Propagation Channel Characterization and Modeling
Outdoor Power Supply Grids
as Communication Channels
Prof. Dr.-Ing. habil.
Klaus Dostert
Institute of Industrial Information Systems
UNIVERSITY OF KARLSRUHE (TH)
Overview
Communication over outdoor electrical power supply lines
Network structures and their basic properties
 Access domain in Europe, ASIA, America
Analysis of line and cable properties
 characteristic impedance
 branching & matching
General aspects of channel modeling
 transfer function, impulse response, channel parameterization
 interference scenario
PLC channel simulation and emulation
 channel adapted system development
Conclusions and further work
2
History: Carrier Frequency Transmission since 1920
(on the high voltage level only)
 no branching
 optimal „wave guiding“
by network conditioning
3
Current and Upcoming PLC Applications
Low Speed (10…100 kbits/s)
- Office and home automation (intelligent appliances)
- Energy information systems
- Urban rail-based traffic systems
Broadband Services: 1…30 MHz (1…2 Mbits/s
- „Last Mile“ and „Last Meter“ high-speed internet access,
voice over IP etc.
High Speed Indoor Applications: 12 …  70MHz
- PLC for digital entertainment systems (>100 Mbits/s)
 PLC in automobiles
 PLC for factory automation
 PLC for advanced safety systems in the mining industry
4
The European Power Supply Network Structure
3-phase supply
details
high voltage level: 110..380 kV
transformer
station
LV transformer
stations
medium voltage level
10...30kV
low voltage distribution grid
3 Phases: 230V, 400V
supply cells
 up to 350 households
 cable length 100...400m
5
Typical Topology of European Power Distribution
Networks in Residential Areas
Server
Transformer Station
1
5
4
3
2
6
supply cable type
NAYY150SE
9
8
10
11
7
12
14
13
L2 L3
L1
15
N
18
16
17
22
19
33
20
21
23
24
32
28
31
30
29
27 26
25
House connection cable
NAYY50SE
6
Some Details of “Last Mile” and “Last Meter”
Environments
local transformer
station
medium
voltage
network
cross-bar
system
ZL1
points of mismatch
ZL2
house connection forming
a low impedance point
- almost short circuit 7
Power Supply Structures in Asia and America
high voltage level: 110..380 kV
single and
split-phase
transformer
station
1st medium voltage level
10…30 kV
2nd medium voltage distribution level 6 kV
low voltage distribution grid
single or split phase supply
125V, 250V
many LV transformers
 small supply cells
 few households per transformer
 cable length  100m
 grounding of 3rd wire
 highly unsymmetrical
8
The Ideal Two-Wire System
compensation
of exterior field
compensation
of exterior field
X

9
Symmetry in Multi-Wire Structures
open wires
3-phase supply cable
passive
conductors
•
X
passive
conductors
X
“earth” in case of
a three-wire supply
•
10
Simplified Analysis of a Two-Wire System
characteristic impedance
650
2
D

Z L 120
D


 ln      1 
 2r


r
 2r 


open wires: r=1
600
ZL/
550
D
r
R' f 
( f ) 
2  ZL
R '( f ) 
500
450
  f
  r2
400
350
100
attenuation at open wires
due to Skin effect
150
200
250
300
350
400
D in mm
0
120
A(f)/dB
100
-2
cable: r=3.5
ZL/
80
-4
60
40
-6
20
-8
0
5
10
15
20
25
f in MHz
30
10
15
20
25
D in mm
30
11
RF Properties of Typical Supply Cables
Access Cable Types
Model


L3
PEN
L2
L3 r
i
L3
ra
L1
L2
r
L1
L1

  f 0
R 
N
r
r
Characteristic
Impedance
N
L'
ZL 
C'
ZL/
Lossy Line Parameters (low losses)
r

