Kiyomichi Araki

Tokyo Institute of Technology | TITech ·  Department of Electrical and Electronic Engineering

One of the key enablers for the realization of a variety of unmanned aerial vehicle (UAV)-based systems is the high-performance communication system linking many UAVs and ground station. We have proposed a spectrum-efficient full-duplex directional-antennas-equipped multi-UAV communication system with low hardware complexity to address the issues o...

UAV-based wireless systems, such as wireless relay and remote sensing, have attracted great attentions from academia and industry. To realize them, a high-performance wireless aerial communication system, which bridges UAVs and ground stations, is one of the key enablers. However, there are still issues hindering its development, such as the severe...

A high performance multi-UAV communication system, which bridges multiple UAVs and ground station, is one of the key enablers to realize a variety of UAV-based systems. To address the issues such as the low spectrum efficiency caused by the co-channel interference, we have proposed a spectrum-efficient full-duplex multi-UA V communication system wi...

Unmanned aerial vehicles (UAVs)-based applications, such as surveillance systems and wireless relays, are attracting increasing attention from academia and industrial fields. The high-performance aerial communication system is one of the key enablers for them. However, due to the low attenuation of radio waves in the air-to-ground channels, the int...

UAV-based wireless systems, such as wireless relay and remote sensing, have attracted great attentions from academia and industry. To realize them, a high-performance wireless aerial communication system, which bridges UAVs and ground stations, is one of the key enablers. However, there are still issues hindering its development, such as the severe...

In this paper, an ultra-thin wave absorber using a resistive patch array closely-placed in front of a back-metal is designed. The positively large susceptance is required for the patch array to cancel out the negatively large input susceptance of the short-circuited ultra-thin spacer behind the array. It is found that the array needs the gap of 1 m...

A compact-range wireless access system in the 60-GHz band has been proposed for multi-Gb/s data transfer. A prototype Gigabit Access Transponder Equipment (GATE) was built to evaluate the system performance in terms of received signal strength, signal-to-noise ratio (SNR), and bit error rate (BER). The proposed system operates in the near-field reg...

Intersymbol interference (ISI) is a significant source of degradation in many digital communication systems including our proposed non-far region communication system using large array antennas in the millimeter-wave band in which the main cause of ISI can be attributed to the path delay differences among the elements of an array antenna. This pape...

This paper proposes optimal beam patterns of analog beamforming for SU (Single User) massive MIMO (Multi-Input Multi-Output) transmission systems. For hybrid beamforming in SU massive MIMO systems, there are several design parameters such as beam patterns, the number of beams (streams), the shape of array antennas, and so on. In conventional hybrid...

An equivalent circuit of a circular patch array absorber has been proposed, however the method to identify a winding ratio of a transformer in its circuit have never been reported. In this paper, it is indicated that the ratio is proportionate to the area ratio between patch and unit cell of the absorber, and the design method of the winding ratio...

This paper proposes optimal beam patterns of analog beamforming for SU (Single User) massive MIMO (Multi-Input Multi-Output) transmission systems. For hybrid beamforming in SU massive MIMO systems, there are several design parameters such as beam patterns, the number of beams (streams), the shape of array antennas, and so on. In conventional hybrid...

This paper proposes a design method of acircular patch array absorber for oblique incidence by using an equivalent circuit with a transformer. In the equivalent circuit with the transformer, a matching angle of the absorber can be determined by using the winding ratio of the transformer. Hence, a calculation model for obtaining an arbitrary winding...

It is known that perturbation elements realize sub-resonance and they can be applied to a circular patch array absorber for improving its bandwidth. The considerable polarization conversion, however, occur due to the perturbation elements. In this paper, the polarization conversion is suppressed by applying the rotation symmetry arrangement of the...

This paper proposes a new methodology to design optimal antennas for MIMO (Multi-Input Multi-Output) communication systems by using spherical mode expansion. Given spatial channel properties of a MIMO channel, such as the angular profile at both sides, the optimal MIMO antennas should provide the largest channel capacity with a constraint of the li...

In the European satellite broadcasting specifications, the symbol rate and the carrier frequency are not regulated. Furthermore, the first generation format DVB-S does not have any control signals. In a practical environment, the received signal condition is not stable due to the imperfect reception environment, i.e., unterminated receiver ports, c...

