12-13 Dec. 2005COST 286 1 «Power Line Communication: Application to Indoor and In-Vehicle Data...
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Transcript of 12-13 Dec. 2005COST 286 1 «Power Line Communication: Application to Indoor and In-Vehicle Data...
12-13 Dec. 2005 COST 286 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/TeliceFrance
COST 286 212-13 Dec. 2005
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
COST 286 312-13 Dec. 2005
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)
Outline
COST 286 412-13 Dec. 2005
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
COST 286 512-13 Dec. 2005
In-VehicleComplicated 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
COST 286 612-13 Dec. 2005
•Conclusion for determining the channel
properties
Indoor: inside a roompresentation of few experimental results +
channel characteristics Indoor (in a building) and in car
presentation of the propagation modelexample of application: in-car
channel characteristics and channel model
Comparison room/vehicle
COST 286 712-13 Dec. 2005
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?
NetworkE
R (50
R (50) V
COST 286 812-13 Dec. 2005
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
COST 286 912-13 Dec. 2005
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
NetworkE
R (50
R (50) V
COST 286 1012-13 Dec. 2005
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)!
Ve
V2V1
a1 a2
b2b1
ZL=50
Z0=50
Vr
COST 286 1112-13 Dec. 2005
Additional comments
Other obvious interpretation of S21 (or H(f)) If Z0 = Zl = R0
Ve
V2V1
a1 a2
b2b1
ZL=50
Z0=50
Vr
22
2 2 0221 2 2
0
/4
/ 4r
i
V RV PS
E E R P
If the source is any generator:Pi corresponds to selected power one can read on the
screen of the generator !
COST 286 1212-13 Dec. 2005
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 50 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 !
COST 286 1312-13 Dec. 2005
Transfer function inside a roomTransfer function: ratio between Vout/Vi, (complex number, f(frequency))Various loads are connected at points Pi
COST 286 1412-13 Dec. 2005
Transfer function inside a roomFrequency domain H(f) – Amplitude and phase
COST 286 1512-13 Dec. 2005
Useful statistical parameters
Coherence bandwidth Bc() Absolute value of the autocorrelation of H(f) Bc: frequency shift to get a given value of Typical example: =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 inside a room: Bc=few MHz
COST 286 1612-13 Dec. 2005
Channel characteristics in time domain: Channel impulse response (Multiple reflections ↔ Multipath propagation)
Power delay profile
Mean delay:1
1 n
m i iit
PP
Delay spread
1
22 2
1
n
i i mi
rmst
P
P
Maximum excess delay
COST 286 1712-13 Dec. 2005
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 >
COST 286 1912-13 Dec. 2005
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)
COST 286 2012-13 Dec. 2005
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, propagation constant
Compact form considering all tubes: [W(l)] = [W(0)] + [Ws]
W(z)=V(z)+Zc I(z)
W(l) = W(0) +Ws
COST 286 2112-13 Dec. 2005
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] [W(0)] = [S] [Ws]
[I] : identity matrix
Inversion of [I] - [S] [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 ..
COST 286 2212-13 Dec. 2005
Application to in-vehicle PLC
Measurement with a network analyzer (S21), inserting a coupling device
COST 286 2312-13 Dec. 2005
Coupling device
5 Ω 5 Ω 1 MΩ
2 nF
5 Ω 5 Ω 1 MΩ
2 nF140Ω
1 : 1
VNA Port 150 Ω
-10 dB
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)
COST 286 2412-13 Dec. 2005
Path classification Preliminary measurements: different behavior of H in 2 cases:
Tx Rx
No branching on DC line between Tx and Rx: called “direct path”
Tx Rx
Branching between Tx and Rx: called “indirect path”
COST 286 2512-13 Dec. 2005
Experimental analysis on a vehicle
Computer
Engine computer __ : 12 V__ : ground
+ AB
cigar lighter
Power plug 12 V
CD
E
F
Engine Passenger cell boot(trunk)
« Direct » paths:
A B: 6m
D E: 2m
Indirect paths:
A C
A E
A F
COST 286 2612-13 Dec. 2005
Experimental approach : long direct path (AB, 6m)
Transfer functions
H1 H2 H3 H4
K1 OFF X X
ON X X
K2 OFF X X
ON X X
-0.5 dB / MHz
Port 1 50Ω
Port 2 50Ω
12 V
K1 K2Bundle x, car y wire B100
Computer boot (PSF2)AB
COST 286 2712-13 Dec. 2005
Direct path: Short (AB, 2m) / long (DE, 6m)
•Path n°1 – long ≈6 m• Path n°2 – short ≈1 m
Bc0.9 ≈ 2 MHz
Computer trunk (PSF2)
Port 1 50Ω
Port 2 50Ω
12 V
Harness xxx - AB
Port 1 50Ω
Port 2 50Ω
12 V
harness xxx - DE interior light at 40 cm from port 2
AB
ED
S21 ≥ -30 dB
Δf = 43 kHz
COST 286 2812-13 Dec. 2005
Indirect paths
Bc0.9 ≈ 600 kHz
S21 ≤ -30 dB
Computercoffre (PSF2)
n°1 – A C •n°2 – A E•n°3 – A F
Port 1 50Ω
Port 2 50Ω
12 V
Network car xxx
Cigar lighter
Port 1 50Ω
Prise 12V
C
Port 1 50Ω
BSIA
E
F
COST 286 2912-13 Dec. 2005
Influence of the load configuration
indirect path n°3 – A F between cigar lighter and the computer in the boot (trunk?)
