Calculate airtime of transmitted and received packets separately

src/mesh/LR11x0Interface.h

@@ -65,5 +65,7 @@ template <class T> class LR11x0Interface : public RadioLibInterface
     virtual void addReceiveMetadata(meshtastic_MeshPacket *mp) override;
 
     virtual void setStandby() override;
+
+    uint32_t getPacketTime(uint32_t pl, bool received) override { return computePacketTime(lora, pl, received); }
 };
 #endif

src/mesh/RF95Interface.h

@@ -65,8 +65,10 @@ class RF95Interface : public RadioLibInterface
      */
     virtual void configHardwareForSend() override;
 
+    uint32_t getPacketTime(uint32_t pl, bool received) override { return computePacketTime(*lora, pl, received); }
+
   private:
     /** Some boards require GPIO control of tx vs rx paths */
     void setTransmitEnable(bool txon);
 };
-#endif
+#endif

src/mesh/RadioInterface.cpp

@@ -230,33 +230,7 @@ The band is from 902 to 928 MHz. It mentions channel number and its respective c
 separated by 2.16 MHz with respect to the adjacent channels. Channel zero starts at 903.08 MHz center frequency.
 */
 
-/**
- * Calculate airtime per
- * https://www.rs-online.com/designspark/rel-assets/ds-assets/uploads/knowledge-items/application-notes-for-the-internet-of-things/LoRa%20Design%20Guide.pdf
- * section 4
- *
- * @return num msecs for the packet
- */
-uint32_t RadioInterface::getPacketTime(uint32_t pl)
-{
-    float bandwidthHz = bw * 1000.0f;
-    bool headDisable = false; // we currently always use the header
-    float tSym = (1 << sf) / bandwidthHz;
-
-    bool lowDataOptEn = tSym > 16e-3 ? true : false; // Needed if symbol time is >16ms
-
-    float tPreamble = (preambleLength + 4.25f) * tSym;
-    float numPayloadSym =
-        8 + max(ceilf(((8.0f * pl - 4 * sf + 28 + 16 - 20 * headDisable) / (4 * (sf - 2 * lowDataOptEn))) * cr), 0.0f);
-    float tPayload = numPayloadSym * tSym;
-    float tPacket = tPreamble + tPayload;
-
-    uint32_t msecs = tPacket * 1000;
-
-    return msecs;
-}
-
-uint32_t RadioInterface::getPacketTime(const meshtastic_MeshPacket *p)
+uint32_t RadioInterface::getPacketTime(const meshtastic_MeshPacket *p, bool received)
 {
     uint32_t pl = 0;
     if (p->which_payload_variant == meshtastic_MeshPacket_encrypted_tag) {
@@ -265,7 +239,7 @@ uint32_t RadioInterface::getPacketTime(const meshtastic_MeshPacket *p)
         size_t numbytes = pb_encode_to_bytes(bytes, sizeof(bytes), &meshtastic_Data_msg, &p->decoded);
         pl = numbytes + sizeof(PacketHeader);
     }
-    return getPacketTime(pl);
+    return getPacketTime(pl, received);
 }
 
 /** The delay to use for retransmitting dropped packets */
@@ -624,8 +598,7 @@ void RadioInterface::applyModemConfig()
     saveFreq(freq + loraConfig.frequency_offset);
 
     slotTimeMsec = computeSlotTimeMsec();
-    preambleTimeMsec = getPacketTime((uint32_t)0);
-    maxPacketTimeMsec = getPacketTime(meshtastic_Constants_DATA_PAYLOAD_LEN + sizeof(PacketHeader));
+    preambleTimeMsec = preambleLength * (pow_of_2(sf) / bw);
 
     LOG_INFO("Radio freq=%.3f, config.lora.frequency_offset=%.3f", freq, loraConfig.frequency_offset);
     LOG_INFO("Set radio: region=%s, name=%s, config=%u, ch=%d, power=%d", myRegion->name, channelName, loraConfig.modem_preset,
@@ -635,7 +608,7 @@ void RadioInterface::applyModemConfig()
     LOG_INFO("numChannels: %d x %.3fkHz", numChannels, bw);
     LOG_INFO("channel_num: %d", channel_num + 1);
     LOG_INFO("frequency: %f", getFreq());
-    LOG_INFO("Slot time: %u msec", slotTimeMsec);
+    LOG_INFO("Slot time: %u msec, preamble time: %u msec", slotTimeMsec, preambleTimeMsec);
 }
 
