Title: Power Line Communication: Application to Indoor and InVehicle Data Transmission
1Power 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
2Why 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
3Outline
- Transfer function PTx?PRX(f)
- Propagation on interconnected multiwire
transmission lines - Propagation model (Theory/experiments)
- Impulsive noise characteristics
- Measurements?Noise model
- Optimization of the modulation scheme (Telecom.
aspects) - EM Propagation model noise model
- simulation of the link (channel coding, .)
- Radiated emission (EMC aspects)
4Transfer 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
5- In-Vehicle
- Complicated geometry of the cable harness
- Complexity gtgt 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
6Conclusion 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
7Preliminary comments on the definition of the
transfer function
- Let us define H(f) as V/E
- 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?
8- 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 time-varying 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)?
9- 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 - 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
10What is the physical meaning of H(f) Vr/Ve? Why
not measuring S21?
- 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)!
11Additional comments
- Other obvious interpretation of S21 (or H(f)) If
Z0 Zl R0
If the source is any generator Pi corresponds
to selected power one can read on the screen of
the generator !
12- 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 !
13Transfer function inside a room
Transfer function ratio between Vout/Vi,
(complex number, f(frequency)) Various loads are
connected at points Pi
14Transfer function inside a room
Frequency domain H(f) Amplitude and phase
15- 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 r0.7 or 0.9 ?Bc(0.7 or 0.9)
- Within Bc, H(f) does not vary appreciably
- If transmitted bandwidthltltBc, flat channel, no
signal distortion - Indoor inside a room Bcfew MHz
16Channel characteristics in time domain Channel
impulse response (Multiple reflections
? Multipath propagation) Power delay profile
Maximum excess delay
Mean delay
Delay spread
17- If the duration of 1 bit (or symbol) ltltt,
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 gt t
18Impulse response
rms delay spread t lt 0.2ms for a probability lt10-3
19Transfer 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)
20Channel 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) - Relation between the waves at the ends of the
tube ( length l) -
- Ws source terms at the end of the tube, g
propagation constant - Compact form considering all tubes W(l) g
W(0) Ws
W(z)V(z)Zc I(z)
W(l) g W(0) Ws
21Channel 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 ..
22Application to in-vehicle PLC
Measurement with a network analyzer (S21),
inserting a coupling device
23Coupling device
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)
24Path classification
- Preliminary measurements different behavior of H
in 2 cases
No branching on DC line between Tx and Rx called
direct path
Branching between Tx and Rx called indirect
path
25Experimental analysis on a vehicle
Indirect paths A ? C A ? E A ? F
Direct paths A ? B 6m D ? E 2m
Engine
Passenger cell
boot(trunk)
cigar lighter
__ 12 V __ ground
Engine computer
F
Power plug 12 V
E
D
C
A
Computer
B
26Experimental approach long direct path (AB, 6m)
-0.5 dB / MHz
27Direct path Short (AB, 2m) / long (DE, 6m)
Computer trunk (PSF2)
- Path n1 long 6 m
- Path n2 short 1 m
S21 -30 dB
?f 43 kHz
Bc0.9 2 MHz
28Indirect paths
- n1 A ? C
- n2 A ? E
- n3 A ? F
Computercoffre (PSF2)
Bc0.9 600 kHz
S21 -30 dB
29Influence of the load configuration
indirect path n3 A ? F between cigar lighter
and the computer in the boot (trunk?) Measurement
while driving activating electric and
electronic equipment
Correlation coefficient between successive
values of the transfer function
30Propagation modeling
D1 ? D3 5.75 m D2 ? D3 7.55 m Total length
of the cables 205 m
31Example S21between D1 and D3 (about 6m)
50 load combinations Example for 3 load config.
Bc0.9 700 kHz
S21 gt -30 dB
32Another example
Bc0.9 600 kHz
S21 -30 dB
33Statistical results deduced from 50 configurations
34Distribution of the amplitude of H(f) around its
mean value versus freq.
Try to fit exp distribution with known
analytical distribution
35Conclusion on transfer function indoor or
in-vehicle
- 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
36Noise in indoor environment
37Power 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
38I. 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
39I. Impulsive Noise Classification / Noise model
(a) Single transient model
- Parameters of single transient
- peak amplitude - pseudo frequency f0 1/T0-
damping factor- duration- InterArrival Time IAT
(b) Burst Model
40I. Impulsive Noise Classification / Noise
characterization
1.Classification in time and frequency domain
Pb Probability of occurence
Bandwidth of PLT system
5 classes are introduced, depending on the
pseudo frequency f0
41I. 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
422. 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
- and s2 are the mean
- and the variance of x
- Agreement m1, s0.17
43I. Impulsive Noise Classification / Model
validation
Model validation Comparison of the spectral
densities of measured pulses and generated pulses
Good agreement between measurement and model !
44Noise on DC line inside a car
45Noise 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
PC
CH A
Ext trigger
coupler
acquisition IAT
Port //
Trig out
46Typical pulses
Single transient, burst and atypical pulse
47Noise Model Statistical Analysis
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.
48Classification of the pulses Frequency/amplitude
and Frequency/duration
49Amplitude and Pseudo frequency distribution of
bursts during cruising phase
50Cumulative probability distribution of IAT
normalized in OFDM frames (6.4ms in our
application . see later)
51Noise Model Stochastic Model
Time or Frequency domain The Power Spectral
Densities are calculated from measurement and
compared with the generated model.
Measurement
Model
52Noise 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
53Simulation 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
54- N sub channels N sub carriers OFDM
- 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
55Principle of multicarrier-based transmission
Transmission on N orthogonal subcarriers owing to
an IFFT/FFT.
562. Example of simple channel codingReed-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 K239, t 8 bytes. Important data duration
of a pulse (statistical approach)
57Interleaving
- 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?
58- 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
59Optimisation 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 (BERlt10-3) 77 if D16
- Pb (BERlt10-3) 96 if D64
Choice of D depends on acceptable BER
BER
60PLC emission
61Testing room description
62- 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) - Other possibility Normalize to the maximum power
which could be injected in the line (matched
impedances). Expressed in dBm/Hz
63Preliminary measurement of the ambiant noise
64Example (same differential voltage) Car/Indoor
65Field variations in the room
66Standards?Another issue!