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//
// qpacketmodem_example.c
//
// This example demonstrates the basic packet modem encoder/decoder
// operation. A packet of data is encoded and modulated into symbols,
// channel noise is added, and the resulting packet is demodulated
// and decoded.
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <getopt.h>
#include <assert.h>
#include "liquid.h"
void usage()
{
printf("ofdmflexframesync_example [options]\n");
printf(" h : print usage\n");
printf(" n : payload length [bytes], default: 400\n");
printf(" m : modulation scheme (qpsk default)\n");
liquid_print_modulation_schemes();
printf(" v : data integrity check: crc32 default\n");
liquid_print_crc_schemes();
printf(" c : coding scheme (inner): g2412 default\n");
printf(" k : coding scheme (outer): none default\n");
liquid_print_fec_schemes();
printf(" s : signal-to-noise ratio [dB], default: 6\n");
}
int main(int argc, char *argv[])
{
//srand( time(NULL) );
// options
modulation_scheme ms = LIQUID_MODEM_QPSK; // mod. scheme
crc_scheme check = LIQUID_CRC_32; // data validity check
fec_scheme fec0 = LIQUID_FEC_GOLAY2412; // fec (inner)
fec_scheme fec1 = LIQUID_FEC_NONE; // fec (outer)
unsigned int payload_len = 400; // payload length
float SNRdB = 6.0f; // SNR [dB]
const char filename[] = "qpacketmodem_example.m"; // output filename
// get options
int dopt;
while((dopt = getopt(argc,argv,"hn:m:v:c:k:s:")) != EOF){
switch (dopt) {
case 'h': usage(); return 0;
case 'n': payload_len = atol(optarg); break;
case 'm': ms = liquid_getopt_str2mod(optarg); break;
case 'v': check = liquid_getopt_str2crc(optarg); break;
case 'c': fec0 = liquid_getopt_str2fec(optarg); break;
case 'k': fec1 = liquid_getopt_str2fec(optarg); break;
case 's': SNRdB = atof(optarg); break;
default:
exit(-1);
}
}
unsigned int i;
// derived values
float nstd = powf(10.0f, -SNRdB/20.0f);
// create and configure packet encoder/decoder object
qpacketmodem q = qpacketmodem_create();
qpacketmodem_configure(q, payload_len, check, fec0, fec1, ms);
qpacketmodem_print(q);
// initialize payload
unsigned char payload_tx[payload_len];
unsigned char payload_rx[payload_len];
// initialize payload
for (i=0; i<payload_len; i++) {
payload_tx[i] = rand() & 0xff;
payload_rx[i] = 0x00;
}
// get frame length
unsigned int frame_len = qpacketmodem_get_frame_len(q);
// allocate memory for frame samples
float complex frame_tx[frame_len];
float complex frame_rx[frame_len];
// encode frame
qpacketmodem_encode(q, payload_tx, frame_tx);
// add noise
for (i=0; i<frame_len; i++)
frame_rx[i] = frame_tx[i] + nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// decode frame
int crc_pass = qpacketmodem_decode(q, frame_rx, payload_rx);
// count errors
unsigned int num_bit_errors = count_bit_errors_array(payload_tx, payload_rx, payload_len);
// print results
printf("payload pass ? %s, errors: %u / %u\n",
crc_pass ? "pass" : "FAIL",
num_bit_errors,
8*payload_len);
// destroy allocated objects
qpacketmodem_destroy(q);
// write symbols to output file for plotting
FILE * fid = fopen(filename,"w");
if (!fid) {
fprintf(stderr,"error: could not open '%s' for writing\n", filename);
return -1;
}
fprintf(fid,"%% %s : auto-generated file\n", filename);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"frame_len = %u;\n", frame_len);
fprintf(fid,"y = zeros(1,frame_len);\n");
for (i=0; i<frame_len; i++)
fprintf(fid,"y(%6u) = %12.4e + 1i*%12.4e;\n", i+1, crealf(frame_rx[i]), cimagf(frame_rx[i]));
fprintf(fid,"figure('Color','white');\n");
fprintf(fid,"plot(real(y),imag(y),'x','MarkerSize',3);\n");
fprintf(fid,"axis([-1 1 -1 1]*1.5);\n");
fprintf(fid,"axis square;\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"xlabel('real');\n");
fprintf(fid,"ylabel('imag');\n");
fclose(fid);
printf("results written to '%s'\n", filename);
printf("done.\n");
return 0;
}
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