OFDMA Based Power Line Communication for Smart Grids

Noman SHABBIR, Muhammad A. FAWAD, Muhammad N. IQBAL, Junaid ZAFAR
GC University Lahore, Pakistan.
doi:10.15199/48.2015.04.29
OFDMA Based Power Line Communication for Smart Grids
Abstract. This paper investigates the design and simulation of Orthogonal Frequency Division Multiple Access (OFDMA) communication system
using Narrowband-Power Line Communication (NB-PLC) for Smart Grids (SG) communication through extremely difficult channel environments
such as multipath and noise. In OFDMA, sub-band carrier allocation is performed using contiguous, distributed and sorted sub-band carrier
allocations and Bit Error Rate (BER) performance of this system is enhanced by these techniques, which are analyzed in this research. Simulation
results indicates that sorted sub-band carrier allocation scheme gives better performance than contiguous sub-band carrier allocation scheme.
Streszczenie. W artykule zbadano system komunikacyjny typu OFDMA wykorzystujący algorytm NB-PLC w zastosowaniu do sieci typu Smart Grid
pracujący w trudnych warunkach zaszumienia. Do alokacji nośnej międzypasmowej wykorzystano Bit Error Rate BER algorytm. System
komunikacji dla sieci typu Smart Grid bazujący na ,metodzie OFDMA.
Keywords: OFDMA, PLC, Smart Grids
Słowa kluczowe: OFDMA, Smart Grid, komunikacja
Introduction
The traditional grid is an out-of-date infrastructure and
lacks the pervasive electricity control features, which results
in an inefficient power delivery. Therefore, there is a strong
need to develop grids that can provide reliable methods of
energy generation, efficient transmission, distribution, and
control mechanism between utilities/customers. This
emerging next generation of power grid is called Smart Grid
(SG). The SG incorporates, within a physical power system,
Information and Communication Technologies (ICT) that
enhances grid efficiency and provides wide range of
customer oriented services [1,2].
An important part of SG is a robust and ubiquitously
available communication network that will enable various
devices connected to the SG to exchange vital information
at all times. The utilization of modern communication
technologies for information exchange in SG enables
electric utilities to make best possible decisions for efficient
power generation, transmission and distribution. Both wired
and wireless communication technologies have been
proposed in literature for data communication in SG [2,3,4].
Recently, researchers have shown greatest interest to the
use of in-place electricity power cables that have sufficient
potential to serve for data communication in SG. The
reason behind this motivation is that Power Line
Communication (PLC) eliminates the need for installing new
infrastructure for communication and without any doubt,
power lines are the most extensive and ubiquitous network.
PLC is the best option for smart grid communication
because it is pervasive and permeant [5]. PLC even offers
an opportunity to electric utilities to have their own
communication infrastructure. Therefore, it is expected that
PLC will be a dominant technology in an overall hybrid
communication networks that will be utilized in future for SG
communication connectivity. SG applications such as AMR
are usually low data rate for which Narrowband power line
communication is a suitable technology. The power lines
possess several challenges that should be taken into
account to reliably communicate over them. The high
background/impulsive
noise,
multipath
propagation,
frequency selective fading, and varying grid topologies
cause fading of the communication signal in the PLC.
These channel impairments for communicating over Low
Voltage Power Lines Communication (LV-PLC) are welldescribed by the multipath signal propagation model.
This research focuses on the problem of low data rate
Automatic Remote Metering (AMR) communication
between the customer premises and the data concentrator
placed on the transformer using smart meters. Although
Narrowband-Power Line Communication (NB-PLC) systems
are well suited for AMR, but due to the harsh characteristics
in power lines, major concerns exist on the reliability of NBPLC. Orthogonal Frequency Division Multiple Access
(OFDMA) based communication system is proposed to be a
solution to the most of the problems in NB-PLC systems.
Survey of the Related Work
OFDMA subcarrier allocation can be generalized,
adjacent (contiguous) or distributed. As evident by names,
in adjacent subcarrier allocation contiguous or continuous
groups of subsets are allocated to the users. While in
distributed algorithm random mode is adopted and the
resultant sub-band offers frequency diversity.
These
subsets ensure better performance with frequency
selectivity. Different OFDMA based algorithms are
presented in literature [6]. Power line communication is
noisy, robust and frequency selective and for this OFDMA is
preferred. In Fischer’s algorithm, author has proposed a
loading algorithm for discrete multi-tone transmission over
channels with inter-symbol interference [7]. The beauty of
Fischer’s algorithm is this that is well suited for high datarate transmission over copper wires.
Ming have altered Fischer’s algorithm to implement bit
and power allocation in sub-bands rather than subcarriers,
which resultantly minimizes signalling overhead. Two or
more sub-carriers are grouped to form sub-bands and
simulations results disclose that signalling overhead can be
reduced by 75 % for 512 sub-carrier OFDM systems [8].
Srinivasa in [9] developed a simpler model for narrow
band power line communication in smart grids which is a
statistical-time-varying
model.
