/* -*-  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

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 *

 * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>

 */

#include "interference-helper.h"

#include "wifi-phy.h"

#include "error-rate-model.h"

#include "ns3/simulator.h"

#include "ns3/log.h"

#include <algorithm>

NS_LOG_COMPONENT_DEFINE ("InterferenceHelper");

namespace ns3 {

/****************************************************************

 *       Phy event class

 ****************************************************************/

InterferenceHelper::Event::Event (uint32_t size, WifiMode payloadMode, 

					       enum WifiPreamble preamble,

					       Time duration, double rxPower)

  : m_size (size),

    m_payloadMode (payloadMode),

    m_preamble (preamble),

    m_startTime (Simulator::Now ()),

    m_endTime (m_startTime + duration),

    m_rxPowerW (rxPower)

{}

InterferenceHelper::Event::~Event ()

{}

Time 

InterferenceHelper::Event::GetDuration (void) const 

{

  return m_endTime - m_startTime;

}

Time 

InterferenceHelper::Event::GetStartTime (void) const

{

  return m_startTime;

}

Time 

InterferenceHelper::Event::GetEndTime (void) const

{

  return m_endTime;

}

bool 

InterferenceHelper::Event::Overlaps (Time time) const

{

  if (m_startTime <= time &&

      m_endTime >= time) 

    {

      return true;

    } 

  else 

    {

      return false;

    }

}

double 

InterferenceHelper::Event::GetRxPowerW (void) const

{

  return m_rxPowerW;

}

uint32_t 

InterferenceHelper::Event::GetSize (void) const

{

  return m_size;

}

WifiMode 

InterferenceHelper::Event::GetPayloadMode (void) const

{

  return m_payloadMode;

}

enum WifiPreamble 

InterferenceHelper::Event::GetPreambleType (void) const

{

  return m_preamble;

}

/****************************************************************

 *       Class which records SNIR change events for a 

 *       short period of time.

 ****************************************************************/

InterferenceHelper::NiChange::NiChange (Time time, double delta)

  : m_time (time), m_delta (delta) 

{}

Time

InterferenceHelper::NiChange::GetTime (void) const

{

  return m_time;

}

double 

InterferenceHelper::NiChange::GetDelta (void) const

{

  return m_delta;

}

bool 

InterferenceHelper::NiChange::operator < (InterferenceHelper::NiChange const &o) const

{

  return (m_time < o.m_time)?true:false;

}

/****************************************************************

 *       The actual InterferenceHelper

 ****************************************************************/

InterferenceHelper::InterferenceHelper ()

  : m_80211_standard (WIFI_PHY_STANDARD_80211a),

    m_errorRateModel (0)

{}

InterferenceHelper::~InterferenceHelper ()

{

  m_errorRateModel = 0;

}

Ptr<InterferenceHelper::Event> 

InterferenceHelper::Add (uint32_t size, WifiMode payloadMode, 

			 enum WifiPreamble preamble,

			 Time duration, double rxPowerW)

{

  Ptr<InterferenceHelper::Event> event;

  event = Create<InterferenceHelper::Event> 

    (size,

     payloadMode,

     preamble,

     duration,

     rxPowerW);

  AppendEvent (event);

  return event;

}

Time 

InterferenceHelper::GetMaxPacketDuration (void) const

{

  return m_maxPacketDuration;

}

void 

InterferenceHelper::SetNoiseFigure (double value)

{

  m_noiseFigure = value;

}

double 

InterferenceHelper::GetNoiseFigure (void) const

{

  return m_noiseFigure;

}

void 

InterferenceHelper::SetErrorRateModel (Ptr<ErrorRateModel> rate)

{

  m_errorRateModel = rate;

}

Ptr<ErrorRateModel> 

InterferenceHelper::GetErrorRateModel (void) const

{

  return m_errorRateModel;

}

Time 

InterferenceHelper::GetEnergyDuration (double energyW)

{

  Time now = Simulator::Now ();

  // first, we iterate over all events and, each event

  // which contributes energy to the channel now is 

  // appended to the noise interference array.

  Events::const_iterator i = m_events.begin ();

  double noiseInterferenceW = 0.0;

  NiChanges ni;

  while (i != m_events.end ()) 

    {

      Ptr<Event> ev = *i;

      NS_ASSERT (ev->GetStartTime () <= now);

      if (ev->GetEndTime () > now)

	{

          ni.push_back (NiChange (ev->GetEndTime (), -ev->GetRxPowerW ()));

          noiseInterferenceW += ev->GetRxPowerW ();

	}

      i++;

    }

  if (noiseInterferenceW < energyW)

    {

      return MicroSeconds (0);

    }

  /* quicksort vector of NI changes by time. 

