Attachment 575492 Details for Bug 810347 – Fix for the sampling rate estimate (AFSK)

[patch] Fix for the sampling rate estimate (AFSK)

soundmodem-0.16-use-a-minimum-samplerate-for-afsk-v5.patch (text/plain), 9.59 KB, created by g.trentalancia on 2012-04-05 16:31:39 UTC

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Creator: g.trentalancia

Created: 2012-04-05 16:31:39 UTC

Size: 9.59 KB

patch

obsolete

>This patch modifies the AFSK modulator in version 0.16 of the soundmodem
>application as it appears to be problematic in particular at 300 baud
>(in general, it might be buggy for bitrates lower than 1200 baud,
>although I have not done any testing at other bitrates).
>
>In other words, this patch should fix the AFSK modulator for the problem
>reported, for example, here:
>
>- http://he.fi/archive/linux-hams/200608/0005.html
>- http://marc.info/?l=linux-hams&m=129059468102018&w=2
>
>I have also introduced optional windowing functions (other than the
>Hamming one) for experimentation but at the moment they are completely
>untested and they can only be selected during compilation.
>
>After applying this patch, the AFSK modulator should work normally for
>300 baud (or in general bitrates different/less than 1200 baud) and the
>user should be able to select any AFSK tone frequencies. Similar fixes
>are also introduced by this patch for the AFSK demodulator, although for
>successful reception at 300 baud it might also need longer RX filters
>that are eventually more robust against overflows.
>---
> afsk/modem.c |  230 +++++++++++++++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 193 insertions(+), 37 deletions(-)
>
>--- soundmodem-0.16-orig/afsk/modem.c	2012-02-29 20:31:24.356287000 +0100
>+++ soundmodem-0.16/afsk/modem.c	2012-03-03 19:14:07.696345582 +0100
>@@ -32,8 +32,71 @@
> #include "modem.h"
> #include "costab.h"
> 
>+/*
>+ * IZ6RDB 29/02/2012: always use a minimum samplerate
>+ * otherwise some sound cards, might not work well
>+ * especially at bitrates lower than 1200 baud (such
>+ * as 300 baud for HF).
>+ *
>+ * The value is defined in Hz and it should never be
>+ * less than 9600 Hz to avoid problems, although the
>+ * recommended value is 11025 Hz for most soundcards.
>+ *
>+ * Some cards, might even require that only their
>+ * maximum allowed sampling rate of 48kHz is used
>+ * (for example, according to online reports some
>+ * embedded SiS 701x AC'97 controllers).
>+ */
>+#define MINIMUM_SAMPLERATE	11025
>+
>+/*
>+ * IZ6RDB 01/03/2012: define different possible
>+ * window types for the FIR filters and choose
>+ * one of the available types:
>+ * - NONE
>+ * - HAMMING (window used up to version 0.16)
>+ * - HANNING
>+ * - BLACKMAN
>+ * - WELCH (for weak signals)
>+ */
>+#define FIR_WINDOW	HAMMING
>+
>+/*
>+ * IZ6RDB 01/03/2012: introduce a parameter
>+ * called "bandwidth expansion factor", which
>+ * is a real positive number slightly greater
>+ * than unity (up to 2.0) that accounts for
>+ * guard-bands and non-ideal filtering.
>+ *
>+ * This value is only used for estimating the
>+ * required sampling rate.
>+ *
>+ * Values are usually between 1.125 and 1.4.
>+ *
>+ * The recommended value is 1.36.
>+ */
>+#define BANDWIDTH_EXPANSION_FACTOR	1.36
>+
> /* --------------------------------------------------------------------- */
> 
>+#ifdef FIR_WINDOW
>+#if (FIR_WINDOW == NONE)
>+#define WINDOW_FUNCTION(x)	no_window(x)
>+#elif (FIR_WINDOW == HAMMING)
>+#define WINDOW_FUNCTION(x)	hamming_window(x)
>+#elif (FIR_WINDOW == HANNING)
>+#define WINDOW_FUNCTION(x)	hanning_window(x)
