Hello Mallesham, I'm afraid not, since I'm afraid that to my current understanding, what you want is mathematically impossible. Either you want much data – and that seems to be the case, since you want to record 24h of raw IQ data – or you can store it in what comparably little RAM modern computers have.
Maybe, however, we haven't fully understood the problem. Can you, mathematically, define what you want to observe and record? Best regards, Marcus On 01/20/2017 08:28 PM, Mallesham Dasari wrote: > Hello everyone, > > Can anyone give some solution for this? Even writing to the ramdisk is > not enough for running the flow graph for so long. I am facing the > same issue. > > Thank you! > > On Thu, Jan 12, 2017 at 5:41 PM, Hasini Abeywickrama <[email protected] > <mailto:[email protected]>> wrote: > > Hi all, > > Thank you very much for the informative responses. > > My requirement is to run the flowgraph for a long time (ideally 24 > hours) and store the FFT data in the memory (ramdisk) to they can > be processed later or in chunks, not everything at the same time. > > So far, I have increased the size of the ramdisk and it works fine > for a few hours. But it still is not the solution I'm looking for. > > Regards, > Hasini > > On Thu, Jan 12, 2017 at 8:30 PM, Marcus Müller > <[email protected] <mailto:[email protected]>> wrote: > > But if you do a single 1024-FFT, you'd only operate on 1024 of > the input samples! > > And: the FFT doesn't just give you power values, but complex > values; mathematically, the FFT is a DFT, and the DFT is an > invertible linear operator $\mathcal F$: > > $\mathcal F: \mathbb C^{N} \mapsto \mathbb C^{N}$ > > which maps complex vectors to complex vectors of size $N,\quad > 0<N\in\mathbb N$. It is, in fact, representable as square > matrix with column (and row) vectors being samples of the > orthogonal complex sinusoids $e^{j\frac{2\pi}N nk},\, > k=0,\ldots,N-1$; that is, it can also be understood as a /base > change matrix/, that just represents the "input vector" > according to a different base, orthogonal base. > In the physical sense: the input vector base was represented > by the standard basis $\mathbf e_N$, meaning that each base > vector represents a single point in time – the sample time of > the respective entry; the "output" of the transform is > represented on a base of orthogonal frequencies. This is an > invertible operation – really just another way to look at *the > same signal*. I think this is really important to keep in mind: > > The Fourier transforms are /not/ magical by any means. What > they do is represent *the same signal* from a different point > of view. It can be /interpreted/ as transform between time and > frequency domain (or space and impulse, or...). The DFT is > still just a boring, old, square, orthogonal, invertible > matrix that produces output of the same dimensionality as it > takes input. > > As you can see, the DFT/FFT itself never reduces the amount of > data. > > What you might be referring to is some kind PSD estimate done > by first |·|² a lot of DFTed vectors and then averaging them. > The data reduction here lies in the magnitude square operation > and the average, not in the DFT. > The point here is that you're throwing away a whole lot of > information, and I'm not convinced that's what Hasini needs! > > Best regards, > > Marcus > > > On 12.01.2017 05:54, Mallesham Dasari wrote: >> Hi Marcus, >> >> Raw IQ samples take lots of memory because each sample will >> be around 8Bytes. Suppose, if we 1Msps sample rate, just for >> 10 minutes of data, we get 10*60*1M*8B = 4.8GB data. On the >> other hand, if you store just FFT with 1024 bin, we get >> 4.8GB/1024 power values right (which has very less size)? >> >> Please correct me if I am wrong. >> >> Thanks >> >> On Wed, Jan 11, 2017 at 7:32 AM, Marcus Müller >> <[email protected] <mailto:[email protected]>> >> wrote: >> >> Hi Mallesham, >> >> I don't understand – the raw IQ samples and their FFT >> have the same size, and data type. >> >> Maybe you've understood something that I (and Martin) >> didn't – could you elaborate? >> >> Best regards, >> Marcus >> >> >> On 01/11/2017 12:56 AM, Mallesham Dasari wrote: >>> Hi Hasini, >>> >>> If you are trying to print just the FFT, it should not >>> be an issue. If you print raw iq samples, then you will >>> run out of memory. By long, you mean how long? Days? >>> >>> On Tue, Jan 10, 2017 at 3:16 PM, Martin Braun >>> <[email protected] <mailto:[email protected]>> >>> wrote: >>> >>> Hasini, >>> >>> can you please re-state what you're trying to do? >>> That might help you >>> getting some answers. It is not quite clear from >>> this email. >>> >>> Cheers, >>> Martin >>> >>> >>> On 01/02/2017 09:16 PM, Hasini Abeywickrama wrote: >>> > Hi all, >>> > >>> > I have a flowgraph that reads a signal and writes >>> its FFT samples to a >>> > file. I need to run this continuously (for a long >>> time), without running >>> > out of memory. >>> > >>> > I tired deleting the earlier FFT samples from the >>> file but that messes >>> > up with reading the data. I also tried starting >>> writing to a different >>> > file after some time so the initial file can be >>> completely deleted. But >>> > it did not work as well. >>> > >>> > What would be the best approach for this? Any >>> thought would be very much >>> > appreciated. >>> > >>> > Regards, >>> > Hasini >>> > >>> > >>> > _______________________________________________ >>> > Discuss-gnuradio mailing list >>> > [email protected] >>> <mailto:[email protected]> >>> > >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> >>> > >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> [email protected] >>> <mailto:[email protected]> >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> >>> >>> >>> >>> >>> -- >>> Best Regards, >>> *Mallesham Dasari* >>> Department of Computer Science >>> Stony Brook University >>> USA - 11794 >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> [email protected] <mailto:[email protected]> >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> >> _______________________________________________ >> Discuss-gnuradio mailing list [email protected] >> <mailto:[email protected]> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> >> >> -- >> Best Regards, >> *Mallesham Dasari* >> Department of Computer Science >> Stony Brook University >> USA - 11794 > _______________________________________________ > Discuss-gnuradio mailing list [email protected] > <mailto:[email protected]> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> > > -- > Best Regards, > *Mallesham Dasari* > Department of Computer Science > Stony Brook University > USA - 11794
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