Masafumi Tsutsui

A blind calibration method for an adaptive array antenna in DS-CDMA systems using an MMSE algorithm

A new blind calibration method is proposed to compensate for the amplitude and phase errors in the antenna branches of DS-CDMA base stations with adaptive array antennas. The proposed method calibrates these errors using the MMSE (minimum mean square error) algorithm, requiring only the received (or transmitted) signals at the array antenna and not requiring any additional reference signal to be inserted for calibration. The proposed method and structure can be applied to both the downlink and uplink. The fast convergence property of this method ensures a tracking capability against amplitude-phase variances. In an uplink, using the proposed calibrator, a beam steering adaptive array antenna based on a directional finding algorithm of a desired signal has a BER performance that improves by about 2 dB at the BER of 10/sup -3/ when a non-linear RF amplifier is used. We have also evaluated the downlink performance of this method when a non-linear RF amplifier is used and have confirmed its robustness against that of the amplifier.

Throughput Performance of Pre-coding MIMO Transmission with Multi-Beam Selection

We have been proposing multi-beam MIMO (MB- MIMO) as an Evolved UTRA downlink MIMO scheme for 3GPP long term evolution (LTE). MB-MIMO is a pre-coding MIMO scheme that uses a simple combination of multi-beam multiple-data-stream transmission and user equipment (UE)- based adaptive beam selection. The scheme benefits from its simple uplink feedback signalling, because MB-MIMO requires only a subset of the beam indices to be fed back. In this paper via computer simulation, we compare the performance of MB-MIMO and closed-loop MIMO that utilizes antenna selection only without beam-forming at the transmitter. In this comparison we consider the correlation between antenna elements in a temporally and spatially dispersed multi-path channel. Simulation results revealed that MB-MIMO has superior performance due to its beam-forming gain, even with limited feedback signalling. In this paper, we also introduce the MB-MIMO scheme using the cross-polarized (X-pol) antenna arrays and demonstrate its throughput performance comparing to the MB-MIMO using the 4-antenna linear array.

Throughput Performance of Downlink MIMO Transmission with Multi-Beam Selection using a Novel Codebook

We have been proposing multi-beam MIMO (MB-MIMO) as an evolved UTRA downlink MIMO scheme for 3GPP long term evolution (LTE). MB-MIMO is a pre-coding MIMO scheme that uses a simple combination of multi-beam multiple-data-stream transmission and user equipment (UE)-based adaptive beam selection. The scheme benefits from its simple uplink feedback signaling, because MB-MIMO requires only a subset of the beam (codebook) indices to be fed back. However, a hardware calibrator (HW-CAL), which increases the complexity of RF components at a transmitter, should be installed in order to achieve a high beam-forming gain with a small codebook size. In this paper, we propose a novel codebook design for MB-MIMO, which realizes a superior performance without any HW-CAL with a small increase of the codebook size and the feedback signaling. We performed a computer simulation to evaluate the throughput performance of the proposed scheme, considering the phase variation between antenna elements in a spatially distributed multi-path fading channel model.

Field Experiment of High-Capacity Technologies for 5G Ultra High-Density Distributed Antenna Systems

In fifth-generation mobile communication systems (5G), it is necessary to significantly increase system capacity compared with 4G in order to accommodate rapidly increasing mobile data traffic. Cell densification has been considered an effective way to increase system capacity. However, severe intercell interference degrades the system capacity due to the increase of the line-of-sight environment between the transmission point (TP) and user equipment (UE). We propose large-scale coordinated multi-user multiple-input multiple-output (LSC-MU-MIMO), which combines joint transmission from all the TPs connected to a centralized baseband unit and MU-MIMO. We have investigated the downlink performance of LSC-MU-MIMO via both computer simulation and field experiments and showed that LSC-MU-MIMO can significantly reduce severe inter-TP interference and improve the system capacity of high-density small cells. In this paper, we introduce our recent field experiment results where reception antennas of UEs are mounted on a vehicle driving at speeds of 5 km/h to 40 km/h. We also compare distributed TP deployment with localized TP deployment when fixing the total number of transmission antennas.