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// Direct digital synthesizer example. This example demonstrates
// the interface to the direct digital synthesizer. A baseband
// pulse is generated and then efficiently up-converted
// (interpolated and mixed up) using the DDS object. The resulting
// signal is then down-converted (mixed down and decimated) using
// the same DDS object. Results are written to a file.
// SEE ALSO: firinterp_crcf_example.c
// decim_crcf_example.c
// resamp2_crcf_example.c
// nco_example.c
#include <stdio.h>
#include <complex.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "dds_cccf_example.m"
int main() {
// options
float fc = -0.2f; // input (output) decim (interp) frequency
unsigned int num_stages = 3; // number of halfband interp/decim stages
unsigned int num_samples = 64; // number of input samples
float As = 60.0f; // DDS stop-band attenuation [dB]
float bw = 0.25f; // signal bandwidth
// derived values
unsigned int r=1<<num_stages; // resampling rate (output/input)
// create resampler
dds_cccf q = dds_cccf_create(num_stages,fc,bw,As);
dds_cccf_print(q);
// open/initialize output file
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n",OUTPUT_FILENAME);
fprintf(fid,"clear all;\nclose all;\n\n");
fprintf(fid,"n=%u;\n", num_samples);
fprintf(fid,"r=%u;\n", r);
float complex x[num_samples];
float complex y[r*num_samples];
float complex z[num_samples];
unsigned int i;
// generate the baseband signal (filter pulse)
unsigned int h_len = num_samples/2;
h_len += num_samples % 2 ? 0 : 1;
float h[h_len];
liquid_firdes_kaiser(h_len,bw,60.0f,0.0f,h);
for (i=0; i<num_samples; i++)
x[i] = i < h_len ? 2*h[i]*bw : 0.0f;
// run interpolation (up-conversion) stage
for (i=0; i<num_samples; i++) {
dds_cccf_interp_execute(q, x[i], &y[r*i]);
}
// clear DDS object
dds_cccf_reset(q);
// run decimation (down-conversion) stage
for (i=0; i<num_samples; i++) {
dds_cccf_decim_execute(q, &y[r*i], &z[i]);
}
// 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]));
for (i=0; i<r*num_samples; i++)
fprintf(fid,"y(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
for (i=0; i<num_samples; i++)
fprintf(fid,"z(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(z[i]), cimagf(z[i]));
// print results
fprintf(fid,"\n\n");
fprintf(fid,"nfft=1024;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"X = 20*log10(abs(fftshift(fft(x, nfft))));\n");
fprintf(fid,"Y = 20*log10(abs(fftshift(fft(y/r,nfft))));\n");
fprintf(fid,"Z = 20*log10(abs(fftshift(fft(z, nfft))));\n");
fprintf(fid,"plot(f,X,f,Y,f,Z);\n");
fprintf(fid,"legend('original','up-converted','down-converted');\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"axis([-0.5 0.5 -120 20]);\n");
fprintf(fid,"\n\n");
fprintf(fid,"t0 = 0:[n-1];\n");
fprintf(fid,"t1 = 0:[n*r-1];\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," plot(t0,real(x),'-s','MarkerSize',3,t0,imag(x),'-s','MarkerSize',3);\n");
fprintf(fid," legend('I','Q');\n");
fprintf(fid," axis([0 n -0.55 0.55]);\n");
fprintf(fid," ylabel('original');\n");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," plot(t1,real(y),t1,imag(y));\n");
fprintf(fid," axis([0 n*r -0.55 0.55]);\n");
fprintf(fid," ylabel('up-converted');\n");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," plot(t0,real(z),'-s','MarkerSize',3,t0,imag(z),'-s','MarkerSize',3);\n");
fprintf(fid," axis([0 n -0.55 0.55]);\n");
fprintf(fid," ylabel('down-converted');\n");
fclose(fid);
printf("results written to %s\n",OUTPUT_FILENAME);
// clean up allocated objects
dds_cccf_destroy(q);
printf("done.\n");
return 0;
}
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