Comparing the bandwidths of a crossed spherical helix antenna (XSHA) and conventional antennas is challenging owing to significant change in the radiation efficiency with respect to frequency even at low voltage standing wave ratio (VSWR). Thus, two types of evaluation were performed in this work to demonstrate the wideband property of XSHA. First, the antennas were assumed to be made of a perfect conductor and were compared regarding only the VSWR bandwidth. Next, we compared the bandwidth at radiation efficiency of lossy antennas based on the generalized effective fractional bandwidth (B_e).B_e is the product of the bandwidth and the radiation efficiency varying with frequency. Numerical simulations were conducted to compare the bandwidths for VSWR≤3. The bandwidth of the XSHA is 2.19 and 2.11 times wider than those of single resonance antenna in lossless and lossy cases, respectively. Compared with a dual resonance antenna, the bandwidth of the XSHA is 1.36 times greater at acceptable radiation efficiencies of 50%.

This paper evaluates the QoS of Ethernet-based in-vehicle networks with Asynchronous Traffic Shaping (ATS), Credit-Based Shaper (CBS), and Traffic Aware Shaper (TAS), which are QoS controls defined in IEEE 802.1TSN(Time Sensitive Networking), by experiment;it then compares QoS among them. Since the number of ECUs is increasing and moving toward the realization of fully automated vehicles, Ethernet is being introduced to send them. In addition, as Ethernet-based in-vehicle networks are being deployed, adopting IEEE 802.1TSN is also being considered. Although many studies have evaluated QoS controls, such as CBS and TAS, few studies of QoS provided ATS over in-vehicle networks. Thus, the authors evaluate the QoS of ATS and then compare ATS to the other QoS controls by two experiments. One evaluates basic QoS, and the other treats actual use cases. Experimental results show that ATS can suppress maximum delay and frame losses more than the other controls when the frame interval is wide and the size is large over in-vehicle network. Moreover, they also indicate that ATS can reduce the maximum delay and delay jitter at the sacrifice of the frame loss rate by lowering the maximum residence time. Therefore, if the requirement for delay is more important than that for frame losses, it is better to adopt ATS.

This letter deals with the difference-beam operation in a center-feed dual-polarized parallel-plate waveguide slot array antenna at 24.5GHz, which consists of two orthogonally arranged 20×19 arrays of radiating slot pairs. A center-feeding scheme is employed in this design. Each rectangular feeding waveguide, fed by a probe, can feed half of the radiating panel, enabling easy control of the phase difference. Experimental results show that the monopulse antenna array has a bandwidth of 12.8% for reflections below -10 dB while it produces the sum beams, and 13.3% to produce the difference beams. Port isolation between the sum mode and difference mode is above 15 dB within the working frequency band. The measured realized gain of the sum beam is 31.3 dBi at 24.5 GHz, and the measured null-depth is below -33.9 dB for both polarizations.

To analyze the radio wave propagation characteristics, we observed the wavefront as an image using 3-dimensional imaging technology that separates the arrival times of the radio waves. In this paper, by imaging the wavefront, we can observe the radio wave propagation characteristics at each frequency.

When reflector antennas with a beam waveguide feeding system are used in an array configuration, the transmission phase of each reflector antenna must be known and corrected. In this paper, we propose a method in which a reflector plate is placed in the center hole of the main reflector, the reflected phase at the primary radiator horn is measured, and half of the measured phase is used as the transmission phase of the beam waveguide feeding system. The proposed method was verified by calculation, measurement using a simple model with the same path length, and measurement using an actual reflector antenna, and its effectiveness was confirmed.

As an alternative to GPS, we focus on indoor positioning using Wi-Fi RTT (Round Trip Time), which measures the round trip time to a Wi-Fi access point. Wi-Fi RTT-based positioning has not been well studied for indoor drones. As an experimental study of indoor drone positioning using Wi-Fi RTT, this paper presents a positioning method using a combination of on-board altimeter and Wi-Fi RTT ranging, and experimental results of drone positioning when stationary and hovering to clarify the positioning accuracy in both 2.4GHz and 5GHz bands. This paper shows that in both frequency bands, the positioning accuracy is significantly degraded during hovering compared to stationary, and that there is no significant difference between 2.4GHz and 5GHz bands.

Localization techniques for unknown radio wave sources are crucial from the perspective of efficient utilization of frequency resources. The authors have studied methods for localizing a single wave source using unmanned aerial vehicles (UAVs) in non-line-of-sight (NLOS) environments based on maximum likelihood estimation. In this study, we propose a localization method for multiple wave sources by extending the single-wave source localization method. In the proposed method, the direction of arrivals (DoAs) at UAVs is modeled with a mixture of von-Mises distributions, and the wave sources are estimated by superimposing the DoA distributions estimated at the UAVs. The proposed method is validated with a simple simulation experiment with two wave sources.

Spectrum sharing, in which multiple wireless systems share the same radio resources, has been considered to improve frequency utilization efficiency. As a spectrum sharing without control signals, a technique that observes the usage of radio resources, called channel occupation ratio, used by other systems and selects a vacant channel has been considered. However, previous studies have simplified the model of the interfering system, which is different from the real environment. In wireless communications, fluctuations in received power occur due to shadowing caused by the location and the surrounding environment. Previous studies have not clarified the effect of received power fluctuation due to shadowing on observing the occupancy rate. This letter formulates the effects on the observation results of received power fluctuations due to the location of interfering stations and shadowing. Computer simulations with randomly placed interfering stations and shadowing environments show that the proposed formulation almost matches the observed results.

We investigated a nonlinear equalizer based on reservoir computing (RC) with tapped-delay lines for compensating for linear and nonlinear waveform distortion caused by, e.g., chromatic dispersion and self-phase modulation. We evaluated and compared the equalization performance of RC systems with and without tapped-delay lines by numerical simulation, while varying the parameters and the transmission distance. The proposed equalizer construction enables the use of RC with a shorter time-constant than that used for conventional RC-based nonlinear equalizers.

Unmanned aerial vehicles (UAVs) are expected to be used in various applications such as delivery services and sensing from airspaces in smart cities. In the future, UAV control systems must address a densely mixed environment comprising various services and users regardless of individuals or businesses. However, users cannot flexibly join or leave the system because of their centralized design. This letter proposes a distributed UAV management system inspired by packet-switched networks, to address dense UAV environments. The proposed system controls autonomous UAVs as packets in packet-switched networks. Each UAV flies along a path composed of links between ground beacon devices as routers. We analyzed the characteristics of the proposed system in dense situations using computer simulation. Simulation results indicate that the proposed system can handle numerous UAVs based on packet-switched networks.

In our previous studies, we introduced a method for determining the optimal sensor placement of wireless sensor networks for monitoring indoor carbon dioxide (CO2) concentrations. This method, based on brute force, has proven to be accurate and reliable. However, the computational complexity increases exponentially with an increase in the number of sensors. Therefore, this study proposes a novel approach for optimal sensor node placement based on a genetic algorithm (GA) that offers a more efficient alternative to the brute force method. By utilizing the GA, we achieved optimal sensor placement with reduced computational complexity. To validate the effectiveness of our GA based method, we conducted numerical experiments using observed CO2 concentration. The results demonstrate that our proposed approach not only achieves optimal sensor placement but also maintains the accuracy of the observations.