This letter addresses the link availability issue in satellite-based free space optical (FSO) communications. In particular, we present an accurate analysis for the estimation of the link availability in the presence of clouds and atmospheric turbulence. For this purpose, a meteorological ERA-Interim database, produced by the European Center for Medium Range Weather Forecast (ECMWF), is investigated. The obtained data is, then, used to analyze the link availability for several regions in Japan. In addition, site diversity scheme is also investigated to enhance the system availability.

This letter proposes a new precoding design scheme to improve the null-space expansion (NSE) for multi-user massive MIMO systems. In NSE, steering many nulls based on past channel state information (CSI) significantly improves inter-user interference (IUI) suppression capability in a time-varying channel environment. However, extensive nullification consumes a part of the degree of freedom (DoF) resulting in the degradation of the desired signal gain. Our new proposal predicts the desired user’s channel state and derives the precoding weight to compensate for that loss. Computer simulation verifies the improved signal-to-interference-plus-noise power ratio (SINR) performance.

A spinning linear pattern is often used to measure the axial ratio of circularly polarized antennas. The maximum and minimum envelopes of the spinning linear pattern indicate the semi-major and semi-minor axes, respectively, of an elliptically polarized wave. However, there is large volume of sampled data between the maximum and minimum envelopes, which is not useful. Therefore, an envelope extraction method for a spinning linear pattern using a diode detector algorithm was proposed in this study. The diode detector algorithm was applied by solving the circuit equation using the calculus of finite differences. Through numerical verification, envelopes could be successfully extracted. An averaging method was applied to obtain smoother envelopes.

MPEG-DASH (MPEG Dynamic Adaptive Streaming over HTTP) is an international standard for video playback. In MPEG-DASH, the user perceived performance of video playback is determined by the interaction of ABR algorithms on higher layer (application layer) and TCP algorithms on lower layer (transport layer). In this paper, we evaluate several promising combinations of ABR algorithms in the application layer and TCP algorithms in the transport layer and show that carefully selected combinations can improve fairness among users. And we identify specific features of combinations which bring improvement of fairness.

The fifth generation (5G) of mobile communication systems is actively being investigated worldwide. Various systems exist when considering the microwave bands after the introduction of the 5G systems. Considering microwave propagation characteristics is crucial to minimize possible interferences among systems. This study focused on the fact that wireless communication devices such as smartphones and wireless LANs are primarily used in various indoors environments. Previously, we evaluated the loss due to the difference between the incident angles of the vertical plane with respect to a window through which radio waves enter from outdoor to indoor (O2I). In the present study, we measured the loss when radio waves enter from O2I through a window in the 0.9/2.3/5.1GHz band, where many IoT devices are expected to be used. From the data analysis of the measured results, we proposed a simple O2I penetration path-loss model using incident angles in the vertical and horizontal planes.

Increasing carrier frequency and broadening bandwidth speeds up wireless communication, but at the price of a frequency-dependent imbalance between the in-phase/quadrature (IQ) signals in the quadrature modulator/demodulator. We propose a blind compensation system for correcting frequency-dependent IQ imbalance in orthogonal frequency division multiplexing (OFDM) systems. As the convergence characteristic of conventional blind adaptive algorithms limits their compensation performance, we introduce a constant-norm algorithm (CNA) and cascaded structure. Simulation results show that the proposed scheme improves bit error rate performance in a frequency-dependent IQ imbalance environment.

The classical insertion codes were discovered at the same time as the classical deletion codes. The quantum deletion code was presented at IEICE Communications Express last year, but quantum insertion codes were never constructed. In this article, we provide the first quantum insertion code. Its encoding is the same as the four-qubits deletion code, known as the theoretically shortest deletion code.

Future bandwidth-consuming services will require 10 Tbps class network interface. Massively parallel transmission with dynamic bandwidth assignment becomes a key. To realize the 10 Tbps class dynamic bandwidth flexible media access control (MAC) mechanism, we have proposed “Dynamic MAC” concept. The key technical component is round-robin distribution of the MAC signal into parallel transmission lanes. Therefore, we have proposed a hierarchical round-robin mapper (HRRM) and developed a software-based dynamic MAC emulator for evaluating the HRRM. Details of the emulator and experiment results are presented.

As the newly EMC materials, the authors have been proposed the bandpass space filters consisting the metal wire grid with negative relative permittivity and dielectric materials. In this study, the novel space filters using conductive film grid, instead of a metal wire grid, are proposed. Next, the transmission characteristics of the proposed space filters for a Wifi router in the 2.4GHz band or the 5.0GHz band are evaluated by the measurement in free space and the calculation of transmission line theory.

This paper aims to investigate the effects of drop shape on rain attenuation prediction based on the theoretical approach. By comparing the predicted rain attenuation with the measurement results obtained in Skudai, Malaysia, the theoretical method based model utilizing the knowledge of scattering properties and raindrop-size distributions are found to produce better prediction results than the widely-used empirical ITU-R model, particularly at high rain rate. At 26GHz and 38GHz, results calculated using realistic drop shape were found to yield lower RMSE than using spherical shape.

To realize dynamic spectrum sharing, it is necessary to avoid interference from the secondary system to the primary system. Technical information such as the position of the radio station and the antenna specification of the primary system are required to estimate interference to the primary system accurately, but these specifications are not generally disclosed. In this paper, we propose a method for estimating the antenna beam direction using only information on the received power at the radio wave sensors. Using the simulation data and the outdoor measurement data, the evaluation confirmed the effectiveness of the proposed method.

We have proposed an Emergency Rescue Evacuation Support System (ERESS) that is effective in sudden disasters. This is intended to detect disasters by collecting moving data of mobile terminals. In this research, in order to realize behavioral analysis without restricting the terminal holding state, we propose a terminal holding judgment method and an abnormal behavior judgment method using machine learning. Experimental results show the effectiveness of the proposed method.

This study provides a solution for mm-wave FMCW radar-based heart-rate detection of an indoor moving person. The range-bin where the person is located will change during the moving state, and the signal energy is weaker than clutter at farther distances. Therefore, we propose an adaptive range-bin selection method that effectively selects the optimal range-bin cell to obtain the correct radar vital sign before heartbeat signal reconstruction. The experimental results show that the proposed method can reconstruct the heartbeat signal with high precision when used in conjunction with the ICEEMDAN method.

We proposed a ray-tracing (RT) acceleration method using the tensor completion technique for a three-dimensional (3D) radio map. Internet of things (IoT) has become widespread recently, and analysis of indoor radio wave propagation has become important in optimizing the installation location of the IoT devices. Generally, RT is used for radio wave propagation analysis. However, RT is time-consuming to simulate. The simulation time required for RT is even larger when calculating the receiving points in 3D space with many objects. Hence, in the proposed method, we reduced the number of receiving points at which the RT calculation is performed, and we interpolated by tensor completion the received power not calculated by RT.

For Massive IoT systems, various Low Power Wide Area (LPWA) systems have been developed and deployed, i.e., LoRa, SigFox, etc. In this paper, to avoid destructive collisions when multiple IoT LoRa signals simultaneously received in the same channel, we propose a Successive Interference Cancellation (SIC) based collision avoidance mechanism by accessing channel using reinforcement learning for distributed massive IoT systems. Simulation results show the effectiveness of our proposed mechanism in terms of Frame Success Rate (FSR).