uan-mac-rc-gw.cc

Go to the documentation of this file.

/*
 * Copyright (c) 2009 University of Washington
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Leonard Tracy <lentracy@gmail.com>
 */
 
#include "uan-mac-rc-gw.h"
 
#include "uan-header-common.h"
#include "uan-header-rc.h"
#include "uan-mac-rc.h"
#include "uan-phy.h"
#include "uan-tx-mode.h"
 
#include "ns3/assert.h"
#include "ns3/double.h"
#include "ns3/log.h"
#include "ns3/nstime.h"
#include "ns3/trace-source-accessor.h"
#include "ns3/uinteger.h"
 
#include <algorithm>
#include <cfloat>
#include <map>
#include <set>
#include <utility>
#include <vector>
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("UanMacRcGw");
 
NS_OBJECT_ENSURE_REGISTERED(UanMacRcGw);
 
UanMacRcGw::UanMacRcGw()
    : UanMac(),
      m_state(IDLE),
      m_currentRateNum(0),
      m_cleared(false)
{
    UanHeaderCommon ch;
    UanHeaderRcRts rts;
    UanHeaderRcCts cts;
    UanHeaderRcAck ack;
    UanHeaderRcCtsGlobal ctsg;
 
    m_rtsSize = ch.GetSerializedSize() + rts.GetSerializedSize();
    m_ctsSizeN = cts.GetSerializedSize();
    m_ctsSizeG = ch.GetSerializedSize() + ctsg.GetSerializedSize();
    m_ackSize = ch.GetSerializedSize() + ack.GetSerializedSize();
 
    NS_LOG_DEBUG("Gateway initialized");
}
 
UanMacRcGw::~UanMacRcGw()
{
}
 
void
UanMacRcGw::Clear()
{
    if (m_cleared)
    {
        return;
    }
    m_cleared = true;
    if (m_phy)
    {
        m_phy->Clear();
        m_phy = nullptr;
    }
    m_propDelay.clear();
    auto it = m_ackData.begin();
    for (; it != m_ackData.end(); it++)
    {
        it->second.rxFrames.clear();
    }
    m_ackData.clear();
    m_requests.clear();
    m_sortedRes.clear();
}
 
void
UanMacRcGw::DoDispose()
{
    Clear();
    UanMac::DoDispose();
}
 
TypeId
UanMacRcGw::GetTypeId()
{
    static TypeId tid =
        TypeId("ns3::UanMacRcGw")
            .SetParent<UanMac>()
            .SetGroupName("Uan")
            .AddConstructor<UanMacRcGw>()
            .AddAttribute("MaxReservations",
                          "Maximum number of reservations to accept per cycle.",
                          UintegerValue(10),
                          MakeUintegerAccessor(&UanMacRcGw::m_maxRes),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute("NumberOfRates",
                          "Number of rates per Phy layer.",
                          UintegerValue(1023),
                          MakeUintegerAccessor(&UanMacRcGw::m_numRates),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute("MaxPropDelay",
                          "Maximum propagation delay between gateway and non-gateway nodes.",
                          TimeValue(Seconds(2)),
                          MakeTimeAccessor(&UanMacRcGw::m_maxDelta),
                          MakeTimeChecker())
            .AddAttribute(
                "SIFS",
                "Spacing between frames to account for timing error and processing delay.",
                TimeValue(Seconds(0.2)),
                MakeTimeAccessor(&UanMacRcGw::m_sifs),
                MakeTimeChecker())
            .AddAttribute("NumberOfNodes",
                          "Number of non-gateway nodes in this gateway's neighborhood.",
                          UintegerValue(10),
                          MakeUintegerAccessor(&UanMacRcGw::m_numNodes),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute("MinRetryRate",
                          "Smallest allowed RTS retry rate.",
                          DoubleValue(0.01),
                          MakeDoubleAccessor(&UanMacRcGw::m_minRetryRate),
                          MakeDoubleChecker<double>())
            .AddAttribute("RetryStep",
                          "Retry rate increment.",
                          DoubleValue(0.01),
                          MakeDoubleAccessor(&UanMacRcGw::m_retryStep),
                          MakeDoubleChecker<double>())
            .AddAttribute("TotalRate",
                          "Total available channel rate in bps (for a single channel, without "
                          "splitting reservation channel).",
                          UintegerValue(4096),
                          MakeUintegerAccessor(&UanMacRcGw::m_totalRate),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute("RateStep",
                          "Increments available for rate assignment in bps.",
                          UintegerValue(4),
                          MakeUintegerAccessor(&UanMacRcGw::m_rateStep),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute("FrameSize",
                          "Size of data frames in bytes.",
                          UintegerValue(1000),
                          MakeUintegerAccessor(&UanMacRcGw::m_frameSize),
                          MakeUintegerChecker<uint32_t>())
            .AddTraceSource("RX",
                            "A packet was destined for and received at this MAC layer.",
                            MakeTraceSourceAccessor(&UanMacRcGw::m_rxLogger),
                            "ns3::UanMac::PacketModeTracedCallback")
            .AddTraceSource("Cycle",
                            "Trace cycle statistics.",
                            MakeTraceSourceAccessor(&UanMacRcGw::m_cycleLogger),
                            "ns3::UanMacRcGw::CycleCallback")
 
