//
// AUTOTEST:
//
void autotest_firinterp_rrrf_generic()
{
float h[9] = {
-0.2762293319046737,
1.4757679031218007,
0.1432569489572376,
-0.2142368750177835,
1.3471241294836864,
0.1166010284926269,
0.0536534505390281,
0.1412672462812405,
-0.0991854372394269};
unsigned int M = 4; // firinterp factor
firinterp_rrrf q = firinterp_rrrf_create(M,h,9);
float x[] = {1.0, -1.0, 1.0, 1.0};
float y[16];
float test[16] = {
-0.2762293319046737,
1.4757679031218007,
0.1432569489572376,
-0.2142368750177835,
1.6233534613883602,
-1.3591668746291738,
-0.0896034984182095,
0.3555041212990241,
-1.7225388986277870,
1.3591668746291738,
0.0896034984182095,
-0.3555041212990241,
1.1700802348184398,
1.5923689316144276,
0.1969103994962658,
-0.0729696287365430};
float tol = 1e-6;
unsigned int i;
for (i=0; i<4; i++)
firinterp_rrrf_execute(q, x[i], &y[i*M]);
for (i=0; i<16; i++) {
CONTEND_DELTA(y[i], test[i], tol);
if (liquid_autotest_verbose)
printf(" y(%u) = %8.4f;\n", i+1, y[i]);
}
if (liquid_autotest_verbose)
firinterp_rrrf_print(q);
// destroy interpolator object
firinterp_rrrf_destroy(q);
}
int main(int argc, char*argv[]) {
// options
unsigned int k=2; // samples/symbol
unsigned int m=3; // symbol delay
float beta=0.7f; // excess bandwidth factor
unsigned int num_symbols=16;
int ftype_tx = LIQUID_FIRFILT_RRC;
int ftype_rx = LIQUID_FIRFILT_RRC;
int dopt;
while ((dopt = getopt(argc,argv,"uht:k:m:b:n:")) != EOF) {
switch (dopt) {
case 'u':
case 'h':
usage();
return 0;
case 't':
if (strcmp(optarg,"gmsk")==0) {
ftype_tx = LIQUID_FIRFILT_GMSKTX;
ftype_rx = LIQUID_FIRFILT_GMSKRX;
} else {
ftype_tx = liquid_getopt_str2firfilt(optarg);
ftype_rx = liquid_getopt_str2firfilt(optarg);
}
if (ftype_tx == LIQUID_FIRFILT_UNKNOWN) {
fprintf(stderr,"error: %s, unknown filter type '%s'\n", argv[0], optarg);
exit(1);
}
break;
case 'k':
k = atoi(optarg);
break;
case 'm':
m = atoi(optarg);
break;
case 'b':
beta = atof(optarg);
break;
case 'n':
num_symbols = atoi(optarg);
break;
default:
exit(1);
}
}
if (k < 2) {
fprintf(stderr,"error: %s, k must be at least 2\n", argv[0]);
exit(1);
} else if (m < 1) {
fprintf(stderr,"error: %s, m must be at least 1\n", argv[0]);
exit(1);
} else if (beta <= 0.0f || beta >= 1.0f) {
fprintf(stderr,"error: %s, beta must be in (0,1)\n", argv[0]);
exit(1);
}
unsigned int i;
// derived values
unsigned int num_samples = num_symbols*k;
unsigned int h_len = 2*k*m+1; // transmit/receive filter length
unsigned int hc_len = 4*k*m+1; // composite filter length
// arrays
float ht[h_len]; // transmit filter
float hr[h_len]; // receive filter
float hc[hc_len]; // composite filter
// design the filter(s)
liquid_firdes_rnyquist(ftype_tx, k, m, beta, 0, ht);
liquid_firdes_rnyquist(ftype_rx, k, m, beta, 0, hr);
for (i=0; i<h_len; i++) printf("ht(%3u) = %12.8f;\n", i+1, ht[i]);
for (i=0; i<h_len; i++) printf("hr(%3u) = %12.8f;\n", i+1, hr[i]);
#if 0
// generate receive filter coefficients (reverse of transmit)
