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//
// symtrack_cccf_example.c
//
// This example demonstrates how to recover data symbols using the symtrack
// object. A stream of modulated and interpolated symbols are generated using
// the symstream object. The resulting samples are passed through a channel
// to add various impairments. The symtrack object recovers timing, carrier,
// and other information imparted by the channel and returns data symbols
// ready for demodulation.
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <getopt.h>
#include <time.h>
#include <assert.h>
#include "liquid.h"
#define OUTPUT_FILENAME "symtrack_cccf_example.m"
// print usage/help message
void usage()
{
printf("symtrack_cccf_example [options]\n");
printf(" h : print this help file\n");
printf(" k : filter samples/symbol, default: 2\n");
printf(" m : filter delay (symbols), default: 3\n");
printf(" b : filter excess bandwidth, default: 0.5\n");
printf(" s : signal-to-noise ratio, default: 30 dB\n");
printf(" w : timing pll bandwidth, default: 0.02\n");
printf(" n : number of symbols, default: 4000\n");
}
int main(int argc, char*argv[])
{
// options
int ftype = LIQUID_FIRFILT_ARKAISER;
int ms = LIQUID_MODEM_QAM16;
unsigned int k = 2; // samples per symbol
unsigned int m = 7; // filter delay (symbols)
float beta = 0.20f; // filter excess bandwidth factor
unsigned int num_symbols = 4000; // number of data symbols
unsigned int hc_len = 4; // channel filter length
float noise_floor = -60.0f; // noise floor [dB]
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
float bandwidth = 0.10f; // loop filter bandwidth
float dphi = 0.02f; // carrier frequency offset [radians/sample]
float phi = 2.1f; // carrier phase offset [radians]
unsigned int nfft = 2400; // spectral periodogram FFT size
unsigned int num_samples = 200000; // number of samples
int dopt;
while ((dopt = getopt(argc,argv,"hk:m:b:s:w:n:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 's': SNRdB = atof(optarg); break;
case 'w': bandwidth = atof(optarg); break;
case 'n': num_symbols = atoi(optarg); break;
default:
exit(1);
}
}
// validate input
if (k < 2) {
fprintf(stderr,"error: k (samples/symbol) must be greater than 1\n");
exit(1);
} else if (m < 1) {
fprintf(stderr,"error: m (filter delay) must be greater than 0\n");
exit(1);
} else if (beta <= 0.0f || beta > 1.0f) {
fprintf(stderr,"error: beta (excess bandwidth factor) must be in (0,1]\n");
exit(1);
} else if (bandwidth <= 0.0f) {
fprintf(stderr,"error: timing PLL bandwidth must be greater than 0\n");
exit(1);
} else if (num_symbols == 0) {
fprintf(stderr,"error: number of symbols must be greater than 0\n");
exit(1);
}
unsigned int i;
// buffers
unsigned int buf_len = 800; // buffer size
float complex x [buf_len]; // original signal
float complex y [buf_len]; // channel output
float complex syms[buf_len]; // recovered symbols
// window for saving last few symbols
windowcf sym_buf = windowcf_create(buf_len);
// create stream generator
symstreamcf gen = symstreamcf_create_linear(ftype,k,m,beta,ms);
// create channel emulator and add impairments
channel_cccf channel = channel_cccf_create();
channel_cccf_add_awgn (channel, noise_floor, SNRdB);
channel_cccf_add_carrier_offset(channel, dphi, phi);
channel_cccf_add_multipath (channel, NULL, hc_len);
// create symbol tracking synchronizer
symtrack_cccf symtrack = symtrack_cccf_create(ftype,k,m,beta,ms);
symtrack_cccf_set_bandwidth(symtrack,bandwidth);
//symtrack_cccf_set_eq_off(symtrack); // disable equalization
symtrack_cccf_print(symtrack);
// create spectral periodogram for estimating spectrum
spgramcf periodogram = spgramcf_create_default(nfft);
unsigned int total_samples = 0;
unsigned int total_symbols = 0;
while (total_samples < num_samples)
{
// write samples to buffer
symstreamcf_write_samples(gen, x, buf_len);
// apply channel
channel_cccf_execute_block(channel, x, buf_len, y);
// push resulting sample through periodogram
spgramcf_write(periodogram, y, buf_len);
// run resulting stream through synchronizer
unsigned int num_symbols_sync;
symtrack_cccf_execute_block(symtrack, y, buf_len, syms, &num_symbols_sync);
total_symbols += num_symbols_sync;
// write resulting symbols to window buffer for plotting
windowcf_write(sym_buf, syms, num_symbols_sync);
// accumulated samples
total_samples += buf_len;
}
printf("total samples: %u\n", total_samples);
printf("total symbols: %u\n", total_symbols);
// write accumulated power spectral density estimate
float psd[nfft];
spgramcf_get_psd(periodogram, psd);
//
// export output file
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s, auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
// read buffer and write last symbols to file
float complex * rc;
windowcf_read(sym_buf, &rc);
fprintf(fid,"syms = zeros(1,%u);\n", buf_len);
for (i=0; i<buf_len; i++)
fprintf(fid,"syms(%3u) = %12.8f + j*%12.8f;\n", i+1, crealf(rc[i]), cimagf(rc[i]));
// power spectral density estimate
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"f=[0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"psd = zeros(1,nfft);\n");
for (i=0; i<nfft; i++)
fprintf(fid,"psd(%3u) = %12.8f;\n", i+1, psd[i]);
fprintf(fid,"figure('Color','white','position',[500 500 1400 400]);\n");
fprintf(fid,"subplot(1,3,1);\n");
fprintf(fid,"plot(real(syms),imag(syms),'x','MarkerSize',4);\n");
fprintf(fid," axis square;\n");
fprintf(fid," grid on;\n");
fprintf(fid," axis([-1 1 -1 1]*1.6);\n");
fprintf(fid," xlabel('In-phase');\n");
fprintf(fid," ylabel('Quadrature');\n");
fprintf(fid," title('Last %u symbols');\n", buf_len);
fprintf(fid,"subplot(1,3,2:3);\n");
fprintf(fid," plot(f, psd, 'LineWidth',1.5,'Color',[0 0.5 0.2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," pmin = 10*floor(0.1*min(psd - 5));\n");
fprintf(fid," pmax = 10*ceil (0.1*max(psd + 5));\n");
fprintf(fid," axis([-0.5 0.5 pmin pmax]);\n");
fprintf(fid," xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid," ylabel('Power Spectral Density [dB]');\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
// destroy objects
symstreamcf_destroy (gen);
spgramcf_destroy (periodogram);
channel_cccf_destroy (channel);
symtrack_cccf_destroy(symtrack);
windowcf_destroy (sym_buf);
// clean it up
printf("done.\n");
return 0;
}
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