Water-related accidents are occurring all over the world. In Japan, approximately 1,200 water accidents occur every year. In marine activities, divers are exposed to various dangers such as floating objects and hypothermia. Therefore, an undersea position estimation system using kHz waves has been studied to support rescue operations by positioning divers in the sea. In this study, in order to facilitate the installation and retrieval of the undersea position estimation system, we investigated the position estimation of the undersea transmitting antenna using a single receiving device that combines three dipole antennas in electromagnetic field simulation. We confirmed that position estimation using the receiver proposed in this study was possible in some areas, and that the position estimation accuracy was affected by the distance from the receiver and the posture of the transmitting antenna.

This study examines the accuracy and measurement costs associated with room-level indoor-area estimation using a wireless LAN. Utilizing fingerprinting, a method that compares user-measured access point (AP) information with pre-existing AP data from service providers, this study introduces a cost-effective approach. Our proposed machine learning (ML)-based method leverages data collected by users while traversing different locations within an area, thereby significantly reducing the measurement time. Furthermore, this study contrasts the effectiveness of convolutional neural networks (CNN) and support vector machines (SVM) in area estimation using this novel measurement technique. Both CNN and SVM demonstrated comparable accuracy, with SVM exhibiting a shorter processing time.

This paper introduces a newly designed X-shaped slot antenna with high gain and wideband characteristics for use in mm-wave frequency band. The X-shaped slot antenna serves as radiating elements of planar array configuration for high gain. The 4×4 configuration is investigated in this paper. According to simulation results, the 4×4 planar array exhibits a -9.7 dB impedance bandwidth within the range of 26.1-31 GHz and a maximum gain of 18.2 dBi. Furthermore, gain and bandwidth enhancement of the array antenna is studied. As the results, the antenna shows an impedance bandwidth within the range of 25.35-25.95 GHz, and 26.8-30.2 GHz. Within this band the antenna realized gain is ranging from 17.5-20 dBi.

Recently, the practical application of HAPS (High Altitude Platform Station) as the next-generation communication platform is studied actively. HAPS employs adaptive rain attenuation countermeasure techniques such as site diversity methods, therefore it is ideal to predict rain attenuation on the path in real time. We proposed real-time rain attenuation prediction method by convolutional neural network that inputs image of rainfall rate and path distance. Result showed that prediction accuracy of our proposed method is better than a method using conventional formulas.

High-altitude platform stations (HAPSs) have the potential to expand the coverage of sixth-generation mobile communication systems, and several international mobile telecommunications (IMT) bands below 2.7 GHz have already been identified for HAPS service links. Because of the limited frequency resources, spectrum sharing techniques are needed to ensure that HAPSs can coexist with terrestrial base stations (BSs), but this means that a HAPS may interfere with the connection of terrestrial BS users within its line of sight. This letter proposes a scheme that combines an interference canceler and enhanced inter-cell interference coordination to reduce interference in an integrated HAPS-terrestrial system. Numerical simulations demonstrated that the integrated system greatly improved the signal-to-interference-plus-noise ratio of terrestrial BSs and improved the system capacity by 26% compared to a conventional system with no interference reduction.

Mutual coupling reduction is required to miniaturize wireless devices in many applications. The mantle cloak technique has been studied to reduce mutual coupling. This paper proposes a square rod mantle cloak antenna with a low-frequency rejection band. The rejection band is 720 MHz and the operation band is 750 MHz. The proposed antenna structure contains a copper rod-covered dielectric substrate with strip conductors at the center of each face. The proposed antenna was validated by comparing the simulation and measurement results.

This paper presents a antenna composed of metal case with a slot and inner folded dipole antenna. The proposed antenna structure simultaneously achieve the miniaturization of the metal case and the wide bandwidth. The impedance bandwidth of 15.9 % with the size of 0.35λ₀×0.35λ₀×0.03λ₀ (λ₀ is the wavelength of low frequency) can be realized by the proposed structure. The proposed structure is validated by the comparison of the simulation and measurement result.

