tseng:1

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Power Saving and Power Managementin WiFi and
Bluetooth Networks

• Prof. Yu-Chee Tseng
• Dept. of Comp. Sci. Infor. Eng.
• National Chiao-Tung University
• (???? ????? ???)

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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)1647-1657, Sep. 2000.
• Power management
• Y.-C. Tseng, C.-S. Hsu, and T.-Y. Hsieh,
  "Power-Saving Protocols for IEEE 802.11-Based
  Multi-Hop Ad Hoc Networks", Computer Networks,
  Elsevier Science Pub., Vol. 43, No. 3, Oct. 2003,
  pp. 317-337.
• 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. 92-103.

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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

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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?

Yes!
No!
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Power Mode Management

• doze mode vs. active mode
• example
• A is sending to B (based on 802.11)
• Does C need to stay awake?

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Power-Aware Routing

• routing in an ad hoc network with energy-saving
  in mind
• Example in an ad hoc network

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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)

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Abstract

• A New MAC Protocol
• based on RTS/CTS
• with Busy Tones
• with Power Control

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Power Control

• Use an appropriate power level to transmit
  packets.
• to increase the possibility of channel reuse
• to increase channel utilization
• Example
• (a) without power control
• the transmissions from C to D and from E to F are
  prohibited.
• (b) with power control
• all these can coexist.

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How to Tune Power Levels

• Assumptions
• A mobile host can choose on what power level to
  transmit a packet.
• On receiving a packet, the physical layer can
  offer the MAC layer the power level on which the
  packet was received.
• Suppose Pt and Pr are the power levels a packet
  is sent and received, respectively.
• l carrier wavelength
• n path loss coefficient (typically 2 6)
• d distance between sender and receiver
• gt and gr antenna gains at the sender and
  receiver sides, respectively

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• Note during a short period, the values of n and
  d can be treated as a constant. This makes power
  control possible.
• Let Pmin be the minimum power level to decode a
  packet.
• Suppose X sends an RTS to Y with power Pt.
• If Y wants to reply a CTS to X with a power level
  PCTS, such that X receives the packet at the
  smallest power level Pmin, then we have
• Dividing the above formulas, we have

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General Rules in This Paper

• Busy Tone (BT)
• Senders should send BTt, but gauge any BTr.
• Receivers should send BTr, but gauge any BTt.
• General Rules
• Data packet and BTt transmitted with power
  control.
• CTS and BTr transmitted at the normal (largest)
  power.
• RTS at a power level based on how strong the BTr
  are around the requesting host.
• Channel Model

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Illustrative Example (I)

• A is sending to B.
• As data packet and BTt at the minimal level
  (yellow circle).
• Bs BTr at the largest level (white circle).

• C intends to send to D.
• C hears no BTr.
• D hears not BTt.
• So the transmission can be granted (pink circle).

D
C
A
B
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Illustrative Example (II)

• Now we moe C into As circle.
• A is sending to B.
• As data packet and BTt at the minimal level
  (yellow circle).
• Bs BTr at the largest level (white circle).

• C intends to send to D.
• C hears no BTr.
• D hears no BTt.
• So the transmission can be granted (pink circle).

D
C
A
B
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Illustrative Example (III)

• Next we move D into As circle.
• A is sending to B.
• As data packet and BTt at the minimal level
  (yellow circle).
• Bs BTr at the largest level (white circle).

• C intends to send to D.
• C hears no BTr.
• D hears As BTt.
• So the transmission can NOT be granted (pink
  circle).

D
C
A
B
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Illustrative Example (IV)

• A is sending to B.
• As data packet and BTt at the minimal level
  (yellow circle).
• Bs BTr at the largest level (white circle).

• C intends to send to D.
• C hears As BTt and Bs BTr.
• D hears no BTt.
• The transmission can be granted if C controls its
  transmission power (pink circle).

D
C
A
B
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Illustrative Example (V)

• A is sending to B.
• As data packet and BTt at the minimal level
  (yellow circle).
• Bs BTr at the largest level (white circle).

• C intends to send to D.
• C hears As BTt and Bs BTr.
• D hears no BTt.
• The transmission can be granted if C controls its
  transmission power (pink circle).

