Hi Marc, > Currently, I am trying to implement correlation receiver using FIR filters. I am looking into polyphase filterbank channelizer to implement correlation, but currently unable to do so because I currently do not know how to assign taps for channelizer.
I should have pointed you at Tom's article on PFB channelizers and synthesizers [1]. > Oversampling at baseband ? I am currently sampling at 1Msps (usrp sink > sampling rate) for a tone spacing of 125KHz. You mean after the USRP sink > block I should upsample again and then do the correlation? Or you mean > something else ? Please forgive me for asking too many question, I am still > learning. don't worry; this list is meant for GNU Radio discussion, I think things like exploring possibilities to do certain tasks in GNU Radio fit nicely, especially because you are considering using something "cool and new" like the PFBs in your approach. GNU Radio can always use more people actually trying to implement stuff! So: Oversampling is what you do when getting more samples out of your ADC than nyquist forces you to do. If you do 125k spacing 4FSK, then you have a total bandwidth of 750kHz + X, so 1MS/s is "just enough"; anyway, if you sample with let's say 3.125MS/s, than you'll have more samples. Within that received bandwidth, you will have the same signal as before, but now correlating against your known tone will give you a higher value than with only 1MS/s, and because noise stays uncorrelated, this will increase SNR. This is processing gain! >> ... encourage you to read a lot of books [1] and papers on this. > Thanks for the link, nice stuff. If you find something interesting, don't hesitate to add a new heading like "FSK demodulator technology" and add the references there; I think this list is something that could use broader usage :) >> Assuming you don't want phase jumps between symbols, why not just use >> the VCO block to generate frequencies out of your input values? > Wow! modulation is easy using VCO. A question, why would someone want phase > jump between symbols? In FSK systems, you'd usually want to avoid that, because phase jumps lead to spectral components that are not at the frequency you shifted to. With PSK, phase jumps is your only way to encode data, and with QAM "half" of the information is encoded in phase. However, you usually see a pulse shaper after these, because transmitting a real phase discontinuity is somewhat physically impossible[2]. So these modulations get the spectrum of a phase-jumping system, smoothed by the spectral shape of the pulse shaping. Greetings, Marcus [1] http://www.trondeau.com/examples/2014/1/23/pfb-channelizers-and-synthesizers.html [2] Basically, imagine the baseband signal as a sequence of rectangles in time; now, the fourier transform of a rectangle is a sin(x)/x, and that has a support that doesn't fit into a limited bandwidth. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
