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«Power Line Communication:
Application to Indoor and In-Vehicle
Data Transmission»
Virginie Degardin, Pierre Laly, Marc Olivas Carrion,
Martine Liénard and Pierre Degauque
University of Lille, IEMN/Telice
France
12-13 Dec. 2005
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Why PLC for indoor or in-vehicle communication ?

Most of the in-house electronic equipment are supplied by the LV
power line (220V).
Why putting an additional cable between two equipments for
exchanging data since there are already connected to the
same the line (Power line)?

In a car, the number of “intelligent” sensors, computers.. is
continuously increasing. Development of X by wire technique
(Replacing mechanical transmission by data transmission)
Increase the number of dedicated wires, cables, shielded cables..
Weight, cost .. and reliability (connectors).
Use the DC PL as a physical support for the transmission



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Outline

Transfer function PTx→PRX(f)



Impulsive noise characteristics


Measurements→Noise model
Optimization of the modulation scheme (Telecom.
aspects)


Propagation on interconnected multiwire transmission lines
Propagation model (Theory/experiments)
EM Propagation model + noise model
+ simulation of the link (channel coding, .)
Radiated emission (EMC aspects)
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Transfer Function

Indoor
 Within

a room
“Simple” network architecture. Main variable: loads
connected to the PL.
Propagation model: 2-3 wire line + distributed/random
loads (not necessary needed)
 Measurements: easy (not too many variables)

 Inside
a building (between different rooms)
“Complicated” network architecture, known (new
buildings) or unknown
 Combine model + measurements

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
In-Vehicle
 Complicated
geometry of the cable harness
Complexity >> indoor
 Extensive measurements : time consuming +
difficulty to have access points
 Propagation modeling is desirable for a statistical
analysis
 Elaborate a statistical channel model
 Extract the channel properties, check with results
deduced from few measurements

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•Conclusion for determining the channel
properties

Indoor: inside a room
 presentation
of few experimental results +
channel characteristics

Indoor (in a building) and in car
 presentation
of the propagation model
 example of application: in-car


channel characteristics and channel model
Comparison room/vehicle
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Preliminary comments on the definition of
the transfer function
Let us define H(f) as V/E
R (50W)
E
Network
R (50W)
V
Comments: ”Impedance mismatching occurs during the measurements
and thus leading to incorrect measurement results”
“Trying to measure path loss without knowing the
impedance at the emission port is non cense”..
Suggestion: “Insert a wideband impedance matching..”
OK BUT with such a definition of H(f), the “real word” is modeled. Why?
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
For LV/MV, the structure of the network does not change and the
loads are more or less constant. Passive “equalizer” to match
impedances (adapter – line): Enhancement of the performances!

We will see later the architecture of a car harness! A lot of timevarying loads !

An adaptive time varying matching device would be necessary !

Practically: choose a constant value for the input/output impedance
of the modem. On the order of the average characteristic impedance
of the line (for example 60 W - 150W)?
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
Taking the terminal loads into account, one can expect that the input
impedance of the network will be smaller (few Ohms – 100 Ohms)

Usual impedance of commercially available adapter? Have a look
on the data sheet: usually nothing concerning the RF part
R (50W)
E

Network
R (50W)
V
It is TRUE that H(f) does NOT correspond to the path loss of the
network, alone, BUT to the TRANSFER between the transmitter
and the receiver in presence of the network
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What is the physical meaning of H(f) = Vr/Ve? Why
not measuring S21?
Z0=50 W
a1
a2
V1
Ve





V2
b1
Vr
b2
ZL=50 W
If ZL is matched to the transmission line between ZL and network
output: a2 = 0.
S21 = b2/a1
Definition of the injected power : Power delivered by the source on a
matched impedance (a1)
Applying this definition leads to (If Z0 = Zl = R0)
S21 = 2 H(f), whatever R0. Calculating H(f) equivalent to S21 (factor 2)!
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Additional comments

Other obvious interpretation of S21 (or H(f)) If Z0 = Zl = R0
Z0=50 W
a1
a2
V1
Ve
V2
b1
 S21 )
2
Vr
b2
ZL=50 W
V22 V22 / R0
Pr
4 2  2

E
E / 4 R0 Pi
If the source is any generator:
Pi corresponds to selected power one can read on the
screen of the generator !
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
Conclusion

The Tx adapter, the line, the Rx adapter .. are considered as a
whole. The transfer function or S21 does NOT correspond to path
loss BUT to what happens in a practical case.
If needed, for indoor or in-vehicle PLC, the “intrinsic” path loss:
combining the various S parameters BUT still depending on the
terminal load
S21 for any load configuration can be deduced from the S50 matrix
Software “equalization” on the data to cope with the frequency
selectivity of the PLC channel
In the following, transfer function characterized for an impedance of
50W presented by the modem (same as network analyzer)
For optimizing the modulation scheme, “path loss” is not needed.
(only related to average SNR). Channel impulse response !





