Hi Marcus, I want the exact end of the preambles IQ samples, so that I can chop it off from my trace and also find the exact locations where my bits (transmitted sparsely) are. I want to calculate the SNR for the decoder. So, if I know the samples exactly corresponding to data bits, I can extract them and apply the S+N/N = E[noise +signal]/ E[noise] equation.
I am transmitting preamble at double the amplitude than the actual bits due to my experiment requirements (more fidelity at the receiver), so I can't calculate the SNR over the preamble, hence I will do it over samples corresponding to bit 1 pulses in the trace corresponding to data transmission. Thank you for your replies, Abhinav On Tue, Jan 26, 2016 at 3:12 AM, Marcus Müller <marcus.muel...@ettus.com> wrote: > Hi Abhinav, > > point of timing recovery like you do it is that there's no IQ samples that > *exactly and reliably* correspond to the symbol timing; that's why you need > timing recovery. The question here is: what do you actually need? The IQ > samples before timing recovery aren't useful to the decoder. > > Just to assure you: AGC2 doesn't modify the number of samples, it just > multiplies with a factor that changes so that average power stays the same. > > Best regards, > Marcus > > > On 01/25/2016 06:26 PM, abhinav narain wrote: > > Hi All, > > My problem is that above calculation sort of works, and isn't it exact. > I have the following preable of 32 > bits [1,0,1,0,1,1,0,0,1,1,0,1,1,1,0,1,1,0,1,0,0,1,1,0,0,1,1,1,0,1,0,1]. > This can be seen in badpreamble.png, where for some reason I have trailing > 0s or noise and the > start of preamble is missing. > > If I shift the position to 8 bits lag in the bit file and then > plot(8shiftedpreamble.png), the corresponding > IQ samples using above logic, it is almost right (alhough sitll not right. > > Any suggestions how to get the exact IQ samples ? > Thanks, > Abhinav > > On Sun, Jan 24, 2016 at 11:03 AM, abhinav narain < > abhinavnarai...@gmail.com> wrote: > >> Hi all, >> This might be too simple, but I wanted to confirm as I am not sure how the >> blocks manipulate the IQ samples and how AGC works, does it add more >> samples for compensating the noise average or not. >> >> I have a flowgraph(image attached) which dumps the IQ samples and the >> bits after using Polyphase Clock Sync. I want to find exact IQ samples >> corresponding to >> a specific preamble in the bitsequence I have obtained in the output >> file. >> Let say the starting position of sample is= P, the sample rate=S ksps, >> samples \ >> per symbol=Y. >> >> Is it correct to assume that the index of iq samples corresponding to >> preamble in the IQ file will be at index P*Y ? >> If preamble size is 32 bits then there will be 32*Y of them ? >> >> Thanks, >> Abhinav >> >> > > > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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