The number of IoT devices connected to the Internet has been rapidly increasing. On the other hand, some IoT devices may not have sufficient security capabilities because they do not have enough resources. Previous work to monitor IoT device traffic used a monitoring node running packet sniffing software, but it required an extensive resource. We propose new IoT traffic monitoring method which utilizes DNS name resolution. Our method not only decrease CPU resources, but also prevent suspicious communication from IoT devices. We implemented the prototype to verify the proposed method can detect and prevent suspicious communication with lower CPU load.

CAPTCHA is designed to detect automated programs (called bots) by requiring them to perform tasks that are easy for humans but difficult for automations. CAPTCHAs are vulnerable to relay attacks in which the challenges are relayed to remote human-solvers. In our previous paper, we proposed an interactive video type CAPTCHA that is strongly resistant to relay attacks. However, a quantitative evaluation of resistance to automated attacks still has not been carried out. Herein, we implement an automated attack for applying to our CAPTCHA and evaluate its resistance to automated attacks. Our results show the robustness of our proposed method against mean shift algorithm.

A bandwidth of the superdirective antenna composed of an asymmetric dipole element backed by a planar reflector which has been proposed by the authors, is enhanced by incorporating both a self-complementary structure and a T-type monopole element into the original antenna. It is shown that a 6% bandwidth and a 4.8 dBi gain were obtained even though the thickness decreases to 0.02 wavelength at the center frequency. It is also shown that the developed antenna structure maintains a unidirectional property which is benefit for many IoT applications.

A 2 × 2 circularly polarized array antenna integrating a dual-feed network is proposed to provide a dual-beam radiation patterns for the wide-angle rectennas. The two diagonal antenna elements of the array antenna are quarter-wavelength ahead of another diagonal antenna elements. The planar magic-Ts are effectively used to obtain the desired radiation patterns with a simple structure. The design and performance of the array antenna is confirmed with experimental results and the proposed antenna has the same radiation patterns in the x-z and y-z planes. The measured gain of the proposed antenna is more than 9 dBic and 3-dB axial ratio bandwidth is 0.86%. The 10-dB impedance bandwidth of the antenna is better than 4.4%.

In edge computing, users can enjoy various applications without depending on limitations of mobile devices by task offloading. However, a large number of tasks will be offloaded to distant cloud servers when an edge server’s load is too heavy. The long distance between users and cloud servers significantly degrades the quality of mobile applications. To prevent this problem, we propose flow splitting and aggregation schemes to improve offload delay to cloud servers in edge computing and show the effectiveness of our scheme through simulation evaluations.

RFID (Radio Frequency IDentification) system is expected to serve as the distribution management system of the alternative to bar-codes in recent years. If objects storage location detection equipment with RFID technology is introduced in the distribution management system, work efficiency and safety improvement are predicted. The system that can identify massed RF-tags has already been proposed, though it is required to mounting dedicated tags. On the other hand, the massed RF-tag location detection system which can use the ordinary and low-priced tag is proposed in this report.

Multi-layer ceramic capacitors (MLCCs) have been employed for miniaturizing the unit cell structure of metamaterials. In addition, specific absorption rate suppression methods and thin wave absorbers based on metamaterials composed of MLCCs have been reported. This paper proposes a negative effective permeability metamaterial using MLCCs. Firstly, the effective permittivity and permeability of the unit cell are obtained from simulated S-parameters and compared with the dispersion characteristics. Next, transmission S₂₁ characteristic of the stacked metamaterial structure composed of the MLCCs is analyzed and then compared with the measurement result.

Impedance matching mechanism of shielded loop antenna for coupled-resonant wireless power transfer is discussed. It is known that transmission efficiency of the shielded loop antenna is improved as compared with the loop antenna. In this report, we investigate the mechanism of transmission efficiency improvement in shielded loop antenna through equivalent circuit analysis. As a result, impedance matching is achieved due to the capacitance between the inner conductor and the outer conductor to improve transmission efficiency.

