ofdm-ppdu.cc

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/*
 * Copyright (c) 2020 Orange Labs
 *
 * 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: Rediet <getachew.redieteab@orange.com>
 *         Muhammad Iqbal Rochman <muhiqbalcr@uchicago.edu>
 *         Sébastien Deronne <sebastien.deronne@gmail.com> (LSigHeader)
 */
 
#include "ofdm-ppdu.h"
 
#include "ofdm-phy.h"
 
#include "ns3/log.h"
#include "ns3/wifi-phy.h"
#include "ns3/wifi-psdu.h"
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("OfdmPpdu");
 
OfdmPpdu::OfdmPpdu(Ptr<const WifiPsdu> psdu,
                   const WifiTxVector& txVector,
                   uint16_t txCenterFreq,
                   WifiPhyBand band,
                   uint64_t uid,
                   bool instantiateLSig /* = true */)
    : WifiPpdu(psdu, txVector, txCenterFreq, uid),
      m_band(band),
      m_channelWidth(txVector.IsNonHtDuplicate() ? 20 : txVector.GetChannelWidth())
{
    NS_LOG_FUNCTION(this << psdu << txVector << txCenterFreq << band << uid);
    if (instantiateLSig)
    {
        SetPhyHeaders(txVector, psdu->GetSize());
    }
}
 
void
OfdmPpdu::SetPhyHeaders(const WifiTxVector& txVector, std::size_t psduSize)
{
    NS_LOG_FUNCTION(this << txVector << psduSize);
 
#ifdef NS3_BUILD_PROFILE_DEBUG
    LSigHeader lSig;
    SetLSigHeader(lSig, txVector, psduSize);
    m_phyHeaders->AddHeader(lSig);
#else
    SetLSigHeader(m_lSig, txVector, psduSize);
#endif
}
 
void
OfdmPpdu::SetLSigHeader(LSigHeader& lSig, const WifiTxVector& txVector, std::size_t psduSize) const
{
    lSig.SetRate(txVector.GetMode().GetDataRate(txVector), m_channelWidth);
    lSig.SetLength(psduSize);
}
 
WifiTxVector
OfdmPpdu::DoGetTxVector() const
{
    WifiTxVector txVector;
    txVector.SetPreambleType(m_preamble);
 
#ifdef NS3_BUILD_PROFILE_DEBUG
    LSigHeader lSig;
    if (m_phyHeaders->PeekHeader(lSig) == 0)
    {
        NS_FATAL_ERROR("Missing L-SIG in PPDU");
    }
 
    SetTxVectorFromLSigHeader(txVector, lSig);
#else
    SetTxVectorFromLSigHeader(txVector, m_lSig);
#endif
 
    return txVector;
}
 
void
OfdmPpdu::SetTxVectorFromLSigHeader(WifiTxVector& txVector, const LSigHeader& lSig) const
{
    NS_ASSERT(m_channelWidth <= 20);
    // OFDM uses 20 MHz, unless PHY channel width is 5 MHz or 10 MHz
    txVector.SetMode(OfdmPhy::GetOfdmRate(lSig.GetRate(m_channelWidth), m_channelWidth));
    txVector.SetChannelWidth(m_channelWidth);
}
 
Time
OfdmPpdu::GetTxDuration() const
{
    const WifiTxVector& txVector = GetTxVector();
    uint16_t length = 0;
#ifdef NS3_BUILD_PROFILE_DEBUG
    LSigHeader lSig;
    m_phyHeaders->PeekHeader(lSig);
    length = lSig.GetLength();
#else
    length = m_lSig.GetLength();
#endif
    return WifiPhy::CalculateTxDuration(length, txVector, m_band);
}
 
Ptr<WifiPpdu>
OfdmPpdu::Copy() const
{
    return Ptr<WifiPpdu>(new OfdmPpdu(*this), false);
}
 
OfdmPpdu::LSigHeader::LSigHeader()
    : m_rate(0b1101),
      m_length(0)
{
}
 
TypeId
OfdmPpdu::LSigHeader::GetTypeId()
{
    static TypeId tid = TypeId("ns3::LSigHeader")
                            .SetParent<Header>()
                            .SetGroupName("Wifi")
                            .AddConstructor<LSigHeader>();
    return tid;
}
 
