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//
// qdetector_example.c
//
// This example demonstrates the functionality of the qdetector object
// to detect an arbitrary signal in time in the presence of noise,
// carrier frequency/phase offsets, and fractional-sample timing
// offsets.
//
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <math.h>
#include <time.h>
#include "liquid.h"
#define OUTPUT_FILENAME "qdetector_cccf_example.m"
// print usage/help message
void usage()
{
printf("qdetector_cccf_example\n");
printf("options:\n");
printf(" h : print usage/help\n");
printf(" n : number of sync symbols, default: 80\n");
printf(" k : samples/symbol, default: 2\n");
printf(" m : filter delay, default: 7 sybmols\n");
printf(" b : excess bandwidth factor, default: 0.3\n");
printf(" F : carrier frequency offset, default: -0.01\n");
printf(" T : fractional sample offset, default: 0\n");
printf(" S : SNR [dB], default: 20 dB\n");
printf(" t : detection threshold, default: 0.3\n");
printf(" r : carrier offset search range,default: 0.05\n");
}
int main(int argc, char*argv[])
{
// options
unsigned int sequence_len = 80; // number of sync symbols
unsigned int k = 2; // samples/symbol
unsigned int m = 7; // filter delay [symbols]
float beta = 0.3f; // excess bandwidth factor
int ftype = LIQUID_FIRFILT_ARKAISER;
float tau = -0.3f; // fractional sample timing offset
float dphi = -0.01f; // carrier frequency offset
float phi = 0.5f; // carrier phase offset
float noise_floor = -30.0f; // noise floor [dB]
float SNRdB = 20.0f; // signal-to-noise ratio [dB]
float threshold = 0.5f; // detection threshold
float range = 0.05f; // carrier offset search range [radians/sample]
int dopt;
while ((dopt = getopt(argc,argv,"hn:k:m:b:F:T:S:t:r:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'n': sequence_len = atoi(optarg); break;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 'T': tau = atof(optarg); break;
case 'S': SNRdB = atof(optarg); break;
case 't': threshold = atof(optarg); break;
case 'r': range = atof(optarg); break;
default:
exit(1);
}
}
unsigned int i;
// validate input
if (tau < -0.5f || tau > 0.5f) {
fprintf(stderr,"error: %s, fractional sample offset must be in [-0.5,0.5]\n", argv[0]);
exit(1);
}
// derived values
float nstd = powf(10.0f, noise_floor/20.0f);
float gamma = powf(10.0f, (SNRdB + noise_floor)/20.0f);
// generate synchronization sequence (QPSK symbols)
float complex sequence[sequence_len];
for (i=0; i<sequence_len; i++) {
sequence[i] = (rand() % 2 ? 1.0f : -1.0f) * M_SQRT1_2 +
(rand() % 2 ? 1.0f : -1.0f) * M_SQRT1_2 * _Complex_I;
}
//
float rxy = 0.0f;
float tau_hat = 0.0f;
float gamma_hat = 0.0f;
float dphi_hat = 0.0f;
float phi_hat = 0.0f;
int frame_detected = 0;
// create detector
qdetector_cccf q = qdetector_cccf_create_linear(sequence, sequence_len, ftype, k, m, beta);
qdetector_cccf_set_threshold(q, threshold);
qdetector_cccf_set_range (q, range);
qdetector_cccf_print(q);
//
unsigned int seq_len = qdetector_cccf_get_seq_len(q);
unsigned int buf_len = qdetector_cccf_get_buf_len(q);
unsigned int num_samples = 2*buf_len; // double buffer length to ensure detection
unsigned int num_symbols = buf_len;
// arrays
float complex y[num_samples]; // received signal
float complex syms_rx[num_symbols]; // recovered symbols
