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The power line home automation type communication
system for voice communication and data
transmission using an existing power line
Md. Imamul Arefeen1, *Md. Abdus Samad2, Md. Asadujjaman Nur3
Electronics and communication Engineering
Khulna University of Engineering & Technology
Khulna, Bangladesh
2
[email protected]
Abstract—This paper states about the voice communication
and data transmission at a time on a single existing power line
that reduces the complexity of so much wires used in
communication system and it is applicable in a large automated
area with low cost and easy installation process. The message
(voice, tone or digital data) is modulated with a high frequency
carrier by frequency modulation (FM) or frequency shift keying
(FSK) process and after amplification it passes to the power line
through the bidirectional coupler. At the receiver section the
signal (FM or FSK) is recovered by coupler and then
demodulated. The demodulated signal is then passed through the
low pass filter to recover the voice or tone signal and a
comparator is used to recover data signal. Here the authors use
different carrier frequencies for different users and also use
corresponding filter and comparator. A trap circuit is used here
to localize the communication area which obstructs the
transmitted signal to pass out of that area and hence losses are
reduced.
Keywords—modulation,
filter, carrier;
I.
coupler,
comparator,
trap-circuit,
INTRODUCTION
Power line communication (PLC) technology defines
transmitting of message through power line using carrier
modulation. PLC can control and diagnose information such
as temperature monitoring, vibrations measurements etc. are
measured by various sensors convert to power and transmit
through power cable [1]. The external electrical grid helps in
many applications and provides opportunities for equipment
for vendors [2]. It can provide broadband connection to rural
or remote areas specially where telephone and cable
connection do not have existence and also provide data
services (broadband Internet service, VoIP service, remote
metering, light control at street, home security and so on) [3].
In PLC communication the major drawbacks are noise
influence, signal attenuation, and multipath feeding and
reflection [4]. Broadband over power line (BPL) gives the
opportunity of broadband marketplace and increase its
demand widely [5]. Wireless local area network (LAN) can
also attach with wireless modems that connects to one or more
wireless hubs (infrastructure-based) or to each other. This is
978-1-4799-6062-0/14/$31.00©2014 IEEE
used as a communication tool especially at telecommunication
sector, at home automation and network access technology as
its popularity is increased for using RF frequency. The
wireless system is used for less number of nodes in the small
network such as home or office and it also requires wireless
networking hardware and software which is typically based on
the IEEE 802.11b standard [6]. External plant applications of
PLC are practicing widely. Now a days PLC systems have
made vast popularity at Neighborhood Area Network systems
in Europe and also at North America [7]. The field of power
line communications has recently seen a revival of interest,
with increased research activities, as well as new standards
and products being introduced. The authors use here 150 KHz
carrier for a single voice communication for hardware
implementation and use different frequencies for transmitting
more messages over a single power line. For each carrier the
recovered message signal is found noiseless. The message
recovering performance is excellent and the data recovery also
shows better performance. This communication system is
mainly home appliance based i.e. it is used at home, office or
an institution automation for voice and data communication
for no bill cost except only use of low power. This also can be
used between the two power line substations. Limitations and
difficulties which can obstruct communication are also
revealed here. And also possible solutions are discussed here
about the mismatch probabilities of coupler, different carrier
frequencies related problems.
II.
SYSTEM DESIGN
The total system runs at three parts named transmitter part,
power line carrying part and the receiving part. At transmitter
part the signal is modulated with carrier and then it is
transmitted through power line. At receiver the modulated
signal is received from power line with the help of coupler and
then message signal is separated from carrier by demodulation
and finally the message signal is recovered through filtering.
In a PLC user module both transmitter and receiver circuit
exists for bidirectional communication. Power line isolator
which works for bidirectional coupling.
comparator input and pin-4 is VCO output. The pin-3 & 4 must
be shorted and the VCO output can be found here. If the FM
modulated frequency is greater than VCO output, then the PLL
gives a higher voltage according to the frequency variation and
if the FM modulated frequency is less than VCO output, then
Fig. 3. Circuit diagram of FM demodulation.
Fig. 1. Functional block diagram of power line communication system.
A. Modulation
CD4046 IC can easily perform modulation. It contains a
VCO (voltage control oscillator) which gives oscillating
frequency according to voltage given at pin-9. At pin-4 free
running oscillation occurs if any voltage isn’t provided at pin9 but if voltage is provided(message signal) at pin-9 then
CD4046 gives modulated output in the manner that free
Fig. 2. Circuit diagram of FM modulation.
running frequency will be high if signal voltage is positive and
low if message signal is negative. Simply, pin-3, 5,8,14 should
be grounded, pin-11, 12 should contain resistors, a non-polar
capacitor should be inserted between pin-6 & 7, message
signal should be given in pin-9 with the addition of dc voltage
to get modulated output.
B. Demodulation
For demodulation, the FM modulated signal should be
given at pin-14 and the demodulated signal will be found at
pin-10. The pin-5 & 8 should be grounded. A capacitor should
be inserted between pin-6 & 7. Here, pin-3 is a phase
the PLL(Phase-Locked Loop) gives a voltage according to the
frequency variation. This demodulated output contains high
frequency components. So a low pass filter is needed to
recover the original message signal.