Radar cross section (RCS) of a patch array antenna is reduced using a switchable absorption/transmission surface. The switchable surface performs as between a radar absorber and transmission surface using diodes at 9GHz. The switchable surface was applied to the radome of a patch array and its radiation pattern and RCS reduction were evaluated. The...

Although 60 GHz millimeter wave (mm-Wave) systems employing OFDM can provide multi-Gbps data rate, the high level of phase noise (PN) of the mm-Wave transceivers induces inter-carrier interference (ICI) that degrades the performance of the OFDM systems. In the conventional method, the effects of PN can be well compensated by the iterative receiver...

Coordinated Multi-point (CoMP) transmission has long been known for its ability to improve cell edge throughput. However, in a CoMP cellular network, fixed CoMP clustering results in cluster edges where system performance degrades due to non-coordinated clusters. To solve this problem, conventional studies proposed dynamic clustering schemes. Howev...

Because of the license-free and wideband properties, 60 GHz band has become one of the candidates for the next generation wireless communication systems. In 60 GHz millimeter wave (mmWave) wireless systems, orthogonal frequency division multiplexing (OFDM) scheme can provide high data rate over than 6 Gbps; however, the high peak-to-average power r...

Cognitive radio (CR) is an important technology to provide high-efficiency data communication for the IoT (Internet of Things) era. Signal detection is a key technology of CR to detect communication opportunities. Energy detection (ED) is a signal detection method that does not have high computational complexity. It, however, can only estimate the...

This paper empirically validates battery-less sensor activation via wireless energy transmission to release sensors from wires and batteries. To seamlessly extend the coverage and activate sensor nodes distributed in any indoor environment, we proposed multi-point wireless energy transmission with carrier shift diversity. In this scheme, multiple t...

A 60GHz-band compact-range wireless access system using a large array antenna can provide an uniform signal reception zone (less than 14 m distance from the antenna) and an almost multipath-free propagation environment. To evaluate the system performance, a wireless communication system for demonstration is constructed and the bit error rate (BER)...

Mobile traffic is increasing exponentially year by year and it will be over 1000 times higher than that of today in the near future. In order to tackle this matter, millimeter wave mobile access networks which can provide several GHz bandwidth attract international attention. This paper investigates the candidates of millimeter wave spectrum for 5G...

The mobile traffic explosion predicted to be increased by 1000 times in the next 10 years has become a remarkable issue due to the proliferation of smart devices such as smart phones or tablets. Energy consumption of information processing is also becoming an economic issue for operators. It is a critical task to design the next generation cellular...

An active frequency selective surface (FSS) which is switched as a radar absorber and transmission surface using pin diodes at the same frequency is proposed. The diodes are arranged on the both sides of the active FSS. The active FSS performs as a radar absorber and transmission surface with OFF- and ON-state diodes. The active FSS is fabricated a...

Vertical- and horizontal-polarization RCS of a dipole antenna was reduced using a switchable reflector. The switchable reflector can switch reflection level for the vertical-polarization and have absorption for the horizontal-polarization. The reflection level of the reflector for the vertical-polarization can be switched using pin diodes and the r...

Novel multi-band mixers that can receive multiple band signals concurrently are proposed and evaluated. The mixers achieve independent gain control through novel relative power control method of the multiple local oscillator (LO) signals. Linear control is also achieved through multiple LO signal input with total LO power control. Theoretical analy...

In traditional heterogeneous cellular networks (Het-Net), base stations (BS) basically associate users based on received signal power. However, in the case of multiband HetNet, in which macro BSs and smallcell BSs use different frequency bands, this conventional cell association method is not effective because there is no interference between macro...

This paper addresses an impedance matching problem with mutual coupling in the presence of signal and noise coupling in compact MIMO receivers. The optimal matching for minimizing the noise figure is employed. A closed-form result of ergodic capacity theoretically shows that the ergodic capacity on the optimal matching is independent of antenna cha...

Millimeter-wave communication is expected to be the next-generation wireless communication. Local oscillator phase noise in such transceiver, however, degrades the performance of orthogonal frequency division multiplexing (OFDM) modulation that has been a key technology in high data-rate communication. To address this issue, a low-complexity inter-...

In this paper we describe and experimentally validate a dual-band digital predistortion (DPD) model we propose that takes account of the intermodulation and harmonic distortion produced when the center frequencies of input bands have a harmonic relationship. We also describe and experimentally validate our proposed novel dual-band power amplifier (...

