decider80211.cc

基于omnet++开发的Mf框架下的802.11协议仿真。

/***************************************************************************
 * file:        Decider80211.cc
 *
 * authors:     David Raguin / Marc Loebbers
 *
 * copyright:   (C) 2004 Telecommunication Networks Group (TKN) at
 *              Technische Universitaet Berlin, Germany.
 *
 *              This program is free software; you can redistribute it 
 *              and/or modify it under the terms of the GNU General Public 
 *              License as published by the Free Software Foundation; either
 *              version 2 of the License, or (at your option) any later 
 *              version.
 *              For further information see file COPYING 
 *              in the top level directory
 ***************************************************************************
 * part of:     framework implementation developed by tkn
 * description: - Decider for 802.11
 *              - decides if frames are lost based on the SNR calculated in
 *                SnrEval80211
 *
 ***************************************************************************
 * changelog:   $Revision$
 *              last modified:   $Date: 2005-01-15 18:20:07 +0100 (Sat, 15 Jan 2005) $
 *              by:              $Author: koepke $
 ***************************************************************************/


#include <Mac80211Pkt_m.h>

#include "Decider80211.h"
#include "Consts80211.h"


#define EV (ev.disabled()||!debug) ? (std::ostream&)ev : ev << logName() << "::Decider80211: "

Define_Module( Decider80211 );

/**
 * First we have to initialize the module from which we derived ours,
 * in this case BasicDecider.
 *
 * This decider also needs the bitrate and some 802.11 parameters are
 * initialized
 *
 **/
void Decider80211::initialize(int stage)
{
  BasicDecider::initialize(stage);

  if(stage==0){
    EV <<"initializing stage 0\n";
    bitrate=par("bitrate");
    if(bitrate!=1E+6 && bitrate!=2E+6 && bitrate!=5.5E+6 && bitrate!=11E+6)
      error("Wrong bitrate!! Please chose 1E+6, 2E+6, 5.5E+6 or 11E+6 as bitrate!!");
    snirThreshold=dB2fraction(par("snirThreshold"));
  }
}



 /**
  * Handle message from lower layer. The minimal snir is read in and
  * it is computed wether the packet has collided or has bit errors or
  * was received correctly. The corresponding kind is set and it is
  * handed on to the upper layer.
  *
  **/
  //处理底层消息，判断是否误码和冲突
void Decider80211::handleLowerMsg(AirFrame *af, SnrList &receivedList){

  double snirMin;

  //initialize snirMin:
  snirMin=receivedList.begin()->snr;

  for(SnrList::iterator iter=receivedList.begin();iter!=receivedList.end();iter++){
    if(iter->snr<snirMin)
      snirMin = iter->snr;
  }
  EV <<"packet from: "<<((Mac80211Pkt*)(af->encapsulatedMsg()))->getSrcAddr()<<" snrMin: "<<snirMin<<endl;
  //if snir is big enough so that packet can be recognized at all
  if(snirMin>snirThreshold){
    if(packetOk(snirMin, af->encapsulatedMsg()->length())){
      EV <<"packet was received correctly, it is now handed to upper layer...\n";
      sendUp(af);
    }else{
      EV <<"Packet has BIT ERRORS! It is lost!\n";
      af->setName("ERROR");
      af->encapsulatedMsg()->setKind(BITERROR);
      sendUp(af);
    }
  }else{
    EV <<"COLLISION! Packet got lost\n";
    af->setName("COLLISION");
    af->encapsulatedMsg()->setKind(COLLISION);
    sendUp(af);
  }
}
  

bool Decider80211::packetOk(double snirMin, int lengthMPDU)
{
  double berHeader,berMPDU;
  
  berHeader = 0.5*exp(-snirMin*BANDWIDTH/BITRATE_HEADER);
  //if PSK modulation
  if (bitrate == 1E+6 || bitrate == 2E+6) 
    berMPDU = 0.5*exp(-snirMin*BANDWIDTH/bitrate);
  //if CCK modulation (modeled with 16-QAM)
  else if(bitrate == 5.5E+6)
    berMPDU = 0.5*(1 - 1/sqrt(pow(2.0,4)))*erfc(snirMin*BANDWIDTH/bitrate);
  else // CCK, modelled with 256-QAM
    berMPDU = 0.25*(1 - 1/sqrt(pow(2.0,8)))*erfc(snirMin*BANDWIDTH/bitrate);
  //probability of no bit error in the PLCP header
  double headerNoError =  pow(1.0 - berHeader, HEADER_WITHOUT_PREAMBLE);

  //probability of no bit error in the MPDU
  double MpduNoError = pow(1.0-berMPDU, lengthMPDU);
  EV <<"berHeader: "<<berHeader<<" berMPDU: "<<berMPDU<<endl;
  double rand=dblrand();

  //if error in header
  if (rand>headerNoError) 
    return (false);
  else {
    rand = dblrand();
    
    //if error in MPDU
    if (rand>MpduNoError ) 
      return(false);
    //if no error
    else 
      return(true);
  }
}

double Decider80211::dB2fraction(double dB)
{
  return pow(10.0,(dB/10));
}


#ifdef _WIN32
double Decider80211::erfc(double x)
{
  double t, u, y;

  if (x <= -6) return 2;
  if (x >= 6) return 0;

    t = 3.97886080735226 / (fabs(x) + 3.97886080735226);
    u = t - 0.5;
    y = (((((((((0.00127109764952614092 * u + 1.19314022838340944e-4) * u -
        0.003963850973605135) * u - 8.70779635317295828e-4) * u +
        0.00773672528313526668) * u + 0.00383335126264887303) * u -
        0.0127223813782122755) * u - 0.0133823644533460069) * u +
        0.0161315329733252248) * u + 0.0390976845588484035) * u +
        0.00249367200053503304;
    y = ((((((((((((y * u - 0.0838864557023001992) * u -
        0.119463959964325415) * u + 0.0166207924969367356) * u +
        0.357524274449531043) * u + 0.805276408752910567) * u +
        1.18902982909273333) * u + 1.37040217682338167) * u +
        1.31314653831023098) * u + 1.07925515155856677) * u +
        0.774368199119538609) * u + 0.490165080585318424) * u +
        0.275374741597376782) * t * exp(-x * x);

  return x < 0 ? 2 - y : y;
}
#endif