size_t demodulator_recv(demodulator *d, const sample_t *samples, size_t sample_len,
float complex *symbols) {
if (!d) {
return 0;
}
if (sample_len % d->opt.samples_per_symbol != 0) {
printf("must receive multiple of samples_per_symbol samples");
return 0;
}
float complex post_mixer[d->opt.samples_per_symbol];
size_t written = 0;
for (size_t i = 0; i < sample_len; i += d->opt.samples_per_symbol) {
for (size_t j = 0; j < d->opt.samples_per_symbol; j++) {
nco_crcf_mix_down(d->nco, samples[i + j], &post_mixer[j]);
nco_crcf_step(d->nco);
}
if (d->decim) {
firdecim_crcf_execute(d->decim, &post_mixer[0],
&symbols[(i / d->opt.samples_per_symbol)]);
symbols[(i / d->opt.samples_per_symbol)] /=
d->opt.samples_per_symbol;
} else {
symbols[i] = post_mixer[0];
}
written++;
}
return written;
}
int main(int argc, char*argv[]) {
// options
unsigned int k=2; // samples/symbol
unsigned int m=2; // filter delay
float beta = 0.5f; // filter excess bandwidth
unsigned int num_data_symbols=8; // number of data symbols
int dopt;
while ((dopt = getopt(argc,argv,"uhk:m:b:n:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'n': num_data_symbols = atoi(optarg); break;
default:
usage();
return 1;
}
}
// validate options
if (k < 2) {
fprintf(stderr,"error: %s, interp factor must be greater than 1\n", argv[0]);
return 1;
} else if (m < 1) {
fprintf(stderr,"error: %s, filter delay must be greater than 0\n", argv[0]);
return 1;
} else if (beta <= 0.0 || beta > 1.0f) {
fprintf(stderr,"error: %s, beta (excess bandwidth factor) must be in (0,1]\n", argv[0]);
return 1;
} else if (num_data_symbols < 1) {
fprintf(stderr,"error: %s, must have at least one data symbol\n", argv[0]);
return 1;
}
// derived values
unsigned int h_len = 2*k*m+1;
unsigned int num_symbols = num_data_symbols + 2*m;
unsigned int num_samples = k*num_symbols;
// design filter and create interpolator and decimator objects
float h[h_len]; // transmit filter
float g[h_len]; // receive filter (reverse of h)
liquid_firdes_rrcos(k,m,beta,0.3f,h);
unsigned int i;
for (i=0; i<h_len; i++)
g[i] = h[h_len-i-1];
firinterp_crcf interp = firinterp_crcf_create(k,h,h_len);
firdecim_crcf decim = firdecim_crcf_create(k,g,h_len);
// allocate memory for buffers
float complex x[num_symbols]; // input symbols
float complex y[num_samples]; // interpolated sequence
float complex z[num_symbols]; // decimated (received) symbols
// generate input symbols, padded with zeros at the end
for (i=0; i<num_data_symbols; i++) {
x[i] = (rand() % 2 ? 1.0f : -1.0f) +
(rand() % 2 ? 1.0f : -1.0f) * _Complex_I;
}
for ( ; i<num_symbols; i++)
x[i] = 0.0f;
// run interpolator
for (i=0; i<num_symbols; i++) {
firinterp_crcf_execute(interp, x[i], &y[k*i]);
}
// run decimator
for (i=0; i<num_symbols; i++) {
firdecim_crcf_execute(decim, &y[k*i], &z[i]);
// normalize output by samples/symbol
z[i] /= k;
}
// destroy objects
firinterp_crcf_destroy(interp);
firdecim_crcf_destroy(decim);
// print results to screen
printf("filter impulse response :\n");
for (i=0; i<h_len; i++)
printf(" [%4u] : %8.4f\n", i, h[i]);
printf("input symbols\n");
for (i=0; i<num_symbols; i++) {
printf(" [%4u] : %8.4f + j*%8.4f", i, crealf(x[i]), cimagf(x[i]));
// highlight actual data symbols
if (i < num_data_symbols) printf(" *\n");
else printf("\n");
}
printf("interpolator output samples:\n");
for (i=0; i<num_samples; i++) {
printf(" [%4u] : %8.4f + j*%8.4f", i, crealf(y[i]), cimagf(y[i]));
if ( (i >= k*m) && ((i%k)==0)) printf(" **\n");
else printf("\n");
}
printf("output symbols:\n");
for (i=0; i<num_symbols; i++) {
printf(" [%4u] : %8.4f + j*%8.4f", i, crealf(z[i]), cimagf(z[i]));
// highlight symbols (compensate for filter delay)
if ( i < 2*m ) printf("\n");
else printf(" *\n");
}
// open output file
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"k = %u;\n", k);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"h_len=%u;\n",h_len);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = k*num_symbols;\n");
fprintf(fid,"h = zeros(1,h_len);\n");
fprintf(fid,"x = zeros(1,num_symbols);\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
for (i=0; i<h_len; i++)
fprintf(fid,"h(%4u) = %12.4e;\n", i+1, h[i]);
for (i=0; i<num_symbols; i++)
fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
for (i=0; i<num_samples; i++)
fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
for (i=0; i<num_symbols; i++)
fprintf(fid,"z(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(z[i]), cimagf(z[i]));
fprintf(fid,"\n\n");
fprintf(fid,"tx = [0:(num_symbols-1)];\n");
fprintf(fid,"ty = [0:(num_samples-1)]/k - m;\n");
fprintf(fid,"tz = [0:(num_symbols-1)] - 2*m;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," plot(ty,real(y),'-',tx,real(x),'s',tz,real(z),'x');\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('real');\n");
fprintf(fid," grid on;\n");
fprintf(fid," legend('interp','data in','data out',0);\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," plot(ty,imag(y),'-',tx,imag(x),'s',tz,imag(z),'x');\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('imag');\n");
fprintf(fid," grid on;\n");
fclose(fid);
printf("results written to %s.\n",OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
