ModemKit *ModemFMStereo::buildKit(long long sampleRate, int audioSampleRate) {
ModemKitFMStereo *kit = new ModemKitFMStereo;
kit->audioResampleRatio = double(audioSampleRate) / double(sampleRate);
kit->sampleRate = sampleRate;
kit->audioSampleRate = audioSampleRate;
float As = 60.0f; // stop-band attenuation [dB]
kit->audioResampler = msresamp_rrrf_create(kit->audioResampleRatio, As);
kit->stereoResampler = msresamp_rrrf_create(kit->audioResampleRatio, As);
// Stereo filters / shifters
double firStereoCutoff = 16000.0 / double(audioSampleRate);
// filter transition
float ft = 1000.0f / double(audioSampleRate);
// fractional timing offset
float mu = 0.0f;
if (firStereoCutoff < 0) {
firStereoCutoff = 0;
}
if (firStereoCutoff > 0.5) {
firStereoCutoff = 0.5;
}
unsigned int h_len = estimate_req_filter_len(ft, As);
float *h = new float[h_len];
liquid_firdes_kaiser(h_len, firStereoCutoff, As, mu, h);
kit->firStereoLeft = firfilt_rrrf_create(h, h_len);
kit->firStereoRight = firfilt_rrrf_create(h, h_len);
// stereo pilot filter
float bw = float(sampleRate);
if (bw < 100000.0) {
bw = 100000.0;
}
unsigned int order = 5; // filter order
float f0 = ((float) 19000 / bw);
float fc = ((float) 19500 / bw);
float Ap = 1.0f;
kit->iirStereoPilot = iirfilt_crcf_create_prototype(LIQUID_IIRDES_CHEBY2, LIQUID_IIRDES_BANDPASS, LIQUID_IIRDES_SOS, order, fc, f0, Ap, As);
kit->firStereoR2C = firhilbf_create(5, 60.0f);
kit->firStereoC2R = firhilbf_create(5, 60.0f);
kit->stereoPilot = nco_crcf_create(LIQUID_VCO);
nco_crcf_reset(kit->stereoPilot);
nco_crcf_pll_set_bandwidth(kit->stereoPilot, 0.25f);
return kit;
}
//
// test phase-locked loop
// _type : NCO type (e.g. LIQUID_NCO)
// _phase_offset : initial phase offset
// _freq_offset : initial frequency offset
// _pll_bandwidth : bandwidth of phase-locked loop
// _num_iterations : number of iterations to run
// _tol : error tolerance
void nco_crcf_pll_test(int _type,
float _phase_offset,
float _freq_offset,
float _pll_bandwidth,
unsigned int _num_iterations,
float _tol)
{
// objects
nco_crcf nco_tx = nco_crcf_create(_type);
nco_crcf nco_rx = nco_crcf_create(_type);
// initialize objects
nco_crcf_set_phase(nco_tx, _phase_offset);
nco_crcf_set_frequency(nco_tx, _freq_offset);
nco_crcf_pll_set_bandwidth(nco_rx, _pll_bandwidth);
// run loop
unsigned int i;
float phase_error;
float complex r, v;
for (i=0; i<_num_iterations; i++) {
// received complex signal
nco_crcf_cexpf(nco_tx,&r);
nco_crcf_cexpf(nco_rx,&v);
// error estimation
phase_error = cargf(r*conjf(v));
// update pll
nco_crcf_pll_step(nco_rx, phase_error);
// update nco objects
nco_crcf_step(nco_tx);
nco_crcf_step(nco_rx);
}
// ensure phase of oscillators is locked
float nco_tx_phase = nco_crcf_get_phase(nco_tx);
float nco_rx_phase = nco_crcf_get_phase(nco_rx);
CONTEND_DELTA(nco_tx_phase, nco_rx_phase, _tol);
// ensure frequency of oscillators is locked
float nco_tx_freq = nco_crcf_get_frequency(nco_tx);
float nco_rx_freq = nco_crcf_get_frequency(nco_rx);
CONTEND_DELTA(nco_tx_freq, nco_rx_freq, _tol);
// clean it up
nco_crcf_destroy(nco_tx);
nco_crcf_destroy(nco_rx);
}
// create ampmodem object
// _m : modulation index
// _fc : carrier frequency
