On Thu, Sep 06, 2007 at 11:56:30AM -0400, Jeffrey Karrels wrote: > Ok. I am having a world of problems today, the main one being > determining if it is my issues causing the headache or the headache > causing the issues. ;) > > I have a basic bandwidth limit that I am hitting and for some reason I > cannot do basic math today. > > I am trying to see how many carriers I can transmit on. I am mixing a > single gmsk modulated source with LOs in software and seeing how many > times I can do that. A single channel is 250kHz wide and the channels > are 400kHz apart center to center. In other words my LOs are 400e3, > 800e3, ... > > How many carriers would you expect that I could transmit on? > > > Thanks > Jeff > P.S. Sorry in advance, I am nuts today.
In theory, 20. In reality probably about 16, unless you run out of CPU first. You can get 8Mz of IF bandwidth across the USB. This is 8MS/s * 2 * 2 = 32MB/s (16-bit I & Q). 8e6/4e5 = 20 "bins" (ignoring roll off) Allow for roll off because of CIC interpolator in FPGA. Say that 80% is usable (depends on your app, whether you preemph signal etc). 20 * .8 = 16 bins. There's a fence post problem here ;) So, 1 carrier needs 250kHz 3 carriers needs 2 * 400 + 2 * 125 5 carriers needs 4 * 400 + 2 * 125 N carriers needs (N-1) * 400 + 250 (for odd N) 15 -> 5.85MHz 17 -> 6.65MHz 19 -> 7.45MHz Put the middle carrier at 0 Hz, then arrange the others symmetrically about it. Eric _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
