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
82
83
84
85
86
87
88
89
90
91
92
|
// Example demonstrating the GMSK flexible frame synchronizer.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include "liquid.h"
#define OUTPUT_FILENAME "gmskframesync_example.m"
// callback function
int callback(unsigned char * _header,
int _header_valid,
unsigned char * _payload,
unsigned int _payload_len,
int _payload_valid,
framesyncstats_s _stats,
void * _userdata)
{
printf("***** gmskframesync callback invoked *****\n");
return 0;
}
int main(int argc, char*argv[])
{
unsigned int k = 2; // samples/symbol
unsigned int m = 3; // filter delay (symbols)
float BT = 0.5f; // filter bandwidth-time product
unsigned int payload_len = 40; // length of payload (bytes)
crc_scheme check = LIQUID_CRC_32;
fec_scheme fec0 = LIQUID_FEC_HAMMING128;
fec_scheme fec1 = LIQUID_FEC_NONE;
unsigned int i;
// allocate memory for payload and initialize
unsigned char header[8] = {0,1,2,3,4,5,6,7};
unsigned char payload[payload_len];
memset(payload, 0x00, payload_len);
// create frame generator and assemble
gmskframegen fg = gmskframegen_create_set(k, m, BT);
gmskframegen_assemble(fg, header, payload, payload_len, check, fec0, fec1);
// create frame synchronizer
gmskframesync fs = gmskframesync_create_set(k, m, BT, callback, NULL);
// allocate buffer for storing entire frame
unsigned int num_samples = gmskframegen_getframelen(fg) + 800;
float complex buf[num_samples];
memset(buf, 0x00, num_samples*sizeof(float complex));
// generate frame in one shot with sample offset
gmskframegen_write(fg, buf+250, num_samples-250);
// add channel gain and noise
for (i=0; i<num_samples; i++)
buf[i] = 0.3*buf[i] + 0.01f*(randnf() + randnf()*_Complex_I)*M_SQRT1_2;
// push samples through synchronizer
gmskframesync_execute(fs, buf, num_samples);
gmskframesync_print(fs);
// destroy objects
gmskframegen_destroy(fg);
gmskframesync_destroy(fs);
// export output
FILE * fid = fopen(OUTPUT_FILENAME,"w");
if (fid == NULL) {
fprintf(stderr,"error: %s, could not open '%s' for writing\n", argv[0], OUTPUT_FILENAME);
exit(1);
}
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"\n");
fprintf(fid,"clear all\n");
fprintf(fid,"close all\n");
fprintf(fid,"\n");
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"y = zeros(1,num_samples);\n");
fprintf(fid,"\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"y(%6u) = %12.4e + j*%12.4e;\n", i+1, crealf(buf[i]), cimagf(buf[i]));
fprintf(fid,"\n");
fprintf(fid,"t = 0:(num_samples-1);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(t, real(y), t,imag(y));\n");
fprintf(fid,"xlabel('time');\n");
fprintf(fid,"ylabel('received signal');\n");
fprintf(fid,"legend('real','imag',0);\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
|
