CMPSCI 791L: Sensor Networks

Experiences Building a Experiences Building a Real Distributed Sensor Real Distributed Sensor

NetworkNetwork

Victor R. LesserVictor R. Lesser

Computer Science DepartmentComputer Science DepartmentUniversity of Massachusetts, AmherstUniversity of Massachusetts, Amherst

September 12, 2003September 12, 2003

AcknowledgementsAcknowledgements

Bryan HorlingBryan Horling Roger MaillerRoger Mailler Jiaying ShenJiaying Shen Dr. Regis Vincent (SRI)Dr. Regis Vincent (SRI)

http://mas.cs.umass.edu/~bhorling/papers/02-14.ps.gzhttp://mas.cs.umass.edu/~bhorling/papers/02-14.ps.gz http://mas.cs.umass.edu/~bhorling/papers/00-49.ps.gzhttp://mas.cs.umass.edu/~bhorling/papers/00-49.ps.gz

OutlineOutline An example DSN problemAn example DSN problem Issues in Distributed Resource Issues in Distributed Resource

AllocationAllocation An example of one approachAn example of one approach

Distributed Sensor Network Distributed Sensor Network Challenge ProblemChallenge Problem•Small 2D

Doppler radar units (30’s)

– Scan one of three 120 sectors at a time

• Commodity Processor associated with each radar

•Communicate short messages using one of 8 radio channels

•Triangulate radars to do tracking

Representative of Representative of Distributed Sensor Distributed Sensor

Network IssuesNetwork Issues Need for Coordination/Distributed Need for Coordination/Distributed

Resource AllocationResource Allocation Multiple sensors need to collaborate on Multiple sensors need to collaborate on

taskstasks View objects of interest from multiple angles with View objects of interest from multiple angles with

different types of sensorsdifferent types of sensors Sensing time windows need to be closely alignedSensing time windows need to be closely aligned

Environmental DynamicsEnvironmental Dynamics Sensor configuration changes as target movesSensor configuration changes as target moves

Potential for Resource OverloadsPotential for Resource Overloads Multiple target in overlapping sensor regionsMultiple target in overlapping sensor regions Limited Communication ChannelsLimited Communication Channels

Representative of DSN Issues, Representative of DSN Issues, cont.cont.

Soft Real-timeSoft Real-time Limited time window for sensingLimited time window for sensing Must anticipate where target is moving in order to Must anticipate where target is moving in order to

effectively allocate sensor resourceseffectively allocate sensor resources Time for coordination affects time for sensingTime for coordination affects time for sensing

Distribution: communication latency/limited Distribution: communication latency/limited bandwidth precludes global knowledge/controlbandwidth precludes global knowledge/control distributed data fusiondistributed data fusion

Scalability: need to be able to handle large Scalability: need to be able to handle large numbers of sensor nodesnumbers of sensor nodes

Robustness: local failures should not induce Robustness: local failures should not induce global collapseglobal collapse Handle uncertain information, Handle uncertain information,

sensor/processor/communication failuressensor/processor/communication failures

Real-Time Tornado Real-Time Tornado TrackingTracking

supercomputers

Internet2

radar

Fractional T1 (100K)

802.11b (0,1,2,4Mb)

Legend

Weather/Computation/Weather/Computation/Sensor Integrated ControlSensor Integrated Control

radars signalprocessing

QualityControl(clutter removal,

de-aliasing)

HazardousWeather Detection algorithms

Retrieval of3D wind,

other fields

Assimilation, Multiple Doppleranalysis (more

Compete gridding

Determine initial conditions for

near-term dynamic forecasting models

(NWP)

Resource databaseweather-algorithm-provided

utility functions

Control:what to sense,

when

How to Allocate How to Allocate Processing/Sensing Processing/Sensing

TasksTasks Avoid processing overloadsAvoid processing overloads Avoid communication overloadsAvoid communication overloads Have information/processing co-locatedHave information/processing co-located Avoid failure of network based on single Avoid failure of network based on single

location failurelocation failure Allocate sensing so that as many targets Allocate sensing so that as many targets

can be tracked with reasonable fidelitycan be tracked with reasonable fidelity Allocate processing/sensing so that real-Allocate processing/sensing so that real-

time constraints can be mettime constraints can be met

Additional QuestionsAdditional Questions What tasks can be assigned statically What tasks can be assigned statically

which have to be dynamically which have to be dynamically allocatedallocated

When do static and dynamically made When do static and dynamically made decisions need to be revisiteddecisions need to be revisited