float hr[h_len];
for (i=0; i<h_len; i++)
hr[i] = ht[h_len-i-1];
#endif
// compute composite filter response
for (i=0; i<4*k*m+1; i++) {
int lag = (int)i - (int)(2*k*m);
hc[i] = liquid_filter_crosscorr(ht,h_len, hr,h_len, lag);
}
// compute filter inter-symbol interference
float rxy0 = liquid_filter_crosscorr(ht,h_len, hr,h_len, 0);
float isi_rms=0;
for (i=1; i<2*m; i++) {
float e = liquid_filter_crosscorr(ht,h_len, hr,h_len, i*k) / rxy0;
isi_rms += e*e;
}
isi_rms = sqrtf( isi_rms / (float)(2*m-1) );
printf(" isi (rms) : %12.8f dB\n", 20*log10f(isi_rms));
// compute relative stop-band energy
unsigned int nfft = 2048;
float As = liquid_filter_energy(ht, h_len, 0.5f*(1.0f + beta)/(float)k, nfft);
printf(" As : %12.8f dB\n", 20*log10f(As));
// generate signal
float sym_in[num_symbols];
float y[num_samples];
float sym_out[num_symbols];
// create interpolator and decimator
firinterp_rrrf interp = firinterp_rrrf_create(k, ht, h_len);
firdecim_rrrf decim = firdecim_rrrf_create( k, hr, h_len);
for (i=0; i<num_symbols; i++) {
// generate random symbol
sym_in[i] = (rand() % 2) ? 1.0f : -1.0f;
// interpolate
firinterp_rrrf_execute(interp, sym_in[i], &y[i*k]);
// decimate
firdecim_rrrf_execute(decim, &y[i*k], &sym_out[i]);
// normalize output
sym_out[i] /= k;
printf(" %3u : %8.5f", i, sym_out[i]);
if (i>=2*m) printf(" *\n");
else printf("\n");
}
// clean up objects
firinterp_rrrf_destroy(interp);
firdecim_rrrf_destroy(decim);
//
// export results
//
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");
fprintf(fid,"k = %u;\n", k);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"beta = %12.8f;\n", beta);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = k*num_symbols;\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++)
fprintf(fid," y(%3u) = %12.8f;\n", i+1, y[i]);
for (i=0; i<h_len; i++) fprintf(fid,"ht(%3u) = %20.8e;\n", i+1, ht[i]);
for (i=0; i<h_len; i++) fprintf(fid,"hr(%3u) = %20.8e;\n", i+1, hr[i]);
for (i=0; i<hc_len; i++) fprintf(fid,"hc(%3u) = %20.8e;\n", i+1, hc[i]);
fprintf(fid,"nfft=1024;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"Ht = 20*log10(abs(fftshift(fft(ht/k, nfft))));\n");
fprintf(fid,"Hr = 20*log10(abs(fftshift(fft(hr/k, nfft))));\n");
fprintf(fid,"Hc = 20*log10(abs(fftshift(fft(hc/k^2, nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f,Hc,'-','LineWidth',2,...\n");
fprintf(fid," [0.5/k],[-6],'or',...\n");
fprintf(fid," [0.5/k*(1-beta) 0.5/k*(1-beta)],[-100 10],'-r',...\n");
fprintf(fid," [0.5/k*(1+beta) 0.5/k*(1+beta)],[-100 10],'-r');\n");
fprintf(fid,"xlabel('normalized frequency');\n");
fprintf(fid,"ylabel('PSD');\n");
fprintf(fid,"axis([-0.5 0.5 -100 10]);\n");
fprintf(fid,"grid on;\n");
// compute composite filter
fprintf(fid,"figure;\n");
fprintf(fid,"hc = conv(ht,hr)/k;\n");
fprintf(fid,"t = [(-2*k*m):(2*k*m)]/k;\n");
fprintf(fid,"i0 = [0:k:4*k*m]+1;\n");
fprintf(fid,"plot(t, hc, '-s',...\n");
