1 / 46

Power Saving and Clock Sync

Power Saving and Clock Sync. Ten H. Lai. Problem, Problem, Problem!. ???. Energy Efficiency. Done at every level from physical to application. Energy-efficient routing. Energy-efficient MAC. Energy-efficient everything. Power Saving at MAC Layer. Beacon interval. awake sleep.

roanna-cox
Download Presentation

Power Saving and Clock Sync

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Power Saving and Clock Sync Ten H. Lai

  2. Problem, Problem, Problem! ???

  3. Energy Efficiency • Done at every level from physical to application. • Energy-efficient routing. • Energy-efficient MAC. • Energy-efficient everything.

  4. Power Saving at MAC Layer Beacon interval awake sleep Beacon window ATIM window

  5. Time Sync Is Necessary/Important • Really? • What if it is difficult or impossible to synchronize clocks?

  6. To sync or not to sync? • Yes global synchronization • Nono synchronization • Partially local synchronization

  7. No Synchronization (0) • “Power-Saving Protocols for IEEE 802.11-BasedMulti-Hop Ad Hoc Networks” • INFOCOM 2002 • Y.C.Tseng, C.S. Hsu, T.Y. Hsieh • NCTU

  8. No Synchronization (1) • Basic idea: nodes be awake more frequently. • Extreme case: awake all the time. Beacon interval awake sleep

  9. No Synchronization (1) • Dominating-Awake-Interval • Awake ≥ BI/2 + BW Beacon interval awake sleep

  10. No Synchronization (1) • Dominating-Awake-Interval • Awake > BI/2 + BW Beacon interval awake sleep

  11. No Synchronization (2) • Periodical-Fully-Awake-Interval

  12. No Synchronization (2) • Quorum-based 1 4 16 1 4 16 1 2 3 4 • 2 3 4 • 6 7 8 • 10 11 12 • 13 14 15 16 5 6 7 8 • 10 11 12 • 13 14 15 16

  13. Local Synchronization (0) • “An Energy-Efficient MAC Protocol for WirelessSensor Networks” • INFOCOM 2002 • W. Ye, J. Heidemann, D. Estrin • UCLA

  14. Local Synchronization (1) • Offset 10:10 10:04 -0:01 0:05 0:01 10:09 - 0:05

  15. Local Synchronization (2) • Nodes of same color -- synchronize with each other. • Nodes of different colors – know each other’s timing

  16. Local Synchronization (3) A B C

  17. Problem, Problem, Problem! Power saving ??? Physical MAC Routing Awake-sleep Global no partial sync Analysis & Comparison Clock Sync

  18. To sync or not to sync? • Yes (global sync) • No (no sync) • Partially (local sync) • Which one?

  19. Analysis of energy saving (1) • No data traffic • Parameters

  20. Analysis of energy saving (2)

  21. Global Synchronization: pros and cons • Best performance in energy saving • Needs a good synchronization algorithm

  22. No Synchronization – pros and cons • Simple -- no need for clock sync • Less efficient in power saving 1 4 16 1 4 16

  23. No Synchronization: Analysis • A has a packet for B in interval 4. • Q: When should A send it? • In every yellowinterval • Or when yellow meets red. • Q: When will yellowmeetred  ? 1 4 16 1 4 16

  24. The Wisdom of Diamond Sutra • No synchronization, is not reallyno synchronization,it is just called no synchronization.

  25. No Synchronization – pros andcons • Less efficient in power saving • Simple -- no need for clock sync • Simpler – clock sync is simpler and more scalable ? 1 4 16 1 4 16

  26. Time Sync in the “No Sync” Scheme • Why is it simpler, more scalable? Beacon window ATIM window

  27. A major drawback with no sync • Broadcast/multicast is inefficient

  28. Local Synchronization: prosand cons • More scalable • Inefficient with multiple schedules • Protocols incomplete • Broadcast/multicastis inefficient?

  29. To sync or not to sync? • Yes (global sync) • No (no sync) • Partially (local sync) • Which one? Normal situation Neighbor discovery Transient situation All of them

  30. Possible Protocol • Normally, use the global sync scheme. • Switch to the no sync scheme when necessary (for neighbor discovery). • Use the partial sync scheme while merging. ?

  31. Problem, Problem, Problem! Power saving ??? Physical MAC Routing Awake-sleep Global no partial sync Analysis & Comparison Clock sync

  32. Follow-ups on no-sync • “Asynchronous Wakeup for Ad Hoc Networks,” Mobihoc’03 • “Quorum-Based Asynchronous Power-Saving Protocols for IEEE 802.11Ad Hoc Networks,” ICPP’03(Best paper award)

  33. No Synchronization • Quorum-based 1 4 16 1 4 16 1 2 3 4 • 2 3 4 • 6 7 8 • 10 11 12 • 13 14 15 16 5 6 7 8 • 10 11 12 • 13 14 15 16

  34. T = {0, 1, …, n-1} • Quorum: a subset of T • View T as a matrix and pick a row and a column as the quorum • Property A: No matter how asynchronous, every two nodes have at least one overlap in every T intervals. 0 3 15 0 3 15

  35. Desired Property for the Power Saving Problem • Property PSP: No matter how asynchronous, every node’s beacon window is covered by every other node’s active period at least once per T intervals. 0 3 15 0 3 15

  36. Questions • Feasible quorum systems: quorum systems with Property PSP. • How tocharacterize all feasible quorum systems? • Any optimal feasible quorum system? • What if we want to have m overlaps?

  37. Feasible Quorum System • A sufficient condition (rotation closure property): For any two quorums A, B in the system, A ∩ rotate (B, i) ≠ Φ 0 3 15 0 3 15 0 3 15

  38. Quorum Size • T = {0, 1, …, n-1} • Quorum: the smaller, the better (energy efficient) • Closure property |quorum| ≥ √n

  39. Specific Feasible Quorum Systems • Grid Quorum System (≈2√n) • Torus Quorum System (≈√2n ) • Cyclic Quorum System (≈√n) • Finite Projective Plane Quorum System (≈√n)

  40. Quorum Systems with a Single Quorum • T = {0, 1, …, n-1}. H is a subset of T. • {H} is a quorum system iff … H is a difference set of T. • H is a difference set of T iff for every i in T, i = x-y mod n for some x, y in H. • {0, 1, 2, 4} is a difference set of {0,1, …, 7}.

  41. Quorum Systems with multiple overlaps • E-Torus Quorum System • e-torus(k1) and e-torus(k2) have (k1+k2)/2 overlaps. • Can be used to dynamically adjust the number of overlaps.

  42. K=4

  43. Problem, Problem, Problem! Power saving ??? Physical MAC Routing Awake-sleep S-MAC Global no partial sync Analysis & Comparison Clock sync

  44. S-MAC: an energy-efficient MAC • In IEEE INFOCOM 2002, • By Ye, Heidemann, Estrin • IEEE 802.11-like • CSMA/CA

  45. 802.11 MAC S-MAC RTS(t1) DATA(t3) A B C CTS(t2) ACK Back off Turn

  46. What’s next? Power saving ??? Physical MAC Routing Awake-sleep(802.11) S-MAC Global no partial sync Analysis & Comparison Clock sync

More Related