 /** Slottime is the time to detect a transmission has started, consisting of:

src/mesh/RadioInterface.h

@@ -87,9 +87,8 @@ class RadioInterface
     const uint8_t NUM_SYM_CAD = 2;       // Number of symbols used for CAD, 2 is the default since RadioLib 6.3.0 as per AN1200.48
     const uint8_t NUM_SYM_CAD_24GHZ = 4; // Number of symbols used for CAD in 2.4 GHz, 4 is recommended in AN1200.22 of SX1280
     uint32_t slotTimeMsec = computeSlotTimeMsec();
-    uint16_t preambleLength = 16;      // 8 is default, but we use longer to increase the amount of sleep time when receiving
-    uint32_t preambleTimeMsec = 165;   // calculated on startup, this is the default for LongFast
-    uint32_t maxPacketTimeMsec = 3246; // calculated on startup, this is the default for LongFast
+    uint16_t preambleLength = 16;    // 8 is default, but we use longer to increase the amount of sleep time when receiving
+    uint32_t preambleTimeMsec = 165; // calculated on startup, this is the default for LongFast
     const uint32_t PROCESSING_TIME_MSEC =
         4500;                // time to construct, process and construct a packet again (empirically determined)
     const uint8_t CWmin = 3; // minimum CWsize
@@ -202,8 +201,8 @@ class RadioInterface
      *
      * @return num msecs for the packet
      */
-    uint32_t getPacketTime(const meshtastic_MeshPacket *p);
-    uint32_t getPacketTime(uint32_t totalPacketLen);
+    uint32_t getPacketTime(const meshtastic_MeshPacket *p, bool received = false);
+    virtual uint32_t getPacketTime(uint32_t totalPacketLen, bool received = false) = 0;
 
     /**
      * Get the channel we saved.

src/mesh/RadioLibInterface.cpp

@@ -116,16 +116,21 @@ bool RadioLibInterface::receiveDetected(uint16_t irq, ulong syncWordHeaderValidF
     if (detected) {
         if (!activeReceiveStart) {
             activeReceiveStart = millis();
-        } else if (!Throttle::isWithinTimespanMs(activeReceiveStart, 2 * preambleTimeMsec) && !(irq & syncWordHeaderValidFlag)) {
-            // The HEADER_VALID flag should be set by now if it was really a packet, so ignore PREAMBLE_DETECTED flag
-            activeReceiveStart = 0;
-            LOG_DEBUG("Ignore false preamble detection");
-            return false;
-        } else if (!Throttle::isWithinTimespanMs(activeReceiveStart, maxPacketTimeMsec)) {
-            // We should have gotten an RX_DONE IRQ by now if it was really a packet, so ignore HEADER_VALID flag
-            activeReceiveStart = 0;
-            LOG_DEBUG("Ignore false header detection");
-            return false;
+        } else if (!Throttle::isWithinTimespanMs(activeReceiveStart, 2 * preambleTimeMsec)) {
+            if (!(irq & syncWordHeaderValidFlag)) {
+                // The HEADER_VALID flag should be set by now if it was really a packet, so ignore PREAMBLE_DETECTED flag
+                activeReceiveStart = 0;
+                LOG_DEBUG("Ignore false preamble detection");
+                return false;
+            } else {
+                uint32_t maxPacketTimeMsec = getPacketTime(meshtastic_Constants_DATA_PAYLOAD_LEN + sizeof(PacketHeader));
+                if (!Throttle::isWithinTimespanMs(activeReceiveStart, maxPacketTimeMsec)) {
+                    // We should have gotten an RX_DONE IRQ by now if it was really a packet, so ignore HEADER_VALID flag
+                    activeReceiveStart = 0;
+                    LOG_DEBUG("Ignore false header detection");
+                    return false;
+                }
+            }
         }
     }
     return detected;
@@ -411,8 +416,6 @@ void RadioLibInterface::completeSending()
 
 void RadioLibInterface::handleReceiveInterrupt()
 {
-    uint32_t xmitMsec;
-
     // when this is called, we should be in receive mode - if we are not, just jump out instead of bombing. Possible Race
     // Condition?
     if (!isReceiving) {
@@ -425,12 +428,12 @@ void RadioLibInterface::handleReceiveInterrupt()
     // read the number of actually received bytes
     size_t length = iface->getPacketLength();
 
-    xmitMsec = getPacketTime(length);
+    uint32_t rxMsec = getPacketTime(length, true);
 
