tseng:1 Power Saving and Power Management in WiFi and Bluetooth Networks 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 )

yctseng: 2 Outline Power control:  S.-L. Wu, Y.-C. Tseng, and J.-P. Sheu, "Intelligent Medium Access for Mobile Ad Hoc Networks with Busy Tones and Power Control", IEEE Journal on Selected Areas in Communications, 18(9): , Sep Power management:  Y.-C. Tseng, C.-S. Hsu, and T.-Y. Hsieh, "Power-Saving Protocols for IEEE Based Multi-Hop Ad Hoc Networks", Computer Networks, Elsevier Science Pub., Vol. 43, No. 3, Oct. 2003, pp WiFi vs Bluetooth:  T.-Y. Lin and Y.-C. Tseng, "An Adaptive Sniff Scheduling Scheme for Power Saving in Bluetooth", IEEE Wireless Communications, Vol. 9, No. 6, Dec. 2002, pp

tseng:3 Introduction: Basic Concept

4 Introduction 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

5 Transmission Power Control tuning transmission energy for higher channel reuse example:  A is sending to B (based on IEEE )  Can (C, D) and (E, F) join? No! Yes!

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

7 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

wu-ICCCN99:8 WirelessNet Tseng Intelligent Medium Access for Mobile Ad Hoc Networks with Busy Tones and Power Control S.-L. Wu, Y.-C. Tseng, and J.-P. Sheu, IEEE J. of Selected Areas on Communications (JSAC)

wu-ICCCN99:9 WirelessNet Tseng Abstract n A New MAC Protocol ubased on RTS/CTS uwith Busy Tones uwith Power Control

wu-ICCCN99:10 WirelessNet Tseng Power Control n Use an appropriate power level to transmit packets. uto increase the possibility of channel reuse uto increase channel utilization n Example: u(a) without power control: åthe transmissions from C to D and from E to F are prohibited. u(b) with power control: åall these can coexist.

wu-ICCCN99:11 WirelessNet Tseng How to Tune Power Levels n Assumptions: uA mobile host can choose on what power level to transmit a packet. uOn receiving a packet, the physical layer can offer the MAC layer the power level on which the packet was received. n Suppose P t and P r are the power levels a packet is sent and received, respectively.  = carrier wavelength un = path loss coefficient (typically 2 ~ 6) ud = distance between sender and receiver ug t and g r : antenna gains at the sender and receiver sides, respectively

wu-ICCCN99:12 WirelessNet Tseng n Note: during a short period, the values of n and d can be treated as a constant. This makes power control possible. n Let P min be the minimum power level to decode a packet. uSuppose X sends an RTS to Y with power P t. uIf Y wants to reply a CTS to X with a power level P CTS, such that X receives the packet at the smallest power level P min, then we have: n Dividing the above formulas, we have:

wu-ICCCN99:13 WirelessNet Tseng General Rules in This Paper n Busy Tone (BT) uSenders should send BTt, but gauge any BTr. uReceivers should send BTr, but gauge any BTt. n General Rules: uData packet and BTt: transmitted with power control. uCTS and BTr: transmitted at the normal (largest) power. uRTS: at a power level based on how strong the BTr are around the requesting host. n Channel Model: BTt BTr control channel data channel frequency

wu-ICCCN99:14 WirelessNet Tseng Illustrative Example (I) n A is sending to B. uA’s data packet and BTt at the minimal level (yellow circle). uB’s BTr at the largest level (white circle). n C intends to send to D. uC hears no BTr. uD hears not BTt. uSo the transmission can be granted (pink circle). A D C B

wu-ICCCN99:15 WirelessNet Tseng Illustrative Example (II) n Now we moe C into A’s circle. n A is sending to B. uA’s data packet and BTt at the minimal level (yellow circle). uB’s BTr at the largest level (white circle). n C intends to send to D. uC hears no BTr. uD hears no BTt. uSo the transmission can be granted (pink circle). A D C B

