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//
// fskmodem_waterfall_example.c
//
// This example demonstrates the M-ary frequency-shift keying
// (MFSK) modem in liquid by showing the resulting spectral
// waterfall.
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <math.h>
#include "liquid.h"
// print usage/help message
void usage()
{
printf("fskmodem_waterfall_example -- frequency-shift keying waterfall example\n");
printf("options:\n");
printf(" -h : print help\n");
printf(" -m <bps> : bits/symbol, default: 2\n");
printf(" -b <bw> : signal bandwidth default: 0.2\n");
printf(" -n <num> : number of data symbols, default: 80\n");
printf(" -s <snr> : SNR [dB], default: 40\n");
}
int main(int argc, char*argv[])
{
// options
unsigned int m = 2; // number of bits/symbol
unsigned int num_symbols = 400; // number of data symbols
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
float bandwidth = 0.10; // frequency spacing
int dopt;
while ((dopt = getopt(argc,argv,"hm:b:n:s:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'm': m = atoi(optarg); break;
case 'b': bandwidth = atof(optarg); break;
case 'n': num_symbols = atoi(optarg); break;
case 's': SNRdB = atof(optarg); break;
default:
exit(1);
}
}
unsigned int i;
unsigned int j;
// derived values
unsigned int M = 1 << m; // constellation size
unsigned int k = 500 * M; // samples per symbol (highly over-sampled)
float nstd = powf(10.0f, -SNRdB/20.0f); // noise std. dev.
// validate input
if (k < M) {
fprintf(stderr,"errors: %s, samples/symbol must be at least modulation size (M=%u)\n", __FILE__,M);
exit(1);
} else if (k > 2048) {
fprintf(stderr,"errors: %s, samples/symbol exceeds maximum (2048)\n", __FILE__);
exit(1);
} else if (M > 1024) {
fprintf(stderr,"errors: %s, modulation size (M=%u) exceeds maximum (1024)\n", __FILE__, M);
exit(1);
} else if (bandwidth <= 0.0f || bandwidth >= 0.5f) {
fprintf(stderr,"errors: %s, bandwidth must be in (0,0.5)\n", __FILE__);
exit(1);
}
// create spectral waterfall object
unsigned int nfft = 1 << liquid_nextpow2(k);
int wtype = LIQUID_WINDOW_HAMMING;
unsigned int wlen = nfft/2;
unsigned int delay = nfft/2;
unsigned int time = 512;
spwaterfallcf periodogram = spwaterfallcf_create(nfft,wtype,wlen,delay,time);
spwaterfallcf_print(periodogram);
// create modulator/demodulator pair
fskmod mod = fskmod_create(m,k,bandwidth);
float complex buf_tx[k]; // transmit buffer
float complex buf_rx[k]; // transmit buffer
// modulate, demodulate, count errors
for (i=0; i<num_symbols; i++) {
// generate random symbol
unsigned int sym_in = rand() % M;
// modulate
fskmod_modulate(mod, sym_in, buf_tx);
// add noise
for (j=0; j<k; j++)
buf_rx[j] = buf_tx[j] + nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// estimate power spectral density
spwaterfallcf_write(periodogram, buf_rx, k);
}
// export output files
spwaterfallcf_export(periodogram,"fskmodem_waterfall_example");
// destroy objects
spwaterfallcf_print(periodogram);
fskmod_destroy(mod);
return 0;
}
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