CitySense: An Open, Urban-Scale Sensor Network Testbed

© 2007 Matt Welsh – Harvard University © 2007 BBN Technologies 1

CitySense:An Open, Urban-Scale Sensor Network Testbed

Josh BersBBN Technologies

Mobile Networking Systems Group

Matt WelshHarvard University

Division of Engineering and Applied Sciences


Sensor Network TestbedsGoal: Support experimentation with wireless sensor networks at scale

● Simulations are valuable but inherently limited● Understanding characteristics of real sensor networks in diverse environments

requires real testbeds and real applications● Testbeds should be open and easily shared by multiple research groups

CitySense: Planned outdoor testbed of 100 embedded PCs in Cambridge, MA

● Linux-based embedded PCs with meteorological and air quality sensors● 802.11a/b/g interface with multihop wireless networking backbone● Collaboration between BBN Technologies and Harvard University● Funded by NSF under Computing Research Infrastructure program, 2006-2010


CitySenseJoint effort between BBN Technologies and Harvard University (Prof.

Matt Welsh, Co-PI)● NSF Computing Research Infrastructure (CRI) program grant (4 years), Rita Rodriguez

NSF Program Director.● BBN taking lead on hardware design and deployment planning● Harvard taking lead on software design and resource management

Goal: Deploy an outdoor, open wireless sensor network testbedacross the city of Cambridge, MA

Nodes consist of Linux-based embedded PCs with 802.11a/b/g● Mounted on top of light poles with assistance from City of Cambridge● Professional meterological sensor package for environmental monitoring

Web-based interface for job scheduling, debugging, profiling● Draw on experiences with MoteLab and extend to outdoor testbed● Open resource for the sensor network community


CitySense Overview


CitySense OverviewPhotocell (Power)

CitySense Node goes here

Photocell (Power)

CitySense Node goes here

Vaisala meterologicalsensor

● Metrix embedded PC (Soekris single-board PC)● Runs Pebble Linux distribution● 133 Mhz AMD processor● 64 MB RAM and flash, 1 GB USB flash drive● Dual 802.11 a/b/g radios● Multiple sensors possible: weather, air quality, bio/chem

agents, webcams, microphones…

Fixture Arm

Mounting Straps

WiFi Antennas

Vaisala Mouting mast

Power input


BBN Network Topology

• 3 Indoor nodes plus gateway

• 2 nodes on roof of buildings– Racing– Rosario

• Fully connected except for Gateway


Sensor Node Design Iter#1: Racing


Why CitySense?Expand sensor networking testbeds beyond indoor deployments with

resource-constrained nodes● Outdoor testbed with large coverage area● Powered nodes with substantial CPU/memory/radio bandwidth● Provide blueprint for future sensor network designs and deployments

Shared resource open to research community● Leverage experience with Harvard’s MoteLab to provide shared experimental facility

Provide bridge to broader scientific communities● Partnership with Harvard School of Public Health – urban air pollution study● Educational impact at graduate, undergraduate, and K-12 levels

Connection to NSF GENI initiative● Shared facility for experimenting with sensor networks in realistic outdoor environment● Opportunity for connection to evolving network standards and support for

“Internet scale sensor networking”


CitySense sensor packageVaisala Weather Transmitter WXT510

● Wind speed and direction● Precipitation● Barometric pressure● Temperature● Relative humidity

Well-calibrated sensors, robust packaging for outdoor environments

● Designed for precise measurement of environmentalconditions

● More accurate than typical component sensors used on motes

Serial interface for configuration and data access


Example dataRaw sensor ouput as received by our gateway via UDP packets multi-hopped from the sensor nodes:

● Rain accumulation● Wind Speed and Direction● Pressure Temperature and Humidity● Sensor Status Data

Sensor data: net.citysense.sensors.PTHSensorOutput@1decdec Device-type=VAISALA WXT510 Device-name=0 Timestamp=Mon Mar 26 22:15:10 EDT 2007 Sample Interval=-1 Query command=N/A

Measurement airPressure value=1016.3 unit=hPa Measurement airTemperature value=6.3 unit=Celsius Measurement relativeHumidity value=89.5 unit=PERCENT

Sensor data: net.citysense.sensors.WindSensorOutput@12a54f9 Device-type=VAISALA WXT510 Device-name=0 Timestamp=Mon Mar 26 22:15:14 EDT 2007 Sample Interval=-1 Query command=N/A

Measurement directionAvg value=294 unit=DEGREES Measurement directionMax value=330 unit=DEGREES Measurement directionMin value=278 unit=DEGREES Measurement speedAvg value=0.9 unit=METERS_PER_SECOND Measurement speedMax value=1.2 unit=METERS_PER_SECOND Measurement speedMin value=0.6 unit=METERS_PER_SECOND

Go to: http://citysense.bbn.com/ReadVaisala.pl for live data feed.


