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2016 China International Conference on Electricity Distribution (CICED 2016)
Xi’an, 10-13 Aug, 2016
Simulation of Zero Crossings for Power Line
Communication Systems
Chang Liu, Li Bai, Tao Zheng, Benhui Gong and Wei Ba
Department of Electrical Engineering, Xi'an Jiaotong University
Abstract—With the growing demands on the
deployment of devices for power line communication
(PLC), different issues have to be investigated. Due to
the fact that zero crossing is of low noise power and
can be applied for synchronization, zero crossing
communication for power line system was carried out.
However, its feasibility has not been analyzed
thoroughly and the complicated simulation method
also makes it difficult to explore further. This paper
introduces a PLC system based on quadrature
amplitude modulation (QAM) technology and presents
a simple zero crossing simulation method. The
validation of the model and the fitness for PLC are
proved by the comparison of the constellation
diagrams in different environments.
Index Terms—PLC; QAM; Zero Crossing
Communication.
synchronization based on a large number of
experiment results in an OFDM system are compared
in [3]. By applying the three-phase power system AC
voltage zero crossings to frequency synthesis
synchronization technology and combining it with the
high speed digital frequency synthesizer, the problem
of the frequency hopping (FH) system synchronization
and fast frequency synthesis are solved [4]. The
application of micro-controller timing operation
function is proved to be valid when using zero
crossings communication in a PLC system [5]. The
synchronization schematic diagram based on
three-phase AC voltage is shown as Fig.1, if Z0 zero
crossing on u1A is selected as a transmission start point,
then Z1 to Z5 zero crossings can be used for
synchronization.
I. INTRODUCTION
PLC is a communication protocol that uses electrical
wiring to simultaneously carry both data and electric
power transmission or electric power distribution.
With the development of science and technology, the
application fields of PLC technology will not be
limited to the production and operation of power
system, it also can be used for broadband
communication applied to the fields such as smart grid,
smart home, broadband access and lighting control.
Compared with the medium such as Ethernet, ADSL
and wireless, power line has its unique characteristics,
for example, that the medium is already existed and its
structure is sturdy enough.
Nowadays there are two types of AC frequency values
which are 50Hz and 60Hz respectively and their
corresponding periods are 16.7ms and 20ms. For each
alternative period, there are two times where the
voltage value is zero, which is called zero crossing.
And it could be considered as a reference point of
synchronization. The concept of zero synchronization
is firstly carried out by Peter K. van der Gracht in [1]
which describes the design method and the modulation
prototype using pseudo random sequences. Then the
method is gradually applied to the frequency hopping
spread spectrum (FHSS) and orthogonal frequency
division multiplexing technology (OFDM) [2].
Conventional synchronous strategies and zero
CICED2016
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Paper No CP0834
Fig.1 the synchronization schematic diagram
At zero crossings the voltage and the value of all the
harmonics are zero, which leads to a low noise
condition facilitating data transmission [6]. However,
the feasibility of zero crossing communication in
power line system has not been analyzed thoroughly,
the complicated simulation method also makes it
difficult for further exploration.
The thesis presents a simple zero crossing simulation
method based on a QAM-PLC system. The validation
of the model and the fitness for PLC are proved by the
comparison of the constellation diagrams in different
environments.
The structure of this paper is organized as follows: The
low-voltage power line channel model is described in
section II and the power line noise is introduced in
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2016 China International Conference on Electricity Distribution (CICED 2016)
section III. The simulation based on PLC system
model and QAM method is conducted in section IV.
The method of parameter settings and results analysis
are also given. In the last section, a conclusion is
drawn and possible further exploration is suggested.
Xi’an, 10-13 Aug, 2016
TABLE I. The coefficients of power line channel
II. THE MODELING OF THE LOW-VOLTAGE POWER
LINE CHANNEL
Low-voltage power line channel is a multipath channel,
and has frequency-selective fading characteristics.