// _type : AM type (e.g. LIQUID_AMPMODEM_DSB)
// _suppressed_carrier : carrier suppression flag
ampmodem ampmodem_create(float _m,
float _fc,
liquid_ampmodem_type _type,
int _suppressed_carrier)
{
ampmodem q = (ampmodem) malloc(sizeof(struct ampmodem_s));
q->type = _type;
q->m = _m;
q->fc = _fc;
q->suppressed_carrier = (_suppressed_carrier == 0) ? 0 : 1;
// create nco, pll objects
q->oscillator = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(q->oscillator, 2*M_PI*q->fc);
nco_crcf_pll_set_bandwidth(q->oscillator,0.05f);
// suppressed carrier
q->ssb_alpha = 0.01f;
q->ssb_q_hat = 0.0f;
// single side-band
q->hilbert = firhilbf_create(9, 60.0f);
// double side-band
ampmodem_reset(q);
// debugging
#if DEBUG_AMPMODEM
q->debug_x = windowcf_create(DEBUG_AMPMODEM_BUFFER_LEN);
q->debug_phase_error = windowf_create(DEBUG_AMPMODEM_BUFFER_LEN);
q->debug_freq_error = windowf_create(DEBUG_AMPMODEM_BUFFER_LEN);
#endif
return q;
}
// 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) );
// parameters
float phase_offset = M_PI/10;
float frequency_offset = 0.001f;
float SNRdB = 30.0f;
float pll_bandwidth = 0.02f;
modulation_scheme ms = LIQUID_MODEM_QPSK;
unsigned int n=256; // number of iterations
int dopt;
while ((dopt = getopt(argc,argv,"uhs:b:n:P:F:m:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 's': SNRdB = atof(optarg); break;
case 'b': pll_bandwidth = atof(optarg); break;
case 'n': n = atoi(optarg); break;
case 'P': phase_offset = atof(optarg); break;
case 'F': frequency_offset= atof(optarg); break;
case 'm':
ms = liquid_getopt_str2mod(optarg);
if (ms == LIQUID_MODEM_UNKNOWN) {
fprintf(stderr,"error: %s, unknown/unsupported modulation scheme \"%s\"\n", argv[0], optarg);
return 1;
}
break;
default:
exit(1);
}
}
unsigned int d=n/32; // print every "d" lines
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid, "%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid, "clear all;\n");
fprintf(fid, "phi=zeros(1,%u);\n",n);
fprintf(fid, "r=zeros(1,%u);\n",n);
// objects
nco_crcf nco_tx = nco_crcf_create(LIQUID_VCO);
nco_crcf nco_rx = nco_crcf_create(LIQUID_VCO);
modem mod = modem_create(ms);
modem demod = modem_create(ms);
unsigned int bps = modem_get_bps(mod);
// initialize objects
nco_crcf_set_phase(nco_tx, phase_offset);
nco_crcf_set_frequency(nco_tx, frequency_offset);
nco_crcf_pll_set_bandwidth(nco_rx, pll_bandwidth);
float noise_power = powf(10.0f, -SNRdB/20.0f);
// print parameters
printf("PLL example :\n");
printf("modem : %u-%s\n", 1<<bps, modulation_types[ms].name);
printf("frequency offset: %6.3f, phase offset: %6.3f, SNR: %6.2fdB, pll b/w: %6.3f\n",
frequency_offset, phase_offset, SNRdB, pll_bandwidth);
// run loop
unsigned int i, M=1<<bps, sym_in, sym_out, num_errors=0;
float phase_error;
float complex x, r, v, noise;
for (i=0; i<n; i++) {
// generate random symbol
sym_in = rand() % M;
// modulate
modem_modulate(mod, sym_in, &x);
// channel
//r = nco_crcf_cexpf(nco_tx);
nco_crcf_mix_up(nco_tx, x, &r);
// add complex white noise
crandnf(&noise);
r += noise * noise_power;
//
//v = nco_crcf_cexpf(nco_rx);
nco_crcf_mix_down(nco_rx, r, &v);
// demodulate
modem_demodulate(demod, v, &sym_out);
num_errors += count_bit_errors(sym_in, sym_out);