wu-ICCCN99:16 WirelessNet Tseng Illustrative Example (III) n Next we move D into A’s circle. n A is sending to B. uA’s data packet and BTt at the minimal level (yellow circle). uB’s BTr at the largest level (white circle). n C intends to send to D. uC hears no BTr. uD hears A’s BTt. uSo the transmission can NOT be granted (pink circle). A D C B

wu-ICCCN99:17 WirelessNet Tseng Illustrative Example (IV) n A is sending to B. uA’s data packet and BTt at the minimal level (yellow circle). uB’s BTr at the largest level (white circle). n C intends to send to D. uC hears A’s BTt and B’s BTr. uD hears no BTt. uThe transmission can be granted if C controls its transmission power (pink circle). A D C B

wu-ICCCN99:18 WirelessNet Tseng Illustrative Example (V) n A is sending to B. uA’s data packet and BTt at the minimal level (yellow circle). uB’s BTr at the largest level (white circle). n C intends to send to D. uC hears A’s BTt and B’s BTr. uD hears no BTt. uThe transmission can be granted if C controls its transmission power (pink circle). A D C B

wu-ICCCN99:19 WirelessNet Tseng Many Transmission Pairs with Power Control and Busy Tones A F E D C B BTt and DATA: yellow circles BTr: white circles

wu-ICCCN99:20 WirelessNet Tseng The Protocol n P max : the maximum transmission power n P min : the minimum power to distinguish a signal from a noise n P noise : the maximum power at which an antenna will regard a signal as a noise uP min - P noise should be a very small value n Basic “Power” Rules: uData packet and BTt: transmitted with power control. uCTS and BTr: transmitted at the largest power P max. uRTS: at a power level based on how strong the BTr are around the requesting host.

wu-ICCCN99:21 WirelessNet Tseng Detailed Protocol n On a host X intending to send a RTS to Y, uX senses any receive busy tone BTr around it uX sends a RTS on the control channel at power level P x : åIf there is no BTr, let P x = P max. åO/w, let Pr be the power level of BTr that has the highest power among all heard BTr’s. 4The RTS should not go beyond the nearest host that is currently receiving a data packet. 4P max is used because BTr is always transmitted at the maximal power.

wu-ICCCN99:22 WirelessNet Tseng n On Y receiving X’s RTS, uY senses any transmit busy tone BTt around it. åIf there is any BTt, then Y ignores this RTS. åO/w, Y does the following: 4reply with a CTS at the maximum power Pmax 4turn on its receive busy tone BTr at the maximum power Pmax n On X receiving Y’s CTS, uX transmits its data packet at power P x. uX turns on its transmit busy tone BTt at power P x. åP r is the power level at which X receives Y’s CTS. P x is the minimal possible power level to ensure that Y can correctly receive the data packet.

wu-ICCCN99:23 WirelessNet Tseng Many Transmission Pairs with Power Control and Busy Tones F E D C G H BTr BTt A B RTS CTS

wu-ICCCN99:24 WirelessNet Tseng Analysis n Scenario: uA is currently sending to B. uAnother pair, C and D, is intending to communicate. n Goal: We want to find out the probability that C can send to D. n Through complicated calculus, we find that …

wu-ICCCN99:25 WirelessNet Tseng When BC < r max n INTC(Ra, Rb, AB) = the intersection of the circles centered at a and b uRa = radius of the circle centered at a uRb = radius of the circle centered at b uAB = distance of a and b n The probability that C can send to D when A is sending to B: ui.e., the coverage of Rc excluding the coverage of Ra uFig. 6

wu-ICCCN99:26 WirelessNet Tseng

wu-ICCCN99:27 WirelessNet Tseng cont... n Integrating over  = , and then over CB = 0.. r max n Integrating over AB = 0.. r max, we have the final result n On the contrary, the DBTMA has probability of 0.

wu-ICCCN99:28 WirelessNet Tseng When r max < BC < 3r max n Main difference: C’s RTS will be sent with max. power. n The probability that C can send to D when A is sending to B: uSee Fig. 7: åAt point C1, node C can always send. åAt point C2, node C can’t send if D is in A’s range.

