関屋 大雄

In recent years, the sharp growth of data volume has gradually driven communication networks to support more and more high-speed transfers. Accordingly, there are many efforts and interests in researching and developing such high-speed networks. Since Transport Control Protocol (TCP) plays a critical role in reliable communication, it is essential to investigate TCP performance in high-speed environments. This paper performs a measurement and performance analysis of TCP congestion control algorithms (CCAs) in an actual 10 Gbps Ethernet network setup. Unlike the other works, we have extensively investigated 14 CCAs available on Linux kernels in two evaluations: a small number (one and two) of flows and a large, varying number of flows. In the former, we verify CCAs’ responsiveness, fairness, and backward compatibility. In the latter, we measured fairness and throughput under the situation where the number of TCP flows varied by up to 10 flows. The results show that BBR is the best in responsiveness and fairness, while Illinois achieves the best backward compatibility in the two-flow experiments. On the other hand, CDG has the best performance in the evaluations with the large number of flows.

Software-defined networking (SDN) enables network automation and flexibility by offering programmability. However, SDN was originally designed for Ethernet, with its core being an SDN switch controlled by an SDN controller. Hence, integration of wireless interfaces to the SDN switch, which may bring appealing SDN features to wireless networks, is not straightforward. The root cause is the MAC address (of the Ethernet port) may be overwritten by the wireless interface’s one, leading to a MAC address mismatch problem for wireless communication. This paper presents a way to seamlessly integrate a wireless interface into an SDN switch by developing an Automatic ARP Header Modification Algorithm, which avoids the mismatch problem. We realize seamless integration with Open vSwitch (OVS), Pox controller, and a Wi-Fi card. Moreover, we show the usefulness of the integration in a wireless system with TCP and UDP communications. The results show that our algorithm successfully solves the mismatch problem under our wireless environment.

This paper discusses a circuit topology in which a class-D rectifier is employed at the output port of a conventional load-independent class-E inverter instead of a pure resistor. In order to confirm whether the load-independent mode can be still maintained in the class-E inverter with applying class-D rectifier in its output port, a design method based on a numerical design algorithm is given. The Zero-Voltage-Switching (ZVS) and constant-output-voltage conditions, which are considered in the conventional load-independent class-E inverter with a pure resistor load, are utilized as the constraints for designing the class-E inverter with a class-D rectifier. The results obtained from the numerical design algorithm are in good agreement with those obtained from experiments, which indicates the load-independent mode can be maintained even replacing the pure resistor with a class-D rectifier in the class-E inverter. Meanwhile, this result also implies that the class-D rectifier can be equivalent to a pure resistor.

This paper proposes a load-independent high-frequency wireless power transfer (WPT) system for multiple receivers with a single transmitter. The proposed system achieves zero-voltage switching (ZVS) at the transmitter and constant output voltages at all the receivers against load variations without any control. Moreover, the proposed system keeps the load-independent operation even when the number of receivers changes. The circuit analysis for the proposed WPT system is given. Experimental verifications for the proposed WPT systems with two receivers were conducted, which showed the effectiveness. The implemented WPT system achieved a peak efficiency of 83.4% at 6.78 MHz and total output power of 50 W.

Ultra-wide-band (UWB) technology has emerged as a promising solution for providing accurate indoor positioning capabilities. However, indoor environments have various obstacles, which induce significant signal propagation effects. To avoid this issue, UWB signal classification is essential for improving positioning accuracy. This paper proposes a hybrid quantum convolutional neural network (HQCNN) inspired by convolutional neural networks for UWB none-line-of-sight/line-of-sight signal classification. The result shows that the HQCNN outperforms benchmarks.

In this research, we propose a reconfigurable load-independent class-E inverter. Adding only one extra mode switch, the proposed inverter can switch between constant voltage (CV) and constant current (CC) output against load variations. Moreover, for both modes, zero-current switching (ZCS) can be maintained despite load changes, which makes the proposed inverter a suitable candidate for wireless charger applications. For achieving load-independent conditions for both modes, the circuit-components derivation method is proposed in this research. Additionally, an experimental prototype was implemented for verifying the validity of the proposed inverter. The experimental prototype achieved CC and CV output with ZCS maintained despite load variation, which proved the effectiveness of the proposed inverter.

