int main() {
// options
unsigned int num_channels=6; // for now, must be even number
unsigned int num_symbols=32; // num symbols
unsigned int m=2; // ofdm/oqam symbol delay
float beta = 0.99f; // excess bandwidth factor
float dt = 0.0f; // timing offset (fractional sample)
modulation_scheme ms = LIQUID_MODEM_QAM4; // modulation scheme
// number of frames (compensate for filter delay)
unsigned int num_frames = num_symbols + 2*m;
unsigned int num_samples = num_channels * num_frames;
// create synthesizer/analyzer objects
ofdmoqam cs = ofdmoqam_create(num_channels, m, beta, dt, LIQUID_SYNTHESIZER,0);
ofdmoqam ca = ofdmoqam_create(num_channels, m, beta, dt, LIQUID_ANALYZER,0);
// modem
modem mod = modem_create(ms);
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\nclose all;\n\n");
fprintf(fid,"num_channels=%u;\n", num_channels);
fprintf(fid,"num_symbols=%u;\n", num_symbols);
fprintf(fid,"num_frames = %u;\n", num_frames);
fprintf(fid,"num_samples = num_frames*num_channels;\n");
fprintf(fid,"X = zeros(%u,%u);\n", num_channels, num_frames);
fprintf(fid,"y = zeros(1,%u);\n", num_samples);
fprintf(fid,"Y = zeros(%u,%u);\n", num_channels, num_frames);
unsigned int i, j, n=0;
unsigned int s[num_symbols][num_channels];
float complex X[num_channels]; // channelized symbols
float complex y[num_channels]; // interpolated time-domain samples
float complex Y[num_channels]; // received symbols
// generate random symbols
for (i=0; i<num_symbols; i++) {
for (j=0; j<num_channels; j++) {
s[i][j] = modem_gen_rand_sym(mod);
}
}
for (i=0; i<num_frames; i++) {
// generate frame data
for (j=0; j<num_channels; j++) {
if (i<num_symbols) {
modem_modulate(mod,s[i][j],&X[j]);
} else {
X[j] = 0.0f;
}
}
// execute synthesyzer
ofdmoqam_execute(cs, X, y);
// channel
// execute analyzer
ofdmoqam_execute(ca, y, Y);
// write output to file
for (j=0; j<num_channels; j++) {
// frequency data
fprintf(fid,"X(%4u,%4u) = %12.4e + j*%12.4e;\n", j+1, i+1, crealf(X[j]), cimagf(X[j]));
// time data
fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", n+1, crealf(y[j]), cimag(y[j]));
// received data
fprintf(fid,"Y(%4u,%4u) = %12.4e + j*%12.4e;\n", j+1, i+1, crealf(Y[j]), cimagf(Y[j]));
n++;
}
}
// print results
fprintf(fid,"\n\n");
fprintf(fid,"X0 = X(:,1:%u);\n", num_symbols);
fprintf(fid,"Y0 = Y(:,%u:%u);\n", 2*m+1, num_symbols + 2*m);
fprintf(fid,"for i=1:num_channels,\n");
fprintf(fid," figure;\n");
fprintf(fid," subplot(2,1,1);\n");
fprintf(fid," plot(1:num_symbols,real(X0(i,:)),'-x',1:num_symbols,real(Y0(i,:)),'-x');\n");
fprintf(fid," ylabel('Re');\n");
fprintf(fid," title(['channel ' num2str(i-1)]);\n");
fprintf(fid," subplot(2,1,2);\n");
fprintf(fid," plot(1:num_symbols,imag(X0(i,:)),'-x',1:num_symbols,imag(Y0(i,:)),'-x');\n");
fprintf(fid," ylabel('Im');\n");
fprintf(fid," pause(0.2);\n");
fprintf(fid,"end;\n");
// print results
fprintf(fid,"\n\n");
fprintf(fid,"t = 0:(num_samples-1);\n");
fprintf(fid," figure;\n");
fprintf(fid," plot(t,real(y),'-', t,imag(y),'-');\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('signal');\n");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
// destroy objects
ofdmoqam_destroy(cs);
ofdmoqam_destroy(ca);
modem_destroy(mod);
