A Case for Resource Heterogeneity in Large Sensor Networks

Srikanth KandulaMIT

IEEE MILCOMNov 1, 2004

with Jennifer Hou, Lui Sha (UIUC)

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Blindly suppressing alerts is bad

Dissemination Trees process alerts at intermediate sensors?• may not see all alerts• may not have cpu/memory to correlate

Problem

Need dedicated entities that process sensor data close to point of origin

Need dedicated entities that process sensor data close to point of origin

Lot of energy wasted in forwarding alerts

Increased wireless collisions

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Resource-rich Accumulator

HowTo co-ordinate and control sensors using a random deployment of accumulators?

HowTo co-ordinate and control sensors using a random deployment of accumulators?

Resource-Heterogeneous networks

Tunnelled Digest

Also provides fine-grained control Serve as a spine for the n/w

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Accumulator-centered clusters

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Accumulator-centered clusters

Cluster sensors around closest accumulator Many sizes Multiple hops

An overlay of accumulators

Digests are routed along the overlay

Tunneled Path

Improves network lifetime and goodput of updatesImproves network lifetime and goodput of updates

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Accumulator centered clusters– Level 1

Cluster sensors around closest accumulator Clusters vary in size Multiple hops

An overlay of accumulators

Digests are routed along the overlay

Tunneled Path

How to efficiently form these clusters?How to efficiently form these clusters?

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Contributions

Detailed design of a sensor n/w architecture hinged on resource-rich nodes

Protocols for efficient clustering and routing

Demonstrate several distinct benefits through ns2 simulations

Identify opportunities for load-sensitive routing

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Talk Outline

Internal structure of Level-1 Clusters

Hop-by-hop forwarding of join messages

Routing

Results

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Level-0 Hexagonal Cells

Idle radios consume power

Only the leader of a cell forwards traffic

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Level-0 Hexagonal Cells

Idle radios consume power

Only the leader of a cell forwards traffic

Leadership exchanged among all nodes in a cell

Cell size chosen to maintain connectivity

Note: Equivalent Level-0 clusters e.g. SPAN can be used instead

Level-0 clusters save power! Level-0 clusters save power!

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Talk Outline

Internal structure of Level-1 Clusters

Hop-by-hop forwarding of join messages

Routing

Results

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Accumulator Broadcasts join messages

One hop to accumulator A1

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Grids store back-pointer to parent

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Back-pointer to parent cell

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Join messages are re-broadcast!

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Two hops to accumulator A1

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Join messages are re-broadcast!

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Two hops to accumulator A1

Join messages to parent’s neighbors will propagate errors

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Controlled Broadcast - 1

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Two hops to accumulator A1

Suppress Join messages to

neighbors of parent

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Controlled Broadcast - 2

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Suppress Join messages to a neighbor if there is a common neighbor of smaller hop count

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Controlled Broadcast - 2

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Three hops to accumulator A1

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BGP Inefficiencies

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Controlled Broadcast

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Three hops to accumulator A1

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Multiple paths

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A cell may have multiple parents

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Multiple paths

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Multiple dis-joint paths exist!

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Level-1 cluster boundary

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One hop to accumulator A2

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Level-1 cluster boundary

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Two hops to accumulator A2

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Level-1 cluster boundary

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Cell changes allegiance!

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Level-1 cluster boundary

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Three hops to accumulator A2

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Boundary notification

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Negative Ackx hops from A1

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Boundary notification

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Negative Ack:x hops from A1

Border Cell:3 hops to A2

Border Cell:3 hops to A1

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Level-1 Cluster formation: Summary

Controlled broadcast of join messages Naïve O(N^2) O(N) messages, N = # of cells

Routing information piggybacks over join messages Multiple paths from a cell to closest accumulator Multiple paths between adjacent accumulators

Join broadcasts are periodically repeated Join messages route around holes

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Talk Outline

Internal structure of Level-1 Clusters

Hop-by-hop forwarding of join messages

Routing

Results

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Sensor Alerts Accumulator

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1Sensor forwards alert to cell

leader

Alert follows parent pointers back to the

accumulator

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Accumulator Accumulator Sink

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Accumulator forwards digests to some border

cellDigest crosses the border

and follows parent pointers

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Accumulator Accumulator Sink

Accumulators run OSPF on the overlay

Pick one of many paths

Improved resilience

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Talk Outline

Internal structure of Level-1 Clusters

Hop-by-hop forwarding of join messages

Routing

Results

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Power Savings – CDF of remaining power

Pro

babi

lity

Remaining Power (J)

Homogenous Network

Heterogeneous Clusters

Sensors that generate updates gain a little due to decreased forwarding

load

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Power Savings – CDF of remaining power

Pro

babi

lity

Remaining Power (J)

Homogenous Network

Heterogeneous Clusters

Long-haul sensors gain more due to

decrease in forwarded traffic

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Power Savings – CDF of remaining power

Pro

babi

lity

Remaining Power (J)

Homogenous Network

Heterogeneous Clusters

Idle sensors gain a lot by turning off their radios

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Improvement in GoodputF

ract

ion

of U

pdat

es R

ecei

ved

Duration between generation of updates (s)

14 accum

Zero accum

500 sensors spread over 4sq-km

357 Cells, 15 CBR sources

A small number of accumulators is enough to improve goodput

significantly

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Improvement in GoodputF

ract

ion

of U

pdat

es R

ecei

ved

Duration between generation of updates (s)

14 accum

Zero accum

500 sensors spread over 4sq-km

357 Cells, 15 CBR sources

More accumulators are needed when updates are generated

faster

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Reduction in join message overheadT

otal

num

ber

of jo

in m

essa

ges

Number of Accumulators

Naïve Algo.

Controlled Broadcast

Significantly reduces # of join messages when clusters are

large

500 sensors spread over 4sq-km

357 Cells

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Reduction in join message overheadT

otal

num

ber

of jo

in m

essa

ges

Number of Accumulators

Naïve Algo.

Controlled Broadcast

Slightly beneficial even when

Level-1 clusters are small

500 sensors spread over 4sq-km

357 Cells

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Related Work

We explore the use of heterogeneous sensors in designing better dissemination trees.

Clustering and Routing in Sensor Networks Geographic Area Forwarding (GAF), SPAN, k-

cluster based routing, ZRP, Spine, Min-ID/Max degree

Dissemination Trees in sensor networks Diffusion, TTDD

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Conclusion

A small number of resource-rich sensors Improve network lifetime Improve goodput of updates Provide fine-grained control

Hierarchical clusters to use resource-rich sensors can be built efficiently

Scope to design robust routing protocols – more work to be done!

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Questions?