Results
show
that
appropriate carrier allocation provides dependable and
uniform admittance to all units/meters in chorus indifferent
from their physical location. Each smart meter is evaluated
through BER to transmitted power to reach at maximum
efficiency. A simulation models show that total channel
power of one Watt for 20 meters is achievable with the
capacity of few Kbps per meter [9]. It is advocated that
power line communication has extraordinary potential that
can provide up-to 1 Gbps by increasing bandwidth of
present power line communication technology up-to 100
MHz combined along with new modulation schemes. The
considered communication system is having multiuser and
multi-cellular structure. The concept behind the radio
system and power line communication is same. OFDMA
communication System is proposed by the author of [10], as
compared to CDMA, as a solution for throughput problems
that are usually observed in power line communication.
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Research Question & Problem Statement
The existing network of power lines is most effective,
reliable and cost effective for smart grid applications. The
transmission of power and digital data on the existing power
lines is not a child work. The unfriendly features of power
lines offer restrictions for reliable communication.
Notwithstanding, the present improvements in the field of
digital communication with modulation schemes has
inspired the scientists to utilize power line communication
for this unique task.
Narrow band power line communication is a sub-division
of power line communication that is capable of low data rate
communication. Most of the smart grid applications are low
data rate applications thus making narrow band power line
communication more suitable for this purpose. There are
many challenges in power line utilization in the form of
frequency selective fading, time varying noise, high
attenuation resulting in signal fading and impedance
mismatch. In the presence of these stumbling blocks
OFDMA is suggested as a solution to the aforementioned
problems. Carrying the argument further, the characteristics
of OFDMA exhibits appropriate behaviour when compared
to other schemes for power line communication.
Problem Solution
In this research, a smart grid system is designed that
consists of four meters. The rest of the parameters are
defined in Table 1. Two OFDMA based algorithms are used
for simulations, which are as follows:
A. Contiguous / Adjacent Sub-band Allocation Algorithm
(CSAA):
Many continuous groups of sub-carriers are tied up to
form a sub-band. These types of sub-carriers are assigned
to offer multiuser diversity. This multiuser diversity is very
suitable for static users because the static user is relatively
constant in channel response experience. Following is
detail of this OFDMA based algorithm.
 The total available spectrum contains the entire of subcarriers.
 The sub-carriers are arranged in ascending order of
their frequencies such as first subcarrier occupies the
lowest spectrum and subcarrier NC contains the highest
spectrum. All subcarrier indexes are contained in set φ =
{1,2,3,4….NC}.
 All the subcarriers NC are divided in NB sub-bands. Thus
(1)

NCB = NC . NB
Number of bits for every OFDM symbol to transmit is
assumed as:
(2)
Rtot = bave . NC
Here, bave is the average spectral efficiency mandatory for
the system.
th
 The gain of the channel k subcarrier is represented as
hk. The average channel gain of the subcarriers in a
specific sub-band is evaluated as
B. Selected (Sorted) Sub-band Carrier Allocation Algorithm
(SSCA):
High BER is caused due to few subcarriers which are
badly affected by frequency selective fading. To solve this
issue sorted sub-band carrier allocation is adopted so that
we can leave out such subcarriers. In selected sub-band
carrier allocation sub-bands are arranged in ascending
order. Resultantly, only those subcarriers are sent to users
those have better channel gains. The channels with
frequency selectivity show better results under this
algorithm. The algorithm is explained as follows.
 The spectrum comprises of NC subcarriers
 All of the NC subcarriers are arranged according to their
frequencies in ascending direction, such as, subcarrier
one lies at the lowest spectrum, while the subcarrier NC
possesses the highest spectrum. All of the sub-carriers
which are arranged present in the set φ = {1, 2, 3, 4
….NC}.
 The sub-carriers are organized on the bases of their
channel gains hk. This arranged Sub-carrier keys set is
denoted as {a1, a2, a3, a4… aNC} such as ha1≤ ha2 ≤…. ≤
haNC.
 Assemble these arranged NC subcarriers into NB subbands. For Nm consumers with diverse channel
circumstances which they are experiencing from
transmitter to the receiver (local grid station), allocate
the first sorted sub-band to the user.
 Leave the other sub-bands and transmit the user data
over the sorted ones.
 Until all users are assigned a sub-band repeat the
process.
Simulation Results
Performance of these algorithms will be gauged for
OFDMA
communication
system
for
information
transmission. In PLC, each user experiences different
multipath delays due to different number of connections,
joints, cable length and some other on ground factors.
Similarly, the performance of contiguous sub-band
allocation algorithm reduces as number of subcarriers per
sub-band increases. The bit error rate of four meters under
OFDMA communication system is shown in figures below.