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Transfer function inside a room
Transfer function: ratio between Vout/Vi, (complex number, f(frequency))
Various loads are connected at points Pi
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Transfer function inside a room
Frequency domain H(f) – Amplitude and phase
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
Useful statistical parameters
 Coherence
bandwidth Bc(r)
Absolute value r of the autocorrelation of H(f)
 Bc: frequency shift to get a given value of r
 Typical example: r=0.7 or 0.9 →Bc(0.7 or 0.9)
 Within Bc, H(f) does not vary appreciably
 If transmitted bandwidth<<Bc, flat channel, no
signal distortion

 Indoor
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inside a room: Bc=few MHz
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Channel characteristics in time domain: Channel impulse
response (Multiple reflections ↔ Multipath propagation)
Power delay profile
Maximum excess delay
1


Mean delay: m
Pt
n
P 
i 1
i
i
Delay spread
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
2
2 
P


m)
 i i

  i 1
Pt






n
 rms
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2
16

If the duration of 1 bit (or symbol) <<, multiple
reflections “of the same bit or symbol” arrive nearly at the
same time.
 No
“mixing” of the successive bits: No Inter Symbol
Interference (No ISI)
 Application
to PLC: Usually OFDM modulation
scheme → send successive frames.
 Avoid
interference between frames→ Guard interval
between frames > 
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Impulse response
rms delay spread  < 0.2ms for a probability <10-3
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Transfer function for more
complex networks

Theoretical modeling of the propagation
 Multiple
interconnected transmission lines
 “user-friendly” software tool is needed
Possibility to easy change part of the network
configuration
 Model based on the “topological” approach
proposed by Baum, Liu, Tesche (“BLT” eq.) and
developed by ONERA (code Cripte)

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Channel transfer function : Deterministic Model, cont.

The harness is divided into a succession of uniform multi conductor
(N) transmission lines (N “Tubes”). Along each tube, waves W,
combining current and voltages are defined by (matrix form):
W(z)=V(z)+Zc I(z)

Relation between the waves at the ends of the tube ( length l)
W(l) = g W(0) +Ws
Ws : source terms at the end of the tube, g: propagation constant

Compact form considering all tubes: [W(l)] = [g] [W(0)] + [Ws]
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Channel transfer function : Deterministic Model, cont.





Connection between tubes: junctions.
At each junction (including at the ends of the harness), a scattering
matrix S relates incoming and outgoing waves:
[W(0)] = [S] [W(l)]
Combining the various equations leads to:
( [I] - [S] [g] ) [W(0)] = [S] [Ws]
[I] : identity matrix
Inversion of [I] - [S] [g], determination of [W(0)] and thus V and I at
the ends of each tube.
Advantage: high flexibility for modifying the network architecture, the
load impedances ..
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Application to in-vehicle PLC
Measurement with a network analyzer (S21),
inserting a coupling device
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Coupling device
5Ω
VNA
Port 1
50 Ω
5Ω
140Ω
-10 dB
1 MΩ
2 nF
2 nF
1:1
5Ω
5Ω
1 MΩ
Filter cut off frequency : 500 kHz
Z seen from the network: about 50 Ohm . Check by measuring S11
up to 40 MHz.
Z seen from the VNA: 20 – 150 Ohm (depending Z network)
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Path classification