// error estimation
//phase_error = cargf(r*conjf(v));
phase_error = modem_get_demodulator_phase_error(demod);
// perfect error estimation
//phase_error = nco_tx->theta - nco_rx->theta;
// print every line in a format that octave can read
fprintf(fid, "phi(%u) = %10.6E;\n", i+1, phase_error);
fprintf(fid, "r(%u) = %10.6E + j*%10.6E;\n",
i+1, crealf(v), cimagf(v));
if ((i+1)%d == 0 || i==n-1) {
printf(" %4u: e_hat : %6.3f, phase error : %6.3f, freq error : %6.3f\n",
i+1, // iteration
phase_error, // estimated phase error
nco_crcf_get_phase(nco_tx) - nco_crcf_get_phase(nco_rx),// true phase error
nco_crcf_get_frequency(nco_tx) - nco_crcf_get_frequency(nco_rx)// true frequency error
);
}
// update tx nco object
nco_crcf_step(nco_tx);
// update pll
nco_crcf_pll_step(nco_rx, phase_error);
// update rx nco object
nco_crcf_step(nco_rx);
}
fprintf(fid, "figure;\n");
fprintf(fid, "plot(1:length(phi),phi,'LineWidth',2,'Color',[0 0.25 0.5]);\n");
fprintf(fid, "xlabel('Symbol Index');\n");
fprintf(fid, "ylabel('Phase Error [radians]');\n");
fprintf(fid, "grid on;\n");
fprintf(fid, "t0 = round(0.25*length(r));\n");
fprintf(fid, "figure;\n");
fprintf(fid, "plot(r(1:t0),'x','Color',[0.6 0.6 0.6],r(t0:end),'x','Color',[0 0.25 0.5]);\n");
fprintf(fid, "grid on;\n");
fprintf(fid, "axis([-1.5 1.5 -1.5 1.5]);\n");
fprintf(fid, "axis('square');\n");
fprintf(fid, "xlabel('In-Phase');\n");
fprintf(fid, "ylabel('Quadrature');\n");
fprintf(fid, "legend(['first 25%%'],['last 75%%'],1);\n");
fclose(fid);
printf("results written to %s.\n",OUTPUT_FILENAME);
nco_crcf_destroy(nco_tx);
nco_crcf_destroy(nco_rx);
modem_destroy(mod);
modem_destroy(demod);
printf("bit errors: %u / %u\n", num_errors, bps*n);
printf("done.\n");
return 0;
}
// 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;
q->m = 7; // filter delay (symbols)
q->beta = 0.3f; // excess bandwidth factor
unsigned int i;
// generate p/n sequence
q->preamble_pn = (float complex*) malloc(64*sizeof(float complex));
q->preamble_rx = (float complex*) malloc(64*sizeof(float complex));
msequence ms = msequence_create(7, 0x0089, 1);
for (i=0; i<64; i++) {
q->preamble_pn[i] = (msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2) +
(msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2)*_Complex_I;
}
msequence_destroy(ms);
// create frame detector
unsigned int k = 2; // samples/symbol
q->detector = qdetector_cccf_create_linear(q->preamble_pn, 64, LIQUID_FIRFILT_ARKAISER, k, q->m, q->beta);
qdetector_cccf_set_threshold(q->detector, 0.5f);
// 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,k,q->m,q->beta);
#if FLEXFRAMESYNC_ENABLE_EQ
// create equalizer
unsigned int p = 3;
q->equalizer = eqlms_cccf_create_lowpass(2*k*p+1, 0.4f);
eqlms_cccf_set_bw(q->equalizer, 0.05f);
#endif
// create down-coverters for carrier phase tracking
q->mixer = nco_crcf_create(LIQUID_NCO);
q->pll = nco_crcf_create(LIQUID_NCO);
nco_crcf_pll_set_bandwidth(q->pll, 1e-4f); // very low bandwidth
// header demodulator/decoder
q->header_dec = (unsigned char *) malloc(FLEXFRAME_H_DEC*sizeof(unsigned char));
q->header_decoder = qpacketmodem_create();
qpacketmodem_configure(q->header_decoder,
FLEXFRAME_H_DEC,