printf("done.\n");
return 0;
}
int main() {
// options
unsigned int num_channels=64; // must be even number
unsigned int num_symbols=16; // number of symbols
unsigned int m=3; // filter delay (symbols)
float beta = 0.9f; // filter excess bandwidth factor
float phi = 0.0f; // carrier phase offset;
float dphi = 0.04f; // carrier frequency offset
// number of frames (compensate for filter delay)
unsigned int num_frames = num_symbols + 2*m;
unsigned int num_samples = num_channels * num_frames;
unsigned int i;
unsigned int j;
// create filter prototype
unsigned int h_len = 2*num_channels*m + 1;
float h[h_len];
float complex hc[h_len];
float complex gc[h_len];
liquid_firdes_rkaiser(num_channels, m, beta, 0.0f, h);
unsigned int g_len = 2*num_channels*m;
for (i=0; i<g_len; i++) {
hc[i] = h[i];
gc[i] = h[g_len-i-1] * cexpf(_Complex_I*dphi*i);
}
// data arrays
float complex s[num_channels]; // input symbols
float complex y[num_samples]; // time-domain samples
float complex Y0[num_frames][num_channels]; // channelized output
float complex Y1[num_frames][num_channels]; // channelized output
// create ofdm/oqam generator object and generate data
ofdmoqam qs = ofdmoqam_create(num_channels, m, beta, 0.0f, LIQUID_SYNTHESIZER, 0);
for (i=0; i<num_frames; i++) {
for (j=0; j<num_channels; j++) {
if (i<num_symbols) {
#if 0
// QPSK on all subcarriers
s[j] = (rand() % 2 ? 1.0f : -1.0f) +
(rand() % 2 ? 1.0f : -1.0f) * _Complex_I;
s[j] *= 1.0f / sqrtf(2.0f);
#else
// BPSK on even subcarriers
s[j] = rand() % 2 ? 1.0f : -1.0f;
s[j] *= (j%2)==0 ? 1.0f : 0.0f;
#endif
} else {
s[j] = 0.0f;
}
}
// run synthesizer
ofdmoqam_execute(qs, s, &y[i*num_channels]);
}
ofdmoqam_destroy(qs);
// channel
for (i=0; i<num_samples; i++)
y[i] *= cexpf(_Complex_I*(phi + dphi*i));
//
// analysis filterbank (receiver)
//
// create filterbank manually
dotprod_cccf dp[num_channels]; // vector dot products
windowcf w[num_channels]; // window buffers
#if DEBUG
// print coefficients
printf("h_prototype:\n");
for (i=0; i<h_len; i++)
printf(" h[%3u] = %12.8f\n", i, h[i]);
#endif
// create objects
unsigned int gc_sub_len = 2*m;
float complex gc_sub[gc_sub_len];
for (i=0; i<num_channels; i++) {
// sub-sample prototype filter, loading coefficients in
// reverse order
#if 0
for (j=0; j<gc_sub_len; j++)
gc_sub[j] = h[j*num_channels+i];
#else
for (j=0; j<gc_sub_len; j++)
gc_sub[gc_sub_len-j-1] = gc[j*num_channels+i];
#endif
// create window buffer and dotprod objects
dp[i] = dotprod_cccf_create(gc_sub, gc_sub_len);
w[i] = windowcf_create(gc_sub_len);
#if DEBUG
printf("gc_sub[%u] : \n", i);
for (j=0; j<gc_sub_len; j++)
printf(" g[%3u] = %12.8f + %12.8f\n", j, crealf(gc_sub[j]), cimagf(gc_sub[j]));
#endif
}
// generate DFT object
float complex x[num_channels]; // time-domain buffer
float complex X[num_channels]; // freq-domain buffer
#if 0
fftplan fft = fft_create_plan(num_channels, X, x, FFT_REVERSE, 0);
#else
fftplan fft = fft_create_plan(num_channels, X, x, FFT_FORWARD, 0);
#endif
//
// run analysis filter bank
//
#if 0
unsigned int filter_index = 0;
#else
unsigned int filter_index = num_channels-1;
#endif
float complex y_hat; // input sample
float complex * r; // read pointer
for (i=0; i<num_frames; i++) {
