arch:&prac+cal&channel&hopping&for& reliable&home7area...
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ARCH: Prac+cal Channel Hopping for Reliable Home-‐Area Sensor Networks
Chenyang Lu
Home Area Network for Smart Energy
Connecting power meters, thermostats, HVAC, appliances.
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Source: AT&T Labs
Wireless Sensor Networks
Ø Advantage q Do not require wired infrastructure.
q Easily and inexpensively retrofit existing homes.
q Energy efficiency
Ø Reliability challenges q Crowded 2.4 GHz ISM band
q Unpredictable environments
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Empirical Studies from Real Homes
Ø Spectrum study of existing wireless signals. (WiSpy) Ø 802.15.4 link reliability in all 16 channels. (TelosB)
Ø Collected from 10+ apartments in different neighborhoods.
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Design Insights 1. Links have different channel conditions within a home.
2. Link reliability achievable through infrequent channel hopping.
3. Channel-hopping decisions must be made dynamically.
4. Avoid adjacent channels when the current channel becomes unreliable.
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ARCH: Adap+ve and Robust Channel Hopping
Ø Receiver-oriented protocol q Insight: Links have different channel conditions within a home. q Different receivers may have different channels.
Ø Monitor channel condition q Maintain a sliding window of ETX values of incoming links q Mark channel unreliable if ETX values exceed threshold
Ø Select a new channel q Insight: strong correlation in link failures among adjacent channels. q Probabilistically chooses a new channel q The further away a channel is from the current channel, the more likely it
will be chosen.
Ø Upon selecting a new channel, nodes notify neighbors of this change. Neighbors update their neighbor tables.
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Mul+-‐Hop Communica+on
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1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
… …
Mul+-‐Hop Communica+on
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1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
… …
1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
…
Mul+-‐Hop Communica+on
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1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
… …
1 2
Receiving Channel: i
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Sending Channel: i Receiving Channel: j
Mul+-‐Hop Communica+on
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1 2
Sending Channel: j
3
Receiving Channel: j Receiving Channel: k
1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
… …
Mul+-‐Hop Communica+on
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1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
… …
1 2
Receiving Channel: i
3
Receiving Channel: k
…
Sending channel: k
Mul+-‐Hop Communica+on
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1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
1 2
Receiving Channel: i
3
Receiving Channel: j Receiving Channel: k
… …
Mul+-‐Sender Problem
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1
2
Old Receiving Channel: i
New Receiving Channel: j
Sending Channel: j
4
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… Sending Channel: j
Sending Channel: i
Coordinated Hopping (1)
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1
2
Receiving Channel: i 4
5
…
Sending Channel: i
neighbor list
pending => j
pending => j
Coordinated Hopping (2)
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1
2
Receiving Channel: i
Sending Channel: j, i
4
… Sending Channel: j, i
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Sending Channel: i
neighbor list
Coordinated Hopping (3)
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1
2
Receiving Channel: i
Sending Channel: j, i
4
5
… Sending Channel: j, i
Sending Channel: i
neighbor list
now => j
Coordinated Hopping (4)
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1
2
Receiving Channel: j
Sending Channel: j, i
4
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… Sending Channel: j, i
Sending Channel: j
neighbor list
Coordinated Hopping (5)
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1
2
Receiving Channel: j
Sending Channel: j 4
5
… Sending Channel: j
Sending Channel: j
Handling Channel Desynchroniza+on Ø Default channel
q No data transmission, only for resynchronization
Ø When sender reaching maximum number of retransmissions q Sender => default channel
Ø When receiver reaching maximum wait time q Receiver => default channel
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1 2
Receiving Channel: j
Sending Channel: i
Handling Channel Desynchroniza+on
Ø Channel is too noisy à false detection Ø Exchange previous channels when resynchronizing
Ø Blacklist this channel and pick a new one
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1 2
Receiving Channel: i
Sending Channel: i
Single-‐Hop Data Collec+on
Ø 10 real-world apartments Ø 24-hour experiment
Ø 30 TelosB mote pairs Ø BoX-MAC in TinyOS 2.1.1
Ø Data rate: 1 packet/5 minutes
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Single-‐Hop Data Collec+on
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ETX-based ARCH
Fixed channel scheme
Single-‐Hop Data Collec+on
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67%
30%
ETX-based ARCH
Fixed channel scheme
Single-‐Hop Data Collec+on
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Mul+-‐Hop Data Collec+on Ø 11 TelosB motes, LPL BoX-MAC in TinyOS 2.1.1 Ø Fixed routing Ø Three-floor building
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Mul+-‐Hop Data Collec+on
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Mul+-‐Hop Data Collec+on
Ø Power Efficiency
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Mul+-‐Hop Data Collec+on
Ø Number of channel hops per day
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Conclusion Ø ARCH: Practical Channel Hopping for Home Area Networks
q Grounded on insights from empirical studies in real homes
q Adaptive channel selection
q Decentralized q Minimal communication overhead
Ø Promising experimental results in real homes q 42% reduction in the number of packet transmissions
q 32% average reduction in radio on time
q <12 channel hops per day in multi-hop experiment
Reading Ø M. Sha, G. Hackmann and C. Lu, ARCH: Practical Channel Hopping for
Reliable Home-Area Sensor Networks, IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS'11), April 2011.
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