Asynchronous Power-Saving Protocols via Quorum Systems for IEEE 802.11 Ad Hoc Networks Jehn-Ruey Jiang Hsuan-Chuang University

Asynchronous Power-Saving Protocols via Quorum Systems for

IEEE 802.11 Ad Hoc Networks

Jehn-Ruey Jiang

Hsuan-Chuang University

To Rest, to Go Far!

Outline

IEEE 802.11 Overview Power Saving Issues Asynchronous Quorum-based PS Protocols Optimal AQPS Protocols Analysis and Simulation Conclusion

Outline


IEEE 802.11

Approved by IEEE in 1997

Extensions approved in 1999

Standard for Wireless Local Area Networks ( WLAN )

IEEE 802.11 Family(1/2)

802.11a:6 to 54 Mbps in the 5 GHz band

802.11b (WiFi, Wireless Fidelity):5.5 and 11 Mbps in the 2.4 GHz band

802.11g:54 Mbps in the 2.4 GHz band

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

IEEE 802.11 MarketSource: Cahners In-Stat

($ Million)

IEEE 802.11 Components

Station (STA) - Mobile hostAccess Point (AP) - Stations are

connected to access points.Basic Service Set (BSS) - Stations and

the AP within the same radio coverage form a BSS.

Extended Service Set (ESS) - Several BSSs connected through APs form an ESS.

Infrastructure vs Ad-hoc Modesinfrastructure network

ad-hoc network

APAP

AP

wired network

ad-hoc network

Multi-hop ad hoc network

Ad hoc Networks

Ad hoc: formed, arranged, or done (often temporarily) for a particular purpose only

Mobile Ad Hoc Network (MANET):A collection of wireless mobile hosts forming a temporary network without the aid of established infrastructure or centralized administration

Applications of MANETs

Battlefields

Disaster rescue

Spontaneous meetings

Outdoor activities

Single-Hop vs Multi-Hop

Single-HopEach node is within each other’s transmission

rangeFully connected

Multi-HopA node reaches other nodes via a chain of

intermediate nodesNetworks may partition and/or merge

Outline


Power Saving - Overview

Battery is a limited resource for portable devices

Power saving becoming a very hot topic is wireless communication

Solutions:PHY: transmission power controlMAC: power mode managementNetwork Layer: power-aware routing

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?

Source: Prof. Tseng

Power Mode Management

doze mode vs. active mode example:

A is sending to BDoes C need to stay awake?

Source: Prof. Tseng

Power-Aware Routing

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

Example:

Source: Prof. Tseng

+

–

+

–

+

–

+

–

+

–

+

–

SRCN1 N2

DEST

N4N3

IEEE 802.11 PS Mode(1/2)

Power Consumption: (ORiNOCO IEEE 802.11b PC Gold Card)

Vcc:5V, Speed:11Mbps

IEEE 802.11 PS Mode(2/2)

Environments: Infrastructure

Ad hoc (infrastructureless)Single-hopMulti-hop

PS: Infrastructure (1/3) Clock synchronization is required (via TSF)

The AP is responsible for generating beacons each of which contains a valid time stamp

If the channel is in use, defer beacon transmission until it is free

PS: Infrastructure (2/3) A host always notifies AP its mode A PS host periodically wakes up to listen to

beacons AP keeps a PS host awake by sending

”traffic indication map (TIM)”in a beacon for unicast data

AP keeps all PS hosts awake by sending”delivery traffic indication map (DTIM)”in a beacon for broadcast data

PS: Infrastructure (3/3)

PS : 1-hop Ad hoc Network (1/2)

Beacon Interval Beacon Interval

ATIM Window

ATIM Window

Host A

Host B

Beacon

BTA=2, BTB=5

power saving state

power saving state

Beacon

ATIM

ACK

active state

data frame

ACK

Source: Prof. Tseng

PS: 1-hop Ad hoc Network (2/2)

ATIM

ACK

Data Frame

ACK

Host A

Host B

ATIM Window

Beacon Interval

Power Saving Mode

Beacon Interval Beacon Interval Beacon Interval

Beacon

Host C

ATIM

ACK

Data Frame

ACK

Beacon

Beacon

Beacon

Target Beacon Transmission Time (TBTT)

PS: m-hop Ad hoc Network (1/3)

Problems:Clock Synchronization is hard

due to communication delays and mobility

Network Partitionunsynchronized hosts with different wakeup times may not recognize each other

Clock Drift Example

Max. clock drift for IEEE 802.11 TSF (200 DSSS nodes, 11Mbps, aBP=0.1s)

Network-Partitioning Example

Host A

Host B

A

B

C

D

E

F

Host C

Host D

Host E

Host F

╳

╳

ATIM window

╳

╳

Network Partition

Source: Prof. Tseng


Solution:Not to synchronize hosts’ clocks

But to achieveWakeup predictionNeighbor discovery


Three asyn. solutions:Dominating-Awake-IntervalPeriodical-Fully-Awake-IntervalQuorum-BasedRef:

“Power-Saving Protocols for IEEE 802.11-BasedMulti-Hop Ad Hoc Networks,”Yu-Chee Tseng, Chih-Shun Hsu and Ten-Yueng HsiehInfoCom’2002

Outline


Quorum-based PS Protocol

Quorum interval

Touchdown

A PS host’s beacon can be heard twice or more for every n consecutive beacon intervals, which in turn solvesWakeup predictionNeighbor discovery

Observation

A quorum system may be translated to a power-saving protocol, whose power-consumption is proportional to the quorum size.

