bit error rate (BER) performance of the proposed MUD method is evaluated by computer simulation in a frequency selective fading channel. The results show that compared to the conventional method the proposed MUD method reduces the required E(b)/N(0) by 2.6 dB to achieve the BER of 10(-4), when 16QAM and rate 2/3 convolutional codes are used.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Multiuser multiple input multiple output (MU-MIMO) systems are attracting attention due to their frequency efficiency. However, in uplink MU-MIMO systems, different frequency offsets among multiple mobile stations (MSs) significantly degrade the transmission quality, especially when orthogonal frequency division multiplexing (OFDM) is used. In this paper, the influence of these frequency offsets is first analyzed in a frequency selective fading environment. Numerical analysis shows that an error floor occurs in the bit error rate and the influence of the frequency offset becomes larger in short delay spread environments. To overcome this problem. a new beamforming method is proposed to compensate for the frequency offset by introducing an auto frequency controller after frequency-space equalization in each data stream. The effect of the proposed method is evaluated in a frequency selective fading environment by computer simulations and measured results.

DOI： 10.1093/ietcom/e90-b.9.2312

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Multiple input multiple output (MIMO) systems represent a very attractive candidate for future high data rate wireless access systems to increase the channel capacity. To obtain a further increase in the Channel capacity, a distributed wireless communication system that has multiple access points (APs) and an access controller (AC), was proposed. This system increases not only the peak transmission rate but also the overall transmission rate in the service area. In this paper, we consider a cooperative multiple AP system where APs are synchronized in terms of time, but not in terms of phase. We propose a transmission method for the cooperative multiple AP system that enables the mobile station to obtain a high achievable bit rate regardless of decoding algorithms. The performance of the multiple AP systems is evaluated in comparison to the conventional single AP system. To evaluate the effectiveness of the proposed method in the cooperative multiple AP system, computer simulations are performed using the i.i.d. channel in Rayleigh and Ricean fading environments. Furthermore, we evaluate the performance of the cooperative multiple AP system using the channel measured in an actual indoor environment.

DOI： 10.1093/ietcom/e90-b.9.2303

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

This paper proposes a novel interference cancellation scheme that utilizes relay stations in multi-user transmission systems. Unlike conventional relay transmission schemes, the relay stations are used to decode the interference and transfer the pertinent information to the mobile stations. The proposed method takes advantage of the training signals and frame format of the interference at a neighboring cell when time division multiple access (TDMA) systems are applied. Even if external interference simultaneously arrives at the mobile stations during the transmission period from an access point to the mobile stations, the mobile stations employing the proposed scheme can effectively cancel the external interference because the relay station transfers the information related to the interference to the mobile stations. Moreover, we show that the proposed scheme improves the transmission efficiency compared to that for multi-user transmission without interference cancellation or with interference cancellation based on zero forcing algorithm when TDMA-based external interference is considered. (6 pages).

DOI： 10.1049/ic.2007.1327

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In this paper, the possibility for a short-range cognitive radio (secondary communication system) to be located within the service area of the primary system is discussed. Although the secondary system interferes with the primary system, there can be certain locations in the service area of the primary system where the cognitive radio can reuse the frequency of the primary system without disturbing it or being disturbed by the primary system. We say that in those locations there is a spatial opportunity for communication in the secondary system. The primary and secondary systems have different features and usage scenarios, which result in different deployment conditions. This gives rise to differences between the path loss for a link in the primary system and the path loss for the interference from the primary to secondary systems. This paper investigates the impact of the heterogeneous path loss conditions on the spatial opportunity for the secondary system. Our approach can be applied as a general way to investigate the coexistence among multiple systems. We clarify that the change of the path loss coefficient due to the different antenna heights of the primary and secondary systems can largely affect the spatial opportunity for frequency reuse by the cognitive radios.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