        ;
 
    return tid;
}
 
bool
UanMacRcGw::Enqueue(Ptr<Packet> /* packet */,
                    uint16_t /* protocolNumber */,
                    const Address& /* dest */)
{
    NS_LOG_WARN("RCMAC Gateway transmission to acoustic nodes is not yet implemented");
    return false;
}
 
void
UanMacRcGw::SetForwardUpCb(Callback<void, Ptr<Packet>, uint16_t, const Mac8Address&> cb)
{
    m_forwardUpCb = cb;
}
 
void
UanMacRcGw::AttachPhy(Ptr<UanPhy> phy)
{
    m_phy = phy;
    phy->SetReceiveOkCallback(MakeCallback(&UanMacRcGw::ReceivePacket, this));
    phy->SetReceiveErrorCallback(MakeCallback(&UanMacRcGw::ReceiveError, this));
}
 
void
UanMacRcGw::ReceiveError(Ptr<Packet> /* pkt */, double /* sinr */)
{
}
 
void
UanMacRcGw::ReceivePacket(Ptr<Packet> pkt, double /* sinr */, UanTxMode mode)
{
    UanHeaderCommon ch;
    pkt->PeekHeader(ch);
 
    if (ch.GetDest() == Mac8Address::ConvertFrom(GetAddress()) ||
        ch.GetDest() == Mac8Address::GetBroadcast())
    {
        m_rxLogger(pkt, mode);
    }
    else
    {
        return;
    }
 
    pkt->RemoveHeader(ch);
 
    switch (ch.GetType())
    {
    case UanMacRc::TYPE_DATA: {
        UanHeaderRcData dh;
        pkt->RemoveHeader(dh);
        m_propDelay[ch.GetSrc()] = dh.GetPropDelay();
        if (m_ackData.find(ch.GetSrc()) == m_ackData.end())
        {
            NS_LOG_DEBUG(Now().As(Time::S) << " GATEWAY Received unexpected data packet");
        }
        else
        {
            NS_LOG_DEBUG(Now().As(Time::S) << " GW Received data packet from " << ch.GetSrc()
                                           << " length = " << pkt->GetSize());
            m_ackData[ch.GetSrc()].rxFrames.insert(dh.GetFrameNo());
        }
        m_forwardUpCb(pkt, ch.GetProtocolNumber(), ch.GetSrc());
    }
    break;
    case UanMacRc::TYPE_GWPING:
    case UanMacRc::TYPE_RTS:
        if (m_state == CTSING)
        {
            return;
        }
 
        {
            UanHeaderRcRts rh;
            pkt->RemoveHeader(rh);
 
            if (m_requests.find(ch.GetSrc()) == m_requests.end())
            {
                Request req;
                req.numFrames = rh.GetNoFrames();
                req.rxTime = Simulator::Now();
                req.frameNo = rh.GetFrameNo();
                req.retryNo = rh.GetRetryNo();
                req.length = rh.GetLength();
                NS_LOG_DEBUG(Now().As(Time::S) << " GW storing reservation from " << ch.GetSrc()
                                               << " with length " << req.length);
                m_requests.insert(std::make_pair(ch.GetSrc(), req));
                auto it = m_propDelay.find(ch.GetSrc());
                if (it == m_propDelay.end())
                {
                    m_sortedRes.insert(std::make_pair(m_maxDelta, ch.GetSrc()));
                }
                else
                {
                    m_sortedRes.insert(std::make_pair((*it).second, ch.GetSrc()));
                }
            }
        }
        if (m_state == IDLE)
        {
            StartCycle();
        }
        break;
    case UanMacRc::TYPE_CTS:
        NS_FATAL_ERROR("Received CTS at GW.  Currently only support single GW network!");
        break;
    case UanMacRc::TYPE_ACK:
        NS_FATAL_ERROR("Received ACK at GW.  Currently only support single GW network!");
        break;
    default:
        NS_FATAL_ERROR("Received unknown packet at GW!");
    }
}
 
