int main(int argc, char*argv[]) {
srand(time(NULL));
// 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 tau = -0.2f; // fractional symbol offset
float rate = 1.001f; // sample rate offset
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:t:r:")) != 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;
case 't': tau = atof(optarg); break;
case 'r': rate = 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);
} else if (tau < -1.0f || tau > 1.0f) {
fprintf(stderr,"error: timing phase offset must be in [-1,1]\n");
exit(1);
} else if (rate > 1.02f || rate < 0.98f) {
fprintf(stderr,"error: timing rate offset must be in [1.02,0.98]\n");
exit(1);
}
unsigned int i;
// derived/fixed values
unsigned int nx = num_symbols*k;
unsigned int ny = (unsigned int) ceilf(rate * nx) + 64;
float complex x[nx]; // input (interpolated) samples
float complex y[ny]; // 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, nx);
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);
channel_cccf_add_resamp (channel, 0.0f, rate);
// print channel internals
channel_cccf_print(channel);
// apply channel to input signal
channel_cccf_execute(channel, x, nx, y, &ny);
// 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, ny, 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, ny, 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;
}
int main(int argc, char*argv[])
{
// options
unsigned int m = 3; // number of bits/symbol
unsigned int k = 0; // filter samples/symbol
unsigned int num_symbols = 200; // number of data symbols
float SNRdB = 40.0f; // 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 timing offset
float bandwidth = 0.20; // frequency spacing
int dopt;
while ((dopt = getopt(argc,argv,"hm:k:b:n:s:F:P:T:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'm': m = atoi(optarg); break;
case 'k': k = atoi(optarg); break;
case 'b': bandwidth = atof(optarg); break;
case 'n': num_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;
unsigned int j;
// derived values
if (k == 0) k = 2 << m; // set samples per symbol if not otherwise specified
unsigned int num_samples = k*num_symbols;
unsigned int M = 1 << m;
float nstd = powf(10.0f, -SNRdB/20.0f);
float M2 = 0.5f*(float)(M-1);
// validate input
if (k < M) {
fprintf(stderr,"errors: %s, samples/symbol must be at least modulation size (M=%u)\n", __FILE__,M);
exit(1);
} else if (k > 2048) {
fprintf(stderr,"errors: %s, samples/symbol exceeds maximum (2048)\n", __FILE__);
exit(1);
} else if (M > 1024) {
fprintf(stderr,"errors: %s, modulation size (M=%u) exceeds maximum (1024)\n", __FILE__, M);
exit(1);
} else if (bandwidth <= 0.0f || bandwidth >= 0.5f) {
fprintf(stderr,"errors: %s, bandwidht must be in (0,0.5)\n", __FILE__);
exit(1);
}
// compute demodulation FFT size such that FFT output bin frequencies are
// as close to modulated frequencies as possible
unsigned int K = 0; // demodulation FFT size
float df = bandwidth / M2; // frequency spacing
float err_min = 1e9f;
unsigned int K_min = k; // minimum FFT size
unsigned int K_max = k*4 < 16 ? 16 : k*4; // maximum FFT size
unsigned int K_hat;
for (K_hat=K_min; K_hat<=K_max; K_hat++) {
// compute candidate FFT size
float v = 0.5f*df * (float)K_hat; // bin spacing
float err = fabsf( roundf(v) - v ); // fractional bin spacing
// print results
printf(" K_hat = %4u : v = %12.8f, err=%12.8f %s\n", K_hat, v, err, err < err_min ? "*" : "");
// save best result
if (K_hat==K_min || err < err_min) {
K = K_hat;
err_min = err;
}
// perfect match; no need to continue searching
if (err < 1e-6f)
break;
}
// arrays
unsigned int sym_in[num_symbols]; // input symbols
float complex x[num_samples]; // transmitted signal
float complex y[num_samples]; // received signal
unsigned int sym_out[num_symbols]; // output symbols
// determine demodulation mapping between tones and frequency bins
// TODO: use gray coding
unsigned int demod_map[M];