The multiple input multiple output (MMO) technique enables the application of spatial multiplexing as a way of increasing the spectrum efficiency. However, only a few antenna branches are allowed at a simple mobile terminal (MT) and the MMO effect is limited for those MTs. Multiuser (MU)-MIMO techniques were proposed to support such simple terminals to overcome such problems. Among them, the block diagonalization algorithm is well known as a practical linear precoding technique for downlink in the MU-MIMO systems. Because the number of users supported by the access point is limited and the improvement in the spectrum efficiency greatly depends on the combination of spatially multiplexed user, a simple transmission performance estimation method is needed.
In this paper, we propose a new capacity estimation method for MU-MIMO systems. The proposed method estimates the achievable bit rate in MU-MIMO while significantly reducing the calculation load compared to that for direct estimation in the block diagopalization algorithm. Theoretical analysis and the simulation results confirm the validity of the proposed method.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SCRIPTA TECHNICA-JOHN WILEY & SONS  

In this paper, a new SDMA (Space Division Multiple Access) configuration is proposed in which the number of multitudes of SDMA can be increased by using dual polarization antennas at both the smart antenna base stations and the mobile terminals. In the proposed configuration, the smart antennas at the base stations constantly monitor the mutual correlations between the mobile terminals at the time of reception. Then, the polarization (vertical or horizontal) to be transmitted by each mobile terminal is determined in such a way that the mutual correlation between the mobile terminals connected at the same time is minimized. The mobile terminal used in the proposed system has a configuration in which the antennas with vertical and horizontal polarizations can be switched for transmission. Transmission is carried out with the polarization specified by the base station. The proposed configuration is expected not only to improve spatial division capability of SDMA by the smart antenna base station with vertical and horizontal polarizations but also to compensate the deterioration of the transmission quality along with the increase of multiplicity of SDMA by means of the switching configuration of the transmission polarization of the mobile terminal while the interference between the mobile terminals is taken into account. The proposed configuration call be applied to the uplinks in the TDD or FDD channels. By means of the numerical simulation, the basic characteristics of the proposed configuration are clarified in the case where the cross polarization discrimination (XPD) and the number of mobile terminals vary. In this way, it is demonstrated that the mobile terminal discrimination capability is improved over the conventional SDMA with the vertical polarization and the system is useful for increased multiplicity of SDMA. Further, the propagation characteristics (amplitude and phase) of the vertical and horizontal polarizations are obtained when the base station antenna and the mobile terminal antenna are placed oil a steel tower and on a vehicle, respectively. The characteristics of the proposed configuration are presented where several mobile terminals exist. Usefulness of the proposed configuration in all actual environment for increased multiplicity of SDMA is presented. (C) 2006 Wiley Periodicals, Inc.

DOI： 10.1002/ecja.20287

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes a simple antenna switching and a relay technique for cognitive radios using adaptive array antenna to effectively reduce the interference from the primary system. While the adaptive array antenna can create null towards the direction of primary system, the created antenna pattern can result in non-optimized pattern between cognitive nodes. In order to solve such a problem, this paper first introduces a simple antenna pattern switching. With this technique, each cognitive radio node is equipped with three antennas and each node tries to select the antenna configuration resulting in the best antenna pattern for each link. Furthermore, we propose a combination between the above simple antenna switching and the interference-induced multi-hop transmission where the multi-hop transmission is utilized when a link in the network suffers from the low transmission quality due to the created antenna pattern. Our numerical results show that the proposed techniques can significantly improve the achievable data rate in cognitive networks.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

In this paper we investigate the problem of spectrally efficient operation of a cognitive radio (CR), also called Secondary System (SS), under an interference from the primary system (PS). A cognitive receiver (CRX) observes a multiple (MA) access channel of two users, the secondary and the primary transmitter, respectively. We advocate that the SS should apply Opportunistic Interference Cancellation (OIC) and decode the PS signal when such an opportunity is created by the rate selected in the PS and the power received from the PS. We derive the achievable data rate in the SS when OIC is applied. When the PS is decodable, we devise a method applied by the SS to achieve the maximal possible secondary rate. This method has a practical significance, since it enables rate adaptation without requiring any action from the PS. We investigate the power allocation in the SS when OIC is applied over multiple channels. We show that the optimal power allocation can be achieved with intercepted water-filling instead of the conventional water-filling. The results show a significant gain for the rate achieved by OIC.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Experimental results are presented for an 8 x 2 multiple-input multiple-output (MIMO) channel in an actual cellular environment. This paper focuses in particular on the characteristics of the channel capacity based on the number of antennas and the difference in antenna polarizations, i.e., vertical, vertical and horizontal, and slanted +/- 45 degrees, at both the base and the terminal stations. The antenna configuration with the +/- 45 degrees slanted polarization achieves the highest channel capacity when the number of array antennas is less than four at the signal-to-noise ratio (SNR) from 5 to 40 dB in an actual outdoor environment. Moreover, we onfirni that the most effective antenna configuration changes based on the SNR or the number of antennas at the base station.