TypeId
OfdmPpdu::LSigHeader::GetInstanceTypeId() const
{
    return GetTypeId();
}
 
void
OfdmPpdu::LSigHeader::Print(std::ostream& os) const
{
    os << "SIGNAL=" << GetRate() << " LENGTH=" << m_length;
}
 
uint32_t
OfdmPpdu::LSigHeader::GetSerializedSize() const
{
    return 3;
}
 
void
OfdmPpdu::LSigHeader::SetRate(uint64_t rate, uint16_t channelWidth)
{
    if (channelWidth == 5)
    {
        rate *= 4; // corresponding 20 MHz rate if 5 MHz is used
    }
    else if (channelWidth == 10)
    {
        rate *= 2; // corresponding 20 MHz rate if 10 MHz is used
    }
    /* Here is the binary representation for a given rate:
     * 6 Mbit/s: 1101
     * 9 Mbit/s: 1111
     * 12 Mbit/s: 0101
     * 18 Mbit/s: 0111
     * 24 Mbit/s: 1001
     * 36 Mbit/s: 1011
     * 48 Mbit/s: 0001
     * 54 Mbit/s: 0011
     */
    switch (rate)
    {
    case 6000000:
        m_rate = 0b1101;
        break;
    case 9000000:
        m_rate = 0b1111;
        break;
    case 12000000:
        m_rate = 0b0101;
        break;
    case 18000000:
        m_rate = 0b0111;
        break;
    case 24000000:
        m_rate = 0b1001;
        break;
    case 36000000:
        m_rate = 0b1011;
        break;
    case 48000000:
        m_rate = 0b0001;
        break;
    case 54000000:
        m_rate = 0b0011;
        break;
    default:
        NS_ASSERT_MSG(false, "Invalid rate");
        break;
    }
}
 
uint64_t
OfdmPpdu::LSigHeader::GetRate(uint16_t channelWidth) const
{
    uint64_t rate = 0;
    switch (m_rate)
    {
    case 0b1101:
        rate = 6000000;
        break;
    case 0b1111:
        rate = 9000000;
        break;
    case 0b0101:
        rate = 12000000;
        break;
    case 0b0111:
        rate = 18000000;
        break;
    case 0b1001:
        rate = 24000000;
        break;
    case 0b1011:
        rate = 36000000;
        break;
    case 0b0001:
        rate = 48000000;
        break;
    case 0b0011:
        rate = 54000000;
        break;
    default:
        NS_ASSERT_MSG(false, "Invalid rate");
        break;
    }
    if (channelWidth == 5)
    {
        rate /= 4; // compute corresponding 5 MHz rate
    }
    else if (channelWidth == 10)
    {
        rate /= 2; // compute corresponding 10 MHz rate
    }
    return rate;
}
 
void
OfdmPpdu::LSigHeader::SetLength(uint16_t length)
{
    NS_ASSERT_MSG(length < 4096, "Invalid length");
    m_length = length;
}
 
uint16_t
OfdmPpdu::LSigHeader::GetLength() const
{
    return m_length;
}
 
void
OfdmPpdu::LSigHeader::Serialize(Buffer::Iterator start) const
{
    uint8_t byte = 0;
    uint16_t bytes = 0;
 
    byte |= m_rate;
    byte |= (m_length & 0x07) << 5;
    start.WriteU8(byte);
 
    bytes |= (m_length & 0x0ff8) >> 3;
    start.WriteU16(bytes);
}
 
uint32_t
OfdmPpdu::LSigHeader::Deserialize(Buffer::Iterator start)
{
    Buffer::Iterator i = start;
 
    uint8_t byte = i.ReadU8();
    m_rate = byte & 0x0f;
    m_length = (byte >> 5) & 0x07;
 
    uint16_t bytes = i.ReadU16();
    m_length |= (bytes << 3) & 0x0ff8;
 
    return i.GetDistanceFrom(start);
}
 
} // namespace ns3