Thanks for the update! I know that getting the exact right bins in the right place can be hard since every FFT inplementation is slightly different.
Matt On Mon, Oct 14, 2013 at 8:43 AM, xe...@libero.it <xe...@libero.it> wrote: > Hi guys, > > just for letting you know. No offset correction is needed. The problem was > elsewhere in my implementation of 802.11. It was how I was calling the ifft > function in the transmitter side. By putting the correct parameters, I > obtained a perfect spectrum. > > Regards > > Francesca > > > > > > ----Messaggio originale---- > Da: xe...@libero.it > Data: 09/10/2013 16.55 > A: <mle...@ripnet.com>, <discuss-gnuradio@gnu.org> > Ogg: [Discuss-gnuradio] R: Re: R: R: Re: around empty subcarrier in > 802.11n implementation > > > Ok, I was supposing that. > > > So in the python code of the receiver I've put: > > > tr=uhd.tune_request(self._freq,self._offset) > > self.uhd_usrp_source_0.set_center_freq(tr) > > > where freq and offset are passed as parameters. In this way I got no error. > > > Now, the question is: which values are good for "offset"? Hz? KHz? MHz? > > I've tried small values, like 50 Hz, but nothing changes. > > Is there a way to find it? > > > I'm sorry, but really I have not idea > > Thank you again for your support > > francesca > > > > > > > ----Messaggio originale---- > Da: mle...@ripnet.com > Data: 09/10/2013 16.31 > A: <discuss-gnuradio@gnu.org> > Ogg: Re: [Discuss-gnuradio] R: R: Re: around empty subcarrier in 802.11n > implementation > > On 10/09/2013 09:55 AM, xe...@libero.it wrote: > > Hi guys, > > > I've tried to follow the suggested procedure. I guess the problem is > inside the uhd driver I'm using (UHD_003.005.001), since the set_rx_freq() > gives the following error: > > > AttributeError: 'uhd_usrp_source_sptr' object has no attribute > 'set_rx_freq' > > > Or, maybe, the problem is the daughterboard, which is of type XCVR2450. > > > Is there another way to set dc offset? > > > Any hint will be greatly appreciated. > > Francesca > > > > > ----Messaggio originale---- > Da: xe...@libero.it > Data: 09/10/2013 10.52 > A: <discuss-gnuradio@gnu.org> <discuss-gnuradio@gnu.org> > Ogg: [Discuss-gnuradio] R: Re: around empty subcarrier in 802.11n > implementation > > Thanks for your answer. > > > I'm a computer scientist, so I'm not so aware of what DC-offset exactly > means, but I'm going to try this tuning. I'll let you know if I solve the > problem. > > > Best regards > > Francesca > > > > > ----Messaggio originale---- > Da: mle...@ripnet.com > Data: 08/10/2013 16.22 > A: <xe...@libero.it> <xe...@libero.it> > Ogg: Re: [Discuss-gnuradio] around empty subcarrier in 802.11n > implementation > > Likely, if it's the central tones, you're looking at DC-offset (or the > removal thereof) interfering. > > > You can use offset tuning in the hardware to slide the DC offset outside > of your passband. > > http://files.ettus.com/uhd_docs/manual/html/general.html#tuning-notes > > > on Oct 08, 2013, *xe...@libero.it* <xe...@libero.it> <xe...@libero.it>wrote: > > Hi list, > > I'm using gnuradio 3.6.0 together with USRPs N210 for implementing OFDM > 802.11 > n communications, just SISO for the moment (in the future it would be > MIMO). I > have properly modified parameters such as FFT size, number of occupied > tones > and so on. I have also included all preambles (STF, LTF...) and I have > accordingly modified the "correlate" and "calculate_equalizer" functions > in > ofdm_frame_acquisition. FEC is also included in the chain. In the > ofdm_frame_sink file I've added a function that computes SNR in a > per-carrier > basis. > > Everything is working fine, I obtain about 80% of correct packets, but > I've > noticed from the snr plotting, that the carriers around the central empty > one > (3 subcarriers before and 3 subcarriers after) have very poor snr values. > So > I've investigated about this effect, and I've realized that the all > transmission errors are in those subcarriers and, in most cases, FEC is > able to > recover, but I would like to understand why this happens. > > I conducted some searches in the web but unfortunately I didn't find an > answer. > Let me know if you need some other information about my implementation. > > Thanks for your attention > francesca > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > > > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > Since you're likely using the Gnu Radio interface that is a wrapper for > UHD, you'd use the set_center_freq() method. > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > > > > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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