Can someone at least comment on first part of the problem, I mean where I am getting this 'factor' from
Thanks kaleem ahmad wrote: > > Dear All, > > A few weeks ago I was involved in a discussion about calculating the cycle > time of an unknown system present in the area by sensing the spectrum with > the help of RFX2400+USRP1 system. For details you may like to have a look > on previous mails on this thread. > > http://www.nabble.com/cycle-period-detection-of-a-cyclic-periodic-transmitter-td23171564.html#a23174531 > > As Firas suggested to choose a decimation factor with respect to duty > cycle of the cyclic system. I implemented it in this way but I am facing > two problems: > > 1- I am using following formula to calculate the cycle time: > > if > > ADC_rate = 64MHz, D=decimation rate, fft_size, count= total no. of > fft_scans where signal is not present > > Then following would give me the value of cycle time: > > [1/(ADC_rate/D)]*fft_size*count*1e3 ---> where [1/(ADC_rate/D)] simply > gives the time resolution or time gap between two points in fft bin. 1e3 > for conversion in ms. > > with D=128, fft_size=512, I scanned the spectrum for more than one times > and stored the results in an array, then I choose maximum occerence in > that array as 'count' in above formula e.g. > > for 200ms cycle time my array look like [27, 200, 27, 27, 27, 27, 276, > 27], here count = 27, other values are actually some errors > > for 100ms cycle time my array look like [13, 13, 87, 13, 13, 13, 13, 167], > here count = 13, other values are actually some errors > > for 50ms cycle time my array look like [6, 6, 6, 6, 6, 6, 6, 6], here > count = 6. > > From this array with multiple scans I was able to see that some cyclic > behaviour is correctly detected. BUT when I put all values in above > mentioned formula then I found that to get exact value of cycle time I > must multiply my answer with a 'factor' ranging from 7-8 (some times 7.25, > or 7.4, or 7.5 etc). But this 'factor' is not a fixed value and variation > in its value depend on the cycle time. So final formula becomes > > [1/(ADC_rate/D)]*fft_size*count * factor *1.e3 ---> The value of factor > is changing on following pattern: > > for 200ms cycle time factor ~ 7.25 would give me exact answer > for 150ms cycle time factor ~ 7.35 would give me exact answer > for 100ms cycle time factor ~ 7.5 would give me exact answer > for 50ms cycle time factor ~ 8 would give me exact answer > > I cant understand what this factor is and where it is comming from. Is > there any processing in USRP which I am forgetting? Can someone help me to > figureout this factor. > > 2-My second problem is that, I am able to detect cycle time for any duty > cycle with the help of 128, and 256 decimation rates , but with any other > decimation rate my answers are quite random and I cant get a cyclic answer > in my above mentioned array. Or simply you can say as it was looking from > theretical side that for any specific decimation rate I should get a > cyclic answer but the only thing which would change was the no. of > detected and undetected scans. But its not happening in this way. e.g with > any other decimation rate except 128, 256, I am getting answer like > follows: > > for 200ms cycle time my array look like [20, 2, 187, 17, 87, 65, 13, 167], > which dont provide me any clue. Similarly for any other cycle time I am > getting random values. > > Is there any thing wrong with selection of decimation rate? can some one > help me to figure out where I am doing wrong. > > Thanks and Best Regards > > -- View this message in context: http://www.nabble.com/Cycle-time-detection-for-an-unknown-cyclic-radio-system-tp23706892p23718374.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
