wifi: Implement UL MU CS mechanism

src/wifi/model/channel-access-manager.cc

@@ -627,6 +627,30 @@ ChannelAccessManager::GetLargestIdlePrimaryChannel(Time interval, Time end)
     return width;
 }
 
+bool
+ChannelAccessManager::GetPer20MHzBusy(const std::set<uint8_t>& indices) const
+{
+    const auto now = Simulator::Now();
+
+    if (m_phy->GetChannelWidth() < 40)
+    {
+        NS_ASSERT_MSG(indices.size() == 1 && *indices.cbegin() == 0,
+                      "Index 0 only can be specified if the channel width is less than 40 MHz");
+        return m_lastBusyEnd.at(WIFI_CHANLIST_PRIMARY) > now;
+    }
+
+    for (const auto index : indices)
+    {
+        NS_ASSERT(index < m_lastPer20MHzBusyEnd.size());
+        if (m_lastPer20MHzBusyEnd.at(index) > now)
+        {
+            NS_LOG_DEBUG("20 MHz channel with index " << +index << " is busy");
+            return true;
+        }
+    }
+    return false;
+}
+
 void
 ChannelAccessManager::DisableEdcaFor(Ptr<Txop> qosTxop, Time duration)
 {

src/wifi/model/channel-access-manager.h

@@ -149,6 +149,13 @@ class ChannelAccessManager : public Object
      */
     uint16_t GetLargestIdlePrimaryChannel(Time interval, Time end);
 
+    /**
+     * \param indices a set of indices (starting at 0) specifying the 20 MHz channels to test
+     * \return true if per-20 MHz CCA indicates busy for at least one of the
+     *         specified 20 MHz channels, false otherwise
+     */
+    bool GetPer20MHzBusy(const std::set<uint8_t>& indices) const;
+
     /**
      * \param duration expected duration of reception
      *

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

@@ -1752,6 +1752,38 @@ HeFrameExchangeManager::VirtualCsMediumIdle() const
     return m_navEnd <= Simulator::Now() && m_intraBssNavEnd <= Simulator::Now();
 }
 
+bool
+HeFrameExchangeManager::UlMuCsMediumIdle(const CtrlTriggerHeader& trigger) const
+{
+    if (!trigger.GetCsRequired())
+    {
+        NS_LOG_DEBUG("CS not required");
+        return true;
+    }
+
+    // A non-AP STA does not consider the intra-BSS NAV in determining whether to respond to a
+    // Trigger frame sent by the AP with which the non-AP STA is associated.
+    // A non-AP STA considers the basic NAV in determining whether to respond to a Trigger frame
+    // sent by the AP with which the non-AP STA is associated. (Sec. 26.5.2.5 of 802.11ax-2021)
+    const Time now = Simulator::Now();
+    if (m_navEnd > now)
+    {
+        NS_LOG_DEBUG("Basic NAV indicates medium busy");
+        return false;
+    }
+
+    NS_ASSERT_MSG(m_staMac, "UL MU CS is only performed by non-AP STAs");
+    const auto userInfoIt = trigger.FindUserInfoWithAid(m_staMac->GetAssociationId());
+    NS_ASSERT_MSG(userInfoIt != trigger.end(),
+                  "No User Info field for STA (" << m_self
+                                                 << ") AID=" << m_staMac->GetAssociationId());
+
+    const auto indices =
+        m_phy->GetOperatingChannel().Get20MHzIndicesCoveringRu(userInfoIt->GetRuAllocation(),
+                                                               trigger.GetUlBandwidth());
+    return !m_channelAccessManager->GetPer20MHzBusy(indices);
+}
+
 void
 HeFrameExchangeManager::ReceiveMpdu(Ptr<const WifiMpdu> mpdu,
                                     RxSignalInfo rxSignalInfo,

src/wifi/model/he/he-frame-exchange-manager.h

@@ -116,6 +116,16 @@ class HeFrameExchangeManager : public VhtFrameExchangeManager
      */
     bool IsIntraBssPpdu(Ptr<const WifiPsdu> psdu, const WifiTxVector& txVector) const;
 
+    /**
+     * This method is intended to be called a SIFS after the reception of a Trigger Frame
+     * to determine whether the station is allowed to respond.
+     *
+     * \param trigger the Trigger Frame soliciting a response
+     * \return true if CS is not required or the UL MU CS mechanism indicates that the medium
+     *         is idle, false otherwise
+     */
+    bool UlMuCsMediumIdle(const CtrlTriggerHeader& trigger) const;
+
   protected:
     void DoDispose() override;
     void Reset() override;