1. 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

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 (High Rate)  Standard for Wireless Local Area Networks ( WLAN )

6. IEEE 802.11 Family(1/2)  802.11a (1999)(WiFi5): 6 to 54 Mbps in the 5 GHz band  802.11b (1999)(WiFi, Wireless Fidelity): 5.5 and 11 Mbps in the 2.4 GHz band  802.11g (2001): 54 Mbps in the 2.4 GHz band  802.11n (2006)(MIMO): 160 Mbps in the 2.4 and the 5 GHz bands

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

9. Ad hoc Network (1/3)  A collection of wireless mobile hosts forming a temporary network without the aid of established infrastructure or centralized administration (by D. B. Johnson et al.)  Also called MANET (Mobile Ad hoc Network) (by Internet Society IETF)

10. Ad hoc Network (2/3)  Single-Hop  Each node is within each other ’ s transmission range  Fully connected  Multi-Hop  A node reaches another node via a chain of intermediate nodes  Networks may partition and/or merge

11. Ad hoc Network (3/3)  Applications :  Battlefields  Disaster rescue  Spontaneous meetings  Outdoor activities

12. 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

13. 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

14. 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)

15. 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? A B C D F E No!Yes!

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

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

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

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

20. 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  Power Consumption: (ORiNOCO IEEE 802.11b PC Gold Card) Vcc:5V, Speed:11Mbps

21. PS for 1-hop Ad hoc Networks (1/3) Host ATIM Window Beacon Interval Power Saving Mode Beacon Interval Beacon  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

22. 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 an ACK. And the pair of hosts receiving ATIM and ATIM-ACK should keep themselves awake for transmitting and receiving data

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

24. PS: m-hop Ad hoc Network  Problems:  Clock Synchronization it is hard due to communication delays and mobility  Network Partition unsynchronized hosts with different wakeup times may not recognize each other

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

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

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

28. Asynchronous PS Protocols (2/2)  Three existent asyn. PS protocols:  Dominating-Awake-Interval  Periodical-Fully-Awake-Interval  Quorum-Based Ref: “Power-Saving Protocols for IEEE 802.11-Based Multi-Hop Ad Hoc Networks,” Yu-Chee Tseng, Chih-Shun Hsu and Ten-Yueng Hsieh InfoCom’2002

29. 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

30. Numbering beacon intervals 0123 4567 891011 12131415 And they are organized as a  n   n array n consecutive beacon intervals are numbered as 0 to n-1 201514131211109876543210 … Beacon interval

31. Quorum Intervals (1/4) Intervals from one row and one column are called quorum intervals 0123 4567 891011 12131415 Example: Quorum intervals are numbered by 2, 6, 8, 9, 10, 11, 14

32. Quorum Intervals (2/4) Intervals from one row and one column are called quorum intervals 0123 4567 891011 12131415 Example: Quorum intervals are numbered by 0, 1, 2, 3, 5, 9, 13

33. Quorum Intervals (3/4) Any two sets of quorum intervals have two common 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 15141312 111098 7654 3210

34. Quorum Intervals (4/4) 1514131211109876543210 2151413121110987654310 2 overlapping quorum intervals Host D Host C 2151413121110987654310 Host D 1514131211109876543210 Host C Even when the beacon interval numbers are not aligned (they are rotated), there are always at least two overlapping quorum intervals

35. Structure of quorum intervals

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

37. 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.

38. Observation 1 IIt is a simple grid quorum system [Maekawa 1985] in Tseng’s work. TThere are many more complicated quorum systems in the literature of distributed systems: FFPP [Maekawa 1985], Tree [Agrawal 1990], Hierarchical[Kumar 1991], Cohorts [Jiang 1997], Cyclic [Luk 1997], Torus [Lang 1998], etc. QQuestion: Can these quorum systems be directly applied to solve the power-saving problem in a MANET?

39. 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!

40. 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?

41. 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

42. 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

43. 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}

44. Rotation Closure Property (2/3) D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)  .

45. Rotation Closure Property (3/3)  For example,  Q 1 ={{0,1},{0,2},{1,2}} under U={0,1,2}  Q 2 ={{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

46. Examples of quorum systems  Majority quorum system  Tree quorum system  Hierarchical quorum system  Cohorts quorum system  ………  

47. 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 )

48. 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

49. 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

50. 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 a newly approaching PS host in its neighborhood

51. Analysis (2/3)

52. Analysis (3/3) Optimal!

53. Simulation Model  Area: 1000m x 1000m  Speed: 2Mbps  Radio radius: 250m  Battery energy: 100J.  Traffic load: Poisson Dist., 1~4 routes/s, each having ten 1k packets  Mobility: way-point model (pause time: 20s)  Routing protocol: AODV

