diff -r 3489bfd795ab -r af1246d5ec59 src/devices/wimax/simple-ofdm-wimax-channel.h
--- a/src/devices/wimax/simple-ofdm-wimax-channel.h	Wed Apr 21 15:59:25 2010 -0400
+++ b/src/devices/wimax/simple-ofdm-wimax-channel.h	Thu Apr 22 11:31:45 2010 +0200
@@ -50,17 +50,17 @@
   };
   /**
    * \brief Creates a channel and sets the propagation model
-   * \param propModel the propagation model to used
+   * \param propModel the propagation model to use
    */
   SimpleOfdmWimaxChannel (PropModel propModel);
   /**
-   * \brief Sends a fec block to all connected physical dxdevices
+   * \brief Sends a fec block to all connected physical devices
    * \param BlockTime the time needed to send the block
    * \param fecBlock the fec block being sent
    * \param burstSize the size of the burst
    * \param phy the sender device
    * \param isFirstBlock true if this block is the first one, false otherwise
-   * \param frequency the frequency on wich the block is sent
+   * \param frequency the frequency on which the block is sent
    * \param modulationType the modulation used to send the fec block
    * \param direction uplink or downlink
    * \param txPowerDbm the transmission power
diff -r 3489bfd795ab -r af1246d5ec59 src/helper/wimax-helper.cc
--- a/src/helper/wimax-helper.cc	Wed Apr 21 15:59:25 2010 -0400
+++ b/src/helper/wimax-helper.cc	Thu Apr 22 11:31:45 2010 +0200
@@ -80,7 +80,7 @@
       phy = CreateObject<SimpleOfdmWimaxPhy> ();
       if (!m_channel)
         {
-          m_channel = CreateObject<SimpleOfdmWimaxChannel> ();
+          m_channel = CreateObject<SimpleOfdmWimaxChannel> (SimpleOfdmWimaxChannel::COST231_PROPAGATION);
         }
       break;
     default:
@@ -91,6 +91,15 @@
   return phy;
 }
 
+void WimaxHelper::SetPropagationLossModel (SimpleOfdmWimaxChannel::PropModel propagationModel)
+{
+  if (!m_channel)
+    {
+      m_channel = CreateObject<SimpleOfdmWimaxChannel> ();
+    }
+  m_channel->GetObject<SimpleOfdmWimaxChannel> ()->SetPropagationModel (propagationModel);
+}
+
 Ptr<WimaxPhy> WimaxHelper::CreatePhy (PhyType phyType, char * SNRTraceFilePath, bool activateLoss)
 {
   Ptr<WimaxPhy> phy;
@@ -104,7 +113,7 @@
       sphy->ActivateLoss (activateLoss);
       if (!m_channel)
         {
-          m_channel = CreateObject<SimpleOfdmWimaxChannel> ();
+          m_channel = CreateObject<SimpleOfdmWimaxChannel> (SimpleOfdmWimaxChannel::COST231_PROPAGATION);
         }
       break;
     default:
diff -r 3489bfd795ab -r af1246d5ec59 src/helper/wimax-helper.h
--- a/src/helper/wimax-helper.h	Wed Apr 21 15:59:25 2010 -0400
+++ b/src/helper/wimax-helper.h	Thu Apr 22 11:31:45 2010 +0200
@@ -31,6 +31,7 @@
 #include "ns3/deprecated.h"
 #include "ns3/service-flow.h"
 #include "ns3/propagation-loss-model.h"
+#include "ns3/simple-ofdm-wimax-channel.h"
 #include "ns3/bs-uplink-scheduler.h"
 #include "ns3/bs-uplink-scheduler-mbqos.h"
 #include "ns3/bs-uplink-scheduler-simple.h"
@@ -46,9 +47,15 @@
 class WimaxPhy;
 class UplinkScheduler;
 
+
 /**
- * \brief build a set of WimaxNetDevice objects
+ * \brief helps to manage and create WimaxNetDevice objects
+ *
+ * This class can help to create a large set of similar
+ * WimaxNetDevice objects and to configure their attributes
+ * during creation.
  */
+
 class WimaxHelper :public PcapHelperForDevice, public AsciiTraceHelperForDevice
 {
 public:
@@ -84,7 +91,9 @@
     /**< An migration-based uplink scheduler */
 
   };
-
+  /**
+   * \brief Create a Wimax helper in an empty state.
+   */
   WimaxHelper (void);
   ~WimaxHelper (void);
   /**
@@ -133,7 +142,7 @@
    * \param c a set of nodes
    * \param type device type to create
    * \param phyType a phy to use
-   * \param schedulerType a scheduling mechanism
+   * \param schedulerType the type of the scheduling algorithm to install
    *
    * For each of the input nodes, a new WiMAX net device (either
    * ns3::SubscriberStationNetDevice or ns3::BaseStationNetDevice
@@ -175,6 +184,13 @@
                               double frameDuration);
 
   /**
+   * \brief Set the propagation and loss model of the channel. By default the channel
+   *  uses a COST231 propagation and loss model.
+   * \param propagationModel The propagation and loss model to set
+   */
+  void SetPropagationLossModel (SimpleOfdmWimaxChannel::PropModel propagationModel);
+
+  /**
    * \param phyType WiMAX Physical layer type
    * \return WiMAX Phy object
    *
@@ -188,14 +204,14 @@
    * \param activateLoss set to 1 to activate losses 0 otherwise
    * \return WiMAX Phy object
    *
-   * Creates a physical layer without a channel
+   * Creates a physical layer without creating a channel
    */
   Ptr<WimaxPhy> CreatePhyWithoutChannel (PhyType phyType, char * SNRTraceFilePath, bool activateLoss);
 
   /**
    * \param phyType WiMAX Physical layer type
-   * \param SNRTraceFilePath of the repository containing the SNR traces files
-   * \param activateLoss set to 1 to activate losses 0 otherwise
+   * \param SNRTraceFilePath the path to the repository containing the SNR traces files
+   * \param activateLoss set to 1 if you want ton activate losses 0 otherwise
    * \return WiMAX Phy object
    *
    * Creates a physical layer
@@ -206,7 +222,7 @@
    * \param deviceType Device type to create.
    * \param phyType PHY type to create.
    * \param channel A channel to use.
-   * \param schedulerType The scheduling mechanism.
+   * \param schedulerType The scheduling mechanism to install on the device.
    *
    * For each of the input nodes, a new WiMAX net device (either
    * ns3::SubscriberStationNetDevice or ns3::BaseStationNetDevice
@@ -220,7 +236,7 @@
 
   /**
    * \brief Creates a transport service flow.
-   * \param direction the Direction of the service flow: UP or DOWN.
+   * \param direction the direction of the service flow: UP or DOWN.
    * \param schedulinType The service scheduling type to be used: UGS, RTPS, NRTPS, BE
    * \param classifier The classifier to be used for this service flow
    *