History-Based Collision History-Based Collision Resolution of CSMA/CAResolution of CSMA/CA

Dongsoo S. Kim, Ph.D.Dongsoo S. Kim, Ph.D.

Associate ProfessorAssociate Professor

Electrical and Computer EngineeringElectrical and Computer Engineering

Indiana U. Purdue U. IndianapolisIndiana U. Purdue U. Indianapolis

22

PreludePrelude

Introduction to Indiana, and Research InterestsIntroduction to Indiana, and Research Interests Technical BackgroundTechnical Background

Distributed Coordinated Function (DCF) in IEEE Distributed Coordinated Function (DCF) in IEEE 802.11 CSMA/CA 802.11 CSMA/CA

GDCFGDCF History-Based DCFHistory-Based DCF

BackgroundBackground AnalysisAnalysis ExperimentationExperimentation

ConclusionConclusion

33

Indiana Indiana

44

IndianapolisIndianapolis

Capital city of IndianaCapital city of Indiana 1 Millions of population1 Millions of population Major industriesMajor industries

Automobile – Delphi Delco, Automobile – Delphi Delco, Honda, Indy 500, Allison Honda, Indy 500, Allison TransmissionTransmission

Pharmaceutical – Elli Lilly, Pharmaceutical – Elli Lilly, Military – Raytheon, Crane,Military – Raytheon, Crane, AgricultureAgriculture

55

IUPUIIUPUI

Nearby Indianapolis downtownNearby Indianapolis downtown One of 8 IU CampusesOne of 8 IU Campuses

The residential campus - IU Bloomington The residential campus - IU Bloomington The urban campus - IUPUI IndianapolisThe urban campus - IUPUI Indianapolis 6 regional campus - IU East, IPFW Fort Wayne, IU Kokomo, IU 6 regional campus - IU East, IPFW Fort Wayne, IU Kokomo, IU

Northwest, IU South Bend, IU SoutheastNorthwest, IU South Bend, IU Southeast

Schools – Medical, Engineering, Business, Infomatics, Law, Schools – Medical, Engineering, Business, Infomatics, Law, Science, Dentstry, Art&Design, Education, Science, Dentstry, Art&Design, Education, Health&Rehabiliation Science, Journalisms, Liberal Arts, … Health&Rehabiliation Science, Journalisms, Liberal Arts, …

Housing a ELS Language CenterHousing a ELS Language Center 25,000 Students 25,000 Students

66

77

Purdue School of Engineering and Purdue School of Engineering and TechnologyTechnology

2,400 Students2,400 Students 440 Purdue degree options from certificate programs 0 Purdue degree options from certificate programs

to masters and doctorate degreesto masters and doctorate degrees Disciplines – Biomedical, Electrical, Computer, Disciplines – Biomedical, Electrical, Computer,

Mechanical, Construction, Information, Interior Mechanical, Construction, Information, Interior Design Design

http://www.engr.iupui.eduhttp://www.engr.iupui.edu

88

Center for Sensor and Ad Hoc Center for Sensor and Ad Hoc NetworksNetworks

A forum of multi-disciplinaryA forum of multi-disciplinary engineers, scientists, medical doctors, and hospitalsengineers, scientists, medical doctors, and hospitals

To apply embedded and communication technologies to the To apply embedded and communication technologies to the community and interest groups for enhancingcommunity and interest groups for enhancing health and medical services, health and medical services, environment preserve, environment preserve, national security and civilian safetynational security and civilian safety

99

Project: SmartNurseProject: SmartNurse To care chronicle patients and elders in their placesTo care chronicle patients and elders in their places

The fastest growing demographic groupThe fastest growing demographic group The burden on caregivers The burden on caregivers

Consideration:Consideration: the majority of seniors do not use computers or the Internetthe majority of seniors do not use computers or the Internet many patients with a chronicle disease can not care themselves many patients with a chronicle disease can not care themselves