In this paper, we propose a double-layered folded spiral resonator for near field wireless power transfer (WPT). To realize maximum available efficiency, impedance matching of real part and imaginary part is necessary. It is known that a folded dipole antenna, which is used in far-field communication systems, has a capability of adjusting real part of input impedance by changing radius of the resonator wire. In the proposed structure, folded structure is applied to spiral resonator for near-field WPT. Furthermore, to decrease proximity effect and increase capability of impedance matching, folded structure is formed in double layer. Numerical simulation demonstrates that by using the double-layered folded spiral resonator, transfer distance over 80% η_max extends 1.78 times compared with the conventional single-layered folded spiral resonator.

Recently, mobile terminals having small touchscreen such as smartwatches are increasing. PIN or pattern lock are used for personal authentication for smartwatches, but it is possible to leak authentication information by peeking the screen because the information is displayed directly. Therefore, in this paper, we propose Personal Identification with Any Shift (PIAS), which user taps different icon from registered icon on 3 × 3 icons. In addition, we implemented PIAS and evaluated it by confirming the usability and shoulder-surfing resistance. As a result, authentication time and success rate was 13.8 s and 89.4%, and the rate of successful shoulder-surfing attack was 0.0%.

In cyber-physical systems, the reliable data communication between the physical systems and computer systems are inevitable, and it is an essential issue to protect the systems from jamming attacks that obstruct wireless communication. Moreover, for practical uses of the systems, Quality of Service (QoS) is also important. In this paper, we consider a mobile robot and propose an anti-jamming mobile control system that uses QoS-based reinforcement learning. We show that the control system can find a policy that provides planning with a short path while avoiding jamming attacks.

Eigenvalue communication is a promising technology that can overcome capacity limitations caused by the Kerr nonlinearity in optical fibers. In this letter, we propose an artificial neural network-based demodulation method for optical eigenvalue-modulated signals using on-off encoding. The proposed method has a power margin improvement of 9.2 dB at the bit error rate of 3.8 × 10⁻³ compared with the conventional inverse scattering transform-based demodulation method in numerical simulations.

The miniaturization of conventional near field communication (NFC) antennas is required to improve the flexibility of placement of the constituent electrical and electronic components. A small-sized magnetic material loaded solenoid has been proposed. However, the transmission efficiency of this design decreases as the size of the antenna decreases.

This study focuses on a linearly aligned, two-solenoid array and numerically investigates the dependency of the magnetic field distribution radiated from the solenoid array in relation to the excitation direction. The influences of the magnetic material loaded into the solenoids on the magnetic field distribution are also analyzed. Based on the results, the out-of-phase excitation can yield larger magnetic field strengths near the center of the solenoid array compared to the in-phase excitation because the total magnetic field produced by the two solenoids in the former case is the summation of the magnetic fields of the constituent fields generated within the tested area. When the observation point is far from the solenoid, the in-phase excitation can generate a larger magnetic field strength than the out-of-phase excitation because the magnetic field parallel to the solenoid becomes dominant. In addition, it is found that the excitation of the linearly aligned, two-solenoid array suitable for NFC depends on the permeability of the magnetic material and the target distance between the solenoid array and the receiving antenna.

To transmit mechanical signals across long distances, unattenuated transmission lines have been proposed. However, these are difficult to design and manufacture and require external power supplies. Instead, we propose using coupled cylindrical origami units to make up signal lines. Cylindrical origami is easily assembled from a single sheet and can have bistable properties with adjustable energy curves, such as by applying additional springs. This enables continuous mechanical signal transmission down the line. We numerically simulated these systems and confirmed their feasibility for transmitting signals as well as for creating diodes and logic gates.

We are developing a method to acquire position information of a cow outdoors using Received Signal Strength Indicator (RSSI) of Bluetooth Low Energy (BLE). As existing research, there is a localization method using fingerprint database as learning data in deep learning. However, that method has the problem that it costs to create a database by measurement in a vast outdoor environment. Therefore, we considered to build a part of the fingerprint database using virtual space modeling received power measurement environment in a pasture. Experimental results showed that an average distance error to GPS data is about 6 m by training DNN using the database and additionally training DNN using actual GPS data.

