1 //
2 // modem_soft_example.c
3 //
4 // This example demonstates soft demodulation of linear
5 // modulation schemes.
6 //
7
8 #include <stdlib.h>
9 #include <stdio.h>
10 #include <getopt.h>
11 #include "liquid.h"
12
13 #define OUTPUT_FILENAME "modem_soft_example.m"
14
15 // print usage/help message
usage()16 void usage()
17 {
18 printf("modem_soft_example [options]\n");
19 printf(" h : print help\n");
20 printf(" m : modulation scheme (qpsk default)\n");
21 liquid_print_modulation_schemes();
22 }
23
24 // print a string of bits to the standard output
25 // _x : input symbol
26 // _bps : bits/symbol
27 // _n : number of characters to print (zero-padding)
print_bitstring(unsigned int _x,unsigned int _bps,unsigned int _n)28 void print_bitstring(unsigned int _x,
29 unsigned int _bps,
30 unsigned int _n)
31 {
32 unsigned int i;
33 for (i=0; i<_bps; i++)
34 printf("%1u", (_x >> (_bps-i-1)) & 1);
35 for (i=_bps; i<_n; i++)
36 printf(" ");
37 }
38
39
main(int argc,char * argv[])40 int main(int argc, char*argv[])
41 {
42 // create mod/demod objects
43 modulation_scheme ms = LIQUID_MODEM_QPSK;
44
45 int dopt;
46 while ((dopt = getopt(argc,argv,"uhm:")) != EOF) {
47 switch (dopt) {
48 case 'h':
49 usage();
50 return 0;
51 case 'm':
52 ms = liquid_getopt_str2mod(optarg);
53 if (ms == LIQUID_MODEM_UNKNOWN) {
54 fprintf(stderr,"error: %s, unknown/unsupported modulation scheme '%s'\n", argv[0], optarg);
55 return 1;
56 }
57 break;
58 default:
59 exit(1);
60 }
61 }
62
63 // create the modem objects
64 modem mod = modem_create(ms);
65 modem demod = modem_create(ms);
66
67 // ensure bits/symbol matches modem description (only
68 // applicable to certain specific modems)
69 unsigned int bps = modem_get_bps(mod);
70
71 modem_print(mod);
72
73 unsigned int i; // modulated symbol
74 unsigned int s_hard; // demodulated symbol (hard)
75 unsigned char soft_bits[bps];
76 unsigned int s_soft; // demodulated symbol (soft, compacted)
77 unsigned int num_symbols = 1<<bps;
78 float complex x;
79 unsigned int num_sym_errors = 0;
80 unsigned int num_bit_errors = 0;
81
82 printf("\n");
83 printf(" %-11s %-11s %-11s : ", "input sym.", "hard demod", "soft demod");
84 for (i=0; i<bps; i++)
85 printf(" b[%1u]", i);
86 printf("\n");
87
88 for (i=0; i<num_symbols; i++) {
89 // modulate symbol
90 modem_modulate(mod, i, &x);
91
92 // demodulate, including soft decision
93 modem_demodulate_soft(demod, x, &s_hard, soft_bits);
94
95 // re-pack soft bits to hard decision
96 liquid_pack_soft_bits(soft_bits, bps, &s_soft);
97
98 // print results
99 printf(" ");
100 print_bitstring(i, bps,12);
101 print_bitstring(s_hard,bps,12);
102 print_bitstring(s_soft,bps,12);
103 printf(" : ");
104 unsigned int j;
105 for (j=0; j<bps; j++)
106 printf("%7u", soft_bits[j]);
107 printf("\n");
108
109 num_sym_errors += i == s_soft ? 0 : 1;
110 num_bit_errors += count_bit_errors(i,s_soft);
111 }
112 printf("num sym errors: %4u / %4u\n", num_sym_errors, num_symbols);
113 printf("num bit errors: %4u / %4u\n", num_bit_errors, num_symbols*bps);
114
115 modem_destroy(mod);
116 modem_destroy(demod);
117 return 0;
118 }
119