From 383b537fbca01a48f42d688279bed63e8132eae5 Mon Sep 17 00:00:00 2001
From: Sebastien Deronne <sebastien.deronne@gmail.com>
Date: Sun, 1 May 2022 13:37:29 +0200
Subject: [PATCH] wifi: Implement per-20 MHz CCA sensitivity

---
 src/wifi/model/he/he-phy.cc            | 94 ++++++++++++++++++++++++++
 src/wifi/model/he/he-phy.h             | 13 ++++
 src/wifi/model/phy-entity.cc           | 14 +++-
 src/wifi/model/phy-entity.h            |  9 ++-
 src/wifi/model/wifi-phy-state-helper.h |  6 +-
 src/wifi/model/wifi-phy.cc             |  7 ++
 src/wifi/model/wifi-phy.h              |  7 ++
 7 files changed, 142 insertions(+), 8 deletions(-)

diff --git a/src/wifi/model/he/he-phy.cc b/src/wifi/model/he/he-phy.cc
index bb783d63e..e21af85e7 100644
--- a/src/wifi/model/he/he-phy.cc
+++ b/src/wifi/model/he/he-phy.cc
@@ -1015,6 +1015,100 @@ HePhy::GetCcaThreshold (const Ptr<const WifiPpdu> ppdu, WifiChannelListType chan
   return std::max (VhtPhy::GetCcaThreshold (ppdu, channelType), obssPdLevel);
 }
 