Tunneling scheme based on Transmission Control Protocol with Network Coding (TCP/NC Tunnel) is a potential proposal for applying TCP/NC on networks having end devices unable to implement TCP/NC and saving the bandwidth in loss-free but thin networks. However, it currently lacks an efficiency packet dropping method in network congestion resulting in causing many TCP timeouts at end devices, and non-stop increasing the number of redundancy packets on tunneling. It also lacks the method to drop unuseful retransmitted packets cause gateway buffer overloading. In this paper, we propose a new buffer management mechanism for TCP/NC tunnel system to solve all these issues.

The lack of cellular or radio coverage in mountainous regions drives a need for alternate communication or data transmission systems in such areas. We used our proprietary LoRa-based GEO-WAVE system to develop a system for monitoring remote wildlife traps (used for population control) and conducted field tests in a mountain region of Japan. The system achieved a maximum 160 km communication distance between a repeater and source device. Even in areas with poor line-of-site visibility, communication was widely successful due to the diffraction of radio waves. Other dead zones were easily eliminated by adding repeaters at strategic locations.

We proposed and investigated novel methods for polarization demultiplexing using artificial neural networks (ANNs). It was shown that a three-layer ANN includes butterfly operations and has a polarization-demultiplexing capability. Our proposed cascaded construction of a butterfly-structure of FIR filters and an ANN connecting x- and y-polarization components exhibited superior performance in terms of the polarization-demultiplexing speed. By using the proposed method, optical nonlinearity can also be compensated for at the same time. We examined and compared the performance of the proposed methods by numerical simulations using 10-Gsymbol/s polarization multiplexed 16QAM optical signals.

In an era where the number of wireless LAN terminals is sky-rocketing, ubiquitously improving the quality of the user experience at low cost is paramount. To achieve this, we propose a method that automates re-assignment of frequency channels in high-quality communication areas to achieve automated operation in High-Density Wi-Fi systems. The method identifies neighboring Access Points (APs) to re-assign frequency channels efficiently and effectively. The goal of the proposed method is to clarify the effect of the amount of information including errors on the AP identification accuracy by using a huge amount of station (STA) information. Simulation results indicate that neighboring APs can be identified more accurately using STA information in High-Density Wi-Fi systems.

Performance of a Ninja array antenna whose backscattering level is lower than that of conventional phased array antennas is demonstrated experimentally. A linear array antenna which is composed of non-identical Yagi-Uda monopole antenna elements is designed. Designed array is fabricated and its scattering/radiation performance is measured. The fabricated array shows low backscattering performance without losing its beam scanning capability.

A polarization switchable active integrated array antenna is proposed in this letter. The proposed antenna accommodates two microwave circuits; an oscillator and PSK modulator with antennas for both vertical and horizontal polarizations. Employing a PSK modulator in the horizontal feed line, it is possible to flip the horizontal polarization of the antenna and hence the polarization can be switched between ±45°. The basic concept of the proposed antenna is experimentally confirmed by using a 10-GHz band prototype antenna and better than 15-dB cross-polarization suppression is obtained.

To increase both the symbol rate and the number of bits per symbol for optical camera communication (OCC), rolling-shutter (RS)-based quadrature amplitude modulation (QAM) is demonstrated by spatial luminance distribution of a light emitting diode (LED) surface. The spatial luminance distribution method is adapted to different LEDs regardless of the LED shape and configuration, and compared with the conventional pixel value method. The advantages and drawbacks of the spatial luminance distribution method are experimentally investigated. When the symbol length is integer multiples of the line interval of the RS camera, RS-based 16-QAM OCC is demonstrated using a square-shape LED.

In order to detect estrus and abnormalities from the interactions of grazing cattle, we are developing a position estimation method using low-power wireless devices. In this paper, in order to obtain a natural trail of cow’s locations, we propose a localization method based on long short term memory. Our evaluations show that the proposed method suppresses unnatural trail and achieves the average location error of 5.25 m for the cow that is used for learning and about 6 m for the other cows.

In the cellular mobile communication systems using sectored cell configurations, reducing the back-lobe interference of the base station (BTS) sector antenna that arrives at the other sectors in the same cell is very important to improve the Signal to Interference power Ratio (SIR) and thus cell throughput. Setting the beam tilt angle of the back-lobe deeper than that of main-lobe for the BTS sector antenna greatly reduces the back-lobe interference. We investigated the combined beam tilting method in order to realize the function by simulation in the previous work. In this paper, we clarify the improvements in SIR possible when applying the combined tilting technique to cellular systems by field trials in a rural cell near Tokyo.

