1 //
2 // firinterp_firdecim_crcf_example.c
3 //
4 // This example demonstrates interpolation and decimation of a QPSK
5 // signal with a square-root Nyquist filter.
6 // Data symbols are generated and then interpolated according to a
7 // finite impulse response square-root Nyquist filter. The resulting
8 // sequence is then decimated with the same filter, matched to the
9 // interpolator.
10 //
11 // SEE ALSO: firinterp_crcf_example.c
12 //
13
14 #include <stdio.h>
15 #include <stdlib.h>
16 #include <math.h>
17 #include <getopt.h>
18
19 #include "liquid.h"
20
21 #define OUTPUT_FILENAME "firinterp_firdecim_crcf_example.m"
22
23 // print usage/help message
usage()24 void usage()
25 {
26 printf("firinterp_firdecim_crcf_example:\n");
27 printf(" -h : print usage/help\n");
28 printf(" -k <s/sym> : samples/symbol (interp factor), k > 1, default: 2\n");
29 printf(" -m <delay> : filter delay (symbols), m > 0, default: 2\n");
30 printf(" -b <bw> : excess bandwidth factor, 0 < beta < 1, default: 0.5\n");
31 printf(" -n <num> : number of data symbols, default: 8\n");
32 }
33
34
main(int argc,char * argv[])35 int main(int argc, char*argv[]) {
36 // options
37 unsigned int k = 2; // samples/symbol
38 unsigned int m = 3; // filter delay
39 float dt = 0.5f; // filter fractional symbol delay
40 float beta = 0.5f; // filter excess bandwidth
41 unsigned int num_syms = 8; // number of data symbols
42
43 int dopt;
44 while ((dopt = getopt(argc,argv,"hk:m:b:n:")) != EOF) {
45 switch (dopt) {
46 case 'h': usage(); return 0;
47 case 'k': k = atoi(optarg); break;
48 case 'm': m = atoi(optarg); break;
49 case 'b': beta = atof(optarg); break;
50 case 'n': num_syms = atoi(optarg); break;
51 default:
52 usage();
53 return 1;
54 }
55 }
56
57 // validate options
58 if (k < 2) {
59 fprintf(stderr,"error: %s, interp factor must be greater than 1\n", argv[0]);
60 return 1;
61 } else if (m < 1) {
62 fprintf(stderr,"error: %s, filter delay must be greater than 0\n", argv[0]);
63 return 1;
64 } else if (beta <= 0.0 || beta > 1.0f) {
65 fprintf(stderr,"error: %s, beta (excess bandwidth factor) must be in (0,1]\n", argv[0]);
66 return 1;
67 } else if (num_syms < 1) {
68 fprintf(stderr,"error: %s, must have at least one data symbol\n", argv[0]);
69 return 1;
70 }
71
72 // derived values
73 unsigned int h_len = 2*k*m + 1; // prototype filter length
74 unsigned int num_syms_total = num_syms + 2*m; // number of total symbols (w/ delay)
75 unsigned int num_samples = k*num_syms_total; // number of samples
76
77 // design filter and create interpolator and decimator objects
78 float h[h_len]; // transmit filter
79 float g[h_len]; // receive filter (reverse of h)
80 liquid_firdes_rrcos(k,m,beta,dt,h);
81 unsigned int i;
82 for (i=0; i<h_len; i++)
83 g[i] = h[h_len-i-1];
84 firinterp_crcf interp = firinterp_crcf_create(k,h,h_len);
85 firdecim_crcf decim = firdecim_crcf_create(k,g,h_len);
86 firdecim_crcf_set_scale(decim, 1.0f/(float)k);
87
88 // allocate memory for buffers
89 float complex x[num_syms_total]; // input symbols
90 float complex y[num_samples]; // interpolated sequence
91 float complex z[num_syms_total]; // decimated (received) symbols
92
93 // generate input symbols, padded with zeros at the end
94 for (i=0; i<num_syms_total; i++) {
