Hi, You have to explain well in order to get help, for example you said :
[ 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 ] What is [my array]? how we suppose that we know your array? And what are these numbers? and how you get them? What was the input signal? what was its frequency, modulation,...etc? Read: http://gnuradio.org/trac/wiki/ReportingErrors Then post again. BR Firas --- On Tue, 5/26/09, kaleem ahmad <kaleem_...@yahoo.com> wrote: > From: kaleem ahmad <kaleem_...@yahoo.com> > Subject: Re: [Discuss-gnuradio] Cycle time detection for an unknown cyclic > radio system > To: Discuss-gnuradio@gnu.org > Date: Tuesday, May 26, 2009, 10:57 AM > > 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 > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
