dqpsk.h

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/*
 * SPUC - Signal processing using C++ - A DSP library
 * 
 * This program 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.
 * 
 * This program 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 this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include <complex.h>
namespace SPUC {



class dqpsk {
 public:
  int datbase[4][4];
  int previous_encoded_symbol;
  int previous_decoded_symbol;

  dqpsk() {
        //  Initialize previous symbol to zero 
        //  Set up encoding data base as a two element array with arguments of
        //   i) current input symbol, and ii) previous encoded symbol 

        //      static int datbase[4][4] = {0,1,2,3,1,3,0,2,2,0,3,1,3,2,1,0};
        datbase[0][0] = 0;
        datbase[0][1] = 1;
        datbase[0][2] = 2;
        datbase[0][3] = 3;

        datbase[1][0] = 1;
        datbase[1][1] = 3;
        datbase[1][2] = 0;
        datbase[1][3] = 2;

        datbase[2][0] = 2;
        datbase[2][1] = 0;
        datbase[2][2] = 3;
        datbase[2][3] = 1;

        datbase[3][0] = 3;
        datbase[3][1] = 2;
        datbase[3][2] = 1;
        datbase[3][3] = 0;
        previous_encoded_symbol = 0;
        previous_decoded_symbol = 0;
  }
  complex<long> encode(complex<long> c)
        {
          int insym,outsym; 
          insym = qpsk_sym(c);
          outsym = datbase[insym][previous_encoded_symbol];
          previous_encoded_symbol = outsym;
          return(convbits(outsym));
        }
  complex<long> decode(complex<long> c)
        {
          int insym,outsym; 
          insym = qpsk_sym(c);
          outsym = datbase[insym][previous_decoded_symbol];
          previous_decoded_symbol = insym;
          return(convbits(outsym));
        }
  complex<long> convbits(int sym)
        {
          if(sym==0) return(complex<long>(-1,-1));
          else if(sym==1) return(complex<long>(-1,1));
          else if(sym==2) return(complex<long>(1,-1));
          else return(complex<long>(1,1));
        }
  int qpsk_sym(complex<long> c)
        {
          int insym;
          if(c.real()==-1.) {
                if(c.imag()==-1) insym = 0;            
                else insym = 1;
          }
          else  {
                if(c.imag()==-1) insym = 2;            
                else insym = 3;
          }
          return(insym);
        }
};
} // namespace SPUC 

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