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
|
/*
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 <errno.h>
#include <math.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.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;
}
|