(e.g. children with T1D)(e.g. children with T1D) large geographical areas are not supported by broadband Internet serviceslarge geographical areas are not supported by broadband Internet services most of daily activities do not occur in their homemost of daily activities do not occur in their home

MethodsMethods to connect all portable medical/health devices via short-range wireless to an to connect all portable medical/health devices via short-range wireless to an

agent unnoticeable to caretakersagent unnoticeable to caretakers• e.g. glucose tester, blood pressure meter, pedometer, etc)e.g. glucose tester, blood pressure meter, pedometer, etc)

The intelligent agent is customizable based on a caretaker's diseaseThe intelligent agent is customizable based on a caretaker's disease The agent is connected via affordable and available comm. technology The agent is connected via affordable and available comm. technology

( broadband, GSM, SMS, DUN) to health care professionals or caregivers( broadband, GSM, SMS, DUN) to health care professionals or caregivers

1010

SmartNurse Prototype: DiabetesSmartNurse Prototype: Diabetes

Glucose meter and insulin injector with Bluetooth Glucose meter and insulin injector with Bluetooth An intelligent agent are installed to An intelligent agent are installed to

Personal computer, Personal computer, Standalone gateway, orStandalone gateway, or Mobile phoneMobile phone

1111

Project: Project: CyberhandCyberhand (Prosthetic Hand)(Prosthetic Hand)

Requirements: Selective electrode for stimulation (sensory feedback) Selective electrode for recording (volition detection) Multiple channels of information Robust, Biocompatible, Chronically Stable

1212

LIFE – a Bio-Electronic InterfaceLIFE – a Bio-Electronic Interface

1313

Courtesy of KW Horch

1414

Courtesy of KW Horch

1515

Final assembly: 80µm Tungsten needle + poly-aramid link

The realized tfLIFE2The realized tfLIFE2

Photo courtesy of M Schuettler

1616

Implanted tfLIFE and metal LIFEImplanted tfLIFE and metal LIFE

Photo courtesy of M. Schüttler

1717

Total Neuro-Prosthetic SystemTotal Neuro-Prosthetic System Concept Concept

Paraplegia is mainly occurred in Paraplegia is mainly occurred in spinal cord, cause by spinal cord, cause by trauma trauma with with acute spinal cord acute spinal cord

injuryinjury tumors tumors that that chronicchronicallyally compress compress

the cordthe cord, or , or other diseasesother diseases such as such as myelitis myelitis

and multiple sclerosisand multiple sclerosis

AAnterior hornnterior horn and and posterior posterior horhorn in spinal cord act as a hub n in spinal cord act as a hub for for transmittransmitting ting "instructions" "instructions" from the brain to from the brain to peripheral peripheral nerve, and receiving info nerve, and receiving info regarding touch and sensationregarding touch and sensation

Cortex

Spinal Cord

Peripheral Nerve

History-Based Collision History-Based Collision ResolutionResolution

1919

Random Medium Access Random Medium Access

In CSMA/CD (IEEE 802.3), failure due to In CSMA/CD (IEEE 802.3), failure due to propagation delaypropagation delay

In CSMA/CA (IEEE 802.11), failure due to In CSMA/CA (IEEE 802.11), failure due to propagation delay,propagation delay, channel noisechannel noise hidden terminal problem, andhidden terminal problem, and exposed terminal problemexposed terminal problem

2020

CSMA/CACSMA/CA

support of two access methodssupport of two access methods basic access methods basic access methods four-way handshaking (RTS-CTS-DATA-ACK)four-way handshaking (RTS-CTS-DATA-ACK)

A packet will be A packet will be collided with other packets, or collided with other packets, or garbled with noisegarbled with noise

Note: Note: Theoretically, only RTS and CTS packets can be collided.Theoretically, only RTS and CTS packets can be collided. In reality, any packets can be collided due to imperfect channel, In reality, any packets can be collided due to imperfect channel,

and nodes' movementand nodes' movement

2121

Standard Distributed Coordination FunctionStandard Distributed Coordination Function

