Re: [Discuss-gnuradio] Cycle time detection for an unknown cyclic radio system

[Firas Abbas]

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 <address@hidden> wrote:

> From: kaleem ahmad <address@hidden>
> Subject: Re: [Discuss-gnuradio] Cycle time detection for an unknown cyclic 
> radio system
> To: address@hidden
> 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.
> 
> 
> 
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