1 //
2 // modem_example.c
3 //
4 // This example demonstates the digital modulator/demodulator
5 // (modem) object. Data symbols are modulated into complex
6 // samples which are then demodulated without noise or phase
7 // offsets. The user may select the modulation scheme via
8 // the command-line interface.
9 // SEE ALSO: modem_arb_example.c
10 //
11
12 #include <stdlib.h>
13 #include <stdio.h>
14 #include <getopt.h>
15 #include "liquid.h"
16
17 #define OUTPUT_FILENAME "modem_example.m"
18
19 // print usage/help message
usage()20 void usage()
21 {
22 printf("modem_example [options]\n");
23 printf(" h : print help\n");
24 printf(" v/q : verbose/quiet\n");
25 printf(" m : modulation scheme (qam16 default)\n");
26 liquid_print_modulation_schemes();
27 }
28
29
main(int argc,char * argv[])30 int main(int argc, char*argv[])
31 {
32 // create mod/demod objects
33 modulation_scheme ms = LIQUID_MODEM_QAM16;
34 int verbose = 1;
35
36 int dopt;
37 while ((dopt = getopt(argc,argv,"hvqm:")) != EOF) {
38 switch (dopt) {
39 case 'h': usage(); return 0;
40 case 'v': verbose = 1; break;
41 case 'q': verbose = 0; break;
42 case 'm':
43 ms = liquid_getopt_str2mod(optarg);
44 if (ms == LIQUID_MODEM_UNKNOWN) {
45 fprintf(stderr,"error: %s, unknown/unsupported modulation scheme '%s'\n", argv[0], optarg);
46 return 1;
47 }
48 break;
49 default:
50 exit(1);
51 }
52 }
53
54 // create the modem objects
55 modem mod = modem_create(ms);
56 modem demod = modem_create(ms);
57
58 // ensure bits/symbol matches modem description (only
59 // applicable to certain specific modems)
60 unsigned int bps = modem_get_bps(mod);
61
62 modem_print(mod);
63
64 // open output file
65 FILE*fid = fopen(OUTPUT_FILENAME,"w");
66 fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
67 fprintf(fid,"clear all;\n");
68 fprintf(fid,"close all;\n\n");
69 fprintf(fid,"m = %u;\n", bps);
70 fprintf(fid,"M = %u;\n", 1<<bps);
71 fprintf(fid,"c = zeros(1,M);\n");
72 fprintf(fid,"i_str = cell(1,M);\n");
73
74 unsigned int i; // modulated symbol
75 unsigned int s; // demodulated symbol
76 unsigned int num_symbols = 1<<bps;
77 float complex x;
78 unsigned int num_sym_errors = 0;
79 unsigned int num_bit_errors = 0;
80
81 for (i=0; i<num_symbols; i++) {
82 modem_modulate(mod, i, &x);
83 modem_demodulate(demod, x, &s);
84
85 if (verbose)
86 printf("%4u : %12.8f + j*%12.8f\n", i, crealf(x), cimagf(x));
87
88 num_sym_errors += i == s ? 0 : 1;
89 num_bit_errors += count_bit_errors(i,s);
90
91 // write symbol to output file
92 fprintf(fid,"c(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(x), cimagf(x));
93 fprintf(fid,"i_str{%3u} = [num2str(%3u)];\n", i+1, i);
94 }
95 printf("num sym errors: %4u / %4u\n", num_sym_errors, num_symbols);
96 printf("num bit errors: %4u / %4u\n", num_bit_errors, num_symbols*bps);
97
98 // plot results
99 fprintf(fid,"\n\n");
100 fprintf(fid,"figure;\n");
101 fprintf(fid,"plot(c,'o','MarkerSize',2);\n");
102 fprintf(fid,"hold on;\n");
103 fprintf(fid,"text(real(c)+0.02, imag(c)+0.02, i_str);\n");
104 fprintf(fid,"hold off;\n");
105 fprintf(fid,"axis([-1 1 -1 1]*1.6);\n");
106 fprintf(fid,"axis square;\n");
107 fprintf(fid,"grid on;\n");
108 fprintf(fid,"xlabel('in phase');\n");
109 fprintf(fid,"ylabel('quadrature phase');\n");
110
111 fclose(fid);
112 printf("results written to %s.\n", OUTPUT_FILENAME);
113
114 modem_destroy(mod);
115 modem_destroy(demod);
116 return 0;
117 }
118