Drahtlose Kommunikation. Sensornetze

Transcription

1 Drahtlose Kommunikation Sensornetze

2 Übersicht Beispielanwendungen Sensorhardware und Netzarchitektur Herausforderungen und Methoden MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer WSN-Programmierung 2

3 Environmental Monitoring Example: Great Duck Island, Berkeley, Culler et al. 3

4 Precision Agriculture Example: LOFAR project Fighting Phytophtora using micro-climate Temperature and relative humidity 4

5 Forest-Fire Detection 5

6 Exploration of Unknown Territory Example: CotsBots, Berkeley, Pister et al. 6

7 Traffic Telematics 7 Image source:

8 More Scenarios Building Automation Home Automation Industrial Automation Logistics 8

9 Übersicht Beispielanwendungen Sensorhardware und Netzarchitektur Herausforderungen und Methoden MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer WSN-Programmierung 9

10 Sensor Node Hierarchy 10

11 Components of a Sensor Node Location finding system Mobilizer Sensing unit Sensor ADC Processing unit Processor Storage Transceiver unit Power unit Power generator 11

12 Example: Tmote Sky Sensor Module 12

13 Example: Tmote Sky Sensor Module 13

14 But there are much more BEAN BTnode COTS Dot Ember Eyes FireFly Fleck IMote Imote2 KMote Mica Mica2 Mica2Dot MicaZ Mulle Nymph Particles Rene ScatterWeb Sensinode SHIMMER SquidBee SunSPOT Telos TinyNode 584 T-Mote Sky T-Nodes WeBee wec XYZ WINS WiseNet 14

15 Example Generic Sensor Hardware BTNode Mica2 Flash RAM in kb Mica2Dot Internal RAM in kb Tmote Sky Serial attached Flash in kb Source: Imote 15

16 Example Sensor Network Transceivers CC1000 CC1021 CC2420 TR1000 XE1205 Bit Rate [kbps] Sleep Mode [ua] (osc. core off) RX [ma] 9.3 (433MHz) / 11.8 (868MHz) TX Min [ma] 8.6 (-20dBm) 14.5 (- 20dBm) TX Max [ma] 25.4 (+5dBm) 1.8 (core off) (115.2kbps) 25.1 (+5dBm) (-25dBm) 33 (+5dBm) 17.4 (0dBm) 12 (+1.5dBm) 62 (+15dBm) Source: 16

17 How much is 250 kbps? 250 kbit transmit bit rate can serve Two 128 kbit 320 x 240 thumbnail video streams Four 64 kbit digital high quality audio streams 250 * 1000 / bit samples per second Can we use 250 kbps? Error correcting codes Retransmissions Shared media A S B Parallel stream transmissions A B S Serial stream transmission 17

18 Network Architecture Internet and satellite Sink D C B A Task manager node User Sensor Field Sensor Nodes 18

19 Deployment options for WSN Dropped from aircraft! Random deployment Usually uniform random distribution for nodes over finite area is assumed Well planned, fixed! Regular deployment E.g., in preventive maintenance or similar Not necessarily geometric structure, but that is often a convenient assumption Mobile sensor nodes Can move to compensate for deployment shortcomings Can be passively moved around by some external force (wind, water) Can actively seek out interesting areas 19

20 Übersicht Beispielanwendungen Sensorhardware und Netzarchitektur Herausforderungen und Methoden Limitierender Faktor Batterie Schlafzyklen In-Network-Processing Multihop-Kommunikation MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer WSN-Programmierung 20

21 Limiting Factor: Battery Capacity 21

22 Batteries: Joule and Ah (1/2) 1 Ah means one can draw current of 1A for 1 hour Lifetime of 2000 mah Battery under 1 A current consumption? 1 Joule means the amount of energy stored in a battery Lifetime of Battery storing 7.2 kj Energy used to run a 1 W electricity? 22

23 Batteries: Joule and Ah (2/2) Lifetime of a 2000 mah 1.5V battery used to run a 2 W electricity 23

24 Battery examples Non-Rechargeable Chemistry Zinc-air Lithium Alkaline Energy (J/cm 3 ) Rechargeable Chemistry Lithium NiMHd NiCd Energy (J/cm 3 ) How many apples? And how fast? 24