Questions Can any quorum system be translated to

an asyn. PS protocol?

NO!

Which can be?

Those with the Rotation Closure Property !!

Outline


Contributions

Propose the rotation closure property

Propose the lower bound of the quorum size

Propose a novel quorum systems to be translated to an adaptive PS protocol

What are quorum systems? Quorum:

a subset of universal set UE.G. q1={1, 2} and q2= {2, 3} are quorums under U={1,2,3}

Quorum system: a collection of mutually intersecting quorums

E.G. {{1, 2},{2, 3},{1,3}} is a quorum system under U={1,2,3}

Rotation Closure Property

For example,Q1={{0,1},{0,2},{1,2}} under U={0,1,2}Q2={{0,1},{0,2},{0,3},{1,2,3}} under U={0,1,2,3}

Because {0,1} rotate({0,3},3) =

Examples of quorum systems

Majority quorum system Tree quorum system Hierarchical quorum system Cohorts quorum system ………

Optimal Quorum Size

Optimal quorum size:k, where k(k-1)+1=n and k-1 is a prime power (K n)

Optimal Quorum Systems

Near optimal quorum systemsGrid quorum systemTorus quorum systemCyclic (difference set) quorum system

Optimal quorum systemFPP quorum system

Torus quorum system

Cyclic (difference set) quorum system

Def: A subset D={d1,…,dk} of Zn is called a difference set if for every e0 (mod n), thereexist elements di and djD 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

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

E-Torus quorum system

Outline


Analysis (1/3)

Active Ratio:the 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

Analysis (2/3)

Analysis (3/3)

Simulation Model

Area: 1000m x 1000m Speed: 2Mbps Radio radius: 250m Battery energy: 100J. Traffic load: Poisson Dist. , 1~4 routes/s,

each having ten 1k packets Mobility: way-point model (pause time: 20s) Routing protocol: AODV

Simulation ParametersUnicast send 454+1.9 * L

Broadcast send 266+1.9 * L

Unicast receive 356+0.5 * L

Broadcast receive 56+0.5 * L

Idle 843

Doze 27 L: packet length

Unicast packet size 1024 bytes

Broadcast packet size 32 bytes

Beacon window size 4ms

MTIM window size 16ms

Simulation Metrics

Survival ratioNeighbor discovery timeThroughputAggregate throughput

Simulation Results (1/10)

0

20

40

60

80

100

120

100 120 140 160 180 200 220 240 260 280 300 320 340

Simulation time (sec)

Surv

ival ra

tio (

%)

C0(98)C20(98)E0(7x14)E20(7x14)AA0AA20

Survival ratio vs. mobility (beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec).


Neighbor discovery time vs. mobility(beacon interval =100 ms, 100 hosts, traffic load = 1 route/sec).

0

500

1000

1500

2000

2500

3000

0 5 10 15 20

Moving speed (m/sec)

Neig

hb

or

dis

covery

tim

e (

ms)

C(98)

E(7x14)


Throughput vs. mobility(beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec).


Survival ratio vs. beacon interval length(100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with

mean = 10m/sec).


Neighbor discovery time vs. beacon interval length(100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with

mean = 10m/sec).

0

2000

4000

6000

8000

10000

12000

14000

16000

100 200 300 400

Beacon interval (ms)

Nei

ghbor disco

ver

y tim

e (m

s)

C(98)

E(7x14)


Throughput vs. beacon interval length(100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with

mean =10m/sec).


Survival ratio vs. traffic load(beacon interval = 100 ms, 100 hosts, mobility = 0~20 m/sec with mean =

10 m/sec).


Throughput vs. traffic load(beacon interval =100 ms, 100 hosts, mobility = 0~20 m/sec with mean =

10 m/sec).


Survival ratio vs. host density(beacon interval = 100ms, traffic load 1 route/sec, mobility = 0~20 m/sec

with mean= 10 m/sec).


Throughput vs. host density (beacon interval = 100ms, traffic load 1 route/sec, mobility = 0~20m/sec

with mean= 10 m/sec).

Outline


Conclusion (1/2) 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

Conclusion (2/2)Future work:

To incorporate AQPS protocols with those demanding accurate neighboring node’s information, e.g., geometric routing protocols

To incorporate quorum system concept to wireless sensor networks

To incorporate quorum system concept to Bluetooth technology

Q&A

Documents

Asynchronous Power-Saving Protocols via Quorum Systems for IEEE 802.11 Ad Hoc Networks Jehn-Ruey Jiang Hsuan-Chuang University