17-18 Sept. 2003 COST 261 1

Part of this work is sponsored by France Télécom R&D and Region Nord Pas de Calais

University of Lille. Lab. TELICE

Communications on Indoor Power Lines

1)Characterization of the noise ON the power lines

2)Noise modelling

3)Propagation channel model

4)Simulation of the link and optimization of the signal processing algorithms

Researchers: Virginie Degardin, Martine Liénard (Assistant professor)Pierre Degauque (Professor)1 Ph. D. student

17-18 Sept. 2003 COST 261 2

ObjectivesAnalysis of the Bit Error Rate of a Multicarrier-based transmission link in a low voltage power line channel

Optimisation of transmission parameters in presence of impulsive noise

OutlineIII. Impulsive Noise Classification

IV. Transmission Technique

V. Performance of the transmission

VI. Conclusion

VII. Future work

17-18 Sept. 2003 COST 261 3

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 3 MHz

17-18 Sept. 2003 COST 261 4

Impulsive Noise : conducted emissions due to electrical devices connected to the network.

Single transient: Damped sinusoid

Burst: Succession of heavy damped sinusoids

Measurements carried out by France Telecom in a house during 40 h 2 classes of pulses (on 1644 pulses) : single transient and burst

I. Impulsive Noise Classification / Noise model

17-18 Sept. 2003 COST 261 5

I. Impulsive Noise Classification / Noise model

(b) Burst Model

(a) Single transient modelParameters of single transient :

- peak amplitude - pseudo frequency f0 =1/T0

- damping factor- duration- Interarrival Time

17-18 Sept. 2003 COST 261 6

I. Impulsive Noise Classification / Noise characterization

1644 pulses fo<500 kHz 0.5 MHz < fo < 3MHz fo>3 MHzSingle

TransientClass 1 Class 2

Pb = 48 % Pb = 20 %Burst Class 3 Class 4 Class 5

Pb = 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

17-18 Sept. 2003 COST 261 7

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

17-18 Sept. 2003 COST 261 8

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 :

I. Impulsive Noise Classification / Noise characterization

)²

)²(

2

1exp(

2

1)(

s

µx

sxf

and s2 are the meanand the variance of x Agreement: =1, s=0.17

17-18 Sept. 2003 COST 261 9

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 !

Solution to cope with impulsive noise ?

17-18 Sept. 2003 COST 261 10

II. Transmission system / Principle

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

FFTPrefixe

removal

S

/

P

EQUALIZER

P

/

S

IFFTPrefix

Add.

P/S

S/P

EMITTER

17-18 Sept. 2003 COST 261 11

III. Transmission performances / Noise processing

1. Impulsive Noise processing1. Impulsive Noise processingMatsuo process: (iterative) consists in first defining the number M of OFDM symbols which can be corrupted by noise and then removing it (iterative process)

Demodulation Decision Remodulation Subtraction

time

M=3

Critical point: choice of M and number of iteration

17-18 Sept. 2003 COST 261 12

III. Transmission performances / Noise processing

PreprocessingRemove noise >

threshold (As=3.4 V)

{r}Matsuo process

iterative(M, number i of iterations)

{X}

Iteration n° 1 Iteration n° i > 1

Optimization :Since the amplitude of impulsive noise >> signal amplitudes Possibility of determine a threshold As

time

Optimisation : threshold As

17-18 Sept. 2003 COST 261 13

III. Transmission performances / Noise processing

• Example: Signal PSD of – 50 dBm/Hz, impulsive noise randomly generated by the model. Series of 1000 tests. For each one, an impulsive noise is introduced at a random time in the transmission chain.

• At the end of each series of 1000 tests, determination of the number of erroneous bits

One can deduce the average percentage of correction

17-18 Sept. 2003 COST 261 14

III. Transmission performances / Channel coding

2. Channel coding2. 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.

word of K bytes

Reed-Solomoncode

code word of 255 bytes

bytes

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

17-18 Sept. 2003 COST 261 15

III. Transmission performances/ Optimisation in presence of impulsive noiseContribution of channel coding and noise processing on the Bit Error Rate (BER), assuming that all pulses have 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

17-18 Sept. 2003 COST 261 16

IV. Conclusion

Study and optimization of a multi-carrier link in a channel modeling the powerline network for a bit rate of 10Mbit/s, and PSD (emission) = -50 dBm/Hz :

• Statistical analysis of impulsive noise measured in a house during 40 h stochastic noise model

• Study of the transmission performances of two techniques to cope with noise :

- the noise processing- the channel coding (Reed-Solomon code & interleaving)

• Optimization of the transmission parameters

17-18 Sept. 2003 COST 261 17

IV. Conclusion, ctd

• Other important points to optimize the transmission but not really within the scope of this COST action:

- Determination of the channel transfer function. Equalization (Blind or Semi – blind)

- Detection of a sudden change in the transfer function (When electrical devices are plugged or unplugged on the network) Sudden modification of the transfer function Optimization of pilot symbols

17-18 Sept. 2003 COST 261 18

Future research

• Intensive measurement campaigns to characterize the impulsive noise on indoor power lines but in quite different environments: house, buildings, factories, railway or (and) subway stations

• Generalization of the noise model for these types of environments• Simulation of the link, optimization of the transmission scheme• Comparison between the expected Bit Error Rate and the measured

one for a transmission rate equal to or smaller than 2.5 Mbits/s• Measurement of the near field radiation of the indoor power line.

Influence of the network architecture