text: //
  // symsync_crcf_example.c
  //
  // This example demonstrates the basic principles of the symbol timing
  // recovery family of objects, specifically symsync_crcf. A set of random
  // QPSK symbols are generated and interpolated with a timing offset. The
  // resulting signal is run through the symsync_crcf object which applies a
  // matched filter and recovers timing producing a clean constellation.
  //
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <math.h>
  #include <getopt.h>
  #include <time.h>
  #include <assert.h>
  
  #include "liquid.h"
  
  #define OUTPUT_FILENAME "symsync_crcf_example.m"
  
  // print usage/help message
  void usage()
  {
      printf("symsync_crcf_example [options]\n");
      printf("  h     : print help\n");
      printf("  k     : filter samples/symbol, default: 2\n");
      printf("  m     : filter delay (symbols), default: 5\n");
      printf("  b     : filter excess bandwidth, default: 0.5\n");
      printf("  B     : filter polyphase banks, default: 32\n");
      printf("  n     : number of symbols, default: 400\n");
  }
  
  int main(int argc, char*argv[]) {
      srand(time(NULL));
  
      // options
      unsigned int k           = 2;       // samples/symbol (input)
      unsigned int m           = 5;       // filter delay (symbols)
      float        beta        = 0.5f;    // filter excess bandwidth factor
      unsigned int num_filters = 32;      // number of filters in the bank
      unsigned int num_symbols = 400;     // number of data symbols
  
      int dopt;
      while ((dopt = getopt(argc,argv,"hk:m:b:B:s:n:")) != EOF) {
          switch (dopt) {
          case 'h':   usage();                        return 0;
          case 'k':   k           = atoi(optarg);     break;
          case 'm':   m           = atoi(optarg);     break;
          case 'b':   beta        = atof(optarg);     break;
          case 'B':   num_filters = atoi(optarg);     break;
          case 'n':   num_symbols = atoi(optarg);     break;
          default:
              exit(1);
          }
      }
  
      // validate input
      if (k < 2) {
          fprintf(stderr,"error: k (samples/symbol) must be at least 2\n");
          exit(1);
      } else if (m < 1) {
          fprintf(stderr,"error: m (filter delay) must be greater than 0\n");
          exit(1);
      } else if (beta <= 0.0f || beta > 1.0f) {
          fprintf(stderr,"error: beta (excess bandwidth factor) must be in (0,1]\n");
          exit(1);
      } else if (num_filters == 0) {
          fprintf(stderr,"error: number of polyphase filters must be greater than 0\n");
          exit(1);
      } else if (num_symbols == 0) {
          fprintf(stderr,"error: number of symbols must be greater than 0\n");
          exit(1);
      }
  
      unsigned int i;
  
      // static values
      liquid_firfilt_type ftype = LIQUID_FIRFILT_ARKAISER;
      float bandwidth = 0.02f;    // loop filter bandwidth
      float dt = -0.5f;           // fractional sample offset
  
      // derived values
      unsigned int num_samples = k*num_symbols;
  
      float complex s[num_symbols];       // data symbols
      float complex x[num_samples];       // interpolated samples
      float complex y[num_symbols + 64];  // synchronized symbols
  
      // generate random QPSK symbols
      for (i=0; i<num_symbols; i++) {
          // random signal (QPSK)
          s[i] = (rand() % 2 ? -M_SQRT1_2 : M_SQRT1_2) +
                 (rand() % 2 ? -M_SQRT1_2 : M_SQRT1_2) * _Complex_I;
      }
  
      // design interpolating filter with 'dt' samples of delay
      firinterp_crcf interp = firinterp_crcf_create_rnyquist(ftype,k,m,beta,dt);
  
      // run interpolator
      firinterp_crcf_execute_block(interp, s, num_symbols, x);
  
      // destroy interpolator
      firinterp_crcf_destroy(interp);
  
      // create symbol synchronizer
      symsync_crcf sync = symsync_crcf_create_rnyquist(ftype, k, m, beta, num_filters);
      
      // set bandwidth
      symsync_crcf_set_lf_bw(sync,bandwidth);
  
      // execute on entire block of samples
      unsigned int ny=0;
      symsync_crcf_execute(sync, x, num_samples, y, &ny);
  
      // destroy synchronizer
      symsync_crcf_destroy(sync);
  
      // print last several symbols to screen
      printf("output symbols:\n");
      printf("  ...\n");
      for (i=ny-10; i<ny; i++)
          printf("  sym_out(%2u) = %8.4f + j*%8.4f;\n", i+1, crealf(y[i]), cimagf(y[i]));
  
      //
      // export output file
      //
  
      FILE* fid = fopen(OUTPUT_FILENAME,"w");
      fprintf(fid,"%% %s, auto-generated file\n\n", OUTPUT_FILENAME);
      fprintf(fid,"close all;\n");
      fprintf(fid,"clear all;\n");
  
      fprintf(fid,"ny=%u;\n",ny);
  
      for (i=0; i<ny; i++)
          fprintf(fid,"y(%3u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
          
      fprintf(fid,"i0 = 1:round(0.5*ny);\n");
      fprintf(fid,"i1 = round(0.5*ny):ny;\n");
      fprintf(fid,"figure;\n");
      fprintf(fid,"hold on;\n");
      fprintf(fid,"plot(real(y(i0)),imag(y(i0)),'x','MarkerSize',4,'Color',[1 1 1]*0.7);\n");
      fprintf(fid,"plot(real(y(i1)),imag(y(i1)),'o','MarkerSize',4,'Color',[0 0.25 0.5]);\n");
      fprintf(fid,"hold off;\n");
      fprintf(fid,"axis square;\n");
      fprintf(fid,"grid on;\n");
      fprintf(fid,"axis([-1 1 -1 1]*1.6);\n");
      fprintf(fid,"xlabel('In-phase');\n");
      fprintf(fid,"ylabel('Quadrature');\n");
      fprintf(fid,"legend(['first 50%%'],['last 50%%'],'location','northeast');\n");
  
      fclose(fid);
      printf("results written to %s.\n", OUTPUT_FILENAME);
  
      // clean it up
      printf("done.\n");
      return 0;
  }
  