// create flexframesync object
// _callback : callback function invoked when frame is received
// _userdata : user-defined data object passed to callback
flexframesync flexframesync_create(framesync_callback _callback,
void * _userdata)
{
flexframesync q = (flexframesync) malloc(sizeof(struct flexframesync_s));
q->callback = _callback;
q->userdata = _userdata;
unsigned int i;
// generate p/n sequence
msequence ms = msequence_create(6, 0x005b, 1);
for (i=0; i<64; i++)
q->preamble_pn[i] = (msequence_advance(ms)) ? 1.0f : -1.0f;
msequence_destroy(ms);
// interpolate p/n sequence with matched filter
q->k = 2; // samples/symbol
q->m = 7; // filter delay (symbols)
q->beta = 0.25f; // excess bandwidth factor
float complex seq[q->k*64];
firinterp_crcf interp = firinterp_crcf_create_rnyquist(LIQUID_FIRFILT_ARKAISER,q->k,q->m,q->beta,0);
for (i=0; i<64+q->m; i++) {
// compensate for filter delay
if (i < q->m) firinterp_crcf_execute(interp, q->preamble_pn[i], &seq[0]);
else firinterp_crcf_execute(interp, q->preamble_pn[i%64], &seq[q->k*(i-q->m)]);
}
firinterp_crcf_destroy(interp);
// create frame detector
float threshold = 0.4f; // detection threshold
float dphi_max = 0.05f; // maximum carrier offset allowable
q->frame_detector = detector_cccf_create(seq, q->k*64, threshold, dphi_max);
q->buffer = windowcf_create(q->k*(64+q->m));
// create symbol timing recovery filters
q->npfb = 32; // number of filters in the bank
q->mf = firpfb_crcf_create_rnyquist(LIQUID_FIRFILT_ARKAISER, q->npfb,q->k,q->m,q->beta);
q->dmf = firpfb_crcf_create_drnyquist(LIQUID_FIRFILT_ARKAISER,q->npfb,q->k,q->m,q->beta);
// create down-coverters for carrier phase tracking
q->nco_coarse = nco_crcf_create(LIQUID_NCO);
q->nco_fine = nco_crcf_create(LIQUID_VCO);
nco_crcf_pll_set_bandwidth(q->nco_fine, 0.05f);
// create header objects
q->demod_header = modem_create(LIQUID_MODEM_BPSK);
q->p_header = packetizer_create(FLEXFRAME_H_DEC,
FLEXFRAME_H_CRC,
FLEXFRAME_H_FEC0,
FLEXFRAME_H_FEC1);
assert(packetizer_get_enc_msg_len(q->p_header)==FLEXFRAME_H_ENC);
// frame properties (default values to be overwritten when frame
// header is received and properly decoded)
q->ms_payload = LIQUID_MODEM_QPSK;
q->bps_payload = 2;
q->payload_dec_len = 1;
q->check = LIQUID_CRC_NONE;
q->fec0 = LIQUID_FEC_NONE;
q->fec1 = LIQUID_FEC_NONE;
// create payload objects (overridden by received properties)
q->demod_payload = modem_create(LIQUID_MODEM_QPSK);
q->p_payload = packetizer_create(q->payload_dec_len, q->check, q->fec0, q->fec1);
q->payload_enc_len = packetizer_get_enc_msg_len(q->p_payload);
q->payload_mod_len = 4 * q->payload_enc_len;
q->payload_mod = (unsigned char*) malloc(q->payload_mod_len*sizeof(unsigned char));
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
q->payload_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
#if DEBUG_FLEXFRAMESYNC
// set debugging flags, objects to NULL
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_x = NULL;
#endif
// reset state
flexframesync_reset(q);
return q;
}
int main(int argc, char*argv[])
{
srand(time(NULL));
// options
unsigned int k=2; // filter samples/symbol
unsigned int m=4; // filter delay (symbols)
float beta=0.3f; // bandwidth-time product
float dt = 0.0f; // fractional sample timing offset
unsigned int num_sync_symbols = 64; // number of data symbols
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
float dphi = 0.0f; // carrier frequency offset
float phi = 0.0f; // carrier phase offset
unsigned int num_delay_symbols = 12;
unsigned int num_dphi_hat = 21; // number of frequency offset estimates
float dphi_hat_step = 0.01f; // frequency offset step size
int dopt;
while ((dopt = getopt(argc,argv,"uhk:m:n:b:t:F:P:s:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'n': num_sync_symbols = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 't': dt = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 'P': phi = atof(optarg); break;
