Powerline Communications:
Channel Characterization and Modem Design
Yangpo Gao
Helsinki University of Technology
yangpo.gao@nokia.com
2005-10-18
Thesis Contents
Table of Contents
Introduction
PLC Technology Background
Channel Measurement and Modeling
Disturbance over PLC
DMT Based PLC Modem Design
Conclusion
Reference
This thesis is part of project “ PLC controlled LEDs
for general lighting system”, which is sponsored by
TEKES
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Introduction
History of PLC and Motivation of Thesis
What is PLC
PLC – Powerline Communications
Using powerline as transmission medium for data
communication
History of PLC
From high voltage (HV)
low voltage (LV)
Low data rate
high data rate
Control application
multimedia data applications
Motivation
Cheap “the last mile” solution
However, worse channel than other wired network
Channel characterization reliable communications
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PLC Technology Background
PLC Technologies
Three network levels
High voltage (110–380 kV)
Medium voltage (10–30 kV)
Low voltage (230/400 V, in the USA 110 V) (my thesis range)
Efficient coupling
Inductive coupling
Conductive coupling
Modulation and error correction
OFDM, DMT
CDMA
FEC
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EMC Issues
EMC --Electromagnetic compatibility
The ability of a device or system to function
satisfactorily in its electromagnetic environment without
introducing intolerable electromagnetic disturbances in
the form of interferences to any other system in that
environment, even to itself.
Electromagnetic
compatibility (EMC)
electromagnetic
emission (EME)
Conducted
emission (CE)
Radiated
emission (RE)
Electromagnetic
susceptibility (EMS)
Conducted
susceptibility (CS)
Radiated
susceptibility (RS)
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Standardizations
PLC standardization bodies
International
IEC Committee
TC 77
ITU
ISO
CISPR
Aisa and Pacific
organizations
Product Committees
CENELEC
RA
FCC
RegTP
National
Regional
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Channel Measurement and Modeling
Transmission Line Theory
A piece of mains cable can be modeled as following figure
V ( z)  V  ( z)  V  ( z)  V0 e z  V0e z
Attenuation I ( z)  I  ( z)  I  ( z)  I 0 e z  I 0e z
constant
    j   ( R  jwL)(G  jwC )
phase
constant
i( z, t )
R  z
V0 R  jwL

R  jwL
Z0   


I0

G  jwC
G  jwC
i ( z  z , t )
Propagation
constant
Characteristic
impedance
L  z
C  z
G  z
v( z , t )
z
z
v( z  z , t )
R : resistance .
L : inductance.
G : conductance
C : capacitance
z  z
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Channel Measurement Setup
Transmit
test head
Coupler
Network Analyzer (NA)
Coupling Circuit
Coupling circuit
C1
Conductive coupling
High pass filter
Galvanic isolation
Over Voltage protection
NA
PLC
channel
T1
D1
To
powerline
Coupler
Equipment:
Receive
test head
D2
D5
D3
D4
To measurement
device
C2
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PLC Cable Measurements
2
0
r
-2
r
R
Attenuation (dB)
R
-4
(2)
-6
Fluctuation at high frequency
-8
(4)
-10
-12
Cable transversal
-14 -1
10
1.
2.
3.
4.
0.75mm2 Vulcanize rubber cable
1mm2 Vulcanize rubber cable
0.75mm2 PVC/PVC cable
0.5mm2 PVC/PVC cable
0
10
(1)
(3)
1
10
2
10
Frequency (MHz)
Cable Type
Size (mm2)
Vulcanize rubber cable (three-wire)
0.75
Vulcanize rubber cable (three-wire)
1
PVC/PVC cable (three-wire)
0.75
PVC/PVC cable (two-wire)
0.5
• Rapid fluctuation caused by impedance
mismatch
• Maximum of 4 dB attenuation
difference @ 100 MHz
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PLC Channel Measurements
Scenario 1: Internet access and
distribution
Scenario 2: Home networking
Central switch
Path of scenario 1
Multipath
0
Amplitude Attenuation (dB)
(4)
1. socket 1
2. socket 2
3. socket 3
4. 20 m cable
-5
(1 )
Path of scenario 2
-10
Scenario 1: Network topology is known, or
easy to estimate. Channel is simple, and
-15
(2 )
-20
(3)
-25
-30
0
has few multipath components
Scenario 2: Network topology is unknown
or it is hard to define. Channel acts as
20
40
60
Frequency (MHz)
80
100
black box. A lot of multipath
components
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-5
-10
-15
Frequency
Domain
-20
Channel attenuation (dB)
Channel attenuation (dB)
Channel Responses
0
-5
-10
-15
-20
-25
-30
0
20
40
60
80
100
0.02
-25
0
20
Frequency (MHz)
0.1
40
60
80
100
Frequency (MHz)
0.015
0.01
Amplitude
Amplitude
0
0
Time
Domain
-0.1
-0.005
Scenario 1
-0.2
0
0.005
0.1
0.2
0.3
0.4
Time (us)
0.5
0.6
0.7
0.8
Scenario 2
-0.01
-0.015
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Time (us)
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PLC Channel Modeling
According to PLC channel multipath phenomenon, channel can
be modeled as:
Lh
Lh
h(t )   gi   (t   i )
H ( f )   ri   (t   i )
r ( f , li )  ai  ed ( f )li
d ( f )  d R ( f )  dG ( f )
i 1
i 1
Input

