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

examples/simple_repeater/MyMesh.cpp

@@ -541,10 +541,22 @@ int MyMesh::calcRxDelay(float score, uint32_t air_time) const {
 }
 
 uint32_t MyMesh::getRetransmitDelay(const mesh::Packet *packet) {
+  if (_radio->isAS923_1_JP()) {
+    // JP LBT: suppress txdelay to jitter-scale to avoid adding unnecessary
+    // latency on top of LBT backoff. A window equal to jitter_max gives
+    // ~33% collision reduction vs zero, scales naturally with airtime as
+    // CR changes, and keeps average added delay to ~56ms at SF12/BW125.
+    uint32_t jitter_max = _radio->getEstAirtimeFor(MAX_TRANS_UNIT) / RadioLibWrapper::JP_LBT_JITTER_DIVISOR;
+    return getRNG()->nextInt(0, jitter_max + 1);
+  }
   uint32_t t = (_radio->getEstAirtimeFor(packet->getPathByteLen() + packet->payload_len + 2) * _prefs.tx_delay_factor);
   return getRNG()->nextInt(0, 5*t + 1);
 }
 uint32_t MyMesh::getDirectRetransmitDelay(const mesh::Packet *packet) {
+  if (_radio->isAS923_1_JP()) {
+    uint32_t jitter_max = _radio->getEstAirtimeFor(MAX_TRANS_UNIT) / RadioLibWrapper::JP_LBT_JITTER_DIVISOR;
+    return getRNG()->nextInt(0, jitter_max + 1);
+  }
   uint32_t t = (_radio->getEstAirtimeFor(packet->getPathByteLen() + packet->payload_len + 2) * _prefs.direct_tx_delay_factor);
   return getRNG()->nextInt(0, 5*t + 1);
 }

examples/simple_room_server/MyMesh.cpp

@@ -272,10 +272,22 @@ const char *MyMesh::getLogDateTime() {
 }
 
 uint32_t MyMesh::getRetransmitDelay(const mesh::Packet *packet) {
+  if (_radio->isAS923_1_JP()) {
+    // JP LBT: suppress txdelay to jitter-scale to avoid adding unnecessary
+    // latency on top of LBT backoff. A window equal to jitter_max gives
+    // ~33% collision reduction vs zero, scales naturally with airtime as
+    // CR changes, and keeps average added delay to ~56ms at SF12/BW125.
+    uint32_t jitter_max = _radio->getEstAirtimeFor(MAX_TRANS_UNIT) / RadioLibWrapper::JP_LBT_JITTER_DIVISOR;
+    return getRNG()->nextInt(0, jitter_max + 1);
+  }
   uint32_t t = (_radio->getEstAirtimeFor(packet->getPathByteLen() + packet->payload_len + 2) * _prefs.tx_delay_factor);
   return getRNG()->nextInt(0, 5*t + 1);
 }
 uint32_t MyMesh::getDirectRetransmitDelay(const mesh::Packet *packet) {
+  if (_radio->isAS923_1_JP()) {
+    uint32_t jitter_max = _radio->getEstAirtimeFor(MAX_TRANS_UNIT) / RadioLibWrapper::JP_LBT_JITTER_DIVISOR;
+    return getRNG()->nextInt(0, jitter_max + 1);
+  }
   uint32_t t = (_radio->getEstAirtimeFor(packet->getPathByteLen() + packet->payload_len + 2) * _prefs.direct_tx_delay_factor);
   return getRNG()->nextInt(0, 5*t + 1);
 }

examples/simple_sensor/SensorMesh.cpp

@@ -313,12 +313,24 @@ int SensorMesh::calcRxDelay(float score, uint32_t air_time) const {
 }
 
 uint32_t SensorMesh::getRetransmitDelay(const mesh::Packet* packet) {
+  if (_radio->isAS923_1_JP()) {
+    // JP LBT: suppress txdelay to jitter-scale to avoid adding unnecessary
+    // latency on top of LBT backoff. A window equal to jitter_max gives
+    // ~33% collision reduction vs zero, scales naturally with airtime as
+    // CR changes, and keeps average added delay to ~56ms at SF12/BW125.
+    uint32_t jitter_max = _radio->getEstAirtimeFor(MAX_TRANS_UNIT) / RadioLibWrapper::JP_LBT_JITTER_DIVISOR;
+    return getRNG()->nextInt(0, jitter_max + 1);
+  }
   uint32_t t = (_radio->getEstAirtimeFor(packet->getPathByteLen() + packet->payload_len + 2) * _prefs.tx_delay_factor);
-  return getRNG()->nextInt(0, 6)*t;
+  return getRNG()->nextInt(0, 5*t + 1);
 }
 uint32_t SensorMesh::getDirectRetransmitDelay(const mesh::Packet* packet) {
+  if (_radio->isAS923_1_JP()) {
+    uint32_t jitter_max = _radio->getEstAirtimeFor(MAX_TRANS_UNIT) / RadioLibWrapper::JP_LBT_JITTER_DIVISOR;
+    return getRNG()->nextInt(0, jitter_max + 1);
+  }
   uint32_t t = (_radio->getEstAirtimeFor(packet->getPathByteLen() + packet->payload_len + 2) * _prefs.direct_tx_delay_factor);
-  return getRNG()->nextInt(0, 6)*t;
+  return getRNG()->nextInt(0, 5*t + 1);
 }
 int SensorMesh::getInterferenceThreshold() const {
   return _prefs.interference_threshold;

