wifi: Add StaWifiMac and EHT FEM methods to handle EMLSR link switching

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

@@ -852,6 +852,21 @@ ChannelAccessManager::NotifySwitchingStartNow(Time duration)
     NS_ASSERT(m_lastTxEnd <= now);
     NS_ASSERT(m_lastSwitchingEnd <= now);
 
+    ResetState();
+
+    // Notify the FEM, which will in turn notify the MAC
+    m_feManager->NotifySwitchingStartNow(duration);
+
+    NS_LOG_DEBUG("switching start for " << duration);
+    m_lastSwitchingEnd = now + duration;
+}
+
+void
+ChannelAccessManager::ResetState()
+{
+    NS_LOG_FUNCTION(this);
+
+    Time now = Simulator::Now();
     m_lastRxReceivedOk = true;
     UpdateLastIdlePeriod();
     m_lastRx.end = std::min(m_lastRx.end, now);
@@ -859,7 +874,6 @@ ChannelAccessManager::NotifySwitchingStartNow(Time duration)
     m_lastAckTimeoutEnd = std::min(m_lastAckTimeoutEnd, now);
     m_lastCtsTimeoutEnd = std::min(m_lastCtsTimeoutEnd, now);
 
-    // the new operating channel may have a different width than the previous one
     InitLastBusyStructs();
 
     // Cancel timeout
@@ -868,9 +882,6 @@ ChannelAccessManager::NotifySwitchingStartNow(Time duration)
         m_accessTimeout.Cancel();
     }
 
-    // Notify the FEM, which will in turn notify the MAC
-    m_feManager->NotifySwitchingStartNow(duration);
-
     // Reset backoffs
     for (auto txop : m_txops)
     {
@@ -883,9 +894,6 @@ ChannelAccessManager::NotifySwitchingStartNow(Time duration)
         txop->ResetCw(m_linkId);
         txop->GetLink(m_linkId).access = Txop::NOT_REQUESTED;
     }
-
-    NS_LOG_DEBUG("switching start for " << duration);
-    m_lastSwitchingEnd = now + duration;
 }
 
 void

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

@@ -271,6 +271,11 @@ class ChannelAccessManager : public Object
      */
     bool IsBusy() const;
 
+    /**
+     * Reset the state variables of this channel access manager.
+     */
+    void ResetState();
+
   protected:
     void DoInitialize() override;
     void DoDispose() override;

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

@@ -24,6 +24,7 @@
 #include "ns3/abort.h"
 #include "ns3/ap-wifi-mac.h"
 #include "ns3/log.h"
+#include "ns3/sta-wifi-mac.h"
 #include "ns3/wifi-mac-queue.h"
 
 #undef NS_LOG_APPEND_CONTEXT
@@ -237,6 +238,27 @@ EhtFrameExchangeManager::EmlsrSwitchToListening(const Mac48Address& address, con
     }
 }
 
+void
+EhtFrameExchangeManager::NotifySwitchingEmlsrLink(Ptr<WifiPhy> phy, uint8_t linkId, Time delay)
+{
+    NS_LOG_FUNCTION(this << phy << linkId << delay.As(Time::US));
+
+    // TODO Shall we assert that there is no ongoing frame exchange sequence? Or is it possible
+    // that there is an ongoing frame exchange sequence (in such a case, we need to force a
+    // timeout, just like it is done in case of a normal channel switch
+
+    NS_ABORT_MSG_IF(!m_staMac, "This method can only be called on a STA");
+
+    // if we receive the notification from a PHY that is not connected to us, it means that
+    // we have been already connected to another PHY operating on this link, hence we do not
+    // have to reset the connected PHY
+    if (phy == m_phy)
+    {
+        ResetPhy();
+    }
+    m_staMac->NotifySwitchingEmlsrLink(phy, linkId);
+}
+
 void
 EhtFrameExchangeManager::SendEmlOperatingModeNotification(
     const Mac48Address& dest,

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

@@ -77,6 +77,16 @@ class EhtFrameExchangeManager : public HeFrameExchangeManager
                                    uint16_t aid,
                                    const Mac48Address& address) const;
 
+    /**
+     * Notify that the given PHY will switch channel to operate on another EMLSR link
+     * after the given delay.
+     *
+     * \param phy the given PHY
+     * \param linkId the ID of the EMLSR link on which the given PHY is operating
+     * \param delay the delay after which the channel switch will be completed
+     */
+    void NotifySwitchingEmlsrLink(Ptr<WifiPhy> phy, uint8_t linkId, Time delay);
+
   protected:
     void ForwardPsduDown(Ptr<const WifiPsdu> psdu, WifiTxVector& txVector) override;
     void ForwardPsduMapDown(WifiConstPsduMap psduMap, WifiTxVector& txVector) override;