C. Power line isolation
This is the most important part of PLC that should be
designed very carefully. As the modulated signal is
transmitted over power line and a 220Vac (50 Hz) already
existing there so it is needed to isolate the 220Vac (50 Hz)
from our transmitter and receiver circuit for protection. To
isolate the 220Vac (50 Hz) signal it is needed to apply a high
pass filter to allow the high frequency modulated signal to
pass through while blocking the low frequency signal. Here a
high voltage low valued capacitor is used in series with a
coupling transformer between the power line and
Fig. 4. Circuit diagram of power line isolation.
the transmitter or receiver. This will block any signal of a
frequency lower than the cut off frequency and allow passing
any signal having a frequency greater than the cut off
frequency.
D. Line Trap Circuit:
The line trap circuit is used for allowing the transmitted
signal to receive over a limited area such as a building,
institution, market or a town. There may thousands of devices
connected over the power line at a time. So there may have a
great signal loss of our transmitted signal. To reduce this loss
it is needed the line trap circuit. The line trap circuit has been
used in series with the power line which actually consists of
150 KHz. But in Fig. 9 it has shown modulated signal with a
low frequency carrier for easy realization of FM signal using
TABLE I
CIRCUIT SPECIFICATIONS
Imp
edan
ces
Fig. 5. Connection diagram of line trap circuit.
a parallel inductor and capacitor. For the 50 Hz ac signal of
power line it gives a very lower impedance but for our 150
KHz carrier signal it gives high impedance. So there is no
restriction for 50 Hz ac signal of the power line but due to
high impedance for carrier signal the line trap circuit will not
allow to pass the transmitted signal out of the area bounded by
the line trap circuit. The impedances can be easily calculated
from the following equations
XL=2πfL,
XC=1/2πfC,
III.
Z= (XL* XC)/ (XL+XC)
HARDWARE IMPLEMENTED CIRCUIT
The transmitter circuit modulate the message signal with
carrier and mix with power supply and the receiver act
reversely and recover message.
XL1
XL2
XC1
Transmitter/Receiver
side coupler
(for 50
Hz AC
voltage)
0.01 Ω
2.2 Ω
31.83
kΩ
(for 150
kHz
carrier
voltage)
6.6 kΩ
28 Ω
10.61 Ω
Power
line AC
voltage
(p-p)
Modulated
signal
voltage(p-p)
at FM input
side
Modulated
signal
voltage(p-p)
at power line
part
622 V
8V
2V
same circuit. As Capacitor shows high reactance (31.83 kΩ)
at 50 Hz and secondary inductance shows very low (.01Ω)
reactance at 50 Hz frequency (TABLE I) so almost all the 50 Hz
AC power line Voltage is seized at capacitor C1 and hence we
get almost zero ac power line voltage at primary side and
isolates the circuit from power line. Due to mismatch of power
line and transmitter-receiver impedances the carrier wave
shape is slightly changed as shown in fig. 10 but original
carrier is recovered at receiver by the use of comparator. Peak
to peak 50 Hz power line voltage ac voltage is 622V and the
transmitted modulated peak to peak signal is only 2V and has
no adverse effect on the devices connected with power line.
Fig. 8. Waveform of Carrier signal.
Fig. 9. Waveform of audio signal(1)
and FM modulated signal(2).
Fig.10. Coupling effect of carrier
signal.
Fig.11. Input signal(1) and demodulated signal(2) without power line.
Fig. 6. Transmitter circuit.
Fig. 7. Receiver circuit.
IV.
RESULT ANALYSIS
The power line communication circuit carries 1.5 KHz
message signal given from signal generator and a carrier of
Waveform of input signal shown at fig.10. and also the
demodulated signal without power line. The fig. 11 and fig. 12
shows that the output doesn’t changes and hence has no effect
on PLC communication using power line with the circuit
discussed here. Normally power line voice communication
performance of the device. The 98% noise free efficient data
transmission possible here. The coupling effect and the
crosstalk two problems appear here. This can affect a bit in the
output data. The PLC technology can be used in a home
(Home networking (LAN)) to interconnect home computers
and peripherals, and home entertainment devices that have an
Ethernet port. Power line adapter sets plug into power outlets
and establish an Ethernet connection using the existing
electrical wiring in the home. (Power strips with filtering may
absorb the power line signal.) This allows devices to share
data without the inconvenience of running dedicated network
cables.
Fig. 12. Waveform of input signal and final demodulated signal using power
line.
needs 20-200 KHz carrier. The proposed circuit shows good
performances at 20-160 KHz range shown at fig.13. Fixed
amplitude message signal of 800mV is used for various carrier
frequencies and graph shows corresponding outputs. At
various frequencies the output voltage varies but provides
ACKNOWLEDGEMENT
This work was conducted in the Electronics and
Communication Engineering department laboratory (MECE
laboratory) at Khulna University of Engineering and
Technology (KUET) at Khulna and in collaboration with the
Department.
REFERENCES
[1]
Output Voltage(mV)
1400
1200
1000
800
600
400
200
0
[2]
0
50
100
150
Carrier frequency(KHz)
noiseless better output between 20 KHz to 160 KHz and
output amplitude can be amplified to desired level by using
amplifier. As at high frequencies (>160 KHz) CD4046
performs poor and hence lower the output. At lower
frequencies C1 gives greater attenuation and hence outputs of
low amplitudes. Maximum transmitted digital data using the
designed circuit is 10Mbps and then only coupler and
comparator is enough as it is high frequency. The circuit gives
better performance than the others as almost noise free voice
and data recover is done. The circuit installation cost is quite
less than the others.
V.
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200
Fig. 13. Output voltages with the variation of carrier frequencies.
CONCLUSION
Power line communication (PLC) technology adopted in
transmitting the message signal this paper shows this in a
secured way. Efficient transmission is ensured by the output
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