void benchmark_gmskmodem_modulate(struct rusage *_start,
struct rusage *_finish,
unsigned long int *_num_iterations)
{
// options
unsigned int k=2; // filter samples/symbol
unsigned int m=3; // filter delay (symbols)
float BT=0.3f; // bandwidth-time product
// create modem object
gmskmod mod = gmskmod_create(k, m, BT);
float complex x[k];
unsigned int symbol_in = 0;
unsigned long int i;
// start trials
getrusage(RUSAGE_SELF, _start);
for (i=0; i<(*_num_iterations); i++) {
gmskmod_modulate(mod, symbol_in, x);
gmskmod_modulate(mod, symbol_in, x);
gmskmod_modulate(mod, symbol_in, x);
gmskmod_modulate(mod, symbol_in, x);
}
getrusage(RUSAGE_SELF, _finish);
*_num_iterations *= 4;
// destroy modem objects
gmskmod_destroy(mod);
}
// destroy gmskframegen object
void gmskframegen_destroy(gmskframegen _q)
{
// destroy gmsk modulator
gmskmod_destroy(_q->mod);
// destroy/free preamble objects/arrays
msequence_destroy(_q->ms_preamble);
// destroy/free header objects/arrays
free(_q->header_dec);
free(_q->header_enc);
packetizer_destroy(_q->p_header);
// destroy/free payload objects/arrays
free(_q->payload_enc);
packetizer_destroy(_q->p_payload);
// free main object memory
free(_q);
}
int main(int argc, char*argv[]) {
// options
unsigned int k=4; // filter samples/symbol
unsigned int m=3; // filter delay (symbols)
float BT=0.3f; // bandwidth-time product
unsigned int num_data_symbols=200; // number of data symbols
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
float phi = 0.0f; // carrier phase offset
float dphi = 0.0f; // carrier frequency offset
int dopt;
while ((dopt = getopt(argc,argv,"uhk:m:n:b:s:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'n': num_data_symbols = atoi(optarg); break;
case 'b': BT = atof(optarg); break;
case 's': SNRdB = atof(optarg); break;
default:
exit(1);
}
}
// validate input
if (BT <= 0.0f || BT >= 1.0f) {
fprintf(stderr,"error: %s, bandwidth-time product must be in (0,1)\n", argv[0]);
exit(1);
}
// derived values
unsigned int num_symbols = num_data_symbols + 2*m;
unsigned int num_samples = k*num_symbols;
float nstd = powf(10.0f,-SNRdB/20.0f); // noise standard deviation
// create modulator
gmskmod mod = gmskmod_create(k, m, BT);
gmskmod_print(mod);
// create demodulator
gmskdem demod = gmskdem_create(k, m, BT);
gmskdem_set_eq_bw(demod, 0.01f);
gmskdem_print(demod);
unsigned int i;
unsigned int s[num_symbols];
float complex x[num_samples];
float complex y[num_samples];
unsigned int sym_out[num_symbols];
// generate random data sequence
for (i=0; i<num_symbols; i++)
s[i] = rand() % 2;
// modulate signal
for (i=0; i<num_symbols; i++)
gmskmod_modulate(mod, s[i], &x[k*i]);
// add channel impairments
for (i=0; i<num_samples; i++) {
y[i] = x[i]*cexpf(_Complex_I*(phi + i*dphi));
y[i] += nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
}
// demodulate signal
for (i=0; i<num_symbols; i++)
gmskdem_demodulate(demod, &y[k*i], &sym_out[i]);
// destroy modem objects
gmskmod_destroy(mod);
gmskdem_destroy(demod);
// print results to screen
unsigned int delay = 2*m;
unsigned int num_errors=0;
for (i=delay; i<num_symbols; i++) {
//printf(" %4u : %2u (%2u)\n", i, s[i-delay], sym_out[i]);
num_errors += (s[i-delay] == sym_out[i]) ? 0 : 1;
}
printf("symbol errors : %4u / %4u\n", num_errors, num_data_symbols);
// write results to 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,"k = %u;\n", k);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"BT = %f;\n", BT);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = %u;\n", num_samples);
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(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
}
fprintf(fid,"t=[0:(num_samples-1)]/k;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(t,real(y),t,imag(y));\n");
// artificially demodulate (generate receive filter, etc.)