Table 1. Parameters of OFDMA Communication System
Parameters
Type/Value
Communication Method
OFDMA
Modulation Scheme
16-QAM
Number of Carriers
32
Carrier Spacing
400 KHz
Frequency Range
3-500 KHz
FFT Size
256
Length of Cyclic Prefix
16
Channel
LV-PLC Access Channel
-3
LV link BER Specification
10
(3)



For Nm meters with unalike channel circumstances
which they are facing from meter to the data
concentrator, allocate the first sub-band regardless of its
value of Hi to the ith meter (where i = 1, 2, 3, 4… Nm ).
Transmit the data of meter over the given sub-band and
leave the rest of sub-bands.
All users are allocated a sub-band by repeating the last
two steps.
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Fig 1. BER of all meters in CSAA
PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 91 NR 4/2015
Fig. 1. shows the BER of meter 1 to 4 is 10-3 and Eb/N0
for these meters remain 10.7, 10.5, 16.5 and 27.5 dBs
respectively. The results reveal that channel conditions for
meter four are worse as compared to rest of the three
meters. Therefore Eb/N0 for meter four is the highest. The
analytical (speculative) and simulated probability of Bit Error
for OFDMA based communication system using contiguous
sub-band allocation for meter one shown in Fig. 2.
However, Eb/N0 of meter 2, 3 and 4 remains 10.5 dBs, 12
dB, and 17.5 dB. Thus results tell us that the conditions for
meter four are even not better this time. However,
improvement in performance is gauged.
Fig. 5. BER of meter four using CSAA
Fig 2: BER of meter one using CSAA
The analytical (theoretical) and simulated probability of
Bit Error for OFDMA based communication system using
contiguous sub-band allocation for meter two, three and
four are presented in Fig. 3, 4 and 5 respectively.
Fig. 6. BER of all meters using SSCA
Now the individual BER of all the meters and the simulated
and theoretical difference is depicted in graphical
representation in Fig. 7, 8, 9 and 10.
Fig 3: BER of meter two using CSAA
Fig. 7. BER for meter 1 using SSCA
Fig 4: BER of meter three using CSAA
Now selected/sorted sub-band algorithm is used to
observe the behavior of these meters. The simulated results
-3
are shown in the figure below. In Fig. 6., BER of 10 is
achieved for meter one while its Eb/N0 remains 10.5 dB.
-3
Moreover bit error rate of meter 2, 3 and 4 remains 10 .
For meter 1 and 2 there isn’t any significant difference
between the theoretical and simulated results it because of
low attenuation and less multi-paths. Whereas for meter 4
has greater variation in simulated and theoretical results
due to high attenuation and more multi-paths. This
algorithm reduces the difference between the theoretical
and simulated results and produces better results as
compared to contiguous sub-band carrier algorithm. This
improvement is understandable for channels those have
characteristics of frequency selectivity.
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133
both the algorithm. For future work, some more algorithms
such as distributed sub-band allocation algorithm and
hybrid sub-band allocation algorithm can be experimented
for more reliable and swift communication for smart grids by
utilizing
OFDMA
based
communication
system.
Furthermore, for the improvement in BER performance in
OFDMA communication system, some other approaches
such as Least Mean Square Error (LMSE) and Maximum
Like-hood Sequence Estimation (MLSE) can be
experimented for improved digital signal processing.
REFERENCES
Fig. 8. BER for meter 2 using SSCA
Fig. 9. BER for meter 3 using SSCA
Fig. 10. BER for meter 4 using SSCA
Conclusion
In comparison of both algorithms, the sorted sub-band
carrier allocation shows better performance due to better
selection of subcarriers that are to be transmitted between
user and local grid. The result of MATLAB simulation shows
that attenuation will be up-to 10 dB for meters with less than
10 paths while for meters with 15 and above paths it may
increase up-to 42 dB and deep notches are observed in the
graphical representation. These notches clearly indicate the
impedance mismatch. Probability of error is least when
sorted sub-band carrier algorithm is used as compared to
adjacent sub-carrier algorithm in OFDMA communication
system. However, sorted sub-band algorithm is complex to
implement and more time consuming as compared to other
algorithm. It is because of the extensive sorting of the
subcarriers.
As we know, two algorithms such as sorted and
contiguous sub-carrier allocation algorithms are being used
to serve the purpose of communication by using narrow
band power line communication in OFDMA system. We
also discussed some short comings and some benefits of
134
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Authors:
Engr. Noman Shabbir, Dept. of Electrical Engineering,
GC University, Katchehry Road, Lahore, 54000, Pakistan.
E-mail: [email protected];
Engr. Muhammad Atif Fawad, Dept. of Electrical Engineering,
GC University, Katchehry Road, Lahore, 54000, Pakistan.
E-mail: [email protected];
Engr. Muhammad Naveed Iqbal, Dept. of Electrical Engineering,
GC University, Katchehry Road, Lahore, 54000, Pakistan.
E-mail: [email protected]:
Dr. Engr. Junaid Zafar, Dept. of Electrical Engineering,
GC University, Katchehry Road, Lahore, 54000, Pakistan.
E-mail: [email protected]
PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 91 NR 4/2015