Contention window and back-off counterContention window and back-off counter For each collision, a counter is randomly selected between 0 For each collision, a counter is randomly selected between 0

to CWto CW The counter decrements each slot timeThe counter decrements each slot time Contention window Contention window

Increments twice for each failed TX up to CWIncrements twice for each failed TX up to CWMAXMAX. . Resets to CWResets to CWMINMIN for each successful TX for each successful TX

• A success indicates the burst time of other stations is expired. A success indicates the burst time of other stations is expired. • Good for wired channel with very low error rate, and high bandwidthGood for wired channel with very low error rate, and high bandwidth• In wireless, a distant node may suffer from a high channel noise, so a large In wireless, a distant node may suffer from a high channel noise, so a large

CWCW• It is not fair to a distant node that a nearby node resets CW and have a high It is not fair to a distant node that a nearby node resets CW and have a high

channel acquisition probabilitychannel acquisition probability

2222

Gentle DCFGentle DCF

Proposed by C. Wang et al (2004)Proposed by C. Wang et al (2004) To fix the unfairness for a heavy load channelTo fix the unfairness for a heavy load channel

force a success node not to reduce CW rapidly, but force a success node not to reduce CW rapidly, but wait and see the channel statuswait and see the channel status

Assume the wireless channel is error-freeAssume the wireless channel is error-free Gently decrement CWGently decrement CW

double CW for each collisiondouble CW for each collision halve CW for each halve CW for each cc consecutive successes consecutive successes hold CW for other caseshold CW for other cases reset the consecutive variable if a node has either a reset the consecutive variable if a node has either a

collision or collision or cc consecutive successes consecutive successes

2323

Effect of GDCFEffect of GDCF

ConservativeConservative A single success of TX may not necessarily indicate the A single success of TX may not necessarily indicate the

end of burst periodend of burst period ReservednessReservedness

It can achieve better performance for heavy loaded It can achieve better performance for heavy loaded channelchannel

Unconditionally increment CW for each TX failure, Unconditionally increment CW for each TX failure, which was possibly caused by which was possibly caused by Packet collision, orPacket collision, or NoiseNoise

2424

History-Based DCFHistory-Based DCF

A new method for controlling CWA new method for controlling CW To adapt CW according to the history of To adapt CW according to the history of

transmission statustransmission status A binary transmission status A binary transmission status

• 0 → TX success0 → TX success• 1 → TX failure because of either collision or noise1 → TX failure because of either collision or noise

To estimate either a failure-by-collision, or a failure-by-To estimate either a failure-by-collision, or a failure-by-noise noise

2525

H-DCF PolicyH-DCF Policy

If the current status is not consistent with the If the current status is not consistent with the previous, stay in the current back-off stageprevious, stay in the current back-off stage

If the current status is consistent with the previous, If the current status is consistent with the previous, or the previous status cannot be determined, or the previous status cannot be determined, increment the back-off stage for a failed TXincrement the back-off stage for a failed TX decrement the back-off stage for a success TXdecrement the back-off stage for a success TX

2626

Action TableAction Table

p3Increment1 1 17

p2(1-p)Hold1 1 06

p2(1-p)Increment1 0 15

p(1-p)2Decrement1 0 04

p2(1-p)Increment0 1 13

p(1-p)2Decrement0 1 02

p(1-p)2Hold0 0 11

(1-p)3Decrement0 0 00

ProbabilityActionsR2 R1 R0Case

pp is the probability that a transmitted packet is dropped off is the probability that a transmitted packet is dropped off due to either collision or channel noise.due to either collision or channel noise.

