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Tutorial: Wireless experiments using the iMinds w-iLab.t testbed

Live Stream Information



Tuesday 10.30am - 12.30pm

Tutorial Instructors

Pieter Becue
Brecht Vermeulen
Thijs Walcarius

Agenda Details


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Please Arrive With:

A Laptop

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Tutorial materials


In this tutorial, we will show you how to set up one wireless access point and connect with 1 client. The access point will start an iPerf server instance, after which we will run an iPerf client instance on the second node. By using the correct IP addresses, we make sure that the iPerf traffic stream is routed over the wireless interfaces. In this tutorial, we will use a mobile node for setting up the access point. The client will be configured on a fixed wireless node.

In a second part of the tutorial, we will demonstrate how to use OMF/OML & Labwiki to run wireless experiment on the w-iLab.t testbed, including mobile nodes. Using the graph plotting capabilities of Labwiki, you will be able to see the throughput impact of moving the mobile node around the testbed.

Instructions below are not final yet...

Part 1: Wireless & mobile experimentation at w-iLab.t

Reserve 3 wireless nodes using jFed

All of the w-iLab.t nodes have been previously reserved for the "GEC21" project. You should join this project prior to running the tutorial.

Every group has 3 wireless nodes (2 fixed and 1 mobile) which you have to activate using jFed. You should choose specific nodes in jFed by right clicking the node. Name them: ap, client and backup. See the table on the group sheets to see which nodes you can use.

Configure the access point (on the mobile node)

Before running the experiment, we will use the shell script option in the RSpec to install hostapd. Go to the Raw RSpec view and add the following in the node part of the ap (first line is already there):

<sliver_type name="raw-pc"/>
     <execute shell="sh" command="sudo apt-get update ; sudo apt-get install hostapd ; "/>

Configuration of Access Point (on your mobile node)

SSH to your mobile node (from jFed). Become root:

$ sudo su

Create a config file for the hostapd program:

$ nano /root/hostapd.conf

Add the following content to the config file (X=group number, Y=channel, Z=mode lines should be left aligned):


Replace X with your demo number. Replace Y with your channel and Z with the WiFi mode. Start hostapd. The above config will setup an AP on wlan0 using 802.11a or g, channel Y, with SSID demoX:

$ hostapd /root/hostapd.conf

Open a second ssh terminal and give an IP address to the wlan0 interface so we can test the connection to the clients (in the next steps). Be sure to replace X with your group nummber:

$ sudo su; ifconfig wlan0 192.168.X.1/24

Configure the client (on one of the fixed nodes)

Become root:

$ sudo su

Put the wireless interface into managed mode and specify the SSID so it knows to which AP it should connect

$ iwconfig wlan0 mode managed
$ iwconfig wlan0 essid demoX

Specify an IP address and bring up the interface:

$ ifconfig wlan0 192.168.X.10/24 up

Check if you can ping the AP:

$ ping 192.168.X.1

iPerf measurement

Start an iPerf server instance (UDP in this case) on the mobile node (AP):

$ iperf -s -u -i 1 &

Configure the iPerf client:

$ iperf -u -c 192.168.X.1 -b 40M -i 1 -t 6000

If the iperf reports an actual 40Mbit/sec throughput, you probably lost the connection. By tweaking the transmit power (values of 0 to 20dBm) of the access point, you should be able to see a difference in throughput of the iPerf stream:

$ iwconfig wlan0 txpower <0-20>

For this tutorial, leave the txpower to 20 for the first experiment runs. If the effect of moving the mobile node is too limited, you can try lowering the txpower. Note that each antenna at the w-iLab.t is equipped with a 10dB attenuator (so 20dB attenuation per link).

Move the mobile node

Once everything works fine, you can start driving the mobile node and check the impact on the iPerf throutput. The robot control software can be accessed at You can log in with the demoX accounts. For example, the demo5 account will give you the rights to move mobile5. Instructions on how to use the framework: , scroll down to “Setting up paths”. VERY IMPORTANT : You will only be able to SSH to the mobile node while it is docked. (If you want an SSH connection during your experiment, you will have to set up a wireless connection to a fixed node and SSH over the wireless.)

Part 2: Mobile experimentation using Labwiki

In this part, you will learn how to run experiments using the Labwiki tool. This tool uses the OMF framework in combination with the OML measurement library.

Prepare your experiment

Go to, click the prepare text field and type "gec21iperf". You should see a drop down list with some files. Select the gec21iperf.oedl file. Since this version of labwiki only has one user account at the moment, you should copy the contents of this experiment file and create a file with your group number in the file name. Click CTRL-A, followed by CTRL-C and then click the wheel icon. Choose a name for your file (without the .oedl extension), select OEDL and click Create. Now paste (CTRL-V) the contents of the experiment in the field below and click the Save button.

The presentation at the beginning of the session should have given enough explanation to understand this experiment description file.

Change the properties "sender" and "receiver" so they reflect the hostnames of your resources.

Prepare your mobile scenario

Go to and start drawing a scenario for your mobile node. If you are done, click the Save button and copy the list of coordinates.

Be sure to issue the following command when you dock the robot again, otherwise you will not be able to run more experiments.

$ /usr/bin/killall ruby ; /etc/init.d/omf_rc start


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