   */

  std::sort (ni.begin (), ni.end (), std::less<NiChange> ());

  // Now, we iterate the piecewise linear noise function

  Time end = now;

  for (NiChanges::const_iterator i = ni.begin (); i != ni.end (); i++) 

    {

      noiseInterferenceW += i->GetDelta ();

      end = i->GetTime ();

      if (noiseInterferenceW < energyW) 

	{

	  break;

	}

    }

  return end - now;

}

Time

InterferenceHelper::CalculateTxDuration (uint32_t size, WifiMode payloadMode, WifiPreamble preamble) const

{

  uint64_t delay = 0;

  switch (m_80211_standard) 

  {

    case WIFI_PHY_STANDARD_80211a:

    case WIFI_PHY_STANDARD_holland:

      delay += m_plcpLongPreambleDelayUs;

      // symbol duration is 4us

      delay += 4;

      delay += lrint (ceil ((size * 8.0 + 16.0 + 6.0) / payloadMode.GetDataRate () / 4e-6) * 4);

      break;

    case WIFI_PHY_STANDARD_80211b:

      delay += m_plcpLongPreambleDelayUs;

      delay += lrint (ceil ((size * 8.0 + 48.0) / payloadMode.GetDataRate () / 4e-6) * 4);

      break;

    default:

     NS_ASSERT (false);

     break;

  }

  return MicroSeconds (delay);

}

void

InterferenceHelper::Configure80211aParameters (void)

{

  NS_LOG_FUNCTION (this);

  m_80211_standard = WIFI_PHY_STANDARD_80211a;

  m_plcpLongPreambleDelayUs = 16;

  m_plcpShortPreambleDelayUs = 16;

  m_longPlcpHeaderMode = WifiPhy::Get6mba ();

  m_shortPlcpHeaderMode = WifiPhy::Get6mba ();

  m_plcpHeaderLength = 4 + 1 + 12 + 1 + 6;

  /* 4095 bytes at a 6Mb/s rate with a 1/2 coding rate. */

  m_maxPacketDuration = CalculateTxDuration (4095, WifiPhy::Get6mba (), WIFI_PREAMBLE_LONG);

}

void

InterferenceHelper::Configure80211bParameters (void)

{ 

  NS_LOG_FUNCTION (this);

  m_80211_standard = WIFI_PHY_STANDARD_80211b;

  m_plcpLongPreambleDelayUs = 144;

  m_plcpShortPreambleDelayUs = 144; // fixed preamable for 802.11b

  m_longPlcpHeaderMode = WifiPhy::Get1mbb ();

  m_shortPlcpHeaderMode = WifiPhy::Get1mbb ();

  // PLCP Header: signal 8, service 8, length 16, CRC 16 bits

  m_plcpHeaderLength = 8 + 8 + 16 + 16;

  m_maxPacketDuration = CalculateTxDuration (4095, WifiPhy::Get1mbb (), WIFI_PREAMBLE_LONG);

}

void 

InterferenceHelper::AppendEvent (Ptr<InterferenceHelper::Event> event)

{

  /* attempt to remove the events which are 

   * not useful anymore. 

   * i.e.: all events which end _before_

   *       now - m_maxPacketDuration

   */

  if (Simulator::Now () > GetMaxPacketDuration ())

    {

      Time end = Simulator::Now () - GetMaxPacketDuration ();

      Events::iterator i = m_events.begin ();

      while (i != m_events.end () &&

             (*i)->GetEndTime () <= end) 

        {

          i++;

        }

      m_events.erase (m_events.begin (), i);

    } 

  m_events.push_back (event);

}

double

InterferenceHelper::CalculateSnr (double signal, double noiseInterference, WifiMode mode) const

{

  // thermal noise at 290K in J/s = W

  static const double BOLTZMANN = 1.3803e-23;

  // Nt is the power of thermal noise in W

  double Nt = BOLTZMANN * 290.0 * mode.GetBandwidth ();

  // receiver noise Floor (W) which accounts for thermal noise and non-idealities of the receiver

  double noiseFloor = m_noiseFigure * Nt;

  double noise = noiseFloor + noiseInterference;

  double snr = signal / noise;

  return snr;

}

double

InterferenceHelper::CalculateNoiseInterferenceW (Ptr<InterferenceHelper::Event> event, NiChanges *ni) const

{

  Events::const_iterator i = m_events.begin ();

  double noiseInterference = 0.0;

  while (i != m_events.end ()) 

    {

      if (event == (*i)) 

        {

          i++;

          continue;

        }

      if (event->Overlaps ((*i)->GetStartTime ())) 

        {

          ni->push_back (NiChange ((*i)->GetStartTime (), (*i)->GetRxPowerW ()));

        }

      if (event->Overlaps ((*i)->GetEndTime ())) 

        {

          ni->push_back (NiChange ((*i)->GetEndTime (), -(*i)->GetRxPowerW ()));

        }

      if ((*i)->Overlaps (event->GetStartTime ())) 

        {

          noiseInterference += (*i)->GetRxPowerW ();

        }

      i++;

    }

  ni->push_back (NiChange (event->GetStartTime (), noiseInterference));

  ni->push_back (NiChange (event->GetEndTime (), 0));

