1. tseng:1 Power Saving Issues: 802.11 vs. Bluetooth Prof. Yu-Chee Tseng Dept. of Comp. Sci. & Infor. Eng. National Chiao-Tung University ( 交通大學 資訊工程系 曾煜棋 )

2. 2 Power-Related Issues

3. 3 Backgrounds Battery is a limited resource in any portable device.  becoming a very hot topic is wireless communication Power-related issues:  PHY: transmission power control  MAC: power mode management  Network Layer: power-aware routing

4. 4 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?

5. 5 Power Mode Management doze mode vs. active mode example:  A is sending to B (based on 802.11)  Does C need to stay awake?

6. 6 Power-Aware Routing routing in an ad hoc network with energy-saving in mind Example: in an ad hoc network +–+– +–+– +–+– +–+– +–+– +–+– SRC N1 N2 DES T N4 N3

7. 7 Power Mode Management in IEEE 802.11

8. 8 Power Consumption IEEE 802.11 power model  transmit: 1400 mW  receive: 1000 mW  idle: 830 mW  sleep: 130 mW

9. 9 Problem Definition Power modes in IEEE 802.11  PS and ACTIVE Problem Spectrum:  infrastructure  ad hoc network (MANET)  single-hop  multi-hop ad hoc networks

10. 10 Infrastructure Mode two power modes: active and power- saving (PS)

11. 11 Details AP monitors modes of mobile hosts.  A host always notifies AP its mode. Periodically, AP transmits beacons.  A PS host only listens to beacons to check possible coming packets.  signaled by traffic indication map (TIM)

12. 12 Ad Hoc Mode (Single-Hop) PS hosts also wake up periodically.  interval = ATIM (Ad hoc) window 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

13. 13 Details In each ATIM window  every host contends to send a beacon  for clock synchronization  inhibiting (one beacon in each interval)  contends to send ATIM to wake up PS hosts with buffered packets  after the ATIM window, contend to send data frames by CSMA/CA

14. 14 Problems with Multi-Hop MANET Clock Synchronization:  a difficult job due to communication delays and mobility Neighbor Discovery:  by inhibiting other's beacons, hosts may not be aware of others ’ existence Network Partitioning:  with unsynchronized ATIM windows, hosts with different wakeup times may become partitioned networks

15. 15 Network-Partitioning Example Host A Host B AB C DE F DE F Host C Host D Host E Host F ╳ ╳ ATIM window ╳ ╳ Network Partition

16. 16 What Do We Need? PS protocols for multi-hop ad hoc networks  Fully distributed  No need of clock synchronization (i.e., asynchronous PS)  Always able to go to sleep mode, if desired

17. 17 Features of Our Design Guaranteed Overlapping Awake Intervals:  two PS hosts ’ wake-up patterns always overlap  no matter how much time their clocks drift Wake-up Prediction:  with beacons, derive other PS host's wake-up pattern based on their time difference

18. 18 Beacon Int. (BI) Act. Win. (AW) Structure of a Beacon Interval BI: beacon interval (to send beacons) AW: active window  BW: beacon window  MW: MTIM window (for receiving MTIM)  listening period: to monitor the environment BW MW listening

19. 19 Three Protocols Based on the above structure, we propose three protocols  Dominating-Awake-Interval  Periodical-Fully-Awake-Interval  Quorum-Based

20. 20 P1: Dominating-Awake-Interval intuition: impose a PS host to stay awake sufficiently long “ dominating-awake ” property Host A Host B Beacon Interval ╳╳

21. 21 Problem:  only dectectable in ONE direction Adjustment:  odd beacon interval:  Active Window = BW + MW + listening  even beacon interval:  Active Window = listening + MW + BW Host A Host B Odd Beacon IntervalEven Beacon Interval Odd Beacon IntervalEven Beacon Interval B ╳ B BB ╳ M M M M

22. 22 Host A Host B odd beacon interval Beacon window MTIM Window Active window odd beacon interval even beacon interval Unicast Example MTIMData ACK

23. 23 Characteristics dominating awake  wake-up ratio < 1/2 sensibility  A PS host can receive a neighbor ’ s beacon once every two beacon intervals.  suitable for highly mobile environment

24. 24 P2: Periodical-Fully-Awake-Interval Basic Idea:  In every T intervals, stay awake in one full interval.  wake-up ratio  1/T  compared to 1/2 of protocol 1 Two types of beacon intervals:  Low-power interval  Fully-awake interval (in every T intervals)

25. 25 Example (T = 3) Host A Host B T(=3) Beacon Intervals Fully-awake Low-power ╳╳╳ ╳╳╳ T: Interval between the fully awake periods A PS host can receive its neighbor’s beacon frame in every T = 3 beacon intervals

26. 26 Definitions of Intervals Low-power interval:  active window + doze window  AW = BW + MW  i.e., listening period = 0 Fully-awake interval:  no doze window  i.e., AW = BI  very energy-consuming, so only appears once every T beacon intervals

27. 27 P3: Quorum-Based Quorum Sets:  Two quorum sets always have nonempty intersection.  (used here to guarantee detectability) A matrix example: n n c1c1 c2c2 r1r1 r2r2 Host A’s quorum intervals Host B’s quorum intervals Non-quorum intervals intersection

