This paper investigates a relationship between inkdot and one-pebble for two-dimensional finite automata (2-fa's). Especially we show that (1) alternating inkdot 2-fa's are more powerful than nondeterministic one-pebble 2-fa's, and (2) there is a set accepted by an alternating inkdot 2-fa, but not accepted by any alternating one-pebble 2-fa with only universal states.

In this paper, the recent development of GaN bulk substrates is reviewed. Among various works on HVPE thick epitaxial growth, the largest free-standing GaN substrates upto 34 cm2 has been first obtained by the HVPE method using NGO substrates, whose lattice constant has a good matching with that of GaN. For developing larger GaN substrates with lower production cost, the ultra-high pressure solution growth method is being developed not only in Poland but also in Japan under "The Light for the 21st Century" national project.

We demonstrate a simple BER monitoring method for WDM signals. Newly developed 32-channel wavelength selector based on thermo-optic switch and AWG is used. The BER of each channel is estimated from opened eye-diagrams obtained by asynchronous sampling. Good BER monitoring performance is confirmed.

This paper proposes a 2.6 GHz low cost DBF array antenna system and reports its evaluation based on our experimental results. The proposed system is partially constructed by digital devices for the simplification of hardware, and employs some techniques for improving the resolution. The system is evaluated through the DOA estimation by the MUSIC algorithm inside a radio anechoic chamber. As a result, we found that the proposed system estimates the DOA with the highest accuracy at which MUSIC algorithm can perform. Moreover, this paper discusses the estimation errors. We also found that the estimation error is particularly affected from the inaccurate element interval.

The performance in terms of the user separation of multi-user multiple-input multiple-output (MU-MIMO) depends on not only the spatial correlation but also the location of the mobile stations (MSs). In order to take into account the performance in terms of the user separation, we need to consider the granularity of the beam and null width of the precoded antenna pattern in addition to the spatial correlation to determine the base station (BS) antenna configuration. In this paper, we propose Smart Vertical MIMO (SV-MIMO) as the best antenna configuration that achieves both spatial correlation and granularity of the beam and null width of the precoded antenna pattern. We evaluate SV-MIMO in a field experiment using a downlink 4-by-2 MU-MIMO configuration focusing on the dependency of the location of the MSs in Yokosuka, Japan. The majority of the measurement course is under line-of-sight (LOS) conditions in a single cell environment. The MSs are almost uniformly set 30 to 60 degrees in azimuth and 12 to 30 degrees in elevation and the distance from the BS antennas is approximately 150m at maximum. We also evaluate the performance of 4-by-2 MU-MIMO using the conventional type of horizontal array antenna and show the difference. The field experimental results show that throughput of greater than 1Gbps is achieved at the Cumulative Distribution Function (CDF) of 14% by employing SV-MIMO for Rank-4 MU-MIMO. The throughput of SV-MIMO is 30% higher than that for the horizontal array antenna configuration at the CDF of 50%.

We fabricated high-quality domain-inverted MgO: LiNbO$_3$ structures with 3.0 and 2.0~$mu$m periods using applying votage to the corrugation electrode. We found that keeping the crystal temperature at 150$^{circ}$C for 12 hours before applying voltage was effective for obtaining good uniformity. We also demonstrated an application of the structures with 3.0~$mu$m period to electro-optic Bragg deflection modulator for the first time.