95 float complex s = (rand() % 2 ? 1.0f : -1.0f) +
96 (rand() % 2 ? 1.0f : -1.0f) * _Complex_I;
97 x[i] = i < num_syms ? s : 0;
98 }
99
100 // run interpolator
101 for (i=0; i<num_syms_total; i++)
102 firinterp_crcf_execute(interp, x[i], &y[k*i]);
103
104 // run decimator
105 for (i=0; i<num_syms_total; i++)
106 firdecim_crcf_execute(decim, &y[k*i], &z[i]);
107
108 // destroy objects
109 firinterp_crcf_destroy(interp);
110 firdecim_crcf_destroy(decim);
111
112 // print results to screen
113 printf("filter impulse response :\n");
114 for (i=0; i<h_len; i++)
115 printf(" [%4u] : %8.4f\n", i, h[i]);
116
117 printf("input symbols\n");
118 for (i=0; i<num_syms_total; i++) {
119 printf(" [%4u] : %8.4f + j*%8.4f", i, crealf(x[i]), cimagf(x[i]));
120
121 // highlight actual data symbols
122 if (i < num_syms) printf(" *\n");
123 else printf("\n");
124 }
125
126 printf("interpolator output samples:\n");
127 for (i=0; i<num_samples; i++) {
128 printf(" [%4u] : %8.4f + j*%8.4f", i, crealf(y[i]), cimagf(y[i]));
129
130 if ( (i >= k*m) && ((i%k)==0)) printf(" **\n");
131 else printf("\n");
132 }
133
134 printf("output symbols:\n");
135 for (i=0; i<num_syms_total; i++) {
136 printf(" [%4u] : %8.4f + j*%8.4f", i, crealf(z[i]), cimagf(z[i]));
137
138 // highlight symbols (compensate for filter delay)
139 if ( i < 2*m ) printf("\n");
140 else printf(" *\n");
141 }
142
143 //
144 // export results to file
145 //
146 FILE * fid = fopen(OUTPUT_FILENAME,"w");
147 fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
148 fprintf(fid,"clear all;\n");
149 fprintf(fid,"close all;\n");
150 fprintf(fid,"k = %u;\n", k);
151 fprintf(fid,"m = %u;\n", m);
152 fprintf(fid,"dt = %8.6f;\n", dt);
153 fprintf(fid,"h_len=%u;\n",h_len);
154 fprintf(fid,"num_syms_total = %u;\n", num_syms_total);
155 fprintf(fid,"num_samples = k*num_syms_total;\n");
156 fprintf(fid,"h = zeros(1,h_len);\n");
157 fprintf(fid,"x = zeros(1,num_syms_total);\n");
158 fprintf(fid,"y = zeros(1,num_samples);\n");
159
160 for (i=0; i<h_len; i++)
161 fprintf(fid,"h(%4u) = %12.4e;\n", i+1, h[i]);
162
163 for (i=0; i<num_syms_total; i++)
164 fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
165
166 for (i=0; i<num_samples; i++)
167 fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
168
169 for (i=0; i<num_syms_total; i++)
170 fprintf(fid,"z(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(z[i]), cimagf(z[i]));
171
172 fprintf(fid,"\n\n");
173 fprintf(fid,"tx = [0:(num_syms_total-1)];\n");
174 fprintf(fid,"ty = [0:(num_samples-1)]/k - m + dt/k;\n");
175 fprintf(fid,"tz = [0:(num_syms_total-1)] - 2*m;\n");
176 fprintf(fid,"figure;\n");
177 fprintf(fid,"subplot(2,1,1);\n");
178 fprintf(fid," plot(tx,real(x),'s',ty,real(y),'-',tz,real(z),'x');\n");
179 fprintf(fid," xlabel('time');\n");
180 fprintf(fid," ylabel('real');\n");
181 fprintf(fid," grid on;\n");
182 fprintf(fid," legend('symbols in','interp','symbols out',0);\n");
183 fprintf(fid,"subplot(2,1,2);\n");
184 fprintf(fid," plot(tx,imag(x),'s',ty,imag(y),'-',tz,imag(z),'x');\n");
185 fprintf(fid," xlabel('time');\n");
186 fprintf(fid," ylabel('imag');\n");
187 fprintf(fid," grid on;\n");
188
189 fclose(fid);
190 printf("results written to %s.\n",OUTPUT_FILENAME);
191
192 printf("done.\n");
193 return 0;
194 }
195