Add Japan LoRa LBT compliance (ARIB STD-T108) with runtime frequency detection

examples/companion_radio/MyMesh.cpp

@@ -255,7 +255,7 @@ float MyMesh::getAirtimeBudgetFactor() const {
 }
 
 int MyMesh::getInterferenceThreshold() const {
-  return 0; // disabled for now, until currentRSSI() problem is resolved
+  return 1; // non-zero enables hardware CAD (Channel Activity Detection) before TX
 }
 
 int MyMesh::calcRxDelay(float score, uint32_t air_time) const {

examples/simple_repeater/MyMesh.cpp

@@ -871,7 +871,7 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
   _prefs.advert_interval = 1;        // default to 2 minutes for NEW installs
   _prefs.flood_advert_interval = 12; // 12 hours
   _prefs.flood_max = 64;
-  _prefs.interference_threshold = 0; // disabled
+  _prefs.interference_threshold = 1; // non-zero enables hardware CAD before TX
 
   // bridge defaults
   _prefs.bridge_enabled = 1;    // enabled

examples/simple_room_server/MyMesh.cpp

@@ -622,7 +622,7 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
   _prefs.advert_interval = 1;        // default to 2 minutes for NEW installs
   _prefs.flood_advert_interval = 12; // 12 hours
   _prefs.flood_max = 64;
-  _prefs.interference_threshold = 0; // disabled
+  _prefs.interference_threshold = 1; // non-zero enables hardware CAD before TX
 #ifdef ROOM_PASSWORD
   StrHelper::strncpy(_prefs.guest_password, ROOM_PASSWORD, sizeof(_prefs.guest_password));
 #endif

examples/simple_sensor/SensorMesh.cpp

@@ -723,7 +723,7 @@ SensorMesh::SensorMesh(mesh::MainBoard& board, mesh::Radio& radio, mesh::Millise
   _prefs.flood_advert_interval = 0;   // disabled
   _prefs.disable_fwd = true;
   _prefs.flood_max = 64;
-  _prefs.interference_threshold = 0;  // disabled
+  _prefs.interference_threshold = 1;  // non-zero enables hardware CAD before TX
 
   // GPS defaults
   _prefs.gps_enabled = 0;

src/Dispatcher.h

@@ -38,6 +38,9 @@ class Radio {
 
   virtual float packetScore(float snr, int packet_len) = 0;
 
+  virtual int getMaxTextLen() const { return 10 * 16; }  // default: non-JP
+  virtual int getMaxGroupTextLen() const { return 10 * 16; }  // default: non-JP
+
   /**
    * \brief  starts the raw packet send. (no wait)
    * \param  bytes   the raw packet data

src/helpers/BaseChatMesh.cpp

@@ -395,9 +395,9 @@ void BaseChatMesh::onGroupDataRecv(mesh::Packet* packet, uint8_t type, const mes
 
 mesh::Packet* BaseChatMesh::composeMsgPacket(const ContactInfo& recipient, uint32_t timestamp, uint8_t attempt, const char *text, uint32_t& expected_ack) {
   int text_len = strlen(text);
-  if (text_len > MAX_TEXT_LEN) return NULL;
-  if (attempt > 3 && text_len > MAX_TEXT_LEN-2) return NULL;
-
+  int max_len = _radio->getMaxTextLen();
+  if (text_len > max_len) return NULL;
+  if (attempt > 3 && text_len > max_len - 2) return NULL;
   uint8_t temp[5+MAX_TEXT_LEN+1];
   memcpy(temp, &timestamp, 4);   // mostly an extra blob to help make packet_hash unique
   temp[4] = (attempt & 3);
@@ -436,7 +436,8 @@ int  BaseChatMesh::sendMessage(const ContactInfo& recipient, uint32_t timestamp,
 
 int  BaseChatMesh::sendCommandData(const ContactInfo& recipient, uint32_t timestamp, uint8_t attempt, const char* text, uint32_t& est_timeout) {
   int text_len = strlen(text);
-  if (text_len > MAX_TEXT_LEN) return MSG_SEND_FAILED;
+  int max_len = _radio->getMaxTextLen();
+  if (text_len > max_len) return MSG_SEND_FAILED;
 
   uint8_t temp[5+MAX_TEXT_LEN+1];
   memcpy(temp, &timestamp, 4);   // mostly an extra blob to help make packet_hash unique
@@ -469,7 +470,9 @@ bool BaseChatMesh::sendGroupMessage(uint32_t timestamp, mesh::GroupChannel& chan
   char *ep = strchr((char *) &temp[5], 0);
   int prefix_len = ep - (char *) &temp[5];
 