float hr[2*k*m+1];
liquid_firdes_gmskrx(k,m,BT,0,hr);
for (i=0; i<2*k*m+1; i++)
fprintf(fid,"hr(%3u) = %12.8f;\n", i+1, hr[i]);
fprintf(fid,"z = filter(hr,1,arg( ([y(2:end) 0]).*conj(y) ))/k;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(t,z,t(k:k:end),z(k:k:end),'or');\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
// create GMSK frame synchronizer
// _callback : callback function
// _userdata : user data pointer passed to callback function
gmskframesync gmskframesync_create(framesync_callback _callback,
void * _userdata)
{
gmskframesync q = (gmskframesync) malloc(sizeof(struct gmskframesync_s));
q->callback = _callback;
q->userdata = _userdata;
q->k = 2; // samples/symbol
q->m = 3; // filter delay (symbols)
q->BT = 0.5f; // filter bandwidth-time product
#if GMSKFRAMESYNC_PREFILTER
// create default low-pass Butterworth filter
q->prefilter = iirfilt_crcf_create_lowpass(3, 0.5f*(1 + q->BT) / (float)(q->k));
#endif
unsigned int i;
// frame detector
q->preamble_len = 63;
q->preamble_pn = (float*)malloc(q->preamble_len*sizeof(float));
q->preamble_rx = (float*)malloc(q->preamble_len*sizeof(float));
float complex preamble_samples[q->preamble_len*q->k];
msequence ms = msequence_create(6, 0x6d, 1);
gmskmod mod = gmskmod_create(q->k, q->m, q->BT);
for (i=0; i<q->preamble_len + q->m; i++) {
unsigned char bit = msequence_advance(ms);
// save p/n sequence
if (i < q->preamble_len)
q->preamble_pn[i] = bit ? 1.0f : -1.0f;
// modulate/interpolate
if (i < q->m) gmskmod_modulate(mod, bit, &preamble_samples[0]);
else gmskmod_modulate(mod, bit, &preamble_samples[(i-q->m)*q->k]);
}
gmskmod_destroy(mod);
msequence_destroy(ms);
#if 0
// print sequence
for (i=0; i<q->preamble_len*q->k; i++)
printf("preamble(%3u) = %12.8f + j*%12.8f;\n", i+1, crealf(preamble_samples[i]), cimagf(preamble_samples[i]));
#endif
// create frame detector
float threshold = 0.5f; // detection threshold
float dphi_max = 0.05f; // maximum carrier offset allowable
q->frame_detector = detector_cccf_create(preamble_samples, q->preamble_len*q->k, threshold, dphi_max);
q->buffer = windowcf_create(q->k*(q->preamble_len+q->m));
// create symbol timing recovery filters
q->npfb = 32; // number of filters in the bank
q->mf = firpfb_rrrf_create_rnyquist( LIQUID_FIRFILT_GMSKRX,q->npfb,q->k,q->m,q->BT);
q->dmf = firpfb_rrrf_create_drnyquist(LIQUID_FIRFILT_GMSKRX,q->npfb,q->k,q->m,q->BT);
// create down-coverters for carrier phase tracking
q->nco_coarse = nco_crcf_create(LIQUID_NCO);
// create/allocate header objects/arrays
q->header_mod = (unsigned char*)malloc(GMSKFRAME_H_SYM*sizeof(unsigned char));
q->header_enc = (unsigned char*)malloc(GMSKFRAME_H_ENC*sizeof(unsigned char));
q->header_dec = (unsigned char*)malloc(GMSKFRAME_H_DEC*sizeof(unsigned char));
q->p_header = packetizer_create(GMSKFRAME_H_DEC,
GMSKFRAME_H_CRC,
GMSKFRAME_H_FEC,
LIQUID_FEC_NONE);
// create/allocate payload objects/arrays
q->payload_dec_len = 1;
q->check = LIQUID_CRC_32;
q->fec0 = LIQUID_FEC_NONE;
q->fec1 = LIQUID_FEC_NONE;
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_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
#if DEBUG_GMSKFRAMESYNC
// debugging structures
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_x = NULL;
q->debug_fi = NULL;
q->debug_mf = NULL;
q->debug_framesyms = NULL;
#endif
// reset synchronizer
gmskframesync_reset(q);
// return synchronizer object
return q;
}