// load buffers
for (j=0; j<num_channels; j++) {
// grab sample
y_hat = y[i*num_channels + j];
// push sample into buffer at filter index
windowcf_push(w[filter_index], y_hat);
// decrement filter index
filter_index = (filter_index + num_channels - 1) % num_channels;
//filter_index = (filter_index + 1) % num_channels;
}
// execute filter outputs, reversing order of output (not
// sure why this is necessary)
for (j=0; j<num_channels; j++) {
windowcf_read(w[j], &r);
dotprod_cccf_execute(dp[j], r, &X[num_channels-j-1]);
}
#if 1
// compensate for carrier frequency offset (before transform)
for (j=0; j<num_channels; j++) {
X[j] *= cexpf(-_Complex_I*(dphi*i*num_channels));
}
#endif
// execute DFT, store result in buffer 'x'
fft_execute(fft);
#if 0
// compensate for carrier frequency offset (after transform)
for (j=0; j<num_channels; j++) {
x[j] *= cexpf(-_Complex_I*(dphi*i*num_channels));
}
#endif
// move to output array
for (j=0; j<num_channels; j++)
Y0[i][j] = x[j];
}
// destroy objects
for (i=0; i<num_channels; i++) {
dotprod_cccf_destroy(dp[i]);
windowcf_destroy(w[i]);
}
fft_destroy_plan(fft);
#if 0
// print filterbank channelizer
printf("\n");
printf("filterbank channelizer:\n");
for (i=0; i<num_symbols; i++) {
printf("%3u: ", i);
for (j=0; j<num_channels; j++) {
printf(" %8.5f+j%8.5f, ", crealf(Y0[i][j]), cimagf(Y0[i][j]));
}
printf("\n");
}
#endif
//
// export data
//
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\nclose all;\n\n");
fprintf(fid,"num_channels=%u;\n", num_channels);
fprintf(fid,"num_symbols=%u;\n", num_symbols);
fprintf(fid,"num_frames = %u;\n", num_frames);
fprintf(fid,"num_samples = num_frames*num_channels;\n");
fprintf(fid,"y = zeros(1,%u);\n", num_samples);
fprintf(fid,"Y0 = zeros(%u,%u);\n", num_frames, num_channels);
fprintf(fid,"Y1 = zeros(%u,%u);\n", num_frames, num_channels);
for (i=0; i<num_frames; i++) {
for (j=0; j<num_channels; j++) {
fprintf(fid,"Y0(%4u,%4u) = %12.4e + j*%12.4e;\n", i+1, j+1, crealf(Y0[i][j]), cimagf(Y0[i][j]));
fprintf(fid,"Y1(%4u,%4u) = %12.4e + j*%12.4e;\n", i+1, j+1, crealf(Y1[i][j]), cimagf(Y1[i][j]));
}
}
// plot BPSK results
fprintf(fid,"figure;\n");
fprintf(fid,"plot(Y0(:,1:2:end),'x');\n");
fprintf(fid,"axis([-1 1 -1 1]*1.2*sqrt(num_channels));\n");
fprintf(fid,"axis square;\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
ofdmoqamframe64sync ofdmoqamframe64sync_create(unsigned int _m,
float _beta,
ofdmoqamframe64sync_callback _callback,
void * _userdata)
{
ofdmoqamframe64sync q = (ofdmoqamframe64sync) malloc(sizeof(struct ofdmoqamframe64sync_s));
q->num_subcarriers = 64;
// validate input
if (_m < 1) {
fprintf(stderr,"error: ofdmoqamframe64sync_create(), filter delay must be > 0\n");
exit(1);
} else if (_beta < 0.0f) {
fprintf(stderr,"error: ofdmoqamframe64sync_create(), filter excess bandwidth must be > 0\n");
exit(1);
}
q->m = _m;
q->beta = _beta;
// synchronizer parameters
q->rxx_thresh = 0.60f; // auto-correlation threshold
q->rxy_thresh = 0.60f; // cross-correlation threshold
q->zeta = 64.0f/sqrtf(52.0f); // scaling factor
// create analysis filter banks
q->ca0 = firpfbch_create(q->num_subcarriers, q->m, q->beta, 0.0f /*dt*/,FIRPFBCH_ROOTNYQUIST,0/*gradient*/);
