In this letter, we propose a reconfigurable 1-bit reflectarray antenna (RAA ) with a novel varactor diode mounted multi-via mushroom-type (VDMM ) structure for heterogeneous networks (HetNets ). Specifically, its reflection phase and operating frequency band are controlled by changing a reverse bias voltage applied to a varactor diode mounted on the unit cell. Moreover, the proposed VDMM structure reduces frequency dependency in each operating frequency band by introducing multiple vias into the metasurface. As a result, the 1-bit RAA with the proposed VDMM structure can adaptively control the reflection direction and operating frequency band.

In this study, we propose a method for evaluating both the attenuation coefficient spectrum and the intrinsic emission spectrum of fluorescent fibers. The method is based on scanning the excitation position along the fiber and measuring fluorescence spectra simultaneously at both ends. The attenuation coefficient is extracted from the square root of the spectral ratio, and the intrinsic emission spectrum is obtained by normalizing spectra at a reference wavelength. Measurements with a plastic scintillation fiber (Kuraray SCSF-78) yielded attenuation spectra consistent with specifications, confirming the validity of the method. The approach is also applicable to luminescent solar concentrators and fluorescent-fiber antennas for visible light communication.

Various methods have been investigated for constructing UAV routes using ad hoc network protocols implemented on wireless devices, such as residential smart meters. In our previous study, we proposed routereservation methods to prevent link conflicts when many UAVs operate simultaneously. To reduce route construction failures caused by reserved links, we introduced hierarchical link layer approaches. However, these methods did not sufficiently reduce route construction failures. In this study, we propose a method to dynamically configure the number of link layers based on real-time UAV traffic demand. This method utilizes the Erlang B formula from circuit-switching theory to determine the optimal number of layers. These methods aim to reduce route construction failures by optimizing the number of layers. We evaluate the effectiveness of the proposed methods through computer simulations.

This paper investigates Binary-Phase Shift Keying (BPSK) based Time-Domain Single Carrier Index Modulation (TDSC-IM) optical signaling for next generation very high speed Passive Optical Network (VH-PON) systems that use coherent detection. Our preliminary 2.5 GBaud experiments demonstrated that the sensitivity gain attainable with TDSC-IM signaling can be used to reduce local oscillator power at receivers. This paper details additional experiments with the higher baud rate of 12.5 Gbaud and confirms the reproducibility of optical signal detection with 7 dB lower local oscillator power with the assistance of a newly developed adaptive finite-impulse response filter applicable to TDSC-IM optical signaling.

A vertically polarized horizontal-plane omnidirectional antenna with a circular waveguide bent <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{TM}_{01}$</tex> mode converter and an axisymmetric single reflector is designed and fabricated for the 150 GHz band. Determining a frequency range of 147.8 GHz to 170.0 GHz as the operational band, where the transmission coefficient ratio of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{TE}_{11}$</tex> mode to the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{TM}_{01}$</tex> mode is less than 1/3 that in the designed mode converter, the realized gain is 2.2 dBi to 8.8 dBi, and the angular gain variation at the measured frequencies in the band is 4.9 dB at the maximum in the fabricated antenna

This paper presents an antenna design for indoor positioning systems with the Internet of Things (IoT). The problem of direction-finding using a small array antenna with IoT devices is discussed. Theoretical studies clarify the limitations and challenges of using a null to estimate locations accurately and reduce antenna size and cost. Most importantly, electronic null-steering causes fluctuation in null-forming accuracy due to amplitude errors in the antennas and feeding circuits. This article experimentally demonstrates that this deviation error is suppressed using two copper wires and a suitable feeding circuit. The methods are feasible for practice as complicated corrections, such as amplitude controlling or signal processing, are excluded. The prototype steers a null with an angular resolution better than 4° within <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${\pm} 60^{\circ}$</tex>, verifying the simulated results.

In this letter, the relationship between the amount of leaves and leaf attenuation was clarified. We conducted FDTD calculations and measurements for a tree species called Red Robin and within the frequency range of 2.4 GHz to 15 GHz. In addition, we confirmed that the amount of leaves is defined by the product of the density of leaves and the length of the propagation path within the leaf area. We also defined leaf attenuation per unit leaf volume as LAC (leaf attenuation coefficient) to use as an index to quantify the leaf attenuation and clarified its frequency characteristics.

This study proposes a novel data segmentation method for incremental learning in network traffic prediction, leveraging change points in network configuration data (e.g., the number of users and network equipment). Isolating high-variance segments improves the incremental learning performance. Existing methods such as the PELT algorithm in ruptures face challenges in isolating high-variance segments and have the disadvantage of high computational costs. In contrast, the proposed method efficiently identifies high-variance segments by leveraging network configuration data as segmentation criteria. This approach not only circumvents the computational costs associated with parameter tuning but also facilitates more effective isolation of high-variance segments, leading to improved segmentation accuracy. Experiments show an average MSE of 1.799, outperforming baseline methods (No Segmentation: 2.846, RPT: 2.653) and enhancing prediction accuracy.

This paper proposes a hybrid hierarchical network design scheme with wavelength conversion (H2NDS) to design a low-delay network by integrating a conventional IP network and an optical network with wavelength conversion devices. In H2NDS, the network is divided into multiple domains, and wavelength converter devices and router devices are located at the relay node, an interconnection point between these domains. H2NDS is formulated as an integer linear programming problem to the sum of the delay of all end-to-end paths (delay) with constraint of the number of wavelengths in the optical network. Each end-to-end path selects the optimal relay node and selects either the router or wavelength converter devices to minimize the delay. The evaluation results showed that H2NDS significantly improved the delay performance compared to the benchmark model in which all end nodes belong to the nearest relay node, achieving a maximum reduction of 77.9 %.

The Wigner-Ville distribution (WVD) is a high-resolution time-frequency analysis method. However, the discrete WVD (DWVD) has the problem of a narrow frequency observation range. This is because the time sampling of the symmetric instantaneous auto-correlation function (SIAF) changes simultaneously in the positive and negative directions. As a result, the sampling period of the SIAF in the case of DWVD is doubled and the frequency observation range is halved. Therefore, we propose a DWVD that does not narrow the frequency observation range. Specifically, when deriving the SIAF, in addition to the conventional sample that varies in both the positive and negative directions, we consider a sample averaged over two samples that vary only in the positive or negative direction. The proposed process allows the DWVD to be performed without halving the frequency observation range. However, this process causes a small aliasing component, which can be reduced by the use of window functions. This study will demonstrate this effect by using the proposed method for chirp waveforms.