-  if (text_len + prefix_len > MAX_TEXT_LEN) text_len = MAX_TEXT_LEN - prefix_len;
+  int max_len = _radio->getMaxGroupTextLen();
+  if (text_len + prefix_len > max_len) text_len = max_len - prefix_len;
+
   memcpy(ep, text, text_len);
   ep[text_len] = 0;  // null terminator
 

src/helpers/BaseChatMesh.h

@@ -5,7 +5,8 @@
 #include <helpers/AdvertDataHelpers.h>
 #include <helpers/TxtDataHelpers.h>
 
-#define MAX_TEXT_LEN    (10*CIPHER_BLOCK_SIZE)  // must be LESS than (MAX_PACKET_PAYLOAD - 4 - CIPHER_MAC_SIZE - 1)
+#define MAX_TEXT_LEN  (10*CIPHER_BLOCK_SIZE)  
+// must be LESS than (MAX_PACKET_PAYLOAD - 4 - CIPHER_MAC_SIZE - 1)
 
 #include "ContactInfo.h"
 

src/helpers/radiolib/CustomLR1110.h

@@ -36,4 +36,8 @@ class CustomLR1110 : public LR1110 {
       bool detected = ((irq & RADIOLIB_LR11X0_IRQ_SYNC_WORD_HEADER_VALID) || (irq & RADIOLIB_LR11X0_IRQ_PREAMBLE_DETECTED));
       return detected;
     }
-};
+
+    uint8_t getCodingRate() const {
+      return this->codingRate + 4;  // RadioLib stores 1-4, return 5-8
+    }
+};

src/helpers/radiolib/CustomLR1110Wrapper.h

@@ -31,4 +31,11 @@ class CustomLR1110Wrapper : public RadioLibWrapper {
   bool getRxBoostedGainMode() const override {
     return ((CustomLR1110 *)_radio)->getRxBoostedGainMode();
   }
+
+  uint8_t getCodingRate() const override {
+    return ((CustomLR1110 *)_radio)->getCodingRate();
+  }
+  float getFreqMHz() const override {
+    return ((CustomLR1110 *)_radio)->getFreqMHz();
+  }
 };

src/helpers/radiolib/CustomSTM32WLxWrapper.h

@@ -23,4 +23,11 @@ class CustomSTM32WLxWrapper : public RadioLibWrapper {
   }
 
   void doResetAGC() override { sx126xResetAGC((SX126x *)_radio); }
+
+  uint8_t getCodingRate() const override {
+    return ((CustomSTM32WLx *)_radio)->codingRate + 4;
+  }
+  float getFreqMHz() const override {
+    return ((CustomSTM32WLx *)_radio)->freqMHz;
+  }
 };

src/helpers/radiolib/CustomSX1262.h

@@ -97,4 +97,4 @@ class CustomSX1262 : public SX1262 {
       readRegister(RADIOLIB_SX126X_REG_RX_GAIN, &rxGain, 1);
       return (rxGain == RADIOLIB_SX126X_RX_GAIN_BOOSTED);
     }
-};
+};

src/helpers/radiolib/CustomSX1262Wrapper.h

@@ -36,4 +36,11 @@ class CustomSX1262Wrapper : public RadioLibWrapper {
   bool getRxBoostedGainMode() const override {
     return ((CustomSX1262 *)_radio)->getRxBoostedGainMode();
   }
+
+  uint8_t getCodingRate() const override {
+    return ((CustomSX1262 *)_radio)->codingRate + 4;  // RadioLib stores 1-4, return 5-8
+  }
+  float getFreqMHz() const override {
+    return ((CustomSX1262 *)_radio)->freqMHz;
+  }
 };

src/helpers/radiolib/RadioLibWrappers.cpp

@@ -2,6 +2,13 @@
 #define RADIOLIB_STATIC_ONLY 1
 #include "RadioLibWrappers.h"
 
+// Platform-safe yield for use in busy-wait loops
+#ifdef NRF52_PLATFORM
+  #define YIELD_TASK() vTaskDelay(1)
+#else
+  #define YIELD_TASK() delay(1)
+#endif
+
 #define STATE_IDLE       0
 #define STATE_RX         1
 #define STATE_TX_WAIT    3
@@ -34,6 +41,7 @@ void RadioLibWrapper::begin() {
 
   _noise_floor = 0;
   _threshold = 0;
+  _busy_count = 0;  // initialize exponential backoff counter
 
   // start average out some samples
   _num_floor_samples = 0;
@@ -165,13 +173,51 @@ bool RadioLibWrapper::isSendComplete() {
 void RadioLibWrapper::onSendFinished() {
   _radio->finishTransmit();
   _board->onAfterTransmit();
+  if (isJapanMode()) {
+    // ARIB STD-T108: wait >= 50ms after TX before next transmission
+    delay(50);
+  }
   state = STATE_IDLE;
 }
 