This paper proposes a novel centralized beamforming scheme for Radio-over-Fiber (RoF) systems with fixed wavelength allocation. The proposed scheme offers more wavelength utilization efficiency than the conventional beamforming methods that control wavelength allocation, and can control beam direction without explicit control by the base stations (BSs). Moreover, the scheme makes information about optical fiber length unnecessary, and supports systems that use high radio frequency (RF) signals or long optical fiber. Simulations evaluate and confirm the feasibility of the scheme for a system that uses 60 GHz RF signals, 10 km optical fiber, and 8-element linear array antennas.

The future is likely to see millimeter-wave systems used in urban street canyons for high data rate communications. Space limitations in urban areas will necessitate using small size antennas for building millimeter-wave systems in mobile front-haul application. Such antennas have broad beamwidth and consequently the systems in street canyons will incur multi-path interference. This letter addresses the issue of such multi-path interference. We conducted experiments in 72 GHz bands to ascertain the interference effects and a strategy we devised for avoiding them. We found that harmful interference can be evaded by rotating the radio transmission direction.

Vehicular antenna are seriously affected by their body due to current flowing on the surface. Therefore, several near field measurements have been proposed to estimate the current distribution on the conductor surface by hemispherical scanning, but errors are not enough small by complex model in high frequency. This paper presents Hermitian transpose to improve the estimation, which is verified in simulations.

CAPTCHA is a technology designed to prevent automated programs (known as bots) from acquiring access to on-line accounts to send spam mail, manipulate vote numbers in on-line polls, or take other malicious actions. In addition, access to Web services has been incorporated into mobile devices, such as smartphones. However, because most CAPTCHAs are not designed for mobile devices, user-friendly CAPTCHA for mobile devices is required. Thus, we implemented CAPTCHA on mobile devices and evaluated its resistance to bots. Our CAPTCHA showed robustness against bots, with good usability.

Multicarrier heterogeneous networks (HetNets) are promising technique of 5th-generation mobile systems to increase system capacity. This paper proposes a personal-cell scheme using an adaptive control cell range expansion (CRE) in multicarrier HetNets, which combined with a macrocell with a carrier frequency of 2.0 GHz and a picocell with a carrier frequency of 3.4 GHz. Average and 5-percentile user throughputs of the proposed adaptive control CRE are presented using system-level computer simulations in comparison with the conventional CRE.

Using these results, we validate the design of the adaptive control CRE in multicarrier HetNets.

In recent years, wireless network systems are utilized in various industry fields and the wireless service area planning became one of the important tasks to realize efficient and high-quality wireless communication service. The machine learning technology attracts the interests of researchers to improve the efficiency of the area planning task because the radio propagation loss in unknown locations can be predicted by the training data without explicit algorithms. Our previous work showed that the path loss (PL) characteristics become complicated in the high PL region, and it can degrade the entire prediction accuracy. In this paper, we propose the two-step PL prediction method by the artificial neural network (ANN) to solve the issue. Firstly, the area is classified into several zones according to the PL range. And then the PL is predicted by ANNs that were trained for respective zones. Our proposal was evaluated by the ray-tracing simulation data, and the result showed that it improved the root mean square error (RMSE) of PL prediction from 7.9 dB to 4.1 dB. The method is expected to be utilized for the wireless service area planning in various environments.

Near-field wireless power transfer scheme using collinear array antenna for moving vehicle is proposed. Although a collinear array antenna is known as a high-gain antenna for far-field communication system, this antenna can generate near-field distribution along the cable. In the proposed scheme, a collinear array antenna is set under the road to feed running vehicle. As a receiving antenna, half-wavelength dipole antenna is set under the vehicle. The transmitting collinear-array antenna and receiving dipole antenna couples in near-field to feed power to a vehicle. Experimental demonstration shows that this scheme is applicable for power feeding to running vehicle.

