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Power Saving Issues: 802.11 vs. Bluetooth

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 ). Power-Related Issues. Backgrounds. Battery is a limited resource in any portable device. becoming a very hot topic is wireless communication

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Power Saving Issues: 802.11 vs. Bluetooth

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  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. Power-Related Issues

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

  7. Power Mode Management in IEEE 802.11

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

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

  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. Beacon Interval Beacon Interval ATIM Window ATIM Window power saving state active state ATIM Host A Beacon BTA=2, BTB=5 data frame power saving state Host B ACK ACK Beacon Ad Hoc Mode (Single-Hop) • PS hosts also wake up periodically. • interval = ATIM (Ad hoc) window

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

  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. 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. 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 Beacon Int. (BI) Act. Win. (AW) BW MW listening BW MW listening

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

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

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

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

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

  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. n Host A’s quorum intervals c1 Host B’s quorum intervals n c2 Non-quorum intervals r1 r2 intersection P3: Quorum-Based • Quorum Sets: • Two quorum sets always have nonempty intersection. • (used here to guarantee detectability) • A matrix example:

  28. Overlapping intervals Host B’s quorum intervals Group 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Group 2 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Example (2D matrix quorum) Host A’s quorum intervals Host B’s quorum intervals Non-quorum intervals Host A’ quorum intervals Group 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Group 2 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

  29. Overlapping Property • Overlap no matter how clocks drift • demo ... Host A’s quorum intervals Host B’s quorum intervals 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

  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 Interval Beacon Interval Quorum Interval Non-quorum Interval Active window MTIM Window Beacon window

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

  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. Torus quorum system

  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), thereexist 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. FPP quorum system • FPP:Finite Projective Plane • Proposed byMaekawa in 1985 • For solving distributed mutual exclusion • Constructed with a hypergraph • Also a Singer difference set quorum system

  36. E-Torus quorum system

  37. Summary 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. 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. Sniff Scheduling for Power Saving in Bluetooth

  40. 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 Overview (cont.)

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

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

  43. Low-Power Sniff Mode • A slave can enter the low-power sniff mode by setting a parameter • (Tsniff, Nsniff_attempt, Dsniff) • in per slave basis

  44. LMP_PDUs for Sniff

  45. Sniff Scheduling Problem • How to determine the sniff parameters? • Goal: balancing power consumption and traffic need • Earlier Works • naïvely 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. 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. Proposed Architecture

  48. the evaluator • Tk,Nk,Ok: current sniff parameters for slave k. • Uk: the slot utilization of slave k. • Bk: the buffer backlog of slave k. • Wk: a weighted value to indicate the current requirement of slave k. • Bmax is the maximum buffer space • Sk: the desired slot occupancy of slave k, which is the expected ratio of Nk / Tk. • 0 < δ < 1 (to tolerate some unexpected traffic)

  49. Resource Pool (RP) • Resource = time slots • represented as a 2-D matrix M of the size 2u × 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. RP Example • M’s size = 23 × 15

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