What is the appropriate context for What is the appropriate context for making these decisionmaking these decision What decisions can be made locallyWhat decisions can be made locally What decisions need to made with in a What decisions need to made with in a

non-local contextnon-local context Is this context fixed or dynamically evolvedIs this context fixed or dynamically evolved

Sensor Processing IssuesSensor Processing Issues

Integrating Target Acquisition with Integrating Target Acquisition with Target TrackingTarget Tracking Re-acquiring lost targetsRe-acquiring lost targets

Data-Correlation IssuesData-Correlation Issues Recognizing which data belongs to which Recognizing which data belongs to which

targettarget Handling Uncertainty in Sensor Handling Uncertainty in Sensor

InformationInformation How to make resource allocation issues in How to make resource allocation issues in

face of faulty sensor dataface of faulty sensor data

Tasks, Processes and Tasks, Processes and AgentsAgents

Issue of Autonomy -- Locus of ControlIssue of Autonomy -- Locus of Control How much leeaway is allowed in what How much leeaway is allowed in what

goals to pursue, how to do them, who goals to pursue, how to do them, who to interact with, what resources to to interact with, what resources to use, …use, … Where are these decisions being madeWhere are these decisions being made How decentralized are these decisionsHow decentralized are these decisions How dynamic/context-dependent these How dynamic/context-dependent these

decisions aredecisions are

Soft vs. Hard Real-TimeSoft vs. Hard Real-Time

There are There are notnot catastrophic effects if catastrophic effects if events are occasionally not events are occasionally not interpreted correctlyinterpreted correctly If lose sight of target for a few time steps If lose sight of target for a few time steps

and then reacquire generally okayand then reacquire generally okay

Computation/Sensing after the Computation/Sensing after the deadline may still have some valuedeadline may still have some value Reduction in certainty of target locationReduction in certainty of target location

How to Evaluate a Sensor How to Evaluate a Sensor NetworkNetwork

Communication LocalityCommunication Locality Information and Processing BottlenecksInformation and Processing Bottlenecks Organizational Control OverheadOrganizational Control Overhead Overall EffectivenessOverall Effectiveness …………..

What’s Best --What’s Best --Multi-attributed Evaluation?Multi-attributed Evaluation?

One Approach from an MAS One Approach from an MAS perspectiveperspective

Decompose environment to form a Decompose environment to form a partitioned partitioned organizationorganization.. Each partition (sector) will contain a set of sensor nodes, Each partition (sector) will contain a set of sensor nodes,

each with its own controlling agent.each with its own controlling agent. Individual sectors are relatively autonomous.Individual sectors are relatively autonomous.

Specialize members of the agent population to Specialize members of the agent population to dynamically take on multiple, differentdynamically take on multiple, different goals/roles.goals/roles. Individual agents become “managers” of different Individual agents become “managers” of different

aspects of the problem.aspects of the problem. Managers form high-level plans to address their Managers form high-level plans to address their

goals, and negotiate with other nodes to achieve goals, and negotiate with other nodes to achieve themthem..

Sectored-Based Agent Sectored-Based Agent OrganizationOrganization

Agents Multiplex among Different rolesAgents Multiplex among Different roles

Sector Manager

Tracking Manager

Tracking Agent

Scanning Agent

Organizationally-Structured Organizationally-Structured Communication among Communication among

AgentsAgents DrADrQ

DrRTBRRTDPTCRBPCDATBUES

Sector Manager

Tracking Manager

Scanning Agent

Tracking Agent

Managing Conflicted Managing Conflicted Resources:Resources:

Sensors, Processors, Sensors, Processors, CommunicationCommunication SensorsSensors

