Yuichiro Okugawa

Experimental Evaluation of Coexistence Method for ZigBee under WLAN Interference

ZigBee has attracted attention for constructing the sensor network such as home energy management system. Both ZigBee and wireless LAN (WLAN) use a 2.4GHz band, called the industrial, scientific, and medical unlicensed band; therefore, ZigBee faces severe interference problems in the presence of WLAN. Frame collisions are serious problems between ZigBee and WLAN. Both employ a carrier sense mechanism to avoid collision, but both use different channel access mechanisms. The primary problem is the competition that exists between WLAN data frames and ZigBee ACK frames, i.e., because of WLAN interference, ZigBee may not receive any given ACK frame; therefore, the ZigBee transmission success ratio is degraded. To overcome this problem, the authors propose an interference avoidance method that improves ZigBee and WLAN coexistence and utilizes actual equipment to present the experimental evaluation. The experimental results reveal that the ZigBee transmission success ratio increases as the WLAN transmission rate increases. In addition, we clarified the distance in which the proposed method can effectively operate. Index Terms—Wireless LAN, ZigBee, CSMA, interference, frame collisions

Mode conversion and transfer characteristics of conducted disturbance to Ethernet device from power supply cable

Conducted disturbances from communication or power supply cables affect Ethernet devices. A conducted disturbance, which is generated when several switching power devices reach a communication device, degrades the quality of signal communications. In addition, a disturbance passing through an Ethernet device influences neighboring devices connected by the communication cables. Herein we propose a system to measure the propagation modes of conducted disturbances in power supply cables and Ethernet cables. The results indicate that mode conversion occurs in not only an Ethernet hub but also an AC adapter supplying DC voltage to Ethernet devices. The conducted disturbance to the AC and DC power supply cable is strongly transmitted to the Ethernet cable as the primary common mode and the differential mode. Conversion from the common mode in the power supply cable to the primary common mode in the Ethernet cable is dominant in the measured frequency range.

Linear predictive coding without Yule-Walker approximation for transient signal analysis: Application to switching noise

We are investigating countermeasure techniques against electric noise on telecommunication and related equipment. There are many types of electric noise, and we focus on the characterization of transient noise such as the switching noise of switching power supplies. We are developing a method of transient signal analysis based on linear predictive coding (LPC) for the purpose. Unfortunately, as standard LPC contains Yule-Walker (YW) approximation, which replaces a given time series with a periodic time series for simplification, it is not suitable for transient signal analysis. Therefore, our method of transient signal analysis does not contain YW approximation. Instead, we use the local linearization technique, which was developed in the field of quantum mechanics. Our method makes it possible to obtain instantaneous frequencies and instantaneous decay rates simultaneously with high precision from a small number of samples. We discuss our LPC method avoid using YW approximation and using the local linearization technique and its application to repetitive ringing signals, which mimics the switching noise of a switching power supply, to show the efficiency of our method.

Evaluation on active power of common-mode conducted disturbance

Power conversion equipment is known to generate common-mode conducted disturbance. The authors have studied about common-mode apparent power evaluation, which have magnitude and phase information of the disturbance, for clarifying the generating mechanism of the disturbance. This paper describes the importance of evaluation of active power, a part of apparent power of common-mode conducted disturbance, and the validation of the active power evaluation. Additionally, verification of the active power evaluation with using DC-DC converter as EUT has been considered. As a result, validation of evaluation result has been proved by comparing common-mode apparent power, calculated from active power and measured common-mode apparent power.

Detection method for overclocking by intentional electromagnetic interference

Overclocking due to the disruption of a clock signal sometimes causes malfunctions (i.e., temporal faults) in LSI modules. It is known that electromagnetic interference can also cause overclocking. However, there is no specific method for detecting the occurrence of such overclocking in LSI modules. This paper proposes a method for detecting overclocking in LSI modules and its implementation as a detection circuit. We evaluate the validity of the proposed circuit through two kind of experiments (i) with a clock signal with artificially-inserted glitches and (ii) with CWs injected externally. From the 1st experiment, we confirm that our detection circuit can correctly determine whether overclocking (i.e., glitchy clock signal) is generated or not. From the 2nd experiment, we observe that the output sequence of our detection circuit indicates the occurrence of overclocking by injected CWs. At the same time, we also show the corresponding fluctuation in the voltage of clock signal due to the overlapped CW.

Measurement of transfer characteristics of conducted disturbance from AC power supply port to Ethernet port considering transmission mode

Conducted disturbance from AC power supply reaches a communication cable (e.g. Ethernet cable) through a communication device (e.g. switching hub). Then it affects quality of the signal communication and/or the other communication devices because the conducted disturbance propagates along the communication cable. Transmission modes in a power supply cable or a Ethernet cable are defined in this paper. Two orthogonal transmission modes, normal mode and common mode, are defined in the power supply cable. And three modes, differential mode, primary common mode, and secondary common mode, are determined in the Ethernet cable. Additionally, a measurement system of transmission and mode conversion characteristics of the conducted disturbance considering transmission modes are constructed.