The 5-th generation of mobile communication systems (5G) are being actively investigated all over the world. Various systems exist when considering the microwave bands after the introduction of the 5G systems. It is very important to consider the microwave propagation characteristics in order to minimize possible interferences among systems. In this paper, we propose a simple outdoor to indoor (O2I) propagation model based on the 2 and 5-GHz bands. The proposed model focuses on the variation in incident angle on a vertical plane when the microwaves move from O2I environments. This model shows realizes the additional loss by using only angles on the vertical plane.

Bluetooth MANETs, which are wireless networks with Bluetooth-enabled terminals, only have proposed flooding-based methods for one-to-many communication among terminals. In general, however, to develop and implement useful applications, we have to prepare routing-enabled frameworks for Bluetooth MANETs. In this paper, we have proposed a new Bluetooth MANET-based routing scheme through the development of an attendance confirmation system. We also have implemented the system on Android- and Raspberry Pi-based terminals, and have conducted 10 terminals-based experiments. As a result, we have confirmed that our proposed method worked properly.

Electromagnetic induction between power lines and telecommunication cables may cause physical injury of service personnel, and malfunction or quality degradation of telecommunication services. Therefore, the influence of electromagnetic induction on telecommunication cables has been studied since early 1900’s. However, due to a complicated configuration and multi-point connection to the ground, there were few studies on induction phenomenon to a suspension wires that support overhead telecommunication cable. In this paper, we have studied on induction phenomena upon multiple point grounded conductors, theoretically and experimentally. As a result, we confirmed that calculated and measured results are in good agreement with ideal conditions.

This paper proposes a new traffic classification method for peer-to-peer-based video streaming (P2PTV) by using machine learning. Since P2PTV is a promising technology for video delivery, it is important to comprehend its traffic characteristics. Our previous studies classified and analyzed traffic obtained in viewing P2PTV on a per content basis. However, users’ participation would be dynamic, and then the traffic characteristics may change momentarily. In the proposed method, we divide per-content traffic into short-time data units and then classify them by machine learning. From the experimental results on 80 contents data, six types of unit traffic patterns appear. Moreover, we also analyze their occurrence patterns.

This paper proposes an electric power based incentive mechanism that source nodes compensate the electric power required for packet transmissions in mobile ad hoc network (MANET). Although MANET forces the relay cooperation on nodes for the multi-hop communication, the relay transmission consumes their resources for other nodes, which may cause nodes to be uncooperative. We assume electric power exchange between nodes, which has been getting practical in recent years. The proposed routing method uses incentive power based on the energy consumption for relaying packets as a metric. Computer simulation confirmed that the method implemented to AODV can reduce the power consumption on the relay nodes.

A cubic Yagi-Uda array antenna with high gain for 500 MHz rectenna is proposed. The proposed antenna is composed of two elements of Yagi-Uda antenna. The proposed antenna is compact and its volume is λ/3 × λ/3 × λ/3 because the Yagi-Uda antennas share a reflector and director. Performance of the proposed antenna is demonstrated and resultant gain is as high as 8.5 dBi. Finally, the proposed antenna is applied to a 500 MHz rectenna system with voltage doubler rectifiers and its performance is demonstrated experimentally.

A circularly polarized feed circuit in a primary radiator of a reflector antenna is often required to have a low axial ratio. Therefore, it is necessary to accurately evaluate the axial ratio. The left- and right-handed circular polarized components are numerically obtained from the complex coefficients measured for dual linear polarized waves. The transmission phase measurement is difficult to measure accurately, particularly at high frequencies such as Ka band. Authors proposed a method to measure the axial ratio of the circular polarization feeding circuit from the reflection coefficient only, and the proposed method has been validated by the numerical simulation.

In collaborative multi-input multi-output detection, a virtual terminal consisting of neighboring mobile stations (MSs) is formed. This virtual terminal acts as a single MS with a large number of antennas. In this system, received signals of MSs in collaboration with each other are shared through short-range wireless communications. In this paper, in order to reduce the amount of collaboration traffic, simple adaptive MS selection schemes are studied by an urban measurement campaign using a software-defined testbed operating at 5.1 GHz. The MS selection schemes perform close to the full collaboration scheme, and outperform the round-robin scheme.