freeswitch/libs/libcodec2/octave/fdmdv_mod.m

% fdmdv_mod.m
%
% Modulator function for FDMDV modem, uses test frames as input and
% outputs a raw file of 16 bit shorts at a sample rate of 8 kHz.
%
% Copyright David Rowe 2012
% This program is distributed under the terms of the GNU General Public License 
% Version 2
%

function tx_fdm = fdmdv_mod(rawfilename, nbits)

  fdmdv; % include modem code

  frames = floor(nbits/(Nc*Nb))
  tx_fdm = [];
  gain = 1000; % Scale up to 16 bit shorts
  prev_tx_symbols = ones(Nc+1,1);

  for i=1:frames
    tx_bits = get_test_bits(Nc*Nb);
    tx_symbols = bits_to_qpsk(prev_tx_symbols, tx_bits,'dqpsk');
    prev_tx_symbols = tx_symbols;
    tx_baseband = tx_filter(tx_symbols);
    tx_fdm = [tx_fdm real(fdm_upconvert(tx_baseband))];
  end

  tx_fdm *= gain;
  fout = fopen(rawfilename,"wb");
  fwrite(fout, tx_fdm, "short");
  fclose(fout);
endfunction