// initialize coherent demodulator
void cpfskdem_init_coherent(cpfskdem _q)
{
// specify coherent receiver
_q->demod_type = CPFSKDEM_COHERENT;
// set demodulate function pointer
_q->demodulate = cpfskdem_demodulate_coherent;
// create object depending upon input type
float bw = 0.0f;
float beta = 0.0f;
float gmsk_bt = _q->beta;
switch(_q->type) {
case LIQUID_CPFSK_SQUARE:
//bw = 0.9f / (float)k;
bw = 0.4f;
_q->symbol_delay = _q->m;
_q->data.coherent.mf = firfilt_crcf_create_kaiser(2*_q->k*_q->m+1, bw, 60.0f, 0.0f);
firfilt_crcf_set_scale(_q->data.coherent.mf, 2.0f * bw);
break;
case LIQUID_CPFSK_RCOS_FULL:
if (_q->M==2) {
_q->data.coherent.mf = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,_q->k,_q->m,0.5f,0);
firfilt_crcf_set_scale(_q->data.coherent.mf, 1.33f / (float)_q->k);
_q->symbol_delay = _q->m;
} else {
_q->data.coherent.mf = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,_q->k/2,2*_q->m,0.9f,0);
firfilt_crcf_set_scale(_q->data.coherent.mf, 3.25f / (float)_q->k);
_q->symbol_delay = 0; // TODO: fix this value
}
break;
case LIQUID_CPFSK_RCOS_PARTIAL:
if (_q->M==2) {
_q->data.coherent.mf = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,_q->k,_q->m,0.3f,0);
firfilt_crcf_set_scale(_q->data.coherent.mf, 1.10f / (float)_q->k);
_q->symbol_delay = _q->m;
} else {
_q->data.coherent.mf = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,_q->k/2,2*_q->m,0.27f,0);
firfilt_crcf_set_scale(_q->data.coherent.mf, 2.90f / (float)_q->k);
_q->symbol_delay = 0; // TODO: fix this value
}
break;
case LIQUID_CPFSK_GMSK:
bw = 0.5f / (float)_q->k;
// TODO: figure out beta value here
beta = (_q->M == 2) ? 0.8*gmsk_bt : 1.0*gmsk_bt;
_q->data.coherent.mf = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,_q->k,_q->m,_q->beta,0);
firfilt_crcf_set_scale(_q->data.coherent.mf, 2.0f * bw);
_q->symbol_delay = _q->m;
break;
default:
fprintf(stderr,"error: cpfskdem_init_coherent(), invalid tx filter type\n");
exit(1);
}
}
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 gamma = 10.0f; // channel gain
float tau = -0.3f; // fractional sample timing offset
float dphi = -0.01f; // carrier frequency offset
float phi = 0.5f; // carrier phase offset
float SNRdB = 20.0f; // signal-to-noise ratio [dB]
float threshold = 0.5f; // detection threshold
int dopt;
while ((dopt = getopt(argc,argv,"hn:k:m:b:F:T:S:t:")) != 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;
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);
}
// 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 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_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);
float nstd = 0.1f;
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
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");
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;
}
int main(int argc, char*argv[]) {
// options
unsigned int k = 8; // filter samples/symbol
unsigned int bps= 1; // number of bits/symbol
float h = 0.5f; // modulation index (h=1/2 for MSK)
unsigned int num_data_symbols = 20; // number of data symbols
float SNRdB = 80.0f; // signal-to-noise ratio [dB]
float cfo = 0.0f; // carrier frequency offset
float cpo = 0.0f; // carrier phase offset
float tau = 0.0f; // fractional symbol offset
enum {
TXFILT_SQUARE=0,
TXFILT_RCOS_FULL,
TXFILT_RCOS_HALF,
TXFILT_GMSK,
} tx_filter_type = TXFILT_SQUARE;
float gmsk_bt = 0.35f; // GMSK bandwidth-time factor
int dopt;
while ((dopt = getopt(argc,argv,"ht:k:b:H:B:n:s:F:P:T:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 't':
if (strcmp(optarg,"square")==0) {
tx_filter_type = TXFILT_SQUARE;
} else if (strcmp(optarg,"rcos-full")==0) {
tx_filter_type = TXFILT_RCOS_FULL;
} else if (strcmp(optarg,"rcos-half")==0) {
tx_filter_type = TXFILT_RCOS_HALF;
} else if (strcmp(optarg,"gmsk")==0) {
tx_filter_type = TXFILT_GMSK;
} else {
fprintf(stderr,"error: %s, unknown filter type '%s'\n", argv[0], optarg);
exit(1);
}
break;
case 'k': k = atoi(optarg); break;
case 'b': bps = atoi(optarg); break;
case 'H': h = atof(optarg); break;
case 'B': gmsk_bt = atof(optarg); break;
case 'n': num_data_symbols = atoi(optarg); break;
case 's': SNRdB = atof(optarg); break;
case 'F': cfo = atof(optarg); break;
case 'P': cpo = atof(optarg); break;
case 'T': tau = atof(optarg); break;
default:
exit(1);
}
}
unsigned int i;
// derived values
unsigned int num_symbols = num_data_symbols;
unsigned int num_samples = k*num_symbols;
unsigned int M = 1 << bps; // constellation size
float nstd = powf(10.0f, -SNRdB/20.0f);
// arrays
unsigned char sym_in[num_symbols]; // input symbols
float phi[num_samples]; // transmitted phase
float complex x[num_samples]; // transmitted signal
float complex y[num_samples]; // received signal
float complex z[num_samples]; // output...