+void
+HePhy::NotifyCcaBusy (const Ptr<const WifiPpdu> ppdu, Time duration, WifiChannelListType channelType)
+{
+  NS_LOG_FUNCTION (this << duration << channelType);
+  NS_LOG_DEBUG ("CCA busy for " << channelType << " during " << duration.As (Time::S));
+  m_state->SwitchMaybeToCcaBusy (duration, channelType, GetPer20MHzDurations (ppdu));
+}
+
+std::vector<Time>
+HePhy::GetPer20MHzDurations (const Ptr<const WifiPpdu> ppdu)
+{
+  NS_LOG_FUNCTION (this);
+
+  /**
+   * 27.3.20.6.5 Per 20 MHz CCA sensitivity:
+   * If the operating channel width is greater than 20 MHz and the PHY issues a PHY-CCA.indication primitive,
+   * the PHY shall set the per20bitmap to indicate the busy/idle status of each 20 MHz subchannel.
+   */
+  if (m_wifiPhy->GetChannelWidth () < 40)
+    {
+      return {};
+    }
+
+  std::vector<Time> per20MhzDurations {};
+  const auto indices = m_wifiPhy->GetOperatingChannel ().GetAll20MHzChannelIndicesInPrimary (m_wifiPhy->GetChannelWidth ());
+  for (auto index : indices)
+    {
+      auto band = m_wifiPhy->GetBand (20, index);
+      /**
+       * A signal is present on the 20 MHz subchannel at or above a threshold of –62 dBm at the receiver's antenna(s).
+       * The PHY shall indicate that the 20 MHz subchannel is busy a period aCCATime after the signal starts and shall
+       * continue to indicate the 20 MHz subchannel is busy while the threshold continues to be exceeded.
+       */
+      double ccaThresholdDbm = -62;
+      Time delayUntilCcaEnd = GetDelayUntilCcaEnd (ccaThresholdDbm, band);
+
+      if (ppdu)
+        {
+          const uint16_t subchannelMinFreq = m_wifiPhy->GetFrequency () - (m_wifiPhy->GetChannelWidth () / 2) + (index * 20);
+          const uint16_t subchannelMaxFreq = subchannelMinFreq + 20;
+          const uint16_t ppduBw = ppdu->GetTxVector ().GetChannelWidth ();
+
+          if (ppduBw <= m_wifiPhy->GetChannelWidth () && ppdu->DoesOverlapChannel (subchannelMinFreq, subchannelMaxFreq))
+            {
+              std::optional<double> obssPdLevel {std::nullopt};
+              if (m_obssPdAlgorithm)
+                {
+                  obssPdLevel = m_obssPdAlgorithm->GetObssPdLevel ();
+                }
+              switch (ppduBw)
+                {
+                  case 20:
+                  case 22:
+                    /**
+                     * A 20 MHz non-HT, HT_MF, HT_GF, VHT, or HE PPDU at or above max(–72 dBm, OBSS_ PDlevel) at the receiver's antenna(s) is present
+                     * on the 20 MHz subchannel. The PHY shall indicate that the 20 MHz subchannel is busy with > 90% probability within a period aCCAMidTime.
+                     */
+                    ccaThresholdDbm = obssPdLevel.has_value () ? std::max (-72.0, obssPdLevel.value ()) : -72.0;
+                    band = m_wifiPhy->GetBand (20, index);
+                    break;
+                  case 40:
+                    /**
+                     * The 20 MHz subchannel is in a channel on which a 40 MHz non-HT duplicate, HT_MF, HT_GF, VHT or HE PPDU at or above
+                     * max(–72 dBm, OBSS_PDlevel + 3 dB) at the receiver's antenna(s) is present. The PHY shall indicate that the 20 MHz
+                     * subchannel is busy with > 90% probability within a period aCCAMidTime.
+                     */
+                    ccaThresholdDbm = obssPdLevel.has_value () ? std::max (-72.0, obssPdLevel.value () + 3) : -72.0;
+                    band = m_wifiPhy->GetBand (40, std::floor (index / 2));
+                    break;
+                  case 80:
+                    /**
+                     * The 20 MHz subchannel is in a channel on which an 80 MHz non-HT duplicate, VHT or HE PPDU at or above
+                     * max(–69 dBm, OBSS_PDlevel + 6 dB) at the receiver's antenna(s) is present. The PHY shall indicate that
+                     * the 20 MHz subchannel is busy with > 90% probability within a period aCCAMidTime.
+                     */
+                    ccaThresholdDbm = obssPdLevel.has_value () ? std::max (-69.0, obssPdLevel.value () + 6) : -69.0;
+                    band = m_wifiPhy->GetBand (80, std::floor (index / 4));
+                    break;
+                  case 160:
+                    //Not defined in the standard: keep -62 dBm
+                    break;
+                  default:
+                    NS_ASSERT_MSG (false, "Invalid channel width: " << ppduBw);
+                }
+            }
+          Time ppduCcaDuration = GetDelayUntilCcaEnd (ccaThresholdDbm, band);
+          delayUntilCcaEnd = std::max (delayUntilCcaEnd, ppduCcaDuration);
+        }
+      per20MhzDurations.push_back (delayUntilCcaEnd);
+    }
+
+  return per20MhzDurations;
+}
+
 uint64_t
 HePhy::ObtainNextUid (const WifiTxVector& txVector)
 {
diff --git a/src/wifi/model/he/he-phy.h b/src/wifi/model/he/he-phy.h
index 00fa2e5b4..1e0ba9da2 100644
--- a/src/wifi/model/he/he-phy.h
+++ b/src/wifi/model/he/he-phy.h
@@ -104,6 +104,7 @@ public:
   void StartTx (Ptr<const WifiPpdu> ppdu) override;
   Time CalculateTxDuration (WifiConstPsduMap psduMap, const WifiTxVector& txVector, WifiPhyBand band) const override;
   double GetCcaThreshold (const Ptr<const WifiPpdu> ppdu, WifiChannelListType channelType) const override;
+  void NotifyCcaBusy (const Ptr<const WifiPpdu> ppdu, Time duration, WifiChannelListType channelType) override;
 
   /**
    * \return the BSS color of this PHY.
@@ -478,6 +479,18 @@ private:
   uint8_t GetNumberBccEncoders (const WifiTxVector& txVector) const override;
   Time GetSymbolDuration (const WifiTxVector& txVector) const override;
 
