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
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
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
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)