void
UanMacRcGw::StartCycle()
{
    auto numRts = static_cast<uint32_t>(m_sortedRes.size());
 
    if (numRts)
    {
        NS_LOG_DEBUG(Now().As(Time::S) << " Simulator starting non-empty cycle");
    }
    else
    {
        NS_LOG_DEBUG(Now().As(Time::S) << " Simulator starting EMPTY cycle");
    }
 
    // Calculate dataRate
    uint32_t totalBytes = 0;
    uint32_t totalFrames = 0;
    Time pDelay = Seconds(0);
    if (numRts > 0)
    {
        auto rit = m_requests.begin();
        for (; rit != m_requests.end(); rit++)
        {
            totalBytes += (*rit).second.length;
            totalFrames += (*rit).second.numFrames;
        }
        pDelay = 2 * m_sortedRes.begin()->first;
    }
 
    double minRate = m_phy->GetMode(m_numRates).GetDataRateBps();
 
    uint32_t optA = m_maxRes;
    if (m_maxRes == 0)
    {
        optA = FindOptA();
    }
    double thAlpha =
        ComputeAlpha(totalFrames, totalBytes, m_numNodes, optA, (pDelay / 2.0).GetSeconds());
 
    double thCtlRate = m_totalRate * thAlpha;
 
    double temprate = (thCtlRate - minRate) / ((double)m_rateStep) + 0.5;
    m_currentRateNum = (uint32_t)temprate;
    if (m_currentRateNum >= m_numRates)
    {
        m_currentRateNum = m_numRates - 1;
    }
 
    NS_LOG_DEBUG("Found theoretical alpha: " << thAlpha << " Found associated rate = " << thCtlRate
                                             << " Giving rate number: " << temprate);
    double thX = thAlpha * m_totalRate / (2.0 * m_numNodes * m_rtsSize * 8.0);
 
    double dataRate = m_phy->GetMode(m_currentRateNum).GetDataRateBps();
 
    if (thX < m_minRetryRate)
    {
        NS_LOG_WARN("Gateway found optimum RTS retry rate is below minimum");
        m_currentRetryRate = 0;
    }
    else
    {
        m_currentRetryRate = (uint16_t)((thX - m_minRetryRate) / m_retryStep + 0.5);
    }
 
    double actualX = m_currentRetryRate * m_retryStep + m_minRetryRate;
 
    uint32_t ctlRate = m_phy->GetMode(m_currentRateNum + m_numRates).GetDataRateBps();
 
    Time winSize = Seconds(totalBytes * 8.0 / dataRate) + m_sifs * totalFrames + pDelay;
    if (numRts == 0)
    {
        winSize = Seconds((optA * std::exp(1.0) + 0.5) * 2.0 * 8.0 * m_rtsSize /
                          (thAlpha * m_totalRate)) +
                  (2 * m_maxDelta);
    }
    Time effWinSize = winSize - Seconds(m_rtsSize * 8.0 / ctlRate) - (2 * m_maxDelta);
 
    // Before fast CTS/ACK(below)
    Time ctsTxTimeG = Seconds(m_ctsSizeG * 8.0 / dataRate);
    Time cycleSeconds = winSize + ((totalFrames + 1.0) * m_sifs) + ctsTxTimeG +
                        Seconds((m_ctsSizeN + m_ackSize) * 8.0 / dataRate);
 
    Time ctsTxTimeTotal = Seconds(m_ctsSizeN * 8.0 * numRts / dataRate) + ctsTxTimeG;
    if (numRts == 0)
    {
        UanHeaderRcCtsGlobal ctsg;
        ctsg.SetWindowTime(effWinSize);
        ctsg.SetRateNum(static_cast<uint16_t>(m_currentRateNum));
        ctsg.SetRetryRate(m_currentRetryRate);
        ctsg.SetTxTimeStamp(Simulator::Now());
 
