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
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
|
// This example demonstrates the interfaces to the fskframegen and
// fskframesync objects used to completely encapsulate data for
// over-the-air transmission.
//
// SEE ALSO: flexframesync_example.c
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <getopt.h>
#include <time.h>
#include "liquid.h"
#define OUTPUT_FILENAME "fskframesync_example.m"
void usage()
{
printf("fskframesync_example [options]\n");
printf(" h : print usage\n");
printf(" d : enable debugging\n");
printf(" S : signal-to-noise ratio [dB], default: 20\n");
printf(" F : carrier frequency offset, default: 0\n");
printf(" P : carrier phase offset, default: 0\n");
printf(" T : fractional sample timing offset, default: 0.01\n");
}
// static callback function
static int callback(unsigned char * _header,
int _header_valid,
unsigned char * _payload,
unsigned int _payload_len,
int _payload_valid,
framesyncstats_s _stats,
void * _userdata);
// global arrays
unsigned char header[8];
unsigned char payload[200];
int main(int argc, char*argv[])
{
srand( time(NULL) );
// options
float SNRdB = 20.0f; // signal-to-noise ratio
float noise_floor = -20.0f; // noise floor
float dphi = 0.01f; // carrier frequency offset
float theta = 0.0f; // carrier phase offset
float dt = -0.2f; // fractional sample timing offset
crc_scheme check = LIQUID_CRC_32; // data validity check
fec_scheme fec0 = LIQUID_FEC_NONE; // fec (inner)
fec_scheme fec1 = LIQUID_FEC_NONE; // fec (outer)
unsigned int payload_len = 200; // payload length
int debug_enabled = 0;
// get options
int dopt;
while((dopt = getopt(argc,argv,"hdS:F:P:T:")) != EOF){
switch (dopt) {
case 'h': usage(); return 0;
case 'd': debug_enabled = 1; break;
case 'S': SNRdB = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 'P': theta = atof(optarg); break;
case 'T': dt = atof(optarg); break;
default:
exit(-1);
}
}
printf("channel offsets: dt=%.3f, dphi=%.3f, theta=%.3f\n", dt, dphi, theta);
// derived values
float nstd = powf(10.0f, noise_floor/20.0f); // noise std. dev.
float gamma = powf(10.0f, (SNRdB+noise_floor)/20.0f); // channel gain
// create frame generator
fskframegen fg = fskframegen_create();
fskframegen_print(fg);
// create frame synchronizer using default properties
fskframesync fs = fskframesync_create(callback,NULL);
fskframesync_print(fs);
if (debug_enabled)
fskframesync_debug_enable(fs);
// data payload
unsigned int i;
// initialize header and payload data
for (i=0; i<8; i++)
header[i] = i;
for (i=0; i<200; i++)
payload[i] = rand() & 0xff;
// allocate memory for the frame samples
unsigned int buf_len = 64;
float complex buf_tx[buf_len]; // receive buffer
float complex buf_rx[buf_len]; // transmit buffer
// assemble the frame
fskframegen_assemble(fg, header, payload, payload_len, check, fec0, fec1);
// spectral periodogram
unsigned int nfft = 4200;
spgramcf periodogram = spgramcf_create_default(nfft);
// write frame in blocks
int frame_complete = 0;
while (!frame_complete)
{
frame_complete = fskframegen_write_samples(fg, buf_tx, buf_len);
// add noise, channel gain
for (i=0; i<buf_len; i++)
buf_rx[i] = buf_tx[i]*gamma + nstd*(randnf() + randnf()*_Complex_I)*M_SQRT1_2;
// synchronize/receive the frame
fskframesync_execute_block(fs, buf_rx, buf_len);
// estimate power spectral density
spgramcf_write(periodogram, buf_rx, buf_len);
}
// compute power spectral density of received signal
float psd[nfft];
spgramcf_get_psd(periodogram, psd);
// clean up allocated objects
spgramcf_destroy(periodogram);
fskframegen_destroy(fg);
fskframesync_destroy(fs);
//
// export results
//
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,"nfft = %u;\n", nfft);
// save power spectral density
fprintf(fid,"psd = zeros(1,nfft);\n");
for (i=0; i<nfft; i++)
fprintf(fid,"psd(%4u) = %12.8f;\n", i+1, psd[i]);
// plot PSD
fprintf(fid,"figure('Color','white');\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"plot(f,psd,'LineWidth',1.5,'Color',[0.5 0 0]);\n");
fprintf(fid,"axis([-0.5 0.5 -30 30]);\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
// static callback function
static int callback(unsigned char * _header,
int _header_valid,
unsigned char * _payload,
unsigned int _payload_len,
int _payload_valid,
framesyncstats_s _stats,
void * _userdata)
{
printf("*** callback invoked ***\n");
printf(" error vector mag. : %12.8f dB\n", _stats.evm);
printf(" rssi : %12.8f dB\n", _stats.rssi);
printf(" carrier offset : %12.8f\n", _stats.cfo);
printf(" mod. scheme : %s\n", modulation_types[_stats.mod_scheme].fullname);
printf(" mod. depth : %u\n", _stats.mod_bps);
printf(" payload CRC : %s\n", crc_scheme_str[_stats.check][1]);
printf(" payload fec (inner) : %s\n", fec_scheme_str[_stats.fec0][1]);
printf(" payload fec (outer) : %s\n", fec_scheme_str[_stats.fec1][1]);
printf(" header crc : %s\n", _header_valid ? "pass" : "FAIL");
printf(" header data : %.2x %.2x %.2x %.2x %.2x %.2x %.2x %.2x\n",
_header[0], _header[1], _header[2], _header[3],
_header[4], _header[5], _header[6], _header[7]);
printf(" num header errors : %u / %u\n",
count_bit_errors_array(_header, header, 8),
8*8);
printf(" payload crc : %s\n", _payload_valid ? "pass" : "FAIL");
printf(" num payload errors : %u / %u\n",
count_bit_errors_array(_payload, payload, 64),
64*8);
return 0;
}
|
