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Wireless Sensor Mote (TelosB)
• Ultra low-power wireless module– for sensor networks, monitoring app, rapid
prototyping
• Key Features– 2.4GHz 802.15.4 radio, 250kps– 8MHz processor, 10k RAM, 48k Flash– Fast wakeup (6s) – 1MB external flash (16 segments, each 64kB)– Ultra low current consumption– TinyOS support
Some Useful Components of Mote/TOS
• Radio
• UART
• Timer (unique)
• Flash memory
• LEDs
• Sensor(s)
Some Research Area in WSN
• Wireless Communication• Localization• Calibration• Time Synchronization• Routing (Data-Centric Routing)• Deployment, Lifetime optimization• Signal Processing - compression, detection• Storage (Data-Centric Storage)• Mobility
Wireless Communication
Ideal model Real model
*
[Ganesan TR ’02][ Marco Zuniga et al., USC]
Wireless Communication
transitional
con
ne
cte
d
dis
con
ne
cte
d
distance (m)
PR
R
Empirical: link behavior *– Three regions*:
•Connected
•Disconnected
•Transitional
– Transitional region :
•Asymmetric links
•High variance space/time
•Large extent
– Significant impact on some routing
protocols**
* [Zhao SenSys ’03] [Woo SenSys ’03] [Ganesan TR ’02] [Aguayo SIGCOMM’04] ** [Zhou MobiSys’03]
Routing (Information Gradient-based Active Routing)Isoseismal (intensity) maps ((North Palm Springs earthquake of July 8, 1986North Palm Springs earthquake of July 8, 1986))
Ref.: Southern California Earthquake Center. (http://www.scec.org)Ref.: Southern California Earthquake Center. (http://www.scec.org)
ChallengesChallenges
- In real life, sensors are unable to detect or measure the event’s effect In real life, sensors are unable to detect or measure the event’s effect below certain threshold. So, diffusion curve has finite tail below certain threshold. So, diffusion curve has finite tail - Lack of sensitivity of sensor- Lack of sensitivity of sensor device(s)device(s) - Creates flat information region - Creates flat information region
- Erroneous reading of the malfunctioning sensors Erroneous reading of the malfunctioning sensors - Due to calibration error or obstacle- Due to calibration error or obstacle - Cause local maxima or minima - Cause local maxima or minima
- Environmental noiseEnvironmental noise
0
20
40
60
80
100
0 50 100 150 200
distance
magnitude of effect
Routing (Information Gradient-based Active Routing)
Brief Description of Routing ApproachesBrief Description of Routing Approaches
Single-path Query forwarding with look-ahead, r = 1
Multiple-path Query forwarding
17.2 17.217.2 17.2
17.2 18.9 3.1 18.9
17.2 18.9 21.1 21.1
17.2 92.1 21.1 23.8
21.1 6.9 21.1 21.1
23.8 4.1 98.1 23.8 23.8 23.8 23.8
67.0 3.2 21.1 23.8 27.5 27.5 27.5 27.5 27.5 27.5 27.5
18.9 21.1 30.0 27.5 29.0 32.9 32.9 80.5 32.9 32.9
23.8 31.0 32.9 41.5 41.5 41.5 41.5 41.5
23.8 27.8 3.4 41.5 57.4 57.4 57.4 41.5
23.8 27.8 32.9 41.5 57.4 100 57.4 41.5
57.4 41.557.457.441.5
Q
17.2 17.217.2 17.2
17.2 18.9 3.8 18.9
17.2 18.9 21.1 21.1
17.2 92.1 21.1 23.8
21.1 6.9 21.1 21.1
23.8 4.1 98.1 23.8 23.8 23.8 23.8
67.0 3.2 21.1 23.8 27.5 27.5 27.5 27.5 27.5 27.5 27.5
18.9 21.1 30.0 27.5 29.0 32.9 32.9 9.0 32.9 32.9
21.1 23.8 31.0 32.9 41.5 41.5 41.5 41.5 41.5
23.8 27.8 3.4 41.5 57.4 57.4 57.4 41.5
23.8 27.8 32.9 41.5 57.4 100 57.4 41.5
57.4 41.557.457.441.5
Q
S S
Look-ahead = 1
Active Node
Candidate Node
Active Nodes
9
Still Have Limitations
Multiple EventsMultiple Events
• Flooding overhead is high for sparsely distributed eventsFlooding overhead is high for sparsely distributed events• Unable to detect sparsely located events Unable to detect sparsely located events