DOI： 10.1109/TAP.2006.883967

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

To achieve a very high data rate within a limited frequency band in orthogonal frequency division multiplexing (OFDM) systems, multi-input multi-output (MIMO) techniques are very promising. Moreover, if a transmitter has the channel state information (CSI), the achievable spectrum efficiency can be maximized using the eigenbeam-space. division multiplexing (E-SDM). However, this scheme demands accurate channel estimation. Therefore, in a closed-loop transmission scheme, an increase in the amount of feedback is absolutely necessary for the E-SDM. This paper describes a downlink beamforming method that significantly reduces the amount of feedback needed by using the common transmission weight vectors in all sub-carriers, compared to the amount required for E-SDM. The proposed method also applies transmission diversity to compensate for the quality. The effectiveness of the proposed method was confirmed using computer simulations in both Ricean and Rayleigh fading environments.

DOI： 10.1093/ietcom/e89-b.8.2170

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Multiple Input Multiple Output (MIMO) systems have attracted much attention as they can provide increased channel capacity within a limited frequency band. In some important applications, such as wireless LAN and cellular systems, MIMO systems will likely operate in environments for which a single base station should simultaneously communicate with many users. Such applications require development of Multiuser(MU)-MIMO techniques. The prior work on MU-MIMO systems have resulted in derivation of the ideal channel capacity as well as various proposed schemes for transmission control and scheduling. In order to incorporate MU-MIMO technologies into commercial systems, extensive evaluations are needed, since the amount of system parameters in MU-MIMO is much larger as compared to the Signleuser(SU)-MIMO. Due to such a volume of system parameters, the performance of MU-MIMO in actual systems is still not well understood. This paper describes MU-MIMO testbed which can deal with 8×8 MIMO-OFDM transmission based on the IEEE802.11a signal format. We have conducted experiments in an actual indoor environment in order to evaluate the frequency utilization for downlink scheme implemented in the MU-MIMO testbed. Finally, we discuss the effectiveness of MU-MIMO for SU-MIMO when the number of receiving antennas is changed. ©2006 IEEE.

DOI： 10.1109/PIMRC.2006.253924

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Multiple input multiple output (MIMO) systems increase the channel capacity within the limited frequency band. MIMO techniques can be combined with orthogonal frequency division multiplexing (OFDM), which is known to combat frequency selectivity in wireless channels. When channel state information (CSI) is available at the transmitter, the eigenvector beamforming method is well known to achieve the maximum channel capacity. However, the performance of eigenvector beamforming, which employs both modulation and forward error correction schemes, is not very well understood. In this paper, we evaluate the channel capacity and the frequency utilization of an eigenvector beamforming method in an actual indoor environment using an 8X4 MIMO-OFDM testbed that we developed. The experiment results indicate that the transmission bit rate increases offered by the eigenvector beamforming method in 4X4 MIMO and 8X4 MIMO channels are 3.83 fold and 4.90 fold larger than the performance of conventional transmission in SISO channel respectively and these ratios are larger than the increases in the channel capacity.

