725 31-10-08 haley jones slides

7/29/2019 725 31-10-08 Haley Jones Slides

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Channel Aware Routing inMANETs with Route Handoff

Sandra Chen, Haley Jones and Dhammika Jayalath


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Ad-hoc On-demand Distance

Vector (AODV) Routing Protocol

On-demand/reactive route discovery

Single path identified

RREQ contains:Source IP address (constant)

Source sequence number (freshness indicator)Broadcast ID (unique)

Destination IP address (constant)

Destination sequence number (last known)

Hop-count (incremented at each intermediate node)

RREQ uniquely identified by Source SequenceNumber and broadcast ID.

Duplicate RREQs discarded.


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AODV cont.

RREP generated when intermediate node has recent

enough path to destination, or from destination node, itself.

RREP contains:

Source IP address (constant)


Destination sequence number (last known)

Hop-count (incremented at each node)

Route expiration time (time for new route discovery)

Duplicate RREPs discarded, except if same DestinationSequence Number but smaller Hop-Count.


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AODV cont.

RERR packet generated by up-link node when linkin active route breaks.

RERR has:

Source IP address (constant)


Destination sequence number (incremented from

RREP)

Hop-count =

New route discovery process required by source ifit has remaining packets for destination


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Ad-hoc On-demand Multipath Distance

Vector (AOMDV) Routing Protocol

AODV: Destination IP address

Destination sequencenumber

Next hop IP address

Hop-count

Entry expiration time

AOMDV: Destination IP address

Destination sequence number

Advertised hop-count

Route list:

Next hop IP 1, hop-count 1



Similar to AODV, but with Multiple paths identified on each

route discovery.

Paths are loop-free and link-disjoint. Routing Table Entries:


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Multiple Link-Disjoint Paths


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Shortcomings of AOMDV

Paths chosen based only on hop-countPath stability and channel quality measures are

ignored

Tends towards paths with few, but long, hopsclose to breaking point

Channel fading conditions ignored and,therefore, unable to be exploited


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Mobile-to-Mobile Channel Model

Required because both nodes in a link may be

moving

Simple: Uses individual node speeds rather than

relative speeds

Has a Rayleigh envelope

Can define average fading duration (AFD) and

average non-fading duration (ANFD)


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Fading

3 2 1 0 1 2 30

1

2

3

4

5

6

Threshold


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AFD & ANFD

= ratio of signal threshold to RMS power

= maximum Doppler shift of transmitter

= ratio of receiver velocity to transmitter velocity

ANFD = 1

fT

q2(1 + 2)

AFD =e2 1

fTq2(1 + 2)

=Rth

Rrms

fT

=

vR

vT


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ANFD as a Link Selection Metric

Decreases withincreasing normalisedthreshold (indication of

channel quality andnode separationdistance)

Decreases with

increasing (indicationofnode mobility)

ANFD is a goodindicator oflink

reliability use asMETRIC


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LMMSE Channel Prediction

is the predicted signal at time n+kbasedonMincoming signal sample values up until timeinterval n

is the prediction weight for the ith previous inputsignal sample value

is the incoming signal sample value at timeinterval n-i

Precalculate and tabulate w(i) indexed by Doppler shiftand discrete time shift

x(n + k) = MX

i=1

w(i)x(n i)

x(n + k)

w(i)

x(n

i)


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Channel-Aware AOMDV Protocol

Use ANFD as measure of path lifetime/duration

Path duration is defined as the minimum ANFD overall hops in the path

Implemented by including node speed and directionin RREQ header

D , min1hH ANFDh


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CA-AOMDV cont.

AOMDV: Destination IP address

Destination sequence numberAdvertised hop-count

Route list:




CA-AOMDV: Destination IP address

Destination sequence numberAdvertised hop-count

Dmin Route list:

Next hop IP 1, hop-count 1, D1Next hop IP 2, hop-count 2, D2


Handoff dormant time

Comparison of Routing Table Entries:


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CA-AOMDV cont.

RREPs processed on basis of Destination

sequence number, Advertised hop-count and Dmin

Handoff dormant time

Amount of time a path should be marked as unusableafter handoff

Set equal to maximum AFD over all links in path


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Path Handoff

Triggered by prediction of a forthcoming fade

on one of the path links

The node at the receiving end of the fading

link initiates a handoff request via a HREQpacket

HREQ includes: AFD, Source IP address,Destination IP address and Source sequence

number


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Path Handoff cont.

Avoidance of repeat HREQ via maintenance of ahandoff table at each node, similar to routingtable Includes expiration time field to indicate when path is

expected to again be available for use (out of fade)

A node forwards a valid HREQ unless it has analternative path to the destination

When a path has come out of its fade, it may beused again, saving on route discovery overhead,

unless it has reached its expiry time


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CA-AOMDV Summary

Route Discovery

ANFD and hop-count used to select stable, butreasonable length paths

AOMDV chooses on hop-count only

Route Maintenance

Predicted signal strength used for handoff

initiation

AFD used to choose when to bring path out of

dormancy


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Theory

Average number of hops between 2nodes, with transmission rangeR:

Average number of hops before

encountering broken link is

With Cconnections at any time, andn neighbours, average number ofconnections over a given link is

s

s

N nodes in network

H =S(

2 + l n ( 1 +

2))

3R.

(H + 1)/2

B = 2CH

nN.


