diff --git a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/ap-wifi-mac.cc b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/ap-wifi-mac.cc
index 061b0e7..48f7ecf 100644
--- a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/ap-wifi-mac.cc
+++ b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/ap-wifi-mac.cc
@@ -74,6 +74,7 @@ ApWifiMac::ApWifiMac ()
   m_beaconDca->SetMaxCw (0);
   m_beaconDca->SetLow (m_low);
   m_beaconDca->SetManager (m_dcfManager);
+  m_beaconDca->SetTxMiddle(m_txMiddle);
 
   // Let the lower layers know that we are acting as an AP.
   SetTypeOfStation (AP);

diff --git a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.cc b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.cc
index e38af9f..6bd2698 100644
--- a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.cc
+++ b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.cc
@@ -137,7 +137,6 @@ DcaTxop::DcaTxop ()
   m_dcf = new DcaTxop::Dcf (this);
   m_queue = CreateObject<WifiMacQueue> ();
   m_rng = new RealRandomStream ();
-  m_txMiddle = new MacTxMiddle ();
 }
 
 DcaTxop::~DcaTxop ()
@@ -155,11 +154,9 @@ DcaTxop::DoDispose (void)
   delete m_transmissionListener;
   delete m_dcf;
   delete m_rng;
-  delete m_txMiddle;
   m_transmissionListener = 0;
   m_dcf = 0;
   m_rng = 0;
-  m_txMiddle = 0;
 }
 
 void
@@ -169,6 +166,10 @@ DcaTxop::SetManager (DcfManager *manager)
   m_manager = manager;
   m_manager->Add (m_dcf);
 }
+  
+void DcaTxop::SetTxMiddle (MacTxMiddle *txMiddle){
+  m_txMiddle = txMiddle;
+}
 
 void
 DcaTxop::SetLow (Ptr<MacLow> low)
diff --git a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.h b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.h
index fea76c6..e7ca715 100644
--- a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.h
+++ b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/dca-txop.h
@@ -80,6 +80,7 @@ public:
   void SetLow (Ptr<MacLow> low);
   void SetManager (DcfManager *manager);
   void SetWifiRemoteStationManager (Ptr<WifiRemoteStationManager> remoteManager);
+  void SetTxMiddle (MacTxMiddle *txMiddle);
 
   /**
    * \param callback the callback to invoke when a

diff --git a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/regular-wifi-mac.cc b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/regular-wifi-mac.cc
index 092dca1..b3593e7 100644
--- a/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/regular-wifi-mac.cc
+++ b/ns3/ns-allinone-3.14.1/ns-3.14.1/src/wifi/model/regular-wifi-mac.cc
@@ -61,6 +61,7 @@ NS_OBJECT_ENSURE_REGISTERED (RegularWifiMac);
   m_dca = CreateObject<DcaTxop> ();
   m_dca->SetLow (m_low);
   m_dca->SetManager (m_dcfManager);
+  m_dca->SetTxMiddle(m_txMiddle);
   m_dca->SetTxOkCallback (MakeCallback (&RegularWifiMac::TxOk, this));
   m_dca->SetTxFailedCallback (MakeCallback (&RegularWifiMac::TxFailed, this));