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記述言語：英語  

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1109/APS.2005.1551807

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper investigates the transmission quality of a proposed space division multiple access (SDMA) configuration that employs a smart antenna that adopts vertical pattern and polarization control with terminal polarization assignment in an actual cellular environment in an urban area in Japan. In a sector cell system, we clarified that this configuration is effective based on an evaluation of the spatial correlation characteristics. We also found that the output Carrier to Interference and Noise power Ratio (CINR) of the proposed configuration is from 10 to 17 dB higher than that of the conventional SDMA configuration when the number of users is greater than four. The proposed configuration can reduce the antenna size from 1/15 to 1/60 compared to conventional SDMA.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SCRIPTA TECHNICA-JOHN WILEY & SONS  

An adaptive array for a frequency division duplex (FDD) system requires calibration among the antennas, the cables, and the transmitters and receivers to form the desired transmission directivity. In this paper, we propose the Automatic Calibration method of adaptive array using Transmitting signals for FDD systems with Linear array (ACT-FL) by using the signal circulation among the antennas and not using any additional elements or external information for calibrating the antennas and cables. By studying the calibration accuracy of the ACT-FL through analysis and tests including the mutual coupling of the antennas, we explain the applicable element spacing and the beam width in ACT-FL. We also evaluate the signal-to-interference power ratio (SIR) at the interference arrival time from radiation pattern measurements by using a testbed implementing ACT-FL and demonstrate the effectiveness of ACT-FL. (C) 2004 Wiley Periodicals, Inc.

DOI： 10.1002/ecjb.20105

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The adaptive base station antenna is an attractive candidate for establishing high-speed and highly-reliable wireless communication systems. From a commercial viewpoint, since the cost and complexity of adaptive antennas depend on the number of elements, optimizing the antenna configuration while considering the propagation environment is necessary to reduce the number of elements. This paper first presents the Angle of Arrival (AOA) characteristics of delayed waves in a street microcell environment, typically used in urban microcell systems. Then the antenna configuration and antenna spacing suitable for the street microcell are investigated utilizing bit error rate (BER) performance simulations using practical delay profiles and AOAs. The effectiveness of bidirectional elements with respect to the BER performance is also investigated. As the results, we found that broadside array with the spacing of 2.5 wavelengths is suitable for adaptive base station antennas for high data-rate wireless systems placed in a street microcell environment. We also found that bidirectional elements alleviate the BER degradation due to the grating lobe of the antenna with wide element spacing without increasing the antenna size.

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes a hardware configuration using only single pole dual throw (SPDT) switches to realize the previously proposed automatic calibration method using transmitting Signals (ACT) for the adaptive array in TDD communication systems. The proposed configuration obtains the same calibration values as the conventional ACT does while reducing the number of switch branches. The transmission pattern using the proposed calibration method is also presented based on an experimental adaptive array testbed in an actual microcell environment. The experimental results show that the ideal radiation pattern formation is achieved by employing the proposed calibration method in an environment with a moving terminal station and where arriving co-channel interference exists.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes a novel adaptive array configuration that reduces high-power co-channel interference (CCI) by utilizing the difference in arrival times between CCI and the desired signal in asynchronous TDD systems. The proposed adaptive array extracts only the CCI and employs pre-null steering for only the CCI by utilizing the fact that only the CCI arrives during the guard time in asynchronous TDD systems. Since the proposed adaptive array enables us to apply the Minimum Mean Square Error (MMSE) algorithm through synchronization with the desired signal using the output signal obtained by pre-null steering, high quality transmission can be achieved even in the presence of high-power CCI. Moreover, based on measurements using a fading simulator and field data, an adaptive array testbed exemplifying the proposed configuration is presented to show the reduction in the high-power CCI.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes a novel space division multiple access system that comprises base station smart antennas and mobile terminals employing a dual-polarized antenna. The smart antennas adaptively control radiation patterns and polarization using a dual-polarized antenna array. Each mobile terminal communicates with the base station by assigning polarization to minimize the interference caused by the other mobile terminals. The simulation results indicate that the proposed system is advantageous in a large capacity cellular environment. Furthermore, we measured vertically- and horizontally-polarized propagation in an urban environment to confirm the actual performance or the proposed system.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes an automatic calibration method for the adaptive array based on transmitting signals for Frequency Division Duplex (FDD) systems with a linear array (ACT-FL). This method utilizes signal circulation between antennas and calibrates transceivers, antennas, and cables between branches without requiring an additional antenna for the calibration. In order to show the effectiveness of ACT-FL, we clarify the calibration accuracy and the element spacing suitable for ACT-FL. The SIR characteristics are also evaluated using an experimental adaptive array testbed in the presence of co-channel interference (CCI).

