Ryochi Kataoka

Simple analog beamforming method for short range MIMO transmission

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.

Performance evaluation of massive MIMO with analog-digital hybrid processing in a real microcell environment

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.

Basic performance of very large MIMO in small cell systems

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.

Interference detection using wireless LAN based MIMO transmission

This paper proposes an interference detection method in MIMO transmission, which utilizes periodical preamble signals in a frequency domain. The signals are mapped in only several subcarriers in short preamble signals of IEEE802.11 based OFDM signals and the signal in a frequency domain is transformed by IFFT at the transmitter. We assume the collision due to multiple short preamble signals. In the propose method, second antenna receives the preamble signals while first antenna transmits the preamble signals. The interference can be detected by subtracting the short preamble signal which is multiplied by the estimated channel response from the received signal after the FFT processing. Moreover, we utilize the dual polarization to reduce the mutual coupling between the transmitter and receiver. By a computer simulation, it is shown that proposed method can successfully detect interference in OFDM signal when the interfering power is greater than the noise power.

Evaluation of Massive MIMO Considering Real Propagation Characteristics in the 20-GHz Band

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.

Performance evaluation of massive MIMO using cylindrical array in a real microcell environment

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.

Nove l antenna arrangement for 4×4 LOS-MIMO systems

This paper proposes novel antenna arrangements which improve the channel capacity for 4×4 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.