1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
|
//
// resamp2_cccf_example.c
//
// This example demonstrates the halfband resampler cenetered at the
// quarter sample rate to split the signal into positive and negative
// frequency bands. Two distinct narrow-band signals are generated; one
// at a positive frequency and one at a negative frequency. The resamp2
// object is run as a filter to separate the two about the zero-
// frequency center point.
//
#include <stdio.h>
#include <complex.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "resamp2_cccf_example.m"
int main() {
unsigned int m = 12; // filter semi-length (actual length: 4*m+1)
float As = 60.0f; // stop-band attenuation [dB]
unsigned int num_samples = 400; // number of input samples
unsigned int i;
// allocate memory for data arrays
float complex x [num_samples]; // input signal
float complex y0[num_samples]; //
float complex y1[num_samples]; //
// generate the two signals
iirfilt_crcf lowpass = iirfilt_crcf_create_lowpass(6,0.02);
for (i=0; i<num_samples; i++) {
// signal at negative frequency: tone
float complex x_neg = cexpf(-_Complex_I*2*M_PI*0.059f*i);
// signal at positive frequency: filtered noise
float complex v;
iirfilt_crcf_execute(lowpass, 4*randnf(), &v);
float complex x_pos = v * cexpf(_Complex_I*2*M_PI*0.073f*i);
// composite
x[i] = (x_neg + x_pos) * liquid_hamming(i,num_samples);
}
iirfilt_crcf_destroy(lowpass);
// create/print the half-band resampler, with a specified
// stopband attenuation level
resamp2_cccf q = resamp2_cccf_create(m,-0.25f,As);
resamp2_cccf_print(q);
// run filter
for (i=0; i<num_samples; i++)
resamp2_cccf_filter_execute(q,x[i],&y0[i],&y1[i]);
//
// print results to file
//
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n",OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n\n");
fprintf(fid,"num_samples=%u;\n", num_samples);
// output results
for (i=0; i<num_samples; i++) {
fprintf(fid,"x( %3u) = %12.4e + j*%12.4e;\n", i+1, crealf( x[i]), cimagf( x[i]));
fprintf(fid,"y0(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(y0[i]), cimagf(y0[i]));
fprintf(fid,"y1(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(y1[i]), cimagf(y1[i]));
}
// plot temporal results
fprintf(fid,"\n\n");
fprintf(fid,"t = 0:(num_samples-1);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(t,real(x),'Color',[1 1 1]*0.7,'LineWidth',1);\n");
fprintf(fid," plot(t,imag(x),'Color',[1 1 1]*0.5,'LineWidth',2);\n");
fprintf(fid," hold off;\n");
fprintf(fid," grid on;\n");
fprintf(fid," legend('real','imag','location','northeast');\n");
fprintf(fid," axis([0 num_samples -2 2]);\n");
fprintf(fid," ylabel('original');\n");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(t,real(y0),'Color',[1 1 1]*0.7,'LineWidth',1);\n");
fprintf(fid," plot(t,imag(y0),'Color',[0 0.5 0.2],'LineWidth',2);\n");
fprintf(fid," hold off;\n");
fprintf(fid," grid on;\n");
fprintf(fid," legend('real','imag','location','northeast');\n");
fprintf(fid," axis([0 num_samples -2 2]);\n");
fprintf(fid," ylabel('negative band');\n");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(t,real(y1),'Color',[1 1 1]*0.7,'LineWidth',1);\n");
fprintf(fid," plot(t,imag(y1),'Color',[0 0.2 0.5],'LineWidth',2);\n");
fprintf(fid," hold off;\n");
fprintf(fid," grid on;\n");
fprintf(fid," legend('real','imag','location','northeast');\n");
fprintf(fid," axis([0 num_samples -2 2]);\n");
fprintf(fid," ylabel('positive band');\n");
fprintf(fid," xlabel('sample index');\n");
// plot spectrum results
fprintf(fid,"\n\n");
fprintf(fid,"nfft=2400;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"w = hamming(num_samples)' / num_samples;\n");
fprintf(fid,"X = 20*log10(abs(fftshift(fft( x.*w, nfft))));\n");
fprintf(fid,"Y0 = 20*log10(abs(fftshift(fft(y0.*w, nfft))));\n");
fprintf(fid,"Y1 = 20*log10(abs(fftshift(fft(y1.*w, nfft))));\n");
fprintf(fid,"figure('Color','white');\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(f,X, 'Color',[1 1 1]*0.7,'LineWidth',2);\n");
fprintf(fid," plot(f,Y0,'Color',[0 0.2 0.5]);\n");
fprintf(fid," plot(f,Y1,'Color',[0 0.5 0.2]);\n");
fprintf(fid," hold off;\n");
fprintf(fid,"legend('original','negative','positive','location','northeast');\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"axis([-0.5 0.5 -120 20]);\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('Power Spectral Density [dB]');\n");
fclose(fid);
printf("results written to %s\n",OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
|