D
C
A
B
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Many Transmission Pairs with Power Control and
Busy Tones
D
C
E
B
A
F
BTt and DATA yellow circles BTr white circles
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The Protocol

• Pmax the maximum transmission power
• Pmin the minimum power to distinguish a signal
  from a noise
• Pnoise the maximum power at which an antenna
  will regard a signal as a noise
• Pmin - Pnoise should be a very small value
• Basic Power Rules
• Data packet and BTt transmitted with power
  control.
• CTS and BTr transmitted at the largest power
  Pmax.
• RTS at a power level based on how strong the BTr
  are around the requesting host.

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Detailed Protocol

• On a host X intending to send a RTS to Y,
• X senses any receive busy tone BTr around it
• X sends a RTS on the control channel at power
  level Px
• If there is no BTr, let Px Pmax.
• O/w, let Pr be the power level of BTr that has
  the highest power among all heard BTrs.
• The RTS should not go beyond the nearest host
  that is currently receiving a data packet.
• Pmax is used because BTr is always transmitted at
  the maximal power.

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• On Y receiving Xs RTS,
• Y senses any transmit busy tone BTt around it.
• If there is any BTt, then Y ignores this RTS.
• O/w, Y does the following
• reply with a CTS at the maximum power Pmax
• turn on its receive busy tone BTr at the maximum
  power Pmax
• On X receiving Ys CTS,
• X transmits its data packet at power Px.
• X turns on its transmit busy tone BTt at power
  Px.
• Pr is the power level at which X receives Ys
  CTS. Px is the minimal possible power level to
  ensure that Y can correctly receive the data
  packet.

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Many Transmission Pairs with Power Control and
Busy Tones
BTr
BTt
RTS
D
C
CTS
E
B
A
F
H
G
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Analysis

• Scenario
• A is currently sending to B.
• Another pair, C and D, is intending to
  communicate.
• Goal We want to find out the probability that C
  can send to D.
• Through complicated calculus, we find that

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When BC lt rmax

• INTC(Ra, Rb, AB) the intersection of the
  circles centered at a and b
• Ra radius of the circle centered at a
• Rb radius of the circle centered at b
• AB distance of a and b
• The probability that C can send to D when A is
  sending to B
• i.e., the coverage of Rc excluding the coverage
  of Ra
• Fig. 6

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(No Transcript)
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cont...

• Integrating over ? 0 .. 2?, and then over CB
  0 .. rmax
• Integrating over AB 0 .. rmax, we have the
  final result
• On the contrary, the DBTMA has probability of 0.

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When rmax lt BC lt 3rmax

• Main difference Cs RTS will be sent with max.
  power.
• The probability that C can send to D when A is
  sending to B
• See Fig. 7
• At point C1, node C can always send.
• At point C2, node C cant send if D is in As
  range.

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(No Transcript)
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cont...

• Integrating over ? 0 .. 2?, and then over CB
  rmax..3rmax
• Integrating over AB 0 .. rmax, we have the
  final result

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cont.

• On the contrary, the DBTMA has a success
  probability of

X
change to rmax
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Discrete Power Control

• The levels of power provided by hardware may not
  be infinitely tunable.
• We may have a discrete number of power levels.
• Theorem
• Given a fixed integer k, evenly spreading the k
  power levels will be the best choice.
• I.e., (1/k)Pmax, (2/k)Pmax, (3/k)Pmax, ,
  (k/k)Pmax.

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Simulation Parameters

• Simulation parameters
• physical area 8km ? 8km
• max transmission distance (rmax) 0.5 or 1.0 km
• number of mobile hosts 600
• Speed of mobile hosts 0 or 125 km/hr.
• length of control packet 100 bits
• link speed 1 Mbps
• transmission bit error rate 10-5/bit

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Simulation Results Channel utilization vs.
traffic load

• (a) rmax 0.5 km

• (b) rmax 1.0 km

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Channel utilization vs. data packet length at
various traffic loads
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Channel Utilization vs. Number of Power Levels

• rmax 1 km arrival rate 200 or 400
  packets/ms packet length 1 or 2 Kbits
• So 4 to 6 levels will be sufficient.

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Channel Utilization vs. Traffic Load

• mobility 0 km/hr and 125 km/hr
• The transmission distance rmax 1.0 km

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Short Conclusion

• a new MAC protocol
• power control on top of RTS/CTS and busy tones
• Channel utilization can be significantly
  increased because the severity of signal
  overlapping is reduced.

