QuorumBased Asynchronous PowerSaving Protocols for IEEE 802'11 Ad Hoc Networks

1
Quorum-Based Asynchronous Power-Saving Protocols
forIEEE 802.11 Ad Hoc Networks

• Presented by
• Jehn-Ruey Jiang
• Department of Computer Science and Information
  Engineering
• National Central University

2
To Rest, to Go Far!
3
Outline

• IEEE 802.11 Ad hoc Network
• Power Saving Problem
• Asynchronous Quorum-based PS Protocols
• Optimal Asyn. Quorum-Based PS Protocols
• Analysis and Simulation
• Conclusion

4
Outline

• IEEE 802.11 Ad hoc Network
• Power Saving Problem
• Asynchronous Quorum-based PS Protocols
• Optimal Asyn. Quorum-Based PS Protocols
• Analysis and Simulation
• Conclusion

5
IEEE 802.11 Overview

• Approved by IEEE in 1997
• Extensions approved in 1999
• Standard for Wireless Local Area Networks
  ( WLAN )

6
IEEE 802.11 Family(1/2)

• 802.11a6 to 54 Mbps in the 5 GHz band
• 802.11b (WiFi, Wireless Fidelity)5.5 and 11
  Mbps in the 2.4 GHz band
• 802.11g54 Mbps in the 2.4 GHz band

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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
Infrastructure vs Ad-hoc Modes
infrastructure network
AP
AP
wired network
AP
Multi-hop ad hoc network
ad-hoc network
ad-hoc network
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Ad hoc Network Applications

• Battlefields
• Disaster rescue
• Spontaneous meetings
• Outdoor activities

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Outline

• IEEE 802.11 Ad hoc Network
• Power Saving Problem
• Asynchronous Quorum-based PS Protocols
• Optimal Asyn. Quorum-Based PS Protocols
• Analysis and Simulation
• Conclusion

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Power Saving

• Battery is a limited resource for portable
  devices
• Battery technology does not progress fast enough
• Power saving becomes a critical issue in MANETs,
  in which devices are all supported by batteries

13
Solutions to Power Saving

• PHY Layer transmission power control
• Huang (ICCCN01), Ramanathan (INFOCOM00)
• MAC Layer power mode management
• Tseng (INFOCOM02), Chiasserini (WCNC00)
• Network Layer power-aware routing
• Singh (ICMCN98), Ryu (ICC00)

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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?

No!
Yes!
B
C
D
A
E
F
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Power Mode Management

• doze mode vs. active mode
• Example
• A is sending to B
• Does C need to stay awake?

No!
It can turn off its radio to save energy!
B
A
But it should turn on its radio periodiclally for
possible data comm.
C
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Power-Aware Routing

• Routing in an ad hoc network with energy-saving
  (prolonging network lifetime) in mind
• Example

N2
N1
SRC
DEST
Better!!
N3
N4
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Our Focus

• Among the three solutions
• PHY Layer transmission power control
• MAC Layer power mode management
• Network Layer power-aware routing

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IEEE 802.11 PS Mode(2/2)

• Environments
• Infrastructure (O)
• Ad hoc (infrastructureless)
• Single-hop (O)
• Multi-hop

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IEEE 802.11 PS Mode(1/2)

• An IEEE 802.11 Card is allowed to turn off its
  radio to be in the PS mode to save energy
• Power Consumption(ORiNOCO IEEE 802.11b PC Gold
  Card)

Vcc5V, Speed11Mbps
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PS for 1-hop Ad hoc Networks (1/3)

• Time axis is divided into equal-length intervals
  called beacon intervals
• In the beginning of a beacon interval, there is
  ATIM window, in which hosts should wake up and
  contend to send a beacon frame with the backoff
  mechanism for synchronizing clocks

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PS for 1-hop Ad hoc Networks (2/3)

• A possible sender also sends ATIM (Ad hoc Traffic
  Indication Map) message with DCF procedure in the
  ATIM window to its intended receivers in the PS
  mode
• ATIM demands an ACK. And the pair of hosts
  receiving ATIM and ATIM-ACK should keep
  themselves awake for transmitting and receiving
  data

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PS for 1-hop Ad hoc Networks (3/3)
Target Beacon Transmission Time (TBTT)
Beacon Interval
Beacon Interval
Host A
No ATIM means no data to send or to receive
Host B
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PS m-hop Ad hoc Network

• Problems
• Clock Synchronizationit is hard due to
  communication delays and mobility
• Network Partitionunsynchronized hosts with
  different wakeup times may not recognize each
  other

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Clock Drift Example
Max. clock drift for IEEE 802.11 TSF (200 DSSS
nodes, 11Mbps, aBP0.1s)
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Network-Partitioning Example
The red ones do not know the existence of the
blue ones, not to mention the time when they are
awake.
The blue ones do not know the existence of the
red ones, not to mention the time when they are
awake.
C
A
B
Host A
ATIM window
Host B
Host C
Host D
Host E
Host F
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Asynchronous PS Protocols (1/2)