fprintf(fid," t(i0),hc(i0),'or');\n");
fprintf(fid,"xlabel('symbol index');\n");
fprintf(fid,"ylabel('matched filter response');\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
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;
}
// create cpfskmod object (frequency modulator)
// _bps : bits per symbol, _bps > 0
// _h : modulation index, _h > 0
// _k : samples/symbol, _k > 1, _k even
// _m : filter delay (symbols), _m > 0
// _beta : filter bandwidth parameter, _beta > 0
// _type : filter type (e.g. LIQUID_CPFSK_SQUARE)
cpfskmod cpfskmod_create(unsigned int _bps,
float _h,
unsigned int _k,
unsigned int _m,
float _beta,
int _type)
{
// validate input
if (_bps == 0) {
fprintf(stderr,"error: cpfskmod_create(), bits/symbol must be greater than 0\n");
exit(1);
} else if (_k < 2 || (_k%2)) {
fprintf(stderr,"error: cpfskmod_create(), samples/symbol must be greater than 2 and even\n");
exit(1);
} else if (_m == 0) {
fprintf(stderr,"error: cpfskmod_create(), filter delay must be greater than 0\n");
exit(1);
} else if (_beta <= 0.0f || _beta > 1.0f) {
fprintf(stderr,"error: cpfskmod_create(), filter roll-off must be in (0,1]\n");
exit(1);
} else if (_h <= 0.0f) {
fprintf(stderr,"error: cpfskmod_create(), modulation index must be greater than 0\n");
exit(1);
}
// create main object memory
cpfskmod q = (cpfskmod) malloc(sizeof(struct cpfskmod_s));
// set basic internal properties
q->bps = _bps; // bits per symbol
q->h = _h; // modulation index
q->k = _k; // samples per symbol
q->m = _m; // filter delay (symbols)
q->beta = _beta; // filter roll-off factor (only for certain filters)
q->type = _type; // filter type
// derived values
q->M = 1 << q->bps; // constellation size
// create object depending upon input type
float b[2] = {0.5f, 0.5f}; // integrator feed-forward coefficients
float a[2] = {1.0f, -1.0f}; // integrator feed-back coefficients
q->ht_len = 0;
q->ht = NULL;
unsigned int i;
switch(q->type) {
case LIQUID_CPFSK_SQUARE:
q->ht_len = q->k;
q->symbol_delay = 1;
// modify integrator
b[0] = 0.0f;
b[1] = 1.0f;
break;
case LIQUID_CPFSK_RCOS_FULL:
q->ht_len = q->k;
q->symbol_delay = 1;
break;
case LIQUID_CPFSK_RCOS_PARTIAL:
// TODO: adjust reponse based on 'm'
q->ht_len = 3*q->k;
q->symbol_delay = 2;
break;
case LIQUID_CPFSK_GMSK:
q->symbol_delay = q->m + 1;
q->ht_len = 2*(q->k)*(q->m) + (q->k) + 1;
break;
default:
fprintf(stderr,"error: cpfskmodem_create(), invalid filter type '%d'\n", q->type);
exit(1);
}
// create pulse-shaping filter and scale by modulation index
q->ht = (float*) malloc(q->ht_len *sizeof(float));
cpfskmod_firdes(q->k, q->m, q->beta, q->type, q->ht, q->ht_len);
for (i=0; i<q->ht_len; i++)
q->ht[i] *= M_PI * q->h;
q->interp = firinterp_rrrf_create(q->k, q->ht, q->ht_len);
// create phase integrator
q->phase_interp = (float*) malloc(q->k*sizeof(float));
q->integrator = iirfilt_rrrf_create(b,2,a,2);
// reset modem object
cpfskmod_reset(q);
return q;
}
