Ieee80211RadioModel.cc

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//
// Copyright (C) 2006 Andras Varga, Levente Meszaros
// Based on the Mobility Framework's SnrEval by Marc Loebbers
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this program; if not, see <http://www.gnu.org/licenses/>.
//


#include "Ieee80211RadioModel.h"
#include "Ieee80211Consts.h"
#include "FWMath.h"


Register_Class(Ieee80211RadioModel);


void Ieee80211RadioModel::initializeFrom(cModule *radioModule)
{
    snirThreshold = dB2fraction(radioModule->par("snirThreshold"));
}

double Ieee80211RadioModel::calculateDuration(AirFrame *airframe)
{
    // The physical layer header is sent with 1Mbit/s and the rest with the frame's bitrate
    return airframe->getBitLength()/airframe->getBitrate() + PHY_HEADER_LENGTH/BITRATE_HEADER;
}


bool Ieee80211RadioModel::isReceivedCorrectly(AirFrame *airframe, const SnrList& receivedList)
{
    // calculate snirMin
    double snirMin = receivedList.begin()->snr;
    for (SnrList::const_iterator iter = receivedList.begin(); iter != receivedList.end(); iter++)
        if (iter->snr < snirMin)
            snirMin = iter->snr;

    cPacket *frame = airframe->getEncapsulatedPacket();
    EV << "packet (" << frame->getClassName() << ")" << frame->getName() << " (" << frame->info() << ") snrMin=" << snirMin << endl;

    if (snirMin <= snirThreshold)
    {
        // if snir is too low for the packet to be recognized
        EV << "COLLISION! Packet got lost\n";
        return false;
    }
    else if (isPacketOK(snirMin, airframe->getEncapsulatedPacket()->getBitLength(), airframe->getBitrate()))
    {
        EV << "packet was received correctly, it is now handed to upper layer...\n";
        return true;
    }
    else
    {
        EV << "Packet has BIT ERRORS! It is lost!\n";
        return false;
    }
}


bool Ieee80211RadioModel::isPacketOK(double snirMin, int lengthMPDU, double bitrate)
{
    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 (rand > headerNoError)
        return false; // error in header
    else if (dblrand() > MpduNoError)
        return false;  // error in MPDU
    else
        return true; // no error
}

double Ieee80211RadioModel::dB2fraction(double dB)
{
    return pow(10.0, (dB / 10));
}