28. 28 Example (2D matrix quorum) 0123 4567 891011 12131415 0123 4567 891011 12131415 Host A’s quorum intervals Host B’s quorum intervals Non-quorum intervals Host A’ quorum intervals 1514131211109876543210 31302928272625242322212019181716 Group 1 Group 2 Host B’s quorum intervals 1514131211109876543210 31302928272625242322212019181716 Group 1 Group 2 Overlapping intervals

29. 29 Overlapping Property Overlap no matter how clocks drift demo... 0123 4567 891011 12131415 0123 4567 891011 12131415 14131211109876543210 1514131211109876543210 Host A’s quorum intervals Host B’s quorum intervals

30. 30 Quorum and Non-quorum Intervals Quorum interval:  AW = BI (i.e., fully awake) Non-quorum interval:  no beacon, only MTIM window  AW < BI  BW = 0, AW = MW Beacon window MTIM Window Active window Beacon Interval Quorum Interval Non-quorum Interval

31. 31 Optimal Quorum Size Optimal quorum size: k, where k(k-1)+1=n and k-1 is a prime power (K  n)

32. 32 Optimal Quorum Systems Near optimal quorum systems  Grid quorum system  Torus quorum system  Cyclic (difference set) quorum system Optimal quorum system  FPP quorum system

33. 33 Torus quorum system

34. 34 Cyclic (difference set) quorum system Def: A subset D={d1, …,dk} of Zn is called a difference set if for every e  0 (mod n), there exist elements di and dj  D such that di-dj=e. {0,1,2,4} is a difference set under Z8 { {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

35. 35 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

36. 36 E-Torus quorum system

37. 37 Summary ProtocolNumbers of beacons Active ratioNeighbor sensitivity Dominating11/2+BW/BIBI Periodical11/TT*BI/2 Quorum(2n-1)/n 2 (n 2 /4) * BI BI: length of a beacon interval AW: length of an active window BW: length of a beacon window MW: length of an MTIM window T: interval between the fully awake periods n: length of the square

38. 38 Summary Identify the problems of PS mode in IEEE 802.11 in multi-hop ad hoc networks.  clock drifting, network-partitioning Propose several PS protocols Connecting this problem to quorum issue in distributed systems.

39. 39 Sniff Scheduling for Power Saving in Bluetooth

40. 40 Overview (cont.) Addressing  48-bit Bluetooth Device Address (BD_ADDR)  3-bit Active Member Address (AM_ADDR)  8-bit Parked Member Address (PM_ADDR) Four operational modes:  Active  Sniff  Hold  Park

41. 41 Bluetooth Networks Piconet  one master + at most 7 active slaves Scatternet  multiple piconets to form a larger network

42. Packets Exchange Scenario MASTER SLAVE 1 SLAVE 2 SLAVE 3 ACLSCO ACL

43. 43 Low-Power Sniff Mode A slave can enter the low-power sniff mode by setting a parameter  (T sniff, N sniff_attempt, D sniff )  in per slave basis

44. 44 LMP_PDUs for Sniff

45. 45 Sniff Scheduling Problem How to determine the sniff parameters?  Goal: balancing power consumption and traffic need Earlier Works  na ï vely adjust parameters in an exponential way  double/halve sniff interval or active window whenever polling fails/succeeds  The placement of active windows of multiple slaves on the time axis is not addressed.

46. 46 Design Goals consider multiple slaves together adaptively schedule sniff parameters  more accurate in determining the sniff- related parameters based on slaves ’ traffic loads include solutions of placing of active windows of sniffed slaves on the time axis

47. 47 Proposed Architecture

48. 48  T k,N k,O k : current sniff parameters for slave k.  U k : the slot utilization of slave k.  B k : the buffer backlog of slave k.  W k : a weighted value to indicate the current requirement of slave k.  B max is the maximum buffer space  S k : the desired slot occupancy of slave k, which is the expected ratio of N k / T k.  0 < δ < 1 (to tolerate some unexpected traffic) the evaluator

49. 49 Resource Pool (RP) Resource = time slots  represented as a 2-D matrix M of the size 2 u × T.  (infinite) slots appearing with period 2u ． T are grouped into one set Each entry in M represents the availability of one such slots group.

50. 50 RP Example M ’ s size = 2 3 × 15

51. 51 Example: to allocate a slot occupancy of 16/120 (** Note: 16/120 = 8/60)

52. 52 Example: to allocate a slot occupancy of 16/120 (** Note: 16/120 = 4/30 = 2/15)

53. 53 Scheduling Policies: Longest Sniff Interval First (LSIF) a) initial state (equal shares) b) reduce S2 to 2/60 c) reduce S3 to 3/120 d) increase S4 to 6/30

54. 54 Scheduling Policies: Shortest Sniff Interval First (SSIF) a) initial state (equal shares) b) reduce S2 to 1/30 c) reduce S3 to 1/60 d) increase S4 to 3/15

55. 55 Conclusions Proposed:  Power-saving protocols for IEEE 802.11-based multi-hop ad hoc networks  Sniff-scheduling schemes for Bluetooth-based piconets References: 1.T.-Y. Lin and Y.-C. Tseng, “ An Adaptive Sniff Scheduling Scheme for Power Saving in Bluetooth ”, IEEE Personal Communications (to appear). 2.Y.-C. Tseng, C.-S. Hsu, and T.-Y. Hsieh, “ Power-Saving Protocols for IEEE 802.11-Based Multi-Hop Ad Hoc Networks ”, IEEE INFOCOM, 2002.