channel switching support for wifi

src/devices/wifi/yans-wifi-phy.cc

 /* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
 /*
  * Copyright (c) 2005,2006 INRIA
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as 
  * published by the Free Software Foundation;
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 294 matching lines @@
 Ptr<WifiChannel> 
 YansWifiPhy::GetChannel (void) const
 {
   return m_channel;
 }
 void 
 YansWifiPhy::SetChannel (Ptr<YansWifiChannel> channel)
 {
   m_channel = channel;
   m_channel->Add (this);
-  m_channelId = 1;      // always start on channel starting frequency (channel 1)
+  m_channelNumber = 1;      // always start on channel starting frequency (channel 1)
 }
 
 void 
 YansWifiPhy::SetChannelNumber (uint16_t nch)
 {
-  // TODO implement channel switching state machine here
-  DoSetChannelNumber (nch);
+  NS_ASSERT(!IsStateSwitching()); 
+  switch (m_state->GetState ()) {
+  case YansWifiPhy::SYNC:
+    NS_LOG_DEBUG ("drop packet because of channel switching while reception");
+    m_endSyncEvent.Cancel();
+    goto switchChannel;
+    break;
+  case YansWifiPhy::TX:
+      NS_LOG_DEBUG ("channel switching postponed until end of current transmission");
+      Simulator::Schedule (GetDelayUntilIdle(), &YansWifiPhy::SetChannelNumber, this, nch);
+    break;
+  case YansWifiPhy::CCA_BUSY:
+  case YansWifiPhy::IDLE:
+    goto switchChannel;
+    break;
+  default:
+    NS_ASSERT (false);
+    break;
+  }
+
+  return;
+
+  switchChannel: 
+
+  NS_LOG_DEBUG("switching channel " << m_channelNumber << " -> " << nch);
+  m_state->SwitchToChannelSwitching(m_channelSwitchDelay); 
+  m_interference.EraseEvents(); 
+  /*
+   * Needed here to be able to correctly sensed the medium for the first
+   * time after the switching. The actual switching is not performed until
+   * after m_channelSwitchDelay. Packets received during the switching
+   * state are added to the event list and are employed later to figure
+   * out the state of the medium after the switching.
+   */
+  m_channelNumber = nch;

[Mathieu Lacage, 2009/08/19 08:19:12]

I am curious: do you ever use m_channelNumber anywhere ? it seems all you do in
this patchset is keep track of this number, but never use it to implement an
actual model of receiving packets on different channels ?

[Ramon Bauza, 2009/09/08 11:36:08]

On 2009/08/19 08:19:12, Mathieu Lacage wrote:
> I am curious: do you ever use m_channelNumber anywhere ? it seems all you do
in
> this patchset is keep track of this number, but never use it to implement an
> actual model of receiving packets on different channels ?

Yes, m_channelNumber is used (through YansWifiPhy::GetChannelNumber) in
YansWifiChannel::Send.

 }
 
+/*
+ * This function wouldn't be really needed because channel switching delay is

[Mathieu Lacage, 2009/08/19 08:19:12]

so, why is it needed ?

[Ramon Bauza, 2009/09/08 11:36:08]

On 2009/08/19 08:19:12, Mathieu Lacage wrote:
> so, why is it needed ?

removed.

+ * modelled in WifiPhyStateHelper.
+ */
 void
 YansWifiPhy::DoSetChannelNumber (uint16_t nch)
 {
-  NS_LOG_DEBUG("switching channel " << m_channelId << " -> " << nch);
-  m_channelId = nch;
+  NS_LOG_DEBUG("switching channel " << m_channelNumber << " -> " << nch);
+  m_channelNumber = nch;
 }
 
 uint16_t 
 YansWifiPhy::GetChannelNumber() const
 {
-  return m_channelId;
+  return m_channelNumber;
 }
 
 double
 YansWifiPhy::GetChannelFrequencyMhz() const
 {
   return m_channelStartingFrequency + 5 * (GetChannelNumber() - 1);
 }
 
 void 
 YansWifiPhy::SetReceiveOkCallback (SyncOkCallback callback)
@@ skipping 18 matching lines @@
   Time endRx = Simulator::Now () + rxDuration;
 
   Ptr<InterferenceHelper::Event> event;
   event = m_interference.Add (packet->GetSize (), 
                               txMode,
                               preamble,
                               rxDuration,
                               rxPowerW);
 
   switch (m_state->GetState ()) {
+  case YansWifiPhy::SWITCHING: 
+    NS_LOG_DEBUG ("drop packet because of channel switching (power="<<

[Mathieu Lacage, 2009/08/19 08:19:12]

is this debug message really relevant ? I don't see how rx power is used here.