CitySense NetworkingMost CitySense nodes will not have wired network connectivity

● Several nodes (at BBN and Harvard) will act as gateways to the Internet.● Must use wireless mutihop network for all communications to nodes:

control/management, debugging, application traffic

Plan: Use multihop routing network based on OLSR● 100's of meters range between nodes possible with appropriate antennas● Provide stable communications backplane with IP routing to individual nodes● User applications may implement their own routing protocols directly on 802.11 MAC

CitySense testbed will be timeshared across multiple users● CPU, memory, and radio bandwidth must be shared across applications● While not as limited as motes, this still raises some important resource

management questions● We expect demands on CitySense to vary widely across research groups.


CitySense Plug-and-Play Sensors● On-node software enables easy

addition of new sensors

● Adaptation layer defines a common meta-data for sensors to declare themselves to the shared infrastructure

● Meta-data are used to allocate nodes to applications based upon their sensing requirements

Sensor Adaptation Layer (SAL)

SensorHardware

Vendor-specific sensor API

Device Independent Control API

SensorDescriptionDocument maintains

SensorHardwareSensor

HardwareSensor

Hardware

Sensor Adaptor

CitySense Sensor Data Schema

MeasurementName : StringValue : ObjectUnit : Type

SensorOutputTimestamp : longQueryCommand : StringSampleInterval : int

1..*1..*

SensorDeviceName : StringType : String

1..*1..* Generates


Open ChallengesRemote maintenance and programming

● Physical access to nodes difficult or impossible● Must ensure software can be updated safely● Rollback to known-good “safe mode” if node loses network connectivity

Resource management and sandboxing● CitySense will be open to research community● How to prevent naïve or malicious users from dominating resources?● What are appropriate scheduling policies?

Application programming model● Should we allow arbitrary Linux binaries? Or require users to conform to constrained interface?● What distributed services should the system provide to applications?

Experimental support● Time synchronization, GPS vs. NTP● Distributed control: separate channel for management plane vs. in band

Some non-goals of this project…● Reinvent mesh networking: try to leverage existing solutions● Provide public Internet access: too latency sensitive; not appropriate for multihop mesh


GENI Wireless Research Enabled● Characterize URBAN RF environment: good urban propagation

models do not exist

● Wireless Network Management

● Dynamic RF channel selection


SummaryCitySense presents huge opportunity

for the sensor network community● Develop, deploy, and experiment with sensor networks at scale

in complex real-world outdoor urban environment● Shared research facilities for supporting diverse research groups

Planned 100-node outdoor testbed in Cambridge, MA● Linux-based embedded PCs with 802.11 and professional weather sensor● Planned future sensors include pollution/smog sensors.

For more information:● Josh Bers ([email protected]) and Matt Welsh ([email protected])● http://www.citysense.net


Related Work / FacilitiesWINLab, ORBIT Rutgers [Raychaudhari ]

ENL, USC motes [Govindan]

sMote, Berkeley [Culler]

RoofNET, MIT [Morris, et. al]

U Colorado [Sicker & Grunwald]

Others…

Community networks:

CUWin, Corpus Christie, TEX, etc.


Acknowledgements

BBN● Abhimanyu Gosain, Tufts Intern● Frank Bronzo

Harvard● Amal Fahad● Jon Hyman● Kevin Bombino● Geoff Mainland● Rohan Murty● Matt Tierney


Current Status

BBN Testbed● 3 indoor nodes● 2 outdoors with weather sensors

Node Design ● 2 Prototype designs tested● Working on City approval of streetlight mounted enclosure

Wireless Network● OLSR mesh active● Characterized basic performance

City Streetlight Mounting● Received approval from City of Cambridge


Next Steps

BBN & Harvard Testbeds● Grow size of each testbed to ~ 10 nodes outdoors● Link 2 networks via advantaged nodes

Wireless Network● Characterization:

● Establish performance benchmark suite● Management plane:

● Test high-power, 700 mW, 900 MHz radios (ubiquiti networks)

City Deployment● First Nodes targeted for Summer-Fall ‘07


Preliminary Results: Urban RF ActivityFrom BBN’s rooftop mounted nodes

● Total 5MHz Channels in use: 29 out of 74● 802.11b/g: 11/14● 802.11a: lower 11/40, upper 7/20

● Total devices seen (distinct MAC addresses)● in 15 days: 205● in 12 hours: 25


Collaborators / Target Users

Magid Ezzati: Co-PI Harvard School of Public Health Urban pollution studies

Ken Mandl: Director of CHIP’s program Childrens Hospital, Boston real-time tracking of ER symptom reports

David Gute: Tufts University EE department: water quality sensors

Tom Little: BU EECS: video sensors

Chris Rogers & Marina Bers: Tufts EE: Educational Outreach K-12 curriculum in sensor nets.

CitySense: An Open, Urban-Scale Sensor Network Testbed

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