|
|
|
|
|
Power Line CommunicationPower line communication (PLC), also called Broadband over Power Lines (BPL), is wireline method of communication using the existing electric power transmission and electricity distribution lines. The carrier can communicate voice and data by superimposing an analogue signal over the standard 50 or 60 Hz alternating current (AC). Types of PLC technology There are two main classes of PLC : PLIC PLIC Power Line Indoors or Internal Telecoms(also called In-House BPL): This is using the home grid to establish telecoms, such as the Homeplug system. PLIC is one of the technologies used in domotics (another is wireless telecoms); the utilities can offer too wireless middleware (integrated PLC and WiFi based structure). PUA is the PLC Utilities Alliance. There are also some very low-bitrate power line communication systems used for meter reading. The X10 home automation system uses power line communication at the zero crossing voltage point in the AC wave. PLOC PLOC Power Line Outdoors Telecoms: this is the telecoms between the electric substations and home networks (PLC modems). The standard is ETSI PLT, twenty times faster than ADSL. PLC modems employs 11 volts and transmit in high frequency (1.6 to 30 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. Usage (Source: http://de.wikipedia.org/wiki/Powerline_Communications ) Broadcasting systems using PLC PLC is not a new technology, but decades ago for the spreading by broadcast programs in the long-wave range over current and voice grade channels was already used. In Germany this technology became as wire broadcasting, in which Switzerland calls telephone round saying as a Swiss and in Norway Linjesender. In Russia this system was very common, because it permitted only the reception of Russian transmitters. Still today this technology in some countries is used for the broadcast supply. It is based on the transmission of information with the help of modulated high frequency currents, which are led over cables for power installation and in the head act ions over special transformers on the lines are given. In order to prevent uncontrolled propagation of PLC signals in the high-voltage transmission systems, at line branches and in transformer stations special check coils for PLC signals - usually in current loops of anchor masts or removing portals - are installed. Telecontrol and Data transmission PLC procedures for decades for the control of devices e.g. the road lighting or transformer stations, for the change-over from the nachtstromtarif to the day current tariff or for the transmission by measuring data and message (occasionally also discussions, which will usually transfer in the procedure of the single-sideband modulation) are already used. Here different frequency ranges are used. For tasks of remote controlling, like tariff change-over of counters, which can be implemented central, frequencies are used below the long-wave range (approx. 1 kHz), since signals with these frequencies can be subject to only relatively small absorptions, which are caused by line inductances and interconnect capacitances, and reach thus each terminal (see http://www.vlf.it/polard/rcf.html in English). These plants do not cause disturbances of the broadcast recording because of their low frequency. News exchange between installations of power grid Broadband over power lines Broadband over Power Lines (BPL) is the use of PLOC 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. BPL offers obvious benefits over regular cable or DSL connections: the intensive infrastructure already available would allow more people in more locations to have access to the Internet. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up. The amount of bandwidth a BPL system can provide compared to cable and wireless is in question, however. Some groups oppose the proliferation of this technology, mostly due to its potential to interfere with radio transmissions. As power lines are typically untwisted and unshielded, they are essentially large antennas, and will broadcast large amounts of radio energy (see the American Radio Relay League's article). Recently, power and telecommunications companies have started tests of the BPL technology, over the protests of the radio groups. After claims of interference by these groups, many of the trials were ended early, proclaimed successes, though the ARRL and other groups claimed otherwise. Some of the providers conducting those trials have now begun commercial roll-outs in limited neighborhoods in selected cities, with some level of user acceptance. There have been many documented cases of interference reported to the FCC by Amateur Radio users. A video clearly showing the interference at a site at Briarcliff Manor, NY is available on the ARRL website. Because of these continued problems, Amateur Radio operators and others filed a petition for reconsideration with the the FCC in February 2005. Austria, Australia, New Zealand and other locations have also experienced BPL's spectrum pollution and raised concerns within their governing bodies. New FCC rules require BPL systems to be capapble of remotely notching out frequencies on which interference occurs, and of shutting down remotely if necessary to resolve the interference. BPL systems operating within FCC Part 15 emissions limits may still interfere with wireless radio communications and are required to resolve interference problems. Standards Several competing standards are evolving including the HomePlug powerline alliance (which has defined the HomePlug 1.0 and is finalizing the HomePlug AV high-speed networking technology), Universal Powerline Association, and the IEEE. It is unclear which standard will come out ahead. FCC On October 14, 2004, the U.S. Federal Communications Commission adopted rules to facilitate the deployment of "Access BPL" -- i.e., use of BPL to deliver broadband service to homes and businesses. The technical rules are more liberal than those advanced by ARRL and other spectrum users, but include provisions that require BPL providers to investigate and correct any interference they cause. These rules may be subject to future litigation. BPL vendors such as Amperion Inc. and Current Technologies LLC have begun offering BPL service in limited areas. External links
|
 |
|
| Copyright 2005-2009 OnPedia.com. All Rights Reserved |
|
|