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//
// pll_example.c
//
// Demonstrates a basic phase-locked loop to track the phase of a
// complex sinusoid.
//
#include <stdio.h>
#include <stdlib.h>
#include <complex.h>
#include <math.h>
#include <time.h>
#include "liquid.h"
// output to octave-friendly format
#define OUTPUT_FILENAME "pll_example.m"
int main() {
// parameters
float phase_offset = 0.8f; // carrier phase offset
float frequency_offset = 0.01f; // carrier frequency offset
float wn = 0.05f; // pll bandwidth
float zeta = 0.707f; // pll damping factor
float K = 1000; // pll loop gain
unsigned int n = 256; // number of samples
unsigned int d = n/32; // print every "d" lines
//
float theta[n]; // input phase
float complex x[n]; // input sinusoid
float phi[n]; // output phase
float complex y[n]; // output sinusoid
// generate iir loop filter object
iirfilt_rrrf H = iirfilt_rrrf_create_pll(wn, zeta, K);
iirfilt_rrrf_print(H);
unsigned int i;
// generate input
float t=phase_offset;
float dt = frequency_offset;
for (i=0; i<n; i++) {
theta[i] = t;
x[i] = cexpf(_Complex_I*theta[i]);
t += dt;
}
// run loop
float phi_hat=0.0f;
for (i=0; i<n; i++) {
y[i] = cexpf(_Complex_I*phi_hat);
// compute error
float e = cargf(x[i]*conjf(y[i]));
if ( (i%d)==0 )
printf("e(%3u) = %12.8f;\n", i, e);
// filter error
iirfilt_rrrf_execute(H,e,&phi_hat);
phi[i] = phi_hat;
}
// destroy filter
iirfilt_rrrf_destroy(H);
// open output file
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"clear all;\n");
fprintf(fid,"n=%u;\n",n);
for (i=0; i<n; i++) {
fprintf(fid,"theta(%3u) = %16.8e;\n", i+1, theta[i]);
fprintf(fid," phi(%3u) = %16.8e;\n", i+1, phi[i]);
}
fprintf(fid,"t=0:(n-1);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(t,theta,t,phi);\n");
fprintf(fid,"xlabel('sample index');\n");
fprintf(fid,"ylabel('phase');\n");
fclose(fid);
printf("output written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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