2727

Evolution of Back-off StageEvolution of Back-off Stage

0 1 i m-1 m…

… …

…λ λ λ λ λ λ

μ μ μ μ μ μ

1-μ1-λ 1-λ-μ 1-λ-μ1-λ-μ

0 1 wi-2 wi-1…1 111

PiIN/wi PiIN/wi PiIN/wi PiIN/wi

PiINC

PiDEC

PiHOLD

λ = 2p2-p3

μ = 1 – p – p2 + p3

For the For the ii-th Stage:-th Stage:

2828

Example of Markov ChainExample of Markov Chain

0 11

0 1 2 31 1 1

0 1 2 31 1 1 4 5 6 71 1 11

2929

Stationary ProbabilityStationary Probability

1

0,

0,0,

,

1),(

),()0,2(),2()0,(

),()0,2(2

),()0,2(),2()0,(

)0,2()0,2(2

1

+−≡Ψ

ΨΨ+ΨΨΨΨ=

=

ΨΨ+ΨΨΨΨ=

−=

=

∑

∑ ∑

k

i i

i

i

iki

i k ki

xkx

mmW

m

b

mmW

bw

kwb

b

ρρρρρρ

τ

ρρρρρρ

ρ

bi,k : a stationary probability that the system is in the i-th stage with the back-off counter value of k

τ : a probability that a node attempts to transmit a packet in a randomly chosen slot time

ρ : λ/μ

3030

Case 1. Moving AwayCase 1. Moving Away

0

200

400

600

800

1000

1200

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97

Rounds

Co

nte

nti

on

Win

do

ws

COLLISION

SDCF

GDCF4

HDCF

3131

Case 2. Coming to CloseCase 2. Coming to Close

0

200

400

600

800

1000

1200

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97

Rounds

Co

nte

nti

on

Win

do

w

COLLISION

SDCF

GDCF4

HDCF

3232

SimulationSimulation

ns-2ns-2 a node at a centera node at a center nn nodes are randomly placed in the TX range of the nodes are randomly placed in the TX range of the

center nodecenter node Each node exchanges 36Kbps bidirectional CBR Each node exchanges 36Kbps bidirectional CBR

traffic with the center nodetraffic with the center node 900 second run-time for each testcase900 second run-time for each testcase

3333

Throughput on Perfect ChannelThroughput on Perfect Channel

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20 25 30 35 40

# of Nodes

Th

rou

gh

pu

t

SDCF

GDCF4

GDCF8

HDCF

3434

Mean RTT on Perfect ChannelMean RTT on Perfect Channel

3.4

3.45

3.5

3.55

3.6

3.65

3.7

3.75

0 5 10 15 20 25 30 35 40 45

# of Nodes

Mean

RT

T (

msec)

SDCF

GDCF4

GDCF8

HDCF

3535

Throughput on Noisy ChannelThroughput on Noisy Channel

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.02 0.04 0.06 0.08 0.1

Error Rate

Th

rou

gh

pu

t

SDCF

GDCF4

GDCF8

HDCF

3636

Mean RTT on Noisy ChannelMean RTT on Noisy Channel

0

1

2

3

4

5

6

7

0 0.02 0.04 0.06 0.08 0.1

Error Rate

Me

an

RT

T (

mse

c)

SDCF

GDCF4

GDCF8

HDCF

3737

Max RTT on Noisy ChannelMax RTT on Noisy Channel

0

10

20

30

40

50

60

70

0 0.02 0.04 0.06 0.08 0.1Error Rate

Ma

x R

TT

(m

se

c)

SDCF

GDCF4

GDCF8

HDCF

3838

ConclusionConclusion

A new DCFA new DCF for noisy channel, and for noisy channel, and for moving nodesfor moving nodes

Immunity of the worst-case RTT to channel noiseImmunity of the worst-case RTT to channel noise toward QOS of mobile nodestoward QOS of mobile nodes

Future WorksFuture Works Will a longer history pattern be beneficial?Will a longer history pattern be beneficial? Thorough simulations Thorough simulations