case 's': SNRdB = atof(optarg); break;
default:
exit(1);
}
}
unsigned int i;
// validate input
if (beta <= 0.0f || beta >= 1.0f) {
fprintf(stderr,"error: %s, bandwidth-time product must be in (0,1)\n", argv[0]);
exit(1);
} else if (dt < -0.5 || dt > 0.5) {
fprintf(stderr,"error: %s, fractional sample offset must be in (0,1)\n", argv[0]);
exit(1);
}
// derived values
unsigned int num_symbols = num_delay_symbols + num_sync_symbols + 2*m;
unsigned int num_samples = k*num_symbols;
unsigned int num_sync_samples = k*num_sync_symbols;
float nstd = powf(10.0f, -SNRdB/20.0f);
// arrays
float complex seq[num_sync_symbols]; // data sequence (symbols)
float complex s0[num_sync_samples]; // data sequence (interpolated samples)
float complex x[num_samples]; // transmitted signal
float complex y[num_samples]; // received signal
float rxy[num_dphi_hat][num_samples]; // pre-demod output matrix
// generate sequence
for (i=0; i<num_sync_symbols; i++) {
float sym_i = rand() % 2 ? M_SQRT1_2 : -M_SQRT1_2;
float sym_q = rand() % 2 ? M_SQRT1_2 : -M_SQRT1_2;
seq[i] = sym_i + _Complex_I*sym_q;
}
// create interpolated sequence, compensating for filter delay
firinterp_crcf interp_seq = firinterp_crcf_create_rnyquist(LIQUID_RNYQUIST_RRC,k,m,beta,0.0f);
for (i=0; i<num_sync_symbols+m; i++) {
if (i < m) firinterp_crcf_execute(interp_seq, seq[i], &s0[0]);
else if (i < num_sync_symbols) firinterp_crcf_execute(interp_seq, seq[i], &s0[k*(i-m)]);
else firinterp_crcf_execute(interp_seq, 0, &s0[k*(i-m)]);
}
firinterp_crcf_destroy(interp_seq);
// compute g = E{ |s0|^2 }
float g = 0.0f;
for (i=0; i<num_sync_samples; i++)
g += crealf( s0[i]*conjf(s0[i]) );
// create transmit interpolator and generate sequence
firinterp_crcf interp_tx = firinterp_crcf_create_rnyquist(LIQUID_RNYQUIST_RRC,k,m,beta,dt);
unsigned int n=0;
for (i=0; i<num_delay_symbols; i++) {
firinterp_crcf_execute(interp_tx, 0, &x[k*n]);
n++;
}
for (i=0; i<num_sync_symbols; i++) {
firinterp_crcf_execute(interp_tx, seq[i], &x[k*n]);
n++;
}
for (i=0; i<2*m; i++) {
firinterp_crcf_execute(interp_tx, 0, &x[k*n]);
n++;
}
assert(n==num_symbols);
firinterp_crcf_destroy(interp_tx);
// add channel impairments
for (i=0; i<num_samples; i++) {
y[i] = x[i]*cexp(_Complex_I*(dphi*i + phi)) + nstd*( randnf() + _Complex_I*randnf() );
}
float complex z; // filter output sample
for (n=0; n<num_dphi_hat; n++) {
float dphi_hat = ((float)n - 0.5*(float)(num_dphi_hat-1)) * dphi_hat_step;
printf(" dphi_hat : %12.8f\n", dphi_hat);
// create flipped, conjugated coefficients
float complex s1[num_sync_samples];
for (i=0; i<num_sync_samples; i++)
s1[i] = conjf( s0[num_sync_samples-i-1]*cexpf(_Complex_I*(dphi_hat*i)) );
// create matched filter and detect signal
firfilt_cccf fsync = firfilt_cccf_create(s1, num_sync_samples);
for (i=0; i<num_samples; i++) {
firfilt_cccf_push(fsync, y[i]);
firfilt_cccf_execute(fsync, &z);
rxy[n][i] = cabsf(z) / g;
}
// destroy filter
firfilt_cccf_destroy(fsync);
}
// print results
//printf("rxy (max) : %12.8f\n", rxy_max);
//
// 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,"m = %u;\n", m);
fprintf(fid,"beta = %f;\n", beta);
fprintf(fid,"num_sync_symbols = %u;\n", num_sync_symbols);
fprintf(fid,"num_sync_samples = k*num_sync_symbols;\n");
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"num_dphi_hat = %u;\n", num_dphi_hat);
fprintf(fid,"dphi_hat_step = %f;\n", dphi_hat_step);
// save sequence symbols
fprintf(fid,"seq = zeros(1,num_sync_symbols);\n");
for (i=0; i<num_sync_symbols; i++)
fprintf(fid,"seq(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(seq[i]), cimagf(seq[i]));
// save interpolated sequence
fprintf(fid,"s = zeros(1,num_sync_samples);\n");
