Kazuhiro Takaya

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

Experimental evaluation of the induced current by the PLC leakage electromagnetic wave

The influence of electromagnetic radiation from power-line communication (PLC) systems on various types of communication or broadcast services has been investigated. This paper describes experimental results of the influence of electromagnetic radiation from a PLC system on other communication services. The influence was evaluated by measuring the current induced in a communication cable close to a power-line cable. The evaluation involved measuring the induced current for different communication cable structures, different lengths over which the communication and power-line cable ran parallel, and different distances of separation between the cables. It was found that the induced current that occurs in the adjacent communication cable depends on the length over which the cables run parallel and the distance of separation, but does not depend on the structure of the communication cable. Furthermore, the minimum length of parallel cabling to result in saturation of the induced current, which depends on the output power of the PLC modems, was obtained experimentally.

Technical Problems of the Shunt-Type Asymmetric Artificial Network

Theoretical and experimental investigations were carried out on the characteristics of the shunt-type asymmetric artificial network (AAN). The findings are as follows: 1) The theoretical formulas for the differential- and common-mode impedances as well as the longitudinal conversion loss (LCL) were derived for the shunt-type AAN in terms of the AAN circuit parameters. 2) The common-mode disturbance voltage estimated from the measured voltage is not proportional to the actual common-mode current flowing in the network cable of the equipment under test (EUT). 3) For the common-mode EUT, the shunt-type AAN with a low LCL of less than about 42 dB yields incorrect measurement results with an error greater than 0.5 dB. 4). A more crucial problem is that, for the differential-mode EUT, the measured disturbance voltage decreases as the EUT common-mode impedance decreases.

A study on conducted disturbance below 150 kHz from commercial power-conditioning system

We discuss the conduction modes of conducted disturbance from power-conditioning systems (PCSs), which are used for effective utilization of renewable energy, by measuring the voltage at the DC input and AC output ports of three PCSs. By using three different PCSs, which have different circuit characteristics, as equipment under test and using a voltage probe and artificial mains network as the measurement system, we found that only differential-mode (DM) disturbance was generated at the AC ports, and that both DM disturbance and common-mode (CM) disturbance were generated at the DC ports due to the internal filtering circuit. We also considered the relation between peak level of conducted disturbance and input power.

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.

Remote Visualization of Screen Images Using a Pseudo-Antenna That Blends Into the Mobile Environment

This paper presents a potential threat of remote visualization for screen displays of various mobile devices used in public spaces via electromagnetic waves (electromagnetic (EM) screen remote visualization). The traditional EM screen remote visualization uses nonportable equipment on a specific target device, and requires sufficient time to estimate the parameters related to information leakage of each target. In contrast, this paper proposes a method that allows for real-time estimation of information leakage parameters without requiring to know the target of remote visualization in details. The proposed method models the process of information leakage for each device, and consequently determines the frequency that leaks screen information faster than ever before. In addition, in this paper, portable equipment and a pseudo-antenna that blends into the mobile environment were used to implement the proposed method. The experiment shows that the screen image can be reconstructed from EM emanation obtained from the areas near some target devices. Furthermore, we discuss the measures against EM remote visualization of mobile devices.

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.

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.

The influence of the electrical characteristics of premises cables on the interference immunity of VDSL

The VDSL service has been progressed because it allows high-speed Internet access to be achieved using copper premises cables. Although VDSL offers an inexpensive means of providing FTTH service, the link between the VDSL Transceiver Unit at the Optical Network Unit (VTU-O) and the VDSL Transceiver Unit - Remote Terminal (VTU-R) is influenced by electromagnetic interference induced into the premises cables. There are different types of premises cables in use in Japan such as a single-layer cable, twisted-pair cable, and a star-quad cable. The electrical characteristics of these cables are different (e.g., transmission loss, longitudinal conversion loss, and cross-talk) because they differ in composition. This paper describes the relationship between the electrical characteristics of premises cables and the immunity to interference of the link between the VTU-O and the VTU-R.