Changeset 2162

Timestamp:

11/26/11 22:06:19 (18 months ago)

Author:

sm0svx

Message:

The tone detector has now been further improved. Instead of using the
tone power to passband power relation, the passband power is recalculated
to a noise floor estimation. This estimation can then be used to calculate an
SNR value for the tone detector. Doing this have at least two benefits.
One is that the CTCSS detector now work all over the CTCSS band with good
performance. There is still a problem though if the frequency response is
not flat over the whole band. However, this can now be easily compensated
for by changing the thresholds in the configuration.
That bring us to the second benefit. The threshold is now expressed in dB
which make it an understandable parameter which users can change in the
configuration, much like they turn the squelch knob on their radio.

Location:

branches/improved_tone_detector/src

Files:

• svxlink/remotetrx/remotetrx.conf (modified) (2 diffs)
• svxlink/svxlink/svxlink.conf (modified) (1 diff)
• svxlink/trx/SquelchCtcss.h (modified) (5 diffs)
• svxlink/trx/ToneDetector.cpp (modified) (5 diffs)
• svxlink/trx/ToneDetector.h (modified) (1 diff)
• versions (modified) (1 diff)

branches/improved_tone_detector/src/svxlink/remotetrx/remotetrx.conf

@@ -51 +51 @@
 VOX_FILTER_DEPTH=20
 VOX_THRESH=1000
+#CTCSS_MODE=3
 CTCSS_FQ=136.5
 CTCSS_THRESH=10
+CTCSS_SNR_OPEN_THRESH=16
+CTCSS_SNR_CLOSE_THRESH=10
 SERIAL_PORT=/dev/ttyS0
 SERIAL_PIN=CTS:SET
@@ -103 +106 @@
 VOX_FILTER_DEPTH=20
 VOX_THRESH=1000
+#CTCSS_MODE=3
 CTCSS_FQ=136.5
 CTCSS_THRESH=10
+CTCSS_SNR_OPEN_THRESH=16
+CTCSS_SNR_CLOSE_THRESH=10
 SERIAL_PORT=/dev/ttyS0
 SERIAL_PIN=CTS:SET

branches/improved_tone_detector/src/svxlink/svxlink/svxlink.conf

@@ -135 +135 @@
 VOX_FILTER_DEPTH=20
 VOX_THRESH=1000
+#CTCSS_MODE=3
 CTCSS_FQ=136.5
 CTCSS_THRESH=10
+CTCSS_SNR_OPEN_THRESH=16
+CTCSS_SNR_CLOSE_THRESH=10
 SERIAL_PORT=/dev/ttyS0
 SERIAL_PIN=CTS:SET

branches/improved_tone_detector/src/svxlink/trx/SquelchCtcss.h

@@ -161 +161 @@
       int ctcss_mode = 1;
       cfg.getValue(rx_name, "CTCSS_MODE", ctcss_mode);
+      
+      float snr_open_thresh = 16;
+      cfg.getValue(rx_name, "CTCSS_SNR_OPEN_THRESH", snr_open_thresh);
+
+      float snr_close_thresh = 10;
+      cfg.getValue(rx_name, "CTCSS_SNR_CLOSE_THRESH", snr_close_thresh);
 
       det = new ToneDetector(ctcss_fq, 8.0f);
@@ -170 +176 @@
       {
         case 2:
-          std::cout << "### CTCSS mode: Center to total passband power\n";
+          std::cout << "### CTCSS mode: Estimated SNR\n";
           //det->setDetectBw(6.0f);
           det->setDetectUseWindowing(false);
           det->setDetectPeakThresh(0.0f);
-          det->setDetectPeakToTotPwrThresh(0.6f);
+          //det->setDetectPeakToTotPwrThresh(0.6f);
+          det->setDetectSnrThresh(snr_open_thresh, 210.0f);
           det->setDetectStableCountThresh(1);
 
@@ -180 +187 @@
           det->setUndetectUseWindowing(false);
           det->setUndetectPeakThresh(0.0f);
-          det->setUndetectPeakToTotPwrThresh(0.3f);
+          //det->setUndetectPeakToTotPwrThresh(0.3f);
+          det->setUndetectSnrThresh(snr_close_thresh, 210.0f);
           det->setUndetectStableCountThresh(2);
 
@@ -190 +198 @@
 
         case 3:
-          std::cout << "### CTCSS mode: Phase\n";
+          std::cout << "### CTCSS mode: Estimated SNR + Phase\n";
           //det->setDetectUseWindowing(false);
           det->setDetectBw(16.0f);
           det->setDetectPeakThresh(0.0f);
-          det->setDetectPeakToTotPwrThresh(0.6f);
+          //det->setDetectPeakToTotPwrThresh(0.6f);
+          det->setDetectSnrThresh(snr_open_thresh, 210.0f);
           det->setDetectStableCountThresh(1);
           det->setDetectPhaseBwThresh(2.0f, 2.0f);
@@ -201 +210 @@
           det->setUndetectUseWindowing(false);
           det->setUndetectPeakThresh(0.0f);
-          det->setUndetectPeakToTotPwrThresh(0.3f);
+          //det->setUndetectPeakToTotPwrThresh(0.3f);
+          det->setUndetectSnrThresh(snr_close_thresh, 210.0f);
           det->setUndetectStableCountThresh(2);
           //det->setUndetectPhaseBwThresh(4.0f, 16.0f);

branches/improved_tone_detector/src/svxlink/trx/ToneDetector.cpp

@@ -104 +104 @@
   float               peak_to_tot_pwr_thresh;
   float               passband_energy_thresh;
+  float               snr_thresh;
+  float               passband_bw;
 };
 
