So, I'm sure everyone has been eagerly awaiting the results of simulations....
Dave's answer is indeed correct. For a 16-point biplex_core FFT, with pol1 and pol2 being independent time-streams, presented in normal time order (i.e., with consecutive time samples) and output channels defined such that: chan 0 is DC chan 7 is the max positive frequency chan 8 is the negative frequency furthest from DC chan 15 is the negative frequency closest to DC The output channel order from the biplex_core is (immediately following the sync): out1 = FFT(pol1)[0, 4, 2, 6, 1, 5, 3, 7] followed by FFT(pol2) [0, 4, 2, 6, 1, 5, 3, 7] out2 = FFT(pol1)[8, 12, 10, 14, 9, 13, 11, 15] followed by FFT(pol2)[8, 12, 10, 14, 9, 13, 11, 15]. These, when bit-reversed, result in: bit_reverse(out1) = FFT(pol1)[0, 1, 2, 3, 4, 5, 6, 7] followed by FFT(pol2) [0, 1, 2, 3, 4, 5, 6, 7] bit_reverse(out2) = FFT(pol1)[8, 9, 10, 11, 12, 13, 14, 15] followed by FFT(pol2)[8, 9, 10, 11, 12, 13, 14, 15] How exciting! Jack On Wed, 21 Feb 2018 at 22:50 David MacMahon <dav...@berkeley.edu> wrote: > Hi, Jack, > > I haven’t used the biplex_core block in a while, but I believe the inputs, > pol1 and pol2, are two independent complex input signals. The outputs, out1 > and out2, first output the frequency channels for input pol1, with the low > half of the band being output in bit reversed order on out1 and the high > half of the band being output on out2 in bit reversed order. After > outputting the channels for pol1, out1 and out2 output the channels for > pol2 in a similar order. > > For a 16 channel fft, I think out1 will have channels: pol1[0 4 2 6 1 5 3 > 7] followed by pol2[0 4 2 6 1 5 3 7]. Out2 will have the same output order > but 8 (ie N/2) channels higher. I hope that makes sense, but if not I can > make a better diagram for you tomorrow. > > Of course this should be verified with simulation, but I think it’s a good > starting point. BTW, this assumes the inputs are presented in natural tone > order at both inputs with the t=0 samples of pol1 and pol2 being presented > at the respective inputs simultaneously. > > Dave > > On Feb 21, 2018, at 18:04, Jack Hickish <jackhick...@gmail.com> wrote: > > Howdy, > > Partly motivated by a search for RAM savings, and partly for fun, I'm > looking through the innards of the fft_biplex_real_4x block. Can someone > tell me, using short words and/or pictures, what the the relationship > between the inputs (pol1, pol2) and the outputs (out1, out2) on the > biplex_core block is. > > I'm in the midst of reverse engineering the block by simulation / staring > at the unscrambler / reading about fft biplex implementations, but surely > someone must(!) know what this block actually does (or claims to do)? > > Yours, optimistically, > > Jack > > -- > > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To post to this group, send email to casper@lists.berkeley.edu. > > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To post to this group, send email to casper@lists.berkeley.edu. > -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu" group. To unsubscribe from this group and stop receiving emails from it, send an email to casper+unsubscr...@lists.berkeley.edu. To post to this group, send email to casper@lists.berkeley.edu.