Measurement while driving + activating electric and electronic equipment
]),([.]),([
),(),(
22
*
jfHifH
jfHifHf ij
Port 2 50Ω
12 V
Faisceau xxx – fil B100Allume cigare
Calculateur coffre (PSF2)Port 1
50ΩF A
Correlation coefficient between successive values of the transfer function
COST 286 3012-13 Dec. 2005
Propagation modeling
Z2
3 fils 100 cm
3 fils 30 cm
16 fils 10 cm
1 fils 1 mm
16 fils 50 cm
20 fils 80 cm
10 fils 50 cm
10 fils 30 cm
3 fils 50 cm
3 fils 50 cm
1 fils 10 cm
1 fils 10 cm
2 fils 50 cm
Z1
Batt.
Z6
D1F
1 fils 1 mm
1 fils 10 cm
1 fils 40 cm
3 fils 15 cm
14 fils 50 cm
14 fils 100 cm
20fils 50 cm
11fils 100 cm
16 fils 50 cm
30 fils 50 cm
Z15
Z33 fils 50 cm
1 fils 10cm
11 fils 100 cm
Z11
Z14
D3
30 fils 50 cm
20 fils 150 cm
1 fils 10 cmM
M
5 fils 10 cmM
5 fils 40 cm 10 fils
50 cm
3 fils 50 cm
Z185 fils 100 cm
Z16
3 fils 10 cm
Engine
Dashboard
Passenger cell5 fils 10 cm
Z4
M
Z9
10 fils 100 cm
Z8
1 fils 40 cm
D2
Z7
CC
Z10
Z17
Z12
Z13Z5
1 fils 25 cm
11 fils 100 cm
5 fils 100 cm
9 fils 50 cm
10 fils 50 cm
5 fils 1 m
15 fils 30 cm
Z35 fils 50 cm
M
M
3 fils 50 cm
CC
D1 D3 : 5.75 m
D2 D3 : 7.55 m
Total length of the cables = 205 m
COST 286 3112-13 Dec. 2005
50 load combinations
Example for 3 load config.
D3 50Ω
Config. N°2 (5.75 m)
D1 50Ω
Example: S21between D1 and D3 (about 6m)
S21 > -30 dB
Bc0.9 ≈ 700 kHz
COST 286 3312-13 Dec. 2005
Statistical results deduced from 50 configurations
Statistical parameters
Experiments Deterministic model
Direct paths
Bc0.9 / Hz * 2 MHz 1.5 MHz
Rms Delay Spread / nS *
60 nS 61 nS
Indirect
paths
Bc0.9 / Hz * 700 kHz 780 kHz
Rms Delay Spread / nS *
84 nS 108 nS
COST 286 3412-13 Dec. 2005
Distribution of the amplitude of H(f) around its mean value versus freq.
Try to fit exp distribution with known analytical distribution
COST 286 3512-13 Dec. 2005
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
COST 286 3712-13 Dec. 2005
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 transmissionbandwidth above 500 kHz
COST 286 3812-13 Dec. 2005
Impulsive Noise : conducted emissions due to electrical devices connected to the network.