25 Übersicht Beispielanwendungen Sensorhardware und Netzarchitektur Herausforderungen und Methoden Limitierender Faktor Batterie Schlafzyklen In-Network-Processing Multihop-Kommunikation MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer WSN-Programmierung 25

26 How long do they last? while(true) { } x = read sensor; transmit x; Sensor Constant data stream Gateway Tmote sky product description Processor: 500 ua Radio TX: 17.4 ma Standard AA Alkaline Battery Single battery: 2200 mah Tmote battery pack: 2 Batteries Sensor node s lifetime L: 26

27 How to extend the lifetime? while(true) { x = read sensor; transmit x; await next sec; Sensor 16 Bits 250 * 1024 Bits per second Gateway } Tmote sky product description Processor: 500 ua Radio TX: 17.4 ma Radio on: 365 ua Idea: sample periodically Lifetime L for one 16 bit sample per second; idealized channel: 27

28 Transceiver states Transceivers can be put into different operational states, typically: Transmit Receive Idle ready to receive, but not doing so Some functions in hardware can be switched off, reducing energy consumption a little Sleep significant parts of the transceiver are switched off Not able to immediately receive something Recovery time and startup energy to leave sleep state can be significant Research issue: Wakeup receivers can be woken via radio when in sleep state 28

29 Can they Survive a whole Year? while(true) { turn on consumers; x = read sensor; transmit x; turn off consumers; await next sec; } Idea: switch off unnecessary current consumers Tmote sky product description Processor: 500 ua Radio TX: 17.4 ma Radio power down: 1 ua Example: one 16 bit sample per second; idealized channel: 29

30 Can they Survive for many Years? Idea: set MCU in sleep mode Example: one 16 bit sample per second; idealized channel 16 Bit 250 * 1024 Bit/s Transmission time = 16/(250*1024) s = 62.5 us Duty cycling Wakeup 62.5 us Transmit Sleep 30

31 Can they Survive for many Years? Tmote sky product description Processor: 500 ua Processor 2.6 ua Radio TX: 17.4 ma Radio Idle: 365 ua Radio power down: 1 ua Processor wakeup: 6 us Radio oscillator startup: 580 us MCU 6 us 500 ua + 1 ua Radio 580 us 500 ua ua TX 62.5 us 500 ua ma Idle 10^6 ( ) us 2.6 ua + 1 ua Current consumption: Y = 6/10^6 * (500+1) + In practice 580/10^6 lifetime * ( ) of + a few years: 62.5/10^6 * ( ) + More sources of power dissipation (10^ )/10^6 * (2.6+1) Y = Synchronization 5.22 ua of communication nodes Battery looses current Lifetime: 4400 mah / ma h 35121days 96years 31

32 Übersicht Beispielanwendungen Sensor-Hardware und Netzarchitektur Herausforderungen und Methoden Limitierender Faktor Batterie Schlafzyklen In-Network-Processing Multihop-Kommunikation MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer S-MAC und T-MAC B-MAC X-MAC und Wise-MAC WSN-Programmierung Laufzeitumgebungen Fallstudie TinyOS MAC-Layer-Programmierung mit der MLA 32

33 Where to Process the Data? Example determine max value S1 send(d1) S3 send(d3) Sink: compute max(d1,d2,d3) S2 send(d2) How to reduce communication load on S3? 33

34 Data Aggregation S1 send(d1) S3 send(m) Sink S2 send(d2) compute m = max(d1,d2,d3) Additional: data processing in the event source 34

35 Übersicht Beispielanwendungen Sensor-Hardware und Netzarchitektur Herausforderungen und Methoden Limitierender Faktor Batterie Schlafzyklen In-Network-Processing Multihop-Kommunikation MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer WSN-Programmierung 35

36 Observation: Energy Efficiency 100 njoule/bit 100 m 36

37 Observation: Energy Efficiency 1 njoule/bit 10 m Signal Strength Bluetooth Example 100m in one hop: 100nJ/Bit 100m in ten hops: 10nJ/Bit Distance 37

38 Broadcast Property Sender Receiver 38