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Power line communication or power line carrier (PLC), also known as Power line Digital Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line networking (PLN), is a system for carrying data on a conductor also used for electric power transmission. Broadband over Power Lines (BPL) uses PLC by sending and receiving information bearing signals over power lines to provide access to the Internet.
Electrical power is transmitted over high voltage transmission lines, distributed over medium voltage, and used inside buildings at lower voltages. Powerline communications can be applied at each stage. Most PLC technologies limit themselves to one set of wires (for example, premises wiring), but some can cross between two levels (for example, both the distribution network and premises wiring).
All power line communications systems operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of AC power, the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications.
Data rates over a power line communication system vary widely. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles (kilometres) long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates installation of dedicated network cabling.
High-frequency communication (MHz)
High frequency communication may (re)use large portions of the radio spectrum for communication, or may use select (narrow) band(s), depending on the technology.
Home networking (broadband)
Power line communications can also be used to interconnect home computers, peripherals or other networked consumer peripherals. Proprietary specifications for power line home networking have been developed by a number of different companies within the framework of the HomePlug Powerline Alliance, the Universal Powerline Association and the HD-PLC Alliance.
On December 12 2008, the ITU-T adopted Recommendation G.hn/G.9960 as the first worldwide standard for high-speed powerline communications[1]. G.hn also specifies communications over phonelines and coaxial wiring.
A few days later, on December 19 2008, IEEE P1901 confirmed[2] the baseline text for another standard for high-speed powerline communications, which includes both in-home and access applications. Although IEEE P1901 specifies multiple non-interoperable PHY and MAC options[3], it provides mechanisms for coexistence between them[4].
Internet access (broadband over powerlines)
Broadband over power lines (BPL), also known as power-line Internet or powerband, is the use of PLC technology to provide broadband Internet access through ordinary power lines. A computer (or any other device) would need only to plug a BPL "modem" into any outlet in an equipped building to have high-speed Internet access. International Broadband Electric Communications or IBEC and other companies currently offer BPL service to several electric cooperatives.
BPL may offer benefits over regular cable or DSL connections: the extensive infrastructure already available appears to allow people in remote locations to access the Internet with relatively little equipment investment by the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up.
But variations in the physical characteristics of the electricity network and the current lack of IEEE standards mean that provisioning of the service is far from being a standard, repeatable process. And, the amount of bandwidth a BPL system can provide compared to cable and wireless is in question. The prospect of BPL could motivate DSL and cable operators to more quickly serve rural communities. [5]
PLC modems transmit in medium and high frequency (1.6 to 80 MHz electric carrier). 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 the speed is up to 45 Mbit/s and can be connected to 256 PLC modems. In the medium voltage stations, the speed from the head ends to the Internet is up to 135 Mbit/s. To connect to the Internet, utilities can use optical fiber backbone or wireless link.
The system has a number of issues. The primary one is that power lines are inherently a very noisy environment. Every time a device turns on or off, it introduces a pop or click into the line. Energy-saving devices often introduce noisy harmonics into the line. The system must be designed to deal with these natural signaling disruptions and work around them.
Broadband over power lines has developed faster in Europe than in the United States due to a historical difference in power system design philosophies. Power distribution uses step-down transformers to reduce the voltage for use by customers. But BPL signals cannot readily pass through transformers, as their high inductance makes them act as low-pass filters, blocking high-frequency signals. So, repeaters must be attached to the transformers. In the U.S., it is common for a small transformer hung from a utility pole to service a single house or a small number of houses. In Europe, it is more common for a somewhat larger transformer to service 10 or 100 houses. For delivering power to customers, this difference in design makes little difference for power distribution. But for delivering BPL over the power grid in a typical U.S. city requires an order of magnitude more repeaters than in a comparable European city. On the other hand, since bandwidth to the transformer is limited, this can increase the speed at which each household can connect, due to fewer people sharing the same line. One possible solution is to use BPL as the backhaul for wireless communications, for instance by hanging Wi-Fi access points or cellphone base stations on utility poles, thus allowing end-users within a certain range to connect with equipment they already have. In the near future, BPL may also be used as a backhaul for WiMAX networks.
The second major issue is signal strength and operating frequency. The system is expected to use frequencies of 10 to 30 MHz, which has been used for many decades by amateur radio operators, as well as international shortwave broadcasters and a variety of communications systems (military, aeronautical, etc.). Power lines are unshielded and will act as antennas for the signals they carry, and have the potential to interfere with shortwave radio communications. Modern BPL systems use OFDM modulation, which allows to mitigate interference with radio services by removing specific frequencies used. A 2001 joint study by the ARRL and HomePlug Powerline Alliance showed that for modems using this technique "in general that with moderate separation of the antenna from the structure containing the HomePlug signal that interference was barely perceptible at the notched frequencies" and interference only happened when the "antenna was physically close to the power lines" (however other frequencies still suffer from interference).