Single transient: Damped sinusoid
Burst: Succession of heavy damped
sinusoids
Measurements in a house during 40 h 2 classes of pulses (on 1644 pulses) : single transient and burst
I. Impulsive Noise Classification / Noise model
COST 286 3912-13 Dec. 2005
I. Impulsive Noise Classification / Noise model
(b) Burst Model
(a) Single transient model
Parameters of single transient :
- peak amplitude - pseudo frequency f0
=1/T0
- damping factor- duration- InterArrival Time IAT
COST 286 4012-13 Dec. 2005
I. Impulsive Noise Classification / Noise characterization
1644 pulsesfo<500
kHz0.5 MHz < fo <
3MHzfo>3 MHz
Single Transient
Class 1 Class 2Pb = 48 % Pb = 20 %
Burst Class 3 Class 4 Class 5Pb = 3 % Pb = 11 % Pb = 18 %
Bandwidth of
PLT system
1.Classification in time and frequency domain :
5 classes are introduced, depending on the pseudo frequency f0
Pb: Probability of occurence
COST 286 4112-13 Dec. 2005
2. Statistical analysis: Noise Parameters are approximated by well-known analytical distributions to build a noise model
Pseudo Frequency :
Weibull distributionbaxb eabxxf 1)(
I. Impulsive Noise Classification / Noise characterization
COST 286 4212-13 Dec. 2005
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 :
)²
)²(
2
1exp(
2
1)(
s
µx
sxf
and s2 are the meanand the variance of x Agreement: =1, s=0.17
COST 286 4312-13 Dec. 2005
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 !
COST 286 4512-13 Dec. 2005
System parameters : mobile platform Sampling rate = 100 MHz (Sampling period : 10ns) Observation window : 650 µs Peak limiting 15V Trigger : 300 mV
Noise Model : Experimental setting
Noise acquisition
acquisitionIAT
PC
CH AExt trigger
Port //Trig out
coupler
COST 286 4712-13 Dec. 2005
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.
Noise Model : Statistical Analysis
COST 286 4812-13 Dec. 2005
Classification of the pulses : Frequency/amplitude and Frequency/duration
COST 286 4912-13 Dec. 2005
Amplitude and Pseudo frequency distribution of bursts during cruising phase
COST 286 5012-13 Dec. 2005
Cumulative probability distribution of IAT normalized in OFDM frames (6.4s in our application . see later)
COST 286 5112-13 Dec. 2005
Time or Frequency domain : The Power Spectral Densities are calculated from measurement and compared with the generated model.
Measurement Model
Noise Model : Stochastic Model
COST 286 5212-13 Dec. 2005
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
COST 286 5312-13 Dec. 2005
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
COST 286 5412-13 Dec. 2005
N sub channels : N sub carriers OFDM
fk
Bf
f f
(b) (a)
(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
COST 286 5512-13 Dec. 2005
Principle of multicarrier-based transmission : Transmission on N orthogonal subcarriers owing to an IFFT/FFT.
TransferFunction (H)
Noise
Analog/digital
Interface
Channel decoding
ChannelCoding
Digital/analog
Interface + Filter CHANNEL
RECEIVER
FFT
Prefixe
removal
S
/
P
EQUALIZER
P
/
S
IFFTPrefix
Add.
P/S
S/P
EMITTER
COST 286 5612-13 Dec. 2005
2. Example of simple channel coding2. 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 K=239, t = 8 bytes.
Important data: duration of a pulse (statistical approach)
word of K bytes
Reed-Solomon
code code word of 255 bytes
bytes
COST 286 5712-13 Dec. 2005
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?
COST 286 5812-13 Dec. 2005
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
COST 286 5912-13 Dec. 2005
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
Pb (BER<10-3) = 77% if D=16
Pb (BER<10-3) = 96 % if D=64
Choice of D depends on acceptable BER
BER
Cumulative probability distributionof the mean BER for three differentvalues of the interleaving depth D
COST 286 6112-13 Dec. 2005
Testing room description
Computer
Receiver
S1
S2
SocketsMagnetic loop
Balun
C.W. source
Data bus Three wires bundle 23 m length
Switch220 V – 50 Hz supply line
Plaster walls
S3
COST 286 6212-13 Dec. 2005
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
Signal generator
Coupling device
Coupling device
50Ω
Spectrum Analyser
Active probe
PLC Line
COST 286 6312-13 Dec. 2005
Signal generator
Coupling Coupling 50Ω
Spectrum Analyzer
LOOP Antenna
Preliminary measurement of the “ambiant noise”
COST 286 6512-13 Dec. 2005
Field variations in the room
100 1012 3 4 5 6 7 8 9 2
Fréquence MHz
0.0
20.0
40.0
60.0
Cham
p H dB
uA/m
Mesure du champ H
dBµA / m
1 MHz 30 MHz
D = 10 cm
D = 20 cm
D = 3 m
D: distance of the antenna from the wallMagnetic field
10 MHz