        UanHeaderCommon ch;
        ch.SetSrc(Mac8Address::ConvertFrom(GetAddress()));
        ch.SetDest(Mac8Address::GetBroadcast());
        ch.SetType(UanMacRc::TYPE_CTS);
        ch.SetProtocolNumber(0);
 
        Ptr<Packet> p = Create<Packet>();
        p->AddHeader(ctsg);
        p->AddHeader(ch);
        SendPacket(p, m_currentRateNum);
 
        Simulator::Schedule(cycleSeconds, &UanMacRcGw::StartCycle, this);
        m_state = INCYCLE;
        m_cycleLogger(Simulator::Now(),
                      Seconds(0),
                      numRts,
                      totalBytes,
                      effWinSize.GetSeconds(),
                      ctlRate,
                      actualX);
        return;
    }
 
    Time nextEarliest = ctsTxTimeTotal + m_sifs;
 
    m_state = CTSING;
    Simulator::Schedule(nextEarliest, &UanMacRcGw::CycleStarted, this);
 
    auto it = m_sortedRes.begin();
    Time minPdelay = (*it).first;
    Ptr<Packet> cts = Create<Packet>();
 
    for (; it != m_sortedRes.end(); it++)
    {
        Request req = m_requests[(*it).second];
        Time pdelay = (*it).first;
 
        AckData newData;
        newData.expFrames = req.numFrames;
        newData.frameNo = req.frameNo;
        Mac8Address dest = (*it).second;
        m_ackData.insert(std::make_pair(dest, newData));
 
        Time earliestArr = ctsTxTimeTotal + pdelay + pdelay + m_sifs;
        Time arrivalTime = std::max(earliestArr, nextEarliest);
        NS_LOG_DEBUG(Now().As(Time::S)
                     << " GW: Scheduling request for prop. delay " << pdelay.As(Time::S) << " for "
                     << (*it).second << " Earliest possible arrival=" << earliestArr.As(Time::S)
                     << "  Next arrival time=" << nextEarliest.As(Time::S));
        nextEarliest = arrivalTime + Seconds(req.length * 8.0 / dataRate) + m_sifs * req.numFrames;
 
        UanHeaderRcCts ctsh;
        ctsh.SetAddress(dest);
        ctsh.SetRtsTimeStamp(req.rxTime);
        ctsh.SetFrameNo(req.frameNo);
        ctsh.SetRetryNo(req.retryNo);
        ctsh.SetDelayToTx(arrivalTime);
        cts->AddHeader(ctsh);
 
        NS_LOG_DEBUG(Now().As(Time::S)
                     << " GW Scheduling reception for " << (uint32_t)req.numFrames << " frames at "
                     << (Simulator::Now() + arrivalTime).As(Time::S) << "  (delaytiltx of "
                     << arrivalTime.As(Time::S) << ")  Total length is " << req.length
                     << " with txtime " << req.length * 8 / dataRate << " seconds");
    }
 
    UanHeaderRcCtsGlobal ctsg;
    ctsg.SetRateNum(static_cast<uint16_t>(m_currentRateNum));
    ctsg.SetRetryRate(m_currentRetryRate);
    ctsg.SetWindowTime(effWinSize);
    ctsg.SetTxTimeStamp(Simulator::Now());
    UanHeaderCommon ch;
    ch.SetDest(Mac8Address::GetBroadcast());
    ch.SetSrc(Mac8Address::ConvertFrom(GetAddress()));
    ch.SetType(UanMacRc::TYPE_CTS);
    cts->AddHeader(ctsg);
    cts->AddHeader(ch);
    SendPacket(cts, m_currentRateNum);
 
    m_requests.clear();
    m_sortedRes.clear();
    Simulator::Schedule(nextEarliest, &UanMacRcGw::EndCycle, this);
 
    m_cycleLogger(Simulator::Now(),
                  minPdelay,
                  numRts,
                  totalBytes,
                  cycleSeconds.GetSeconds(),
                  ctlRate,
                  actualX);
}
 
void
UanMacRcGw::CycleStarted()
{
    m_state = INCYCLE;
}
 
void
UanMacRcGw::EndCycle()
{
    NS_LOG_DEBUG(Now().As(Time::S) << " GW Ending cycle");
 