 #ifndef DISABLE_WELCOME_UNSET
     if (config.lora.region == meshtastic_Config_LoRaConfig_RegionCode_UNSET) {
         LOG_WARN("lora rx disabled: Region unset");
-        airTime->logAirtime(RX_ALL_LOG, xmitMsec);
+        airTime->logAirtime(RX_ALL_LOG, rxMsec);
         return;
     }
 #endif
@@ -446,7 +449,7 @@ void RadioLibInterface::handleReceiveInterrupt()
                   radioBuffer.header.to, radioBuffer.header.from, radioBuffer.header.flags);
         rxBad++;
 
-        airTime->logAirtime(RX_ALL_LOG, xmitMsec);
+        airTime->logAirtime(RX_ALL_LOG, rxMsec);
 
     } else {
         // Skip the 4 headers that are at the beginning of the rxBuf
@@ -456,7 +459,7 @@ void RadioLibInterface::handleReceiveInterrupt()
         if (payloadLen < 0) {
             LOG_WARN("Ignore received packet too short");
             rxBad++;
-            airTime->logAirtime(RX_ALL_LOG, xmitMsec);
+            airTime->logAirtime(RX_ALL_LOG, rxMsec);
         } else {
             rxGood++;
             // altered packet with "from == 0" can do Remote Node Administration without permission
@@ -494,7 +497,7 @@ void RadioLibInterface::handleReceiveInterrupt()
 
             printPacket("Lora RX", mp);
 
-            airTime->logAirtime(RX_LOG, xmitMsec);
+            airTime->logAirtime(RX_LOG, rxMsec);
 
             deliverToReceiver(mp);
         }

src/mesh/RadioLibInterface.h

@@ -61,6 +61,17 @@ class RadioLibInterface : public RadioInterface, protected concurrency::Notified
     MeshPacketQueue txQueue = MeshPacketQueue(MAX_TX_QUEUE);
 
   protected:
+    ModemType_t modemType = RADIOLIB_MODEM_LORA;
+    DataRate_t getDataRate() const { return {.lora = {.spreadingFactor = sf, .bandwidth = bw, .codingRate = cr}}; }
+    PacketConfig_t getPacketConfig() const
+    {
+        return {.lora = {.preambleLength = preambleLength,
+                         .implicitHeader = false,
+                         .crcEnabled = true,
+                         // We use auto LDRO, meaning it is enabled if the symbol time is >= 16msec
+                         .ldrOptimize = (1 << sf) / bw >= 16}};
+    }
+
     /**
      * We use a meshtastic sync word, but hashed with the Channel name.  For releases before 1.2 we used 0x12 (or for very old
      * loads 0x14) Note: do not use 0x34 - that is reserved for lorawan
@@ -209,6 +220,36 @@ class RadioLibInterface : public RadioInterface, protected concurrency::Notified
      */
     virtual void setStandby();
 
+    /**
+     * Derive packet time either for a received (using header info) or a transmitted packet
+     */
+    template <typename T> uint32_t computePacketTime(T &lora, uint32_t pl, bool received)
+    {
+        if (received) {
+            // First get the actual coding rate and CRC status from the received packet
+            uint8_t rxCR;
+            bool hasCRC;
+            lora.getLoRaRxHeaderInfo(&rxCR, &hasCRC);
+            // Go from raw header value to denominator
+            if (rxCR < 5) {
+                rxCR += 4;
+            } else if (rxCR == 7) {
+                rxCR = 8;
+            }
+
+            // Received packet configuration must be the same as configured, except for coding rate and CRC
+            DataRate_t dr = getDataRate();
+            dr.lora.codingRate = rxCR;
+
+            PacketConfig_t pc = getPacketConfig();
+            pc.lora.crcEnabled = hasCRC;
+
+            return lora.calculateTimeOnAir(modemType, dr, pc, pl) / 1000;
+        }
+
+        return lora.getTimeOnAir(pl) / 1000;
+    }
+
     const char *radioLibErr = "RadioLib err=";
 
     /**

src/mesh/ReliableRouter.cpp

@@ -76,7 +76,7 @@ bool ReliableRouter::shouldFilterReceived(const meshtastic_MeshPacket *p)
        If we don't add this, we will likely retransmit too early.
     */
     for (auto i = pending.begin(); i != pending.end(); i++) {
-        i->second.nextTxMsec += iface->getPacketTime(p);
+        i->second.nextTxMsec += iface->getPacketTime(p, true);
     }
 
     return isBroadcast(p->to) ? FloodingRouter::shouldFilterReceived(p) : NextHopRouter::shouldFilterReceived(p);

src/mesh/SX126xInterface.h

@@ -72,6 +72,8 @@ template <class T> class SX126xInterface : public RadioLibInterface
 
     virtual void setStandby() override;
 
