Implementation of Test Bed for Dynamic Channel Selection In

WLANs

Communications Laboratory TKK/HUT

WLANs – Increasing Popularity

Growing Popularity of WLANsInexpensive and FlexibleGrowing Trend in ad hoc networkingEasy to configure

WLANs – Shortfalls and Issues

Intrinsic unreliable nature of the wireless channel

Unreliable and unpredicable Transmission medium

Speeds less than wired networksSecurity

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 linuxwireless_tools.28 toolkit from IBMTraffic Generator IPerfShell Scripting Knowledge Patience to install WLAN drivers on linuxConfiguring WLANs

Lab enviornment 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

DSC Application

Node-A Start

Channel Quality Monitoring

Quality < Threshold

Channel Change Procedure

Send Channel No. to Peer Node

Probe Channel for Change Request

Change Channel& Send ACK

Received

ACK

Received

Wait for Confirmation

Send Confirmation

Channel Quality Measurements

Start Again/Stop

Delay

Self Channel Change Procedure

Yes

Yes

No

No

No ACK within a Time Frame

Node-B

Node-A

Node-A

Text based signallingClient Server3-way AcksLink Quality analysis

and selection AlgorithmApplication Layer

Implementation

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 – 2.1UDP 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 minutesAlternatively 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

1.1

1.15

1.2

1.25

1.3

1.35

1.4

1.45

1.5

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Time (sec)

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rou

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pu

t (M

b)

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

1.32

1.34

1.36

1.38

1.4

1.42

1.44

1.46

1.48

1.5

06:0

006

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Time (sec)

thro

ug

hp

ut

(Mb

its/

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

1.1

1.15

1.2

1.25

1.3

1.35

1.4

1.45

1.5

1.55

06:0

006

:2006

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Time (Sec)

Th

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bit

s/se

c)

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