Propagation Channel Characterization and Modeling Outdoor Power Supply

Propagation Channel Characterization and Modeling Outdoor Power Supply Grids as Communication Channels Prof. Dr. -Ing. habil. Klaus Dostert Institute of Industrial Information Systems UNIVERSITY OF KARLSRUHE (TH)

Overview Communication over outdoor electrical power supply lines Network structures and their basic properties Ø Access domain in Europe, ASIA, America Analysis of line and cable properties Ø characteristic impedance Ø branching & matching General aspects of channel modeling Ø transfer function, impulse response, channel parameterization Ø interference scenario PLC channel simulation and emulation Ø channel adapted system development Conclusions and further work 2

History: Carrier Frequency Transmission since 1920 (on the high voltage level only) Ø no branching Ø optimal „wave guiding“ by network conditioning 3

Current and Upcoming PLC Applications Low Speed (10… 100 kbits/s) - Office and home automation (intelligent appliances) - Energy information systems - Urban rail-based traffic systems Broadband Services: 1… 30 MHz (1… 2 Mbits/s - „Last Mile“ and „Last Meter“ high-speed internet access, voice over IP etc. High Speed Indoor Applications: 12 … 70 MHz - PLC for digital entertainment systems (>100 Mbits/s) Ø PLC in automobiles Ø PLC for factory automation Ø PLC for advanced safety systems in the mining industry 4

The European Power Supply Network Structure 3 -phase supply details V 400 high voltage level: 110. . 380 k. V 40 0 V 230 V 400 V transformer station 0 V 23 LV transformer stations medium voltage level 10. . . 30 k. V low voltage distribution grid 3 Phases: 230 V, 400 V supply cells Ø up to 350 households Ø cable length 100. . . 400 m 5

Typical Topology of European Power Distribution Networks in Residential Areas Server Transformer Station 1 5 4 3 m 2 1 k 6 x. supply cable type NAYY 150 SE ma th: 8 eng 10 11 7 12 14 13 le l L 2 L 3 N 15 cab L 1 9 18 16 17 22 19 33 20 21 23 24 32 28 31 30 29 27 26 25 House connection cable NAYY 50 SE 6

Some Details of “Last Mile” and “Last Meter” Environments local transformer station medium voltage network cross-bar system ZL 1 points of mismatch ZL 2 house connection forming a low impedance point - almost short circuit 7

Power Supply Structures in Asia and America high voltage level: 110. . 380 k. V single and split-phase 250 V transformer station 1 st medium voltage level 10… 30 k. V 125 5 V 12 V 2 nd medium voltage distribution level 6 k. V low voltage distribution grid single or split phase supply 125 V, 250 V many LV transformers Ø small supply cells Ø few households per transformer Ø cable length 100 m Ø grounding of 3 rd wire Ø highly unsymmetrical 8

The Ideal Two-Wire System compensation of exterior field X 9

Symmetry in Multi-Wire Structures open wires 3 -phase supply cable passive conductors • X passive conductors X “earth” in case of a three-wire supply • 10

Simplified Analysis of a Two-Wire System characteristic impedance 650 600 open wires: r=1 m ZL/ r 550 D m =2 m m r 4 m r= 500 5 m r= 450 r m 400 350 100 attenuation at open wires due to Skin effect 0 120 l =500 m A(f)/d. B 100 l =1000 m -2 ZL/ l =2000 80 m -4 150 200 l =5 d=2 r=5 mm 350 D in mm r m 5 m = 400 r m m =7 0 m m 1 40 000 m 300 cable: r=3. 5 60 -6 250 r= 20 -8 0 5 10 15 20 25 f in MHz 30 10 15 20 25 D in mm 30 11

RF Properties of Typical Supply Cables Access Cable Types Model J J L 3 PEN L 2 L 3 r i ra r L 1 L 2 ZL/ L 1 Lossy Line Parameters (low losses) L 3 N L 1 N r Characteristic Impedance Attenuation Coefficient Characteristic Impedance Attenuation over 1 km 50 0 NAYY 150 SE 10 40 House Connection NAYY 50 SE 30 20 Main Supply Cable NAYY 150 SE NAYY 50 SE 40 50 A(f) [d. B] 60 10 0 70 1 2 5 10 f /MHz 20 12

The problem of Branching and Possible Solutions ZL L >> ZL R=ZL/3 ZL ZL matched to ZL ZL/2 mismatch: 13

Some Ideas for Signal Coupling with Enhanced Symmetry Improving EMC Transformer Station typical RF coupling devices decoupling cross-bar system L>10µH RF-shorts cable: ZLC 25 House Connection decoupling cable: ZLC 35 impedance matching L > 10µH MODEM BALUN power meter impedance matching BALUN RF-shorts MODEM ØFerrite material is required for these decoupling coils, which carry high currents! Ø Transformer: >150 A Ø House connection: >30 A 14

Reflections Causing Echoes and Inter-Symbol Interference T wireless channel as example direct path echo path R delay: = 2 - 1 simplified analysis of a line with 1 unmatched branch Tbit direct in practice: multiple echoes echo result strong inter-symbol interference: Tbit 2 T R 1 impulse response 1 2 t 15

