// execute framing synchronizer on input buffer
// _q : framing synchronizer object
// _buffer : input buffer [size: _n x 1]
// _n : input buffer size
void wlanframesync_execute(wlanframesync _q,
liquid_float_complex * _buffer,
unsigned int _n)
{
unsigned int i;
float complex x;
for (i=0; i<_n; i++) {
x = _buffer[i];
// correct for carrier frequency offset (only if not in
// initial 'seek PLCP' state)
if (_q->state != WLANFRAMESYNC_STATE_SEEKPLCP) {
nco_crcf_mix_down(_q->nco_rx, x, &x);
nco_crcf_step(_q->nco_rx);
}
// save input sample to buffer
windowcf_push(_q->input_buffer,x);
#if DEBUG_WLANFRAMESYNC
if (_q->debug_enabled) {
// apply agc (estimate initial signal gain)
float complex y;
agc_crcf_execute(_q->agc_rx, x, &y);
windowcf_push(_q->debug_x, x);
windowf_push(_q->debug_rssi, agc_crcf_get_rssi(_q->agc_rx));
}
#endif
switch (_q->state) {
case WLANFRAMESYNC_STATE_SEEKPLCP:
wlanframesync_execute_seekplcp(_q);
break;
case WLANFRAMESYNC_STATE_RXSHORT0:
wlanframesync_execute_rxshort0(_q);
break;
case WLANFRAMESYNC_STATE_RXSHORT1:
wlanframesync_execute_rxshort1(_q);
break;
case WLANFRAMESYNC_STATE_RXLONG0:
wlanframesync_execute_rxlong0(_q);
break;
case WLANFRAMESYNC_STATE_RXLONG1:
wlanframesync_execute_rxlong1(_q);
break;
case WLANFRAMESYNC_STATE_RXSIGNAL:
wlanframesync_execute_rxsignal(_q);
break;
case WLANFRAMESYNC_STATE_RXDATA:
wlanframesync_execute_rxdata(_q);
break;
default:;
// should never get to this point
fprintf(stderr,"error: wlanframesync_execute(), invalid state\n");
exit(1);
}
} // for (i=0; i<_n; i++)
}
//
// Test RSSI on noise input
//
void autotest_agc_crcf_rssi_noise()
{
// set paramaters
float gamma = -30.0f; // nominal signal level [dB]
float bt = 0.01f; // agc bandwidth
float tol = 0.2f; // error tolerance [dB]
// signal properties
float nstd = powf(10.0f, gamma/20);
// create AGC object and initialize
agc_crcf q = agc_crcf_create();
agc_crcf_set_bandwidth(q, bt);
unsigned int i;
float complex x, y;
for (i=0; i<2000; i++) {
// generate sample (circular complex noise)
x = nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// execute agc
agc_crcf_execute(q, x, &y);
}
// get received signal strength indication
float rssi = agc_crcf_get_rssi(q);
if (liquid_autotest_verbose)
printf("gamma : %12.8f, rssi : %12.8f\n", gamma, rssi);
// Check results
CONTEND_DELTA( rssi, gamma, tol );
// destroy agc object
agc_crcf_destroy(q);
}
int main(int argc, char*argv[])
{
// options
float noise_floor= -40.0f; // noise floor [dB]
float SNRdB = 20.0f; // signal-to-noise ratio [dB]
float bt = 0.05f; // loop bandwidth
unsigned int num_symbols= 100; // number of iterations
unsigned int d = 5; // print every d iterations
unsigned int k = 2; // interpolation factor (samples/symbol)
unsigned int m = 3; // filter delay (symbols)
float beta = 0.3f; // filter excess bandwidth factor
float dt = 0.0f; // filter fractional sample delay
// derived values
unsigned int num_samples=num_symbols*k;
float gamma = powf(10.0f, (SNRdB+noise_floor)/20.0f); // channel gain
float nstd = powf(10.0f, noise_floor / 20.0f);
// arrays
float complex x[num_samples];
float complex y[num_samples];
float rssi[num_samples];
// create objects
modem mod = modem_create(LIQUID_MODEM_QPSK);
firinterp_crcf interp = firinterp_crcf_create_prototype(LIQUID_FIRFILT_RRC,k,m,beta,dt);
agc_crcf p = agc_crcf_create();
agc_crcf_set_bandwidth(p, bt);
unsigned int i;
// print info
printf("automatic gain control // loop bandwidth: %4.2e\n",bt);
unsigned int sym;
float complex s;
for (i=0; i<num_symbols; i++) {
// generate random symbol
sym = modem_gen_rand_sym(mod);
modem_modulate(mod, sym, &s);
s *= gamma;
firinterp_crcf_execute(interp, s, &x[i*k]);
}
// add noise
for (i=0; i<num_samples; i++)
x[i] += nstd*(randnf() + _Complex_I*randnf()) * M_SQRT1_2;
// run agc
for (i=0; i<num_samples; i++) {
agc_crcf_execute(p, x[i], &y[i]);
rssi[i] = agc_crcf_get_rssi(p);
}
// destroy objects
modem_destroy(mod);
agc_crcf_destroy(p);
firinterp_crcf_destroy(interp);
// print results to screen
printf("received signal strength indication (rssi):\n");
for (i=0; i<num_samples; i+=d) {
printf("%4u : %8.2f\n", i, rssi[i]);
}
//
// export results
//
FILE* fid = fopen(OUTPUT_FILENAME,"w");
if (!fid) {
fprintf(stderr,"error: %s, could not open '%s' for writing\n", argv[0], OUTPUT_FILENAME);
exit(1);
}
fprintf(fid,"%% %s: auto-generated file\n\n",OUTPUT_FILENAME);
fprintf(fid,"n = %u;\n", num_samples);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n\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,"rssi(%4u) = %12.4e;\n", i+1, rssi[i]);
}
fprintf(fid,"\n\n");
fprintf(fid,"n = length(x);\n");
fprintf(fid,"t = 0:(n-1);\n");
fprintf(fid,"figure('position',[100 100 800 600]);\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," plot(t,rssi,'-k','LineWidth',2);\n");
fprintf(fid," xlabel('sample index');\n");
fprintf(fid," ylabel('rssi [dB]');\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," plot(t,real(y),t,imag(y));\n");
fprintf(fid," xlabel('sample index');\n");
fprintf(fid," ylabel('agc output');\n");
fprintf(fid," grid on;\n");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
