wifi: Wait some more time for PHY-RXSTART.indication if the PHY is decoding a PHY header

src/wifi/model/eht/eht-frame-exchange-manager.cc

@@ -35,9 +35,24 @@
 namespace ns3
 {
 
-/// generic value for aRxPHYStartDelay PHY characteristic (used when we do not know the preamble
-/// type of the next frame)
-static constexpr uint8_t RX_PHY_START_DELAY_USEC = 48;
+/// aRxPHYStartDelay value to use when waiting for a new frame in the context of EMLSR operations
+/// (Sec. 35.3.17 of 802.11be D3.1)
+static constexpr uint8_t RX_PHY_START_DELAY_USEC = 20;
+/**
+ * Additional time (exceeding 20 us) to wait for a PHY-RXSTART.indication when the PHY is
+ * decoding a PHY header.
+ *
+ * Values for aRxPHYStartDelay:
+ * - OFDM : 20 us (for 20 MHz) [Table 17-21 of 802.11-2020]
+ * - ERP-OFDM : 20 us [Table 18-5 of 802.11-2020]
+ * - HT : 28 us (HT-mixed), 24 us (HT-greenfield) [Table 19-25 of 802.11-2020]
+ * - VHT : 36 + 4 * max N_VHT-LTF + 4 = 72 us [Table 21-28 of 802.11-2020]
+ * - HE : 32 us (for HE SU and HE TB PPDUs)
+ *        32 + 4 * N_HE-SIG-B us (for HE MU PPDUs) [Table 27-54 of 802.11ax-2021]
+ * - EHT : 32 us (for EHT TB PPDUs)
+ *         32 + 4 * N_EHT-SIG us (for EHT MU PPDUs) [Table 36-70 of 802.11be D3.2]
+ */
+static constexpr uint8_t WAIT_FOR_RXSTART_DELAY_USEC = 52;
 
 NS_LOG_COMPONENT_DEFINE("EhtFrameExchangeManager");
 
@@ -739,6 +754,19 @@ EhtFrameExchangeManager::TxopEnd()
 {
     NS_LOG_FUNCTION(this);
 
+    if (m_phy->IsReceivingPhyHeader())
+    {
+        // we may get here because the PHY has not issued the PHY-RXSTART.indication before
+        // the expiration of the timer started to detect new received frames, but the PHY is
+        // currently decoding the PHY header of a PPDU, so let's wait some more time to check
+        // if we receive a PHY-RXSTART.indication when the PHY is done decoding the PHY header
+        NS_LOG_DEBUG("PHY is decoding the PHY header of PPDU, postpone TXOP end");
+        m_ongoingTxopEnd = Simulator::Schedule(MicroSeconds(WAIT_FOR_RXSTART_DELAY_USEC),
+                                               &EhtFrameExchangeManager::TxopEnd,
+                                               this);
+        return;
+    }
+
     if (m_staMac && m_staMac->IsEmlsrLink(m_linkId))
     {
         m_staMac->GetEmlsrManager()->NotifyTxopEnd(m_linkId);

src/wifi/model/wifi-phy.cc

@@ -1899,6 +1899,12 @@ WifiPhy::StartReceivePreamble(Ptr<const WifiPpdu> ppdu,
     }
 }
 
+bool
+WifiPhy::IsReceivingPhyHeader() const
+{
+    return m_endPhyRxEvent.IsRunning();
+}
+
 void
 WifiPhy::EndReceiveInterBss()
 {

src/wifi/model/wifi-phy.h

@@ -111,6 +111,11 @@ class WifiPhy : public Object
                               RxPowerWattPerChannelBand& rxPowersW,
                               Time rxDuration);
 
+    /**
+     * \return whether the PHY is busy decoding the PHY header fields of a PPDU
+     */
+    bool IsReceivingPhyHeader() const;
+
     /**
      * For HE receptions only, check and possibly modify the transmit power restriction state at
      * the end of PPDU reception.