International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Power Line Communication by Using Advanced
Signal Processing Schemes
A.Mounika1, M.Anil Kumar2
1
B Tech, Department of Electronics and Communication Engineering
K L University, AP, INDIA
2
Asst professor, Department of Electronics and Communication Engineering
K L University, AP, INDIA
Abstract--Power Line Communication (PLC) refers to
provisioning of communication services over the
electricity power grid. A PLC Carrier unit can send high
frequencies over power lines and injects the frequencies
(or picking them up) via a coupler linked directly to the
power grid. It is general to categorize the PLC systems as
Broadband PLC and Narrowband PLC. India provided
broadband connectivity to 15 million subscribers
increasing 0.24% month on month to 15.01 million at the
end of January 2013.The broadband subscriber market is
expected to increase to 24 million by 2016.Broadband
services are the current requirement of rural
development. Where broadband access has lagged
notably in rural areas, PLC opens up a new
communication infrastructure. Nearly 70% of the
population lives in rural areas in India, where the issues
of information, education and communication become
paramount for development of the same. At this juncture
it is relevant to mention that gap between target and
achievement to accomplish broadband penetration in
India will go over 24 million by 2016.
Keywords--Orthogonal
frequency
division
modulation(OFDM),Supervisory
control
and
data
acquisition(SCADA),Fast Fourier Transform(FFT),Inter symbol
interference(ISI)
I. INTRODUCTION
Adequate infrastructure for Internet information
services in the rural areas need to be made
available to rural folk to connect them with urban
and semi urban population as knowledge and
education help develop stronger economies and
more social equalities. SCADA (also called tele
control) in substations has one or more computers
with appropriate application software (Master
ISSN: 2231-5381
Stations) connected by a communication system
(wire, radio, power line carrier or fiber optics), to a
number of remote terminal units (RTUs) which are
referred to as intelligent electronic devices (IEDs),
placed at various locations to collect data and to
perform intelligent autonomous (local) control of
electrical systems and report results back to the
remote master(s). Use of an appropriate data
highway which loops through the substation is thus
necessary. The design of PLC modem (modulator
demodulator) to facilitate the power line as a
medium of communication is a challenging task.
Power lines constitute a rather hostile medium for
data
transmission.
Varying
impedance,
considerable noise and high attenuation are the
source of degradation of the signals on power line.
Moreover, typical power lines are unshielded, high
frequency current flowing in power lines turns
power lines into antennas and electromagnetic
radiation will propagate out of the wires.
International Amateur Radio Union (IARU) are
complaining
because
the
claim
that
communication through the power lines,
particularly those operating in the range 1.6
megahertz to 30 megahertz, challenge the
fundamental purpose of EMC (Electromagnetic
Compatibility) standards. Optimum signal to noise
ratio (SNR) or in other words, carrier that requires
much less power becomes the significant
performance parameter in this case. We need to not
only utilize existing technologies to build the
http://www.ijettjournal.org
Page 1092
International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Modems but also create novel ones. Efficient
MODEM design mainly concerns with efficient
modulation scheme that suits the power line
channel. Efficiency of the modulator clearly is the
transmission power which in turn radiates less.
With the availability of fast processing signal
processors, the claim is that PLC is now mature
and ready to be standardized worldwide within an
international body of standardization. The
technological consortiums are working together to
achieve this within the IEEE, and is also working
on the issues of interoperability and coexistence of
different PLC devices on a common electrical
network. In this paper two of the signal processing
schemes of PLC, modulation and coding are
discussed. In Section II of this paper the use of
orthogonal frequency division modulation (OFDM)
for a power line channel is acknowledged. In
Section III details of different schemes to combat
noise effects are given. In Section IV the simulated
results for data transmission over fading channel,
modeled as power line channel are discussed. The
concluding remarks in the Section V provide the
knowledge of very recent technical advances that
need to be tested for appropriate physical
implementation.
II. MODULATION SCHEME FOR PLC
An easy way to comply with the conference
paper formatting requirements is to use this
document as a template and simply type your text
into it. Electric power companies such as Cinergy,
Consolidated Edison and Progress Energy reported
encouraging results to suppress noise effects, with
Intellon largely contributing to the advances to
solve noise problems. INT 5130 chipset, the first
to offer, lead other networking companies to
announce products to meet standards set by an
industrial alliance called Home plug. Intellon’s
chip uses orthogonal frequency division
modulation to combat multipath channel effects
that are inherent of power line channel so that the
data suffers less loss.
A.OFDM
Orthogonal frequency division multiplexing is a
communications technique that divides a
communications channel into a number of equally
spaced frequency bands. A sub carrier carrying a
ISSN: 2231-5381
portion of the user information is transmitted in
each band. Each sub carrier is orthogonal
(independent of each other) with every other sub
carrier, differentiating OFDM from the commonly
used frequency division multiplexing (FDM).
B.Working of OFDM
In practice, the OFDM bundles data over
narrowband carriers transmitted in parallel at
different frequencies. Spectral efficiency is
achieved by using these parallel sub channels that
are as closely spaced as possible in frequency
without
overlapping/interfering,
by
being
orthogonal. Typically, ISI (Inter symbol
Interference) comes from multipath delays. By its
very nature OFDM defeats multipath distortion.
OFDM combats it by transmitting bits in parallel,
with each bit being transmitted rather slowly. For
example, suppose to transmit 1,000,000 bits per
second and to transmit them one at a time, each
takes one microsecond to send. Any delay spread
longer than one microsecond would cause delayed
reflections from multipath to overlap the direct
signal for the next bit, thus causing ISI. If instead
1000 bits are transmitted in parallel at a time, on
1000 separate OFDM sub channels, the
transmission is 1000 times slower; that is, one
millisecond to send them. A multipath delay spread
of 1 microsecond would only overlap 1/1000th of
the transmission interval for any given bit, thus
avoiding the ISI.
