Yoshio Yamada’s research while affiliated with Ehime University and other places

Simple and low-cost PLC will be required to play a role in the Internet-of-Things (IoT) market such as ubiquitous wireless sensor networks. From the viewpoints of temporal connectivity and obtaining high SNR and stable channels, inductive coupling techniques for the kHz band PLC have been proposed in this paper. The results of three feasibility studies using a photovoltaic power system installed in our laboratory have been described. First, an inductive coupler is applied to the DC powerline channel, because it forms a low impedance loop circuit. It was proved that the DC power-line provided a high SNR channel, so that the simple modulation technique was enough to realize the ubiquitous PLC networks. The second topic is the contactless power supply using the same ferrite core as the PLC coupler. It has been shown that the proposed circuit could supply power of 35mW at the maximum to a wireless sensor node. The third topic is an application of the 1-wire PLC system to aerial cables. A suitable coupling method has been proposed to provide a low signal attenuation channel. The noise characteristic peculiar to photovoltaic (PV) power-line is also pointed out, that is the amount of noise on a sunny day with cloud occasionally exceeded that on a cloudless sunny day.

The conventional narrowband power-line communication (NB-PLC) is a two-wire system, that has injected its signal between wires using a capacitive coupler. When communicating between floors at a large-sized building, the signal has to travel over long-distances across a switchboard which supplies electricity to distribution boards. Moreover, the signal is attenuated not only at the switchboard but also at the distribution boards. Therefore signal amplifiers had to be installed at the boards. In this paper, a single wire PLC solution is proposed to shorten the communication distance and reduce the attenuation by taking a shortcut of the signal traveling path. It is described experimentally that the earth could be used as its signal returning path to the signal source. Therefore a single wire is enough to inject and receive the signal. An inductive coupling method suitable to this system is also proposed. The signal attenuation of the proposed system was 30 dB better than that of the conventional two-wire system for our university building. The achieved performances of PLC modems also showed that the proposed system was useful.

The interference with existing radio broadcasting services because of unintentional radiation is a serious problem in power-line communication (PLC) systems. A radiation detection method based on burst packets, which had been proposed by the authors and was called scan and sum (SAS) method, was a low cost method and used to solve the problem. But its measurement took a long time and the burst packets occupied a channel. To shorten the measurement time, a new method based on periodic packets has been proposed in this paper, which is called periodic packet sound (PPS) method. Although both methods record the radiated signal as a sound data, the PPS does not need to scan the frequency of an AM radio receiver but analyses the sound data by a cross-correlation operation with a reference signal. First, how to generate the reference signal that depends on the modems is described. Second, an optimization of the packet size is studied, and finally it is shown that the detection sensitivity of PPS was maintained to be the same as SAS while the measurement time of PPS was 1/9 shorter than that of SAS. Moreover, the channel occupation of PPS was reduced to be 2% of SAS when the packet size was optimized to be 1500 bytes.

To realize an eco-house, a new direct current (DC) distribution system has received widespread attention. This paper has proposed countermeasures to fundamental problems which make difficult to achieve a high-speed PLC over the existing alternating current (AC) systems. To reduce the signal attenuation of the conventional low-voltage (LV) power-line cables made from vinyl insulator, it is recommended to use cables made from polyethylene insulator. It has been also recommended not to use the single pole and 3-way switches supposed to be cut into the hot conductor, and hand-made joint boxes in order to make the electrical balance of the channel high. To prove these proposals, a DC power-line system of 1.5kW capacity was built and the throughput was measured. The proposed simultaneous dual-mode system performed 1.9 times better throughput at maximum comparing with the conventional single-mode system. From these observations, a scenario for a 1Gbps Personal Area Network (PAN) over the new DC power-line channels is proposed.

AEE-PLC (Adaptive power control method to Electromagnetic Environment for the Power-Line Communication) system was proposed by the authors to achieve the maximum throughput performance without radiation. As its radiation detection method, two methods were also proposed. One was called Scan and Sum (SAS) method which detected the radiation of burst packets. Another was Periodic Packet Sound (PPS) method which did it of ICMP (Internet Control Message Protocol) packets generated by the PING (Packet Internet Groper) command. When the throughput performance was measured for the SAS method, the received number of the burst packets was used. For the PPS method, extra burst packets were needed. To avoid them, ICMP packets generated by the utility software of Pchar (Path Characteristics) has been introduced in this paper. The relationship between the size of ICMP packets and the detection sensitivity has been also studied to optimize the size. The result has been confirmed that 1500 Bytes was the optimum size which achieved the high sensitivity with the low channel occupation.

A radiation detection method based on burst packets, which was proposed by the authors and is called Scan and Sum (SAS) method, needed so long time, because frequency scanning and power summation were required. To solve the problem, a new method based on ICMP packets has been proposed in this paper, which is called Periodic Packet Sound (PPS) method. The PPS method doesn't scan but record the packets' signal sound for a while at a frequency band. From the recorded sound data, ICMP packets data are picked up using their periodicity and their signal power is calculated. In this paper, both methods have been examined in the hallway of authors' laboratory. To investigate the sensitivity of both methods, the distance between a radiation point and an antenna was changed. Detection limitation distance of the proposed PPS method was the same as that of SAS, while the measurement time was shorten from 90 seconds to 10 seconds.

To improve the throughput performance of HF-PLC systems, a dual-mode transmission system, which utilizes the mode diversity of differential and common modes, has been studied by the authors. However, the system which uses the common-mode has a risk to cause the unintentional radiation problem. To solve the problem, an Adaptive power control method to the Electromagnetic Environment, which is called AEE, has been proposed. The radiation detection was achieved by receiving emitted PLC signals at affected (or concerned) devices. In this paper, a new detection method and a new mode- selection method have been proposed, and it is shown that their preliminary results are attractive from the viewpoint of usefulness.