1. 12-13 Dec. 2005COST 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/Telice France

2. COST 2862 12-13 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

3. COST 2863 12-13 Dec. 2005 Transfer function P Tx →P RX (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

4. COST 2864 12-13 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

5. COST 2865 12-13 Dec. 2005 In-Vehicle  Complicated 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

6. COST 2866 12-13 Dec. 2005 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. COST 2867 12-13 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? Network E R (50  R (50  ) V

8. COST 2868 12-13 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 

9. COST 2869 12-13 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 Network E R (50  R (50  ) V

10. COST 28610 12-13 Dec. 2005 What is the physical meaning of H(f) = Vr/Ve? Why not measuring S 21? If Z L is matched to the transmission line between Z L and network output: a 2 = 0. S 21 = b 2 /a 1 Definition of the injected power : Power delivered by the source on a matched impedance (a 1 ) Applying this definition leads to (If Z 0 = Z l = R 0 ) S 21 = 2 H(f), whatever R 0. Calculating H(f) equivalent to S 21 (factor 2)! VeVe V2V2 V1V1 a1a1 a2a2 b2b2 b1b1 Z L =50  Z 0 =50  VrVr

11. COST 28611 12-13 Dec. 2005 Additional comments Other obvious interpretation of S 21 (or H(f)) If Z 0 = Z l = R 0 VeVe V2V2 V1V1 a1a1 a2a2 b2b2 b1b1 Z L =50  Z 0 =50  VrVr If the source is any generator: P i corresponds to selected power one can read on the screen of the generator !

12. COST 28612 12-13 Dec. 2005 Conclusion The Tx adapter, the line, the Rx adapter.. are considered as a whole. The transfer function or S 21 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 S 21 for any load configuration can be deduced from the S 50 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 !

13. COST 28613 12-13 Dec. 2005 Transfer function inside a room Transfer function: ratio between V out /V i, (complex number, f(frequency)) Various loads are connected at points P i

14. COST 28614 12-13 Dec. 2005 Transfer function inside a room Frequency domain H(f) – Amplitude and phase

15. COST 28615 12-13 Dec. 2005 Useful statistical parameters  Coherence bandwidth B c (  ) Absolute value  of the autocorrelation of H(f) B c : frequency shift to get a given value of  Typical example:  =0.7 or 0.9 →B c (0.7 or 0.9) Within B c, H(f) does not vary appreciably If transmitted bandwidth<<B c, flat channel, no signal distortion  Indoor inside a room: B c =few MHz

16. COST 28616 12-13 Dec. 2005 Channel characteristics in time domain: Channel impulse response (Multiple reflections ↔Multipath propagation) Power delay profile Mean delay: Delay spread Maximum excess delay

17. COST 28617 12-13 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 > 

18. COST 28618 12-13 Dec. 2005 Impulse response rms delay spread  < 0.2  s for a probability <10 -3

19. COST 28619 12-13 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)

20. COST 28620 12-13 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) W s : 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

21. COST 28621 12-13 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] [W s ] [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..

22. COST 28622 12-13 Dec. 2005 Application to in-vehicle PLC Measurement with a network analyzer (S 21 ), inserting a coupling device

23. COST 28623 12-13 Dec. 2005 Coupling device 5 Ω 1 MΩ 2 nF 5 Ω 1 MΩ 2 nF 140Ω 1 : 1 VNA Port 1 50 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)

24. COST 28624 12-13 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”

25. COST 28625 12-13 Dec. 2005 Experimental analysis on a vehicle Computer Engine computer __ : 12 V __ : ground + A B cigar lighter Power plug 12 V C D E F EnginePassenger cell boot(trunk) « Direct » paths: A  B: 6m D  E: 2m Indirect paths: A  C A  E A  F

26. COST 28626 12-13 Dec. 2005 Experimental approach : long direct path (AB, 6m) Transfer functions H1H2H3H4 K1 OFFXX ONXX K2 OFFXX ONXX -0.5 dB / MHz Port 1 50Ω Port 2 50Ω 12 V K1K2 Bundle x, car y wire B100 Computer boot (PSF2) AB

27. COST 28627 12-13 Dec. 2005 Direct path: Short (AB, 2m) / long (DE, 6m) Path n°1 – long ≈ 6 m Path n°2 – short ≈ 1 m Bc 0.9 ≈ 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 E D S21 ≥ -30 dB Δf = 43 kHz

28. COST 28628 12-13 Dec. 2005 Indirect paths Bc 0.9 ≈ 600 kHz S21 ≤ -30 dB Computercoff re (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 BSI A E F

