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PLC. Power Line Comunications

The initials PLC may also refer to a programmable logic controller

Power Line Communications, also known by its acronym PLC, is an English term that can be translated by cable communications systems and which refers to various technologies that use conventional power lines to transmit radio signals for communication purposes. PLC technology uses the electricity grid to make it a high-speed digital line data transmission, allowing, among other things, access to broadband Internet.

 

PLC technology can use the household electrical wiring as a transmission of signals. INSTEON and X10 technologies are the two most popular de facto standards used for home control. This is a technique used in home automation remote control lighting and equipment without installing additional wiring.

Typically, home control devices operate by modulating a carrier wave whose frequency is between 20 and 200 kHz injected into the power house wiring from the transmitter. This carrier wave is modulated by digital signals. Each receiver control system has a unique address and is processed individually by the signals sent by the transmitter. These devices can be plugged into electrical outlets conventional or permanently wired connection instead. Since the carrier signal can be spread in homes or apartments near the same distribution system, these systems have a "home address" that designates the owner. This of course is true when neighboring homes have such systems, a situation common in the U.S. residential areas.

PLC technology can also be used in the networking of home computers and peripherals, including those that require network connections, although at present there are no standards for this type of application. The existing rules or standards have been developed by different companies within the framework defined by U.S. organizations HomePlug Powerline Alliance and the Universal Powerline Association.

 

 

Broadband over power line (BPL shortened its name for Broadband over Power Lines) is the use of PLC technology to provide broadband access to the Internet through ordinary power lines. In this case, a computer (or other device) would need only connect to a BPL modem plugged into any power outlet in an equipped building to have high-speed Internet access.

At first glance, BPL technology appears to offer advantages over regular connections based broadband coaxial cable or DSL, the extensive infrastructure available would allow people in remote areas have access to the Internet with relatively little equipment investment for power company. Also, such ubiquitous availability would make it much easier for other electronic devices such as televisions or sound systems, the can connect to the network.

However, variations in the physical characteristics of the grid and the current lack of IEEE standards mean by that service delivery is far from standardized and repeatable process, and the bandwidth a BPL system can provide compared to cable and wireless systems is in doubt. Some industry observers believe that the prospect of BPL will motivate companies and DSL operators to provide cable service faster broadband access to rural communities.

PLC modems transmit in the range of medium and high frequency (carrier signal from 1.6 to 30 MHz). The asymmetric speed in the modem is generally from 256 kbit / s to 2.7 Mbit / s. In the repeater situated in the meter room (in the case of supply in a building) the speed is up to 45 Mbit / s can be connected to 256 PLC modems. In the medium voltage stations, the speed from the network control center (head end) to the Internet is up to 134 Mbit / s. To connect to the Internet, utilities can use a backbone (spine) of fiber optic or wireless links.

Differences in the distribution systems of electric power in America and Europe affect the implementation of BPL technology. In the case of North America, relatively few households are connected to each distribution transformer, whereas European practice may be hundreds of homes connected to each substation. Since BPL signals do not propagate through the electrical distribution transformers, additional equipment is needed only in the American case. However, since the bandwidth is limited, this may increase the rate at which each house can connect, because a few users sharing the same line.

The system has a number of complex problems, the first being that power lines are inherently noisy. Each time a device is turned on or off, introduce transient voltages on the line. Energy-saving devices often introduce noisy harmonics into the line. The system must be designed to address these natural breaks of the signals and work with them.

Broadband technologies over power lines were developed faster in Europe than in the U.S. due to a historical difference in the philosophies of energy systems design. Nearly all large power grids transmit power at high voltages to reduce transmission losses, then the next user step-down transformers are used to lower the voltage. Since BPL signals can not readily pass through transformers (their high inductance makes them act as low pass filters, passing only low frequency signals and blocking high) repeaters must be attached to processors . In the U.S., it is common to place a small transformer on a utility pole in one house, while in Europe, is more common for a somewhat larger transformer to serve 10 or 100 homes. To supply energy to customers, this difference in design is small, but it means that provide BPL service on the power grid of a typical city of the United States will require more repeaters in the same perfect proportions, than are required in a comparable European city . A possible alternative is to use BPL as the backhaul for wireless communications, for example by placing access points Wi-Fi or cellular base stations on utility poles, thus allowing end-users within a certain area are connected with the equipment they already have. In a near future, BPL might also be used as backhaul for WiMAX networks.

The second major problem of BPL has to do with the intensity of the signal with the frequency of operation. System is expected to use frequencies in the range of 10 to 30 MHz, which has been used for decades by amateur radio stations as well as international shortwave radio and various communications systems (military, aeronautical, etc.). . Power lines have no armor and can act as antennas for the signals they carry, and have the potential to eliminate the usefulness of the band from 10 to 30 MHz for the purposes of short-wave communications.

BPL modern systems use OFDM modulation which minimizes interference with radio services by removing specific frequencies used. A 2001 study jointly conducted by the ARRL (American Radio Relay League) and HomePlug modems showed that using this technique "in general that with moderate separation of antenna structure containing the HomePlug signal that interference was barely perceptible" and interference occurred only when the "antenna was physically close to power lines.".

Data transfers at speeds much higher microwave frequencies using transmitted through a mechanism recently discovered surface wave propagation, called E-Line which has been demonstrated using only a single power line. These systems have demonstrated the potential for symmetrical communication and full duplex at speeds above 1 Gbit / s in each direction. Multiple WiFi channels with simultaneous analog television signals in the unlicensed bands of 2.4 and 5.3 GHz have been demonstrated operating over a single line of medium voltage. In addition, because it can operate in the band 100 MHz to 10 GHz, this technology can completely avoid the interference problems associated with the use of a shared spectrum while offering greater flexibility for modulation and protocols for any other type found microwave systems.