filter_tools.m

gnuradio软件无线电源程序.现在的手机多基于软件无线电

#
# Copyright 2001 Free Software Foundation, Inc.
# 
# This file is part of GNU Radio
# 
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2, or (at your option)
# any later version.
# 
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING.  If not, write to
# the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
# Boston, MA 02111-1307, USA.
# 
## equivalent to the C++ code in VrComplexFIRfilter::buildFilterComplex

1;

## hamming window, nothing fancy

function taps = build_filter_complex_lp (gain, ntaps)

  taps = gain * (0.54 - 0.46 * cos (2 * pi * (0:ntaps-1)' / (ntaps-1)));

endfunction


## old_taps describes a low pass filter, convert it to bandpass
## centered at center_freq.  center_freq is normalized to Fs (sampling freq)

function new_taps = freq_shift_filter (old_taps, center_freq)

  ntaps = length(old_taps);
  
  new_taps = exp (j*2*pi*center_freq*(0:ntaps-1)') .* old_taps;

endfunction