FLEXFRAME_H_CRC,
FLEXFRAME_H_FEC0,
FLEXFRAME_H_FEC1,
LIQUID_MODEM_QPSK);
q->header_mod_len = qpacketmodem_get_frame_len(q->header_decoder);
q->header_mod = (float complex*) malloc(q->header_mod_len*sizeof(float complex));
// header pilot synchronizer
q->header_pilotsync = qpilotsync_create(q->header_mod_len, 16);
q->header_sym_len = qpilotsync_get_frame_len(q->header_pilotsync);
q->header_sym = (float complex*) malloc(q->header_sym_len*sizeof(float complex));
// payload demodulator for phase recovery
q->payload_demod = modem_create(LIQUID_MODEM_QPSK);
// create payload demodulator/decoder object
q->payload_dec_len = 64;
int check = LIQUID_CRC_24;
int fec0 = LIQUID_FEC_NONE;
int fec1 = LIQUID_FEC_GOLAY2412;
int mod_scheme = LIQUID_MODEM_QPSK;
q->payload_decoder = qpacketmodem_create();
qpacketmodem_configure(q->payload_decoder, q->payload_dec_len, check, fec0, fec1, mod_scheme);
//qpacketmodem_print(q->payload_decoder);
//assert( qpacketmodem_get_frame_len(q->payload_decoder)==600 );
q->payload_sym_len = qpacketmodem_get_frame_len(q->payload_decoder);
// allocate memory for payload symbols and recovered data bytes
q->payload_sym = (float complex*) malloc(q->payload_sym_len*sizeof(float complex));
q->payload_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
// reset global data counters
flexframesync_reset_framedatastats(q);
#if DEBUG_FLEXFRAMESYNC
// set debugging flags, objects to NULL
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_qdetector_flush = 0;
q->debug_x = NULL;
#endif
// reset state and return
flexframesync_reset(q);
return q;
}
int main(int argc, char*argv[])
{
//srand(time(NULL));
// options
unsigned int num_symbols=800; // number of symbols to observe
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
float fc = 0.002f; // carrier offset
unsigned int hc_len=5; // channel filter length
unsigned int k=2; // matched filter samples/symbol
unsigned int m=3; // matched filter delay (symbols)
float beta=0.3f; // matched filter excess bandwidth factor
unsigned int p=3; // equalizer length (symbols, hp_len = 2*k*p+1)
float mu = 0.08f; // equalizer learning rate
// modulation type/depth
modulation_scheme ms = LIQUID_MODEM_QPSK;
int dopt;
while ((dopt = getopt(argc,argv,"hn:s:c:k:m:b:p:u:M:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'n': num_symbols = atoi(optarg); break;
case 's': SNRdB = atof(optarg); break;
case 'c': hc_len = atoi(optarg); break;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'p': p = atoi(optarg); break;
case 'u': mu = atof(optarg); break;
case 'M':
ms = liquid_getopt_str2mod(optarg);
if (ms == LIQUID_MODEM_UNKNOWN) {
fprintf(stderr,"error: %s, unknown/unsupported modulation scheme '%s'\n", argv[0], optarg);
return 1;
}
break;
default:
exit(1);
}
}
// validate input
if (num_symbols == 0) {
fprintf(stderr,"error: %s, number of symbols must be greater than zero\n", argv[0]);
exit(1);
} else if (hc_len == 0) {
fprintf(stderr,"error: %s, channel must have at least 1 tap\n", argv[0]);
exit(1);
} else if (k < 2) {
fprintf(stderr,"error: %s, samples/symbol must be at least 2\n", argv[0]);
exit(1);
} else if (m == 0) {
fprintf(stderr,"error: %s, filter semi-length must be at least 1 symbol\n", argv[0]);