for (i=0; i<M; i++) {
// print frequency bins
float freq = ((float)i - M2) * bandwidth / M2;
float idx = freq * (float)K;
unsigned int index = (unsigned int) (idx < 0 ? roundf(idx + K) : roundf(idx));
demod_map[i] = index;
printf(" s=%3u, f = %12.8f, index=%3u\n", i, freq, index);
}
// check for uniqueness
for (i=1; i<M; i++) {
if (demod_map[i] == demod_map[i-1]) {
fprintf(stderr,"warning: demod map is not unique; consider increasing bandwidth\n");
break;
}
}
// generate message symbols and modulate
// TODO: use gray coding
for (i=0; i<num_symbols; i++) {
// generate random symbol
sym_in[i] = rand() % M;
// compute frequency
float dphi = 2*M_PI*((float)sym_in[i] - M2) * bandwidth / M2;
// generate random phase
float phi = randf() * 2 * M_PI;
// modulate symbol
for (j=0; j<k; j++)
x[i*k+j] = cexpf(_Complex_I*phi + _Complex_I*j*dphi);
}
// push through channel
for (i=0; i<num_samples; i++)
y[i] = x[i] + nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
#if 0
// demodulate signal: high SNR method
float complex buf_time[k];
unsigned int n = 0;
j = 0;
for (i=0; i<num_samples; i++) {
// start filling time buffer with samples (assume perfect symbol timing)
buf_time[n++] = y[i];
// demodulate symbol
if (n==k) {
// reset counter
n = 0;
// estimate frequency
float complex metric = 0;
unsigned int s;
for (s=1; s<k; s++)
metric += buf_time[s] * conjf(buf_time[s-1]);
float dphi_hat = cargf(metric) / (2*M_PI);
unsigned int v=( (unsigned int) roundf(dphi_hat*M2/bandwidth + M2) ) % M;
sym_out[j++] = v;
printf("%3u : %12.8f : %u\n", j, dphi_hat, v);
}
}
#else
// demodulate signal: least-squares method
float complex buf_time[K];
float complex buf_freq[K];
fftplan fft = fft_create_plan(K, buf_time, buf_freq, LIQUID_FFT_FORWARD, 0);
for (i=0; i<K; i++)
buf_time[i] = 0.0f;
unsigned int n = 0;
j = 0;
for (i=0; i<num_samples; i++) {
// start filling time buffer with samples (assume perfect symbol timing)
buf_time[n++] = y[i];
// demodulate symbol
if (n==k) {
// reset counter
n = 0;
// compute transform, storing result in 'buf_freq'
fft_execute(fft);
// find maximum by looking at particular bins
float vmax = 0;
unsigned int s;
unsigned int s_opt = 0;
for (s=0; s<M; s++) {
float v = cabsf( buf_freq[demod_map[s]] );
if (s==0 || v > vmax) {
s_opt = s;
vmax =v;
}
}
// save best result
sym_out[j++] = s_opt;
}
}
// destroy fft object
fft_destroy_plan(fft);
#endif
// count errors
unsigned int num_symbol_errors = 0;
for (i=0; i<num_symbols; i++)
num_symbol_errors += (sym_in[i] == sym_out[i]) ? 0 : 1;
printf("symbol errors: %u / %u\n", num_symbol_errors, num_symbols);
// compute power spectral density of received signal
unsigned int nfft = 1200;
float psd[nfft];
spgramcf_estimate_psd(nfft, y, num_samples, psd);
//
// export results
//
// truncate to at most 10 symbols
if (num_symbols > 10)
num_symbols = 10;
num_samples = k*num_symbols;
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,"M = %u;\n", M);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = 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]));
}
// save power spectral density
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");
// plot time signal
fprintf(fid,"subplot(2,1,1),\n");
fprintf(fid,"hold on;\n");
fprintf(fid," plot(t,real(y),'-', 'Color',[0 0.3 0.5]);\n");
fprintf(fid," plot(t,imag(y),'-', 'Color',[0 0.5 0.3]);\n");
fprintf(fid,"hold off;\n");
fprintf(fid,"ymax = ceil(max(abs(y))*5)/5;\n");
fprintf(fid,"axis([0 num_symbols -ymax ymax]);\n");
fprintf(fid,"xlabel('time');\n");
fprintf(fid,"ylabel('x(t)');\n");
fprintf(fid,"grid on;\n");
// plot PSD
fprintf(fid,"subplot(2,1,2),\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"plot(f,psd,'LineWidth',1.5,'Color',[0.5 0 0]);\n");
fprintf(fid,"axis([-0.5 0.5 -40 40]);\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
int main(int argc, char*argv[])
{
// options
unsigned int bps = 1; // number of bits/symbol