Approaches Toward Deterministic Network Modeling source bq ri sink line element a a 1 b b 1 S 12 S 21 S 22 branch a 2 b 2 a b ra example b 1 b 2 b 3 a 2 a 3 a 1 Ø high computational effort Ø requires detailed knowledge of network topology and device parameters not applicable in practice 16

The Echo-based Channel Model k 1 1 k 2 2 considering only echoes : ki=const N k 3 impulse response k. N S low-pass behavior dependent on number, length and matching of branches generally complex r(t) Fourier transform s(t) transfer function Result Attenuation Coefficient: skin-effect dielectric losses 17

h(t): impulse response H(f): single reflection, no losses 0 1 d. B path 1 path 2 FT -5 -10 0. 5 -15 -20 0 5 10 15 20 f in MHz 25 1 1. 17 225 m 2 T 200 m 1 attenuation 0 0 30 0 d. B 1. 33 1. 5 1. 67 t in µs 1. 83 2 R single reflection, including losses d. B -20 path 1 path 2 -40 0 5 10 15 20 f in MHz 25 30 18

Two-Path Channel without Losses but Varying Path Weights Path 1 0. 52 0. 26 Path 2 0. 347 0. 208 0. 149 0. 173 0. 46 0. 71 0. 793 0. 627 0. 76 0. 817 19

A First Realistic Example 0 -10 ¥ G» 30 m 11 m 170 m |H(f)| d. B ZL -20 -30 -40 -50 0 5 10 15 20 25 frequency in MHz 30 1 0 path di/m gi 1 200 0. 64 1 calculation measurement -10 - 20 h(t) 0. 5 - 30 2 222. 4 0. 38 3 244. 8 -0. 15 4 267. 5 0. 05 0 - 40 - 50 0 0 5 10 15 f in MHz 0 0. 5 20 1 0 1. 5 1 2 2 3 4 t in µs 2. 5 3 time in µs 5 3. 5 20

A Second Example (more complex) 110 m 15 m |H(f)| -20 d. B -40 -60 path di/m gi 1 90 0. 029 2 102 0. 043 3 113 0. 103 4 143 -0. 058 5 148 -0. 045 6 200 -0. 040 7 260 0. 038 8 322 -0. 038 9 411 0. 071 10 490 -0. 035 11 567 0. 065 12 740 -0. 055 13 960 0. 042 14 1130 -0. 059 15 1250 0. 049 -80 0 5 10 15 20 25 frequency in MHz 30 1 h(t) 0. 5 0 -0. 5 0 0. 5 1 1. 5 2 2. 5 3 time in µs 3. 5 21

Attenuation in d. B Transmission Characteristics According to Length Classes 0 10 20 150 30 40 20 50 0 m 380 70 0 m 30 60 m m 80 2 4 6 8 10 12 14 16 18 Frequency in MHz 22

A General Powerline Interference Model narrowbandinterference periodic impulsive noise synchronous with the mains periodic impulsive noise asynchronous with the mains background noise + Interference Channel as a Linear Filter h(t) aperiodic asynchronous impulsive noise Amplitude H(f) t. B A threat of burst errors t. A t. IAT time A, t. B and t. A are random variables with exponential distributions 23

Idea of a Universal PLC-Channel Emulator PLC Modem Host-PC Configuration Interface LPF A D FIR Filter Noise Generator + PGA LPF A D D D LPF PGA A LPF + Noise Generator FIR Filter D A D 24

Some Details Toward Emulator Realization channel emulation filters from 8 ADC 20 FIR Notch 5 x 7 bit delay 5 x 5 bit coeff. 14 FIR lowpass delay FPGA signal DAC FIFO 14 D A control 32 x 8 bit coeff. periodic, synchronous, asynchronous impulsive noise & background noise interference DAC 8 m-sequences of 8 length 220 -1 Amplitude 14 + 14 14 control 20 bit shift register 8 x 20 bits load D A narrow band noise 8 -bit-circular memory of length 500 P_ADDR 26 P_DATA 32 8 Amplitude 500 x 8 bits load 14 control / load 25

A First Powerline Channel Emulator Prototype reference channel |H| in d. B modified filter structure coeff. filter 1 coeff. filter 2 simulations, implementation |H| in d. B f in MHz hardware verification measurements f in MHz 26

Why OFDM for PLC? Channel Transfer Function FSK, GMSK restricted e. g. for protection of broadcast services not usable due to high attenuation OFDM sub-channel f 1 f 2 f 3 f. N f 27

Conclusions and Further Work PLC or BPL offers a variety of valuable applications Ø data rates exceeding many Mbits/s will enable numerous new services Mature channel models are covering any channel of interest Ø successful development of a new generation of ”channel adapted” PLC systems is possible Ø no more pitfalls: sophisticated simulation and emulation Building advanced and user-friendly simulation and emulation environments is now an important issue Further development and standardization of PLC or BPL goes on Ø ETSI, CENELEC, CISPR Ø EU Project OPERA (Open PLC European Research Alliance) Ø Home. Plug Alliance (USA) Ø IEEE PHY/MAC Working Group 28