The line-of-sight (LOS) probability in an urban environment assuming unmanned aerial vehicle base stations (UAV-BSs) is studied. We establish an estimation formula to calculate the minimum density of UAV-BSs required to achieve a certain LOS probability over an area.

Utilizing an analog to digital converter (ADC) with low-resolution is preferred in terms of high sampling rate, low energy consumption and low implementation cost. Against these advantages, utilizing low-resolution ADCs would lead to degrade the signal detection performance. This paper focuses on addressing this issue by introducing a novel receiver that incorporates a new stochastic resonance (SR) processing method, which adaptively adjusts the intentional noise base on the modulation level of the signal, for the detection of multilevel amplitude modulated signals. Through computer simulation, we confirmed the further improvement by applying the proposed adaptive SR. Moreover, we observed that the proposed receiver is more resistant to channel noise.

In this study, we propose a novel method for network-anomaly detection and failure-scale estimation using autoencoders, which are a type of neural network. The proposed method first divides the network into several groups. Subsequently, anomalies are detected using an autoencoder for each intergroup traffic, and the failure-scale is estimated from the number of autoencoders that have detected anomalies. We experimentally investigated anomaly detection during communication through a virtual network built using the network emulator Mininet and confirmed that the proposed method can successfully detect anomalies and estimate the failure scale.

In the passive intermodulation (PIM) measurement of microstrip lines using non-contact planar connector, this letter presents a proper sample length for the 3rd-order PIM measurement due to closely frequency-spaced transmission waves. Our experimental study using nickel-plated samples as a distributed PIM source reveals that a spacing between non-contact connectors should be a quarter guided wavelength in order to suppress the effect of non-contact connectors on the PIM measurement results and maximize the observed reverse PIM. We also demonstrate a circuit-network simulation using the harmonic balance method, which agrees well with and validates the experiments.

This paper presents a capacitive wireless power transfer system that employs a three-dimensional (3D)-functional coupler for obtaining maintenance-free industrial robots. To enhance the vital coupling coefficient of the coupler within a confined space, such as a rotary joint, we fabricated a 3D capacitive coupler. Additionally, by employing polytetrafluoroethylene (PTFE) resin with a high Q factor for electrode fixation, a theoretical maximum efficiency of 99.3% was achieved. Finally, we designed a system that successfully produced a transmission of 5.76 W with a total DC-DC efficiency of 73.0% at 13.56 MHz and an arm chuck operations utilizing both power and pneumatic pressure.

This study investigates the characteristics of signal detection parameters, such as target signal detection probability and false alarm probability of an energy detection based carrier sense, which can effectively avoid interferences in the same frequency band, in low power wide area networks (LPWANs). The aforementioned target probabilities strongly affect the characteristics of energy detection and its application, and revealing the characteristics that enhance the performance of energy detection based carrier sense is important. Two types of numerical example based analysis are presented from the viewpoints of signal detection and wireless networks. The analytical results show the presence of an optimal target false alarm probability.

QUIC is a transport protocol that adds congestion control, retransmission control, and TLS to UDP. QUIC can use the same congestion control algorithms as TCP. In previous work, we have shown that communication performance becomes unfair concerning the buffer size of the shared bottleneck link of two flows, one using CUBIC and the other BBR congestion control algorithms within QUIC. In this study, we improve the communication fairness performance at different bottleneck link buffer sizes by using Round Trip Time (RTT) and Explicit Congestion Notification (ECN) to regulate congestion control aggressiveness when CUBIC and BBR compete within QUIC through actual experiments.

This letter introduces a transmitter design algorithm that prioritizes user fairness for OFDMA-based full-duplex wireless powered communication networks. In the energy transmitter, beamforming is determined to efficiently transmit energy signals to user terminals while minimizing interference to the information receiver, and the transmit power is allocated according to a proportional fairness criterion. In user terminals, subbands are allocated based on minimum rate maximization for information transmission using the harvested power. The simulation results demonstrate that the proposed design algorithm achieves superior user fairness compared to the conventional sum-rate maximization algorithm.