exit(1);
} else if (beta < 0.0f || beta > 1.0f) {
fprintf(stderr,"error: %s, filter excess bandwidth must be in [0,1]\n", argv[0]);
exit(1);
} else if (p == 0) {
fprintf(stderr,"error: %s, equalizer semi-length must be at least 1 symbol\n", argv[0]);
exit(1);
} else if (mu < 0.0f || mu > 1.0f) {
fprintf(stderr,"error: %s, equalizer learning rate must be in [0,1]\n", argv[0]);
exit(1);
}
// derived values
unsigned int hm_len = 2*k*m+1; // matched filter length
unsigned int hp_len = 2*k*p+1; // equalizer filter length
unsigned int num_samples = k*num_symbols;
// bookkeeping variables
float complex syms_tx[num_symbols]; // transmitted data symbols
float complex x[num_samples]; // interpolated time series
float complex y[num_samples]; // channel output
float complex z[num_samples]; // equalized output
float complex syms_rx[num_symbols]; // received data symbols
float hm[hm_len]; // matched filter response
float complex hc[hc_len]; // channel filter coefficients
float complex hp[hp_len]; // equalizer filter coefficients
unsigned int i;
// generate matched filter response
liquid_firdes_rnyquist(LIQUID_FIRFILT_RRC, k, m, beta, 0.0f, hm);
firinterp_crcf interp = firinterp_crcf_create(k, hm, hm_len);
// create the modem objects
modem mod = modem_create(ms);
modem demod = modem_create(ms);
unsigned int M = 1 << modem_get_bps(mod);
// generate channel impulse response, filter
hc[0] = 1.0f;
for (i=1; i<hc_len; i++)
hc[i] = 0.09f*(randnf() + randnf()*_Complex_I);
firfilt_cccf fchannel = firfilt_cccf_create(hc, hc_len);
// generate random symbols
for (i=0; i<num_symbols; i++)
modem_modulate(mod, rand()%M, &syms_tx[i]);
// interpolate
for (i=0; i<num_symbols; i++)
firinterp_crcf_execute(interp, syms_tx[i], &x[i*k]);
// push through channel
float nstd = powf(10.0f, -SNRdB/20.0f);
for (i=0; i<num_samples; i++) {
firfilt_cccf_push(fchannel, x[i]);
firfilt_cccf_execute(fchannel, &y[i]);
// add carrier offset and noise
y[i] *= cexpf(_Complex_I*2*M_PI*fc*i);
y[i] += nstd*(randnf() + randnf()*_Complex_I)*M_SQRT1_2;
}
// push through equalizer
// create equalizer, intialized with square-root Nyquist filter
eqlms_cccf eq = eqlms_cccf_create_rnyquist(LIQUID_FIRFILT_RRC, k, p, beta, 0.0f);
eqlms_cccf_set_bw(eq, mu);
// get initialized weights
eqlms_cccf_get_weights(eq, hp);
// filtered error vector magnitude (emperical RMS error)
float evm_hat = 0.03f;
// nco/pll for phase recovery
nco_crcf nco = nco_crcf_create(LIQUID_VCO);
nco_crcf_pll_set_bandwidth(nco, 0.02f);
float complex d_hat = 0.0f;
unsigned int num_symbols_rx = 0;
for (i=0; i<num_samples; i++) {
// print filtered evm (emperical rms error)
if ( ((i+1)%50)==0 )
printf("%4u : rms error = %12.8f dB\n", i+1, 10*log10(evm_hat));
eqlms_cccf_push(eq, y[i]);
eqlms_cccf_execute(eq, &d_hat);
// store output
z[i] = d_hat;
// decimate by k
if ( (i%k) != 0 ) continue;
// update equalizer independent of the signal: estimate error
// assuming constant modulus signal
eqlms_cccf_step(eq, d_hat/cabsf(d_hat), d_hat);
// apply carrier recovery
float complex v;
nco_crcf_mix_down(nco, d_hat, &v);
// save resulting data symbol
if (num_symbols_rx < num_symbols)
syms_rx[num_symbols_rx++] = v;
