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Power Line Communication: Application to Indoor and InVehicle Data Transmission

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Virginie Degardin, Pierre Laly, Marc Olivas Carrion, Martine Li nard and Pierre Degauque ... Why putting an additional cable between two equipments for ... – PowerPoint PPT presentation

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Title: Power Line Communication: Application to Indoor and InVehicle Data Transmission


1
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

2
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

3
Outline
  • 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)

4
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

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

6
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

7
Preliminary 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

10
What 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)!

11
Additional 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 !

13
Transfer function inside a room
Transfer function ratio between Vout/Vi,
(complex number, f(frequency)) Various loads are
connected at points Pi
14
Transfer 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

16
Channel 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

18
Impulse response
rms delay spread t lt 0.2ms for a probability lt10-3
19
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)

20
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)
  • 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
21
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 ..

22
Application to in-vehicle PLC
Measurement with a network analyzer (S21),
inserting a coupling device
23
Coupling 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)
24
Path 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
25
Experimental 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

26
Experimental approach long direct path (AB, 6m)
-0.5 dB / MHz
27
Direct 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
28
Indirect paths
  • n1 A ? C
  • n2 A ? E
  • n3 A ? F

Computercoffre (PSF2)
Bc0.9 600 kHz
S21 -30 dB
29
Influence 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
30
Propagation modeling
D1 ? D3 5.75 m D2 ? D3 7.55 m Total length
of the cables 205 m
31
Example S21between D1 and D3 (about 6m)
50 load combinations Example for 3 load config.
Bc0.9 700 kHz
S21 gt -30 dB
32
Another example
Bc0.9 600 kHz
S21 -30 dB
33
Statistical results deduced from 50 configurations
34
Distribution of the amplitude of H(f) around its
mean value versus freq.
Try to fit exp distribution with known
analytical distribution
35
Conclusion 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

36
Noise in indoor environment
37
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
38
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

39
I. 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
40
I. 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
41
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
42
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
  • and s2 are the mean
  • and the variance of x
  • Agreement m1, s0.17

43
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 !
44
Noise on DC line inside a car
45
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
PC
CH A
Ext trigger
coupler
acquisition IAT
Port //
Trig out
46
Typical pulses
Single transient, burst and atypical pulse
47
Noise 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.
48
Classification of the pulses Frequency/amplitude
and Frequency/duration
49
Amplitude and Pseudo frequency distribution of
bursts during cruising phase
50
Cumulative probability distribution of IAT
normalized in OFDM frames (6.4ms in our
application . see later)
51
Noise Model Stochastic Model
Time or Frequency domain The Power Spectral
Densities are calculated from measurement and
compared with the generated model.
Measurement
Model
52
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

53
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

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

55
Principle of multicarrier-based transmission
Transmission on N orthogonal subcarriers owing to
an IFFT/FFT.
56
2. 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)
57
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?

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

59
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 (BERlt10-3) 77 if D16
  • Pb (BERlt10-3) 96 if D64

Choice of D depends on acceptable BER
BER
60
PLC emission
61
Testing 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

63
Preliminary measurement of the ambiant noise
64
Example (same differential voltage) Car/Indoor
65
Field variations in the room
66
Standards?Another issue!
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