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes a new digital beamforming adaptive array antenna (DBFAAA) that is effective in severe multipath environments in which timing and carrier synchronization circuits cannot function ideally resulting in the DBFAAA losing control. The proposed DBFAAA has two stages. In the first, the DBFAAA captures the desired signal and establishes synchronization. In the second, the DBFAAA optimizes the beam pattern of the signal. The proposed configuration employs an eigenvector beam of the maximum eigenvalue in the first stage beam-forming. in addition, a fractionally-spaced-tapped-delay-line (FS-TDL) with real tap weights, which is placed after the beam-former, is applied to achieve timing synchronization. The behavior of the proposed DBFAAA for asynchronous sampling data is investigated and the results indicate that the proposed configuration enables asynchronous sampling at the A/D converter. A prototype of the proposed DBFAAA achieving 38-Mbps real-time data communication is introduced and the transmission performance is shown.

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Space-division-mulriple-access (SDMA) is a promising candidate for improving channel capacity in future wireless communication systems. Since the discrimination performance of the user in the spatial domain depends on the array arrangement, an optimum element arrangement for SDMA should be defined. This paper proposes a formula to determine the optimum element arrangement of smart antennas for SDMA systems. The formula is based on spatial correlation. The dependency of the output SINR performance on element arrangements is also evaluated by computer simulation.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

This paper proposes a novel adaptive array configuration that reduces high-power co-channel interference (CCI) by utilizing the difference in arrival time of CCI from the desired signal in an asynchronous TDMA system. The proposed adaptive array extracts only the CCI and employs pre-null steering for only the CCI. Because the Minimum Mean Square Error (MMSE) algorithm can be realized through accurately sampling the timing based on synchronization of the desired signal using the output signal obtained by pre-null steering, a high quality transmission can be realized even in the presence of high-power CCI. Moreover, an adaptive array testbed exemplifying the proposed configuration is described that shows the reduction in the high-power CCI.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

This paper proposes a new adaptive base-station antenna configuration employing an additional switching element that reduces the influence of grating lobes caused by wide inter-element spacing. The influence of fading, the angle spread of incoming waves, and inter-element spacing of the array on the proposed antenna performance is investigated by computer simulation. The output Signal-to-interference and Noise Ratio (SINR) of the proposed antenna compared to the conventional adaptive antenna employing an equilateral triangular array shows a maximum 5-dB improvement when applying the proposed antenna to two-user Space Division Multiple Access (SDMA) systems. © 1999 IEEE.

DOI： 10.1109/VETECF.1999.801733

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electrical and Electronics Engineers Inc.  

This paper proposes a new calibration method for adaptive base station antennas that is suitable for TDD communication systems
it offers real-time calibration. The effectiveness of the proposed calibration method is also demonstrated using an experimental adaptive array testbed. This paper first shows the distortion in the radiation pattern due to the amplitude and phase variations over time. The proposed calibration method is then described. Finally, a comparison of the measured radiation pattern between transmission and reception modes is shown that confirms the effectiveness of the proposed calibration method.

DOI： 10.1109/APS.1999.789586

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：I E E E  

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記述言語：英語  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,バイスタティックMIMO(Multiple Input Multiple Output)レーダを用いたマルチパス環境における生体位置推定法を提案し,実験により評価を行う.本提案法では,MIMOチャネル行列のフーリエ変換より得られる周波数応答行列から生体由来の成分のみを抽出し,MUSIC(MUltiple SIgnal Classification)法を適応することにより送受信アンテナ双方から生体方向を推定する.双方から推定された2つの生体方向の交点から位置推定を行う.実験は屋内環境にて行い,被験者の立ち位置を変化させチャネルを測定した.実験により位置推定誤差を評価した結果,抽出周波数範囲を直流成分の影響を除いた0.03Hz≦f≦1.5Hzとした場合のCDF(Cumulative-Distribution-Function)90%値が0.32mであることが分かり,本提案法によってマルチパス環境下でも精度よく生体位置を推定可能であることを明らかとなった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,マルチアンテナシステムのマイクロ波センサへの応用法について述べる.第1の応用例として侵入者を検出するセキュリティセンサを実現する方法を紹介する.屋内外における評価結果より,MIMO (Multiple-Input Multiple-Output)アンテナシステムの利用はマイクロ波を用いたセキュリティセンサの高感度化に有効であることを示す.第2の応用例として,生体活動を検出する見守りセンサについて述べる.チャネル情報から人物の心拍や呼吸に由来する成分を取り出すことによって,生体の存在を検出できることを示すとともに,これらの情報を活用することによって生体の方向情報を推定が可能であることを示す.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,マルチアンテナシステムのマイクロ波センサへの応用法について述べる.第1の応用例として侵入者を検出するセキュリティセンサを実現する方法を紹介する.屋内外における評価結果より,MIMO (Multiple-Input Multiple-Output)アンテナシステムの利用はマイクロ波を用いたセキュリティセンサの高感度化に有効であることを示す.第2の応用例として,生体活動を検出する見守りセンサについて述べる.チャネル情報から人物の心拍や呼吸に由来する成分を取り出すことによって,生体の存在を検出できることを示すとともに,これらの情報を活用することによって生体の方向情報を推定が可能であることを示す.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

