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Quorum-Based Asynchronous Power-Saving Protocols for IEEE 802.11 Ad Hoc Networks

Quorum-Based Asynchronous Power-Saving Protocols for IEEE 802.11 Ad Hoc Networks. Presented by Jehn-Ruey Jiang Department of Computer Science and Information Engineering National Central University. To Rest, to Go Far!. Outline. IEEE 802.11 Ad hoc Network Power Saving Problem

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Quorum-Based Asynchronous Power-Saving Protocols for IEEE 802.11 Ad Hoc Networks

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  1. Quorum-Based Asynchronous Power-Saving Protocols forIEEE 802.11 Ad Hoc Networks Presented by Jehn-Ruey Jiang Department of Computer Science and Information Engineering National Central University

  2. To Rest, to Go Far!

  3. Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion

  4. Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion

  5. IEEE 802.11 Overview • Approved by IEEE in 1997 • Extensions approved in 1999 • Standard for Wireless Local Area Networks ( WLAN )

  6. IEEE 802.11 Family(1/2) • 802.11a:6 to 54 Mbps in the 5 GHz band • 802.11b (WiFi, Wireless Fidelity):5.5 and 11 Mbps in the 2.4 GHz band • 802.11g:54 Mbps in the 2.4 GHz band

  7. IEEE 802.11 Family(2/2) • 802.11c: support for 802.11 frames • 802.11d: new support for 802.11 frames • 802.11e: QoS enhancement in MAC • 802.11f: Inter Access Point Protocol • 802.11h: channel selection and power control • 802.11i: security enhancement in MAC • 802.11j: 5 GHz globalization

  8. IEEE 802.11 Market Source: Cahners In-Stat ($ Million)

  9. Infrastructure vs Ad-hoc Modes infrastructure network AP AP wired network AP Multi-hop ad hoc network ad-hoc network ad-hoc network

  10. Ad hoc Network Applications • Battlefields • Disaster rescue • Spontaneous meetings • Outdoor activities

  11. Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion

  12. Power Saving • Battery is a limited resource for portable devices • Battery technology does not progress fast enough • Power saving becomes a critical issue in MANETs, in which devices are all supported by batteries

  13. Solutions to Power Saving • PHY Layer: transmission power control • Huang (ICCCN’01), Ramanathan (INFOCOM’00) • MAC Layer: power mode management • Tseng (INFOCOM’02), Chiasserini (WCNC’00) • Network Layer: power-aware routing • Singh (ICMCN’98), Ryu (ICC’00)

  14. Transmission Power Control • Tuning transmission energy for higher channel reuse • Example: • A is sending to B (based on IEEE 802.11) • Can (C, D) and (E, F) join? No! Yes! B C D A E F

  15. Power Mode Management • doze mode vs. active mode • Example: • A is sending to B • Does C need to stay awake? No! It can turn off its radio to save energy! B But it should turn on its radio periodiclally for possible data comm. A C

  16. + – + – + – + – + – + – Power-Aware Routing • Routing in an ad hoc network with energy-saving (prolonging network lifetime) in mind • Example: N2 N1 SRC DEST Better!! N3 N4

  17. Our Focus • Among the three solutions: • PHY Layer: transmission power control • MAC Layer: power mode management • Network Layer: power-aware routing

  18. IEEE 802.11 PS Mode(2/2) • Environments: • Infrastructure (O) • Ad hoc (infrastructureless) • Single-hop (O) • Multi-hop

  19. IEEE 802.11 PS Mode(1/2) • An IEEE 802.11 Card is allowed to turn off its radio to be in the PS mode to save energy • PowerConsumption:(ORiNOCO IEEE 802.11b PC Gold Card) Vcc:5V, Speed:11Mbps

  20. Beacon Interval Beacon Interval Beacon Interval Beacon Interval Power Saving Mode ATIM Window Host Beacon PS for 1-hop Ad hoc Networks (1/3) • Time axis is divided into equal-length intervals called beacon intervals • In the beginning of a beacon interval, there is ATIM window, in which hosts should wake up and contend to send a beacon frame with the backoff mechanism for synchronizing clocks

  21. PS for 1-hop Ad hoc Networks (2/3) • A possible sender also sends ATIM(Ad hoc Traffic Indication Map) message with DCF procedure in the ATIM window to its intended receivers in the PS mode • ATIM demands anACK. And the pair of hosts receiving ATIM and ATIM-ACK should keep themselves awake for transmitting and receiving data

  22. ATIM Window ATIM Window ATIM Window ATIM Window power saving mode active state ATIM Beacon BTA=2, BTB=5 data frame power saving mode ACK ACK Beacon PS for 1-hop Ad hoc Networks (3/3) Target Beacon Transmission Time (TBTT) Beacon Interval Beacon Interval Host A No ATIM means no data to send or to receive Host B

  23. PS: m-hop Ad hoc Network • Problems: • Clock Synchronizationit is hard due to communication delays and mobility • Network Partitionunsynchronized hosts with different wakeup times may not recognize each other