• Try to solve the network partitioning problem to
  achieve
• Neighbor discovery
• Wakeup prediction
• without synchronizing hosts clocks

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Asynchronous PS Protocols (2/2)

• Three asyn. PS protocols by Tseng
• Dominating-Awake-Interval
• Periodical-Fully-Awake-Interval
• Quorum-Based
• RefPower-Saving Protocols for IEEE
  802.11-BasedMulti-Hop Ad Hoc Networks,Yu-Chee
  Tseng, Chih-Shun Hsu and Ten-Yueng
  HsiehInfoCom2002

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Outline

• IEEE 802.11 Ad hoc Network
• Power Saving Problem
• Asynchronous Quorum-based PS Protocols
• Optimal Asyn. Quorum-Based PS Protocols
• Analysis and Simulation
• Conclusion

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Numbering beacon intervals
n consecutive beacon intervals are numbered as 0
to n-1
And they are organized as a ?n ? ?n array
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Quorum Intervals (1/4)
Intervals from one row and one column are
called quorum intervals
Example Quorum intervals arenumbered by 2, 6,
8, 9, 10, 11, 14
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Quorum Intervals (2/4)
Intervals from one row and one column are
called quorum intervals
Example Quorum intervals arenumbered by 0, 1,
2, 3, 5, 9, 13
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Quorum Intervals (3/4)
Any two sets of quorum intervals have two common
members
For example The set of quorum intervals 0, 1,
2, 3, 5, 9, 13 and the set of quorum
intervals 2, 6, 8, 9, 10, 11, 14 have two
common members 2 and 9
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Quorum Intervals (4/4)
Host D
2
15
14
13
12
11
10
9
8
7
6
5
4
3
1
0
Host C
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
2 overlapping quorum intervals
Even when the beacon interval numbers are not
aligned (they are rotated), there are always at
least two overlapping quorum intervals
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Structure of quorum intervals
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Networks Merge Properly
C
A
B
Host A
ATIM window
Host B
Beacon window
Host C
Monitor window
Host D
Host E
Host F
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Short Summary

• There is an asynchronous power-saving protocol
  that achieves
• asynchronous neighbor discovery
• Hearing beacons twice or more in every n
  consecutive beacon intervals
• wakeup prediction
• via a simple quorum concept.

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Observation 1

• It is a simple grid quorum system Maekawa 1985
  in Tsengs work.
• There are many more complicated quorum systems in
  the literature of distributed system
• FPP Maekawa 1985, Tree Agrawal 1990,
  HierarchicalKumar 1991, Cohorts Jiang 1997,
  Cyclic Luk 1997, Torus Lang 1998, etc.
• Question Can these quorum systems be directly
  applied to solve the power-saving problem in a
  MANET?

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The Answer Is

• Not all quorum systems can be used here!
• Counter example 1 under 1,2,3
• Only those quorum systems with the rotation
  closure property can be used!

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Observation 2

• Smaller quorums are better because they imply
  lower active ratio (better energy-efficiency)
• But quorums cannot be too small less the quorum
  system does not satisfy the rotation closure
  property
• Question 1 What is the smallest quorum size?
• Question 2 Is there any quorum systems to have
  the smallest quorum size?

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Outline

• IEEE 802.11 Ad hoc Network
• Power Saving Problem
• Asynchronous Quorum-based PS Protocols
• Optimal Asyn. Quorum-Based PS Protocols
• Analysis and Simulation
• Conclusion

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What are quorum systems?

• Quorum system
• a collection of mutually intersecting subsets
  of a universal set U, where each subset is called
  a quorum
• E.G. 1, 2,2, 3,1,3 is a quorum system
  under U1,2,3
• A quorum system is a collection of sets
  satisfying the intersection property

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Rotation Closure Property (1/3)

• Definition. Given a non-negative integer i and a
  quorum H in a quorum system Q under U 0,,
  n?1, we define rotate(H, i) ji?j?H (mod n).
• E.G. Let H0,3 be a subset of U0,,3. We
  have rotate(H, 0)0, 3, rotate(H, 1)1,0,
  rotate(H, 2)2, 1, rotate(H, 3)3, 2

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Rotation Closure Property (2/3)

• Definition. A quorum system Q under U 0,,
  n?1 is said to have the rotation closure
  property if
• ?G,H ? Q, i ? 0,, n?1 G ? rotate(H, i) ? ?.