C '  2  0  r 
L   0 

2r
2
G  2 f C   tan 
Attenuation Coefficient
 ( f )   R ( f )  G ( f ) 
Characteristic Impedance
R'
G ' Z L

2  ZL
2
Attenuation over 1km
50
0
NAYY 150SE
10
40
House Connection
NAYY50SE
30
20
30
NAYY50SE
40
20
Main Supply Cable
NAYY150SE
50
A(f)
[dB] 60
10
0
70
1
2
5
10
f /MHz
20
1
2
5
10
f /MHz
20
12
The problem of Branching and Possible Solutions
ZL
L >> ZL
R=ZL/3
ZL
ZL/3
ZL/3
ZL
ZL ZL
ZL
matched
to ZL ZL/2
mismatch:
13
Some Ideas for Signal Coupling with Enhanced Symmetry
Improving EMC
Transformer Station
typical RF coupling devices
decoupling
cross-bar system
L>10µH
RF-shorts
cable: ZLC 
House Connection
decoupling
cable: ZLC
impedance
matching
MODEM
L > 10µH
BALUN
power
meter
impedance
matching
BALUN
RF-shorts
MODEM
Ferrite material is required
for these decoupling coils,
which carry high currents!
 Transformer: >150A
 House connection: >30A
14
Reflections Causing Echoes and Inter-Symbol Interference
wireless channel as example
T
2  d 2 / v
1  d1 / v
R
delay:  =2-1
simplified analysis of a
line with 1 unmatched branch
Tbit

direct
echo
result
strong inter-symbol interference:   Tbit
in practice:
multiple
echoes
2
T
R
1
impulse response
1 2
t
15
Approaches Toward Deterministic Network Modeling
source
bq
ri
sink
line element
a
a1
b
b1
S11 S12
S21 S22
branch
b2
a
b
ra
example
a2
b1
b2
b3
a1
a3
a2
 high computational effort
 requires detailed knowledge of
network topology and device parameters
 not applicable in practice
16
The Echo-based Channel Model
s(t)
1

d
i  i
v
N
considering only echoes : ki=const
impulse response
N
k2
k3
kN
S
r(t)
Fourier
transform
k1
hE  t    ki    t   i 
i 1
transfer function
N
H E  f    ki  e  j2 f  i
i 1
low-pass behavior
k i  k ( f , d i )  g i  e  ( f )  d i
Result
N
H  f    gi  e
 j2 f
di
v
e
  f  di
i 1
dependent on number, length
and matching of branches
generally complex
Attenuation Coefficient:
 ( f )  c1  f  c2  f  a0  a1  f 0.5...1
skin-effect dielectric losses
17
h(t): impulse response
H(f): single reflection, no losses
0
path 1
1
dB
-5
gi  e
-10
path 2
FT
 j2 f  i
0.5
-15
-20
0
0
5
10
15
20
25
30
T
0
0
gi  e  a1 f di
1.5
1.67
1.83
2
t in µs
single reflection, including losses
dB
-20
path 1
path 2
1.33
R
200m  1
attenuation
-20
1.17
225m  2
f in MHz
dB
1
-40
-40
0
5
10
15
20
f in MHz
25
30
0
5
10
15
20
f in MHz
25
30
18
Two-Path Channel without Losses but
Varying Path Weights
Path 1
0.52
0.26
0.173
0.46
0.71
0.793
Path 2
0.347
0.208
0.149
0.627 0.76
0.817
19
A First Realistic
Example
0
-10