In the globalization era, a university's homepage on the Internet has become more critical since it can give an insight into the technologies valued by the university. In this research, we compared the university homepages/websites in Germany and Japan. We aimed to learn about the differences between these countries' university websites. We first compiled a list of 492 German and 716 Japanese university websites. We then conducted experiments where users from two countries accessed all the websites. We gathered and analyzed the performance metrics related to technical and loading speed-related data for comparison. The results show that Japanese websites perform better regarding returned HTTP error codes, fewer redirects, and smaller download sizes. Regarding the loading speed, we observed that the Japanese websites could be accessed faster on average, locally and from overseas, than their German counterparts.

This paper proposes a load-independent wireless power transfer (WPT) system for multiple receivers with fixed coupling coils. The proposed WPT system consists of the single load-independent class-E inverter with LCC filters and multiple receivers based on a current-driven class-D rectifier. In this system, the output power can be individually designed according to the circuit parameter of the LCC filter independent of turns ratio of each coupling coil. It's possible to use the fixed receiving coil in all receivers. The experimental results confirmed the maintenance of constant output dc-voltages and the ZVS operation even with load variations. The effectiveness of the proposed WPT system indicated by the demonstrations.

To address the communication congestion and high energy consumption issues in IoT networks, prior research has proposed a distributed information processing system called WiBIC. As an exploratory step towards implementing the basic functionalities of the WiBIC system, this study focuses on the wireless integration of SNNs. Considering the data transmission and learning characteristics of SNNs, we propose using the APCMA protocol to effectively stabilize the operation of the wireless SNN. By modeling Pavlovian conditioning on this network, the learning capabilities of the implemented system can be determined.

This paper proposes a load-independent (LI) constant-current (CC)/zero-current-switching (ZCS) inverter with a series resonant (SR) filter. The conditions for realizing the LI operation are derived through the analysis of the proposed inverter. The circuit experiment was conducted to verify the effectiveness of the proposed inverter. The proposed inverter achieved high power output capability and low total harmonic distortion (THD) output compared with the LI class-EF inverter. The implemented prototype achieved 93.7% efficiency at 1 MHz frequency with 76.5 W output power in the rated condition.

This study proposes a self-tuned series resonant power oscillator capable of load-independent operation. The proposed power oscillator has a self-tuning feedback loop that provides a gate-driving voltage with a constant phase shift and amplitude. Therefore, it is robust against component tolerances in a series resonant filter. It is also robust against load variations owing to its load-independent design. Consequently, it maintains a high-efficiency and constant AC output against load variations and component tolerances. Experimental results demonstrated the effectiveness of the proposed power oscillator.

This paper presents a simulator-based design-optimization software for high-frequency power-electronics circuits, which consists of the heuristic algorithm, magnetic-component design tool, and commercial simulator, SPICE. Because we can use the SPICE component library, the software suggests high-accurate design results, and the experimental adjustments can be reduced. Besides, by using the heuristic algorithm, the optimization algorithm converges stably. The magnetic-component design tool provides a precise estimation of the power losses, which is important for high-frequency power-electronics circuit designs. As an example, we design the class-DE inverter by applying the developed software, which shows the usefulness of the software.

This paper introduces a host-based method for investigating IPv6 adoption and performance in academia that targets universities in Japan and Vietnam. Unlike other works, the investigation has been utilized on a host native IPv6 host with a standard tool (i.e., curl). We first probe the IPv6 capabilities of the universities' websites. Second, within the IPv6-supported websites, we compare the performances of IPv4 and IPv6 when letting the two IP versions access the websites concurrently. We find that, despite the popularity of IPv6 in the two countries, a significant number of academic websites are not yet IPv6 capable. The native IPv6 client can only access fifty of the more than one thousand websites in Japan. Furthermore, there are no IPv6-supported websites at Vietnamese universities. Among the accessible IPv6 websites in Japan, we observe that the web access performances of IPv4 and IPv6 are similar.