+  /**
+   * Compute the per-20 MHz CCA durations vector that indicates
+   * for how long each 20 MHz subchannel (corresponding to the
+   * index of the element in the vector) is busy and where a zero duration
+   * indicates that the subchannel is idle. The vector is non-empty if the
+   * operational channel width is larger than 20 MHz.
+   *
+   * \param ppdu the incoming PPDU or nullptr for any signal
+   * \return the per-20 MHz CCA durations vector
+   */
+  std::vector<Time> GetPer20MHzDurations (const Ptr<const WifiPpdu> ppdu);
+
   /**
    * Create and return the HE MCS corresponding to
    * the provided index.
diff --git a/src/wifi/model/phy-entity.cc b/src/wifi/model/phy-entity.cc
index cfd170006..2f5fba3ce 100644
--- a/src/wifi/model/phy-entity.cc
+++ b/src/wifi/model/phy-entity.cc
@@ -275,7 +275,7 @@ PhyEntity::StartReceiveField (WifiPpduField field, Ptr<Event> event)
   NS_ABORT_MSG_IF (!supported, "Unknown field " << field << " for this PHY entity"); //TODO see what to do if not supported
   Time duration = GetDuration (field, event->GetTxVector ());
   m_wifiPhy->m_endPhyRxEvent = Simulator::Schedule (duration, &PhyEntity::EndReceiveField, this, field, event);
-  m_state->SwitchMaybeToCcaBusy (duration); //keep in CCA busy state up to reception of Data (will then switch to RX)
+  m_wifiPhy->NotifyCcaBusy (event->GetPpdu (), duration); //keep in CCA busy state up to reception of Data (will then switch to RX)
 }
 
 void
@@ -311,7 +311,7 @@ PhyEntity::EndReceiveField (WifiPpduField field, Ptr<Event> event)
                 m_wifiPhy->m_phyRxPayloadBeginTrace (txVector, NanoSeconds (0)); //this callback (equivalent to PHY-RXSTART primitive) is also triggered for filtered PPDUs
               }
             m_wifiPhy->NotifyRxDrop (GetAddressedPsduInPpdu (ppdu), status.reason);
-            m_state->SwitchMaybeToCcaBusy (GetRemainingDurationAfterField (ppdu, field)); //keep in CCA busy state till the end
+            m_wifiPhy->NotifyCcaBusy (ppdu, GetRemainingDurationAfterField (ppdu, field));
           //no break
           case IGNORE:
             //Keep in Rx state and reset at end
@@ -896,7 +896,7 @@ PhyEntity::EndPreambleDetectionPeriod (Ptr<Event> event)
 
       //Continue receiving preamble
       Time durationTillEnd = GetDuration (WIFI_PPDU_FIELD_PREAMBLE, event->GetTxVector ()) - m_wifiPhy->GetPreambleDetectionDuration ();
-      m_state->SwitchMaybeToCcaBusy (durationTillEnd); //will be prolonged by next field
+      m_wifiPhy->NotifyCcaBusy (event->GetPpdu (), durationTillEnd); //will be prolonged by next field
       m_wifiPhy->m_endPhyRxEvent = Simulator::Schedule (durationTillEnd, &PhyEntity::EndReceiveField, this, WIFI_PPDU_FIELD_PREAMBLE, event);
     }
   else
@@ -1102,6 +1102,14 @@ PhyEntity::GetCcaIndication (const Ptr<const WifiPpdu> ppdu)
   return std::nullopt;
 }
 