+int16_t RadioLibWrapper::performChannelScan() {
+  return _radio->scanChannel();
+}
+
 bool RadioLibWrapper::isChannelActive() {
-  return _threshold == 0 
-          ? false    // interference check is disabled
-          : getCurrentRSSI() > _noise_floor + _threshold;
+  if (_threshold == 0) return false;    // interference check is disabled
+
+  // Activate JP_STRICT LBT on Japan 920MHz band 3 channels only
+  // CH25=920.800MHz, CH26=921.000MHz, CH27=921.200MHz (ARIB STD-T108)
+  if (isJapanMode()) {
+    // ARIB STD-T108 compliant LBT: continuous RSSI sensing for >= 5ms
+    // Energy-based sensing required; LoRa CAD not used 
+    uint32_t sense_start = millis();
+    while (millis() - sense_start < 5) {
+      if (getCurrentRSSI() > -80.0f) {
+        // Channel busy: exponential backoff (tuned for JP 4s airtime)
+        _busy_count++;
+        uint32_t base_ms = 2000;
+        uint32_t max_backoff = min(base_ms * (1u << _busy_count), (uint32_t)16000);
+        uint32_t backoff_until = millis() + random(max_backoff / 2, max_backoff);
+        while (millis() < backoff_until) {
+          YIELD_TASK();
+        }
+        return true;
+      }
+      YIELD_TASK();
+    }
+    // Channel free: reset busy counter and add small jitter
+    _busy_count = 0;
+    uint32_t jitter_until = millis() + random(0, 500);
+    while (millis() < jitter_until) {
+      YIELD_TASK();
+    }
+    return false;
+  }
+
+  // Non-JP: original behavior (RSSI threshold only)
+  return getCurrentRSSI() > _noise_floor + _threshold;
 }
 
 float RadioLibWrapper::getLastRSSI() const {

src/helpers/radiolib/RadioLibWrappers.h

@@ -9,6 +9,7 @@ class RadioLibWrapper : public mesh::Radio {
   mesh::MainBoard* _board;
   uint32_t n_recv, n_sent, n_recv_errors;
   int16_t _noise_floor, _threshold;
+  uint8_t _busy_count;  // consecutive busy detections for exponential backoff
   uint16_t _num_floor_samples;
   int32_t _floor_sample_sum;
 
@@ -31,14 +32,43 @@ class RadioLibWrapper : public mesh::Radio {
   bool isInRecvMode() const override;
   bool isChannelActive();
 
-  bool isReceiving() override { 
+  bool isReceiving() override {
     if (isReceivingPacket()) return true;
 
     return isChannelActive();
   }
 
   virtual float getCurrentRSSI() =0;
+  virtual uint8_t getCodingRate() const { return 8; }   // default CR4/8, override in subclass
+  virtual float getFreqMHz() const { return 0.0f; }     // default unknown, override in subclass
+						      //
+  bool isJapanMode() const {
+    float freq = getFreqMHz();
+    return (fabsf(freq - 920.800f) < 0.05f ||
+            fabsf(freq - 921.000f) < 0.05f ||
+            fabsf(freq - 921.200f) < 0.05f);
+  }
+
+  int getMaxTextLen() const {
+    if (!isJapanMode()) return 10 * 16;  // default 160 bytes
+    uint8_t cr = getCodingRate();
+    if (cr <= 5) return 64;  // 3874ms @ SF12/BW125/CR4-5
+    if (cr == 6) return 48;  // 3874ms @ SF12/BW125/CR4-6
+    if (cr == 7) return 32;  // 3678ms @ SF12/BW125/CR4-7
+    return 24;               // 3547ms @ SF12/BW125/CR4-8
+  }
+
+  int getMaxGroupTextLen() const {
+    if (!isJapanMode()) return 10 * 16;  // default 160 bytes
+    uint8_t cr = getCodingRate();
+    if (cr <= 5) return 64;  // 3710ms @ SF12/BW125/CR4-5
+    if (cr == 6) return 48;  // 3678ms @ SF12/BW125/CR4-6
+    if (cr == 7) return 39;  // 3907ms @ SF12/BW125/CR4-7
+    return 29;               // 3809ms @ SF12/BW125/CR4-8
+  }
 
+  virtual int16_t performChannelScan();
+
   int getNoiseFloor() const override { return _noise_floor; }
   void triggerNoiseFloorCalibrate(int threshold) override;
   void resetAGC() override;

variants/rak_wismesh_tag/platformio.ini

@@ -118,4 +118,4 @@ build_flags =
 ;  -D MESH_PACKET_LOGGING=1
   -D MESH_DEBUG=1
 build_src_filter = ${rak4631.build_src_filter}
-  +<../examples/simple_sensor>
+  +<../examples/simple_sensor>