A switchable reflector which can switch reflection level using pin diodes for the vertical polarization and absorb for the horizontal polarization was proposed. The vertical polarized reflection coefficient was switched-29 dB with OFF-state diodes and-0.5 dB with ON-state diodes, and horizontal polarized one was less than-15 dB at 9 GHz. The reflec...

This paper presents a new concept of wireless grid to realize battery-less sensor networks in indoor environments. In this environment, multiple wireless energy transmitters are distributed on the ceiling, and activate battery-less sensors located anywhere in the field. Carrier shift diversity is introduced to remove huge received power attenuation...

This paper addresses a noise matching problem for MIMO receiver with mutual coupling in the presence of signal and antenna noise coupling. The matching network in this paper is designed to maximize the system's ergodic capacity by means of minimizing the noise figure matrix.For reducing RF circuit complexity, low noise matching design without cross...

This paper presents a method to seamlessly extend the coverage of energy supply field for wireless sensor networks in order to free sensors from wires and batteries, where the multi-point scheme is employed to overcome path-loss attenuation, while the carrier shift diversity is introduced to mitigate the effect of interference between multiple wave...

Noise analysis of Direct Sampling Mixer (DSM) has been described in this paper. The output noise of the DSM is determined by the sum of continuous time noise and discrete time noise. The discrete time noise is calculated from the discrete time transfer function and Fourier transform of the sample/hold function. The input referred noise of the DSM i...

The discrete time analog circuit (100) is provided with: a rotate capacitor circuit (150); an amplifier (141) that is connected to the input line or the output line of the rotate capacitor (150), and amplifies the input potential or input charge; a coefficient circuit (140) that is positioned in series with the amplifier (141), and has two history...

In conventional wireless cellular networks, each user equipment (UE) is connected to one or a few local base stations (BS). However, the users' distribution in the network area is commonly fluctuating during a day. Especially, if a high density of small cell BSs is available, some user-dense areas or hotspots can be sensed by BSs. When there is som...

This paper proposes a new power amplifier's linearization architecture for a unified access point uses a wideband power amplifier and transmits multi-band signals concurrently for system's flexibility. To achieve high power efficiency and low interference of the access point, we evaluate a concurrent dual-band digital predistortion (DPD) technique...

This paper introduces a concept of cloud cooperated heterogeneous cellular network (C-HetNet) where small power pico basestations (BSs) overlaid on a macrocell are connected to cloud radio access network (C-RAN) to operate cooperatively with the macro BS. Since the macro BS assists operation of the pico BSs, it is easy to deploy multi-band HetNet w...

The linearity analysis of a passive mixer is presented. The distortion mechanism caused by switching operation of a MOS transistor is elucidated from the static and dynamic analysis of passive mixers. Furthermore, the maximum input and output level to keep linear operation and its required bias conditions are expressed by simple equations. The maxi...

In the recently developed Flexible Wireless System (FWS), the same platform needs to deal with different wireless systems. This increases nonlinear distortion in its wideband power amplifier (PA) because the PA needs to concurrently amplify multi-band signals. By taking higher harmonics as well as inter- and cross-modulation distortion into conside...

In conventional studies on Coordinated Multi-Point (CoMP) cellular networks, dynamic clustering schemes have been introduced to achieve CoMP gain at all cell edges. However, such schemes increase complexity of the network drastically and are unfeasible in the current network topology. In this paper, small power basestations (BSs) are introduced ins...

This paper presents an indoor experiment to verify the battery-less sensor activation via multi-point wireless energy transmission with carrier shift diversity which realizes seamless coverage extension of the sensor activation. The multi-point scheme is employed to overcome path-loss attenuation. The carrier shift diversity has been developed to a...

Spatial spectrum sharing with MIMO cognitive radio is efficient and attractive for wireless systems with limited communication resources. MIMO cognitive radio is a kind of cognitive radios using MIMO beamforming techniques to avoid interference to other nodes. There are many theoretical works on this topic but validation of the algorithm on real ha...

Relay deployment has been gaining attention for network designers. Recently, MIMO Two-way Multi-hop Network (M2WMN) where all links share the same frequency is introduced as a relaying scheme which achieves higher spectral efficiency than other conventional multi-hop schemes. A power control strategy for M2WMN has been proposed to alleviate the fre...

