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// test GMSK equalization
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "gmsk_eqlms_example.m"
int main(int argc, char*argv[]) {
// options
unsigned int k = 4; // filter samples/symbol
float beta = 0.3f; // bandwidth-time product
unsigned int p = 3; // equalizer length (symbols, hp_len = 2*k*p+1)
float mu = 0.08f; // learning rate
unsigned int num_symbols = 2400;// number of symbols to simulate
unsigned int nfft = 1200;// number of symbols to simulate
// create modulator
gmskmod mod = gmskmod_create(k, 3, beta);
// create equalizer
eqlms_cccf eq = eqlms_cccf_create_rnyquist(LIQUID_FIRFILT_GMSKRX, k, p, beta, 0.0f);
eqlms_cccf_set_bw(eq, mu);
// create spectral periodogram
spgramcf q = spgramcf_create_default(nfft);
// write results to output 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");
fprintf(fid,"k = %u;\n", k);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"syms = zeros(1,num_symbols);\n");
fprintf(fid,"psd = zeros(1,nfft);\n");
float complex buf[k];
unsigned int i;
for (i=0; i<num_symbols; i++)
{
// generate input GMSK signal
gmskmod_modulate(mod, rand() & 1, buf);
// write samples into equalizer
eqlms_cccf_push_block(eq, buf, k);
// compute equalizer output
float complex d_hat;
eqlms_cccf_execute(eq, &d_hat);
spgramcf_write(q, buf, k);
// write results to file
fprintf(fid,"syms(%4u) = %12.4e + %12.4ej;\n", i+1, crealf(d_hat), cimagf(d_hat));
// update equalizer appropriately
if (i < p) continue;
float complex d_prime = (crealf(d_hat) > 0 ? 1 : -1) * M_SQRT1_2 +
(cimagf(d_hat) > 0 ? 1 : -1) * M_SQRT1_2 * _Complex_I;
eqlms_cccf_step(eq, d_prime, d_hat);
}
// get equalizer weights
unsigned int hp_len = 2*k*p+1; // equalizer filter length
float complex hp[hp_len]; // equalizer filter coefficients
eqlms_cccf_copy_coefficients(eq, hp);
fprintf(fid,"hp = zeros(1,%u);\n", hp_len);
for (i=0; i<hp_len; i++)
fprintf(fid,"hp(%3u) = %12.4e + %12.4ej;\n", i+1, crealf(hp[i]), cimagf(hp[i]));
float psd[nfft];
spgramcf_get_psd(q, psd);
for (i=0; i<nfft; i++)
fprintf(fid,"psd(%6u) = %12.4e;\n", i+1, psd[i]);
fprintf(fid,"np = round(0.75*num_symbols);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(syms(1:np), 'x','Color',[1 1 1]*0.7,...\n");
fprintf(fid," syms(np:end),'x','Color',[0 0.2 0.4]);\n");
fprintf(fid,"axis([-1 1 -1 1]*1.2); grid on; axis square;\n");
fprintf(fid,"xlabel('I'); ylabel('Q'); legend('first half','last half');\n");
fprintf(fid,"figure;\n");
fprintf(fid,"f=[0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid,"plot(f, psd-10*log10(k), f, 20*log10(abs(fftshift(fft(hp,nfft)))));\n");
fprintf(fid,"axis([-0.5 0.5 -50 10]); grid on;\n");
fprintf(fid,"xlabel('Normalized Frequency'); ylabel('PSD [dB]');\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
// destroy objects
gmskmod_destroy(mod);
eqlms_cccf_destroy(eq);
spgramcf_destroy(q);
return 0;
}
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