// get pointer to sequence and generate full sequence
float complex * v = (float complex*) qdetector_cccf_get_sequence(q);
unsigned int filter_delay = 15;
firfilt_crcf filter = firfilt_crcf_create_kaiser(2*filter_delay+1, 0.4f, 60.0f, -tau);
for (i=0; i<num_samples; i++) {
// add delay
firfilt_crcf_push(filter, i < seq_len ? v[i] : 0);
firfilt_crcf_execute(filter, &y[i]);
// channel gain
y[i] *= gamma;
// carrier offset
y[i] *= cexpf(_Complex_I*(dphi*i + phi));
// noise
y[i] += nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
}
firfilt_crcf_destroy(filter);
// run detection on sequence
for (i=0; i<num_samples; i++) {
v = qdetector_cccf_execute(q,y[i]);
if (v != NULL) {
printf("\nframe detected!\n");
frame_detected = 1;
// get statistics
rxy = qdetector_cccf_get_rxy(q);
tau_hat = qdetector_cccf_get_tau(q);
gamma_hat = qdetector_cccf_get_gamma(q);
dphi_hat = qdetector_cccf_get_dphi(q);
phi_hat = qdetector_cccf_get_phi(q);
break;
}
}
unsigned int num_syms_rx = 0; // output symbol counter
unsigned int counter = 0; // decimation counter
if (frame_detected) {
// recover symbols
firfilt_crcf mf = firfilt_crcf_create_rnyquist(ftype, k, m, beta, tau_hat);
firfilt_crcf_set_scale(mf, 1.0f / (float)(k*gamma_hat));
nco_crcf nco = nco_crcf_create(LIQUID_VCO);
nco_crcf_set_frequency(nco, dphi_hat);
nco_crcf_set_phase (nco, phi_hat);
for (i=0; i<buf_len; i++) {
//
float complex sample;
nco_crcf_mix_down(nco, v[i], &sample);
nco_crcf_step(nco);
// apply decimator
firfilt_crcf_push(mf, sample);
counter++;
if (counter == k-1)
firfilt_crcf_execute(mf, &syms_rx[num_syms_rx++]);
counter %= k;
}
nco_crcf_destroy(nco);
firfilt_crcf_destroy(mf);
}
// destroy objects
qdetector_cccf_destroy(q);
// print results
printf("\n");
printf("frame detected : %s\n", frame_detected ? "yes" : "no");
if (frame_detected) {
printf(" rxy : %8.3f\n", rxy);
printf(" gamma hat : %8.3f, actual=%8.3f (error=%8.3f)\n", gamma_hat, gamma, gamma_hat - gamma);
printf(" tau hat : %8.3f, actual=%8.3f (error=%8.3f) samples\n", tau_hat, tau, tau_hat - tau );
printf(" dphi hat : %8.5f, actual=%8.5f (error=%8.5f) rad/sample\n", dphi_hat, dphi, dphi_hat - dphi );
printf(" phi hat : %8.5f, actual=%8.5f (error=%8.5f) radians\n", phi_hat, phi, phi_hat - phi );
printf(" symbols rx : %u\n", num_syms_rx);
}
printf("\n");
//
// export results
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all\n");
fprintf(fid,"close all\n");
fprintf(fid,"sequence_len= %u;\n", sequence_len);
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"y = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"y(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"num_syms_rx = %u;\n", num_syms_rx);
fprintf(fid,"syms_rx = zeros(1,num_syms_rx);\n");
for (i=0; i<num_syms_rx; i++)
fprintf(fid,"syms_rx(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(syms_rx[i]), cimagf(syms_rx[i]));
fprintf(fid,"t=[0:(num_samples-1)];\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(4,1,1);\n");
fprintf(fid," plot(t,real(y), t,imag(y));\n");
fprintf(fid," grid on;\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('received signal');\n");
fprintf(fid,"subplot(4,1,2:4);\n");
fprintf(fid," plot(real(syms_rx), imag(syms_rx), 'x');\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", OUTPUT_FILENAME);
return 0;
}
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