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?
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> wrote: > > > On May 9, 2018, at 4:07 PM, Marcus D. Leech via USRP-users < > 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 > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
_______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