Preliminary measurements: different behavior of H in 2 cases:
Rx
Tx
No branching on DC line between Tx and Rx: called “direct path”
Rx
Tx
Branching between Tx and Rx: called “indirect path”
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Experimental analysis on a vehicle
« Direct » paths:
Indirect paths:
A  B: 6m
AC
D  E: 2m
AE
AF
Engine
Passenger cell
boot(trunk)
cigar
lighter
Engine computer
__ : 12 V
__ : ground
F
Power plug 12 V
E
D
C
+
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A
B
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Computer
25
Experimental approach : long direct path (AB, 6m)
Bundle x, car y
wire B100
K1
12 V
B
Port 1
50Ω
K2
Port 2
A
50Ω
Computer boot
(PSF2)
-0.5 dB / MHz
Transfer
functions
K1
OFF
H1
H2
X
X
ON
K2
OFF
ON
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X
H3
H4
X
X
X
X
X
26
Direct path: Short (AB, 2m) / long (DE, 6m)
Harness xxx - AB
•Path n°1 – long ≈6 m
• Path n°2 – short ≈1 m
12 V
B
Port 1
50Ω
Port 2
A
50Ω
Computer
trunk (PSF2)
harness xxx - DE
S21 ≥ -30 dB
12 V
D Port 1
50Ω
Port 2
E
50Ω
interior light at
40 cm from
port 2
Δf = 43 kHz
Bc0.9 ≈ 2 MHz
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Indirect paths
Prise 12V
Cigar
lighter
Port 1
E 50Ω
Port 1
F
50Ω
n°1 – A  C
•n°2 – A  E
•n°3 – A  F
Network car xxx
BSI
C
12 V
Port 1
50Ω
Port 2 A
50Ω
Computercoff
re (PSF2)
Bc0.9 ≈ 600 kHz
S21 ≤ -30 dB
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Influence of the load configuration
Faisceau xxx – fil B100
Allume
cigare
indirect path n°3 – A  F between cigar lighter
and the computer in the boot (trunk?)
Port 1
50Ω
F
Measurement while driving + activating electric
and electronic equipment
Correlation coefficient between
successive values of the transfer function
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r f ) 
Port 2 A
50Ω
12 V
[
Calculateur
coffre (PSF2)
 H ( f , i) H * ( f , j )
]
ij
 [ H 2 ( f , i) ] .  [ H 2 ( f , j ) ]
29
Propagation modeling
D1  D3 : 5.75 m
D3
D2  D3 : 7.55 m
Z3
Total length of the cables = 205 m
3 fils
30 cm
3 fils
100 cm
M
5 fils
10
cm
5 fils
40 cm
M
2 fils
50 cm
11 fils
100 cm
M
D1
16 fils
10 cm
3 fils
50 cm
1 fils
10
cm
Batt.
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1 fils
M 10 cm
1 fils
10
cm
10 fils
F
50 cm
3 fils
50
cm
16 fils
50 cm
1 fils
1 mm
10 fils
50 cm
Z4
Z5
Z1
1 fils
25 cm
1 fils
40 cm
CC
1 fils
40 cm
Z2
Z17
14 fils
50 cm
5 fils Z8
1m
D2
5 fils
Z3 50 cm
3 fils
15 cm
3 fils
50 cm
Dashboard
Engine
5 fils
Z18
100
cm
11fils
3 fils
100 cm
10 cm
11 fils
100 cm
9 fils
Z13 50 cm
CC
1 fils
1 mm
Z12
5 fils
100
cm
10 fils
30 cm
1 fils
10 cm
3 fils Z15
50 cm
Z14
5 fils
10 cm
Z7
15 fils
30 cm
Z6
20 fils
80 cm
3 fils
50 cm Z16
16 fils
50 cm
Z11
14 fils
100
cm
Passenger cell
30 fils
50 cm
Z9
10 fils
100 cm
30 fils
50 cm
M
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20 fils
150 cm
Z10
10 fils
50 cm
20fils
50 cm
1 fils
10cm
M
30
Example: S21between D1 and D3 (about 6m)
Config. N°2 (5.75 m)
D1
50Ω
50 load combinations
Example for 3 load config.
D3
50Ω
Bc0.9 ≈ 700 kHz
S21 > -30 dB
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Another example
Bc0.9 ≈ 600 kHz
S21 ≤ -30 dB
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Statistical results deduced from 50 configurations
Direct
paths
Indirect
paths
Statistical
parameters
Experiments
Deterministic model
Bc0.9 / Hz *
2 MHz
1.5 MHz
Rms Delay
Spread / nS *
60 nS
61 nS
700 kHz
780 kHz
84 nS
108 nS
Bc0.9 / Hz *
Rms Delay
Spread / nS *
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Distribution of the amplitude of H(f) around its mean value versus freq.
Try to fit exp distribution with known
analytical distribution
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Conclusion on transfer function : indoor or invehicle

Use the average statistical values of the channel parameter (transfer
function, Bc, delay spread) for a first optimization of the transmission
scheme

Build a statistical channel model (knowing the probability distribution
of the discretized channel impulse response from meas. +
deterministic modeling)

Insert this model in a software simulating the communication link to
deduce system performance ..but also in presence of noise !

