This paper considers the scenario where the base station and legitimate user are blocked by obstacles and uses an intelligent reflecting surface (IRS) to assist communication. To improve physical layer security, we model the eavesdropper channel as the Rican channel and establish a mathematical model with the goal of minimizing eavesdropper’s rate subject to eavesdropper’s outage probability constraint and legitimate user’s secrecy rate constraint. The resulting problem is very challenging due to the continuous angle range of the eavesdropper’s outage probability constraint and the coupling constraints imposed by the IRS. We first use a Bernstein-Type inequality to transform the continuous constraints into discrete constraints and then propose an alternating algorithm to obtain a sub-optimal solution. Numerical results show that the proposed algorithm can reduce the eavesdropper’s communication rate in different cases, which verifies the effectiveness of the proposed algorithm.

When disasters such as earthquakes occur, telephone traffic to the disaster area increases rapidly, to confirm the safety of residents, leading to telephone network congestion. The existing congestion control for telephone networks consists of call regulation control, through which call demands at the subscriber network switches or cellular phones are suppressed. This results in a drastic decrease in the call completion rate. Disaster emergency message dial services do not meet users’ needs either to confirm the safety of people at the disaster area or to speak with them directly. In this paper, we propose a priority control scheme based on call reservations and evaluate its transient characteristics. We also propose an improved scheme to shorten the desired holding time by a fixed rate, when the number of waiting reservation calls exceeds a threshold, which can suppress the divergence of the number of reservations. We evaluated the average waiting time and threshold excess rate characteristics, and confirmed that the proposed scheme can provide stabilization.

This paper proposes a simple method of proportional fairness-based user pairing and power allocation for power-domain NOMA. Compared with the conventional method, the proposed method simplifies the fairness calculation and comparison algorithm, by which the computational complexity reduces significantly. Using computer simulations, we show that its characteristics are identical to those of the conventional method.

The deep-learning aided parameter optimization method for the average consensus problem with a complex network has been proposed by Kishida et al., which can significantly accelerate its convergence performance. However, the optimized parameters cannot be applied to the different network topology from the one used in the training. This work proposes a new optimization method constrained by the restriction caused by the network centrality, in which the optimized weighting factors can apply to the different network topology used in the training. Specifically, this work considers five types of network centralities and discusses which centrality is most suitable for the constraint of the proposed method.

This paper discusses a visible light communication (VLC) system using a digital signage and an image sensor. We propose a modulation scheme that data information signals are superimposed on a chroma component of the displayed image of the digital signage by taking advantage of the fact that human eyes are difficult to perceive chroma difference than brightness difference. Especially, the proposed scheme utilizes uniform color space to realize hardly perceivable data signal modulation. We show that the proposed scheme has better performance than the conventional scheme with the non-uniform color space.

Dispersion compensation performance of a waveband-shift-free optical phase conjugator (WBSF-OPC) on multi-span transmission of 20-Gbit/s quadrature phase-shift keying × 3-ch. WDM signals is numerically investigated. Provided that linear distortion owing to chromatic dispersion is considered, the middle channel of the WDM signals is perfectly compensated by WBSF-OPCs. Further, it is shown that the 3-channel WDM signals with a 2.2-THz optical frequency interval can be transmitted via a 640-km transmission fiber owing to the WBSF-OPCs, although their signal qualities degrade owing to residual dispersion.

Toward a battery-free wearable system, we have investigated a semi-passive human body communication wherein power and information are transmitted via the human body. In particular, we evaluated the effect of the position of the wearable device, the contact between the body and electrodes, and the contribution of the floor ground (GND) on the transmission between the HBC transceivers, using both subject experiment and numerical simulation. The results confirmed that, depending on the usage conditions, the floor GND deteriorates the transmission characteristics by increasing the electrical field that does not contribute to communication.

We proposed a novel optical power measurement scheme, which significantly improved optical power resolution (OPR) by implementing an amplified-spontaneous-emission feedback circuit (ASEFC) ahead of a conventional optical power meter. The scheme was named “ASEFC scheme.” The ASEFC operates in regions near the lasing threshold. The OPR characteristics of the ASEFC scheme were clarified experimentally. We demonstrated significantly improved OPRs in optical loss measurement of an optical component. The OPRs were less than 0.00014dB, and the sensitivity was greater than 67, at a display resolution of 0.01dB for the power meter.

The unit cell of a composite right-/left-handed (CRLH) rod-shaped leaky wave antenna (LWA) is represented by a lossless T-type circuit, and the circuit parameters that suppress the beam squint with respect to the frequency fluctuation are investigated. As a result, it was found that reducing the right-handed circuit parameter values contributes to suppressing the beam squint. In addition, it was found that the beam squint depends on the ratio of right-handed inductance and left-handed inductance when the CRLH transmission line was formed on the basis of a conventional transmission line, and a ratio condition that minimizes the beam squint was derived.

Recently, fifth-generation (5G) wireless communication systems have been spreading rapidly, and 5G mobile phone services started in 2020 in Japan. 5G wireless communication systems can provide not only greater capacities and higher speeds, but also ultrahigh-reliability, low latency, and multi-connectivity. Electromagnetic (EM) waves in the 28GHz band are also used for 5G communications. At such high frequencies, only a few paths can reach a receiving antenna, owing to the high propagation loss and high directivity of antennas used. Consequently, when an obstacle, such as office partitions, exists in a room, the quality of wireless communications deteriorates abruptly in the blocked region. In this paper, we confirm the improvement in the diffusion characteristics of an EM scattering wall with a modified checkerboard pattern. We design and optimize an EM scattering wall that exhibits a wide EM diffusion characteristic for both TE and TM polarizations of incident fields.

An phase-sensitive amplifier (PSA) is capable of low-noise optical amplification. A frequency non-degenerate PSA (ND-PSA) requires idler light co-propagating with signal light. Therefore, spectral efficiency is reduced by at least half compared to the system using phase-in-sensitive amplifiers such as an erbium-doped fiber amplifier. In this letter, we propose and demonstrate an inter-band phase-sensitive amplification scheme using signal and idler light propagating in different transmission bands. With this scheme, an ND-PSA can be applied to deployed single-band wavelength-division-multiplexing transmission systems without sacrificing the original bandwidth. Using wideband ND-PSA with PPLN waveguides, we demonstrate the proposed scheme with a 10-Gbaud 64QAM signal in the C-band and its idler in the S-band. The experimental results show the feasibility of inter-band phase-sensitive amplification with 4-THz signal bandwidth.