On Wed, Jul 29, 2009 at 2:46 PM, George Nychis <gnyc...@cmu.edu> wrote:
> > > On Wed, Jul 29, 2009 at 1:43 PM, Shizheng Li <shizhen...@gmail.com> wrote: > >> Dear all, >> I am reading the GMSK demodulator code (gmsk.py) and I have a question. In >> the modulator, Gaussian filter is used before the FM modulator. In the >> demodulator, no matched filter is used. The signal go through FM >> demodulator, then clock recovery, then make the decision. Why not use a >> matched filter after the demodulator, as in standard diagrams of the >> receivers? Thank you very much! >> > > I think that one reason may be is that the output from the USRP to the host > is not normalized. With a matched filter, you're going to convolve the > input signal with your coefficients, and if your input signal is not > normalized then a higher input signal to the USRP will generate stronger > output from the matched filter (whether it's a match or not). Therefore > you're going to have trouble thresholding to determine the peak in > synchronization. > actually, I'm thinking an acquisition matched filter, so you might want to ignore that :) - George
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