/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2010 The Boeing Company
 *
 * 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: Gary Pei <guangyu.pei@boeing.com>
 */

#include <math.h>
#include "inet/common/INETDefs.h"
#include "inet/physicallayer/ieee80211/packetlevel/errormodel/dsss-error-rate-model.h"

namespace inet {

namespace physicallayer {

#ifndef ENABLE_GSL
const double DsssErrorRateModel::WLAN_SIR_PERFECT = 10.0;
const double DsssErrorRateModel::WLAN_SIR_IMPOSSIBLE = 0.1;
#endif // ifndef ENABLE_GSL

#ifdef BOEING_MODEL
const double DsssErrorRateModel::spectralEfficiency1bit = 22000000.0 / 1000000.0;    // 1 bit per symbol with 1 MSPS
const double DsssErrorRateModel::spectralEfficiency2bit = 22000000.0 / 1000000.0 / 2.0;    // 2 bits per symbol, 1 MSPS
#else // ifdef BOEING_MODEL
const double DsssErrorRateModel::spectralEfficiency1bit = 2000000.0 / 1000000.0;    // 1 bit per symbol with 1 MSPS
const double DsssErrorRateModel::spectralEfficiency2bit = 2000000.0 / 1000000.0 / 2.0;    // 2 bits per symbol, 1 MSPS
#endif // ifdef BOEING_MODEL

double DsssErrorRateModel::DqpskFunction(double x)
{
    return ((sqrt(2.0) + 1.0) / sqrt(8.0 * 3.1415926 * sqrt(2.0)))
           * (1.0 / sqrt(x))
           * exp(-(2.0 - sqrt(2.0)) * x);
}

double DsssErrorRateModel::GetDsssDbpskSuccessRate(double sinr, uint32_t nbits)
{
    double EbN0 = sinr * spectralEfficiency1bit;    // 1 bit per symbol with 1 MSPS
    double ber = 0.5 * exp(-EbN0);
    return pow((1.0 - ber), (int)nbits);
}

double DsssErrorRateModel::GetDsssDqpskSuccessRate(double sinr, uint32_t nbits)
{
    double EbN0 = sinr * spectralEfficiency2bit;    // 2 bits per symbol, 1 MSPS
    double ber = DqpskFunction(EbN0);
    return pow((1.0 - ber), (int)nbits);
}

double DsssErrorRateModel::GetDsssDqpskCck5_5SuccessRate(double sinr, uint32_t nbits)
{
#ifdef ENABLE_GSL
    // symbol error probability
    double EbN0 = sinr * 22000000.0 / 1375000.0 / 4.0;
    double sep = SymbolErrorProb16Cck(4.0 * EbN0 / 2.0);
    return pow(1.0 - sep, nbits / 4.0);
#else // ifdef ENABLE_GSL
    EV << "Running a 802.11b CCK Matlab model less accurate than GSL model" << endl;
    // The matlab model
    double ber;
    if (sinr > WLAN_SIR_PERFECT) {
        ber = 0.0;
    }
    else if (sinr < WLAN_SIR_IMPOSSIBLE) {
        ber = 0.5;
    }
    else {    // fitprops.coeff from matlab berfit
        double a1 = 5.3681634344056195e-001;
        double a2 = 3.3092430025608586e-003;
        double a3 = 4.1654372361004000e-001;
        double a4 = 1.0288981434358866e+000;
        ber = a1 * exp(-(pow((sinr - a2) / a3, a4)));
    }
    return pow((1.0 - ber), (int)nbits);
#endif // ifdef ENABLE_GSL
}

double DsssErrorRateModel::GetDsssDqpskCck11SuccessRate(double sinr, uint32_t nbits)
{
#ifdef ENABLE_GSL
    // symbol error probability
    double EbN0 = sinr * 22000000.0 / 1375000.0 / 8.0;
    double sep = SymbolErrorProb256Cck(8.0 * EbN0 / 2.0);
    return pow(1.0 - sep, nbits / 8.0);
#else // ifdef ENABLE_GSL
    EV << "Running a 802.11b CCK Matlab model less accurate than GSL model" << endl;
    // The matlab model
    double ber;
    if (sinr > WLAN_SIR_PERFECT) {
        ber = 0.0;
    }
    else if (sinr < WLAN_SIR_IMPOSSIBLE) {
        ber = 0.5;
    }
    else {    // fitprops.coeff from matlab berfit
        double a1 = 7.9056742265333456e-003;
        double a2 = -1.8397449399176360e-001;
        double a3 = 1.0740689468707241e+000;
        double a4 = 1.0523316904502553e+000;
        double a5 = 3.0552298746496687e-001;
        double a6 = 2.2032715128698435e+000;
        ber = (a1 * sinr * sinr + a2 * sinr + a3) / (sinr * sinr * sinr + a4 * sinr * sinr + a5 * sinr + a6);
    }
    return pow((1.0 - ber), (int)nbits);
#endif // ifdef ENABLE_GSL
}

#ifdef ENABLE_GSL
double IntegralFunction(double x, void *params)
{
    double beta = ((FunctionParameters *)params)->beta;
    double n = ((FunctionParameters *)params)->n;
    double IntegralFunction = pow(2 * gsl_cdf_ugaussian_P(x + beta) - 1, n - 1)
        * exp(-x * x / 2.0) / sqrt(2.0 * M_PI);
    return IntegralFunction;
}

double DsssErrorRateModel::SymbolErrorProb16Cck(double e2)
{
    double sep;
    double error;

    FunctionParameters params;
    params.beta = sqrt(2.0 * e2);
    params.n = 8.0;

    gsl_integration_workspace *w = gsl_integration_workspace_alloc(1000);

    gsl_function F;
    F.function = &IntegralFunction;
    F.params = &params;

    gsl_integration_qagiu(&F, -params.beta, 0, 1e-7, 1000, w, &sep, &error);
    gsl_integration_workspace_free(w);
    if (error == 0.0) {
        sep = 1.0;
    }

    return 1.0 - sep;
}

double DsssErrorRateModel::SymbolErrorProb256Cck(double e1)
{
    return 1.0 - pow(1.0 - SymbolErrorProb16Cck(e1 / 2.0), 2);
}

#endif // ifdef ENABLE_GSL

} // namespace physicallayer

} // namespace inet

