//
// AUTOTEST: static channel filter, blind equalization on QPSK symbols
//
void autotest_eqlms_cccf_blind()
{
// parameters
float tol = 2e-2f; // error tolerance
unsigned int k = 2; // samples/symbol
unsigned int m = 7; // filter delay
float beta = 0.3f; // excess bandwidth factor
unsigned int p = 7; // equalizer order
float mu = 0.7f; // equalizer bandwidth
unsigned int num_symbols = 400; // number of symbols to observe
// create sequence generator for repeatability
msequence ms = msequence_create_default(12);
// create interpolating filter
firinterp_crcf interp = firinterp_crcf_create_prototype(LIQUID_FIRFILT_ARKAISER,k,m,beta,0);
// create equalizer
eqlms_cccf eq = eqlms_cccf_create_rnyquist(LIQUID_FIRFILT_ARKAISER,k,p,beta,0);
eqlms_cccf_set_bw(eq, mu);
// create channel filter
float complex h[5] = {
{ 1.00f, 0.00f},
{ 0.00f, -0.01f},
{-0.11f, 0.02f},
{ 0.02f, 0.01f},
{-0.09f, -0.04f} };
firfilt_cccf fchannel = firfilt_cccf_create(h,5);
// arrays
float complex buf[k]; // filter buffer
float complex sym_in [num_symbols]; // input symbols
float complex sym_out[num_symbols]; // equalized symbols
// run equalization
unsigned int i;
unsigned int j;
for (i=0; i<num_symbols; i++) {
// generate input symbol
sym_in[i] = ( msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2 ) +
( msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2 ) * _Complex_I;
// interpolate
firinterp_crcf_execute(interp, sym_in[i], buf);
// apply channel filter (in place)
firfilt_cccf_execute_block(fchannel, buf, k, buf);
// apply equalizer as filter
for (j=0; j<k; j++) {
eqlms_cccf_push(eq, buf[j]);
// decimate by k
if ( (j%k) != 0 ) continue;
eqlms_cccf_execute(eq, &sym_out[i]);
// update equalization (blind operation)
if (i > m + p)
eqlms_cccf_step(eq, sym_out[i]/cabsf(sym_out[i]), sym_out[i]);
}
}
// compare input, output
unsigned int settling_delay = 285;
for (i=m+p; i<num_symbols; i++) {
// compensate for delay
j = i-m-p;
// absolute error
float error = cabsf(sym_in[j]-sym_out[i]);
if (liquid_autotest_verbose) {
printf("x[%3u] = {%12.8f,%12.8f}, y[%3u] = {%12.8f,%12.8f}, error=%12.8f %s\n",
j, crealf(sym_in [j]), cimagf(sym_in [j]),
i, crealf(sym_out[i]), cimagf(sym_out[i]),
error, error > tol ? "*" : "");
if (i == settling_delay + m + p)
printf("--- start of test ---\n");
}
// check error
if (i > settling_delay + m + p)
CONTEND_DELTA(error, 0.0f, tol);
}
// clean up objects
firfilt_cccf_destroy(fchannel);
eqlms_cccf_destroy(eq);
msequence_destroy(ms);
}
int main() {
// options
unsigned int num_samples = 600; // number of samples
unsigned int m = 25; // prototype filter semi-length
float As = 30.0f; // prototype filter stop-band suppression
float f0 = 0.15f; // notch frequency
// design filter from prototype
firfilt_cccf q = firfilt_cccf_create_notch(m,As,f0);
firfilt_cccf_print(q);
// allocate memory for data arrays
float complex x[num_samples]; // original input
float complex y[num_samples]; // filtered signal
// generate input signal
unsigned int i;
for (i=0; i<num_samples; i++) {
x[i] = cexpf(_Complex_I*2*M_PI*0.037*i) +
cexpf(_Complex_I*2*M_PI*f0* i);
}
// run notch filter
firfilt_cccf_execute_block(q, x, num_samples, y);
// destroy filter object
firfilt_cccf_destroy(q);
//
// plot results to output file
//
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,"\n");
fprintf(fid,"num_samples=%u;\n",num_samples);
fprintf(fid,"x=zeros(1,num_samples);\n");
fprintf(fid,"y=zeros(1,num_samples);\n");
// save input, output arrays
for (i=0; i<num_samples; i++) {
fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
}
// plot output
fprintf(fid,"t=0:(num_samples-1);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," plot(t,real(x),'-','Color',[1 1 1]*0.5,'LineWidth',1,...\n");
fprintf(fid," t,imag(x),'-','Color',[0 0.2 0.5],'LineWidth',2);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('original input');\n");
fprintf(fid," legend('real','imag','location','northeast');\n");
fprintf(fid," axis([0 num_samples -2.2 2.2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," plot(t,real(y),'-','Color',[1 1 1]*0.5,'LineWidth',1,...\n");
fprintf(fid," t,imag(y),'-','Color',[0 0.5 0.2],'LineWidth',2);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('notch filter output');\n");
fprintf(fid," legend('real','imag','location','northeast');\n");
fprintf(fid," axis([0 num_samples -2.2 2.2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," nfft = 2^nextpow2(num_samples);\n");
fprintf(fid," f = [0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid," X = 20*log10(abs(fftshift(fft(x,nfft))));\n");
fprintf(fid," Y = 20*log10(abs(fftshift(fft(y,nfft))));\n");
fprintf(fid," plot(f,X,'-','Color',[1 1 1]*0.5,'LineWidth',1,...\n");
fprintf(fid," f,Y,'-','Color',[0.5 0 0], 'LineWidth',2);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('PSD (dB)');\n");
fprintf(fid," legend('original','filtered','location','northeast');\n");
fprintf(fid," axis([-0.5 0.5 -20 60]);\n");
fprintf(fid," grid on;\n");
// close output file
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