It is known that demand and supply power balancing is an essential method to operate power delivery system and prevent blackouts caused by power shortage. In this paper, we focus on the implementation of demand response strategy to save power during peak hours by using Smart Grid. It is obviously impractical with centralized power control network t...

MIMO two-way multi-hop networks are considered in which the radio resource is fully reused in all multi-hop links to increase spectrum efficiency while the adjacent interference signals are cancelled by MIMO processing. In addition, the nodes in the multi-hop network optimize their transmit powers to mitigate the remaining overreach interference. O...

To realize reliable Vehicle-to-Vehicle (V2V) communication systems, it is significant to design the system margin which is defined as the difference between received signal power and receiver sensitivity. This requires the prediction of received signal power variation. Propagation loss and fading characteristics which determine the received signal...

The linearity analysis of a passive mixer is presented. The distortion mechanism caused by switching operation of an NMOS transistor is elucidated from the DC analysis of passive mixers. Furthermore, the maximum input level to keep linear operation and its required bias condition is derived. The calculated linearity performances agree well with sim...

In conventional cellular systems, transmission rate degrades at cell-edge because of inter-cell interference and pathloss. This problem is called “cell-edge problem”. To solve this problem, Coordinated Multi-Point (CoMP) technique has been proposed recently. CoMP can convert inter-cell interference signals from neighbor base stations (BSs) to desir...

Basically there are three application fields in microwave technologies; wireless communications, radar and remote sensing, and microwave power applications including a plasma processing and wireless power transmission. In this paper we will describe research & development activities of microwave technologies in Japan in terms of the above three fie...

This paper proposes a novel method for location estimation of a cell-phone in an indoor environment with experimental validation. The proposed method is a location fingerprint scheme which employs the statistical characteristics of the signal cross-correlation among multiple sensors. As the cross-correlation between a pair of antennas fully stores...

In 1990's a concept of software-defined radio has been proposed by Mitola. A reconfigurability of the operating parameters; center frequency, bandwidth and power level in transceivers only altered by software is one of the most important features in the software-defined radio to realize a versatile transceiver. Here we will review research and deve...

As there are demands for OFDM transmission at 60GHz band, researchers need to deal with the problem of frequency offset and phase noise, especially at the high frequency band. This paper builds a theoretical framework for analyzing the Inter-Carrier-Interference (ICI) incurred due to phase noise and frequency offset of in OFDM transmission system....

MIMO-OFDM combining OFDM and MIMO techniques achieves high spectral efficiency and is able to increase throughput. MIMOOFDM systems can be classified into either "open loop" or "closed loop" depending on whether the CSI is fed back from the Rx to the Tx. As a closed loop scheme, SVD-MIMO is the optimal single user MIMO-OFDM transmission scheme whil...

Recently wireless sensor networks have gained more interests. However limited life-time of sensor nodes has long been an issue in wireless sensor networks. On the other hand, wireless energy transmission at 950MHz band has been applied to many applications, especially RFID (Radio Frequency IDentification) systems. However, the problems of restricte...

Single front-end architecture with parasitic antenna element (PAE) in compact array system has been proposed for enhancing spectral efficiency and miniaturizing the receiver. Although most of studies paid attention to design optimal receiver with antenna mutual coupling on fading correlation, relatively little attention has been paid to noise. In t...

This work analyzes the optimal pico base station (BS) deployment in heterogeneous cellular networks (HetNet) with hotspots. Most of conventional works for HetNet focused on interference coordination and effective cell association methods, however, the problem of pico BS deployment (cell planning) for HetNet with hotspots has not been analyzed so mu...

MIMO 2-way relay network is known as a solution to realize high data rate relay networks. 2-way relaying is possible provided that interference cancellation techniques, e.g. MIMO beamforming or network coding are properly introduced. Many theoretical works on relaying using beamforming exist, but no implementation on real hardware has been reported...

The Direct Sampling Mixer (DSM) with a complex coefficient transfer function is demonstrated. The operation theory and the detail design methodology are discussed for the high order complex DSM, which can achieve large image rejection ratio by introducing the attenuation pole at the image frequency band. The proposed architecture was fabricated in...

This paper develops the first prototype hardware for a TDD two-way multi-hop relay network with MIMO network coding. Since conventional wireless multi-hop relay networks have the drawback of low data rate, TDD two-way multi-hop relay networks have been studied as a solution to realize high data rate recently. In these networks, forward and backward...