float h = 0.5f; // modulation index (h=1/2 for MSK)
unsigned int k = 4; // filter samples/symbol
unsigned int m = 3; // filter delay (symbols)
float beta = 0.35f; // GMSK bandwidth-time factor
unsigned int num_symbols = 20; // number of data symbols
float SNRdB = 40.0f; // 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 timing offset
int filter_type = LIQUID_CPFSK_SQUARE;
int dopt;
while ((dopt = getopt(argc,argv,"ht:p:H:k:m:b:n:s:F:P:T:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 't':
if (strcmp(optarg,"square")==0) {
filter_type = LIQUID_CPFSK_SQUARE;
} else if (strcmp(optarg,"rcos-full")==0) {
filter_type = LIQUID_CPFSK_RCOS_FULL;
} else if (strcmp(optarg,"rcos-half")==0) {
filter_type = LIQUID_CPFSK_RCOS_PARTIAL;
} else if (strcmp(optarg,"gmsk")==0) {
filter_type = LIQUID_CPFSK_GMSK;
} else {
fprintf(stderr,"error: %s, unknown filter type '%s'\n", argv[0], optarg);
exit(1);
}
break;
case 'p': bps = atoi(optarg); break;
case 'H': h = atof(optarg); 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;
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_samples = k*num_symbols;
unsigned int M = 1 << bps; // constellation size
float nstd = powf(10.0f, -SNRdB/20.0f);
// arrays
unsigned int sym_in[num_symbols]; // input symbols
float complex x[num_samples]; // transmitted signal
float complex y[num_samples]; // received signal
unsigned int sym_out[num_symbols]; // output symbols
// create modem objects
cpfskmod mod = cpfskmod_create(bps, h, k, m, beta, filter_type);
cpfskdem dem = cpfskdem_create(bps, h, k, m, beta, filter_type);
// print modulator
cpfskmod_print(mod);
// generate message signal
for (i=0; i<num_symbols; i++)
sym_in[i] = rand() % M;
// modulate signal
for (i=0; i<num_symbols; i++)
cpfskmod_modulate(mod, sym_in[i], &x[k*i]);
// push through channel
float sample_offset = -tau * k;
int sample_delay = (int)roundf(sample_offset);
float dt = sample_offset - (float)sample_delay;
printf("symbol delay : %f\n", tau);
printf("sample delay : %f = %d + %f\n", sample_offset, sample_delay, dt);
firfilt_crcf fchannel = firfilt_crcf_create_kaiser(8*k+2*sample_delay+1, 0.45f, 40.0f, dt);
for (i=0; i<num_samples; i++) {
// push through channel delay
firfilt_crcf_push(fchannel, x[i]);
firfilt_crcf_execute(fchannel, &y[i]);
// add carrier frequency/phase offset
y[i] *= cexpf(_Complex_I*(cfo*i + cpo));
// add noise
y[i] += nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
}
firfilt_crcf_destroy(fchannel);
// demodulate signal
unsigned int nw=0;
cpfskdem_demodulate(dem, y, num_samples, sym_out, &nw);
printf("demodulator wrote %u symbols\n", nw);
// destroy modem objects
cpfskmod_destroy(mod);
cpfskdem_destroy(dem);
// 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, x, 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", m);
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = 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]));
}
// save power spectral density
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)),'ob',...\n");
fprintf(fid," t,imag(x),'-', t(i),imag(x(i)),'og');\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,real(y),'-', t(i),real(y(i)),'ob',...\n");
fprintf(fid," t,imag(y),'-', t(i),imag(y(i)),'og');\n");
fprintf(fid," axis([0 num_symbols -1.2 1.2]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('y(t)');\n");
fprintf(fid," grid on;\n");
// plot I/Q constellations
fprintf(fid,"subplot(3,4,4);\n");
fprintf(fid," plot(real(x),imag(x),'-',real(x(i)),imag(x(i)),'rs','MarkerSize',4);\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(y),imag(y),'-',real(y(i)),imag(y(i)),'rs','MarkerSize',4);\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 -60 20]);\n");
fprintf(fid," xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid," ylabel('PSD [dB]');\n");
fprintf(fid," grid on;\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;
}