When the power line is considered as a medium of
signal transmission, the performance of the system is
limited due to the disadvantages such as multipath
effect and time-varying characteristic, strong noise
interference and serious channel attenuation, which
severely restrict the transmission rate [7]. In power
line channels, branches of T-structure and the change
of material or wire diameter leads to signal reflection,
which creates many different paths to the receiver. In
addition, the inter symbol interference (ISI) caused by
multipath time-delay also results in signal distortion.
Transmission performance is also affected by the
change of the power load, and the influence changes as
time goes by.
Manfred and Klaus's research (called "MK model" in
this paper) shows that top down method can be used to
determine the related parameters through the measured
data with the assumption that power line channel is a
black box. With the frequency range from 500kHz to
20MHz, the frequency response function is expressed
in (1).
N
H ( f )   gi A( f , di )e  j 2 f  i
(1)
i 1
Where,
g i is the weighted coefficient of path i , i is a path
number, A( f , di ) is the attenuation coefficient which
depends on the size and the length of the path,
and A( f , d i )  e  ( a  a f ) d with the attenuation parameters
of 0 , 1 , k . d i is the length of the path i ,  i is the
delay of the path i , c0 is the speed of light,  r is the
dielectric constant of power line.
The simulated four-path channel parameters are shown
in TABLE I, where each path number corresponds
with its weighted coefficient and path length. The
simulation result based on the four-path MK model is
presented in Fig.2. It is observed that the channel
attenuation becomes more serious with the increase of
the frequency. Besides, the frequency selective
characteristic also can be clearly seen with the notches
around 3MHz, 10MHz and 17MHz, which brings a
hostile condition for broadband data transmission on
the high frequency range.
k
0
1
i
Fig.2 the amplitude frequency characteristics
III. THE MODELING OF THE LOW-VOLTAGE
POWER LINE NOISE
Compared with other types of communication
channels, power line no more reflects the characteristic
of the additive white Gaussian noise (AWGN), and has
much more complex interference. The noise in power
line systems can be divided into five categories called
colored back-ground noise, narrowband noise,
asynchronous periodic impulsive noise, synchronous
periodic impulsive noise and random pulse
respectively, as shown in Fig.2 [10].
Fig.3 different kinds of the noise in power line system
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2016 China International Conference on Electricity Distribution (CICED 2016)
The descriptions on five kinds of noise are as follows:
1) Colored back-ground noise: The power spectrum
density (PSD) of the colored background noise is
relatively low, but has a significant increase in lower
frequency bands. It can cause the interference in the
frequency range up to 30 MHz.
2) Narrowband noise: Mainly produced by continuous
waveform signals modulated by amplitude modulation.
In general, it changes in a day as time goes by.
3) Asynchronous periodic impulsive noise: Typically
caused by the transformation of the power supply. The
frequency interval has corresponding relationship with
the repetition rate.
4) Synchronous periodic impulsive noise: It is
synchronous to the main cycle 50Hz or 100Hz (in the
United States are 60Hz and 120Hz) respectively, and
with the main cycle synchronization. The duration of
the noise is very short (10 to 100 microseconds), and
its PSD decreases with the increase of the frequency.
Synchronous periodic impulsive noise is mainly
caused by silicon controlled rectifier (SCR) adjusting
devices.
5) Random impulse noise: Mainly caused by the
transient process of the internal switch network, with
no regular time interval in the whole power grid, and it
could appears at any time of the day. The duration lasts
from several microseconds to several milliseconds,
and is regarded as the most complicated type which
influence the signal severely.
The noise in a power line communication system is the
combination of all the noise above. For the noise
simulation, in order to realize the synthesis of the
noise, the first step is to unify the time of every noise,
then add them together. From the amplified waveform
of the synthetic noise, the characteristics can be
obtained. The period of the noise is 10 milliseconds in
time domain, which implies that the noise is
synchronous with the power frequency. Another way
of obtaining noise data is from the measurement
results, the physical connection diagram and an
instance of measuring result is as shown in Fig.4 and
Fig.5.
