arch:&prac+cal&channel&hopping&for& reliable&home7area...

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

… …


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1 2


3


… …

1 2


3


…


9

1 2


3


… …

1 2


3

Sending Channel: i Receiving Channel: j


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1 2

Sending Channel: j

3


1 2


3


… …


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1 2


3


… …

1 2


3

Receiving Channel: k

…

Sending channel: k


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1 2


3


1 2


3


… …

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


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1

2


Sending Channel: j, i

4

… Sending Channel: j, i

5

Sending Channel: i

neighbor list


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1

2



4

5


Sending Channel: i

neighbor list

now => j


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1

2

Receiving Channel: j


4

5


Sending Channel: j

neighbor list


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1

2


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


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


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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ETX-based ARCH

Fixed channel scheme


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67%

30%

ETX-based ARCH

Fixed channel scheme


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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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Ø  Power Efficiency

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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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