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//
// channel_cccf_example.c
//
// This example demonstrates how the channel_cccf object can be used to
// emulate a multi-path fading, log-normal shadowing, and AWGN channel.
// 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 "channel_cccf_example.m"
// print usage/help message
void usage()
{
printf("channel_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(" H : multi-path channel length, default: 4000\n");
printf(" n : number of symbols, default: 4000\n");
printf(" s : signal-to-noise ratio, default: 30 dB\n");
printf(" w : timing pll bandwidth, default: 0.02\n");
}
int main(int argc, char*argv[])
{
// options
unsigned int k = 2; // samples per symbol
unsigned int m = 7; // filter delay (symbols)
float beta = 0.25f; // filter excess bandwidth factor
unsigned int num_symbols = 4000; // number of data symbols
unsigned int hc_len = 5; // channel filter length
float noise_floor = -60.0f; // noise floor [dB]
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
float bandwidth = 0.02f; // loop filter bandwidth
float dphi = 0.00f; // carrier frequency offset [radians/sample]
float phi = 2.1f; // carrier phase offset [radians]
modulation_scheme ms = LIQUID_MODEM_QPSK;
int dopt;
while ((dopt = getopt(argc,argv,"hk:m:b:H:n:s:w:")) != 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 'H': hc_len = atoi(optarg); break;
case 'n': num_symbols = atoi(optarg); break;
case 's': SNRdB = atof(optarg); break;
case 'w': bandwidth = atof(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;
// derived/fixed values
unsigned int num_samples = num_symbols*k;
float complex x[num_samples]; // input (interpolated) samples
float complex y[num_samples]; // channel output samples
float complex sym_out[num_symbols + 64];// synchronized symbols
//
// generate input sequence using symbol stream generator
//
symstreamcf gen = symstreamcf_create_linear(LIQUID_FIRFILT_ARKAISER,k,m,beta,ms);
symstreamcf_write_samples(gen, x, num_samples);
symstreamcf_destroy(gen);
// create channel
channel_cccf channel = channel_cccf_create();
// add channel impairments
channel_cccf_add_awgn (channel, noise_floor, SNRdB);
channel_cccf_add_carrier_offset(channel, dphi, phi);
channel_cccf_add_multipath (channel, NULL, hc_len);
channel_cccf_add_shadowing (channel, 1.0f, 0.1f);
// print channel internals
channel_cccf_print(channel);
// apply channel to input signal
channel_cccf_execute_block(channel, x, num_samples, y);
// destroy channel
channel_cccf_destroy(channel);
//
// create and run symbol synchronizer
//
symtrack_cccf symtrack = symtrack_cccf_create(LIQUID_FIRFILT_RRC,k,m,beta,ms);
// set tracking bandwidth
symtrack_cccf_set_bandwidth(symtrack,0.05f);
unsigned int num_symbols_sync = 0;
symtrack_cccf_execute_block(symtrack, y, num_samples, sym_out, &num_symbols_sync);
symtrack_cccf_destroy(symtrack);
// print results
printf("symbols in : %u\n", num_symbols);
printf("symbols out : %u\n", num_symbols_sync);
// estimate spectrum
unsigned int nfft = 1200;
float psd[nfft];
spgramcf_estimate_psd(nfft, y, num_samples, psd);
//
// export output file
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s, auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"close all;\nclear all;\n\n");
fprintf(fid,"num_symbols=%u;\n",num_symbols_sync);
for (i=0; i<num_symbols_sync; i++)
fprintf(fid,"z(%3u) = %12.8f + j*%12.8f;\n", i+1, crealf(sym_out[i]), cimagf(sym_out[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,"iz0 = 1:round(length(z)*0.5);\n");
fprintf(fid,"iz1 = round(length(z)*0.5):length(z);\n");
fprintf(fid,"figure('Color','white','position',[500 500 800 800]);\n");
fprintf(fid,"subplot(2,2,1);\n");
fprintf(fid,"plot(real(z(iz0)),imag(z(iz0)),'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('First 50%% of symbols');\n");
fprintf(fid,"subplot(2,2,2);\n");
fprintf(fid," plot(real(z(iz1)),imag(z(iz1)),'x','MarkerSize',4);\n");
fprintf(fid," axis square;\n");
fprintf(fid," grid on;\n");
fprintf(fid," axis([-1 1 -1 1]*1.5);\n");
fprintf(fid," xlabel('In-phase');\n");
fprintf(fid," ylabel('Quadrature');\n");
fprintf(fid," title('Last 50%% of symbols');\n");
fprintf(fid,"subplot(2,2,3:4);\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);
// clean it up
printf("done.\n");
return 0;
}
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