g
0
1
2

g
1
3

g
2

...
GZ 0
R


 v1 
2Z 0
2
L
h

g
...
3
...
f  v2  f
d ( f )  (c0  c1  f  )

g Lh
Output
...
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Disturbance over PLC
PLC Noise
Noise Classification:
Colored background noise
Narrowband noise
Periodic impulsive noise, asynchronous to the main
frequency
Periodic impulsive noise, noise, synchronous to the main
frequency
Asynchronous impulsive noise
Our concentration
Colored background noise
Asynchronous impulsive noise
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Noise Measurement setup
Equipment:
Oscilloscope
Spectrum Analyzer
Coupler
Coupler
PLC
channel
Spectrum
analyzer
(frequency domain)
Oscilloscope
(time domain)
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Colored Background Noise
-30
1. Maximum background noise PSD
2. Average background noise PSD
3. Minimum background noise PSD
Curve fitting
-40
Background Noise PSD (dBm)
Quasi-Static behavior
Statistic information is
extracted in table
Can be modeled as:
s  b f c
N ( f )  10
(W/Hz)
-50
-60
(1)
(2)
-70
-80
-90
-100
(3)
-110
-120
-130
0
20
40
60
80
100
Frequency (MHz)
s
b
c
Max
-94
-80
-0.4
Min
-124
-100
-0.6
Average
-105
-90
-0.5
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Random Impulsive Noise
Caused by frequency bursts
generated by electrical devices
connected to the powerline.
Statistic information is
extracted
0.6
0.5
Impulsive noise amplitude (V)
Impulsive noise amplitude (v)
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
0.4
0.2
0
-0.2
-0.4
-0.6
-0.4
-0.5
0
2
4
6
8
10
12
Time (ms)
14
16
18
20
-0.8
0
200
400
600
800
1000 1200 1400 1600 1800 2000
Time (us)
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Other Disturbance
NEXT (Near End crosstalk)
FEXT (Far End crosstalk).
Transmit
NEXT
Receive
ELFEXT  FEXT  Cable Attenuation
NEXT Formation
20
(2)
FEXT Attenuation (dB)
0
Transmit
-20
-40
FEXT
(4)
(1)
Receive
-60
-80
1. PLC FEXT
2. Cable Attenuation
3. PLC ELFEXT
4. xDSL FEXT
-100
-120
0
20
40
FEXT Formation
(3)
60
80
100
Frequency (MHz)
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DMT Based PLC Modem Design
DMT Technology
Discrete Multi-tone Modulation (DMT)
Advantages:
Multicarrier technology – combat frequency selective fading
Dynamic bit loading based on SNR – efficient spectrum utilization
High channel capacity
Encoder
Constellation
mapping and Tone
shuffle
IFFT
Cyclic
prefix
P/S
Transmitter
filter
Noise
Decoder
Constellation
de-mapping and
Tone shuffle
FFT
Cyclic
prefix
remove
S/P
PLC Channel
Receiver
filter
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DMT Based PLC Modem Design
-5
Simulation environment:
Simulated channel
Measured channel
-10
Attenuation (dB)
MATLAB SimuLink
MATLAB DSP Blockset
Simulated channel response
-15
-20
-25
Expected result
Bit Error Rate (BER)
-30
0
20
40
Noise
Generator
Bit
Source
Adaptive
Loading
Algorithm
DMT
Modulator
PLC Channel
Spectrum
Observation
60
80
100
Frequency (MHz)
DMT
Demodulator
BER
Comparison
Spectrum
Observation
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Simulation and Performance
15
10
10
BER
0
Number of bits per chanel
10
10
10
10
Optimized bit
loading algorithm
-1
10
-2
-3
5
Modem performance
PLC vs AWGN
-4
-5
0
0
64
32
128
96
192
160
224
256
Channel Number
10
10
-6
-7
0
DMT over AWGN channel
DMT over PLC channel
Signal spectrum
after PLC channel
10
20
30
Signal spectrum
before PLC channel
40
50
SNR (dB)
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Publications Related to My Thesis
Publications
More information can be found in my publications:
“Channel modeling and modem design for broadband
power line communications”, Proceeding of ISPLC 2004,
April, Spain
“Broadband characterization of indoor powerline channel”,
Proceeding of ISPLC 2004, April, Spain
“Broadband Characterization of Indoor Powerline Channel
and Its Capacity Consideration”, Proceeding of ICC 2005,
May, Korea
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Any Questions?
Thank You!