  24. Clock Drift Example Max. clock drift for IEEE 802.11 TSF (200 DSSS nodes, 11Mbps, aBP=0.1s)

  25. D ╳ F Network Partition ╳ E ╳ ╳ Network-Partitioning Example The red ones do not know the existence of the blue ones, not to mention the time when they are awake. The blue ones do not know the existence of the red ones, not to mention the time when they are awake. C A B Host A ATIM window Host B Host C Host D Host E Host F

  26. Asynchronous PS Protocols (1/2) • Try to solve the network partitioning problem to achieve • Neighbor discovery • Wakeup prediction without synchronizing hosts’ clocks

  27. Asynchronous PS Protocols (2/2) • Three asyn. PS protocols by Tseng: • Dominating-Awake-Interval • Periodical-Fully-Awake-Interval • Quorum-Based Ref:“Power-Saving Protocols for IEEE 802.11-BasedMulti-Hop Ad Hoc Networks,”Yu-Chee Tseng, Chih-Shun Hsu and Ten-Yueng HsiehInfoCom’2002

  28. Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion

  29. … 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 2 Beacon interval Numbering beacon intervals n consecutive beacon intervals are numbered as 0 to n-1 And they are organized as an n array

  30. Quorum Intervals (1/4) Intervals from one row and one column are called quorum intervals Example: Quorum intervals arenumbered by 2, 6, 8, 9, 10, 11, 14

  31. Quorum Intervals (2/4) Intervals from one row and one column are called quorum intervals Example: Quorum intervals arenumbered by 0, 1, 2, 3, 5, 9, 13

  32. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Quorum Intervals (3/4) Any two sets of quorum intervals havetwocommon members For example: The set of quorum intervals {0, 1, 2, 3, 5, 9, 13} and the set of quorum intervals {2, 6, 8, 9, 10, 11, 14} have two common members: 2 and 9

  33. Host D 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Host C 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Quorum Intervals (4/4) Host D 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Host C 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 2 overlapping quorum intervals Even when the beacon interval numbers are not aligned (they are rotated), there are always at least two overlapping quorum intervals

  34. Structure of quorum intervals

  35. D F E Networks Merge Properly C A B Host A ATIM window Host B Beacon window Host C Monitor window Host D Host E Host F

  36. Short Summary • There is an asynchronous power-saving protocol that achieves • asynchronous neighbor discovery • Hearing beacons twice or more in every n consecutive beacon intervals • wakeup prediction via a simple quorum concept.

  37. Observation 1 • It is a simple grid quorum system [Maekawa 1985] in Tseng’s work. • There are many more complicated quorum systems in the literature of distributed system: • FPP [Maekawa 1985], Tree [Agrawal 1990], Hierarchical[Kumar 1991], Cohorts[Jiang 1997], Cyclic [Luk 1997], Torus [Lang 1998], etc. • Question: Can these quorum systems be directly applied to solve the power-saving problem in a MANET?

  38. The Answer Is … • Not all quorum systems can be used here! • Counter example: { {1}} under {1,2,3} • Only those quorum systems with the rotation closure property can be used!

  39. Observation 2 • Smaller quorums are better because they imply lower active ratio (better energy-efficiency) • But quorums cannot be too small less the quorum system does not satisfy the rotation closure property • Question 1: What is the smallest quorum size? • Question 2: Is there any quorum systems to have the smallest quorum size?

  40. Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion

  41. What are quorum systems? • Quorum system: a collection of mutually intersecting subsets of a universal set U, where each subset is called a quorum • E.G. {{1, 2},{2, 3},{1,3}} is a quorum system under U={1,2,3} • A quorum system is a collection of sets satisfying the intersection property

  42. Rotation Closure Property (1/3) • Definition. Given a non-negative integer i and a quorum H in a quorum system Q under U = {0,…, n1}, we define rotate(H, i) = {j+ijH} (mod n). • E.G. Let H={0,3} be a subset of U={0,…,3}. We have rotate(H, 0)={0, 3}, rotate(H, 1)={1,0}, rotate(H, 2)={2, 1}, rotate(H, 3)={3, 2}

  43. Rotation Closure Property (2/3) • Definition. A quorum system Q under U = {0,…, n1} is said to have the rotation closure property if • G,HQ, i {0,…, n1}: Grotate(H, i) .

  44. Rotation Closure Property (3/3) • For example, • Q1={{0,1},{0,2},{1,2}} under U={0,1,2} • Q2={{0,1},{0,2},{0,3},{1,2,3}} under U={0,1,2,3}   Because {0,1} rotate({0,3},3) = {0,1}  {3, 2} =  Closure

  45. Examples of quorum systems • Majority quorum system • Tree quorum system • Hierarchical quorum system • Cohorts quorum system • ………    

  46. Optimal Quorum System (1/2) • Quorum Size Lower Bound for quorum systems satisfying the rotation closure property:k, where k(k-1)+1=n, the cardinality of the universal set,and k-1 is a prime power(k n)

  47. Optimal Quorum System (2/2) • Optimal quorum system • FPP quorum system • Near optimal quorum systems • Grid quorum system • Torus quorum system • Cyclic (difference set) quorum system

  48. Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion

  49. Analysis (1/3) • Active Ratio:the number of quorum intervals over n,where n is cardinality of the universal set • Neighbor Sensibility (NS)the worst-case delay for a PS host to detect the existence of anewly approaching PS host in its neighborhood

  50. Analysis (2/3)

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