Power Line
coupler
PC
Fig.4 physical connection diagram
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Xi’an, 10-13 Aug, 2016
Fig.5 measurement instance
IV. POWER LINE COMMUNICATION SYSTEM
SIMULATION
A. Low voltage PLC system model
A PLC system can be described as shown in Fig.6 and
the relationship of the parameters is shown in (2).
N(t)
S(t)
H(f)
+
R(t)
Fig.6 low voltage power line communication
system model
R(t )  N (t )  H (t )* S (t )
(2)
Where,
s ( t ) represents the transmission signal, H ( f ) is the
transfer function of the power line channel, H (t ) is
channel impulse response, N (t ) is the total power line
noise, R(t ) represents the receiving data.
B. QAM modulation
QAM is both an analog and a digital modulation
scheme. It conveys two analog message signals, or two
digital bit streams, by modulating the amplitudes of
two carrier waves, using the amplitude-shift keying
(ASK) digital modulation scheme or amplitude
modulation (AM) analog modulation scheme.
The two carrier waves of the same frequency, usually
sinusoids, are out of phase with each other by 90°and
are thus called quadrature carriers or quadrature
components. The modulated waves are summed, and
the final waveform is a combination of both
phase-shift keying (PSK) and amplitude-shift keying
(ASK), or, in the analog case, of phase modulation
(PM) and AM.
In the digital QAM case, a finite number of at least
two phases and at least two amplitudes are used. PSK
modulators are often designed using the QAM
principle, but are not considered as QAM since the
amplitude of the modulated carrier signal is constant.
QAM is used extensively as a modulation scheme for
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2016 China International Conference on Electricity Distribution (CICED 2016)
digital telecommunication systems, also can be a
communication system for power line simulation.
C. Parameter Settings and Simulation
The value of the parameters are displayed in TABLE II.
The channel model is aforementioned four-path power
line channel in section II. The simulation of the
integrated noise is made up of colored background
noise, narrowband noise, synchronous periodic
impulsive noise and asynchronous periodic impulsive
noise. In order to reduce the system sampling rate and
accelerate the simulation time, the carrier frequency is
set to be 50 kHz. Generally, the simulation system of
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sampling rate should be greater than or equal to 10
times of the carrier frequency, which is set to be
60MHz in the system. The flow chart of the zero
crossing algorithm is shown in Fig.7.
TABLE II. Simulation parameters
Fig.7 16QAM-PLC simulation flow chart
D. Simulation Results and Analysis
With the combination of the modulation signal and the
synthetic noise at zero crossings, the purpose of
realizing zero communication is accomplished by the
novel simple method.
When the AWGN channel is used, the decision from
the receiver is correct, and most of the transmission
data are extremely close to the corresponding dots in
the position of the constellation graph, which proves
the reliability of the system. According to the sampling
time and sampling points, 50Hz sinusoidal wave is
used as a benchmark, the voltage value of zero and the
maximum can be detected respectively. At the receiver,
the transmission constellation diagrams are obtained,
as shown in Fig.8 and Fig.9.
In Fig.8 and Fig.9, the black dots represents the
initially transmitted symbol, while the red dots
represents the received symbols. The mesh grid
represents the decision region for each symbol in
QAM16 system. It is shown that after adding power
line channel and power line noise, the communication
environment is more severe, leading to the fact that the
point deviation between receiving data and sending
data is bigger on the constellation graph mapping.
Fig.8 shows that after simulation for a thousand times,
all the receiving data are almost decided correctly
when sending data at zero crossings due to the
relatively weak noise characteristic. However, in Fig.9
it can be seen that some symbols are greatly deviated
from the initial symbols, which will fall into wrong
CICED2016
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decision region. Therefore, it will degrade the signal
transmission performance in the QAM16 power line
system.
Compared the constellation diagrams in two different
environments, it directly shows that the performance
of signal transmission at zero crossing is better than
that at the maximum value of the mains. And the
distinct results are caused by the fact that the noise
power density at zero crossing is lower than that in
another environment.