@@ -156 +158 @@
   det_par->peak_to_tot_pwr_thresh = 0.0f;
   det_par->passband_energy_thresh = 0.0f;
+  det_par->snr_thresh = 0.0f;
+  det_par->passband_bw = 0.0f;
 
   setDetectBw(width_hz);
@@ -376 +380 @@
 
 
+void ToneDetector::setDetectSnrThresh(float thresh_db, float passband_bw_hz)
+{
+  det_par->snr_thresh = thresh_db;
+  det_par->passband_bw = passband_bw_hz;
+} /* ToneDetector::setDetectSnrThresh */
+
+
+void ToneDetector::setUndetectSnrThresh(float thresh_db, float passband_bw_hz)
+{
+  undet_par->snr_thresh = thresh_db;  
+  undet_par->passband_bw = passband_bw_hz;
+} /* ToneDetector::setUndetectSnrThresh */
+
+
 void ToneDetector::setDetectPhaseBwThresh(float bw_hz, float stddev_hz)
 {
@@ -556 +574 @@
       // are doing:
       //
-      //    float Ptone = res_center / ((par->block_len*par->block_len) / 2);
+      //    float Ptone = 2.0f * res_center / (par->block_len*par->block_len);
       //    float Ppassband = passband_energy / par->block_len;
       //    float peak_to_tot_pwr = Ptone / Ppassband;
@@ -565 +583 @@
   }
 
+  if (par->passband_bw > 0.0f)
+  {
+      // Calculate mean tone power
+    float Ptone = 2.0f * res_center / (par->block_len*par->block_len);
+    
+      // Calculate mean passband power
+    float Ppassband = passband_energy / par->block_len;
+    
+      // Estimate the mean noise floor over the whole passband
+    float Pnoise = (Ppassband - Ptone) / ((par->passband_bw-par->bw) / par->bw);
+    
+      // Calculate the signal to noise ratio
+    float snr = 10 * log10(Ptone / Pnoise);
+    
+      // Check if the SNR is over the threshold
+    active = active && (snr > par->snr_thresh);
+  }
+  
     // If phase checking is active, check the phase
   if (phase_check_left > 0)

branches/improved_tone_detector/src/svxlink/trx/ToneDetector.h

@@ -292 +292 @@
      */
     void setUndetectPeakToTotPwrThresh(float thresh);
+
+    /**
+     * @brief  Set the peak to noise floor SNR threshold when inactive
+     * @param  thresh_db        The threshold in dB
+     * @param  passband_bw_hz   Passband bandwidth in Hz
+     *
+     * This function is used to set the signal to noise ratio
+     * threshold when the tone detector is in its inactive state, that is
+     * when a tone is not being detected.
+     * This will compare the narrow band Goertzel tone detector power to
+     * an estimated noise floor. The noise floor estimation is deduced from
+     * the total passband power where the tone has been removed. This will
+     * be a mean value of the noise floor for the whole passband. If the
+     * amplitude response for the passband is not flat, the noise floor will
+     * have an offset and so will the tone. This will mean that the SNR will
+     * also have an offset. So, for example, if the part of the passband where
+     * the tone is expected to appear is attenuated by 6dB in comparision to
+     * the mean passband gain, the threshold need to also be lowered by 6dB.
+     */
+    void setDetectSnrThresh(float thresh_db, float passband_bw_hz);
+
+    /**
+     * @brief  Set the peak to noise floor SNR threshold when active
+     * @param  thresh_db        The threshold in dB
+     * @param  passband_bw_hz   Passband bandwidth in Hz
+     *
+     * This function is used to set the signal to noise ratio
+     * threshold when the tone detector is in its active state, that is
+     * when a tone is being detected.
+     * This will compare the narrow band Goertzel tone detector power to
+     * an estimated noise floor. The noise floor estimation is deduced from
+     * the total passband power where the tone has been removed. This will
+     * be a mean value of the noise floor for the whole passband. If the
+     * amplitude response for the passband is not flat, the noise floor will
+     * have an offset and so will the tone. This will mean that the SNR will
+     * also have an offset. So, for example, if the part of the passband where
+     * the tone is expected to appear is attenuated by 6dB in comparision to
+     * the mean passband gain, the threshold need to also be lowered by 6dB.
+     */
+    void setUndetectSnrThresh(float thresh_db, float passband_bw_hz);
 
     /**

branches/improved_tone_detector/src/versions

@@ -12 +12 @@
 
 # SvxLink versions
-SVXLINK=0.13.99.0
+SVXLINK=0.13.99.1
 SVXLINK_RPM_RELEASE=1
 MODULE_HELP=0.7.0.99.0