// demodulate
unsigned int sym_out; // output symbol
float complex d_prime; // estimated input sample
modem_demodulate(demod, v, &sym_out);
modem_get_demodulator_sample(demod, &d_prime);
float phase_error = modem_get_demodulator_phase_error(demod);
// update pll
nco_crcf_pll_step(nco, phase_error);
// update rx nco object
nco_crcf_step(nco);
// update filtered evm estimate
float evm = crealf( (d_prime-v)*conjf(d_prime-v) );
evm_hat = 0.98f*evm_hat + 0.02f*evm;
}
// get equalizer weights
eqlms_cccf_get_weights(eq, hp);
// destroy objects
eqlms_cccf_destroy(eq);
nco_crcf_destroy(nco);
firinterp_crcf_destroy(interp);
firfilt_cccf_destroy(fchannel);
modem_destroy(mod);
modem_destroy(demod);
//
// export output
//
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,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = num_symbols*k;\n");
// save transmit matched-filter response
fprintf(fid,"hm_len = 2*k*m+1;\n");
fprintf(fid,"hm = zeros(1,hm_len);\n");
for (i=0; i<hm_len; i++)
fprintf(fid,"hm(%4u) = %12.4e;\n", i+1, hm[i]);
// save channel impulse response
fprintf(fid,"hc_len = %u;\n", hc_len);
fprintf(fid,"hc = zeros(1,hc_len);\n");
for (i=0; i<hc_len; i++)
fprintf(fid,"hc(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(hc[i]), cimagf(hc[i]));
// save equalizer response
fprintf(fid,"hp_len = %u;\n", hp_len);
fprintf(fid,"hp = zeros(1,hp_len);\n");
for (i=0; i<hp_len; i++)
fprintf(fid,"hp(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(hp[i]), cimagf(hp[i]));
// save sample sets
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
fprintf(fid,"z = zeros(1,num_samples);\n");
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]));
fprintf(fid,"z(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(z[i]), cimagf(z[i]));
}
fprintf(fid,"syms_rx = zeros(1,num_symbols);\n");
for (i=0; i<num_symbols; i++) {
fprintf(fid,"syms_rx(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(syms_rx[i]), cimagf(syms_rx[i]));
}
// plot time response
fprintf(fid,"t = 0:(num_samples-1);\n");
fprintf(fid,"tsym = 1:k:num_samples;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(t,real(z),...\n");
fprintf(fid," t(tsym),real(z(tsym)),'x');\n");
// plot constellation
fprintf(fid,"syms_rx_0 = syms_rx(1:(length(syms_rx)/2));\n");
fprintf(fid,"syms_rx_1 = syms_rx((length(syms_rx)/2):end);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(real(syms_rx_0),imag(syms_rx_0),'x','Color',[1 1 1]*0.7,...\n");
fprintf(fid," real(syms_rx_1),imag(syms_rx_1),'x','Color',[1 1 1]*0.0);\n");
fprintf(fid,"xlabel('In-Phase');\n");
fprintf(fid,"ylabel('Quadrature');\n");
fprintf(fid,"axis([-1 1 -1 1]*1.5);\n");
fprintf(fid,"axis square;\n");
fprintf(fid,"grid on;\n");
// compute composite response
fprintf(fid,"g = real(conv(conv(hm,hc),hp));\n");
// plot responses
fprintf(fid,"nfft = 1024;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"Hm = 20*log10(abs(fftshift(fft(hm/k,nfft))));\n");
fprintf(fid,"Hc = 20*log10(abs(fftshift(fft(hc, nfft))));\n");
fprintf(fid,"Hp = 20*log10(abs(fftshift(fft(hp, nfft))));\n");
fprintf(fid,"G = 20*log10(abs(fftshift(fft(g/k, nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f,Hm, f,Hc, f,Hp, f,G,'-k','LineWidth',2, [-0.5/k 0.5/k],[-6.026 -6.026],'or');\n");
