By analyzing the behavior of the detectability of stations with
different SDR settings we can separate some SDR artifacts from
weak stations.
Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
---
libavradio/sdr.h | 5 +++++
libavradio/sdrdemux.c | 36 +++++++++++++++++++++++++++++++++++-
2 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/libavradio/sdr.h b/libavradio/sdr.h
index 838fb1cef7..1053e45efe 100644
--- a/libavradio/sdr.h
+++ b/libavradio/sdr.h
@@ -66,6 +66,8 @@ typedef enum Modulation {
//QAM, PSK, ...
} Modulation;
+#define HISTOGRAMM_SIZE 9
+
typedef struct Station {
char *name;
enum Modulation modulation;
@@ -78,6 +80,9 @@ typedef struct Station {
int timeout; //since how many blocks was this detectable but
not detected
int multiplex_index; //DAB can have multiple stations on one frequency
+ int detection_per_mix_frequency[HISTOGRAMM_SIZE];
+ int non_detection_per_mix_frequency[HISTOGRAMM_SIZE];
+
struct SDRStream *stream;
} Station;
diff --git a/libavradio/sdrdemux.c b/libavradio/sdrdemux.c
index 6cb9d3b70a..1fc528317c 100644
--- a/libavradio/sdrdemux.c
+++ b/libavradio/sdrdemux.c
@@ -111,6 +111,23 @@ static void free_station(Station *station)
av_free(station);
}
+static inline int histogram_index(SDRContext *sdr, double f)
+{
+ f = HISTOGRAMM_SIZE*((f - sdr->block_center_freq) / sdr->sdr_sample_rate +
0.5);
+ return av_clip((int)f, 0, HISTOGRAMM_SIZE-1);
+}
+
+static int histogram_score(Station *s)
+{
+ int score = 0;
+ for(int i = 0; i<HISTOGRAMM_SIZE; i++) {
+ score +=
+ (5*s->detection_per_mix_frequency[i] >
s->non_detection_per_mix_frequency[i])
+ -(5*s->detection_per_mix_frequency[i] <
s->non_detection_per_mix_frequency[i]);
+ }
+ return score;
+}
+
typedef struct FindStationContext {
double freq;
double range;
@@ -184,6 +201,10 @@ static int create_station(SDRContext *sdr, Station
*candidate_station) {
if (candidate_station->in_station_list)
return 0;
+ // suspect looking histogram
+ if (histogram_score(candidate_station) <= 0)
+ return 0;
+
Station *station_list[1000];
int nb_stations = find_stations(sdr, sdr->block_center_freq,
sdr->sdr_sample_rate*0.5, station_list, FF_ARRAY_ELEMS(station_list));
for (i=0; i<nb_stations; i++) {
@@ -328,8 +349,20 @@ static void decay_stations(SDRContext *sdr)
station->frequency + station->bandwidth/2 > sdr->block_center_freq
+ sdr->bandwidth/2)
continue;
+ if (station->timeout)
+ station->non_detection_per_mix_frequency[histogram_index(sdr,
station->frequency)] ++;
+
if (station->in_station_list) {
- if (station->timeout++ > STATION_TIMEOUT) {
+ int station_timeout = STATION_TIMEOUT;
+ int hs = histogram_score(station);
+
+ if (hs == 0) {
+ station_timeout = 5; //give the station a moment to be
properly detected and then discard it
+ } else if(hs < 0) {
+ station_timeout = 0; //probably not a station
+ }
+
+ if (station->timeout++ > station_timeout) {
if (!station->stream)
station->in_station_list = 0;
}
@@ -376,6 +409,7 @@ static int create_candidate_station(SDRContext *sdr, enum
Modulation modulation,
}
station->frequency /= ++station->nb_frequency;
+ station->detection_per_mix_frequency[histogram_index(sdr, freq)] ++;
station->modulation = modulation;
station->bandwidth = bandwidth;
station->bandwidth_p2 = bandwidth_p2;
--
2.31.1
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