Wireless Sensor Network Deployment Lessons Learned Steven Lanzisera Environmental Energy...
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Transcript of Wireless Sensor Network Deployment Lessons Learned Steven Lanzisera Environmental Energy...
Wireless Sensor Network Deployment Lessons Learned
Steven LanziseraEnvironmental Energy Technologies Division, LBNL
21 January 2011
3
Project Overview – Commercial Buildings
• LBNL Building 90– 90,000 s.f. office
• Plug-in device metering network• 6 months of data collection (on going)
4
Current Building 90 Deployment
• 300+ ACmes installed throughout building• 500 at full build-out
– 0.5 nodes per 100 s.f.
• 802.15.4, CSMA, 6LowPAN, RPL (draft), SMAP (custom)
• Power, apparent power, energy every 10s
245 ft / 75 m
5
Residential Deployments
• 5 Houses (4 bay area, 1 Boston area)– ~80 nodes installed per house– 1 gateway– Data reported every 10s– 6 months of data collection (ongoing)
• Gearing up for 70 homes in next year– 15-20 nodes per home
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Overview
• Zigbee & Standards Context• Why Wireless Networks Fail
– Communication Issues– Other Issues
• Final Thoughts
8
IEEE 802.15.4 – Overview
• Emphasis of IEEE 802.15.4 is:– low-cost, low-speed ubiquitous communication between nearby devices with little to
no underlying infrastructure– Nominal communication at 250 kb/s– 10m communication range assumed – to meet embedded constraints, several PHY layers are available
• Key technology features are: – collision avoidance through CSMA/CA– integrated support for secure communications (128-bit AES encryption)– power management functions such as link quality and energy detection– 16 channels in the 2.4 GHz band– star and mesh topologies can theoretically be built
9
IEEE 802.15.4 – MAC Layer
• There are two general channel access methods:
• Non-Beacon Network:– simple, traditional multiple access system used in simple peer networks– standard CSMA conflict resolution– positive acknowledgement for successfully received packets
• Beacon-Enabled Network– can be used in beacon-request mode without superframes– superframe structure - network coordinator transmits beacons at predetermined
intervals– dedicated bandwidth and low latency– low power consumption mode for coordinator
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Mischa Dohler & Thomas Watteyne @ ICC 2009
IEEE 802.15.4 – MAC Layer
• Super-Frame Structure for Beacon-Enabled Mode:
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IEEE 802.15.4 MAC in Practice
• Beacons are rarely used• Contention based networks are common• Zigbee doesn’t require one or the other
– Often implemented without beacons
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ZigBee
• ZigBee in short:– international alliance for wireless control applications; SIG certifies platforms– based on IEEE 802.15.4 PHY & MAC– millions of products today are embedding a chipset of the ZigBee family– Small numbers of ZigBee certified products are available
• Provides network through application layers• Most devices listen all the time (and must be mains powered)
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Full function device
Reduced function device
Communications flow
Mesh for full functionListen all the time
Star for reduced functionSleep between transmissions
Zigbee General Topology
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Overview
• Zigbee & Standards Context• Why Wireless Networks Fail
– Communication Issues– Other Issues
• Final Thoughts
15
Assumptions
• Multi-hop network of low power wireless sensors
• Communicating using IEEE802.15.4 radio chips (16 frequency channels in the 2.4GHz band)
2.4 GHz
Channels 11-26
2.4835 GHz
5 MHz
2.4 GHz PHY
A
B
C
D
E
F
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Single Channel Solutions
• The quality of a link varies
with frequency with time
there is no “best channel”!
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Second Challenge: Multipath Fading
ch.11
ch.13
ch.15
ch.17
ch.12
ch.14
ch.16
ch.18
ch.19
ch.21
ch.23
ch.25
ch.20
ch.22
ch.24
ch.26
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Impact of Interference
• Noise
• Interference
2.4 GHz
Channels 11-26
2.4835 GHz
5 MHz
2.4 GHz PHY
Relative Noise Power
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BT & WLAN interfere with ZigBee
• Theoretical results indicate that interference is an issue [SPC07]:
26
Mischa Dohler & Thomas Watteyne @ ICC 2009
Reservation vs. Contention MAC
• Example of throughput versus offered load:
Offered Load
Nor
mal
ized
Thr
ough
put
reservation based
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Data Collection Network Reliability%
of P
ossi
ble
Pac
kets
% o
f Pos
sibl
e P
acke
ts
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Latency
• Multihop latency suffers because of communication failures
• 1-hop latency is < 10ms if it works• Backoff after failure increases latency• Tests w/50 ms backoff & 5 hops
– Average latency ~100ms– 90% of packets arrive by 500ms– MAC time out occurs before 99% (1s)
29
Link Length & Routing Stability
In B90 (Office building)• Typical links 30ft• Longest (reliable) links 50ft• 60% of routes didn’t change this week• 20% of routes changed >5 times (Check daily)
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Why Zigbee?
• Zigbee is a “new” protocol• Limited industry experience• Known for interoperability, reliability problems• Latency, packet size are far from ideal• Very few products on the market
• Plus side: could be cheap(er)– Somewhat lower power
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Consider WiFi
• Over 2M WiFi chips shipped every day• Same MAC, but better coexistance• SEP 2.0 is not linked to a PHY• SEP 2.0 and other Zigbee will work on IP• Power difference isn’t large (0.3W vs 0.1W)• Cost difference negligible
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Recommendations
• Early study of Zigbee in intended environment– Multihop network– Test latency, reliability, etc
• Consider draft SEP 2.0 (available on the web)