著者らはこれまでMultiple Input Multiple Output (MIMO)チャネルを利用した屋内侵入検出法(MIMOセンサ)を提案している.MIMOセンサでは,伝搬特性の変化がその特性に大きく影響することを利用して,伝搬環境の変化をセンサの入力として利用することを特徴としている.これまでの検討では,狭帯域のMinimu Shift Keying (MSK)信号を用いたMIMOセンサ用伝搬チャネル推定法を提案した.本報告では,この手法をZigbeeなどで使用されている変調方式であるOffset QPSK (Quaternary Phase Shift Keying)に拡張した信号同期法を提案する.MSKではキャリア同期を確保するため,一定の連続したビットを使用していたが,OQPSKではこの方法をそのまま適用できないため,送信信号の位相変化をテーブル化する手法を提案する.また,計算機シミュレーションより提案方法のチャネル推定精度を明らかにする.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,SIMO (Single-Input Multiple-Output)構成マイクロ波センサを用いたマルチパス環境における生体方向推定法を提案し,実験により評価を行う.本提案法では,マイクロ波センサで測定した伝搬チャネル行列のフーリエ変換より得られる周波数応答行列にMUSIC (MUltiple Slgnal Classification)法を適応することにより生体方向を推定する.実験は屋内環境にて行い,被験者の数や立ち位置を様々に変化させてチャネルを測定する.実験結果より,検出対象が1名の場合,検出対象が複数の場合,アンテナ検出対象間距離が離れた場合に関して提案法はマルチパス環境下にて精度よく生体方向が推定可能であることを明らかにする.さらに,アレー素子数を増加させることにより生体方向推定精度が向上することを明らかにする.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

著者らはこれまでMultiple Input Multiple Output(MIMO)チャネルを利用した屋内侵入検出法(MIMOセンサ)を提案してきた.通常,MIMO伝送によるチャネル容量は,伝搬環境の変動によるチャネル推定誤差により大きく劣化することが知られているが,MIMOセンサではこの特性を逆に利用し,伝搬特性の変化をセンサとして利用することを特徴としている.これまでの検討では,MIMOシステムが導入されている無線LANの信号を用いた検討を用いていたが,装置はできるだけ簡便な構成が望ましい.本報告では,狭帯域のFrequency Shift Keying(FSK)の信号を取り上げ,狭帯域FSK信号を用いた信号同期法を考慮したチャネル推定法を提案する.また,本同期方法を用いたMIMOセンサによる屋内侵入検出の基本特性を示す.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：英語   出版者・発行元：IEEE  

This paper proposes a novel interference cancellation technique using the concept of a distributed array, for the secondary use of the frequency resources in frequency division duplexing (FDD) based cellular systems. In order to achieve efficient distributed interference cancellation, the secondary system exploit intervals for periodic training signals transmitted by FDD-time division multiple access (TDMA) based cellular systems. We show that an efficient interference cancellation can be achieved by introducing helpers that decode the interference and transfer it to the secondary nodes. We take advantage of the high-speed links within the secondary system and devise a data compressing scheme that reduces time for transferring the decoded interference. We clarify the effectiveness of the proposed scheme by using computer simulation. As a parameter, the transmission quality between the helper and secondary nodes is varied. The results indicate that the proposed distributed interference cancellation is effective compared to a conventional adaptive array using a zero forcing algorithm, when the signal to noise ratio between the helper and the target secondary node is greater than 20 dB.

