1. 1 O-MAC: A Receiver Centric Power Management Protocol Hui Cao, *Kenneth W. Parker, Anish Arora The Ohio State University, *The Samraksh Company

2. 2 Outline 1. Receiver centric design 2. Energy efficiency comparison 3. O-MAC protocol design

3. 3 Part I: Receiver Centric Design

4. 4 Dominant Receiver Power Consumption Large portion of energy is consumed in receiver radio One typical surveillance application: Receiver Radio ~2100 J/day Signal processing ~60 J/day Everything else ~8 J/day

5. 5 Increasing Rx Power Consumption Rx becomes higher than Tx! with evolution of Berkeley motes Other popular radio chips also have higher Rx power consumption

6. 6 Receiver Centric vs. Transmitter Centric Transmitter Centric MAC design: Transmitter implicitly knows receiver will wakeup during transmission Collision avoidance is transmitter driven (i.e., RTS-CTS, CCA) Receiver Centric MAC design: Receiver explicitly communicates its wakeup schedule to transmitter Collision avoidance is receiver driven (i.e., receivers use TDMA) Transmitter Receiver Transmitter Receiver Transmitter Receiver

7. 7 Why Receiver Centric Design? We claim: Receiver Centric approach yields substantially higher Receiver Efficiency Receiver Efficiency ≈Total Energy Efficiency ≠ Transmitter Efficiency Receiver Efficiency = Goodput Receiver Power Consumption Transmitter Efficiency = Goodput Transmitter Power Consumption Total Energy Efficiency = Goodput Transmitter + Receiver Power Consumption Historically, MAC design has focused on Transmitter Efficiency However, dominant cost of receiver radio has implied that

8. 8 Part II: Energy Efficiency Comparison

9. 9 Assumptions and Notations Traffic model Uniform random traffic Notations: E : energy efficiency Goodput (Msgs Sent + Receive) Total (Msgs Sent + Receive)

10. 10 Theoretical Energy Efficiency We’ll consider: Synchronous Blinking (S-MAC, T-MAC) Long Preamble (B-MAC, WiseMAC) Asynchronous Wake-up Random Time-Spreading Staggered On Pseudo-random Staggered On

11. 11 1)Synchronous Blinking (e.g. S-MAC & T-MAC)  : number of interfering nodes

12. 12 2) Long Preamble (e.g. B-MAC, WiseMAC)  : duty cycle

13. 13 3) Asynchronous Wakeup  : duty cycle

14. 14 4) Random Time Spreading In each time slot, each node wakes up randomly No time sync Power efficiency:  : duty cycle  : number of interfering nodes

15. 15 5) Staggered On Only one receiver wakes up in the interference region at one time Scheduled globally to avoid receiver collision

16. 16 6) Pseudo-random Staggered On r is a factor near 1

17. 17 Energy efficiency comparison

18. 18 Part III: O-MAC Protocol Design

19. 19 O-MAC Protocol Design Based on: Pseudo-random Staggered On The Core Protocol Interfaces Neighbor list Send Receive Synchronous ACK Pseudo-random Scheduler

20. 20 O-MAC Analysis and Simulation 1.Simulation confirms theoretical analysis 2.Maximal energy efficiency for particular traffic load!  Adaptive duty cycle

21. 21 O-MAC Key Implementation Issues Time Synchronization Current technique: < 10 PPM Every 2 minutes, to guarantee 1ms accuracy Cost: 0.001% duty cycle Adaptive Duty Cycle A cross layer design issue Sender Centric Application Receiver Centric Communication

22. 22 Conclusion and Future work Conclusion: Receiver Centric has substantial impact on power management Receiver vs. Transmitter Collision Avoidance OMAC has been implemented and is being integrated for mobile sensor network experiments on Dec.7 at OSU Future work: Receiver Centric higher layer protocol (Network, Transport, Application) Adaptive duty cycle scheme