src/wifi/model/sta-wifi-mac.cc

@@ -1922,6 +1922,83 @@ StaWifiMac::PhyCapabilitiesChanged()
     }
 }
 
+/**
+ * Initial configuration:
+ *
+ *        ┌───┬───┬───┐        ┌────┐       ┌───────┐
+ * Link A │FEM│RSM│CAM│◄──────►│Main├──────►│Channel│
+ *        │   │   │   │        │PHY │       │   A   │
+ *        └───┴───┴───┘        └────┘       └───────┘
+ *
+ *        ┌───┬───┬───┐        ┌────┐       ┌───────┐
+ * Link B │FEM│RSM│CAM│        │Aux │       │Channel│
+ *        │   │   │   │◄──────►│PHY ├──────►│   B   │
+ *        └───┴───┴───┘        └────┘       └───────┘
+ *
+ * A link switching/swapping is notified by the EMLSR Manager and the Channel Access Manager
+ * (CAM) notifies us that a first PHY (i.e., the Main PHY) switches to Channel B. We connect
+ * the Main PHY to the MAC stack B:
+ *
+ *
+ *        ┌───┬───┬───┐        ┌────┐       ┌───────┐
+ * Link A │FEM│RSM│CAM│   ┌───►│Main├───┐   │Channel│
+ *        │   │   │   │   │    │PHY │   │   │   A   │
+ *        └───┴───┴───┘   │    └────┘   │   └───────┘
+ *                        │             │
+ *        ┌───┬───┬───┐   │    ┌────┐   │   ┌───────┐
+ * Link B │FEM│RSM│CAM│◄──┘    │Aux │   └──►│Channel│
+ *        │   │   │   │◄─ ─ ─ ─│PHY ├──────►│   B   │
+ *        └───┴───┴───┘INACTIVE└────┘       └───────┘
+ *
+ * MAC stack B keeps a PHY listener associated with the Aux PHY, even though it is inactive,
+ * meaning that the PHY listener will only notify channel switches (no CCA, no RX).
+ * If the EMLSR Manager requested a link switching, this configuration will be kept until
+ * further requests. If the EMLSR Manager requested a link swapping, link B's CAM will be
+ * notified by its (inactive) PHY listener upon the channel switch performed by the Aux PHY.
+ * In this case, we remove the inactive PHY listener and connect the Aux PHY to MAC stack A:
+ *
+ *        ┌───┬───┬───┐        ┌────┐       ┌───────┐
+ * Link A │FEM│RSM│CAM│◄─┐ ┌──►│Main├───┐   │Channel│
+ *        │   │   │   │  │ │   │PHY │ ┌─┼──►│   A   │
+ *        └───┴───┴───┘  │ │   └────┘ │ │   └───────┘
+ *                       │ │          │ │
+ *        ┌───┬───┬───┐  │ │   ┌────┐ │ │   ┌───────┐
+ * Link B │FEM│RSM│CAM│◄─┼─┘   │Aux │ │ └──►│Channel│
+ *        │   │   │   │  └────►│PHY ├─┘     │   B   │
+ *        └───┴───┴───┘        └────┘       └───────┘
+ */
+
+void
+StaWifiMac::NotifySwitchingEmlsrLink(Ptr<WifiPhy> phy, uint8_t linkId)
+{
+    NS_LOG_FUNCTION(this << phy << linkId);
+
+    // if any link points to the PHY that switched channel, reset the phy pointer
+    for (auto& [id, link] : GetLinks())
+    {
+        // auto& link = GetStaLink(lnk);
+        if (link->phy == phy)
+        {
+            link->phy = nullptr;
+        }
+    }
+
+    auto& newLink = GetLink(linkId);
+    // The MAC stack associated with the new link uses the given PHY
+    newLink.phy = phy;
+    // Setup a PHY listener for the given PHY on the CAM associated with the new link
+    newLink.channelAccessManager->SetupPhyListener(phy);
+    NS_ASSERT(m_emlsrManager);
+    if (m_emlsrManager->GetCamStateReset())
+    {
+        newLink.channelAccessManager->ResetState();
+    }
+    // Disconnect the FEM on the new link from the current PHY
+    newLink.feManager->ResetPhy();
+    // Connect the FEM on the new link to the given PHY
+    newLink.feManager->SetWifiPhy(phy);
+}
+
 void
 StaWifiMac::NotifyChannelSwitching(uint8_t linkId)
 {

src/wifi/model/sta-wifi-mac.h

@@ -308,6 +308,14 @@ class StaWifiMac : public WifiMac
      */
     bool IsEmlsrLink(uint8_t linkId) const;
 
+    /**
+     * Notify that the given PHY switched channel to operate on another EMLSR link.
+     *
+     * \param phy the given PHY
+     * \param linkId the ID of the EMLSR link on which the given PHY is operating
+     */
+    void NotifySwitchingEmlsrLink(Ptr<WifiPhy> phy, uint8_t linkId);
+
     /**
      * Assign a fixed random variable stream number to the random variables
      * used by this model.  Return the number of streams (possibly zero) that