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Rotation Closure Property (3/3)

• For example,
• Q10,1,0,2,1,2 under U0,1,2
• Q20,1,0,2,0,3,1,2,3 under U0,1,2,3

?
?
Because 0,1 ? rotate(0,3,3) 0,1 ? 3,
2 ?
Closure
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Examples of quorum systems

• Majority quorum system
• Tree quorum system
• Hierarchical quorum system
• Cohorts quorum system

?
?
?
?
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Optimal Quorum System (1/2)

• Quorum Size Lower Bound for quorum systems
  satisfying the rotation closure propertyk,
  where k(k-1)1n, the cardinality of the
  universal set, and k-1 is a prime power(k? ?n )

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Optimal Quorum System (2/2)

• Optimal quorum system
• FPP quorum system
• Near optimal quorum systems
• Grid quorum system
• Torus quorum system
• Cyclic (difference set) quorum system

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Outline

• IEEE 802.11 Ad hoc Network
• Power Saving Problem
• Asynchronous Quorum-based PS Protocols
• Optimal Asyn. Quorum-Based PS Protocols
• Analysis and Simulation
• Conclusion

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Analysis (1/3)

• Active Ratiothe 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

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Analysis (2/3)
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Analysis (3/3)
Optimal!
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Simulation Model

• Area 1000m x 1000m
• Speed 2Mbps
• Radio radius 250m
• Battery energy 100J.
• Traffic load Poisson Dist. , 14 routes/s, each
  having ten 1k packets
• Mobility way-point model (pause time 20s)
• Routing protocol AODV

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Simulation Parameters
L packet length
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Simulation Metrics

• Survival ratio
• Neighbor discovery time
• Throughput
• Aggregate throughput

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Simulation Results (1/10)
E-torus quorum system
Cyclic quorum system
Always Active
Survival ratio vs. mobility (beacon interval
100 ms, 100 hosts, traffic load 1 route/sec).
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Simulation Results (2/10)
A faster host can be discovered in shorter time.
Neighbor discovery time vs. mobility(beacon
interval 100 ms, 100 hosts, traffic load 1
route/sec).
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Simulation Results (3/10)
For the throughput AAgtE(7x74)gtC(98)
For the aggregate throughput C(98)gtE(7x74)gtAA
Throughput vs. mobility(beacon interval 100
ms, 100 hosts, traffic load 1 route/sec).
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Simulation Results (4/10)
Survival ratio vs. beacon interval length(100
hosts, traffic load 1 route/sec, moving speed
020 m/sec with mean 10m/sec).
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Simulation Results (5/10)
Neighbor discovery time vs. beacon interval
length (100 hosts, traffic load 1 route/sec,
moving speed 020 m/sec with mean 10m/sec).
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Simulation Results (6/10)
Throughput vs. beacon interval length (100 hosts,
traffic load 1 route/sec, moving speed 020
m/sec with mean 10m/sec).
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Simulation Results (7/10)
Survival ratio vs. traffic load (beacon interval
100 ms, 100 hosts, mobility 020 m/sec with
mean 10 m/sec).
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Simulation Results (8/10)
Throughput vs. traffic load(beacon interval 100
ms, 100 hosts, mobility 020 m/sec with mean
10 m/sec).
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Simulation Results (9/10)
Survival ratio vs. host density (beacon interval
100ms, traffic load 1 route/sec, mobility
020 m/sec with mean 10 m/sec).
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Simulation Results (10/10)
Throughput vs. host density (beacon interval
100ms, traffic load 1 route/sec, mobility
020m/sec with mean 10 m/sec).
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Outline

• IEEE 802.11 Ad hoc Network
• Power Saving Problem
• Asynchronous Quorum-based PS Protocols
• Optimal Asyn. Quorum-Based PS Protocols
• Analysis and Simulation
• Conclusion

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Conclusion

• 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

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Publication

• ICPP03 Best Paper Award
• ACM Journal on Mobile Networks and Applications

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Future work

• To incorporate the clustering concept into the
  design of hybrid (syn. and asyn.) power saving
  protocols (NSC 93-2213-E-008-046-)
• To design more flexible adaptive asyn. power
  saving protocols with the aid of the expectation
  quorum system (a novel quorum system which is a
  general form of probabilistic quorum systems)
  (93CAISER-????????)
• To incorporate power saving mode management to
  wireless sensor networks with comm. and sensing
  coverage in mind (????????????????)

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• Thanks!

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FPP quorum system

• Proposed by Maekawa in 1985
• For solving distributed mutual exclusion
• Constructed with a hypergraph
• An edge can connect more than 2 vertices
• FPPFinite Projective Plane
• A hypergraph with each pair of edges having
  exactly one common vertex
• Also a Singer difference set quorum system

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FPP quorum system Example
A FPP quorum system 0,1,2, 1,5,6,
2,3,6, 0,4,6, 1,3,4, 2,4,5,
0,3,5
5
5
3
4
3
6
2
0
0
1
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Torus quorum system
5
4
3
2
1
0
1,7,13,8,3,10, 5,11,17,12,1,14,
11
10
9
8
7
6
17
16
15
14
13
12
One half column cover in a wrap around manner
One full column
For a t?w torus, a quorum contains all elements
from some column c, plus ?w/2? elements, each of
which comes from column ci, i1.. ?w/2?
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Cyclic (difference set) quorum system

• Def A subset Dd1,,dk of Zn is called a
  difference set if for every e?0 (mod n),
  thereexist elements di and dj?D such that
  di-dje.
• 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 C(8)

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E-Torus quorum system
Trunk
E(t x w, k)
Branch
Branch
cyclic
Branch
Branch
cyclic