// Helper function to keep code base small
// _num_subcarriers : number of subcarriers
// _cp_len : cyclic prefix lenght
// _taper_len : taper length
void ofdmframesync_acquire_test(unsigned int _num_subcarriers,
unsigned int _cp_len,
unsigned int _taper_len)
{
// options
unsigned int M = _num_subcarriers; // number of subcarriers
unsigned int cp_len = _cp_len; // cyclic prefix lenght
unsigned int taper_len = _taper_len; // taper length
float tol = 1e-2f; // error tolerance
//
float dphi = 1.0f / (float)M; // carrier frequency offset
// subcarrier allocation (initialize to default)
unsigned char p[M];
ofdmframe_init_default_sctype(M, p);
// derived values
unsigned int num_samples = (3 + 1)*(M + cp_len);
// create synthesizer/analyzer objects
ofdmframegen fg = ofdmframegen_create(M, cp_len, taper_len, p);
//ofdmframegen_print(fg);
float complex X[M]; // original data sequence
float complex X_test[M]; // recovered data sequence
ofdmframesync fs = ofdmframesync_create(M,cp_len,taper_len,p,ofdmframesync_autotest_callback,(void*)X_test);
unsigned int i;
float complex s0[M]; // short PLCP sequence
float complex s1[M]; // long PLCP sequence
float complex y[num_samples]; // frame samples
// assemble full frame
unsigned int n=0;
// write first S0 symbol
ofdmframegen_write_S0a(fg, &y[n]);
n += M + cp_len;
// write second S0 symbol
ofdmframegen_write_S0b(fg, &y[n]);
n += M + cp_len;
// write S1 symbol
ofdmframegen_write_S1( fg, &y[n]);
n += M + cp_len;
// generate data symbol (random)
for (i=0; i<M; i++) {
X[i] = cexpf(_Complex_I*2*M_PI*randf());
X_test[i] = 0.0f;
}
// write data symbol
ofdmframegen_writesymbol(fg, X, &y[n]);
n += M + cp_len;
// validate frame length
assert(n == num_samples);
// add carrier offset
for (i=0; i<num_samples; i++)
y[i] *= cexpf(_Complex_I*dphi*i);
// run receiver
ofdmframesync_execute(fs,y,num_samples);
// check output
for (i=0; i<M; i++) {
if (p[i] == OFDMFRAME_SCTYPE_DATA) {
float e = crealf( (X[i] - X_test[i])*conjf(X[i] - X_test[i]) );
CONTEND_DELTA( cabsf(e), 0.0f, tol );
}
}
// destroy objects
ofdmframegen_destroy(fg);
ofdmframesync_destroy(fs);
}
// create ofdmflexframesync object
// _M : number of subcarriers
// _cp_len : length of cyclic prefix [samples]
// _taper_len : taper length (OFDM symbol overlap)
// _p : subcarrier allocation (PILOT/NULL/DATA) [size: _M x 1]
// _callback : user-defined callback function
// _userdata : user-defined data structure passed to callback
ofdmflexframesync ofdmflexframesync_create(unsigned int _M,
unsigned int _cp_len,
unsigned int _taper_len,
unsigned char * _p,
framesync_callback _callback,
void * _userdata)
{
ofdmflexframesync q = (ofdmflexframesync) malloc(sizeof(struct ofdmflexframesync_s));
// validate input
if (_M < 8) {
fprintf(stderr,"warning: ofdmflexframesync_create(), less than 8 subcarriers\n");
} else if (_M % 2) {
fprintf(stderr,"error: ofdmflexframesync_create(), number of subcarriers must be even\n");
exit(1);
} else if (_cp_len > _M) {
fprintf(stderr,"error: ofdmflexframesync_create(), cyclic prefix length cannot exceed number of subcarriers\n");
exit(1);
}
// set internal properties
q->M = _M;
q->cp_len = _cp_len;
q->taper_len = _taper_len;
q->callback = _callback;
q->userdata = _userdata;
// allocate memory for subcarrier allocation IDs