29. COST 28629 12-13 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 Port 2 50Ω 12 V Faisceau xxx – fil B100 Allume cigare Calculateur coffre (PSF2) Port 1 50Ω FA Correlation coefficient between successive values of the transfer function

30. COST 28630 12-13 Dec. 2005 Propagation modeling D1  D3 : 5.75 m D2  D3 : 7.55 m Total length of the cables = 205 m

31. COST 28631 12-13 Dec. 2005 50 load combinations Example for 3 load config. D3 50Ω Config. N°2 (5.75 m) D1 50Ω Example: S 21 between D 1 and D 3 (about 6m) S21 > -30 dB Bc 0.9 ≈ 700 kHz

32. COST 28632 12-13 Dec. 2005 Another example Bc 0.9 ≈ 600 kHz S21 ≤ -30 dB

33. COST 28633 12-13 Dec. 2005 Statistical results deduced from 50 configurations Statistical parameters ExperimentsDeterministic model Direct paths Bc 0.9 / Hz *2 MHz1.5 MHz Rms Delay Spread / nS * 60 nS61 nS Indirect paths Bc 0.9 / Hz *700 kHz780 kHz Rms Delay Spread / nS * 84 nS108 nS

34. COST 28634 12-13 Dec. 2005 Distribution of the amplitude of H(f) around its mean value versus freq. Try to fit exp distribution with known analytical distribution

35. COST 28635 12-13 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

36. COST 28636 12-13 Dec. 2005 Noise in indoor environment

37. COST 28637 12-13 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 transmission bandwidth above 500 kHz

38. COST 28638 12-13 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

39. COST 28639 12-13 Dec. 2005 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 IAT

40. COST 28640 12-13 Dec. 2005 I. Impulsive Noise Classification / Noise characterization 1644 pulses fo<500 kHz 0.5 MHz < fo < 3MHz fo>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

41. COST 28641 12-13 Dec. 2005 2. 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

42. COST 28642 12-13 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 :  and s 2 are the mean and the variance of x Agreement:  =1, s=0.17

43. COST 28643 12-13 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 !

44. COST 28644 12-13 Dec. 2005 Noise on DC line inside a car

45. COST 28645 12-13 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 acquisition IAT PC CH A Ext trigger Port // Trig out coupler

46. COST 28646 12-13 Dec. 2005 Typical pulses Single transient, burst and “atypical pulse”

47. COST 28647 12-13 Dec. 2005 3 MHz  fo < 7 MHz7 MHz  fo < 15 MHz30 MHz  fo < 35 MHz Single pulse Class 1Class 2Class 3 67.2 %7.2 %4.9 % BurstClass 4Class 5Class 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

48. COST 28648 12-13 Dec. 2005 Classification of the pulses : Frequency/amplitude and Frequency/duration

49. COST 28649 12-13 Dec. 2005 Amplitude and Pseudo frequency distribution of bursts during cruising phase

50. COST 28650 12-13 Dec. 2005 Cumulative probability distribution of IAT normalized in OFDM frames (6.4  s in our application. see later)

51. COST 28651 12-13 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

52. COST 28652 12-13 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

53. COST 28653 12-13 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

54. COST 28654 12-13 Dec. 2005 N sub channels : N sub carriers OFDM fkfk B ff 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

55. COST 28655 12-13 Dec. 2005 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 FF T Prefixe removal S/PS/P EQUALIZEREQUALIZER P/SP/S IFFT Prefix Add. P/SP/S S/PS/P EMITTER

56. COST 28656 12-13 Dec. 2005 2. Example of simple channel coding 2. Example of simple 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. Important data: duration of a pulse (statistical approach) word of K bytes Reed- Solomon code code word of 255 bytes bytes

57. COST 28657 12-13 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?

58. COST 28658 12-13 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

59. COST 28659 12-13 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 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

60. COST 28660 12-13 Dec. 2005 PLC emission

61. COST 28661 12-13 Dec. 2005 Testing room description Computer Receiver S1S1 S2S2 Sockets Magnetic loop Balun C.W. source Data bus Three wires bundle 23 m length Switch 220 V – 50 Hz supply line Plaster walls S3S3

62. COST 28662 12-13 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 50Ω Spectrum Analyser Active probe PLC Line

63. COST 28663 12-13 Dec. 2005 Signal generator Coupling 50Ω Spectrum Analyzer LOOP Antenna Preliminary measurement of the “ambiant noise”

64. COST 28664 12-13 Dec. 2005 Example: (same differential voltage) Car/Indoor

65. COST 28665 12-13 Dec. 2005 Field variations in the room

66. COST 28666 12-13 Dec. 2005 Standards? Another issue!