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/*
FILE...: ldpc_enc.c
AUTHOR.: Don Reid
CREATED: Aug 2018
Add noise to LDPC soft decision samples for testing. Simulates use
of LDPC code with PSK modem.
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include <errno.h>
int main(int argc, char *argv[]) {
FILE *fin, *fout;
float datain, dataout;
if (argc < 3) {
fprintf(stderr, "\n");
fprintf(stderr, "usage: %s InputFile OutputFile NodB\n", argv[0]);
fprintf(stderr, "\n");
exit(1);
}
if (strcmp(argv[1], "-") == 0) fin = stdin;
else if ( (fin = fopen(argv[1],"rb")) == NULL ) {
fprintf(stderr, "Error opening input bit file: %s: %s.\n",
argv[1], strerror(errno));
exit(1);
}
if (strcmp(argv[2], "-") == 0) fout = stdout;
else if ( (fout = fopen(argv[2],"wb")) == NULL ) {
fprintf(stderr, "Error opening output bit file: %s: %s.\n",
argv[2], strerror(errno));
exit(1);
}
double NodB = atof(argv[3]);
double No = pow(10.0, NodB/10.0);
double sum_xx = 0; double sum_x = 0.0; long n = 0;
fprintf(stderr, "Uncoded PSK Eb/No simulation:\n");
fprintf(stderr, "No = % 4.2f dB (%4.2f linear)\n", NodB, No);
fprintf(stderr, "Eb = % 4.2f dB (%4.2f linear)\n", 0.0, 1.0);
fprintf(stderr, "Eb/No = %4.2f dB (%4.2f linear)\n", -NodB, pow(10,-NodB/10.0));
while (fread(&datain, sizeof(float), 1, fin) == 1) {
// Gaussian from uniform:
double x = (double)rand() / RAND_MAX;
double y = (double)rand() / RAND_MAX;
double z = sqrt(-2 * log(x)) * cos(2 * M_PI * y);
double noise = sqrt(No/2) * z;
dataout = datain + noise;
fwrite(&dataout, sizeof(float), 1, fout);
// keep running stats to calculate actual noise variance (power)
sum_xx += noise*noise;
sum_x += noise;
n++;
}
fclose(fin);
fclose(fout);
double noise_var = (n * sum_xx - sum_x * sum_x) / (n * (n - 1));
fprintf(stderr, "measured double sided (real) noise power: %f\n", noise_var);
return 0;
}
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