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fix(jp-lbt): reduce LBT backoff parameters for SF10 airtime #3103

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fix(jp-lbt): reduce LBT backoff parameters for SF10 airtime #3103

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55 changes: 52 additions & 3 deletions src/helpers/radiolib/RadioLibWrappers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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;
}

Expand All @@ -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 = 500;
uint32_t max_backoff = min(base_ms * (1u << _busy_count), (uint32_t)4000);
_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
Expand Down
46 changes: 35 additions & 11 deletions src/helpers/radiolib/RadioLibWrappers.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3,9 +3,6 @@
#include <Mesh.h>
#include <RadioLib.h>

#ifdef USE_CC310_HW_CRYPTO
#include <Adafruit_nRFCrypto.h>
#endif
struct PacketMillis {
uint32_t preambleMillis; // preamble-detect -> header-valid deadline
uint32_t payloadMillis; // header-valid -> rx-done deadline
Expand All @@ -18,18 +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(); }
Expand All @@ -56,6 +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; }
Expand Down Expand Up @@ -89,15 +120,8 @@ class RadioNoiseListener : public mesh::RNG {
RadioNoiseListener(PhysicalLayer& radio): _radio(&radio) { }

void random(uint8_t* dest, size_t sz) override {
#ifdef USE_CC310_HW_CRYPTO
// CC310 TRNG is higher quality and environment-independent vs radio RSSI noise.
nRFCrypto.begin();
nRFCrypto.Random.generate(dest, (uint16_t)sz);
nRFCrypto.end();
#else
for (int i = 0; i < sz; i++) {
dest[i] = _radio->randomByte() ^ (::random(0, 256) & 0xFF);
}
#endif
}
};