Problem Tiny low-power devices for sensing environment

1. DuraNet: Energy-Efficient Durable Slot-Free Power Scheduling Terence Tong, David Molnar, and Alec Woo UC-Berkeley • Goals • Energy conservation • Minimize idle listening • Reliable • Issues • Density, Scale, Clock skew, Joins / Leave • Queue Overflow, Aggregation • Simple • Distributed, Low memory footprint • Protocol Details • Sync Phase • Schedule Negotiation • Hidden Node Problem, Backoff on RTS • Buffer Queue Problem, RTS/CTS abort • Sequence Number Protocol • Backoff • Additive, Wait Queue Heuristic • Data Phase • Media Access: No backoff CSMA • Time Sync on ACK • Adaptivity / Recovery • Base Station Failure Detection • Low power listen fallback • Could add announcement channel • Problem • Tiny low-power devices for sensing environment • Data collection, Pursuer/Evader applications • Berkeley Mica2 mote platform • 8-bit 8MHz Atmel processor, ChipCon 1000 radio • Must conserve energy and extend battery lifetime • 2 AA batteries = 2000 mAh, lasts for ~7days if node leaves idle • Can’t replace batteries every 7 days • Schedule Negotiation • DuraNet Phases • Route Phase: routing layer figures out a good tree • Sync Phase: parent and children agree when to send • Data Phase: nodes wake up to listen and send periodically • Local fix-up and Restart cycle • Simulation Methodology • TOSSIM, TinyOS 1.1 w/Blast routing • Fixed MT topology on grid • Periodic synthetic workload C->P: Blah Blah Blah P->C: ACK C: Let’s Talk P: Come by 6 everyday • Conclusions • Can build near-optimal schedules at low cost • Overall savings depends on schedule durability • Increase durability with parent ACK • Factors affecting durability • Clock Skew – do time sync in ACK • Link Reliability – retransmit • Interference Neighborhood Change • Need experiment to determine real rate of change