On Tue, Feb 21, 2012 at 11:35 AM, Florian Schlembach < florian.schlemb...@tu-ilmenau.de> wrote:
> Are you seeing the 1 MHz offset when you use the uhd_siggen.py? Or is it >> just with the OFDM transmitter? >> > > What is this tool doing? Transmitting a sine and checking the offset. > Sorry, for the moment I have no possibilitie to check that. Yes. > > It's because with the larger bandwidth, the subcarriers, too, have a > > larger bandwidth. The coarse frequency correction is only set to look at > > so large an offset based on a number of subcarriers (+/-5 or 10), so now > > with the same frequency offset, 5 (or 10) carriers is a larger frequency > > span to check. > > @Tom > does that mean that there is only a coarse frequency correction > implemented? How could I overcome the offset in the easiest way? Checking > it by usrp_siggen.py and adjust in manually or are there some smart > correction algorithms implemented? > There is a coarse and a fine frequency offset correction. The fine correct makes sure that the subcarrier is centered in the bin; the coarse adjusts for an integer number of subcarriers off from the center frequency. By default, the OFDM receiver will correct for some number of subcarrier bins (it's either +/-5 or +/-10; I can't remember). If your radios have a frequency offset that is greater than the maximum number of subcarriers specified here, the receiver cannot receive the symbols correctly. Yes, you can transmit a tone using uhd_siggen.py to fine out a rough estimate of the frequency offset and adjust either the transmitter or receiver based on this number. Tom
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