[Ramon Bauza, 2009/09/08 11:36:08]

On 2009/08/19 08:19:12, Mathieu Lacage wrote:
> is this debug message really relevant ? I don't see how rx power is used here.

This message allows tracking those packets received during a switching period
(YansWifiPhy::m_channelSwitchDelay).

+                  rxPowerW<<"W)");
+    NotifyRxDrop (packet);
+    /*
+     * Packets received on the upcoming channel are added to the event list
+     * during the switching state. This way the medium can be correctly sensed
+     * when the device listens to the channel for the first time after the
+     * switching e.g. after channel switching, the channel may be sensed as
+     * busy due to other devices' tramissions started before the end of
+     * the switching.
+     */
+    if (endRx > Simulator::Now () + m_state->GetDelayUntilIdle ()) 
+      {
+        // that packet will be noise _after_ the completion of the
+        // channel switching.
+        goto maybeCcaBusy;
+      }
+    break;
   case YansWifiPhy::SYNC:
     NS_LOG_DEBUG ("drop packet because already in Sync (power="<<
                   rxPowerW<<"W)");
     NotifyRxDrop (packet);
     if (endRx > Simulator::Now () + m_state->GetDelayUntilIdle ()) 
       {
         // that packet will be noise _after_ the reception of the
         // currently-received packet.
         goto maybeCcaBusy;
       }
@@ skipping 50 matching lines @@
 void 
 YansWifiPhy::SendPacket (Ptr<const Packet> packet, WifiMode txMode, WifiPreamble preamble, uint8_t txPower)
 {
   NS_LOG_FUNCTION (this << packet << txMode << preamble << (uint32_t)txPower);
   /* Transmission can happen if:
    *  - we are syncing on a packet. It is the responsability of the
    *    MAC layer to avoid doing this but the PHY does nothing to 
    *    prevent it.
    *  - we are idle
    */
-  NS_ASSERT (!m_state->IsStateTx ());
+    NS_ASSERT (!m_state->IsStateTx () && !m_state->IsStateSwitching ()); 
 
   Time txDuration = CalculateTxDuration (packet->GetSize (), txMode, preamble);
   if (m_state->IsStateSync ())
     {
       m_endSyncEvent.Cancel ();
     }
   NotifyTxBegin (packet);
   uint32_t dataRate500KbpsUnits = txMode.GetDataRate () / 500000;   
   bool isShortPreamble = (WIFI_PREAMBLE_SHORT == preamble);
   NotifyPromiscSniffTx (packet, (uint16_t)GetChannelFrequencyMhz(), dataRate500KbpsUnits, isShortPreamble);
@@ skipping 111 matching lines @@
 bool 
 YansWifiPhy::IsStateSync (void)
 {
   return m_state->IsStateSync ();
 }
 bool 
 YansWifiPhy::IsStateTx (void)
 {
   return m_state->IsStateTx ();
 }
+bool 
+YansWifiPhy::IsStateSwitching (void)
+{
+  return m_state->IsStateSwitching ();
+}
 
 Time
 YansWifiPhy::GetStateDuration (void)
 {
   return m_state->GetStateDuration ();
 }
 Time
 YansWifiPhy::GetDelayUntilIdle (void)
 {
   return m_state->GetDelayUntilIdle ();
@@ skipping 75 matching lines @@
       m_state->SwitchFromSyncEndOk (packet, snrPer.snr, event->GetPayloadMode (), event->GetPreambleType ());
     } 
   else 
     {
       /* failure. */
       NotifyRxDrop (packet);
       m_state->SwitchFromSyncEndError (packet, snrPer.snr);
     }
 }
 } // namespace ns3