USRP2 high data throughout for WiFi 802.11 processing or GALILEO E5

Hello guys,
I suppose some people out there are interested, like me, in doing
stuff with relatively large-bandwidth signals like 20MHz WiFi stuff or
even 50 MHz GALILEO E5.
on a linux ubuntu 10.04, USRP2/XCVR2450, GNURadio 3.2 (I think) with
two week old FPGA firmware, I am trying to collect some data file with
the command:
sudo usrp2_rx_cfile.py -v -s -e eth1 -f 2462.0M -g 25 -d 5 -N 250M
wifi_d5.bin

and (with a WBX front end) also this:
sudo usrp2_rx_cfile.py -v -e eth1 -f 1575.42M -s -g 25 -d 14 -N 700M
galileoE1.bin

  1. I however do not seem to set the decimation d=4, for the XCVR2450
    front end. Is it a firmware problem? Does anybody knows why?

  2. Regarding the USRP 2 bandwidth, digging into the GNU Radio forum I
    found people confirming this:

In (USRP2) RX path:
if ADC sampling = 100MHz,
and if Min decimation = 4
=> max IF bandwidth = 25MHz
=> Max IF Ethernet rate = 4 bytes per sample * 25 MSPS = 100 Mbyte/sec
= 800 Mbit/sec (Every thing is clear)

My question is: with a decimation of 4 you get a fs = 25MHz and
therefore I would think that the bandwidth that you can capture is
actually half that, meaning ~12MHz. Could somebody explain to me why I
am wrong?

Thank you in advance for your attention
Regards,
Fabrizio

On Fri, Oct 29, 2010 at 8:48 AM, Fabrizio T.
[email protected] wrote:

Hello guys,
I suppose some people out there are interested, like me, in doing
stuff with relatively large-bandwidth signals like 20MHz WiFi stuff or
even 50 MHz GALILEO E5.

There is some existing work on Wifi with the USRP2 - check out the
BBN802.11 project page on CGRAN, and take a look at the usrp2_version
branch.

My question is: with a decimation of 4 you get a fs = 25MHz and
therefore I would think that the bandwidth that you can capture is
actually half that, meaning ~12MHz. Could somebody explain to me why I
am wrong?

The USRP2 uses complex sampling: each ‘sample’ consists of both an
16-bit in-phase (I) and a 16-bit quadrature phase (Q) sample. This
effectively doubles the bandwidth of the signal you can observe.

Thank you in advance for your attention
Regards,
Fabrizio


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Doug G.
[email protected]

On Fri, 2010-10-29 at 14:48 +0200, Fabrizio T. wrote:

sudo usrp2_rx_cfile.py -v -e eth1 -f 1575.42M -s -g 25 -d 14 -N 700M
galileoE1.bin

  1. I however do not seem to set the decimation d=4, for the XCVR2450
    front end. Is it a firmware problem? Does anybody knows why?

I don’t understand what you are asking here. The daughterboard should
not affect decimation or sample rate in any way.

My question is: with a decimation of 4 you get a fs = 25MHz and
therefore I would think that the bandwidth that you can capture is
actually half that, meaning ~12MHz. Could somebody explain to me why I
am wrong?

Complex sampling.

Thank you in advance for your attention
Regards,
Fabrizio

–n