+    uint32_t getPacketTime(uint32_t pl, bool received) override { return computePacketTime(lora, pl, received); }
+
   private:
     /** Some boards require GPIO control of tx vs rx paths */
     void setTransmitEnable(bool txon);

src/mesh/SX128xInterface.h

@@ -67,4 +67,6 @@ template <class T> class SX128xInterface : public RadioLibInterface
     virtual void addReceiveMetadata(meshtastic_MeshPacket *mp) override;
 
     virtual void setStandby() override;
+
+    uint32_t getPacketTime(uint32_t pl, bool received) override { return computePacketTime(lora, pl, received); }
 };

src/platform/portduino/SimRadio.cpp

@@ -182,7 +182,7 @@ void SimRadio::onNotify(uint32_t notification)
                     assert(txp);
                     startSend(txp);
                     // Packet has been sent, count it toward our TX airtime utilization.
-                    uint32_t xmitMsec = getPacketTime(txp);
+                    uint32_t xmitMsec = RadioInterface::getPacketTime(txp);
                     airTime->logAirtime(TX_LOG, xmitMsec);
 
                     notifyLater(xmitMsec, ISR_TX, false); // Model the time it is busy sending
@@ -252,7 +252,7 @@ void SimRadio::startReceive(meshtastic_MeshPacket *p)
     if (isActivelyReceiving()) {
         LOG_WARN("Collision detected, dropping current and previous packet!");
         rxBad++;
-        airTime->logAirtime(RX_ALL_LOG, getPacketTime(receivingPacket));
+        airTime->logAirtime(RX_ALL_LOG, getPacketTime(receivingPacket, true));
         packetPool.release(receivingPacket);
         receivingPacket = nullptr;
         return;
@@ -270,7 +270,7 @@ void SimRadio::startReceive(meshtastic_MeshPacket *p)
     }
     isReceiving = true;
     receivingPacket = packetPool.allocCopy(*p);
-    uint32_t airtimeMsec = getPacketTime(p);
+    uint32_t airtimeMsec = getPacketTime(p, true);
     notifyLater(airtimeMsec, ISR_RX, false); // Model the time it is busy receiving
 #else
     isReceiving = true;
@@ -311,7 +311,7 @@ void SimRadio::handleReceiveInterrupt()
 
     printPacket("Lora RX", mp);
 
-    airTime->logAirtime(RX_LOG, getPacketTime(mp));
+    airTime->logAirtime(RX_LOG, RadioInterface::getPacketTime(mp, true));
 
     deliverToReceiver(mp);
 }
@@ -332,4 +332,29 @@ int16_t SimRadio::readData(uint8_t *data, size_t len)
     }
 
     return state;
+}
+
+/**
+ * Calculate airtime per
+ * https://www.rs-online.com/designspark/rel-assets/ds-assets/uploads/knowledge-items/application-notes-for-the-internet-of-things/LoRa%20Design%20Guide.pdf
+ * section 4
+ *
+ * @return num msecs for the packet
+ */
+uint32_t SimRadio::getPacketTime(uint32_t pl, bool received)
+{
+    float bandwidthHz = bw * 1000.0f;
+    bool headDisable = false; // we currently always use the header
+    float tSym = (1 << sf) / bandwidthHz;
+
+    bool lowDataOptEn = tSym > 16e-3 ? true : false; // Needed if symbol time is >16ms
+
+    float tPreamble = (preambleLength + 4.25f) * tSym;
+    float numPayloadSym =
+        8 + max(ceilf(((8.0f * pl - 4 * sf + 28 + 16 - 20 * headDisable) / (4 * (sf - 2 * lowDataOptEn))) * cr), 0.0f);
+    float tPayload = numPayloadSym * tSym;
+    float tPacket = tPreamble + tPayload;
+
+    uint32_t msecs = tPacket * 1000;
+    return msecs;
 }

src/platform/portduino/SimRadio.h

@@ -88,6 +88,8 @@ class SimRadio : public RadioInterface, protected concurrency::NotifiedWorkerThr
     /**
      * If a send was in progress finish it and return the buffer to the pool */
     void completeSending();
+
+    virtual uint32_t getPacketTime(uint32_t pl, bool received = false) override;
 };
 
 extern SimRadio *simRadio;