//unsigned char sym_out[num_symbols]; // output symbols
unsigned int ht_len = 0;
unsigned int tx_delay = 0;
float * ht = NULL;
switch (tx_filter_type) {
case TXFILT_SQUARE:
// regular MSK
ht_len = k;
tx_delay = 1;
ht = (float*) malloc(ht_len *sizeof(float));
for (i=0; i<ht_len; i++)
ht[i] = h * M_PI / (float)k;
break;
case TXFILT_RCOS_FULL:
// full-response raised-cosine pulse
ht_len = k;
tx_delay = 1;
ht = (float*) malloc(ht_len *sizeof(float));
for (i=0; i<ht_len; i++)
ht[i] = h * M_PI / (float)k * (1.0f - cosf(2.0f*M_PI*i/(float)ht_len));
break;
case TXFILT_RCOS_HALF:
// partial-response raised-cosine pulse
ht_len = 3*k;
tx_delay = 2;
ht = (float*) malloc(ht_len *sizeof(float));
for (i=0; i<ht_len; i++)
ht[i] = 0.0f;
for (i=0; i<2*k; i++)
ht[i+k/2] = h * 0.5f * M_PI / (float)k * (1.0f - cosf(2.0f*M_PI*i/(float)(2*k)));
break;
case TXFILT_GMSK:
ht_len = 2*k*3+1+k;
tx_delay = 4;
ht = (float*) malloc(ht_len *sizeof(float));
for (i=0; i<ht_len; i++)
ht[i] = 0.0f;
liquid_firdes_gmsktx(k,3,gmsk_bt,0.0f,&ht[k/2]);
for (i=0; i<ht_len; i++)
ht[i] *= h * 2.0f / (float)k;
break;
default:
fprintf(stderr,"error: %s, invalid tx filter type\n", argv[0]);
exit(1);
}
for (i=0; i<ht_len; i++)
printf("ht(%3u) = %12.8f;\n", i+1, ht[i]);
firinterp_rrrf interp_tx = firinterp_rrrf_create(k, ht, ht_len);
// generate symbols and interpolate
// phase-accumulating filter (trapezoidal integrator)
float b[2] = {0.5f, 0.5f};
if (tx_filter_type == TXFILT_SQUARE) {
// square filter: rectangular integration with one sample of delay
b[0] = 0.0f;
b[1] = 1.0f;
}
float a[2] = {1.0f, -1.0f};
iirfilt_rrrf integrator = iirfilt_rrrf_create(b,2,a,2);
float theta = 0.0f;
for (i=0; i<num_symbols; i++) {
sym_in[i] = rand() % M;
float v = 2.0f*sym_in[i] - (float)(M-1); // +/-1, +/-3, ... +/-(M-1)
firinterp_rrrf_execute(interp_tx, v, &phi[k*i]);
// accumulate phase
unsigned int j;
for (j=0; j<k; j++) {
iirfilt_rrrf_execute(integrator, phi[i*k+j], &theta);
x[i*k+j] = cexpf(_Complex_I*theta);
}
}
iirfilt_rrrf_destroy(integrator);
// push through channel
for (i=0; i<num_samples; i++) {
// add carrier frequency/phase offset
y[i] = x[i]*cexpf(_Complex_I*(cfo*i + cpo));
// add noise
y[i] += nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
}
// create decimator
unsigned int m = 3;
float bw = 0.0f;
float beta = 0.0f;
firfilt_crcf decim_rx = NULL;
switch (tx_filter_type) {
case TXFILT_SQUARE:
//bw = 0.9f / (float)k;
bw = 0.4f;
decim_rx = firfilt_crcf_create_kaiser(2*k*m+1, bw, 60.0f, 0.0f);
firfilt_crcf_set_scale(decim_rx, 2.0f * bw);
break;
case TXFILT_RCOS_FULL:
if (M==2) {
decim_rx = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,k,m,0.5f,0);
firfilt_crcf_set_scale(decim_rx, 1.33f / (float)k);
} else {
decim_rx = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,k/2,2*m,0.9f,0);
firfilt_crcf_set_scale(decim_rx, 3.25f / (float)k);
}
break;
case TXFILT_RCOS_HALF:
if (M==2) {
decim_rx = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,k,m,0.3f,0);
firfilt_crcf_set_scale(decim_rx, 1.10f / (float)k);
} else {