>+#elif (FIR_WINDOW == BLACKMAN)
>+#define WINDOW_FUNCTION(x)	blackman_window(x)
>+#elif (FIR_WINDOW == WELCH)
>+#define WINDOW_FUNCTION(x)	welch_window(x)
>+#else
>+#error "A valid FIR Window must be selected !"
>+#endif
>+#else // default to Hamming window
>+#define WINDOW_FUNCTION(x)	hamming_window(x)
>+#endif
>+
> struct modstate {
> 	struct modemchannel *chan;
> 	unsigned int bps, f0, f1, notdiff, maxbitlen;
>@@ -53,6 +116,9 @@ static const struct modemparams modparam
> static void *modconfig(struct modemchannel *chan, unsigned int *samplerate, const char *params[])
> {
> 	struct modstate *s;
>+	unsigned int bandwidth, expanded_bandwidth;
>+	unsigned int min_samplerate, optimized_samplerate;
>+	unsigned int f_carrier;
> 	
> 	if (!(s = malloc(sizeof(struct modstate))))
> 		logprintf(MLOG_FATAL, "out of memory\n");
>@@ -63,22 +129,45 @@ static void *modconfig(struct modemchann
> 			s->bps = 100;
> 		if (s->bps > 9600)
> 			s->bps= 9600;
>-	} else
>-		s->bps = 1200;
>-	if (params[1]) {
>+	}
>+	if (params[1])
> 		s->f0 = strtoul(params[1], NULL, 0);
>-		if (s->f0 > s->bps * 4)
>-			s->f0 = s->bps * 4;
>-	} else
>-		s->f0 = 1200;
>-	if (params[2]) {
>+	if (params[2])
> 		s->f1 = strtoul(params[2], NULL, 0);
>-		if (s->f1 > s->bps * 4)
>-			s->f1 = s->bps * 4;
>-	} else
>-		s->f1 = 2200;
> 	s->notdiff = params[3] ? !strtoul(params[3], NULL, 0) : 0;
>-	*samplerate = 8 * s->bps;
>+
>+	/*
>+	 * Calculate the bandwidth of the baseband (audio) signal:
>+	 * basically this is the highest frequency of the two
>+	 * possible tones.
>+	 */
>+	bandwidth = (s->f0 > s->f1) ? s->f0 : s->f1;
>+
>+	/*
>+	 * Calculate the expanded bandwidth (with guard-bands)
>+	 * to get a better estimate.
>+	 */
>+	expanded_bandwidth = BANDWIDTH_EXPANSION_FACTOR * bandwidth;
>+
>+	/* Nyquist criteria (minimum sampling rate) */
>+	min_samplerate = 2 * expanded_bandwidth;
>+
>+	/* Calculate the (audio) carrier frequency */
>+	f_carrier = (s->f0 + s->f1)/2;
>+
>+	/* Calculate intermediate operating point sampling rate */
>+	optimized_samplerate = 4 * f_carrier;
>+	if (optimized_samplerate > min_samplerate)
>+		min_samplerate = optimized_samplerate;
>+
>+	/*
>+	 * Make sure that the minimum recommended sampling
>+	 * rate for the soundcard is exceeded.
>+	 */
>+	if (min_samplerate < MINIMUM_SAMPLERATE)
>+		min_samplerate = MINIMUM_SAMPLERATE;
>+
>+	*samplerate = min_samplerate;
> 	return s;
> }
> 
>@@ -147,10 +236,28 @@ struct modulator afskmodulator = {
> 
> #define max(a, b) (((a) > (b)) ? (a) : (b))
> 
>-/* RxFilter */
>+/* Rx FIR Filter parameters */
>+
>+/*
>+ * Rx FIR Filter window expansion parameter
>+ * is normally equal to 1.5.
>+ */
> #define WINDOWEXPAND  1.5
>+
>+/*
>+ * Rx FIR Filter length is normally equal
>+ * to 16.
>+ */
> #define RXFILTLEN       16
>-#define RXFILTOVERBITS   3
>+
>+/*
>+ * Rx FIR Filter length is normally equal
>+ * to 16. This parameter should represent
>+ * the minimum wordlength to avoid
>+ * overflow.
>+ */
>+#define RXFILTOVERBITS	3
>+
> #define RXFILTOVER      (1<<(RXFILTOVERBITS))
> #define RXFILTFIDX(x)   (((x)>>(16-(RXFILTOVERBITS)))&(RXFILTOVER-1))
> #define RXFILTFSAMP(x)  ((x)>>16)
>@@ -202,7 +309,9 @@ static const struct modemparams demodpar
> static void *demodconfig(struct modemchannel *chan, unsigned int *samplerate, const char *params[])
> {
> 	struct demodstate *s;
>-	unsigned int f;
>+	unsigned int bandwidth, expanded_bandwidth;
>+	unsigned int min_samplerate, optimized_samplerate;
>+	unsigned int f_carrier;
> 
> 	if (!(s = malloc(sizeof(struct demodstate))))