for (i=0; i<num_sync_samples; i++)
fprintf(fid,"s(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(s0[i]), cimagf(s0[i]));
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(%6u) = %12.8f + j*%12.8f;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%6u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
}
// save cross-correlation output
fprintf(fid,"rxy = zeros(num_dphi_hat,num_samples);\n");
for (n=0; n<num_dphi_hat; n++) {
for (i=0; i<num_samples; i++) {
fprintf(fid,"rxy(%6u,%6u) = %12.8f;\n", n+1, i+1, rxy[n][i]);
}
}
fprintf(fid,"t=[0:(num_samples-1)]/k;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(1:length(s),real(s), 1:length(s),imag(s));\n");
fprintf(fid,"dphi_hat = ( [0:(num_dphi_hat-1)] - (num_dphi_hat-1)/2 ) * dphi_hat_step;\n");
fprintf(fid,"mesh(dphi_hat, t, rxy');\n");
#if 0
fprintf(fid,"z = abs( z );\n");
fprintf(fid,"[zmax i] = max(z);\n");
fprintf(fid,"plot(1:length(z),z,'-x');\n");
fprintf(fid,"axis([(i-8*k) (i+8*k) 0 zmax*1.2]);\n");
fprintf(fid,"grid on\n");
#endif
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
int main() {
// spectral periodogram options
unsigned int nfft=512; // spectral periodogram FFT size
unsigned int num_samples = 4000; // number of samples
float beta = 10.0f; // Kaiser-Bessel window parameter
float noise_floor = -60.0f; // noise floor [dB]
unsigned int i;
// derived values
float nstd = powf(10.0f, noise_floor/20.0f);
// allocate memory for data arrays
float complex X[nfft]; // output spectrum
float psd[nfft]; // power spectral density
// initialize PSD estimate
for (i=0; i<nfft; i++)
psd[i] = 0.0f;
// create spectral periodogram
unsigned int window_size = nfft/2; // spgram window size
unsigned int delay = nfft/8; // samples between transforms
spgram q = spgram_create_kaiser(nfft, window_size, beta);
// generate signal (interpolated symbols with noise)
unsigned int k = 4; // interpolation rate
unsigned int m = 7; // filter delay (symbols)
firinterp_crcf interp = firinterp_crcf_create_rnyquist(LIQUID_RNYQUIST_RKAISER, k, m, 0.3f, 0.0f);
int spgram_timer = nfft;
unsigned int n=0;
float complex x[k]; // interpolator output
unsigned int num_transforms = 0;
while (n < num_samples) {
// generate random symbol
float complex s = ( rand() % 2 ? 0.707f : -0.707f ) +
( rand() % 2 ? 0.707f : -0.707f ) * _Complex_I;
// interpolate
firinterp_crcf_execute(interp, s, x);
// add noise
for (i=0; i<k; i++)
x[i] += nstd * ( randnf() + _Complex_I*randnf() ) * M_SQRT1_2;
// push resulting samples through spgram
spgram_push(q, x, k);
//
spgram_timer -= k;
n += k;
//
if (spgram_timer <= 0) {
// update timer, counter
spgram_timer += delay;
num_transforms++;
// run spectral periodogram
spgram_execute(q, X);
// accumulate PSD and FFT shift
for (i=0; i<nfft; i++) {
float complex X0 = X[(i+nfft/2)%nfft];
psd[i] += crealf(X0*conjf(X0));
}
}
}
// destroy objects
firinterp_crcf_destroy(interp);
spgram_destroy(q);
// normalize result
printf("computed %u transforms\n", num_transforms);
// TODO: ensure at least one transform was taken
for (i=0; i<nfft; i++)
psd[i] = 10*log10f( psd[i] / (float)(num_transforms) );
//
// export 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\n");
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"H = zeros(1,nfft);\n");
fprintf(fid,"noise_floor = %12.6f;\n", noise_floor);
for (i=0; i<nfft; i++)
fprintf(fid,"H(%6u) = %12.4e;\n", i+1, psd[i]);
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f, H, '-', 'LineWidth',1.5);\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('Power Spectral Density [dB]');\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"ymin = 10*floor([noise_floor-20]/10);\n");
fprintf(fid,"ymax = 10*floor([noise_floor+80]/10);\n");
fprintf(fid,"axis([-0.5 0.5 ymin ymax]);\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