Conflicting Scanning Tasks from different Sector ManagersConflicting Scanning Tasks from different Sector Managers Locally resolved by agent connected to sensor -- SRTA agentLocally resolved by agent connected to sensor -- SRTA agent

Tracking Tasks wanting same sensor resourcesTracking Tasks wanting same sensor resources Negotiation among track managers -- SPAM protocolNegotiation among track managers -- SPAM protocol

CommunicationCommunication Communication Degradation due to lack of LocalityCommunication Degradation due to lack of Locality

Track manager migration among sectorsTrack manager migration among sectors Communication Channel OverloadCommunication Channel Overload

Sector manager assignment of track manager rolesSector manager assignment of track manager roles ProcessorsProcessors

Data Fusion Overload/Knowledge localityData Fusion Overload/Knowledge locality Sector manager assignment of data fusion/track manager rolesSector manager assignment of data fusion/track manager roles

Multiplexing Roles -- SRTA agentMultiplexing Roles -- SRTA agent

Centralizing Information in Centralizing Information in Sector ManagerSector Manager

Handling Data Correlation with Multiple Handling Data Correlation with Multiple TracksTracks

Targets are represented by uncertainty boundsTargets are represented by uncertainty bounds Bounds are affected by speed of target and age of supporting Bounds are affected by speed of target and age of supporting

measurementsmeasurements Bounds are shared with sector manager, who in turn shares them with Bounds are shared with sector manager, who in turn shares them with

other track managersother track managers Sector managerSector manager

Uses target uncertainty bounds to determine if new target detections Uses target uncertainty bounds to determine if new target detections (from scanning) are known targets(from scanning) are known targets

Data from known target detections are used to focus attention of Data from known target detections are used to focus attention of relevant track managerrelevant track manager

Track managersTrack managers Uses amplitude lobe intersections to estimate position in times of needUses amplitude lobe intersections to estimate position in times of need Prevents data fusion if estimated resolved position is within another Prevents data fusion if estimated resolved position is within another

target’s boundstarget’s bounds Throws out ambiguous measurements which intersect another target’s Throws out ambiguous measurements which intersect another target’s

boundsbounds

Fault ToleranceFault Tolerance Node information is propagated through the Node information is propagated through the

use of directory services (x, y, orientation, etc.).use of directory services (x, y, orientation, etc.). Sensors provide sector managers with their Sensors provide sector managers with their

information.information. Track managers query sector managers for sensor Track managers query sector managers for sensor

details.details. This information is cached for future use at each This information is cached for future use at each

stepstep The directory held in sector manager maintains The directory held in sector manager maintains

historical query informationhistorical query information New data are analyzed for relevance to those queriesNew data are analyzed for relevance to those queries Relevant information is automatically propagated to Relevant information is automatically propagated to

the query sourcethe query source This process quickly updates agents’ beliefs, This process quickly updates agents’ beliefs,

allowing them to adapt to changeallowing them to adapt to change

Major Issues in This Major Issues in This ApproachApproach

What is an appropriate organization for What is an appropriate organization for agentsagents Scalability and RobustnessScalability and Robustness Self-Organization and AdaptationSelf-Organization and Adaptation

What is the protocol for distributed What is the protocol for distributed resource allocationresource allocation Soft Real-Time, Graceful Degradation, EfficientSoft Real-Time, Graceful Degradation, Efficient

What is the structure of an agent What is the structure of an agent architecture that supportsarchitecture that supports Agents functioning in an organizational contextAgents functioning in an organizational context Agents implementing complex distributed Agents implementing complex distributed

resource protocols resource protocols Agents operating under soft real-time constraintsAgents operating under soft real-time constraints

Some Final ThoughtsSome Final Thoughts Can not isolate one set of issues from Can not isolate one set of issues from

anotheranother Strict layering of issues does not seem to Strict layering of issues does not seem to

workwork

There is no one best approachThere is no one best approach Very sensitive to characteristics/capabilities Very sensitive to characteristics/capabilities

of sensors, quality of sensor data, the of sensors, quality of sensor data, the character of required sensor fusion, amount character of required sensor fusion, amount and type of processing required, system and type of processing required, system objectives, communication and processing objectives, communication and processing capabilities, environment …capabilities, environment …