decim_rx = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,k/2,2*m,0.27f,0);
firfilt_crcf_set_scale(decim_rx, 2.90f / (float)k);
}
break;
case TXFILT_GMSK:
bw = 0.5f / (float)k;
// TODO: figure out beta value here
beta = (M == 2) ? 0.8*gmsk_bt : 1.0*gmsk_bt;
decim_rx = firfilt_crcf_create_rnyquist(LIQUID_FIRFILT_GMSKRX,k,m,beta,0);
firfilt_crcf_set_scale(decim_rx, 2.0f * bw);
break;
default:
fprintf(stderr,"error: %s, invalid tx filter type\n", argv[0]);
exit(1);
}
printf("bw = %f\n", bw);
// run receiver
unsigned int n=0;
unsigned int num_errors = 0;
unsigned int num_symbols_checked = 0;
float complex z_prime = 0.0f;
for (i=0; i<num_samples; i++) {
// push through filter
firfilt_crcf_push(decim_rx, y[i]);
firfilt_crcf_execute(decim_rx, &z[i]);
// decimate output
if ( (i%k)==0 ) {
// compute instantaneous frequency scaled by modulation index
float phi_hat = cargf(conjf(z_prime) * z[i]) / (h * M_PI);
// estimate transmitted symbol
float v = (phi_hat + (M-1.0))*0.5f;
unsigned int sym_out = ((int) roundf(v)) % M;
// save current point
z_prime = z[i];
// print result to screen
printf("%3u : %12.8f + j%12.8f, <f=%8.4f : %8.4f> (%1u)",
n, crealf(z[i]), cimagf(z[i]), phi_hat, v, sym_out);
if (n >= m+tx_delay) {
num_errors += (sym_out == sym_in[n-m-tx_delay]) ? 0 : 1;
num_symbols_checked++;
printf(" (%1u)\n", sym_in[n-m-tx_delay]);
} else {
printf("\n");
}
n++;
}
}
// print number of errors
printf("errors : %3u / %3u\n", num_errors, num_symbols_checked);
// destroy objects
firinterp_rrrf_destroy(interp_tx);
firfilt_crcf_destroy(decim_rx);
// compute power spectral density of transmitted signal
unsigned int nfft = 1024;
float psd[nfft];
spgramcf periodogram = spgramcf_create_kaiser(nfft, nfft/2, 8.0f);
spgramcf_estimate_psd(periodogram, y, num_samples, psd);
spgramcf_destroy(periodogram);
//
// 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,"k = %u;\n", k);
fprintf(fid,"h = %f;\n", h);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"delay = %u; %% receive filter delay\n", tx_delay);
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
fprintf(fid,"z = zeros(1,num_samples);\n");
fprintf(fid,"phi = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++) {
fprintf(fid,"x(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"z(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(z[i]), cimagf(z[i]));
fprintf(fid,"phi(%4u) = %12.8f;\n", i+1, phi[i]);
}
// save PSD
fprintf(fid,"psd = zeros(1,nfft);\n");
for (i=0; i<nfft; i++)
fprintf(fid,"psd(%4u) = %12.8f;\n", i+1, psd[i]);
fprintf(fid,"t=[0:(num_samples-1)]/k;\n");
fprintf(fid,"i = 1:k:num_samples;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,4,1:3);\n");
fprintf(fid," plot(t,real(x),'-', t(i),real(x(i)),'bs','MarkerSize',4,...\n");
fprintf(fid," t,imag(x),'-', t(i),imag(x(i)),'gs','MarkerSize',4);\n");
fprintf(fid," axis([0 num_symbols -1.2 1.2]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('x(t)');\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,4,5:7);\n");
fprintf(fid," plot(t-delay,real(z),'-', t(i)-delay,real(z(i)),'bs','MarkerSize',4,...\n");
