Why is Barker Spreading difficult to usrp?

Hi guys,

   With BBN codes and FLEX2400 d'borads, now I can received 802.11b

packets from standard wireless cards, and communicate between two USRPs
with
barker spreading off. These make me really excited :slight_smile:

   However, I failed trying to send any packet from USRP to PC.  I

believe it is because the barker spreading of the tx path was not
working
well and PC could not interpret the packets correctly. I also sent
packets
between USRP with barker on. That did not work too.

   It seems barker demodulator works but modulator does not. Why is 

the
barker spreading difficult for usrp? Is it because the 1MSps symbol rate
is
too tough for the USRP board? ( USRP is not that fast to deal with 1
million 11-bit batter sequence?)

  Best,

  Dix


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DiX [email protected] writes:

   With BBN codes and FLEX2400 d'borads, now I can received 802.11b

packets from standard wireless cards, and communicate between two USRPs with
barker spreading off. These make me really excited :slight_smile:

That’s good to hear - that matches where we got to.

   However, I failed trying to send any packet from USRP to PC.  I

believe it is because the barker spreading of thej tx path was not working
well and PC could not interpret the packets correctly. I also sent packets
between USRP with barker on. That did not work too.

I am not sure if we ever thought that we had the barker transmit
working.

   It seems barker demodulator works but modulator does not. Why is the

barker spreading difficult for usrp? Is it because the 1MSps symbol rate is
too tough for the USRP board? ( USRP is not that fast to deal with 1
million 11-bit batter sequence?)

It’s because the bandwidth of the signal from 1 Msample/s times 11
chip/symbol is 11 Mchip/s. I think we used 8-bit i/q and 8 Msample/s to
get 16 MB/s across the USB. For the barker receiver, the code computes
pre-distorted waveforms of the barker code. I don’t know that the
transmitter does, but really I think it just has to hope for the best in
terms of the receiver receiving a distorted signal.

You may be able to up the rate to 32 MB/s (16 Msample/sec) and tx may
work better.

Or, you could implement the barker code in the fpga.

The BBN code is assigned to FSF, so you are welcome to integrate it into
GNU Radio proper.

Tomek schrieb:

Hello!

I´m really new to gnu-radio. I installed the 3.0.4 version on my Ubuntu
system finally and now I need some ideas, here is what I want to do: I want
to use the USRP to sniff everything going on between 2 WLAN-PCMCIA Laptops
on 2,4GH.
How do I do that…? Does GNU Radio give me any tools making it possible to
visualize this in any way?

This will not be possible at the moment. The USRP can transmit 8MHz of
complex bandwith over USB 2.0, and a WLAN-Channel has a bandwith of
22MHz. You can sweep over the WLAN-Area and detect power to see if a
range has traffic, but you won’t be able to decode a lot.

See the archives of this list, it has been discusses a few time in the
last year or so.

Patrick

Engineers motto: cheap, good, fast: choose any two
Patrick S.
Student of Telematik, Techn. University Graz, Austria

Hello!

I´m really new to gnu-radio. I installed the 3.0.4 version on my Ubuntu
system finally and now I need some ideas, here is what I want to do: I
want
to use the USRP to sniff everything going on between 2 WLAN-PCMCIA
Laptops
on 2,4GH.
How do I do that…? Does GNU Radio give me any tools making it possible
to
visualize this in any way?

Thx!
Tomek

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