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Decode 802.11b SSID with NI USRP

Credit

Code Developed in the Lab of Dr. Murat Torlak at University of Texas at Dallas

Required Hardware

  • NI USRP-2921: 781907-01
  • Vert2450 Antenna:  781913-01

Required Software

  • LabVIEW Full, Pro or Student 2011
  • LabVIEW MathScript RT Module (included in kit 781907-01)

Running the Example

1. Set up your computer as an Ad-Hoc 802.11b network

- on my Windows 7 Dell, I open the "Network and Sharing Center"

- Click 'Manage Wireless Networks'

- Click 'Add'

- Click 'Create an Ad Hoc Nework'

- Click the 'Save this Network' tick box

2. On my computer it defaults to 802.11g, so I have to force it to 802.11b

- From 'Network and Sharing Center' select 'Adapter Settings'

- Right click the wireless adapter and select 'Properties'

- Click 'Configure' at the top of the 'Wireless Connection Properties' page

- Look for something about Ad Hoc Channel in the 'Advanced' tab (screen shot below)

- for my computer, 0 = b and 1 = g Ad Hoc network.  I set it to 0.

set network card.png

3. Begin transmitting beacon signals

- left click on the wireless icon in the start menu bar on the far right

- your Ad-Hoc network should appear in the list of possible networks to connect to

- double click it and you're live! (hovering over it will tell you the status. Its transmitting if it says 'Waiting for Users'

create 80211b ad hoc.png

4. Open the VI: USRP wifi demo.vi (inside the Wifi-Demo.llb library)

- Set the IP address and press run

- You should see the SSID's appear in the top center of the VI's front panel

802.11b Demodulate and Descramble - FP.png

5. How does it work?

A state machine does simple energy detection to detect a Wifi packet coming in between channels 7 and 17 in the 'read' state. When a trigger is found the work is done in the brx.vi inside the connect subVI in the process state of the state machine.  Inside brx.vi the flow is, frequency offset correction, (the equalization block isn't really used), and then its demodulated and de-scrambled (according to the spec).  The ASCII look-up table takes over and the bits become characters.  On the high level block some logic makes sure it's good data before logging it into an array and displaying it on the front panel. Occasionally there are a few characters that are not recognized properly but enabling equalization and adding a few other tuning parameters should minimize these.

802.11b Demodulate and Descramble - BD.png

Comments
Jaeweon
NI Employee (retired)
on

Very nice!

Interestingly, the mathworks demoed this SSID decoding at SDR-Boston using USRP + simulink + matlab script (very similar with mathscript node in LV). They also demoed FM radio demodulation on USRP, which we had a year ago.

seano_ajie_suka
Member
Member
on

Wow, it's Great..

If i want to change the standard to 802.11g, what kind of modification should I use?

Thanks

imad82
Member
Member
on

Hi there:

this is really pretty nice but i wonder if there is a similair example to retrieve the payload packets sent over the WiFi as well.

R

Im

Ramya20
Member
Member
on

Hi,

I am using USRP 2953. When I run this VI accordingly, I am getting 1299 error saying no device found for that particular IP address. But I can find the USRP in NI configuration untility and NI max. Can any one help me out?

Best Regards,

Ramya

ErikL
NI Employee (retired)
on

Please try using the name RIO0 (not an IP Address since its connected by

cabled PCIe)

Erik

From: Ramya20 <web.community@ni.com>

To: ErikL <erik.luther@ni.com>

Date: 07/07/2015 05:10 AM

Subject: Re: - Decode 802.11b SSID with NI

USRP

Community

Decode 802.11b SSID with NI USRP

new comment by Ramya20 View all comments on this document

Hi,

I am using USRP 2953. When I run this VI accordingly, I am getting 1299

error saying no device found for that particular IP address. But I can

find the USRP in NI configuration untility and NI max. Can any one help me

out?

Best Regards,

Ramya

Reply to this email to respond to Ramya20's comment.

Ramya20
Member
Member
on

Hi Erik,

It worked. Thankyou.

Ramya

Omar_R
Member
Member
on

Hello ErikL

 

Can this example run on a USRP 2901 model ? I only see a difference in the Bandwidth between the two models, so I don´t know if that could affect while running the example. Looking forward for your input. 

 

Regards.

Omar R.
Technical Support Manager
CLA | CTD
Contributors