Fig.8 voltage of zero value transceiver constellation
diagram
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2016 China International Conference on Electricity Distribution (CICED 2016)
Xi’an, 10-13 Aug, 2016
[8] Guo Junchang. Intelligent distribution network reliability of the
power line carrier-current communication research. Changsha:
changsha university of science and technology institute of electrical
engineering, 2012.
[9] Dong Wang, The simulation and application of OFDM system in
low-voltage power line carrier. Chengdu: University of Electronic
Science and Technology Institute of Communication Engineering,
2008.
[10] Ceng Yu. Under the background of high noise signal detection
and estimation method research. Zhejiang: information institute,
zhejiang university, 2006.
[11] Changxin Fan, Lina Cao. Communication principle (7th
edition). Beijing: national defence industry press, 2012.
Fig.9 voltage of maximum values transceiver
constellation diagram
V. CONCLUSION
This paper introduces zero crossing communication in
power system communication technology, on the basis
of building a QAM-PLC simulation system,
introducing the power line transmission channel model
and different kinds of power line noise. After that a
simple zero communication method is proposed, the
signal transmission at power frequency voltage zero
crossings and the maximum value crossings is
discussed through the simulation. Moreover, the error
bit rate needs to be calculated on the basis of large
simulation results for further application.
REFERENCES
[1] Van Der Gracht P, Donaldson R W. Communication using
pseudonoise modulation on electric power distribution circuits.
Communications, IEEE Transactions on, 1985, 33(9): 964-974.
[2] Dostert K M. Frequency-hopping spread-spectrum modulation
for digital communications over electrical power lines. Selected
Areas in Communications, IEEE Journal on, 1990, 8(4): 700-710.
[3] Kistner T, Bauer M, Hetzer A, et al. Analysis of zero crossing
synchronization for ofdm-based amr system. Power Line
Communications and Its Applications, 2008. ISPLC 2008. IEEE
International Symposium on. IEEE, 2008: 204-208.
[4] Tao Zheng, Baohui Zhang, Shichang Ding. Frequency hopping
technology in the application of power line communication . Electric
power automation equipment, 2003, 23 (5) : 26-29.
[5] Yuan Liu, Hongyi Wang. Waveform of zero power carrier
communication system research. Electric measurement and
instrument, 2001, 38 (7) : 12-14.
[6] Jiajin Qi, Xueping Chen, Liu Xiaosheng. Low voltage power
line carrier communication technology research progress. Power
grid technology, 2010 (5) : 161-172.
[7]Zimmermann M, Dostert K. A Multipath Model for the Power
Line Channel. IEEE Trans. Commun. 2002, 50(4): 553-559.
CICED2016
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Paper No CP0834
Chang Liu received the B.E. Degree from North China Electric
Power University, China, 2014.
Currently, she is pursuing the M.E. Degree at Xi`an Jiaotong
University and her research interests are power-line communications
and multi-conductor transmission line theory.
Email: [email protected]
Bai Li received the B.E. Degree from Xi`an Jiaotong University,
China, 2013.
Currently, she is pursuing the M.E. Degree at Xi`an Jiaotong
University and her research interests are power-line communications
and noise suppression.
Tao Zheng received the M.S and Ph.D. degree in electrical
engineering from Xi`an Jiaotong University, Xi`an, China, in 2003
and 2007, respectively. He was a Postdoctoral Researcher with the
University of Udine, Italy, in 2008 and Postdoctoral Fellow with the
University of Pisa, Pisa, Italy, from 2008 to 2012.
Currently, he is an Associate Professor at Xi`an Jiaotong University.
His research interests include data analysis and signal processing
with applications in power systems automation and power-line
communications.
Benhui Gong received the Bachelor’s degree in electrical
engineering from Shandong University, Jinan, China, in 2014.
Currently, he is pursuing the ME Degree at Xi’an Jiaotong
University and his research interests are power system planning and
demand response of power market.
Wei Ba received the B.E. Degree from Xi`an Jiao tong University,
China, 2015.
Currently, she is pursuing the M.E. Degree at Xi`an Jiaotong
University and her research interests are power-line communications
and network relay technology .
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