Implementation of Test Bed for
Dynamic Channel Selection In
WLANs
Communications Laboratory
TKK/HUT
WLANs – Increasing Popularity
Growing Popularity of WLANs
Inexpensive and Flexible
Growing Trend in ad hoc networking
Easy to configure
WLANs – Shortfalls and Issues
Intrinsic unreliable nature of the wireless
channel
Unreliable and unpredicable Transmission
medium
Speeds less than wired networks
Security
WLAN Standards
 IEEE 802.11 - 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF
and IR standard (1997)
 IEEE 802.11a - 54 Mbit/s, 5 GHz standard
(1999, shipping products in 2001)
 IEEE 802.11b - Enhancements to 802.11 to
support 5.5 and 11 Mbit/s (1999)
 IEEE 802.11g - 54 Mbit/s, 2.4 GHz standard
(backwards compatible with b) (2003)
 IEEE 802.11h - Spectrum Managed 802.11a (5
GHz) for European compatibility (2004)
Contribution of Thesis
Comparative Study of DFS in 802.11b Vs
Static Channels In Ad hoc Networks
Multiple radio interferences on a limited
Bandwidth
Multilple networks on a Single Channel
Degradation in Throughput
Inflexibility of Channel allocation
Better quality link possible of unused channel
The Solution
Creating a Dynamic Channel Selection
(DSC) Mechanism for WLANs in the
2.4GHz band
Providing a testbed to obsreve the
Improvements offered by the use of a DSC
Application
Analyse the improvement in Throughput
Dynamic Frequency Selection in WLANs
Provided by the IEEE 802.11h extention to
the IEEE 802.11a standard
No mechanism currently being employed
in IEEE 802.11b/g WLANs
A Simple DFS Algorithm
Channel Deployment Issues in the
2.4GHz band
A total of 11 channels in both IEEE
802.11b and IEEE 802.11g standards
Limited to 3 usable channels due to the
interchannel interfernces
Limits the DSC scheme to effectively only
switch between 3 channels
Channelization scheme for IEEE 802.11b
Setting Up Test Enviornment
Pentium III Desktop PCs with Realtek
802.11b/g wireless lan cards
Ubuntu v 5.10 linux
wireless_tools.28 toolkit from IBM
Traffic Generator IPerf
Shell Scripting Knowledge 
Patience to install WLAN drivers on linux
Configuring WLANs
Lab enviornment
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iwlist wlan0 scan
wlan0
Scan completed :
Cell 01 - Address: 00:14:BF:E6:53:5E
ESSID:"dtn_demo"
Mode:Master
Frequency:2.412 GHz (Channel 1)
Quality=37/100 Signal level=12/100 Noise level=0/100
Encryption key:off
Bit Rates:54 Mb/s
Cell 02 - Address: 00:16:B6:5B:E4:A4
ESSID:"aalto"
Mode:Master
Frequency:2.412 GHz (Channel 1)
Quality=38/100 Signal level=13/100 Noise level=0/100
Encryption key:off
Bit Rates:54 Mb/s
Cell 03 - Address: 00:16:B6:5B:CB:FB
ESSID:"aalto"
Mode:Master
Frequency:2.437 GHz (Channel 6)
Quality=32/100 Signal level=5/100 Noise level=0/100
Encryption key:off
Bit Rates:54 Mb/s
Cell 04 - Address: 42:DC:B9:77:91:7B
ESSID:"wrt54gs"
Mode:Ad-Hoc
Frequency:2.437 GHz (Channel 6)
Quality=36/100 Signal level=11/100 Noise level=0/100
Encryption key:off
Bit Rates:11 Mb/s
Cell 05 - Address: 6E:FF:7B:87:23:1B
ESSID:"adhoc_test"
Mode:Ad-Hoc
Frequency:2.412 GHz (Channel 1)
Quality=62/100 Signal level=47/100 Noise level=0/100
Encryption key:off
Bit Rates:22 Mb/s
Node-A Start
Channel Quality
Monitoring
DSC Application
Quality <
Threshold
No
Yes
Text based signalling
Client Server
3-way Acks
Link Quality analysis
and selection Algorithm
Application Layer
Implementation
Channel Change
Procedure
Node-A
Send
Channel No.
to Peer
Node
Self Channel
Change Procedure
Delay
Probe Channel for
Change Request
Yes
Change Channel&
Send ACK
Node-B
ACK
Received
No ACK within a
Time Frame
Send Confirmation
Node-A
Channel Quality
Measurements
Start Again/Stop
No
Receive
d
Wait for
Confirmation
Sequence Diagram for the DCS tool
Test Case – 1
Comparison of channel performance in a
bad channel versus a channel selected by
using the Channel Selection Utility for TCP
traffic
Intervals of 300, 900, 3600, 7200, 10800,
21600
Data sheet – 1.1
TCP Traffic Without Channel Selection Utility
Time (sec)
Data Transferred (Kbytes)
Throughput (Mbits/sec)
240
42086.4
1.43
300.5
52428.8
1.43
600.5
104448
1.43
900.5
157696
1.43
3600.5
624640
1.42
7200.5
1139160
0.158
10800.7
1866465
1.42
21600.5
3718705
1.42
Data Sheet – 1.2
TCP Traffic With Channel Selection Utility
Time (sec)
Data Transferred (Kbytes)
Throughput (Mbits/sec)
240.5
18124.8
0.617
300.4
30617.6
0.833
600.4
82227.2
1.12
900.5
142336
1.3
3600.6
615424
1.4
7717
1290824
0.167
10800.8
1939865.6
1.47
21600.4
3845923
1.46
Results
Time consumed in the execution of DCS
degrades throughput at smaller intervals
due to the silent period
Improvement only seen in times greater
than one hour
Test Case – 2
Comparison of channel performance in a
bad channel versus a channel selected by
using the Channel Selection Utility for
UDP traffic with a continuous data transfer.
