Wie viel Energie braucht Echtzeit? Drahtlose Messsysteme für den industriellen Einsatz

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1 Wie viel Energie braucht Echtzeit? Drahtlose Messsysteme für den industriellen Einsatz G. Scholl, H.-J. Körber, H. Wattar Professur für Elektrische Messtechnik Helmut-Schmidt-Universität Universität der Bundeswehr Hamburg

2 Energieverbrauch drahtloser Kommunikation Drahtloses Sensor/Aktor-Netzwerk für die Fertigungsautomatisierung Ergebnisse

3 Free Space Propagation Resisitive/Dielectric Losses Matching Losses Transmit Polarisation Directivity P P r t = e cdt e cdr ( )( ) r r 2 ( ) ( ) λ 1 Γt 1 Γr et er Dt θt, φt Dr θr, φr ( ) 2 4π R Receive Directivity Polarisation Matching Losses Resisitive/Dielectric Losses

4 Large-Scale Propagation Model 1m 2m 10m 20m PL = 4π 20log λ + 10 n log ( R) n = 2, 869 MHz: 31 db 37 db 51 db 57 db n = 2, 2.4 GHz: 40 db 46 db 60 db 66 db n = 3.3, 2.4 GHz: 40 db 50 db 73 db 83 db Location n Office, moveable walls 2.4 Office, fixed walls 3.0 Textilefactory, LOS 2.0 Textilefactory, OLOS 2.1 Metalworking factory, LOS 1.6 Metalworking factory, OLOS 3.3 Moveable walls Doors Windows Fixed walls Metalpartitions 1.4 db 2.0 db 2.0 db 3.0 db 5.0 db

5 Small-Scale Fading E(x,y) in db H(f, x, y) in db y/λ x/λ Simulation der Wellenausbreitung, 8 Pfade, NLOS Messung der Wellenausbreitung, Maschinenhalle: 40m x 50m x 9m, Frequenz: 2405 MHz, LOS

6 Small-Scale Fading Probability density Probability density E(x,y) Wahrscheinlichkeitsdichte der Feldstärke ϕ {E(x,y)} Wahrscheinlichkeitsdichte Phasenverteilung pdf P 1 2 P P P 2 ( P) = exp, P E P =

7 Small-Scale Fading pdf P 1 2 P P P 2 ( P) = exp, P E 2 2 ( ) P = cdf P P P P 2 P 2 P Local Fading Dip Probability / % 0,1 10 db 10 0,01 20 db 1 0, db 0,1 Distance 1m 2m 10m 20m Propagation 2.45 GHz 40 db 50 db 73 db 83 db Fading 30 db 30 db 30 db 30 db Gesamtdämpfung 70 db 80 db 103 db 113 db

8 Antenna Diversity cdf P ( P) N = 2 2 P P exp P P N Anzahl Antennen n = 1 n=2 n=3 Fading Dip Wahrscheinlichkeit / % 10 db ,1 20 db 1 0, db 0,1 0, Wahrscheinlichkeit für Pegeleinbrüche bei RSSI-Diversity mit N = 1, 2, 3 und 4 Antennen

9 Small-Scale Fading Coherence Length L c and Cohenrence Bandwidth B c

10 Process Gain / Zigbee 868 MHz band 20 kb/s 900 MHz band 40 kb/s 2.4 GHz band 250 kb/s 1 bit/symbol 1 bit/symbol 4 bit/symbol 1 bit DBPSK modulation 1 bit DBPSK modulation 1 of 16 near-orthogonal spreading sequences OQPSK modulation 15-chip m-sequence 300 kchips/s 15-chip m-sequence 300 kchips/s 32-chip spreading sequence 2.0 Mchips/s Process Gain / db = 10 log (N) 12 db 12 db 15 db

11 Modulation Techniques , OQPSK; , DBPSK, DQPSK; DQPSK; , GFSK

12 Error Detection/Correction Bluetooth Error Control Process Transmitting Node Append CRC to a set of data Divide new data set into blocks of k bits Run FEC encoding algorithm for each block Concatenate sequence of codewords, each of length n Receiving Node Separate the payload from the rest of the packet Divide the sequence into blocks of n bits Run FEC decoding algorithm for each block to obtain k bits of data Concatenate k bits blocks Run CRC Shortened Hamming Code n = 15 Block Length k = 10 Information Bits n-k = 5 Check Bits r = k/n=2/3 Code Rate 1/r = % Code Overhead Correct 1 / Detect 2 Bit Errors

13 Medium Access Control Offered rate G = Throughput (S ) + Rejected Packets (R) Rate S Rate S Source Channel Destination Rejected Packets Rate R

14 Medium Access Control Normalized Delay Comparisons Normalized delay (packet length) ALOHA Slotted ALOHA Slotted 1-persistent Throughput S Nonpersistent Optimum p-persistent M/D/1

15 Sensor/Actuator Network for Factory Automation Customer Requirements Energy autonomous operation Real-time capability (5 ms) Multisensor/actuator handling in a production cell with typical dimensions of 5 x 5 x 3 m 3 High reliability, communication errors comparable to conventional wired fieldbus sensor/actuator systems Coexistence with other wireless standards Scalability and modularity Employ standard components and modules to keep development, system and service costs low With only slight modifications applicable for the global market

16 Data Rate Estimation AS-i Fieldbus Master 14 bits Slave (31x) Polling Cycle: 150 µs Master 7 bits Slave (31x) 17 bits payload 4 bits protocol overhead Gross Data Rate = 167 kbit/s Wireless Sensor/Actor System Protocol Overhead: 8 bytes/telegram ( ) bits / telegram Gross Data Rate = 966 kbit/s = 5,8 x AS-i

17 RF Modules

18 Sensor/Actuator-Module

19 System Architecture Base Station XILINX FPGA Spartan 3 mit MicroBlaze-Core Sensor/Actuator-Modules

20 Spectrogram

21 Client-Server Test-Setup

22 Timing Diagram 6 ms 200 µs 1 ms

23 Best/Worst Case Scenario

24 Energy Consumption I Low-Power Modus II Empfangsbetrieb III Sendebetrieb IV Frequenzwechsel 10,13 mw 0,3 mw

25 Energy Sources

26 Vielen Dank! G. Scholl, H.-J. Körber, H. Wattar Professur für Elektrische Messtechnik Helmut-Schmidt-Universität Universität der Bundeswehr Hamburg