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Single Link and Path Lifetimes

Link lifetime,Zl, has exponential distribution

Assume a path withL i.i.d. links. Path lifetime,Zp,also has exponential distribution

Expected Path Lifetime

fZ

(t) = `e`t

fZp(t) = et

PLk=1 k

L

X`=1

` = pept = LeLt

E{Zp} =Z

0tpeptdt = 1

p= 1

L


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AOMDV Multiple Path System Lifetime

Assume all paths haveL i.i.d. links.

The AOMDV multiple path system lifetime isZA.

System is up as long as any of theNp paths are still up(though once down they are discarded)

Expected lifetime of AOMDV multiple path system ANFD

Pr{ZA < t} = Pr{(Zp1 < t)

(Zp2 < t)

(ZpNp < t)}

= (1 ept)Np = FZA(t).

E{ZA} = Npp

Xk=0

(1) Np

1

Np k 1

Np 1k

!1

(Np k)2.


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Single Link and Path Downtimes

Link downtime, Yl, has exponential distribution

Assume a path withL i.i.d. links. Path downtime, Yp,also has exponential distribution.

The CA-AOMDV multiple path system downtime is

YC

FY (t) = 1 et

CA AOMDV Multiple Path System


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CA-AOMDV Multiple Path System

Downtime

The CA-AOMDV system is down only when all paths

are down.

Expected System Downtime AFD

Pr{YC > t} =

NpYi=1

Pr{Ypi > t} =

NpYi=1

1

LYk=1

FYk

(t)

=

1

1

etLNp

FYC(t) = 1 1

1 et

L

Np

{YC} = NpL

Np1Xk=0

(1)Npk1

Np

1k

!L(Npk)1Xi=0

(1)L(Npk)1i

L(Np

k)

1i

!1

(L[Np k] i)2

.

CA AOMDV Multiple Path System


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CA-AOMDV Multiple Path System

Lifetime

Probability that a path is down is the probability that

at least one link is in a fade.

Recall that a link signal strength has Rayleighdistribution, with parameter, .

AFD)fadeinischannelPr(

)fadeinischannelPr(1

RateCrossingLevel)fadeainnotischannelPr(ANFD

RateCrossingLevel

)fadeainischannelPr(AFD

=

=

=

CA-AOMDV Multiple Path


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CA-AOMDV Multiple Path

System Lifetime cont.

Based on the Rayleigh distribution of the link gains,

probability CA-AOMDV system in fade is

So, ifZC is CA-AOMDV system lifetime

Pr(system in fade) =

Np

Yi=1

1

L

Y`=1

e2

= 1 e

L2

Np

E{ZC} =1

1 eL2

Np1 eL

2NpE{YC}

AOMDV vs CA-AOMDV Multiple


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Path System Lifetimes

5 4 3 2 1 0 1 20

0.5

1

1.5

2

(dB)C

A

AOMDVtoA

OMDVlifetimer

atio

Np

= 2

L=3L=4

L=5

L=6

5 4 3 2 1 0 1 20

0.5

1

1.5

2

(dB)C

A

AOMDVtoA

OMDVlifetimer

atio

Np

= 6

L=3L=4

L=5

L=6



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AOMDV vs CA AOMDV Multiple


5 4 3 2 1 0 1 20

0.5

1

1.5

2

(dB)C

A

AOMDVtoA

OMDVlifetimer

atio

Np

= 2

L=3L=4

L=5

L=6

25 20 15 10 5 0 50

1

2

3

4

5

6

7

8

threshold, (dB)

CAAOMDVtoA

OMDVLIfetimeRatio

Np

= 2, L = 1



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AOMDV vs CA AOMDV Multiple


25 20 15 10 5 0 50

50

100

150

200

250

300

350

(dB)

MultiplePathSy

stemL

ifetime

Np

= 2, L = 1

CAAOMDVAOMDV

20 15 10 5 0 50

2

4

6

8

10

12

14

16

18

20

(dB)

MultiplePathSystemL

ifetime

Np

= 2, L = 1

CAAOMDVAOMDV

R ti C t l O h d


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Routing Control Overhead

C = connections in the network

T = average connection time

= route discoveries per second per node pair N = node degree

Np = number of saved paths

Nrq = number of RREQ per path repair B = average number of paths over a breaking link

= average hop-count

A = CTA(N + NpH) + CT NpAB

3H + 2

4+

Nrq

2

!

C

=CT

C(

N+

NpH

) +CT Np

CB

I

H

D l


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Delay

d = delay due to route discovery from failed system

tr= one-hop propagation time of RERR

td = one-hop propagation time of a data packet

th = one-hop propagation time of HREQ

TMAC = channel occupation time due to MAC overhead

= expected number of hops to deliver HREQ

A = dAT + T N

pA(tr + TMAC)(H + 1)2

+ T NpANR(td + TMAC) + TATMACH

C = dCT + T NpC(th + TMAC)I

+ TCNR(td + TMAC) + TCTMACH

I

P k t D li R ti


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Packet Delivery Ratio

q = probability that channel is free for transmission

( )

( )T

qTT

qT

C

C

AA

=

=

Th h t P k t R t


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Throughput vs Packet Rate

33% improvement at

higher packet rates

Choice of stable links in

CA-AOMDV, plus

handover fewer route

discoveries

Thro ghp t s Mobilit


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Throughput vs Mobility

~27% improvement at

7m/s (25km/h)

Delay vs Mobility


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Delay vs Mobility

About 25% improvement

at v = 2.5 m/s

Routing Overhead vs Mobility


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Routing Overhead vs Mobility

18% improvement at

v = 2.4m/s

Conclusions


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Conclusions

Can improve AOMDV performance byTaking into account channel conditions in addition to hop-

count

Using channel prediction to initiate path hand-off

725 31-10-08 haley jones slides

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