Intervals of 300, 900, 3600, 7200, 10800,
21600
Data Sheet – 2.1
UDP Traffic Without Channel Selection Utility
Time
(sec)
Data
Transferred
(Kbytes)
Throughput
(Kbits/sec)
Jitter
(msec)
lost/total
%lost
240
30
1.05
1.867
1/21401
0.0046%
300
37
1.05
0.297
0/26751
0%
600
75
1.05
1.117
0/53501
0%
900
113
1.05
0.04
0/80251
0%
UDP Traffic With Channel Selection Utility
Time (sec)
Data Transferred
(Kbytes)
Throughput
(Kbits/sec)
Jitter (msec)
lost/total
%lost
124
6.98
473
0.554
6219/11198
56%
240
14.3
623
0.069
8689/21401
41%
300
25.7
719
0.261
8403/26751
31%
600
63.2
884
0.014
8398/53501
16%
Results
No retrials so lots of lost packets.
Requires a buffer mechanism to be
effective to cater when the silent period
occurs.
Test Case – 3
The purpose of this test case is to
compare the throughput of the radio
interface when burst of traffic is generated
instead of continuous traffic.
5 Mbytes of traffic every 5 minutes from
0800hrs to 1800hrs
DCS mechanism initated every 20 minutes
Alternatively quality threshold can be used
to initate the DCS Mechanism
Throughput over the time interval of 0600hrs to 1800hrs,
where 5Mbytes of data is transferred every 5 minutes on
the worst channel. Average Throughput 1.408 Mbits/sec
Throughput on worst channel from 0600hrs to 1800hrs
1.5
1.45
1.35
1.3
1.25
1.2
1.15
Time (sec)
18:00
17:40
17:20
17:00
16:40
16:20
16:00
15:40
15:20
15:00
14:40
14:20
14:00
13:40
13:20
13:00
12:40
12:20
12:00
11:40
11:20
11:00
10:40
10:20
10:00
09:40
09:20
09:00
08:40
08:20
08:00
07:40
07:20
07:00
06:40
06:20
1.1
06:00
Throughput (Mb)
1.4
Throughput over the time interval of 0600hrs to 1800hrs,
where 5Mbytes of data is transferred every 5 minutes while
the Channel Selection Utility is used 2-3 times per hour.
Average Throughput 1.467Mbits/sec
Throughput on channel selected after executing the Channel Selection Utility from 0600hrs to
1800hrs
1.5
1.48
1.44
1.42
1.4
1.38
1.36
1.34
1.32
06
:0
06 0
:2
06 0
:4
07 0
:0
07 0
:2
07 0
:4
08 0
:0
08 0
:2
08 0
:4
09 0
:0
09 0
:2
09 0
:4
10 0
:0
10 0
:2
10 0
:4
11 0
:0
11 0
:2
11 0
:4
12 0
:0
12 0
:2
12 0
:4
13 0
:0
13 0
:2
13 0
:4
14 0
:0
14 0
:2
14 0
:4
15 0
:0
15 0
:2
15 0
:4
16 0
:0
16 0
:2
16 0
:4
17 0
:0
17 0
:2
17 0
:4
18 0
:0
0
throughput (Mbits/sec)
1.46
Time (sec)
Comparison of the throughputs when the worst channel is
in use versus when the Channel Selection Utility is used to
select the best channel.
Comparision of Throughputs with the Utility vs the Worst Channel
1.55
1.5
1.4
1.35
1.3
1.25
1.2
1.15
1.1
06
:0
06 0
:2
06 0
:4
07 0
:0
07 0
:2
07 0
:4
08 0
:0
08 0
:2
08 0
:4
09 0
:0
09 0
:2
09 0
:4
10 0
:0
10 0
:2
10 0
:4
11 0
:0
11 0
:2
11 0
:4
12 0
:0
12 0
:2
12 0
:4
13 0
:0
13 0
:2
13 0
:4
14 0
:0
14 0
:2
14 0
:4
15 0
:0
15 0
:2
15 0
:4
16 0
:0
16 0
:2
16 0
:4
17 0
:0
17 0
:2
17 0
:4
18 0
:0
0
Throughput (Mbits/sec)
1.45
Time (Sec)
Channel Selected by Utility
Worst Channel
Conclusions
 Very distinct Improvement in throughput
 Implementation on application layer is not
efficient
 Taking advantage of the Draft IEEE 802.11k
standard for development of DCS mechanim
 Buffer for UDP traffic during silent period
 Development of selection algorithms
 Compatibilty of WLAN drivers in Linux
distribution. www.linux-wlan.org
 Simplification of network configuration needed