q->ca1 = firpfbch_create(q->num_subcarriers, q->m, q->beta, 0.0f /*dt*/,FIRPFBCH_ROOTNYQUIST,0/*gradient*/);
q->X0 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->X1 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->Y0 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->Y1 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
// allocate memory for PLCP arrays
q->S0 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->S1 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->S2 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
ofdmoqamframe64_init_S0(q->S0);
ofdmoqamframe64_init_S1(q->S1);
ofdmoqamframe64_init_S2(q->S2);
unsigned int i;
for (i=0; i<q->num_subcarriers; i++) {
q->S0[i] *= q->zeta;
q->S1[i] *= q->zeta;
q->S2[i] *= q->zeta;
}
q->S1a = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->S1b = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
// set pilot sequence
q->ms_pilot = msequence_create_default(8);
q->x_phase[0] = -21.0f;
q->x_phase[1] = -7.0f;
q->x_phase[2] = 7.0f;
q->x_phase[3] = 21.0f;
// create NCO for pilots
q->nco_pilot = nco_crcf_create(LIQUID_VCO);
q->pll_pilot = pll_create();
pll_set_bandwidth(q->pll_pilot,0.01f);
pll_set_damping_factor(q->pll_pilot,4.0f);
// create agc | signal detection object
q->sigdet = agc_crcf_create();
agc_crcf_set_bandwidth(q->sigdet,0.1f);
// create NCO for CFO compensation
q->nco_rx = nco_crcf_create(LIQUID_VCO);
// create auto-correlator objects
q->autocorr_length = OFDMOQAMFRAME64SYNC_AUTOCORR_LEN;
q->autocorr_delay = q->num_subcarriers / 4;
q->autocorr = autocorr_cccf_create(q->autocorr_length, q->autocorr_delay);
// create cross-correlator object
q->hxy = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
ofdmoqam cs = ofdmoqam_create(q->num_subcarriers,q->m,q->beta,
0.0f, // dt
OFDMOQAM_SYNTHESIZER,
0); // gradient
for (i=0; i<2*(q->m); i++)
ofdmoqam_execute(cs,q->S1,q->hxy);
// time reverse, complex conjugate (same as fftshift for
// this particular sequence)
memmove(q->X0, q->hxy, 64*sizeof(float complex));
for (i=0; i<64; i++)
q->hxy[i] = conjf(q->X0[64-i-1]);
// fftshift
//fft_shift(q->hxy,64);
q->crosscorr = firfilt_cccf_create(q->hxy, q->num_subcarriers);
ofdmoqam_destroy(cs);
// input buffer
q->input_buffer = windowcf_create((q->num_subcarriers));
// gain
q->g = 1.0f;
q->G0 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->G1 = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->G = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
q->data = (float complex*) malloc((q->num_subcarriers)*sizeof(float complex));
// reset object
ofdmoqamframe64sync_reset(q);
#if DEBUG_OFDMOQAMFRAME64SYNC
q->debug_x = windowcf_create(DEBUG_OFDMOQAMFRAME64SYNC_BUFFER_LEN);
q->debug_rxx= windowcf_create(DEBUG_OFDMOQAMFRAME64SYNC_BUFFER_LEN);
q->debug_rxy= windowcf_create(DEBUG_OFDMOQAMFRAME64SYNC_BUFFER_LEN);
q->debug_framesyms= windowcf_create(DEBUG_OFDMOQAMFRAME64SYNC_BUFFER_LEN);
q->debug_pilotphase= windowf_create(DEBUG_OFDMOQAMFRAME64SYNC_BUFFER_LEN);
q->debug_pilotphase_hat= windowf_create(DEBUG_OFDMOQAMFRAME64SYNC_BUFFER_LEN);
q->debug_rssi= windowf_create(DEBUG_OFDMOQAMFRAME64SYNC_BUFFER_LEN);
#endif
q->callback = _callback;
q->userdata = _userdata;
return q;
}
