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HomePlug 1.0 is a power line data communication
system that transfers data through existing power lines at 14 Mbps using
higher frequencies (from 4 MHz to 21 MHz). The HomePlug system uses a
higher frequency range than previous power line data communication systems
which enables signals to couple phases in the electrical distribution
panel. As a result, the coverage of HomePlug power line communication
systems approached 99% without the need for cross phase couplers or
professional installers.
As the signals travel down the power lines, a portion
of the signal is lost through the wires (absorbed or radiated). Signal
frequency, the type of wire, how the wire is installed and the length of
the wire are key factors in determining the amount of energy that is lost.
Generally, as the length of a power line increases and the number of
outlets increases, the amount of attenuation also increases. Signal loss
at high frequencies through power lines can reach 50 dB and the dynamic
range of HomePlug devices can be between 70 dB to 80 dB.
Because it is possible for HomePlug signals to travel
on power lines shared between several homes, the signals are encrypted to
keep the information private. The HomePlug 1.0 system encrypts (scrambles)
information using 56-bit DES security coding. Only devices that share the
same HomePlug encryption codes can share the information transferred
between the devices.
One of the significant challenges for power line
communication systems is the “sources and effects” of interference
signals that can distort power line communication signals. Interference
signals include motor noise, signal reflections, radio interference,
changes in electrical circuit characteristics, variability in the amount
of coupling across different phases of electrical circuits and stray
transmission. The HomePlug system was designed to overcome these types of
interference and in some cases, the HomePlug system can take advantage of
them.
Motor noise is the unwanted emissions of electrical
signals produced by the rapidly changing characteristics of a motor
assembly. In most homes, motors are in a variety of appliances and they
may be used at different locations at any time. The HomePlug system can
adapt in real time to the distortions caused by motors and appliances.
Signal reflection is the changing of direction that a
signal travels as it passes from one transmission medium to another
(transmission channel or device). When the characteristics of the media
are different (impedance), a reflected signal is generated. Some of the
energy of the forward signal (incident signal) is redirected (reflected)
back towards the signal source. When high-frequency HomePlug signals reach
the ends of power lines, some of their signal energy is reflected back
towards the transmitter. These reflected signals combine with the forward
(incident) signals producing distortion. The HomePlug system includes
sophisticated analysis of the signal and it is possible to use the signal
reflections as an advantage rather than a challenge.
Some of the frequencies used by HomePlug systems are
the same radio frequencies used by citizen band (CB) radios or AM
broadcast radio stations. The HomePlug system divides the frequency band
into many independently controlled sub-channels (using a modulation scheme
known as Orthogonal Frequency Division Multiplexing – OFDM) so that when
interference is detected (such as from a hair dryer), the sub-channels
that are affected can be shut off. Because there are so many available
sub-channels, this has little effect on the overall capacity of the
HomePlug system.
Another common challenge with home power line
communication is the dynamic change that can occur in electrical circuit
characteristics as users use light switches and plug into or remove
electrical devices from outlets. The HomePlug system is smart enough to
sense and adjust for the signal channels due to changes in electrical
circuit characteristics.
Each device that is a part of an in-home HomePlug
network requires a HomePlug adapter or a HomePlug converter built into the
device. The HomePlug adapters convert information signals (digital data)
into frequency carriers that travel down the power line. The adapters also
coordinate access to the power line communication system by first
listening to ensure there is no existing activity before transmitting and
stopping transmission when they detect information packet collisions have
occurred.
This figure shows how the HomePlug 1.0 system allows
a power line distribution system to transfer data between devices
connected to electrical outlets in a home. This example shows several
computers operating in a home and communicating between other data
communication devices plugged into outlets. This example shows that a
computer can send a data signal to a printer located at an outlet in
another room. This diagram shows that the high frequency signals from the
computer travel down the electrical line to the electrical panel. Then at
the electrical panel to the power line communication signal, it jumps
across the circuit breakers and travels down the electrical lines to reach
the HomePlug 1.0 adapter connected to a printer. This diagram also shows
that the computer can send data signals down the power line to a HomePlug
router connected to a broadband modem allowing the computer to connect to
the Internet.
Homeplug 1.0 Diagram
Home Media Networks - HMN Books
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Home
Media Networks - HMN
This
book explains the different types of home media data transmission types
including telephone line, power line wireless and coaxial lines and wired data
lines. Discover the different types of access control systems used in home
networks including random data access and reserved media control.
$1 9.99
Printed, $16.99 eBook9.99
Printed, $16.99 eBook
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