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Power Mode Management in IEEE 802.11

• Y.-C. Tseng, C.-S. Hsu, and T.-Y. Hsieh,
  "Power-Saving Protocols for IEEE 802.11-Based
  Multi-Hop Ad Hoc Networks", Computer Networks,
  Elsevier Science Pub., Vol. 43, No. 3, Oct. 2003,
  pp. 317-337 (also in INFOCOM).

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Power Consumption

• IEEE 802.11 power model
• transmit 1400 mW
• receive 1000 mW
• idle 830 mW
• sleep 130 mW

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Power Mode Management

• Power modes in IEEE 802.11
• PS and ACTIVE
• Problem Spectrum
• infrastructure
• ad hoc network (MANET)
• single-hop
• multi-hop ad hoc networks

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Infrastructure Mode

• two power modes active and power-saving (PS)

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Ad Hoc Mode (Single-Hop)

• PS hosts also wake up periodically.
• interval ATIM (Ad hoc) window

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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

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

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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

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Structure of a Beacon Interval
Beacon Int. (BI)
Act. Win. (AW)
BW MW listening
BW MW listening

• BI beacon interval (to send beacons)
• AW active window
• BW beacon window
• MW MTIM window (for receiving MTIM)
• listening period to monitor the environment

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Three Protocols

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

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P1 Dominating-Awake-Interval

• intuition impose a PS host to stay awake
  sufficiently long
• dominating-awake property

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• Problem
• only dectectable in ONE direction
• Adjustment
• odd beacon interval
• Active Window BW MW listening
• even beacon interval
• Active Window listening MW BW

B
B
M
M
?
?
B
B
M
M
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Unicast Example
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Characteristics

• dominating awake
• wake-up ratio lt 1/2
• sensibility
• A PS host can receive a neighbors beacon once
  every two beacon intervals.
• suitable for highly mobile environment

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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)

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Example (T 3)
T Interval between the fully awake periods
A PS host can receive its neighbors beacon frame
in every T 3 beacon intervals
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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

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P3 Quorum-Based

• Quorum Sets
• Two quorum sets always have nonempty
  intersection.
• (used here to guarantee detectability)
• A matrix example

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Example (2D matrix quorum)
Host As quorum intervals
Host Bs quorum intervals
Non-quorum intervals
Host A quorum intervals
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5
4
3
2
1
0
Group 1
31
30
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Group 2
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Overlapping Property

• Overlap no matter how clocks drift
• demo ...

Host As quorum intervals
Host Bs quorum intervals
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5
4
3
2
1
0
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0
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Quorum and Non-quorum Intervals

• Quorum interval
• AW BI (i.e., fully awake)
• Non-quorum interval
• no beacon, only MTIM window
• AW lt BI
• BW 0, AW MW

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

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Sniff Scheduling for Power Saving in Bluetooth
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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

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Bluetooth Networks

• Piconet
• one master at most 7 active slaves
• Scatternet
• multiple piconets to form a larger network

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Packets Exchange Scenario

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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

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LMP_PDUs for Sniff
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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.

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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

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Proposed Architecture
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• Tk,Nk,Dk 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 lt d lt 1 (to tolerate some unexpected traffic)

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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 2u T
• time slots are viewed in a row-major way
• The availability of M

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RP Example

• Ms size 23 15 120

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• Example to allocate a slot occupancy of 16/120
• ( Note 16/120 8/60)

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

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Scheduling PoliciesLongest Sniff Interval
First(LSIF)a) initial state (equal
shares)b) reduce S2 to 2/60c) reduce S3
to 3/120d) increase S4 to 6/30
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Scheduling PoliciesShortest Sniff Interval
First(SSIF)a) initial state (equal
shares)b) reduce S2 to 1/30c) reduce S3
to 1/60d) increase S4 to 3/15
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Conclusions

• Proposed
• Power-saving protocols for IEEE 802.11-based
  multi-hop ad hoc networks
• Sniff-scheduling schemes for Bluetooth-based
  piconets
• References
• T.-Y. Lin and Y.-C. Tseng, An Adaptive Sniff
  Scheduling Scheme for Power Saving in Bluetooth,
  IEEE Personal Communications (to appear).
• 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.