Importance Of Power Line Communications

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Unlike any other communication technology, Power Line Communications (PLC) is a technology whereby a sender modulates the data to be sent, injects it onto medium, and the receiver demodulates the data to read it. The basic difference is that in PLC no extra wiring is needed. Considering the ubiquity of power lines, it implies that with PLC, virtually all line-powered devices can be controlled or monitored.
Generally, PLC uses the same electric cables for the purpose of power delivery and communication. A high-pass filter, called a coupling interface is used in separating the powering and signaling circuits. This coupling interface makes the connecting different circuits with different voltage levels possible. The communication signal is fed
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Fig 2.2 Structure of a PLC access network
On the other hand, PLC can be categorized based on its bandwidth [14],
1. Narrowband PLC (2 Mbps) is applied in Internet access, multiple voice connections, transmission of video signals, in-home networks, high-speed data transmission, and narrowband services.
The transmission characteristics of power line channels are not favorable for data transfer based on the fact that low-voltage supply networks are not designed for communications. The power line cables are divided in an asymmetric way (Figure 2.3), comprising of many customers and irregular connections between network sections. The transitions of the cable cause reflections and changing characteristic impedance [29]. More so, a PLC network changes its structure (e.g. by adding new customers), especially in an in-home PLC network in which every switching event can change the topology of the
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This results in multipath signal propagation, with a frequency-selective fading [31]. Cable losses, losses due to reflections at branching points and mismatched endings of the cables as well as selective fading are the most important effects influencing signal propagation [7].
Attenuation in PLC networks depends on the line, length and changing characteristic impedance of the transmission line. Numerous measurements have shown that the attenuation in power lines is acceptable in relatively short cables (approximately up to 200–300m), but is very bad in longer cables [31]. Hence, longer PLC networks are expected to be equipped with the repeater technique.
Noise is another major problem on the system. The impedance of a power supply network is time variant, because electric devices are randomly connected to the grid. Noise in the electric distribution network is caused by many electric devices, such as halogen lamps, microwave ovens, and other household appliances, impulsive noise is the most problematic noise scenario from the viewpoint of communication and it is produced for example by dimmers, switched-mode power supply units, fluorescent lamps and vacuum

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