This paper presents some results of an experimental trial for the 5th generation (5G) wireless communication systems using 28GHz band. In order to tackle rapidly increasing traffic for 2020 and beyond, new radio access networks for the 5G mobile communication systems will introduce the use of higher frequency bands such as spectra higher than 10GHz to achieve higher capacity and super high bit rate transmission of several tens of Gbps. The target of this experimental trial is to evaluate the feasibility of using the 28GHz band with super-wide bandwidth of 800MHz for 5G wireless communication systems. To compensate large path-loss in higher frequency, the beamforming (BF) based on Massive multiple-input multiple-output (MIMO) is one of promising techniques and can be combined with spatial multiplexing of multiple data streams to achieve much higher capacity. In addition, to support the mobility of mobile station (MS), beam tracking technique is important. In this trial, we first conduct a basic experiment of single-stream transmission by using prototype system with base station (BS) having 96-element antenna and MS having 8-element antenna to evaluate the effectiveness of joint transmitter/receiver BF in 28GHz band in terms of coverage, impact of path loss, shadowing loss and penetration loss under indoor, outdoor and outdoor-to-indoor (O-to-I) environments. We show that by using 28 GHz band with BF based on Massive MIMO, higher throughput near 1.2Gbps can be achieved at many points in the indoor environment. It is also shown that the throughput of over 1Gbps can be achieved at points around 200m distant from BS in outdoor line-of-site (LOS) environment. Secondly, to evaluate the effectiveness of spatial multiplexing and beam tracking under more realistic environment, we also conduct the outdoor experiment of BF combined with 2-stream spatial multiplexing in high mobility environment with MS speed of up to 60km/h by using smartphone-shape MS antenna. We also show that maximum throughput of 3.77Gbps can be achieved with MS speed of 60km/h by using BF with 2-stream multiplexing and beam tracking.

This paper investigates closure properties of one-pebble Turing machines with sublogarithmic space. It shows that for any function log log n L(n) = o(log n), neither of the classes of languages accepted by L(n) space-bounded deterministic and self-verifying nondeterministic one-pebble Turing machines is closed under concatenation, Kleene closure, and length-preserving homomorphism.

Cyber-physical systems, in which ICT systems and field devices are interconnected and interlocked, have become widespread. More threats need to be taken into consideration when designing the security of cyber-physical systems. Attackers may cause damage to the physical world by attacks which exploit vulnerabilities of ICT systems, while other attackers may use the weaknesses of physical boundaries to exploit ICT systems. Therefore, it is necessary to assess such risks of attacks properly. A direct-access attack in the field of automobiles is the latter type of attacks where an attacker connects unauthorized equipment to an in-vehicle network directly and attempts unauthorized access. But it has been considered as less realistic and evaluated less risky than other threats via network entry points by conventional risk assessment methods. We focused on reassessing threats via direct access attacks in proposing effective security design procedures for cyber-physical systems based on a guideline for automobiles, JASO TP15002. In this paper, we focus on “fitting to a specific area or viewpoint” of such a cyber-physical system, and devise a new risk quantification method, RSS-CWSS_CPS based on CWSS, which is also a vulnerability evaluation standard for ICT systems. It can quantify the characteristics of the physical boundaries in cyber-physical systems.

Silica-based planar lightwave circuits (PLCs) are reviewed in terms of WDM applications. Four types of basic multiplexer are described and compared. Some topical applications of these multiplexers are introduced with their WDM systems. We conclude that because of these various applications, silica-based PLCs will play an important role in future WDM systems.

This paper discusses the impact of stacking on-chip inductor on power/ground network. Stacking inductor on other circuit components can reduce the circuit area drastically, however, the impact on signal and power integrity is not clear. We investigate the impact by a field-solver, a circuit simulator and real chip measurement. We evaluate three types of power/ground network and various multi-layered inductors. Experimental results show that dense power/ground structures reduce noise although the coupling capacitance becomes larger than that of sparse structures. Measurement in a 65-nm CMOS shows a woven structure makes the noise voltage half compared to a sparse structure.

Planar lightwave circuits (PLCs) provide various important devices for optical wavelength division multiplexing (WDM) systems, subscriber networks and etc. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating multiplexers, optical add/drop multiplexers, programmable dispersion equalizers and hybrid optoelectronics integration technologies.

