Low Power, Low Delay: Opportunistic Routing meets Duty Cycling

1. Low Power, Low Delay: Opportunistic Routing meets Duty Cycling Olaf Landsiedel1, Euhanna Ghadimi2, Simon Duquennoy3, Mikael Johansson2 1Chalmers University of Technology, Sweden 2KTH Royal Institute of Technology, Sweden 3Swedish Institute of Computer Science (SICS), Sweden IPSN 2012 Presenter: SY

2. This Paper • Opportunistic Routing for wireless sensor network • Duty cycled nodes • Benefits • Improve energy efficiency • Reduce end-to-end delay • Increase resilience to link dynamics

3. Unicast Routing in Duty‐Cycled WSNs • Routing protocol: selects next hop • MAC: wait for next hop to wakeup • Assume: no synchronization

4. Unicast Routing in Duty‐Cycled WSNs • Routing protocol: selects next hop • MAC: wait for next hop to wakeup • Assume: no synchronization

5. Opportunistic Forwarding • The node that • Wakes up first • Successflly receives the packet • Provides routing progress • Forward the packet

6. Outline • System design • Evaluation • Conclusion

7. DODAG • Topology: DODAG • Destination oriented directed acyclic graph • Requirements of routing metric • Builds loop free DODAG • Minimize energy: radio-on time • Minimize delay

8. Expected Duty Cycled Wakeups (EDC) Single hop EDC • Single hop EDC: 1/(sum of neighbors link quality) • Left case: A has a single neighbor with a perfect link, its single hop EDC is 1/1 = 1; • Right case: A has two neighbors both having perfect links, its single hop EDC is 1/(1 + 1) = 0:5; • Middle case: A has two neighbors with link qualities 1 and 0.25. Its single hop EDC is 1/(1 + 0:25) = 0:8. Link quality

9. Overall EDC EDC of neighbor Single hop EDC • Overall EDC • Sum of single hop EDC and neighbors’ EDC • Which neighbors to include? • Forwarder set Weight

10. Forwarders Set • Sort neighbor nodes by EDC • Add one by one (from lowest) • Find minimum EDC

11. Forwarding Cost • Forwarding cost w • Constant value, transmission penalty • Increase w decrease forwarders set • Fewer hops to destination • Increase delay and energy consumption • Too low: increase the risk of routing loop • To balance delay and energy with routing progress and stability

12. Link Estimation • Link quality = (Rate of packet overheard)/(forwarding rate) • Rate of packet overheard • Wakeup, listen to the radio, record packet overheard • Forwarding rate • Header field contain the average forwarding rate • Bootstrap • Probing during initialization

13. Unique Forwarder • Make sure only one node forward the packet • Majority of cases  only one receiver

14. Unique Forwarder – Cont. • Coordination algorithm • Demand a single ACK • If (sender) receives multiple ACK • Resend the packet • If (receiver) detect link-layer duplicate • Send second ACK with 50% probability • Data transmission overhearing • If overhears same packet, cancels transmission • Network-layer duplication detection • Detect duplication at network layer

15. Outline • System design • Evaluation • Conclusion

16. Setup • Testbed • Indriya(Singapore): 120 nodes • Twist(Berlin): 96 nodes • Compare • CTP • Metrics • Delay, Duty cycle, # of TX nodes, Reliability • Implementation • TinyOS, default MAC • Wakeup every 2s (optimal for CTP) • Randomly generate a packet every 4 minutes

17. System Calibration • Choose w=0.1

18. Indriya, 0 dBmTx Power

19. Indriya, -10 dBmTx Power

20. Twist, 0 dBmTx Power

21. Impart of Churn • Remove average 10 nodes every 15 minutes • Reduce from 120 to 30 nodes

22. Convergence

23. Wakeup Interval

24. Outline • System design • Evaluation • Conclusion

25. Discussion And Limitation • Works best at high network density • Optimal at lower wakeup rates • Compare to CTP • At high wakeup rate • CTP and ORW are similar • Not well suited for high throughput applications

26. Conclusion • New routing metric • Taken energy into account • Real implementation • Previous works mostly analytical and simulation • Paper writing • A bit harder to get the big picture