Much faster transmissions using microwave frequencies transmitted via a surface wave propagation mechanism called E-Line have been demonstrated using only a single power line conductor.[citation needed] These systems have shown the potential for symmetric and full duplex communication well in excess of 1 Gbit/s in each direction. Multiple WiFi channels with simultaneous analog television in the 2.4 and 5.3 GHz unlicensed bands have been demonstrated operating over a single medium voltage line. And, because it can operate anywhere in the 100 MHz - 10 GHz region, this technology can completely avoid the interference issues associated with use of shared spectrum while offering flexibility for modulation and protocols of a microwave system.[citation needed]
Medium frequency (kHz)
Home control (narrowband)
Power line communications technology can use the household electrical power wiring as a transmission medium. INSTEON and X10 are the two most popular[unreliable source?], de facto standards using power line communications for home control. This is a technique used in home automation for remote control of lighting and appliances without installation of additional control wiring.
Typically home-control power line communication devices operate by modulating in a carrier wave of between 20 and 200 kHz into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver. These devices may be either plugged into regular power outlets, or permanently wired in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same distribution system, these control schemes have a "house address" that designates the owner.
Since 1999, a new power-line communication technology "universal powerline bus" has been developed, using pulse-position modulation (PPM). The physical layer method is a very different scheme than the modulated/demodulated RF techniques used by X-10. The promoters claim advantages in cost per node, and reliability.
Low-speed narrow-band communication
Narrowband power line communications began soon after electrical power supply became widespread. Around the year 1922 the first carrier frequency systems began to operate over high-tension lines with frequencies of 15 to 500 kHz for telemetry purposes, and this continues.[6] Consumer products such as baby alarms have been available at least since 1940.[7]
In the 1930s, ripple carrier signalling was introduced on the medium (10-20 kV) and low voltage (240/415V) distribution systems. For many years the search continued for a cheap bi-directional technology suitable for applications such as remote meter reading. For example, the Tokyo Electric Power Co ran experiments in the 1970s which reported successful bi-directional operation with several hundred units.[8] Since the mid-1980s, there has been a surge of interest in using the potential of digital communications techniques and digital signal processing. The drive is to produce a reliable system which is cheap enough to be widely installed and able to compete cost effectively with wireless solutions. But the narrowband powerline communications channel presents many technical challenges. A mathematical channel model and a survey of work can be found in reference no. 5[9].
Applications of mains communications vary enormously, as would be expected of such a widely available medium. One natural application of narrow band power line communication is the control and telemetry of electrical equipment such as meters, switches, heaters and domestic appliances. A number of active developments are considering such applications from a systems point of view, such as 'Demand Side Management'.[10] In this, domestic appliances would intelligently co-ordinate their use of resources, for example limiting peak loads.
Control and telemetry applications include both 'utility side' applications, which involves equipment belonging to the utility company (i.e. between the supply transformer substation up to the domestic meter), and 'consumer-side' applications which involves equipment in the consumer's premises. Possible utility-side applications include automatic meter reading(AMR), dynamic tariff control, load management, load profile recording, credit control, pre-payment, remote connection, fraud detection and network management, [11] and could be extended to include gas and water.
A project of EDF, France includes demand side management, street lighting control, remote metering and billing, customer specific tariff optimisation, contract management, expense estimation and gas applications safety [12].
There are also many specialised niche applications which use the mains supply within the home as a convenient data page link for telemetry. For example, in the UK and Europe a TV audience monitoring system uses powerline communications as a convenient data path between devices that monitor TV viewing activity in different rooms in a home and a data concentrator which is connected to a telephone modem.
The most robust low-speed powerline technology uses DCSK technology available from Yitran Communications[dubious “ discuss]. Renesas Technology licenses this know-how from Yitran and incorporates it in the single chip MCU + PLC family of devices known as M16C/6S. Renesas also licenses a state of the art network layer for AMR/AMM applications which can run on these devices.
High-speed narrow-band powerline communication †distribution line carrier
DLC uses existing electrical distribution network in the medium voltage (MV) i.e., 11 kV, Low Voltage (LV) as well as building voltages. It is very similar to the powerline carrier. DLC uses narrowband powerline communication frequency range of 9 to 500 kHz with data rate up to 576 kbit/s. DLC is suitable (even in very large networks) for multiple realtime energy management applications. It can be implemented under REMPLI System as well as SCADA, AMR and Power Quality Monitoring System. DLC complies with the following standards: EN 50065 (CENELEC), IEC 61000-3 and FCC Part 15 Subpart B.
There are no interference issues with radio users or electromagnetic radiation. With external inductive or capacitive coupling, a distance more than 15 km can be achieved over a medium voltage network. On low voltage networks, a direct connection can be made since the DLC has a built-in capacitive coupler. This allows end-end communications from substation to the customer premises without repeaters.
The latest DLC systems significantly improve upon and differ from other powerline communication segments. DLC is mainly useful for last-mile and backhaul instrastucture that can be integrated with corporate wide area networks (WANs) via TCP/IP, serial communication or leased-line modem to cater for multi-services realtime energy management systems.
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