Reduce probe interval on less busy channels

src/helpers/radiolib/RadioLibWrappers.cpp

@@ -14,10 +14,11 @@
 // ambient CAD auto-calibration: probe CAD periodically while idle, and raise/lower detPeak
 // so ambient activity (sub-decode-threshold distant traffic, interference) stops tripping LBT
 #define CAD_PROBE_INTERVAL     4000   // millis between ambient CAD probes
-#define CAD_PROBE_WINDOW         32   // probes per evaluation window
-#define CAD_PROBE_RAISE_HITS     10   // >= ~30% ambient detect rate -> desensitize
-#define CAD_PROBE_LOWER_HITS      3   // <= ~10% ambient detect rate -> re-sensitize
-#define CAD_PEAK_OFFSET_MAX      10
+#define CAD_PROBE_INTERVAL_QUIET 16000  // slower probing while offset is 0 and channel is clean
+#define CAD_PROBE_WINDOW         16   // probes per evaluation window
+#define CAD_PROBE_RAISE_HITS      5   // >= ~30% ambient detect rate -> desensitize
+#define CAD_PROBE_LOWER_HITS      2   // <= ~12% ambient detect rate -> re-sensitize
+#define CAD_PEAK_OFFSET_MAX       6
 
 static volatile uint8_t state = STATE_IDLE;
 
@@ -49,6 +50,7 @@ void RadioLibWrapper::begin() {
   _cad_probe_count = _cad_probe_hits = 0;
   _cad_last_count = _cad_last_hits = 0;
   _last_cad_probe = 0;
+  _cad_probe_interval = CAD_PROBE_INTERVAL;
 
   // start average out some samples
   _num_floor_samples = 0;
@@ -116,7 +118,7 @@ void RadioLibWrapper::loop() {
   }
 
   if (_cad_enabled && state == STATE_RX && getCADDetPeakBase() > 0
-      && millis() - _last_cad_probe >= CAD_PROBE_INTERVAL) {
+      && millis() - _last_cad_probe >= _cad_probe_interval) {
     _last_cad_probe = millis();
     if (!isReceivingPacket()) {
       int16_t result = performChannelScan();
@@ -130,6 +132,7 @@ void RadioLibWrapper::loop() {
       } else if (result == RADIOLIB_LORA_DETECTED || result == RADIOLIB_PREAMBLE_DETECTED) {
         _cad_probe_count++;
         _cad_probe_hits++;
+        _cad_probe_interval = CAD_PROBE_INTERVAL;   // activity -> resume fast probing
       }
       // else: scan error, don't count the sample
 
@@ -143,10 +146,14 @@ void RadioLibWrapper::loop() {
         _cad_probe_count = _cad_probe_hits = 0;
       } else if (_cad_probe_count >= CAD_PROBE_WINDOW) {
         if (_cad_probe_hits <= CAD_PROBE_LOWER_HITS && _cad_peak_offset > 0) {
-          _cad_peak_offset--;
+          // step down twice as fast when the window was completely clean
+          _cad_peak_offset -= (_cad_probe_hits == 0 && _cad_peak_offset >= 2) ? 2 : 1;
           MESH_DEBUG_PRINTLN("RadioLibWrapper: CAD ambient %d/%d, detPeak offset -> %d",
               (int)_cad_probe_hits, (int)_cad_probe_count, (int)_cad_peak_offset);
         }
+        if (_cad_probe_hits == 0 && _cad_peak_offset == 0) {
+          _cad_probe_interval = CAD_PROBE_INTERVAL_QUIET;   // idle channel, probe less often
+        }
         _cad_last_hits = _cad_probe_hits; _cad_last_count = _cad_probe_count;
         _cad_probe_count = _cad_probe_hits = 0;
       }

src/helpers/radiolib/RadioLibWrappers.h

@@ -21,6 +21,7 @@ protected:
   uint8_t _cad_peak_offset;
   uint8_t _cad_probe_count, _cad_probe_hits;
   uint8_t _cad_last_count, _cad_last_hits;
+  uint16_t _cad_probe_interval;
   unsigned long _last_cad_probe;
 
   void idle();