fprintf(fid," t-delay,imag(z),'-', t(i)-delay,imag(z(i)),'gs','MarkerSize',4);\n");
fprintf(fid," axis([0 num_symbols -1.2 1.2]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('\"matched\" filter output');\n");
fprintf(fid," grid on;\n");
// plot I/Q constellations
fprintf(fid,"subplot(3,4,4);\n");
fprintf(fid," plot(real(y),imag(y),'-',real(y(i)),imag(y(i)),'rs','MarkerSize',3);\n");
fprintf(fid," xlabel('I');\n");
fprintf(fid," ylabel('Q');\n");
fprintf(fid," axis([-1 1 -1 1]*1.2);\n");
fprintf(fid," axis square;\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,4,8);\n");
fprintf(fid," plot(real(z),imag(z),'-',real(z(i)),imag(z(i)),'rs','MarkerSize',3);\n");
fprintf(fid," xlabel('I');\n");
fprintf(fid," ylabel('Q');\n");
fprintf(fid," axis([-1 1 -1 1]*1.2);\n");
fprintf(fid," axis square;\n");
fprintf(fid," grid on;\n");
// plot PSD
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"subplot(3,4,9:12);\n");
fprintf(fid," plot(f,psd,'LineWidth',1.5);\n");
fprintf(fid," axis([-0.5 0.5 -40 20]);\n");
fprintf(fid," xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid," ylabel('PSD [dB]');\n");
fprintf(fid," grid on;\n");
#if 0
fprintf(fid,"figure;\n");
fprintf(fid," %% compute instantaneous received frequency\n");
fprintf(fid," freq_rx = arg( conj(z(:)) .* circshift(z(:),-1) )';\n");
fprintf(fid," freq_rx(1:(k*delay)) = 0;\n");
fprintf(fid," freq_rx(end) = 0;\n");
fprintf(fid," %% compute instantaneous tx/rx phase\n");
if (tx_filter_type == TXFILT_SQUARE) {
fprintf(fid," theta_tx = filter([0 1],[1 -1],phi)/(h*pi);\n");
fprintf(fid," theta_rx = filter([0 1],[1 -1],freq_rx)/(h*pi);\n");
} else {
fprintf(fid," theta_tx = filter([0.5 0.5],[1 -1],phi)/(h*pi);\n");
fprintf(fid," theta_rx = filter([0.5 0.5],[1 -1],freq_rx)/(h*pi);\n");
}
fprintf(fid," %% plot instantaneous tx/rx phase\n");
fprintf(fid," plot(t, theta_tx,'-b', t(i), theta_tx(i),'sb',...\n");
fprintf(fid," t-delay,theta_rx,'-r', t(i)-delay,theta_rx(i),'sr');\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('instantaneous phase/(h \\pi)');\n");
fprintf(fid," legend('transmitted','syms','received/filtered','syms','location','northwest');\n");
fprintf(fid," grid on;\n");
#else
// plot filter response
fprintf(fid,"ht_len = %u;\n", ht_len);
fprintf(fid,"ht = zeros(1,ht_len);\n");
for (i=0; i<ht_len; i++)
fprintf(fid,"ht(%4u) = %12.8f;\n", i+1, ht[i]);
fprintf(fid,"gt1 = filter([0.5 0.5],[1 -1],ht) / (pi*h);\n");
fprintf(fid,"gt2 = filter([0.0 1.0],[1 -1],ht) / (pi*h);\n");
fprintf(fid,"tfilt = [0:(ht_len-1)]/k - delay + 0.5;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(tfilt,ht, '-x','MarkerSize',4,...\n");
fprintf(fid," tfilt,gt1,'-x','MarkerSize',4,...\n");
fprintf(fid," tfilt,gt2,'-x','MarkerSize',4);\n");
fprintf(fid,"axis([tfilt(1) tfilt(end) -0.1 1.1]);\n");
fprintf(fid,"legend('pulse','trap. int.','rect. int.','location','northwest');\n");
fprintf(fid,"grid on;\n");
#endif
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
// free allocated filter memory
free(ht);
return 0;
}
