1. Asynchronous Power-Saving Protocols via Quorum Systems for IEEE 802.11 Ad Hoc Networks Jehn-Ruey Jiang Hsuan-Chuang University

2. To Rest, to Go Far!

3. Outline  IEEE 802.11 Overview  Power Saving Issues  Asynchronous Quorum-based PS Protocols  Optimal AQPS Protocols  Analysis and Simulation  Conclusion

4. Outline  IEEE 802.11 Overview  Power Saving Issues  Asynchronous Quorum-based PS Protocols  Optimal AQPS Protocols  Analysis and Simulation  Conclusion

5. IEEE 802.11  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. IEEE 802.11 Components  Station (STA) - Mobile host  Access Point (AP) - Stations are connected to access points.  Basic Service Set (BSS) - Stations and the AP within the same radio coverage form a BSS.  Extended Service Set (ESS) - Several BSSs connected through APs form an ESS.

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

11. Ad hoc Networks  Ad hoc: formed, arranged, or done (often temporarily) for a particular purpose only  Mobile Ad Hoc Network (MANET): A collection of wireless mobile hosts forming a temporary network without the aid of established infrastructure or centralized administration

12. Applications of MANETs  Battlefields  Disaster rescue  Spontaneous meetings  Outdoor activities

13. Single-Hop vs Multi-Hop  Single-Hop  Each node is within each other ’ s transmission range  Fully connected  Multi-Hop  A node reaches other nodes via a chain of intermediate nodes  Networks may partition and/or merge

14. Outline  IEEE 802.11 Overview  Power Saving Issues  Asynchronous Quorum-based PS Protocols  Optimal AQPS Protocols  Analysis and Simulation  Conclusion

15. Power Saving - Overview  Battery is a limited resource for portable devices  Power saving becoming a very hot topic is wireless communication  Solutions:  PHY: transmission power control  MAC: power mode management  Network Layer: power-aware routing

16. 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? Source: Prof. Tseng

17. Power Mode Management  doze mode vs. active mode  example:  A is sending to B  Does C need to stay awake? Source: Prof. Tseng

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

19. IEEE 802.11 PS Mode(1/2)  Power Consumption: (ORiNOCO IEEE 802.11b PC Gold Card) Vcc:5V, Speed:11Mbps

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

21. PS: Infrastructure (1/3)  Clock synchronization is required (via TSF)  The AP is responsible for generating beacons each of which contains a valid time stamp  If the channel is in use, defer beacon transmission until it is free

22. PS: Infrastructure (2/3)  A host always notifies AP its mode  A PS host periodically wakes up to listen to beacons  AP keeps a PS host awake by sending ”traffic indication map (TIM)” in a beacon for unicast data  AP keeps all PS hosts awake by sending ”delivery traffic indication map (DTIM)” in a beacon for broadcast data

23. PS: Infrastructure (3/3)

24. PS : 1-hop Ad hoc Network (1/2) Beacon Interval ATIM Window Host A Host B Beacon BT A =2, BT B =5 power saving state Beacon ATIM ACK active state data frame ACK Source: Prof. Tseng

25. PS: 1-hop Ad hoc Network (2/2) ATIM ACK Data Frame ACK Host A Host B ATIM Window Beacon Interval Power Saving Mode Beacon Interval Beacon Host C ATIM ACK Data Frame ACK Beacon Target Beacon Transmission Time (TBTT)

26. PS: m-hop Ad hoc Network (1/3)  Problems:  Clock Synchronization is hard due to communication delays and mobility  Network Partition unsynchronized hosts with different wakeup times may not recognize each other

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

28. Network-Partitioning Example Host A Host B AB C DE F Host C Host D Host E Host F ╳ ╳ ATIM window ╳ ╳ Network Partition Source: Prof. Tseng

29. PS: m-hop Ad hoc Network (3/2)  Solution:  Not to synchronize hosts’ clocks  But to achieve  Wakeup prediction  Neighbor discovery

30. PS: m-hop Ad hoc Network (3/3)  Three asyn. solutions:  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

31. Outline  IEEE 802.11 Overview  Power Saving Issues  Asynchronous Quorum-based PS Protocols  Optimal AQPS Protocols  Analysis and Simulation  Conclusion

32. Quorum-based PS Protocol

33. Quorum interval

34. Touchdown  A PS host’s beacon can be heard twice or more for every n consecutive beacon intervals, which in turn solves  Wakeup prediction  Neighbor discovery

35. Observation  A quorum system may be translated to a power-saving protocol, whose power- consumption is proportional to the quorum size.

36. Questions  Can any quorum system be translated to an asyn. PS protocol? NO!  Which can be? Those with the Rotation Closure Property !!

37. Outline  IEEE 802.11 Overview  Power Saving Issues  Asynchronous Quorum-based PS Protocols  Optimal AQPS Protocols  Analysis and Simulation  Conclusion

38. Contributions  Propose the rotation closure property  Propose the lower bound of the quorum size  Propose a novel quorum systems to be translated to an adaptive PS protocol

39. What are quorum systems?  Quorum: a subset of universal set U  E.G. q 1 ={1, 2} and q 2 = {2, 3} are quorums under U={1,2,3}  Quorum system: a collection of mutually intersecting quorums  E.G. {{1, 2},{2, 3},{1,3}} is a quorum system under U={1,2,3}

40. Rotation Closure Property  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) = 

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

42. Optimal Quorum Size  Optimal quorum size: k, where k(k-1)+1=n and k-1 is a prime power (K  n)

43. Optimal Quorum Systems  Near optimal quorum systems  Grid quorum system  Torus quorum system  Cyclic (difference set) quorum system  Optimal quorum system  FPP quorum system

44. Torus quorum system

45. 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

46. FPP quorum system  FPP: Finite Projective Plane  Proposed by Maekawa in 1985  For solving distributed mutual exclusion  Constructed with a hypergraph  Also a Singer difference set quorum system

47. E-Torus quorum system

48. Outline  IEEE 802.11 Overview  Power Saving Issues  Asynchronous Quorum-based PS Protocols  Optimal AQPS 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 a newly approaching PS host in its neighborhood

50. Analysis (2/3)

51. Analysis (3/3)

52. 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

53. 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

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

55. Simulation Results (1/10) Survival ratio vs. mobility (beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec).

56. Simulation Results (2/10) Neighbor discovery time vs. mobility (beacon interval =100 ms, 100 hosts, traffic load = 1 route/sec).

57. Simulation Results (3/10) Throughput vs. mobility (beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec).

58. 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).

59. 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).

60. 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).

61. 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).

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

63. 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).

64. 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).

65. Outline  IEEE 802.11 Overview  Power Saving Issues  Asynchronous Quorum-based PS Protocols  Optimal AQPS Protocols  Analysis and Simulation  Conclusion

66. Conclusion (1/2)  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

67. Conclusion (2/2)  Future work:  To incorporate AQPS protocols with those demanding accurate neighboring node’s information, e.g., geometric routing protocols  To incorporate quorum system concept to wireless sensor networks  To incorporate quorum system concept to Bluetooth technology

68. Q&A