wu-ICCCN99:29 WirelessNet Tseng

wu-ICCCN99:30 WirelessNet Tseng cont... n Integrating over  = , and then over CB = r max..3r max n Integrating over AB = 0.. r max, we have the final result

wu-ICCCN99:31 WirelessNet Tseng cont. n On the contrary, the DBTMA has a success probability of X change to r max

wu-ICCCN99:32 WirelessNet Tseng Discrete Power Control n The levels of power provided by hardware may not be infinitely tunable. uWe may have a discrete number of power levels. n Theorem: uGiven a fixed integer k, evenly spreading the k power levels will be the best choice. uI.e., (1/k)*P max, (2/k)*P max, (3/k)*P max, …, (k/k)*P max.

wu-ICCCN99:33 WirelessNet Tseng Simulation Parameters n Simulation parameters uphysical area = 8km  8km umax transmission distance (rmax) = 0.5 or 1.0 km unumber of mobile hosts = 600 uSpeed of mobile hosts 0 or 125 km/hr. ulength of control packet = 100 bits ulink speed = 1 Mbps utransmission bit error rate = 10-5/bit

wu-ICCCN99:34 WirelessNet Tseng Simulation Results: Channel utilization vs. traffic load (a) r max = 0.5 km(b) r max = 1.0 km

wu-ICCCN99:35 WirelessNet Tseng Channel utilization vs. data packet length at various traffic loads

wu-ICCCN99:36 WirelessNet Tseng Channel Utilization vs. Number of Power Levels n r max = 1 km; arrival rate = 200 or 400 packets/ms; packet length = 1 or 2 Kbits uSo 4 to 6 levels will be sufficient.

wu-ICCCN99:37 WirelessNet Tseng Channel Utilization vs. Traffic Load n mobility = 0 km/hr and 125 km/hr n The transmission distance r max = 1.0 km

wu-ICCCN99:38 WirelessNet Tseng Short Conclusion n a new MAC protocol upower control on top of RTS/CTS and busy tones n Channel utilization can be significantly increased because the severity of signal overlapping is reduced.

39 Power Mode Management in IEEE Y.-C. Tseng, C.-S. Hsu, and T.-Y. Hsieh, "Power-Saving Protocols for IEEE Based Multi-Hop Ad Hoc Networks", Computer Networks, Elsevier Science Pub., Vol. 43, No. 3, Oct. 2003, pp (also in INFOCOM).

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

41 Power Mode Management Power modes in IEEE  PS and ACTIVE Problem Spectrum:  infrastructure  ad hoc network (MANET)  single-hop  multi-hop ad hoc networks

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

43 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

44 Problem Statement (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

45 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

46 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

47 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

48 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

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

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

51 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

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

53 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

54 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)

55 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

56 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

57 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

58 Example (2D matrix quorum) Host A’s quorum intervals Host B’s quorum intervals Non-quorum intervals Host A’ quorum intervals Group 1 Group 2 Host B’s quorum intervals Group 1 Group 2 Overlapping intervals

59 Overlapping Property Overlap no matter how clocks drift demo Host A’s quorum intervals Host B’s quorum intervals

60 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

61 Summary Protocol Numbers of beacons per interval 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

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

63 Sniff Scheduling for Power Saving in Bluetooth

64 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

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

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

67 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

68 LMP_PDUs for Sniff

69 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.

70 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

71 Proposed Architecture

72  T k,N k,D 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

73 Resource Pool (RP) Although time slots are an infinite sequence, we represent them as a sequence of 2-D matrices.  each matrix M is of the size 2 u × T  time slots are viewed in a “ row-major ” way The availability of M:

74 RP Example M ’ s size = 2 3 × 15 = 120

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

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

77 A Running Example 5 slaves Each slave initially has an equal occupancy of 1/5 of the matrix M. We discuss two strategies:  longest sniff interval first  shortest sniff interval first

78 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

79 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

80 Conclusions Proposed:  Power-saving protocols for IEEE 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 Based Multi-Hop Ad Hoc Networks ”, IEEE INFOCOM, 2002.