/* -*-  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 "ns3/log.h"
#include "dsss-error-rate-model.h"
#include <math.h>

NS_LOG_COMPONENT_DEFINE ("DsssErrorRateModel");

namespace ns3 {

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

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 * 22000000.0 / 1000000.0; // 1 bit per symbol with 1 MSPS
  double ber = 0.5 * exp (-EbN0);
  return pow ((1.0 - ber), nbits);
}

double 
DsssErrorRateModel::GetDsssDqpskSuccessRate (double sinr,uint32_t nbits) 
{
  double EbN0 = sinr * 22000000.0 / 1000000.0 / 2.0; // 2 bits per symbol, 1 MSPS
  double ber = DqpskFunction (EbN0);
  return pow ((1.0 - ber), 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
  NS_LOG_WARN ("Running a 802.11b CCK Matlab model less accurate than GSL model"); 
  // 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), nbits);
#endif
}

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
  NS_LOG_WARN ("Running a 802.11b CCK Matlab model less accurate than GSL model"); 
  // 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), nbits);
#endif
}

#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), 2.0);
}

#endif

} // namespace ns3