We fabricated a tunable and polarization-insensitive arrayed-waveguide grating (AWG) 1616 multiplexer that operates around the wavelength of 1. 55 µm using fluorinated polyimides. The wavelength channel spacing was 0. 8 nm, and the 3-dB passband width was 0. 26 nm. The insertion loss at each channel was from 8 to 12 dB, and the crosstalk was less than -28 dB. The transmission pass wavelength was tuned over a wide range of 6 nm by heating from 24 to 64. The slope of the temperature dependence of the pass wavelength was -0. 15 nm/, which is ten times that of a silica-based multiplexer. Polarization-insensitivity was achieved by fabricating a film AWG multiplexer, which was formed by removing the silicon substrate and annealing at 350. The polarization-dependent wavelength shift was smaller than the spectrum analyzers wavelength resolution of 0. 1 nm.

We present a full description of a polarization-independent athermal differential quadrature phase shift keying (DQPSK) demodulator that employs silica-based planar lightwave circuit (PLC) technology. Silica-based PLC DQPSK demodulator has good characteristics including low polarization dependence, mass producibility, etc. However delay line interferometer (DLI) of demodulator had the large temperature dependence of its optical characteristics, so it required large power consumption to stabilize the chip temperature by the thermo-electric cooler (TEC). We previously made a quick report about an athermal DLI to reduce a power consumption by removing the TEC. In this paper, we focus on the details of the design and the fabrication method we used to achieve the athermal characteristics, and we describe the thermal stability of the signal demodulation and the reliability of our demodulator. We described two athermalization methods; the athermalization of the transmission spectrum and the athermalization of the polarization property. These methods were successfully demonstrated with keeping a high extinction ratio and a small footprint by introducing a novel interwoven DLI configuration. This configuration can also limit the degradation of the polarization dependent phase shift (PDf) to less than 1/10 that with the conventional configuration when the phase shifters on the waveguide are driven. We used our demodulator and examined its demodulation performance for a 43 Gbit/s DQPSK signal. We also verified its long-term reliability and thermal stability against the rapid temperature change. As a result, we confirmed that our athermal demodulator performed sufficiently well for use in DQPSK systems.

This paper presents beamforming and beam tracking techniques and downlink performance results from field experiments using a Proof-of-Concept (PoC) system. The PoC implements a 5G mobile radio access system in the millimeter wave band and utilizes beamforming and beam tracking techniques. These techniques are realized with a dielectric lens antenna fed by a switched antenna feeder array. The half-power beamwidth of the antenna is 3° corresponding to massive MIMO using approximately 1000 antenna elements. The system bandwidth is 1GHz and the center frequency is 73.5GHz. Adaptive modulation and coding using four modulation and coding schemes is implemented. The field experiment is conducted in the following small cell environments: a courtyard, a shopping mall and a street canyon. The majority of the test area is Line-Of-Sight (LOS) however the shopping mall course contains 69% Non-LOS (NLOS) conditions. The results show that the maximum throughput of over 2Gbps using rate 7/8 coded 16QAM modulation is achieved in 87%, 34% and 28% of each of the respective environments. The beam tracking achieves high availability of coverage and seamless mobility not only in LOS environments but also under NLOS conditions through the reflected paths.

The use of directional antenna and polarization diversity techniques has been reported to achieve good MIMO performance. Low-profile, small structures are required to configure the MIMO antenna with these techniques. First, we assume downlink transmission in indoor MIMO systems and present the design guidelines for the radiation pattern to obtain large channel capacity by the ray-tracing method. We then propose a uni-directional, dual-polarized MIMO antenna with a thickness of 0.24λ based on the design guidelines. The proposed antenna consists of dipole antennas mounted horizontally to the ground plane and cavity backed slot antennas for vertical polarization. We apply the proposed antenna to 2 2 MIMO transmission and demonstrate the effectiveness of channel capacity enhancement in an actual environment. The improvement factor is revealed to be +16.2% with place averaged value compared to sleeve antenna configuration.

Leakage loss of Conductor Backed Coplanar Waveguide (CBCPW) with air-gap-spacing (AGS) dielectric sheets has been analyzed by using the hybrid 2D-FDTD Method and curve-fitting procedure. From numerical results, the proposed CBCPW with AGS dielectric sheets shows even lower leakage loss characteristics than those of conventional and double-layered one over a wide range of operating frequency. Furthermore, the possibility of the optimum air-gap width for leakage loss has been confirmed.