54. Simulation Parameters Unicast send454+1.9 * L Broadcast send266+1.9 * L Unicast receive356+0.5 * L Broadcast receive56+0.5 * L Idle843 Doze27 L: packet length Unicast packet size 1024 bytes Broadcast packet size 32 bytes Beacon window size 4ms MTIM window size 16ms

55. Simulation Metrics  Survival ratio  Neighbor discovery time  Throughput  Aggregate throughput

56. Simulation Results (1/10) Survival ratio vs. mobility (beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec). Cyclic quorum system E-torus quorum system Always Active

57. Simulation Results (2/10) Neighbor discovery time vs. mobility (beacon interval =100 ms, 100 hosts, traffic load = 1 route/sec). A faster host can be discovered in shorter time.

58. Simulation Results (3/10) Throughput vs. mobility (beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec). For the aggregate throughput: C(98)>E(7x74)>AA For the throughput: AA>E(7x74)>C(98)

59. Simulation Results (4/10) Survival ratio vs. beacon interval length (100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with mean = 10m/sec).

60. Simulation Results (5/10) Neighbor discovery time vs. beacon interval length (100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with mean = 10m/sec).

61. Simulation Results (6/10) Throughput vs. beacon interval length (100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with mean =10m/sec).

62. Simulation Results (7/10) Survival ratio vs. traffic load (beacon interval = 100 ms, 100 hosts, mobility = 0~20 m/sec with mean = 10 m/sec).

63. Simulation Results (8/10) Throughput vs. traffic load (beacon interval =100 ms, 100 hosts, mobility = 0~20 m/sec with mean = 10 m/sec).

64. Simulation Results (9/10) Survival ratio vs. host density (beacon interval = 100ms, traffic load 1 route/sec, mobility = 0~20 m/sec with mean= 10 m/sec).

65. Simulation Results (10/10) Throughput vs. host density (beacon interval = 100ms, traffic load 1 route/sec, mobility = 0~20m/sec with mean= 10 m/sec).

66. 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

67. Conclusion  Quorum systems with the rotation closure property can be translated to an asyn. PS protocol.  The active ratio is bounded by 1/  n, where n is the number of a group of consecutive beacon intervals.  Optimal, near optimal and adaptive AQPS protocols save a lot of energy w/o degrading performance significantly

68. Publication  ICPP’03 Best Paper Award  ACM Journal on Mobile Networks and Applications

69. Future work  To incorporate the clustering concept into the design of hybrid (syn. and asyn.) power saving protocols (NSC 93-2213-E-008-046-)  To design more flexible adaptive asyn. power saving protocols with the aid of the expectation quorum system (a novel quorum system which is a general form of probabilistic quorum systems) (93CAISER- 中央大學分部計畫 )  To incorporate power saving mode management to wireless sensor networks with comm. and sensing coverage in mind ( 中大新進教師學術研究 經費補助計畫 )

70. Thanks!

71. FPP quorum system  Proposed by Maekawa in 1985  For solving distributed mutual exclusion  Constructed with a hypergraph  An edge can connect more than 2 vertices  FPP:Finite Projective Plane  A hypergraph with each pair of edges having exactly one common vertex  Also a Singer difference set quorum system

72. FPP quorum system Example 01 2 34 5 6 A FPP quorum system: { {0,1,2}, {1,5,6}, {2,3,6}, {0,4,6}, {1,3,4}, {2,4,5}, {0,3,5} } 0 3 5

73. Torus quorum system For a t  w torus, a quorum contains all elements from some column c, plus  w/2  elements, each of which comes from column c+i, i=1..  w/2  171615141312 11109876 543210 One full column One half column cover in a wrap around manner { {1,7,13,8,3,10}, {5,11,17,12,1,14},…}

74. Cyclic (difference set) quorum system  Def: A subset D={d 1,…,d k } of Z n is called a difference set if for every e  0 (mod n), there exist elements d i and d j  D such that d i -d j =e.  {0,1,2,4} is a difference set under Z 8  { {0, 1, 2, 4}, {1, 2, 3, 5}, {2, 3, 4, 6}, {3, 4, 5, 7}, {4, 5, 6, 0}, {5, 6, 7, 1}, {6, 7, 0, 2}, {7, 0, 1, 3} } is a cyclic (difference set) quorum system C(8)

75. E-Torus quorum system Trunk Branch cyclic E(t x w, k)