Next step: Noise characterization
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Noise in indoor environment
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Power Spectrum Density, Narrow band noise measured on
indoor power lines
Indoor network connected to an overhead
outdoor power line
Indoor network connected to a buried power line
Broadcast transmitters
Conclusion: Useful transmission
bandwidth above 500 kHz
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I. Impulsive Noise Classification / Noise model
Impulsive Noise : conducted emissions due to electrical devices
connected to the network.
Measurements in a house during 40 h
2 classes of pulses (on 1644 pulses) : single transient and burst
Single transient:
Damped sinusoid
 Burst: Succession of
heavy damped
sinusoids
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I. Impulsive Noise Classification / Noise model
(a) Single transient model
Parameters of single
transient :
(b) Burst Model
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- peak amplitude
- pseudo frequency f0
=1/T0
- damping factor
- duration
- InterArrival Time IAT
39
I. Impulsive Noise Classification / Noise characterization
1.Classification in time and frequency domain :
1644 pulses
Single
Transient
Burst
fo<500
kHz
Class 1
Pb = 48 %
Class 3
Pb = 3 %
0.5 MHz < fo <
fo>3 MHz
3MHz
Class 2
Pb = 20 %
Class 4
Class 5
Pb = 11 %
Pb = 18 %
Pb: Probability of occurence
Bandwidth of
5 classes are introduced,
depending on the pseudo frequency f0
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PLT system
40
I. Impulsive Noise Classification / Noise characterization
2. Statistical analysis: Noise Parameters are approximated
by well-known analytical distributions to build a noise model
Pseudo Frequency
:
Weibull distribution
f ( x)  abx
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b-1 - axb
e
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2. Statistical analysis:
 Careful examination of long bursts
 Pseudo-frequency of the elementary pulse varies with time
(calculated with a running time window)
The pseudo-frequency
distribution around its
mean value follows a
normal distribution :
f ( x) 
1
s 2
exp( -
1 ( x - µ)²
)
2 s²
m and s2 are the mean
and the variance of x
Agreement: m=1, s=0.17
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I. Impulsive Noise Classification / Model validation
Model validation : Comparison of the spectral densities of measured
pulses and generated pulses :
Good agreement between measurement and model !
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Noise on DC line inside a car
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Noise Model : Experimental setting
System parameters : mobile platform
Sampling rate = 100 MHz
(Sampling period : 10ns)
Observation window : 650 µs
Peak limiting  15V
Trigger : 300 mV
Noise
acquisition
coupler
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acquisition
IAT
CH A
Ext trigger
PC
Port //
Trig out
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Typical pulses
Single transient, burst and “atypical pulse”
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Noise Model : Statistical Analysis
3 MHz  fo < 7 MHz
7 MHz  fo < 15 MHz 30 MHz  fo < 35 MHz
Single
pulse
Class 1
Class 2
Class 3
67.2 %
7.2 %
4.9 %
Burst
Class 4
Class 5
Class 6
19.7 %
0.9 %
0.1 %
Objective : For each class, a
mathematical function is found to
fit
the
distribution
of
the
characteristic parameter of the
pulse
The same approach is followed to
model all classes and the others
statistical distributions of the
pulse characteristics.
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Classification of the pulses : Frequency/amplitude and Frequency/duration
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Amplitude and Pseudo frequency distribution of bursts during cruising phase
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Cumulative probability distribution of IAT
normalized in OFDM frames (6.4ms in our application . see later)
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Noise Model : Stochastic Model
Time or Frequency domain : The Power Spectral Densities are
calculated from measurement and compared with the generated model.
Measurement
Model
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Noise model

From the knowledge of known distribution functions fitting exp.
results

Noise model . Generation of single transients and bursts satisfying the
same probability in terms of amplitude, IAT, frequency content..

