Thank you for your explanation, I 've been reading documentation about ofdm in 802.11g, and now I know what values I must put for the parameters. I added the size of the packet with '-s', and it worked. Thanks
2009/4/8 Martin Braun <[email protected]> > On Tue, Apr 07, 2009 at 10:32:20AM -0700, Rita's pfc wrote: > > > > Hi, > > I'm using benchmark_ofdm tx and rx in 2.4 GHz. I'm trying to transmit a > > fixed size of payload everytime (1328 Bytes). My problem is I don't know > > what values I must put in the parameters: fft-length, occupied-tones, > > cp-length. I know that fft-length is the total number of subcarriers, cp > the > > Hi, > just to be clear: fft-length is not the total number of subcarriers, it > is, as the name says, the FFT length. If these were identical, it would > be pretty difficult to filter out the OFDM signal as it would uniformly > fill the Nyquist band. > Sorry if this is what you meant, it jusn't wasn't quite clear to me. > > > cyclic prefix, occupied-tones number of subcarriers used for data. I have > > been running modifications of these benchmarks, and the best performance > I > > get is when the values of these parameters are: fft-length 512, cp 128, > > occupied tones 300. In this case, the 80 % of paquetes I receive are > right. > > How can I calculate the apropiate values ? Must I used the parameter "-s" > > for fixed the packet size to the one I want, 1328? what happen with the > "-i" > > and "-d" in the transmitter and the receiver? > > The packet length and the OFDM settings are not directly connected - > that is, in principle, you can have any combination (although that does > not always make sense). In theory, GNU Radio works well with any OFDM > setting, so all you have to do is adapt the settings according to your > data transmission requirements (bit rate, channel characteristics etc.). > > I haven't got a working setup at my fingertips right now, but -s should > be the right thing to do. However, note that the benchmark_ofdm* code > uses the GNU radio packet module, which itself does stuff to your data, > so perhaps your signal does not look exactly as you expected it to be. > > On a side note, when I was playing around with the OFDM benchmark code, > I never achieved a brilliant packet error rate, 80% was close to the > best I achieved - but I never tore the code apart to check for the > cause. > > Good luck, > MB > > -- > Dipl.-Ing. Martin Braun Phone: +49-(0)721-608 3790 > Institut fuer Nachrichtentechnik Fax: +49-(0)721-608 6071 > Universitaet Karlsruhe (TH) http://www.int.uni-karlsruhe.de/ > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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