src/Dispatcher.cpp

@@ -60,6 +60,7 @@ uint32_t Dispatcher::getCADFailRetryDelay() const {
   return 200;
 }
 uint32_t Dispatcher::getCADFailMaxDuration() const {
+  if (_radio->isAS923_1_JP()) return UINT32_MAX;  // ARIB STD-T108: never force TX during LBT
   return 4000;   // 4 seconds
 }
 

src/Dispatcher.h

@@ -78,6 +78,11 @@ class Radio {
 
   virtual float getLastRSSI() const { return 0; }
   virtual float getLastSNR() const { return 0; }
+
+  virtual bool isAS923_1_JP() const { return false; }
+
+  virtual int getMaxTextLen() const { return 10 * 16; }       // default 160 bytes
+  virtual int getMaxGroupTextLen() const { return 10 * 16; }  // default 160 bytes
 };
 
 /**

src/helpers/BaseChatMesh.cpp

@@ -419,8 +419,9 @@ 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
@@ -460,7 +461,8 @@ 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
@@ -493,7 +495,8 @@ 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/radiolib/CustomLR1110.h

@@ -82,4 +82,5 @@ class CustomLR1110 : public LR1110 {
     }
 
     uint8_t getSpreadingFactor() const { return spreadingFactor; }
+    uint8_t getCodingRate() const { return this->codingRate + 4; }  // RadioLib stores 1-4, return 5-8
 };

src/helpers/radiolib/CustomLR1110Wrapper.h

@@ -43,6 +43,8 @@ class CustomLR1110Wrapper : public RadioLibWrapper {
   float getLastSNR() const override { return ((CustomLR1110 *)_radio)->getSNR(); }
 
   uint8_t getSpreadingFactor() const override { return ((CustomLR1110 *)_radio)->getSpreadingFactor(); }
+  uint8_t getCodingRate() const override { return ((CustomLR1110 *)_radio)->getCodingRate(); }
+  float getFreqMHz() const override { return ((CustomLR1110 *)_radio)->getFreqMHz(); }
 
   bool setRxBoostedGainMode(bool en) override {
     return ((CustomLR1110 *)_radio)->setRxBoostedGainMode(en) == RADIOLIB_ERR_NONE;

src/helpers/radiolib/CustomSX1262Wrapper.h

@@ -37,6 +37,8 @@ class CustomSX1262Wrapper : public RadioLibWrapper {
     return packetScoreInt(snr, sf, packet_len);
   }
   uint8_t getSpreadingFactor() const override { return ((CustomSX1262 *)_radio)->spreadingFactor; }
+  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; }
   virtual void powerOff() override {
     ((CustomSX1262 *)_radio)->sleep(false);
   }

src/helpers/radiolib/RadioLibWrappers.cpp

@@ -2,6 +2,12 @@
 #define RADIOLIB_STATIC_ONLY 1
 #include "RadioLibWrappers.h"
 
+#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
@@ -176,6 +182,9 @@ bool RadioLibWrapper::isSendComplete() {
 void RadioLibWrapper::onSendFinished() {
   _radio->finishTransmit();
   _board->onAfterTransmit();
+  if (isAS923_1_JP()) {
+    delay(50);  // ARIB STD-T108 §3.4.1: >= 50ms between transmissions
+  }
   state = STATE_IDLE;
 }
 
