17-18 Sept. 2003COST 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. 2003COST Objectives Analysis 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 Outline I.Impulsive Noise Classification II.Transmission Technique III.Performance of the transmission IV.Conclusion V.Future work

17-18 Sept. 2003COST 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 3 MHz

17-18 Sept. 2003COST 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. 2003COST I. Impulsive Noise Classification / Noise model (b) Burst Model (a) Single transient model Parameters of single transient : - peak amplitude - pseudo frequency f 0 =1/T 0 - damping factor - duration - Interarrival Time

17-18 Sept. 2003COST I. Impulsive Noise Classification / Noise characterization 1644 pulsesfo<500 kHz0.5 MHz < fo < 3MHzfo>3 MHz Single Transient Class 1Class 2 Pb = 48 %Pb = 20 % BurstClass 3Class 4Class 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 f 0 Pb: Probability of occurence

17-18 Sept. 2003COST Statistical analysis: Noise Parameters are approximated by well- known analytical distributions to build a noise model Pseudo Frequency : Weibull distribution I. Impulsive Noise Classification / Noise characterization

17-18 Sept. 2003COST 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  and s 2 are the mean and the variance of x Agreement:  =1, s=0.17

17-18 Sept. 2003COST 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. 2003COST II. Transmission system / Principle Principle of multicarrier-based transmission : Transmission on N orthogonal subcarriers owing to an IFFT/FFT. Transfer Function (H) Noise Analog/ digital Interface Channel decoding Channel Coding Digital/ analog Interface + Filter CHANNEL RECEIVER FFT Prefixe removal S/PS/P EQUALIZEREQUALIZER P/SP/S IFFT Prefix Add. P/SP/S S/PS/P EMITTER

17-18 Sept. 2003COST III. Transmission performances / Noise processing 1. Impulsive Noise processing 1. Impulsive Noise processing Matsuo 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. 2003COST III. Transmission performances / Noise processing Preprocessing Remove 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. 2003COST 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. 2003COST III. Transmission performances / Channel coding 2. Channel coding 2. 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. word of K bytes Reed-Solomon code 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. 2003COST III. Transmission performances/ Optimisation in presence of impulsive noise Contribution of channel coding and noise processing on the Bit Error Rate (BER), assuming that all pulses have a pseudo frequency f 0 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 distribution of the mean BER for three different values of the interleaving depth D

17-18 Sept. 2003COST 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. 2003COST 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. 2003COST 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