Dynamic channel allocation Dynamic channel allocation in wireless ad-hoc networksin wireless ad-hoc networks

Anup TapadiaAnup Tapadia

Liang ChenLiang Chen

Shaan MahbubaniShaan Mahbubani

BackgroundBackground

802.11 networks have experienced a 802.11 networks have experienced a tremendous growth in last few yearstremendous growth in last few years

Access points work on a single static Access points work on a single static channelchannel

Contention & congestionContention & congestionLow throughput due to inefficient channel Low throughput due to inefficient channel

allocationallocationPresence of other interfering networks Presence of other interfering networks

impacts performanceimpacts performance

Channel variationsChannel variations

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

1 3 5 7 9 11 13 15 17 19 21 23

Channel 1

Channel 6

Channel 11

Hour of the day

Pac

ket

Cou

nt

Traffic on Thursday 26th April at Calit2 6th floor

CogNet testbed setup at Calit2CogNet testbed setup at Calit2

Dynamic Link

Cognet Database

Channel Controller

Node 1 Node 2Monitor 1 Monitor 2

CogNet is supported byNSF SGER-CogNet

CalNodeCalNode

Seokris 4521Seokris 4521 Linux 2.6Linux 2.6 IperfIperf Monitor CardMonitor Card

Atheros w/ Mad WifiAtheros w/ Mad Wifi

Data CardData Card Prism 2.5 802.11bPrism 2.5 802.11b

Wired to UCSD Wired to UCSD networknetwork

What may affect the channel What may affect the channel performance?performance?

Interfering 802.11 TrafficInterfering 802.11 TrafficPacket countPacket count802.11 Rate802.11 RateRSSIRSSI

Other interferenceOther interferenceBluetoothBluetoothCordless phonesCordless phonesMicrowavesMicrowaves

Our Focus

ChallengeChallenge

How do we select the channel that How do we select the channel that permits maximum throughput in an permits maximum throughput in an ad-hoc network ? ad-hoc network ?

Channel Controller (Java & C++)Channel Controller (Java & C++)

SQL Query Decision Logic

Channel Switcher

Iperf Test Scheduler

CogNetDB

Towards NodesConnectionStub

iwlib

WiFiNIC

WiFiNIC

AP

Software ArchitectureSoftware Architecture

Decision Logic

Channel Switcher

Channel Controller

ConnectionStub

iwlib

WiFiNIC

WiFiNIC

AP

ConnectionStub

iwlib

WiFiNIC

WiFiNIC

AP

ConnectionStub

iwlib

WiFiNIC

WiFiNIC

AP

ConnectionStub

iwlib

WiFiNIC

WiFiNIC

AP

Channel SwitchChannel Switch

ConnectionStub

802.11 Driver

802.11 H/W

ConnectionStub

802.11 Driver

802.11 H/W

iwlib iwlib

Decision Logic

Channel Switcher

Channel Controller

Probe

Reply

Switch Channel

Switch Channel

Channel Switch MessageChannel Switch Message

Factors selection test Factors selection test

Tx Tx Tx

15 sec silence 15 sec silence

Factors affecting throughput :RSSIFactors affecting throughput :RSSI

Effect of our transmission rate on Effect of our transmission rate on others RSSI others RSSI

0 1000 2000 3000 4000 5000 6000 700010

15

20

25

30

35

40

45

50

55

60

Applied Rate (Kbps)

Ave

rage

RS

SI

/ P

acke

t

Our packets

Other packets in presence of our packets

Packets during silence period

Factors affecting throughput : RateFactors affecting throughput : Rate

Factors affecting throughput :PacketsFactors affecting throughput :Packets

Channel Selection Algorithm Channel Selection Algorithm

We select the least interference channel We select the least interference channel dynamicallydynamically Channel interference metricChannel interference metric

where where CCii is the interference metric of channel is the interference metric of channel ii, , NNipip, N, Niqiq are the number of other packets captured at node p are the number of other packets captured at node p and q on channel and q on channel i in a 120s windowi in a 120s window..

Selected channel Selected channel jj, s.t., s.t.

2iqip

i

NNC

)(min11,6,1

ii

j CC

Experiment: ProcessExperiment: Process

Send a 3MB file using each schemeSend a 3MB file using each scheme 15s pause interval in between15s pause interval in between

each transfereach transfer RepeatRepeat

S R D

15 sec silence 15 sec silence

120 sec query window

Background TrafficBackground Traffic

0

1000

2000

3000

4000

5000

6000

0 50 100 150 200

Ch1PktCount

Ch6PktCount

Ch11PktCount

Run # (Progressive time)

Oth

er p

acke

ts c

ount

ResultsResults: : Dynamic v. StaticDynamic v. Static

Results: Dynamic v. RandomResults: Dynamic v. Random

Results: Random v. StaticResults: Random v. Static

Channels pickedChannels picked

0

10

20

30

40

50

60

70

1 6 11

Dynamic

Static

Random

Channel #

Num

ber

of t

imes

cha

nnel

was

sel

ecte

d

Results: SummaryResults: Summary

SchemeScheme DynamicDynamic StaticStatic RandomRandom

Avg RateAvg Rate 4042 kbps4042 kbps 2100 kbps2100 kbps 2742 kbps2742 kbps

Average Average Transfer Transfer

Time (3MB)Time (3MB)

6.08s6.08s 11.7s11.7s 8.96s8.96s

Effect of channel switching timeEffect of channel switching time

cs

d

cs

d

csd

scd

trff

r

tr

ft

ttt

ttt

kbpsr

kbpsr

kbitsf

stfor

d

s

c

4096

2100

3072

7.5

td = Tx time on dynamic channelts = Tx time on static channeltc = Time to changerd = Rate on dynamic channelrs = Rate on static channelf = Size of file

Our implementation

Future workFuture work

Multi hop linksMulti hop linksMore complex allocation schemes More complex allocation schemes Finer data granularity and patternsFiner data granularity and patterns Improve channel switching timeImprove channel switching timeEffect of frequency of channel switchingEffect of frequency of channel switching

ConclusionsConclusions

Dynamic performed better than Static and Dynamic performed better than Static and RandomRandom

Static on a free channel provides upper Static on a free channel provides upper bound on Dynamic performance; bound on Dynamic performance; improvements come when static channel improvements come when static channel is loaded (channel usage varies over time)is loaded (channel usage varies over time)