C.Application of OFDM to Power Line channel
Power line is characterized as a multipath
channel and hence the disturbances present in the
line that carries high frequency signal are
equivalent to multipath disturbances. Choice of
OFDM as modulation scheme helps to combat the
noise effects on the line.
D. OFDM Implementation using DFT
OFDM can be seen as either a modulation
technique or a frequency multiplexing technique.
In an OFDM system, data is carried on
narrowband sub carriers modulated with different
possible techniques, such as binary phase shift
keying (BFSK) or quadrature amplitude
modulation (QAM). Each sub channel is
http://www.ijettjournal.org
Page 1093
International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
modulated with a separate symbol and then all the
sub channels are frequency-multiplexed, using
orthogonal frequencies to increase the channel
efficiency. Data is transformed into time domain
using IFFT at the transmitter and transformed back
to frequency-domain using FFT at the receiver.
The total number of sub-carriers is equivalent to
the number of points of the IFFT/FFT.
III.FORWARD ERROR CORRECTION CODING
A. Random and Burst errors:
Random errors are a common phenomenon in
memory less channel. Single randomly distributed
bit errors occur whose occurrence is independent
from bit to bit. Burst errors are associated with
memory channels in which noise is not
independent from one transmitted symbol to the
other; therefore errors tend to occur in clusters.
Error control coding schemes with random error
correction capacity alone do not greatly improve
the system performance of such channels. Only a
low transmitting power density will be possible for
future broadband PLC, due to strict emission
regulations for electromagnetic (EM) compatibility.
Burst error correcting codes such as BCH or RS
(Reed Solomon) codes find application in such
cases to combat the impulse/burst noise effects that
last for certain duration. Durations for which the
impulse effects stay on line can be analyzed and
suitable error correction schemes to be applied.
B. Interleaving and Concatenation:
Thus in general, transmission errors have a
strong time/frequency correlation. Interleaving the
channel coded data provides diversity in the time
domain. Interleaving breaks the time correlation
and enables the decoder to eliminate or reduce
local fading throughout the band. Interleaving
depth should be large enough to break long straight
errors. Concatenation is another means of
improving the error correcting capacity of the
system.
A. Interleaving and Concatenation principles are
utilized to form a revolutionary turbo codes that
claim to approach Shannon limit. Extensive
research on Convolutional Turbo Codes (CTC),
Block Turbo codes (BTC) and means of
implementing them with fast processors is being
conducted. Space time codes are other
revolutionary approaches that utilize diversity in
fading channel to mitigate the channel multipath
noise effects. As power line channel is a multipath
channel, the efficiency of the approach will be
coding gain at reduced decoding complexity.
IV. SIMULATION RESULTS OF OFDM.
MATLAB 7.0 is used for the simulation of the
results. The text data written in ‘input.txt’ file is
applied as input to the OFDM transmitter block.
The power line channel is modeled by adding
random multipath noise to the OFDM data. Text
data being transmitted using phase shift keying
(PSK) modulation is compared with OFDM
transmission. System performance in the form of
probability versus SNR plots are found and are
shown in Figure 1. Figure 2 shows the level of the
IFFT (Inverse Fast Fourier Transform) output of
the transmitter that corresponds to text data of
consideration here. FFT of size 128 with 32 carrier
points is used for the simulation studies. Figure 3
shows the received data which are transmitter
strengths distorted with added multipath noise.
OFDM receiver shows reduced errors with
increase in SNR. There is a coding gain of
approximately 2 to 2.5 dBs (decibels) for
orthogonal frequency modulation as compared to
simple phase shift keying modulation.
C Recent Advances in channel coding for Power Line:
Fig.1.Probability of error plot with SNR for PSK and for OFDM for
ISSN: 2231-5381
http://www.ijettjournal.org
Page 1094
International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
multipath channel
ACKNOWLEDGMENTS:
We like to thank management and department of
ECE,KL University for continuous help and
support during this work.I express thanks to
Mr.Habibullah khan sir for his encouragement
during this work.
REFERENCES
[1] Richard van Nee Ramjee Prasad
OFDM for Wireless Multimedia
Communications.
[2] Stephane Mallat
Fig.2.Transmitter signal strengths
A Wavelet Tour of Signal Processing
[3]Ayman M. Ahmed , Dwight D. Day
Orthogonal Transforms for Digital
Signal Processing
[4] Richard G. Lyons
Understanding Digital Signal Processing, 3/e
[5]Kassam, S.A. 1985 Robust techniques for signal processing:A survey
[6]Muller, S.H. 1997 OFDM with reduced peak-to-average power ratio by
optimum combination of partial transmit sequences
[7]Cheong Yui Wong 1999 Multiuser OFDM with adaptive subcarrier, bit,
and power allocation
[8]Philip Denbigh Univ. of Sussex, Sussex, UK
System analysis and
signal processing: with emphasis on the use of MATLAB
Fig.3.Receiver signal strengths
V. CONCLUSIONS AND SCOPE OF FUTURE WORK
Coding gain of approximately 2 to 2.5 dBs
provided with OFDM over simple PSK
modulation acknowledges the performance of
OFDM. We have to always remember that EMC
constraints put a limit on the carrier power and
efforts to have high coding gain are to be
approached. This can be made possible with coded
OFDM (COFDM) that uses efficient burst error
correction. OFDM and COFDM implementations
for real time data text, voice image and video are
to be studied using presently available processors.
Turbo BCH and Turbo Convolutional codes that
use less complex decoding and modulation with
desired high bit rate signal constellations are to be
developed, proper choice of which results in an
efficient MODEM technology.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 1095