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Add intermediate offset and a marker tone. #429

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Add intermediate offset and a marker tone. #429

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123 changes: 122 additions & 1 deletion gpssim.c
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,9 @@
#endif
#include "gpssim.h"


#define SIN_COS_SCALE 256

int sinTable512[] = {
2, 5, 8, 11, 14, 17, 20, 23, 26, 29, 32, 35, 38, 41, 44, 47,
50, 53, 56, 59, 62, 65, 68, 71, 74, 77, 80, 83, 86, 89, 91, 94,
Expand Down Expand Up @@ -1703,6 +1706,30 @@ int allocateChannel(channel_t *chan, ephem_t *eph, ionoutc_t ionoutc, gpstime_t
return(nsat);
}


/* Calculate the increment for an NCO.
* The increment is the amount added to the NCO on every sample.
*/
int calc_nco_increment(int nco_freq, int sample_freq)
{

double freq_ratio;

printf("nco is %d, sample is %d\n", nco_freq, sample_freq);

#if 1
/* Offset frequency ratio is the ratio between the NCO and the sampling rate. */
freq_ratio = ((double) nco_freq)/((double) sample_freq);

return (int)(freq_ratio * 512.0 * 65536.0);
#else
freq_ratio = ((double) nco_freq) * ((double) sample_freq);

return (int)(freq_ratio / (512.0 * 65536.0));
#endif
}


void usage(void)
{
fprintf(stderr, "Usage: gps-sdr-sim [options]\n"
Expand All @@ -1719,6 +1746,9 @@ void usage(void)
" -d <duration> Duration [sec] (dynamic mode max: %.0f, static mode max: %d)\n"
" -o <output> I/Q sampling data file (default: gpssim.bin)\n"
" -s <frequency> Sampling frequency [Hz] (default: 2600000)\n"
" -I <frequency> Intermediate Frequency Offset [Hz] (default: 0)\n"
" -M <frequency> Add a CW marker at specified frequency offset [Hz] eg (-M0 for centre at 1575.420MHz)\n"
" -m <amplitude> Set amplitude of CW marker. Default 1.0\n"
" -b <iq_bits> I/Q data format [1/8/16] (default: 16)\n"
" -i Disable ionospheric delay for spacecraft scenario\n"
" -p [fixed_gain] Disable path loss and hold power level constant\n"
Expand Down Expand Up @@ -1770,6 +1800,16 @@ int main(int argc, char *argv[])
int iq_buff_size;
int data_format;

int marker_on;
int marker_offset;
int marker_count;
int marker_increment;
double marker_amplitude;

int if_offset;
int if_count;
int if_increment;

int result;

int gain[MAX_CHAN];
Expand Down Expand Up @@ -1809,14 +1849,18 @@ int main(int argc, char *argv[])
verb = FALSE;
ionoutc.enable = TRUE;
ionoutc.leapen = FALSE;
if_offset = 0;
marker_on = 0;
marker_offset = 0;
marker_amplitude = 1.0;

if (argc<3)
{
usage();
exit(1);
}

while ((result=getopt(argc,argv,"e:u:x:g:c:l:o:s:b:L:T:t:d:ipv"))!=-1)
while ((result=getopt(argc,argv,"e:u:x:g:c:l:o:I:M:m:s:b:L:T:t:d:ipv"))!=-1)
{
switch (result)
{
Expand All @@ -1842,6 +1886,16 @@ int main(int argc, char *argv[])
staticLocationMode = TRUE;
sscanf(optarg,"%lf,%lf,%lf",&xyz[0][0],&xyz[0][1],&xyz[0][2]);
break;
case 'I':
if_offset = atof(optarg);
break;
case 'M':
marker_on = 1;
marker_offset = atof(optarg);
break;
case 'm':
marker_amplitude = atof(optarg);
break;
case 'l':
// Static geodetic coordinates input mode
// Added by [email protected]
Expand Down Expand Up @@ -1982,6 +2036,31 @@ int main(int argc, char *argv[])

delt = 1.0/samp_freq;


if_count = 0;
if_increment = 0;
marker_count = 0;
marker_increment = 0;

if (if_offset)
{
if_increment = calc_nco_increment(if_offset, samp_freq);
fprintf(stderr, "if_increment is %d\n", if_increment);

if (fabs(if_offset) >= samp_freq / 2) {
fprintf(stderr, "** WARNING IF frequency is too large relative to sample frequency\n");
}
}

if (marker_on)
{
marker_increment = calc_nco_increment(marker_offset, samp_freq);
fprintf(stderr, "marker_increment is %d\n", marker_increment);
if (fabs(marker_offset) >= samp_freq / 2) {
fprintf(stderr, "** WARNING Marker frequency is too large relative to sample frequency\n");
}
}

////////////////////////////////////////////////////////////
// Receiver position
////////////////////////////////////////////////////////////
Expand Down Expand Up @@ -2239,6 +2318,7 @@ int main(int argc, char *argv[])
// Allocate visible satellites
allocateChannel(chan, eph[ieph], ionoutc, grx, xyz[0], elvmask);

fprintf(stderr, "PRN Az El Delay Iono\n");
for(i=0; i<MAX_CHAN; i++)
{
if (chan[i].prn>0)
Expand Down Expand Up @@ -2368,10 +2448,51 @@ int main(int argc, char *argv[])
}
}


if (marker_on)
{
/*
* If there is a frequency offset then mix with the
* offset frequency.
*/
int m_phase = (marker_count >> 16) & 0x1ff;
int m_sin = sinTable512[m_phase];
int m_cos = cosTable512[m_phase];

i_acc = m_cos * marker_amplitude;
q_acc = m_sin * marker_amplitude;

/* Increment phase. */
marker_count += marker_increment;
}

// Scaled by 2^7
i_acc = (i_acc+64)>>7;
q_acc = (q_acc+64)>>7;


if(if_offset != 0)
{
/*
* If there is a frequency offset then mix with the
* offset frequency.
*/
int if_phase = (if_count >> 16) & 0x1ff;
int if_sin = sinTable512[if_phase];
int if_cos = cosTable512[if_phase];
int tmp_i;
int tmp_q;

tmp_i = (i_acc * if_cos - q_acc * if_sin)/SIN_COS_SCALE;
tmp_q = (i_acc * if_sin + q_acc * if_cos)/SIN_COS_SCALE;

i_acc = tmp_i;
q_acc = tmp_q;

/* Increment phase. */
if_count += if_increment;
}

// Store I/Q samples into buffer
iq_buff[isamp*2] = (short)i_acc;
iq_buff[isamp*2+1] = (short)q_acc;
Expand Down