Combine statistical (noise + propagation) model: statistical channel
model

Performances of the link and optimization of the modulation scheme
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Simulation of the communication link




Frequency selective channel: few frequency bands are
strongly attenuated (multiple reflections)
Wide band communication leads to important distortion
of the signal, interference inter symbol, ..
Rather than using a given large bandwidth: divide them
into a number (64 or 128 or 256) of equivalent parallel
channels, each one with a small bandwidth
In each equivalent channel, no frequency selectivity. Flat
channel
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N sub channels : N sub carriers OFDM
f
B
fk
f
f
(a)
(b)
(a) Spectrum of a sub carrier
(b) Spectrum of an OFDM signal
OFDM
N oscillators? not realistic. Use properties of FFT.
Important data: Statistical behavior of H(f)
If few frequency bands are strongly attenuated: do not use them!
Maximize and optimize bit rate on channels having a good SNR!
Periodically test the channel, detect change in the channel state
(variation of H(f) when the loads vary), new channel equalization
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Principle of multicarrier-based transmission : Transmission on
N orthogonal subcarriers owing to an IFFT/FFT.
S
/ IFFT
P
Channel
Coding
Prefix
Add.
P
/
S
Digital/
analog
Interface
+ Filter
EMITTER
CHANNEL
Transfer
Function (H)
Noise
RECEIVER
Channel
decoding
P
/
S
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E
Q
U
A
L
I
Z
E
R
S
Prefixe
FF
T removal
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/
Analog/
digital
Interface
P
55
2. Example of simple channel coding
Reed-Solomon code : RS(N,K)
Word of K effective symbols
Word of N symb. by adding
redundancy (N-K symbols) ADSL normalization: Symbol: byte and N =
255
This code can correct up t = (N-K)/2 bytes.
if K=239, t = 8 bytes.
Important data: duration of a pulse (statistical approach)
bytes
word of K bytes
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ReedSolomon
code
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code word of 255 bytes
56
Interleaving

Long burst: RS code cannot correct errors. Is it possible to avoid a
long disturbance on the same word?


Interleaving:
An interleaving matrix of 256 rows by D columns,
D interleaving depth, varying from 2 to 64.
Bytes introduced in lines and sent in columns
The disturbance is “distributed” on successive words and RS coding
may thus be efficient
The interleaving depth depends on the statistics of transient duration

Any other problem?


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
YES

What happens when two successive pulses (burst or single
transient) occur?

Other important parameter: statistics of the IAT

When 2 pulses occur during the time of an interleaved matrix, these
two pulses disturb the same matrix and, may be, the RS code will no
more efficient. (Problem when the time interval between two
successive transients is small)
Other signal processing techniques are needed

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Optimisation in presence of impulsive noise (Indoor)
Contribution of channel coding and noise processing on the Bit
Error Rate (BER), assuming for all pulses a pseudo frequency f0
within the signal bandwidth and a PSD of -50 dBm/Hz
Cumulative probability distribution
of the mean BER for three different
values of the interleaving depth D
 Pb (BER<10-3) = 77% if
D=16
 Pb (BER<10-3) = 96 % if
D=64
Choice of D depends on acceptable BER
BER
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PLC emission
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Testing room description
Magnetic loop
S3
Sockets
S2
Plaster walls
Receiver
Balun
Data bus
S1
Computer
C.W. source
Switch
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Three
wires bundle
23 m length
220 V – 50 Hz supply line
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
Radiated field but normalized to a given injection.

Ratio between the differential voltage at the PL input and the
electric field measured at a given distance (1m, 3m). At low
frequency, H is measured. Convert H into E considering the wave
impedance in free space (definition, only)
Signal
generator
Spectrum
Analyser
Coupling
device
Active
probe
50Ω

Coupling
device
PLC Line
Other possibility: Normalize to the maximum power which could be
injected in the line (matched impedances). Expressed in dBm/Hz
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Preliminary measurement of the “ambiant noise”
Signal
generator
Spectrum
Analyzer
12-13 Dec. 2005
Coupling
Coupling
50Ω
LOOP Antenna
COST 286
63
Example: (same differential voltage) Car/Indoor
12-13 Dec. 2005
COST 286
64
Field variations in the room
Magnetic field
D: distance
of the antenna from the wall
Mesure du champ H
dBµA / m
D = 10 cm
60.0
D = 20 cm
D=3 m
40.0
Champ H dBuA/m
12-13 Dec. 2005
20.0
0.0
100
2
3
4
5
6
7
8 9
101
Fréquence MHz
1 MHz
10 MHz
COST 286
2
30 MHz
65
Standards?
Another issue!
12-13 Dec. 2005
COST 286
66