+void
+PhyEntity::NotifyCcaBusy (const Ptr<const WifiPpdu> /*ppdu*/, Time duration, WifiChannelListType channelType)
+{
+  NS_LOG_FUNCTION (this << duration << channelType);
+  NS_LOG_DEBUG ("CCA busy for " << channelType << " during " << duration.As (Time::S));
+  m_state->SwitchMaybeToCcaBusy (duration, channelType, {});
+}
+
 uint64_t
 PhyEntity::ObtainNextUid (const WifiTxVector& /* txVector */)
 {
diff --git a/src/wifi/model/phy-entity.h b/src/wifi/model/phy-entity.h
index d78a346ab..1baeefa2a 100644
--- a/src/wifi/model/phy-entity.h
+++ b/src/wifi/model/phy-entity.h
@@ -433,7 +433,14 @@ public:
    * \param ppdu the incoming PPDU or nullptr for any signal
    */
   virtual void SwitchMaybeToCcaBusy (const Ptr<const WifiPpdu> ppdu);
-
+  /**
+   * Notify PHY state helper to switch to CCA busy state,
+   *
+   * \param ppdu the incoming PPDU or nullptr for any signal
+   * \param duration the duration of the CCA state
+   * \param channelType the channel type for which the CCA busy state is reported.
+   */
+  virtual void NotifyCcaBusy (const Ptr<const WifiPpdu> ppdu, Time duration, WifiChannelListType channelType);
   /**
    * This function is called by SpectrumWifiPhy to send
    * the PPDU while performing amendment-specific actions.
diff --git a/src/wifi/model/wifi-phy-state-helper.h b/src/wifi/model/wifi-phy-state-helper.h
index 65a0541af..07a5cb53d 100644
--- a/src/wifi/model/wifi-phy-state-helper.h
+++ b/src/wifi/model/wifi-phy-state-helper.h
@@ -223,7 +223,6 @@ public:
   void SwitchFromRxEndError (void);
   /**
    * Switch to CCA busy.
-   * TODO: remove default values
    *
    * \param duration the duration of the CCA state
    * \param channelType the channel type for which the CCA busy state is reported.
@@ -232,9 +231,8 @@ public:
    *        indicates that the subchannel is idle. The vector is non-empty if the PHY supports 802.11ax
    *        or later and if the operational channel width is larger than 20 MHz.
    */
-  void SwitchMaybeToCcaBusy (Time duration,
-                             WifiChannelListType channelType = WIFI_CHANLIST_PRIMARY,
-                             const std::vector<Time>& per20MhzDurations = std::vector<Time>{});
+  void SwitchMaybeToCcaBusy (Time duration, WifiChannelListType channelType,
+                             const std::vector<Time>& per20MhzDurations);
   /**
    * Switch to sleep mode.
    */
diff --git a/src/wifi/model/wifi-phy.cc b/src/wifi/model/wifi-phy.cc
index 7eb6419b9..a72b0a031 100644
--- a/src/wifi/model/wifi-phy.cc
+++ b/src/wifi/model/wifi-phy.cc
@@ -1902,6 +1902,13 @@ WifiPhy::SwitchMaybeToCcaBusy (const Ptr<const WifiPpdu> ppdu)
   GetPhyEntity (m_standard)->SwitchMaybeToCcaBusy (ppdu);
 }
 
+void
+WifiPhy::NotifyCcaBusy (const Ptr<const WifiPpdu> ppdu, Time duration)
+{
+  NS_LOG_FUNCTION (this << duration);
+  GetPhyEntity (m_standard)->NotifyCcaBusy (ppdu, duration, WIFI_CHANLIST_PRIMARY);
+}
+
 void
 WifiPhy::AbortCurrentReception (WifiPhyRxfailureReason reason)
 {
diff --git a/src/wifi/model/wifi-phy.h b/src/wifi/model/wifi-phy.h
index f913be51e..37115eabd 100644
--- a/src/wifi/model/wifi-phy.h
+++ b/src/wifi/model/wifi-phy.h
@@ -1104,6 +1104,13 @@ protected:
    * \param ppdu the incoming PPDU or nullptr for any signal
    */
   void SwitchMaybeToCcaBusy (const Ptr<const WifiPpdu> ppdu);
+  /**
+   * Notify PHY state helper to switch to CCA busy state,
+   *
+   * \param ppdu the incoming PPDU or nullptr for any signal
+   * \param duration the duration of the CCA state
+   */
+  void NotifyCcaBusy (const Ptr<const WifiPpdu> ppdu, Time duration);
 
   /**
    * Add the PHY entity to the map of supported PHY entities for the