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The Hitchhiker’s Guide to Successful Residential Sensing Deployments
Timothy W. Hnat, Vijay Srinivasan, Jiakang Lu, Tamim I. Sookoor, Raymond Dawson, John Stankovic, and Kamin
WhitehouseU. VirginiaSensys 11
Presenter: SY
Lesson Learned Paper
• Large scale, long-term deployment in home– 1200 sensors– Over 20 homes– Up to 1 year/home
• Experience sharing– Myths VS facts
Myths
1. Sensors in homes can easily be powered using the wall sockets2. Communication in homes can be achieved with single-hop
wireless and/or power line modems3. Robust enclosures are only important for extreme outdoor
environments4. Maintenance visits are not a problem for homes5. Users can help maintain the system, and can provide
validation data through surveys or questionnaires6. Users won’t mind a few sensors around the house7. Industry has already produced a wide range of suitable
residential sensing systems
What They Learned
Diffi
culty
#Sensors
#Sen
sors
< #Out
lets
#Sen
sors
> #Out
lets
#Hom
es <
#Res
earc
hers
#Hom
es >
#Res
earc
hers
#Homes
#Day
s < ~1
mon
th
#Day
s > ~1
mon
th#Days
Outline
• Deployment• Failure Analysis• Hitchhiker’s Guide
Deployment
# Homes
Weeks
Motion
Object Use
Door Heights
Wearable Tracking
Light Switch
Power (Plugs)
Power (Circuits)
Power (Mains)
Water Mains
Custom Thermostat
Active Register
Light/Temp Humidity
A 11 1-2 25-30
12-20 - - - - - - - - - -
B 1 1 - - 12 12 - - - - - - - -
C 3 3-4 15-25 - - - - - - - - - - 12-
25
D 1 2 4 - - - - 2 - - - - - -
E 1 2 5 - - - - - 1 - - - - -
F 1 28 65 13 13 16 22 - - 1 1 1 12 86
G 1 44 54 7 31 14 22 8 37 1 1 1 12 29
H 1 39 15 7 14 - 11 4 - 1 1 - - -
I 1 32 25 10 30 - 31 3 48 1 1 - - 8
J 1 25 14 5 17 - 7 2 - 1 1 - - -
Deployments
Deployments
Deployments
Why Such Deployments• V. Srinivasan, J. Stankovic, and K. Whitehouse. Protecting your Daily
In-Home Activity Information from a Wireless Snooping Attack. In Proceedings of the 10th international conference on Ubiquitous computing, pages 202–211. ACM New York, NY, USA, 2008.
• J. Lu, T. Sookoor, V. Srinivasan, G. Gao, B. Holben, J. Stankovic, E. Field, and K. Whitehouse. The smart thermostat: using occupancy sensors to save energy in homes. ACM Sensys, 2010.
• V. Srinivasan, J. Stankovic, and K. Whitehouse. Using Height Sensors for Biometric Identification in Multi-resident Homes. In Pervasive, 2010.
• J. Lu, D. Birru, and K. Whitehouse. Using simple light sensors to achieve smart daylight harvesting. In The ACM Workshop on Embedded Sensing Systems for Energy-Efficiency in Building, 2010.
System Architecture
Sub-systems
Gateway
Failure Analysis
• Analyze the sensor down time• Method– Define a longest acceptable report interval τ• For each sensor • About 5x sample period
– Classify root cause• based on the set of simultaneous sensor failures
Classification• Wireless link loss
– single wireless sensor, less than 4 τ• Battery dead
– single battery-powered sensor, longer than 4 τ• Plug disconnected
– single plug powered sensor, longer than 4 τ• Sub-system down
– all sensors in a single sensor sub-system• Internet Down
– all sensors reliant on a broadband link• Power outage
– all sensors reliant on AC power• Gateway down
– simultaneous down time of all sensors
SummaryJanuary 1, 2011 to August 1, 2011
Fault Analysis
15
Reinstall
Hard drive failure
Sub-system failure Plug disconnections
Outline
• Deployment• Failure Analysis• Hitchhiker’s Guide
Homes are Not a Power Panacea
• Myth– Sensors in homes can easily be powered using the
wall sockets
• Fact– Wall sockets provide neither abundant nor reliable
power, especially when deploying hundreds of nodes
18
Wall Sockets– 30-40 outlets per house– Long wires– 2.3x more down time than
batteries• More maintenance calls
In-line Power & Indoor Solar
• In-line power– Wired directly into wiring– Problem• Expensive• Reboot -- rebooting the house
• Indoor Solar– Upper bound: 0.1mW– Compare to outdoor: 102mW
Homes Have Poor Connectivity
• Myth– Communication in homes can be achieved with
single-hop wireless and/or power line modems
• Fact– Homes are small but can still be challenging RF
environments, particularly for large-scale, dense, and heterogeneous networks
21
Wireless or Power-line
• Wireless connectivity
• Power line communications– Wires– 180bit/s – 5 min polling rate
Homes are Hazardous Environments
• Myth– Robust enclosures are only important for extreme
outdoor environments
• Fact– Homes are safe environments for humans but can
be hazardous for sensors, particularly when hundreds of sensors are deployed over long time durations
23
Homes are Hazardous Environments
• Children• Mobile objects• Roomba• Guests and
cleaning services
Verify Failures
• Mean time to failure (MTTF)– Deploy 500 sensors• One year MTTF means more than one sensor fail per
day
• Automated script to check
Network down Services down
Last entry time Minimum frequency
Calibration Time incorrect
Load high Space low
Timestamps incorrect
Report Failure
• By email– Too many
• Project all critical alerts on wall
Homes are Remote Environments
• Myth– Maintenance visits are not a problem for homes
• Fact– Investigators have very limited access to
deployments not in their own homes
27
Homes are Remote Environments• Minimize installation time– Scout– Lab assembly and
configuration– Checklists
• Test three time
Expect Limited User Participation
• Myth– Users can help maintain the system, and can
provide validation data through surveys or questionnaires
• Fact– A user’s ability to monitor and report activities in
the home is limited by the need to do those activities, particularly in long-duration deployments
29
Expect Limited User Participation• Button Tracking• Wearable Tracking• Self-reporting• Surveys
29
Use redundant sensing and multiple ground truth techniques
Aesthetics Matter in Homes
• Myth– Users won’t mind a few sensors around the house
• Fact– Aesthetics constrain deployments, especially at
large scale and over long time durations
31
Aesthetics Matter in Homes• Disappear into the
woodwork • Leave no trace • No LEDS at night• Noise
Simplify the Architecture
• Myth– Industry has already produced a wide range of
suitable residential sensing systems• Fact– Many COTS devices were not designed for large
scale deployments, and integration of many COTS platforms increases the possible modes of system failure
33
Simplify the Architecture
Summary
• Wall socket is neither abundant nor reliable• Communication in home still challenge• Homes are hazardous environments• Homes are remote environments• User has limited participation• Aesthetics matter• COTS are a double-edged sword
Conclusion
• Some we might already expected– But some information still useful
• Useful tips– Verify failure• Automated script• Project on wall
– Check three time– COTS are a double-edged sword