Atsushi Okamura

Performance Evaluation of 44GHz Band Massive MIMO Based on Channel Measurement

5th generation mobile communication system using higher frequency band has gotten much attention, and massive-MIMO technologies have been expected to improve spectral efficiency dramatically. In order to reduce the complexity of massive-MIMO base station, the combination of analog beamforming (APAA: Active Phased Array Antenna) and digital MIMO signal processing for the multi-beam multiplexing is one of the promising approaches. In this paper, channel capacity evaluation with 44GHz-band APAA measurement results will be carried out and the possibility of large capacity transmission in LOS environment is shown. 44GHz band channel parameters - AoA, AoD, delay spread, etc. - will be shown and transmit performance results using cluster model are presented.

Permutation Method for ICA Separated Source Signal Blocks in Time Domain

A new permutation method for ICA (independent component analysis)- based blind separation is presented. The objective here is to concatenate ICA separated signals in adjacent time blocks. The proposed method utilizes the associativity in column vectors of an estimated mixing matrix and a tracking filter. It has advantages of no required array calibration, efficient computation, and real time updatability. These superiorities are highly beneficial for radar or communication system type applications. Furthermore it is shown, by an experiment using radio wave signals, that the proposed permutation algorithm successfully permutes the separated signal blocks.

Performance analysis of Independent Component Analysis to separate mixtures of complex sinusoidal signals

ICA (independent component analysis) has a remarkable capability of separating mixtures of stochastic random signals. However, we often face problems of separating mixtures of deterministic signals, especially sinusoidal signals, in some applications such as radar systems and communication systems. One may ask if ICA is effective for deterministic signals. In this paper, we analyze basic performance of separating mixtures of complex sinusoidal signals for ICA which utilizes the forth cumulant as a criterion of independency of signals. We theoretically show the ICA can separate mixtures of deterministic sinusoidal signals. Then, we conduct computer simulations and radio experiments with a linear array antenna to confirm the theoretical result. We will show that the ICA is successful to separate mixtures of sinusoidal signals with frequencies close to less than FFT resolution and at DOAs (direction of arrival) close to less than Rayleigh criterion.

A flexible and precise APAA system with RF modules including a signal generator

We propose a new concept of an active phased array antenna (APAA) system that realizes multi-frequency and multi-modulation beam forming simultaneously in an array. The proposed APAA system consists of RF modules including an RF signal generator. A distributed array radar system with the proposed configuration can be simplified by not transmitting a signal in RF at the interconnect equipments of modules. The proposed APAA has architectures to measure and compensate the characteristic variations between RF modules by itself. Key features of the proposed APAA are verified by measurements. Transmitter block of the RF module with three SiGe-ICs and signal distribution system are fabricated. The RF module generates various modulated signals of 1Gs/s and operates in C-Ku bands, and measures the RF characteristic variations. The signal distribution system compensates the phase fluctuation of the distributed signals.

Novel Dynamic and Static Methods for Out-of-Band Power Suppression in SC-OFDM

Novel dynamic and static out-of-band (OoB) suppression methods for single carrier (SC)-orthogonal frequency division multiplexing (OFDM) are proposed in this letter. In the dynamic approach, symbols at designated positions from the previous block are inserted at predetermined positions in the current block to maintain continuity between blocks. In the static method, a fixed sequence of symbols is inserted in an SC-OFDM block for OoB power suppression. In both approaches, OoB power can be suppressed significantly by controlling design parameters.

Low range sidelobe pulse compression with complex-valued window to minimize distributed clutter power

In this paper, a pulse compression with complex valued window, termed PCX, is proposed to achieve low range sidelobe, low mismatch loss and small broadening factor simultaneously. By modeling distributed sidelobe clutter with steering vectors, a complex-valued window minimizing the distributed clutter power is derived. Proposed PCX shows superior performance against Taylor windowed pulse compression in integrated range sidelobe level, mismatch loss and broadening factor. Proposed PCX can be implemented affordably by replacing current real-valued window weighting processing with complex-valued processing in the fast convolution circuit.

Cell Structure for High-Speed Land-Mobile Communications

To meet the growing demand for wireless broadband communications in high-mobility cases, we study cell structures using millimeter-wave. Single antenna Cell (SC) and Linear Cell (LC) structures are here considered as typical approach. The cells in LC structures consist of strips while those in SC structures are circular. Distributed Antenna Cell (DAC) and Narrow Beamwidth Distributed Antenna Cell (NBDAC) have already been proposed for LC structures, but rigorous performance evaluations in high mobility case have not been conducted. Thus, in this paper, we compare the performances of SC, LC and NBDAC in a high-mobility environment. The comparison shows that NBDAC is the most suitable structure for high-mobility scenarios. In addition, we propose interference reduction methods for NBDAC to reduce adjacent cell interference and improve throughput at a cell edge. To evaluate effectiveness of the proposed methods, theoretical evaluations and computer simulations are conducted, and it is shown that NBDAC with the proposed methods can achieve 1Gbps throughput even in high-mobility environments.

Monopulse beamforming to achieve Cramer-Rao lower bound for digital array radar

Digital taper for difference beamforming to optimize monopulse angle accuracy is proposed in this paper. For fully-digitized array radar with antenna aperture tapering for low sidelobes sum beamforming, the monopulse angle accuracy with the proposed difference taper is coincide with Cramer-Rao lower bound. For subarray-based digital array radar, the monopulse angle accuracy with the proposed taper is suboptimum and close to the lower bound. Derivation of monopulse angle accuracy with the proposed difference taper for fully-digitized array radar is presented and an improvement of the accuracy over conventional monopulse is proved theoretically. Suboptimum solution for the proposed difference taper for subarray-based digital array radar is provided. Results of computer simulation with Taylor tapered uniform linear array is included to show the accuracy improvement by factor of 1.78, which is equivalently 5.0 dB reduction of SNR for required angle accuracy, over the conventional monopulse in fully-digitized array radar.

Permutation scheme by tracking association for ICA separated signal blocks

A new permutation method for ICA (Independent Component Analysis) separated signal blocks is presented. The proposed method utilizes the associativity in column vectors of estimated mixing matrix and tracking filter. It has advantages of not requiring array calibration, efficient computation, and real time updatability. Furthermore, it is shown, by an experiment using radio wave signals, that the proposed algorithm successfully permutes the separated signal blocks.