11m
-20
170m
30m
G
|H(f)|
dB
ZL
-30
N
H  f    gi  e
 j2 f
di
v
e
  f  di
-40
i 1
m
 1.5  108  
r
s
-50
c
v
0
  f   7.8  1010  f 1  
m
5
10
15
20
25
frequency in MHz
30
1
path
di/m
gi
1
200
0.64
1
0
1
calculation
measurement
-10
- 20
h(t)
0.5
0.5
- 30
2
222.4
0.38
3
244.8
-0.15
4
267.5
0.05
0
- 40
- 50
0
0
5
10
15
f in MHz
0
0.5
20
1
0
1.5
1
2
2
3
4
t in µs
2.5
3
time in µs
5
3.5
20
A Second Example
(more complex)
|H(f)|
-20
dB
110m
15m
-40
-60
 1.5  108  
  f   7.8  1010  f 1   v 
r
s
m
1
path
di/m
gi
1
90
0.029
2
102
0.043
3
113
0.103
4
143
-0.058
5
148
-0.045
6
200
-0.040
7
260
0.038
8
322
-0.038
9
411
0.071
10
490
-0.035
11
567
0.065
12
740
-0.055
13
960
0.042
14
1130
-0.059
15
1250
0.049
c
m
-80
0
5
10
15
20
25
frequency in MHz
30
1
h(t)
0.5
0
-0.5
0
0.5
1
1.5
2
2.5
3
time in µs
3.5
21
Attenuation in dB
Transmission Characteristics According to Length Classes
0
10
20
30
40
50
60
70
80
2
4
6
8
10
12
14
16
18
Frequency in MHz
22
A General Powerline Interference Model
narrowbandinterference
periodic impulsive noise
synchronous with the mains
periodic impulsive noise
asynchronous
with the mains
background
noise
+
Interference
Channel as a Linear Filter
h(t)
aperiodic
asynchronous
impulsive noise
Amplitude
H(f)
threat of burst errors
tB
A
tA
time
tIAT
A, tB and tA are random variables with exponential distributions
23
Idea of a Universal PLC-Channel Emulator
PLC
Modem
PLC
Modem
Host-PC
Configuration
Interface
LPF
A
D
FIR
Filter
Noise
Generator
+
PGA
LPF
A
PGA
LPF
A
D
Noise
Generator
D
FIR
Filter
D
D
D
A
LPF
PGA
A
LPF
PGA
A
LPF
+
24
Some Details Toward Emulator Realization
channel emulation filters
from
8
ADC
20
FIR
Notch
5x7bit
delay
5x5bit
coeff.
14
FIR
lowpass
delay
FPGA
signal DAC
FIFO
14
D
A
control
32x8bit
coeff.
periodic, synchronous, asynchronous impulsive noise
& background noise interference DAC
8 m-sequences of
8
length 220-1
Amplitude
14
control
+
14
14
20bit shift register
8x20bits load
D
A
narrow band noise
8-bit-circular memory
of length 500
P_ADDR 26
P_DATA 32
8
Amplitude
500 x 8bits
load
14
control
control / load
25
A First Powerline Channel Emulator Prototype
PC
Channel
Emulator
Hardware
ADC
PLC Modem
EEPROM
LP
Signal
DAC
PGA
DAC
PGA
FPGA
LP
Noise
PLC Modem
(Transmitter)
reference channel
|H| in dB
modified filter structure
coeff. filter 1
coeff. filter 2
simulations,
implementation
|H| in dB
f in MHz
hardware
verification
measurements
f in MHz
26
Why OFDM for PLC?
Channel Transfer Function
FSK, GMSK
restricted e.g. for protection
of broadcast services
not usable due to
high attenuation
OFDM sub-channel
f1 f2
f3
fN
f
27
Conclusions and Further Work
PLC or BPL offers a variety of valuable applications
 data rates exceeding many Mbits/s will enable numerous
new services
Mature channel models are covering any channel of interest
 successful development of a new generation of
”channel adapted” PLC systems is possible
 no more pitfalls: sophisticated simulation and emulation
Building advanced and user-friendly simulation and emulation
environments is now an important issue
Further development and standardization of PLC or BPL goes on
 ETSI, CENELEC, CISPR
 EU Project OPERA (Open PLC European Research Alliance)
 HomePlug Alliance (USA)
 IEEE PHY/MAC Working Group
28