q->p = (unsigned char*) malloc((q->M)*sizeof(unsigned char));
if (_p == NULL) {
// initialize default subcarrier allocation
ofdmframe_init_default_sctype(q->M, q->p);
} else {
// copy user-defined subcarrier allocation
memmove(q->p, _p, q->M*sizeof(unsigned char));
}
// validate and count subcarrier allocation
ofdmframe_validate_sctype(q->p, q->M, &q->M_null, &q->M_pilot, &q->M_data);
// create internal framing object
q->fs = ofdmframesync_create(_M, _cp_len, _taper_len, _p, ofdmflexframesync_internal_callback, (void*)q);
// create header objects
q->mod_header = modem_create(OFDMFLEXFRAME_H_MOD);
q->p_header = packetizer_create(OFDMFLEXFRAME_H_DEC,
OFDMFLEXFRAME_H_CRC,
OFDMFLEXFRAME_H_FEC,
LIQUID_FEC_NONE);
assert(packetizer_get_enc_msg_len(q->p_header)==OFDMFLEXFRAME_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_len = 1;
q->check = LIQUID_CRC_NONE;
q->fec0 = LIQUID_FEC_NONE;
q->fec1 = LIQUID_FEC_NONE;
// create payload objects (initally QPSK, etc but overridden by received properties)
q->mod_payload = modem_create(q->ms_payload);
q->p_payload = packetizer_create(q->payload_len, q->check, q->fec0, q->fec1);
q->payload_enc_len = packetizer_get_enc_msg_len(q->p_payload);
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
q->payload_dec = (unsigned char*) malloc(q->payload_len*sizeof(unsigned char));
q->payload_mod_len = 0;
// reset state
ofdmflexframesync_reset(q);
// return object
return q;
}
// Helper function to keep code base small
void ofdmframesync_rxsymbol_bench(struct rusage *_start,
struct rusage *_finish,
unsigned long int *_num_iterations,
unsigned int _num_subcarriers,
unsigned int _cp_len)
{
// options
modulation_scheme ms = LIQUID_MODEM_QPSK;
unsigned int M = _num_subcarriers;
unsigned int cp_len = _cp_len;
unsigned int taper_len = 0;
// create synthesizer/analyzer objects
ofdmframegen fg = ofdmframegen_create(M, cp_len, taper_len, NULL);
//ofdmframegen_print(fg);
modem mod = modem_create(ms);
ofdmframesync fs = ofdmframesync_create(M,cp_len,taper_len,NULL,NULL,NULL);
unsigned int i;
float complex X[M]; // channelized symbol
float complex x[M+cp_len]; // time-domain symbol
// synchronize short sequence (first)
ofdmframegen_write_S0a(fg, x);
ofdmframesync_execute(fs, x, M+cp_len);
// synchronize short sequence (second)
ofdmframegen_write_S0b(fg, x);
ofdmframesync_execute(fs, x, M+cp_len);
// synchronize long sequence
ofdmframegen_write_S1(fg, x);
ofdmframesync_execute(fs, x, M+cp_len);
// modulate data symbols (use same symbol, ignore pilot phase)
unsigned int s;
for (i=0; i<M; i++) {
s = modem_gen_rand_sym(mod);
modem_modulate(mod,s,&X[i]);
}
ofdmframegen_writesymbol(fg, X, x);
// add noise
for (i=0; i<M+cp_len; i++)
x[i] += 0.02f*randnf()*cexpf(_Complex_I*2*M_PI*randf());
// normalize number of iterations
*_num_iterations /= M;
// start trials
getrusage(RUSAGE_SELF, _start);
for (i=0; i<(*_num_iterations); i++) {
// receive data symbols (ignoring pilots)
ofdmframesync_execute(fs, x, M+cp_len);
ofdmframesync_execute(fs, x, M+cp_len);
ofdmframesync_execute(fs, x, M+cp_len);
ofdmframesync_execute(fs, x, M+cp_len);
}
getrusage(RUSAGE_SELF, _finish);
*_num_iterations *= 4;
// destroy objects
ofdmframegen_destroy(fg);
ofdmframesync_destroy(fs);
modem_destroy(mod);
}