> 		logprintf(MLOG_FATAL, "out of memory\n");
>@@ -213,27 +322,45 @@ static void *demodconfig(struct modemcha
> 			s->bps = 100;
> 		if (s->bps > 9600)
> 			s->bps= 9600;
>-	} else
>-		s->bps = 1200;
>-	if (params[1]) {
>+	}
>+	if (params[1])
> 		s->f0 = strtoul(params[1], NULL, 0);
>-		if (s->f0 > s->bps * 4)
>-			s->f0 = s->bps * 4;
>-	} else
>-		s->f0 = 1200;
>-	if (params[2]) {
>+	if (params[2])
> 		s->f1 = strtoul(params[2], NULL, 0);
>-		if (s->f1 > s->bps * 4)
>-			s->f1 = s->bps * 4;
>-	} else
>-		s->f1 = 2200;
> 	s->notdiff = params[3] ? !strtoul(params[3], NULL, 0) : 0;
>-	f = s->f0;
>-	if (s->f1 > f)
>-		f = s->f1;
>-	f += s->bps/2;
>-	f = (2*f) + (f >> 1);
>-	*samplerate = f;
>+
>+        /*
>+         * Calculate the bandwidth of the baseband (audio) signal:
>+         * basically this is the highest frequency of the two
>+         * possible tones.
>+         */
>+        bandwidth = (s->f0 > s->f1) ? s->f0 : s->f1;
>+
>+	/*
>+	 * Calculate the expanded bandwidth (with guard-bands)
>+	 * to get a better estimate.
>+	 */
>+        expanded_bandwidth = BANDWIDTH_EXPANSION_FACTOR * bandwidth;
>+
>+        /* Nyquist criteria (minimum sampling rate) */
>+        min_samplerate = 2 * expanded_bandwidth;
>+
>+	/* Calculate the (audio) carrier frequency */
>+	f_carrier = (s->f0 + s->f1)/2;
>+
>+	/* Calculate intermediate operating point sampling rate */
>+	optimized_samplerate = 4 * f_carrier;
>+	if (optimized_samplerate > min_samplerate)
>+		min_samplerate = optimized_samplerate;
>+
>+	/*
>+	 * Make sure that the minimum recommended sampling
>+	 * rate for the soundcard is exceeded.
>+	 */
>+	if (min_samplerate < MINIMUM_SAMPLERATE)
>+		min_samplerate = MINIMUM_SAMPLERATE;
>+
>+	*samplerate = min_samplerate;
> 	return s;
> }
> 
>@@ -317,7 +444,6 @@ static void demod8bits(struct demodstate
>         s->rxphase += phase;
> }
> 
>-
> static void demoddemodulate(void *state)
> {
> 	struct demodstate *s = (struct demodstate *)state;
>@@ -364,11 +490,41 @@ static inline double sinc(double x)
>         return sin(arg) / arg;
> }
> 
>-static inline double hamming(double x)
>+/*
>+ * The Hamming window is the original one (used
>+ * exclusively up to version 0.16).
>+ * From version 0.17 optional windows different
>+ * from the Hamming window have been introduced,
>+ * so that they can be changed and tested in
>+ * order to try achieving reduced passband
>+ * ripples at the expense of slower passband to
>+ * stopband roll-off.
>+ */
>+static inline double no_window(double x)
>+{
>+	return 1;
>+}
>+
>+static inline double hamming_window(double x)
> {
>         return 0.54-0.46*cos((2*M_PI)*x);
> }
> 
>+static inline double hanning_window(double x)
>+{
>+        return 0.5-0.5*cos((2*M_PI)*x);
>+}
>+
>+static inline double blackman_window(double x)
>+{
>+        return 0.42-0.5*cos((2*M_PI)*x)+0.08*cos((4*M_PI)*x);
>+}
>+
>+static inline double welch_window(double x)
>+{
>+	return 1.0-pow((2*x-1),2);
>+}
>+
> static void demodinit(void *state, unsigned int samplerate, unsigned int *bitrate)
> {
> 	struct demodstate *s = (struct demodstate *)state;
>@@ -388,7 +544,7 @@ static void demodinit(void *state, unsig
>                 if (w > 1)
>                         w = 0;
>                 else
>-                        w = hamming(w);
>+			w = WINDOW_FUNCTION(w);
>                 f0r[i] = w * cos(ph0 * i);
>                 f0i[i] = w * sin(ph0 * i);
>                 f1r[i] = w * cos(ph1 * i);

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Attachments on bug 810347: 575492 | 575493