  /* quicksort vector of NI changes by time. */

  std::sort (ni->begin (), ni->end (), std::less<NiChange> ());

  return noiseInterference;

}

double

InterferenceHelper::CalculateChunkSuccessRate (double snir, Time duration, WifiMode mode) const

{

  if (duration == NanoSeconds (0)) {

    return 1.0;

  }

  uint32_t rate = mode.GetPhyRate ();

  uint64_t nbits = (uint64_t)(rate * duration.GetSeconds ());

  double csr = m_errorRateModel->GetChunkSuccessRate (mode, snir, (uint32_t)nbits);

  return csr;

}

double 

InterferenceHelper::CalculatePer (Ptr<const InterferenceHelper::Event> event, NiChanges *ni) const

{  

  double psr = 1.0; /* Packet Success Rate */

  NiChanges::iterator j = ni->begin ();

  Time previous = (*j).GetTime ();

  uint64_t plcpPreambleDelayUs;

  WifiMode payloadMode = event->GetPayloadMode ();

  WifiMode headerMode;

  switch (event->GetPreambleType ()) {

  case WIFI_PREAMBLE_LONG:

    plcpPreambleDelayUs = m_plcpLongPreambleDelayUs;

    headerMode = m_longPlcpHeaderMode;

    break;

  case WIFI_PREAMBLE_SHORT:

    plcpPreambleDelayUs = m_plcpShortPreambleDelayUs;

    headerMode = m_shortPlcpHeaderMode;

    break;

  default:

    NS_ASSERT (false);

    // only to quiet compiler. Really stupid.

    plcpPreambleDelayUs = 0;

    headerMode = m_shortPlcpHeaderMode;

    break;

  }

  Time plcpHeaderStart = (*j).GetTime () + MicroSeconds (plcpPreambleDelayUs);

  Time plcpPayloadStart = plcpHeaderStart + 

    Seconds ((m_plcpHeaderLength + 0.0) / headerMode.GetDataRate ());

  double noiseInterferenceW = (*j).GetDelta ();

  double powerW = event->GetRxPowerW ();

  j++;

  while (ni->end () != j) 

    {

      Time current = (*j).GetTime ();

      NS_ASSERT (current >= previous);

      if (previous >= plcpPayloadStart) 

        {

          psr *= CalculateChunkSuccessRate (CalculateSnr (powerW, 

                                                          noiseInterferenceW, 

                                                          payloadMode), 

                                            current - previous,

                                            payloadMode);

        } 

      else if (previous >= plcpHeaderStart) 

        {

          if (current >= plcpPayloadStart) 

            {

              psr *= CalculateChunkSuccessRate (CalculateSnr (powerW, 

                                                              noiseInterferenceW, 

                                                              headerMode), 

                                                plcpPayloadStart - previous,

                                                headerMode);

              psr *= CalculateChunkSuccessRate (CalculateSnr (powerW, 

                                                              noiseInterferenceW, 

                                                              payloadMode),

                                                current - plcpPayloadStart,

                                                payloadMode);

            } 

          else 

            {

              NS_ASSERT (current >= plcpHeaderStart);

              psr *= CalculateChunkSuccessRate (CalculateSnr (powerW, 

                                                              noiseInterferenceW, 

                                                              headerMode), 

                                                current - previous,

                                                headerMode);

            }

        } 

      else 

        {

          if (current >= plcpPayloadStart) 

            {

              psr *= CalculateChunkSuccessRate (CalculateSnr (powerW, 

                                                              noiseInterferenceW, 

                                                              headerMode), 

                                                plcpPayloadStart - plcpHeaderStart,

                                                headerMode);

              psr *= CalculateChunkSuccessRate (CalculateSnr (powerW, 

                                                              noiseInterferenceW, 

                                                              payloadMode), 

                                                current - plcpPayloadStart,

                                                payloadMode);

            } 

          else if (current >= plcpHeaderStart) 

            {

              psr *= CalculateChunkSuccessRate (CalculateSnr (powerW, 

                                                              noiseInterferenceW, 

                                                              headerMode), 

                                                current - plcpHeaderStart,

                                                headerMode);

            }

        }

      noiseInterferenceW += (*j).GetDelta ();

      previous = (*j).GetTime ();

      j++;

    }

  double per = 1 - psr;

  return per;

}

struct InterferenceHelper::SnrPer 

InterferenceHelper::CalculateSnrPer (Ptr<InterferenceHelper::Event> event)

{

  NiChanges ni;

  double noiseInterferenceW = CalculateNoiseInterferenceW (event, &ni);

  double snr = CalculateSnr (event->GetRxPowerW (),

                             noiseInterferenceW,

                             event->GetPayloadMode ());

  /* calculate the SNIR at the start of the packet and accumulate

   * all SNIR changes in the snir vector.

   */

  double per = CalculatePer (event, &ni);

  struct SnrPer snrPer;

  snrPer.snr = snr;

  snrPer.per = per;

  return snrPer;

}

} // namespace ns3