fprintf(fid,"xlabel('Normalized Frequency');\n");
fprintf(fid,"ylabel('Power Spectral Density');\n");
fprintf(fid,"legend('transmit','channel','equalizer','composite','half-power points','location','northeast');\n");
fprintf(fid,"axis([-0.5 0.5 -12 8]);\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
int main(int argc, char*argv[])
{
// set random seed
srand( time(NULL) );
// parameters
float phase_offset = 0.0f; // initial phase offset
float frequency_offset = 0.40f; // initial frequency offset
float pll_bandwidth = 0.003f; // phase-locked loop bandwidth
unsigned int n = 512; // number of iterations
int dopt;
while ((dopt = getopt(argc,argv,"uhb:n:p:f:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'b': pll_bandwidth = atof(optarg); break;
case 'n': n = atoi(optarg); break;
case 'p': phase_offset = atof(optarg); break;
case 'f': frequency_offset= atof(optarg); break;
default:
exit(1);
}
}
// objects
nco_crcf nco_tx = nco_crcf_create(LIQUID_VCO);
nco_crcf nco_rx = nco_crcf_create(LIQUID_VCO);
// initialize objects
nco_crcf_set_phase(nco_tx, phase_offset);
nco_crcf_set_frequency(nco_tx, frequency_offset);
nco_crcf_pll_set_bandwidth(nco_rx, pll_bandwidth);
// generate input
float complex x[n];
float complex y[n];
float phase_error[n];
unsigned int i;
for (i=0; i<n; i++) {
// generate complex sinusoid
nco_crcf_cexpf(nco_tx, &x[i]);
// update nco
nco_crcf_step(nco_tx);
}
// run loop
for (i=0; i<n; i++) {
#if 0
// test resetting bandwidth in middle of acquisition
if (i == 100) nco_pll_set_bandwidth(nco_rx, pll_bandwidth*0.2f);
#endif
// generate input
nco_crcf_cexpf(nco_rx, &y[i]);
// update rx nco object
nco_crcf_step(nco_rx);
// compute phase error
phase_error[i] = cargf(x[i]*conjf(y[i]));
// update pll
nco_crcf_pll_step(nco_rx, phase_error[i]);
// print phase error
if ( (i+1)%50 == 0 || i==n-1 || i==0)
printf("%4u : phase error = %12.8f\n", i+1, phase_error[i]);
}
nco_crcf_destroy(nco_tx);
nco_crcf_destroy(nco_rx);
// write 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 = %u;\n", n);
fprintf(fid,"x = zeros(1,n);\n");
fprintf(fid,"y = zeros(1,n);\n");
for (i=0; i<n; 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]));
fprintf(fid,"e(%4u) = %12.4e;\n", i+1, phase_error[i]);
}
fprintf(fid,"t=0:(n-1);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(t,real(x),'Color',[1 1 1]*0.8);\n");
fprintf(fid," plot(t,real(y),'Color',[0 0.2 0.5]);\n");
fprintf(fid," hold off;\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('real');\n");
fprintf(fid," axis([0 n -1.2 1.2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(t,imag(x),'Color',[1 1 1]*0.8);\n");
fprintf(fid," plot(t,imag(y),'Color',[0 0.5 0.2]);\n");
fprintf(fid," hold off;\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('imag');\n");
fprintf(fid," axis([0 n -1.2 1.2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," plot(t,e,'Color',[0.5 0 0]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('phase error');\n");
fprintf(fid," axis([0 n -pi pi]);\n");
fprintf(fid," grid on;\n");
fclose(fid);
printf("results written to %s.\n",OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