@@ -184,10 +193,50 @@ int16_t RadioLibWrapper::performChannelScan() {
 }
 
 bool RadioLibWrapper::isChannelActive() {
-  // int.thresh: RSSI-based interference detection (relative to noise floor)
-  if (_threshold != 0 && getCurrentRSSI() > _noise_floor + _threshold) return true;
+  if (isAS923_1_JP()) {
+    // Non-blocking backoff: if a prior busy detection armed a backoff wait,
+    // report busy and let Dispatcher::checkSend() re-poll on the next loop()
+    // pass instead of spin-waiting here (which used to block the Dispatcher
+    // loop for up to 16s).
+    if (_lbt_backoff_active) {
+      if ((int32_t)(millis() - _lbt_deadline) < 0) {
+        return true;  // still waiting; re-checked next call
+      }
+      _lbt_backoff_active = false;
+      return isChannelActive();  // backoff elapsed -- re-sense (bounded, single-level recursion)
+    }
+
+    // ARIB STD-T108: 5ms continuous RSSI sensing, -80dBm absolute threshold
+    uint32_t sense_start = millis();
+    while (millis() - sense_start < 5) {
+      if (getCurrentRSSI() > -80.0f) {
+        _busy_count++;
+        uint32_t base_ms = 2000;
+        uint32_t max_backoff = min(base_ms * (1u << _busy_count), (uint32_t)16000);
+        _lbt_deadline = millis() + random(max_backoff / 2, max_backoff);
+        _lbt_backoff_active = true;
+        return true;
+      }
+      YIELD_TASK();
+    }
+    // Channel free: reset busy counter and add airtime-scaled jitter.
+    // JP_LBT_JITTER_DIVISOR controls jitter upper bound:
+    //   /8  -> SF12/BW125 ~975ms, SF7/BW62.5 ~50ms
+    //   /16 -> SF12/BW125 ~490ms, SF7/BW62.5 ~25ms
+    //   /32 -> SF12/BW125 ~245ms, SF7/BW62.5 ~12ms  (default)
+    _busy_count = 0;
+    uint32_t airtime_ms = getEstAirtimeFor(MAX_TRANS_UNIT);
+    uint32_t jitter_until = millis() + random(0, airtime_ms / JP_LBT_JITTER_DIVISOR);
+    while (millis() < jitter_until) {
+      YIELD_TASK();
+    }
+    // JP RSSI sensing passed; fall through to CAD if enabled
+  } else {
+    // Non-JP: RSSI-based interference detection (relative to noise floor)
+    if (_threshold != 0 && getCurrentRSSI() > _noise_floor + _threshold) return true;
+  }
 
-  // cad: hardware channel activity detection
+  // hardware channel activity detection (JP and non-JP)
   if (_cad_enabled) {
     int16_t result = performChannelScan();
     // scanChannel() triggers DIO interrupt (CAD done) which sets STATE_INT_READY

src/helpers/radiolib/RadioLibWrappers.h

@@ -15,18 +15,22 @@ class RadioLibWrapper : public mesh::Radio {
   uint32_t n_recv, n_sent, n_recv_errors;
   int16_t _noise_floor, _threshold;
   bool _cad_enabled;
+  uint8_t _busy_count;
   uint16_t _num_floor_samples;
   int32_t _floor_sample_sum;
   uint8_t _preamble_sf;
 
+  bool _lbt_backoff_active;   // non-blocking wait after RSSI busy detection (up to 16s)
+  uint32_t _lbt_deadline;
+
   void idle();
   void startRecv();
   float packetScoreInt(float snr, int sf, int packet_len);
   virtual bool isReceivingPacket() =0;
   virtual void doResetAGC();
 
 public:
-  RadioLibWrapper(PhysicalLayer& radio, mesh::MainBoard& board) : _radio(&radio), _board(&board), _preamble_sf(0) { n_recv = n_sent = 0; }
+  RadioLibWrapper(PhysicalLayer& radio, mesh::MainBoard& board) : _radio(&radio), _board(&board), _busy_count(0), _preamble_sf(0), _lbt_backoff_active(false), _lbt_deadline(0) { n_recv = n_sent = 0; }
 
   void begin() override;
   virtual void powerOff() { _radio->sleep(); }
@@ -53,6 +57,36 @@ class RadioLibWrapper : public mesh::Radio {
   static uint16_t preambleLengthForSF(uint8_t sf) { return sf <= 8 ? 32 : 16; }
   void updatePreamble(uint8_t sf) { _preamble_sf = sf; _radio->setPreambleLength(preambleLengthForSF(sf)); }
   PacketMillis calcMaxPacketMillis(uint8_t sf, float bw, uint8_t cr, uint8_t preambleSymbols);
+  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
+
+  static constexpr uint8_t JP_LBT_JITTER_DIVISOR = 32;
+
+  bool isAS923_1_JP() const override {
+    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 override {
+    if (!isAS923_1_JP()) 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 override {
+    if (!isAS923_1_JP()) 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; }