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Powerline Communication Powerline Communication

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					Powerline Communication




  by Yong Soo Deutschle and Sebastian Graf
Contents
Transmission Media ............................................................................................ 3
The Last Mile ....................................................................................................... 3
Regulations ........................................................................................................... 4
Powerline in the OSI-Model ............................................................................... 4
The Digital Powerline Protocol (DPL) .............................................................. 4
Spread Spectrum Concept .................................................................................. 5
Powerline Exchange Protocol (PLX) ................................................................. 5
Future Aspects ..................................................................................................... 5
Conclusion ............................................................................................................ 6
Sources .................................................................................................................. 6
History of PLC

The Communication over a Power Network is rather old. It was introduced in the 1920s by
the energy providers, to establish cheap communication between their plants. The basic idea
was to use an existing network for communication and not introduce or establish a new one.

Later on this concept was adapted to the control of street lightening. So all street lights could
be turned on and off by a central “switch” and the lights only needed a small decoder chip. By
using this technique no additional wires were needed to control the lights.

In the 1980s the technique was introduced on home products, like Baby phones. Today the
Powerline Communication is regarded as an alternative for the so called “last mile.”


Transmission Media
Originally the low and high voltage net was assigned to carry energy and for transmitting
information. Because of this fact, the transmission of data on this media faces a lot of
problems. The main problems are:

       -   big noise
       -   high absorption
       -   huge distortion

This is also the reason, why a transmission over a powerline needs repeaters every 300 – 600
meters, to minimize the interference problems caused by this facts.




The Last Mile
The “Last Mile” is a term introduced by the energy providers. The term refers to a data
connection between a so called “outdoor master” and the “indoor master”, which is located at
the home of a customer.



                                        outdoor master




                                        indoor master

                                         PL Modem


                                          consumer
Regulations
The transmission on a powerline is restricted to certain frequencies, which regulated by
certain institutes. In Europe the institute is called CENELEC (European Committee for
Electrotechnical standardization). This institute has established the restriction, that powerline
communication in Europe is only allowed to use frequencies lower than 148,5 kHz. In the
USA and Japan the regulations allow transmissions up to 540 kHz. This is the main reason,
why powerline products of these regions are not compatible with each other and needs to be
adapted to the other market.


Powerline in the OSI-Model
Powerline covers the lowest 4 levels in the OSI-Model with the Powerline Exchange Protocol
and the Digital Powerline Protocol:



         4 Transport


          3 Network                 PLX (Powerline Exchange Protocol)

         2 Data Link


          1 Physical                  DPL (Digital Powerline Protocol)



The Digital Powerline Protocol (DPL)
The Digital Powerline Protocol is based on the chimney concept. This concept uses a very
narrow frequency spectrum and is so able to use very narrow available frequency gaps. The
transmission levels of this Protocol are higher than in the “spread spectrum concept” which
will be explained later. The Error ration of this protocol is with 10-9 very low.

This concept is used for the communications on the last mile.
Spread Spectrum Concept
This spectrum is not able to use narrow frequency gaps like the chimney concept, because the
signal is spread over a huge frequency spectrum. Therefore it is less sensitive for conductions
bound interfering signals (e.g. turning on and off of electrical devices). The use of a frequency
spectrum is the reason why low levels can be used in this concept. The big disadvantage is the
very high implementation cost. This is why this concept is not designated any longer for the
“last mile”.


Powerline Exchange Protocol (PLX)
The PLX covers the layer 2,3,4 of the OSI-Model. The first idea was to use an existing MAC-
protocol. However, studies resulted, that none of the available protocols was suitable for PLX.
So a new hybrid MAC-protocol was established, that consists of parts of the following
existing MAC-protocols:

       -   Ethernet
       -   Token Ring
       -   Wireless LAN
       -   CEBus

Another technique, that was adapted is the CSMA (Carrier Sense Multiple Access). Most of
this access technique was used to build up the DSMA (Datagram Sensing Multiple Access).
The basic principal of both techniques is that a data station first listens on the transmission
media, before it sends data, to avoid collisions.


Future Aspects
For the internet usage via powerline are 2 providers left in Germany:

       -   MVV Energie AG
             o product name : Vype
       -   DREWAG (Stadtwerke Dresden)
             o product name : PowerKom
Conclusion
In the following, the positive and negative aspects of powerline are mentioned:


       +   no additional cable installation required
       +   high flexibility (works with every power plug)
       +   adaptable to all power networks
       +   high bandwidth (theoretical up to 20 Mbit/s)


       -   no security
       -   high technical equipment needed
       -   high costs (for the last mile, especially the outdoor master)
       -   many incompatible standards
       -   problems in the regulations of frequencies.




Sources
www.cenelec.org
www.speeddoesmatter.ch/showdocument.php3?key=41
www.elektroniknet.de/topics/kommunikation/fachthemen/artikel/inhalt