We report on microcavities comprising para-magnetic garnet and electro-optic films (MPMEO) for modulation of the polarization rotation angle of light at near-UV wavelengths with a slight intensity change, with applying a low voltage. The MPMEO are composed of para-magnetic garnet and electro-optic films sandwiched between two Bragg mirrors. The microcavity states in MPMEO are split and yield both the large rotation angle and high optical efficiency. Significant enhancement and modulation by applied voltages are verified through a conventional matrix calculation approach. High optical efficiency (>90%) and large modulation (~90 degree) of the polarization rotation are proved.

Communication using millimeter wave (mmWave) and terahertz bands between unmanned aerial vehicles (UAVs) is a crucial technology for the realization of non-terrestrial networks envisioned for Beyond 5G. While these frequency bands offer remarkably high-speed transmission capabilities of tens of Gbps and above, they possess strong directivity and limited communication range due to the requirement of high-gain antennas to compensate for substantial propagation loss. When a UAV employs radio of such a high-frequency band, the available communication time can be less than one second, and the feasibility of leveraging this ultra-narrow zone, which is only accessible for a short duration in a confined space, has not been investigated. This paper presents the theory behind the ultra-narrow zone in frequencies beyond mmWave and explores the data transfer characteristics at 60 GHz between two UAVs. We demonstrate the transmission of 120 MB of data within approximately 500 milliseconds utilizing the instantaneous proximity opportunity created as the UAVs pass each other. Additionally, we evaluate data transfer while the UAVs maintain a fixed distance, to sustain the 60 GHz link, successfully transmitting over 10 GB of data in the air with a throughput of approximately 5 Gbps.

We propose equiphase distance following, which is a method to keep a constant distance between mobilities by seeking the position at a certain phase of a carrier wave by using wireless two-way interferometry (Wi-Wi). Wi-Wi offers a high-precision phase sensing capability and leads on to ranging on the order of millimeters. Exploiting this advantage, a millimeter-precision automatic following technique is promising in spite of the used bandwidth of 200 kHz in the 920-MHz band. For stable following behavior, the influence of wireless environment upon the phase sensing capability of Wi-Wi is considerable issue to be examined. In this paper, we investigated the effect of an AWGN channel and co-channel interferences on the error and dispersion of phase detection. The root mean squared error of the detected phase was independent of the magnitude of CNR/CIR, and was kept at the original performance of 1-mm accuracy. The dispersion also stayed almost constant at 4.5 mm as long as CNR/CIR is greater than 10 dB, and otherwise increased rapidly as the channel degraded. Finally, we discuss about a smoothing filter for suppressing this dispersion, and have demonstrated constant-distance following with the accuracy of 5 mm.

mmWave/THz communications depend on highly focused and directive narrow beams. Accurate prediction of the beam’s spatial location and attitude in space, as well as the time it takes to reach its ultra-high-speed coverage area, referred to as the ultra-spot, is crucial for unmanned aerial vehicles (UAVs) to adjust their flight direction and approach velocity. This adjustment increases the likelihood of successful communication between UAVs. This paper introduces a novel approach for detecting these ultra-spots using real-time kinematic (RTK)-GNSS and inertial measurement unit (IMU) sensor fusion positioning powered by an extended Kalman filter (RTK-GNSS-EKF). To achieve this, we implemented a mechanism that exchanges six degrees of freedom (6-DOF) information of positions among UAVs via a 920MHz wireless communication link. Additionally, we propose an algorithm that accurately estimates the time and distance from the in-flight UAV to the ultra-spot. For the first time, this work investigates the real-world 6-DOF fluctuations in position, velocity, and attitude experienced by an in-flight UAV due to wind, and analyzes the impact of these fluctuations on the ultra-spot prediction issue. Additionally, we analyze scenarios where the ultra-spot alters its attitude by actively changing the antenna angle, assessing the consequent effects on the volume of data transmitted and received at the ultra-spot. We demonstrate the effectiveness of the proposed method by simulation and verification with actual UAV-to-UAV and UAV-to-ground-station field experiments. Experimental results indicate an average ultra-spot detection accuracy of 172 ms in time and 32.7 cm in distance, with measurements taken 1 s before the UAV’s actual approach to the ultra-spot. These findings confirm the feasibility of the proposed method for detecting mobile ultra-spots in UAV-to-UAV mmWave communication.

In UAV-to-UAV communication, airborne UAVs need to detect the location and direction of ultra-high-speed millimeter-wave (mmWave) and Terahertz (THz) coverage areas, referred to as ultra-spots. This predictive capability allows UAVs to optimally adjust their flight paths, altitude, and velocity, thereby maximizing the utilization of ultra-spot services. A space time synchronization technique employing multiple Wireless Two-way Interferometry devices (multi-Wi-Wi) is proposed in this paper to detect mmWave/THz ultra-spot locations during UAV operations. This paper proposes an algorithm that estimates the likelihood of nearby ultra-spots by considering the UAV flight route and ultra-spot direction, and by sharing location and pose information among UAVs in the network via a 920MHz wireless communication link. For the first time, this work addresses the problem of optimizing UAV flight routes to maximize ultra spot utilization. To address the inherent challenges of Wi-Wi, such as phase data unreliability, RSSI attenuation, or packet loss caused by obstructions from the UAV's own body, this study proposes the use of multiple Wi-Wi devices equipped with antennas positioned at different positions around the arms of the UAV to leverage spatial diversity effects. The proposed method's effectiveness is confirmed through experimental data derived from real-world UAV-to-UAV communication tests. An error of 37.16cm was observed experimentally in ultra-spot location estimation, corresponding to 186ms error in temporal prediction of ultra-spot entry from an in-flight UAV, demonstrating its effectiveness in addressing ultra-spot detection challenges in mmWave communication.

Bluetooth Low Energy (BLE) is widely used in small IoT devices, where further power reduction is required for long-term operation. Previous studies achieved power savings while maintaining communication reliability by adaptively selecting the transmission channel and advertising interval based on a bandit algorithm, treating all combinations as options. This paper investigates the impact of selection structure on performance by comparing this combinatorial method with two alternatives: an independent method selecting the channel and interval separately, and a hierarchical method determining the interval according to the selected channel. Experimental results show that the effectiveness of each selection structure depends on the interference condition, and that the proposed methods reduce power consumption compared with the conventional combinatorial method under the evaluated conditions.