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. - George
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