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gr_simple_correlator.h

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00001 /* -*- c++ -*- */
00002 /*
00003  * Copyright 2004 Free Software Foundation, Inc.
00004  * 
00005  * This file is part of GNU Radio
00006  * 
00007  * GNU Radio is free software; you can redistribute it and/or modify
00008  * it under the terms of the GNU General Public License as published by
00009  * the Free Software Foundation; either version 2, or (at your option)
00010  * any later version.
00011  * 
00012  * GNU Radio is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00015  * GNU General Public License for more details.
00016  * 
00017  * You should have received a copy of the GNU General Public License
00018  * along with GNU Radio; see the file COPYING.  If not, write to
00019  * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
00020  * Boston, MA 02111-1307, USA.
00021  */
00022 
00023 #ifndef INCLUDED_GR_SIMPLE_CORRELATOR_H
00024 #define INCLUDED_GR_SIMPLE_CORRELATOR_H
00025 
00026 #include <gr_block.h>
00027 #include <assert.h>
00028 
00029 //#define       DEBUG_SIMPLE_CORRELATOR
00030 
00031 class gr_simple_correlator;
00032 typedef boost::shared_ptr<gr_simple_correlator> gr_simple_correlator_sptr;
00033 
00034 gr_simple_correlator_sptr gr_make_simple_correlator (int payload_bytesize);
00035 
00040 class gr_simple_correlator : public gr_block
00041 {
00042   static const int OVERSAMPLE = 8;
00043   enum state_t { ST_LOOKING, ST_UNDER_THRESHOLD, ST_LOCKED };
00044   
00045   int            d_payload_bytesize;
00046   state_t        d_state;
00047   unsigned int   d_osi;                         // over sample index [0,OVERSAMPLE-1]
00048   unsigned int   d_transition_osi;              // first index where Hamming dist < thresh
00049   unsigned int   d_center_osi;                  // center of bit
00050   unsigned long long int d_shift_reg[OVERSAMPLE];
00051   int            d_bblen;                       // length of bitbuf
00052   unsigned char *d_bitbuf;                      // demodulated bits
00053   int            d_bbi;                         // bitbuf index
00054 
00055   static const int AVG_PERIOD = 512;            // must be power of 2 (for freq offset correction)
00056   int   d_avbi;
00057   float d_avgbuf[AVG_PERIOD];
00058   float d_avg;
00059   float d_accum;
00060 
00061 #ifdef DEBUG_SIMPLE_CORRELATOR
00062   FILE          *d_debug_fp;                    // binary log file
00063 #endif
00064 
00065   friend gr_simple_correlator_sptr gr_make_simple_correlator (int payload_bytesize);
00066   gr_simple_correlator (int payload_bytesize);
00067 
00068 
00069   inline int slice (float x)
00070   {
00071     return x >= d_avg ? 1 : 0;
00072   }
00073 
00074   void update_avg(float x);
00075 
00076   void enter_locked ();
00077   void enter_under_threshold ();
00078   void enter_looking ();
00079   
00080   static int add_index (int a, int b)
00081   {
00082     int t = a + b;
00083     if (t >= OVERSAMPLE)
00084       t -= OVERSAMPLE;
00085     assert (t >= 0 && t < OVERSAMPLE);
00086     return t;
00087   }
00088 
00089   static int sub_index (int a, int b)
00090   {
00091     int t = a - b;
00092     if (t < 0)
00093       t += OVERSAMPLE;
00094     assert (t >= 0 && t < OVERSAMPLE);
00095     return t;
00096   }
00097 
00098   
00099  public:
00100   ~gr_simple_correlator ();
00101 
00102   int general_work (int noutput_items,
00103                     gr_vector_int &ninput_items,
00104                     gr_vector_const_void_star &input_items,
00105                     gr_vector_void_star &output_items);
00106 };
00107 
00108 
00109 #endif /* INCLUDED_GR_SIMPLE_CORRELATOR_H */

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