On 05/09/2018 07:57 PM, Jacob Knoles wrote:
Thanks for the quick reply guys.
Marcus the Re-sampling option makes perfect sense, and I believe, in
theory, since I am writing data to a file for later use I could
interpolate it just before writing then read it out at the usrp sample
rate, right?
Yes.
Ian, very interesting suggestion. I will have to give it a try. Thanks
for the input. And since I am doing all of the heavy processing prior
to tx'ing I don't image this change will create too great of a burden
on the CPU. As for reading from the file, I am just creating a small
data set which gets loaded into memory and repeated.
Thanks!!
-----------------------------
Jacob Knoles
On Wed, May 9, 2018 at 4:21 PM Ian Buckley via USRP-users
<usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> wrote:
> On May 9, 2018, at 4:07 PM, Marcus D. Leech via USRP-users
<usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>>
wrote:
>
> On 05/09/2018 06:53 PM, Jacob Knoles via USRP-users wrote:
>> Hello All,
>>
>> I am trying to generate OFDM signals of various bandwidths
using the X300 (UBX-160), particularly 20/40/80 and 160 MHz
bandwidths.
>> I have used the gnuradio ofdm_tx.grc example file to generate a
data file which I then feed into the USRP an monitor on a spectrum
analyzer.
>>
>> To quickly note, I do not care about the data being
transferred, it will not be received or demodulated in any way and
is simply an interfering signal.
>>
>> At this time I can produce a 20 MHz wide OFDM signal as well as
a 100 MHz wide signal (?) but the 40/80 MHz signals are rounded
and look more like an 802.11b signal.
>>
>> I have noted a message from the X300 that the requested sample
rates (40/80 MS respectively) cannot be achieved due to the 200/x
ratio being odd.
>>
>> So my question is this, how do I decouple the USRP's sample
rate with the bandwidth of the signal I am trying to produce?
>> To put it another way, I produce a data file at 40 MS/s rate
then run it on the X300 at 100 MS/s and I get a 100 MHz wide
signal instead of the 40 MHz I want.
>>
>> Thanks for the help.
>> -----------------------------
>> Jacob Knoles
>>
> You would need to interpolate it up to the desired rate. UHD has
no way of knowing that your samples represent data sampled at
40Msps, so when you
> pull it out of your file at 100Msps, it will get presented as
if it were 100Msps data.
>
> You'll need to use some DSP code, or Gnu Radio to up-sample your
sample file.
>
….or perhaps generate it off line using a non 2^n Fourier
transform size that targets the USRP sample rate…for example
instead of 64 bins @ 40MHz, 80 bins @ 50MHz,
With zero data in the extra outlying bins (as you would have
anyway in other bins). Might get interesting getting high bitrates
out of a file, but equally, high bitrate M:N sample rate
conversion will also be tricky for CPU
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