DOI： 10.1109/ICC.2008.573

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記述言語：英語   出版者・発行元：IEEE  

Multiuser (MU) - multiple input multiple output (MIMO) techniques were proposed to increase the spectrum efficiency because only a few antenna branches are allowed at a simple mobile terminal (MT). Among the MU-MIMO techniques, the block diagonalization (BD) algorithm is well known as a practical linear precoding technique for a downlink. In this paper, we analyze an achievable bit rate in MU-MIMO using BD algorithm and derive the simplified expression using the signal spaces of users. Based on the derived expression, two kinds of user selection methods for the BD algorithm (USBD) in MU-MIMO systems are proposed. The proposed methods estimate the improvement in the achievable bit rate compared to that in a single user (SU)-MIMO system using the signal spaces of the supported users. The first proposed method is USBD with a full search (USBD-FS) and it selects the combination of users to achieve the highest total throughput by considering all the combinations. The second proposed method is USBD with a tree structure search (USBD-TS), which drastically reduces the calculation complexity. Although all combinations of users are not considered in USBD-TS, a sufficient achievable bit rate is obtained while the calculation load is much less than that for the conventional method. Computer simulations confirm that USBD-FS and USBD-TS obtain the achievable bit rate of 100.0% and 91.1%, compared to that for the best combination of users when the angle spread at the transmitter is 75 degrees.

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添付ファイル： AP2019-11西森(64ビームMassive_MIMOの屋内実環境における効果).pdf

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添付ファイル： AP2019-176水野(水平方向を考慮した0.9_2.4_5.1GHz帯における屋外-屋内伝搬侵入損失の特性).pdf

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添付ファイル： AP2019-10工藤(マルチビームMassive_MIMOにおける最適ビームパターンに関する検討).pdf

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添付ファイル： CQ2019-74_谷口(複数周波数帯における伝搬損失の比較検討).pdf

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添付ファイル： CQ2019-18_五十嵐正樹(WPT端末のためのFDDに適したビームフォーミング法の提案).pdf

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添付ファイル： CQ2019-19_上村(実データに基づく円形アレーを用いた到来方向推定に関する考察).pdf

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添付ファイル： CQ2019-15_渡部(仮想Massive_アレーを用いた伝搬環境制御法の提案).pdf

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添付ファイル： AP2019-165西森(広帯域信号に対するISTAを用いた圧縮センシングによるDoA推定).pdf

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添付ファイル： 佐藤_(11)［ポスター講演］アンテナ選択型BDを用いたMassive MIMOに関する検討.pdf

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添付ファイル： 八九_(18)［ポスター講演］LTEにおける線形制御型Massive MIMOのスループット特性評価.pdf

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添付ファイル： 松村_(3)［ポスター講演］LOS-MIMO伝送と66GHz帯によるドローン間通信の検討.pdf

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添付ファイル： 谷口_(1)［招待講演］ディープラーニングの通信システムへの応用.pdf

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添付ファイル： 太田_(24)［ポスター講演］機械学習を用いたミリ波帯における伝搬損失推定モデル.pdf

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添付ファイル： 土肥_(8)［ポスター講演］ドローンとMU-MIMOを利用した中継特性の評価.pdf

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添付ファイル： 高世_(7)［ポスター講演］ドローンを用いた仮想アレー到来方向推定の検討.pdf

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添付ファイル： 岡田_(26)［ポスター講演］Massive MIMOの構成の違いによる通信効率の考察.pdf

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添付ファイル： 髙橋_(16)［ポスター講演］高速パターン切替とブラインドアルゴリズムを用いた伝搬環境制御.pdf

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添付ファイル： AP2019-131松村(送受信距離に依存しないLOS-MIMOのアンテナ構成).pdf

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添付ファイル： AP2019-130八九(LTEベース信号の線形制御型Massive_MIMO簡易スループット評価).pdf

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