Exploring the Design Space of Sensor Networks Using Route-aware MAC Protocols

Injong Rhee and Bob Fornaro

Department of Computer ScienceNorth Carolina State University

Motivation and Goal

Expanding design spaceUnder extremely low energy budget

Existing Sensor MACProtocols

New MAC schemes

Our approach: Route-aware MAC (RASMAC)

On-demand routing paradigm (Directed diffusion, SPIN, etc)Route-awareness: the MAC layer of a node knows whether it is on a “currently active routing path” or not.

If not on such a path, it switches off its radio.Reduce idle listening

SINK

Power consumption of node subsystems

0

5

10

15

20

Power (mW)

TDMA + Contention-based MAC

Can we try to merge them together?Contention-based (802.11)

Fast, but under high contention, low throughput

TDMA Under low contention, slowTime synchronizationNot scalable schedulingNot good for changes and mobilityBut, under high contention, high throughput and fair

Testbed: Wildlife trackingEndangered animals in NC (Red wolves, black bears, etc.)Current telemetry techniques are not adequate.Sensor networks can improve monitoring of these animalsOur teams have been working with wildlife biologists and NC zoology association on this project.

Lab Testbed

Testbed with 100 sensor nodes spread around a building in NCSU

Study networking issuesCongestion controlMACRouting issues.Applications: tracking, monitoring

Not just for sensor networks, but general enough to study ad hoc, wireless mesh networks.

Route-aware MAC (RASMAC)If off, how does it know of a new active path?

Software: Periodic synchronizationHardware: passive radio-powered trigger

Decoupling of throughput and response time.

Periodic synchronization (Response time)Wake-up time duration (or frequency) while on active paths (Throughput)

Performance results:Route-aware MACs

RA-TDMA:Extremely low Energy budget

ExistingMAC

RA-SMAC:Low energy budget

c

Design choices :Existing approaches

802.11Good serviceHigh energy

TDMA:Good serviceMedium energy

SMAC:Tradeoff(coupling ofThroughput andResponse time)