1 //
2 // firhilb_interp_example.c
3 //
4 // Hilbert transform: 1:2 complex-to-real interpolator. This
5 // example demonstrates the functionality of firhilb (finite
6 // impulse response Hilbert transform) interpolator which converts
7 // a complex time series into a real one with twice the number of
8 // samples. The input is a complex-valued sinusoid of N samples.
9 // The output is a real-valued sinusoid of 2*N samples.
10 //
11 // SEE ALSO: firhilb_decim_example.c
12
13 #include <stdio.h>
14 #include <complex.h>
15 #include <math.h>
16
17 #include "liquid.h"
18
19 #define OUTPUT_FILENAME "firhilb_interp_example.m"
20
main()21 int main() {
22 unsigned int m=5; // Hilbert filter semi-length
23 float As=60.0f; // stop-band attenuation [dB]
24 float fc=0.31f; // signal center frequency
25 unsigned int num_samples=128; // number of samples
26
27 // data arrays
28 float complex x[num_samples]; // complex input
29 float y[2*num_samples]; // real output
30
31 // initialize input array
32 unsigned int i;
33 for (i=0; i<num_samples; i++)
34 x[i] = cexpf(_Complex_I*2*M_PI*fc*i) + 0.6f*cexpf(_Complex_I*2*M_PI*1.1*fc*i);
35
36 // create Hilbert transform object
37 firhilbf q = firhilbf_create(m,As);
38
39 // execute transform (interpolator) to compute real signal
40 firhilbf_interp_execute_block(q, x, num_samples, y);
41
42 // destroy Hilbert transform object
43 firhilbf_destroy(q);
44
45 printf("firhilb interpolated %u complex samples to %u real samples\n",
46 num_samples, 2*num_samples);
47
48 //
49 // export results to file
50 //
51 FILE*fid = fopen(OUTPUT_FILENAME,"w");
52 fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
53 fprintf(fid,"clear all;\n");
54 fprintf(fid,"close all;\n");
55 fprintf(fid,"h_len=%u;\n", 4*m+1);
56 fprintf(fid,"num_samples=%u;\n", num_samples);
57
58 for (i=0; i<num_samples; i++) {
59 // print results
60 fprintf(fid,"x(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
61 fprintf(fid,"y(%3u) = %12.4e;\n", 2*i+1, y[2*i+0]);
62 fprintf(fid,"y(%3u) = %12.4e;\n", 2*i+2, y[2*i+1]);
63 }
64
65 // plot results
66 fprintf(fid,"nfft=512;\n");
67 fprintf(fid,"%% compute normalized windowing functions\n");
68 fprintf(fid,"wx = 1.8534/num_samples*hamming(length(x)).'; %% x window\n");
69 fprintf(fid,"wy = 1.8534/num_samples*hamming(length(y)).'; %% y window\n");
70 fprintf(fid,"X=20*log10(abs(fftshift(fft(x.*wx,nfft))));\n");
71 fprintf(fid,"Y=20*log10(abs(fftshift(fft(y.*wy,nfft))));\n");
72 fprintf(fid,"f =[0:(nfft-1)]/nfft-0.5;\n");
73 fprintf(fid,"fi=[0:(nfft-1)]/(2*nfft);\n");
74 fprintf(fid,"figure; plot(fi,X,'Color',[0.5 0.5 0.5],f,Y,'LineWidth',2);\n");
75 fprintf(fid,"grid on;\n");
76 fprintf(fid,"axis([-0.5 0.5 -80 20]);\n");
77 fprintf(fid,"xlabel('normalized frequency');\n");
78 fprintf(fid,"ylabel('PSD [dB]');\n");
79 fprintf(fid,"legend('original/complex','transformed/interpolated','location','northeast');");
80
81 fclose(fid);
82 printf("results written to %s\n", OUTPUT_FILENAME);
83
84 printf("done.\n");
85 return 0;
86 }
87