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 Whitehouse U. Virginia Sensys 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 sockets 2.Communication in homes can be achieved with single-hop wireless and/or power line modems 3.Robust enclosures are only important for extreme outdoor environments 4.Maintenance visits are not a problem for homes 5.Users can help maintain the system, and can provide validation data through surveys or questionnaires 6.Users won’t mind a few sensors around the house 7.Industry has already produced a wide range of suitable residential sensing systems

What They Learned Difficulty #Sensors #Sensors < #Outlets #Sensors > #Outlets #Homes < #Researchers #Homes > #Researchers #Homes #Days < ~1 month #Days > ~1 month #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 B C D E F G H I J

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, 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, V. Srinivasan, J. Stankovic, and K. Whitehouse. Using Height Sensors for Biometric Identification in Multi-resident Homes. In Pervasive, 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

Summary January 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

Wall Sockets – outlets per house – Long wires – 2.3x more down time than batteries More maintenance calls 18

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

Wireless or Power-line Wireless connectivity Power line communications – Wires – 180bit/s – 5 min polling rate 21

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

Homes are Hazardous Environments Children Mobile objects Roomba Guests and cleaning services 23

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 downServices down Last entry timeMinimum frequency CalibrationTime incorrect Load highSpace low Timestamps incorrect

Report Failure By – 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

Homes are Remote Environments Minimize installation time – Scout – Lab assembly and configuration – Checklists Test three time 27

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

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

Aesthetics Matter in Homes Disappear into the woodwork Leave no trace No LEDS at night Noise 31

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

Simplify the Architecture 33

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