Page 147 - From Smart Grid to Internet of Energy

Power line communication technologies in smart grids Chapter 4 129

but also can be utilized to transmit communication signals. After this evolution
of the power lines, the PLC systems have been attracted increasing interest and
these systems are considered as innovative technologies for several application
areas such as internet access in indoor and/or outdoor, home automation sys-
tems, in-vehicle communication, SGs, advanced meter reading, demand
response and so on. The most important benefit provided by the PLC systems,
when compared with other wired and wireless communication systems, is that
there is no requirement to establish an external communication channel [2, 4,
6–8].
Even though these systems provide installation cost minimization, the
power lines expose a destructive channel effect since they have not been orig-
inally created for voice, data and image transmission. Furthermore, disruptive
effects of power lines (i.e., high-level frequency-dependent attenuation, vari-
able impedance and different type noises) are highly dynamic different from
other wired communication systems. Noise characteristics of power lines can-
not be defined through only additive white Gaussian noise (AWGN). Even
though noises in power lines are complex, they can be categorized into five clas-
ses as narrowband noise, colored background noise, periodic impulsive noise
synchronous to the main frequency, periodic impulsive noise asynchronous to
the main frequency, and asynchronous impulsive noise. The narrowband noise,
periodic impulsive noise asynchronous to the main frequency and colored back-
ground noise usually exhibit stationary behavior for a few seconds and minutes.
Therefore, these noises are generally taken into account as background noise.
On the other hand, periodic impulsive noise synchronous to the main frequency
and asynchronous impulsive noise change in the level of microsecond swiftly
depending on the on/off state of devices connected to the grid. According to
these mentioned disruptive effects, PLC channels are characterized as a com-
bination of frequency-selective and time-selective channels. In addition, it is
worth noting that the power line channels behave more destructive channel
environment than wireless communication channels. Therefore, secure trans-
mission of high-frequency communication signals over power lines is a hard
process, and to handle this task the PLC channel should be firstly described
as precisely as possible.
In spite of the fact that there exist various methods to define the PLC channel
characteristics, the most popular models can be classified into two categories as
bottom-up and top-down approaches [3, 7, 37–47]. The bottom-up method
defines the PLC channel model through transmission line theory and it requires
some prior information regarding power grid infrastructure such as power line
topology, characteristics of utilized power cables and connected loads to net-
work to figure out impedance variations [37–42]. The other approach, top-down
method, tries to model PLC channel depending on the long-term measurements
of power line characteristics. In top-down method, curve-fitting techniques are
utilized to acquired channel measurements for deriving mathematical expres-
sion of PLC channel variations. Hence, this modeling approach do not require