cellular-infrastructure
/
osmocom-analog
9
1
Fork 2
Code Issues 11 Pull Requests 2 Projects Releases Wiki Activity

NMT: Calculate quality of sync sequence and drop in case of bad quality 

This eliminates chance of findig a sync sequence in noise or speech
This commit is contained in:
Andreas Eversberg 2016-04-24 07:12:21 +02:00
parent c0cd74ac85
commit 5062628e52
2 changed files with 34 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
src/nmt/dsp.c
View File

@ -200,15 +200,33 @@ void dsp_cleanup_sender(nmt_t *nmt)
static void fsk_receive_bit(nmt_t *nmt, int bit, double quality, double level)
{
double frames_elapsed;
int i;
// printf("bit=%d quality=%.4f\n", bit, quality);
if (!nmt->fsk_filter_in_sync) {
nmt->fsk_filter_sync = (nmt->fsk_filter_sync << 1) | bit;
/* level and quality */
nmt->fsk_filter_level[nmt->fsk_filter_count & 0xff] = level;
nmt->fsk_filter_quality[nmt->fsk_filter_count & 0xff] = quality;
nmt->fsk_filter_count++;
/* check if pattern 1010111100010010 matches */
if (nmt->fsk_filter_sync != 0xaf12)
return;
// printf("sync\n");
/* average level and quality */
level = quality = 0;
for (i = 0; i < 16; i++) {
level += nmt->fsk_filter_level[(nmt->fsk_filter_count - 1 - i) & 0xff];
quality += nmt->fsk_filter_quality[(nmt->fsk_filter_count - 1 - i) & 0xff];
}
level /= 16.0; quality /= 16.0;
// printf("sync (level = %.2f, quality = %.2f\n", level, quality);
/* do not accept garbage */
if (quality < 0.65)
return;
/* sync time */
nmt->rx_sample_count_last = nmt->rx_sample_count_current;
@ -218,8 +236,6 @@ static void fsk_receive_bit(nmt_t *nmt, int bit, double quality, double level)
nmt->fsk_filter_sync = 0;
nmt->fsk_filter_in_sync = 1;
nmt->fsk_filter_count = 0;
nmt->fsk_filter_levelsum = 0;
nmt->fsk_filter_qualitysum = 0;
/* set muting of receive path */
nmt->fsk_filter_mute = (int)((double)nmt->sender.samplerate * MUTE_DURATION);
@ -227,20 +243,28 @@ static void fsk_receive_bit(nmt_t *nmt, int bit, double quality, double level)
}
/* read bits */
nmt->fsk_filter_frame[nmt->fsk_filter_count++] = bit + '0';
nmt->fsk_filter_levelsum += level;
nmt->fsk_filter_qualitysum += quality;
if (nmt->fsk_filter_count != 140)
nmt->fsk_filter_frame[nmt->fsk_filter_count] = bit + '0';
nmt->fsk_filter_level[nmt->fsk_filter_count] = level;
nmt->fsk_filter_quality[nmt->fsk_filter_count] = quality;
if (++nmt->fsk_filter_count != 140)
return;
/* end of frame */
nmt->fsk_filter_frame[140] = '\0';
nmt->fsk_filter_in_sync = 0;
/* average level and quality */
level = quality = 0;
for (i = 0; i < 140; i++) {
level += nmt->fsk_filter_level[i];
quality += nmt->fsk_filter_quality[i];
}
level /= 140.0; quality /= 140.0;
/* send telegramm */
frames_elapsed = (double)(nmt->rx_sample_count_current - nmt->rx_sample_count_last) / (double)(nmt->samples_per_bit * 166);
/* convert level so that received level at TX_PEAK_FSK results in 1.0 (100%) */
nmt_receive_frame(nmt, nmt->fsk_filter_frame, nmt->fsk_filter_qualitysum / 140.0, nmt->fsk_filter_levelsum / 140.0 * 32768.0 / TX_PEAK_FSK, frames_elapsed);
nmt_receive_frame(nmt, nmt->fsk_filter_frame, quality, level * 32768.0 / TX_PEAK_FSK, frames_elapsed);
}
char *show_level(int value)

4
src/nmt/nmt.h
View File

@ -108,8 +108,8 @@ typedef struct nmt {
int fsk_filter_mute; /* mute count down after sync */
char fsk_filter_frame[141]; /* receive frame (one extra byte to terminate string) */
int fsk_filter_count; /* next bit to receive */
double fsk_filter_levelsum; /* sum of 140 level infos */
double fsk_filter_qualitysum; /* sum of 140 quality infos */
double fsk_filter_level[256]; /* level infos */
double fsk_filter_quality[256];/* quality infos */
int16_t *super_filter_spl; /* array with sample buffer for supervisory detection */
int super_filter_pos; /* current sample position in filter_spl */
double super_phaseshift256[4]; /* how much the phase of sine wave changes per sample */