    Time nextAck = Seconds(0);
 
    Time ackTime = Seconds(m_ackSize * 8.0 / m_phy->GetMode(m_currentRateNum).GetDataRateBps());
 
    auto it = m_ackData.begin();
    for (; it != m_ackData.end(); it++)
    {
        Mac8Address dest = (*it).first;
        AckData& data = (*it).second;
 
        std::list<uint32_t> toNack;
        for (uint8_t i = 0; i < data.expFrames; i++)
        {
            if (data.rxFrames.find(i) == data.rxFrames.end())
            {
                toNack.push_back(i);
            }
        }
        UanHeaderCommon ch;
        ch.SetDest(dest);
        ch.SetSrc(Mac8Address::ConvertFrom(GetAddress()));
        ch.SetType(UanMacRc::TYPE_ACK);
        UanHeaderRcAck ah;
        ah.SetFrameNo(data.frameNo);
        auto nit = toNack.begin();
        for (; nit != toNack.end(); nit++)
        {
            ah.AddNackedFrame(static_cast<uint8_t>(*nit));
        }
 
        Ptr<Packet> ack = Create<Packet>();
        ack->AddHeader(ah);
        ack->AddHeader(ch);
        Simulator::Schedule(nextAck, &UanMacRcGw::SendPacket, this, ack, m_currentRateNum);
        nextAck = nextAck + ackTime + m_sifs;
    }
    m_ackData.clear();
    Simulator::Schedule(nextAck, &UanMacRcGw::StartCycle, this);
}
 
void
UanMacRcGw::SendPacket(Ptr<Packet> pkt, uint32_t rate)
{
    UanHeaderCommon ch;
    pkt->PeekHeader(ch);
    std::string type;
    switch (ch.GetType())
    {
    case UanMacRc::TYPE_DATA:
        type = "DATA";
        break;
    case UanMacRc::TYPE_RTS:
        type = "RTS";
        break;
    case UanMacRc::TYPE_CTS:
        type = "CTS";
        break;
    case UanMacRc::TYPE_ACK:
        type = "ACK";
        break;
    case UanMacRc::TYPE_GWPING:
        type = "GWPING";
        break;
    default:
        type = "UNKNOWN";
        break;
    }
    NS_LOG_DEBUG(Now().As(Time::S)
                 << " GW sending " << type << " packet with size " << pkt->GetSize() << " to "
                 << ch.GetDest() << " at rate " << rate);
    m_phy->SendPacket(pkt, rate);
}
 
double
UanMacRcGw::ComputeAlpha(uint32_t totalFrames,
                         uint32_t totalBytes,
                         uint32_t /* n */,
                         uint32_t a,
                         double deltaK)
{
    double alpha;
    double lrae = m_rtsSize * 8.0 * a * std::exp(1.0);
    if (totalFrames == 0)
    {
        alpha = (2.0 * lrae + 8.0 * m_rtsSize -
                 std::sqrt(m_ctsSizeG * 8.0 * 8.0 * m_rtsSize +
                           2 * 8.0 * m_ctsSizeG * 8.0 * m_rtsSize * a * std::exp(1.0))) /
                (2 * lrae + 8.0 * m_rtsSize - 8.0 * m_ctsSizeG);
    }
    else
    {
        double w = totalBytes * 8.0 + totalFrames * m_sifs.GetSeconds() * m_totalRate;
        double v = m_rtsSize * 8.0 + 2 * lrae;
        double u = (2 * m_maxDelta.GetSeconds() - 2 * deltaK) * m_totalRate;
 
        double gamma = (w - u + v) / (2 * (u - totalFrames * m_sifs.GetSeconds() * m_totalRate));
 
        alpha = -gamma + std::sqrt(gamma * gamma +
                                   v / (u - totalFrames * m_sifs.GetSeconds() * m_totalRate));
 
        if (alpha < 0 || alpha > 1)
        {
            alpha = -gamma - std::sqrt(gamma * gamma +
                                       v / (u - totalFrames * m_sifs.GetSeconds() * m_totalRate));
        }
    }
    NS_ASSERT_MSG(alpha > 0 && alpha < 1, "Error computing alpha.  Alpha out of valid range!");
    return alpha;
}
 
std::vector<double>
UanMacRcGw::GetExpPdk()
{
    uint32_t n = m_numNodes;
    std::vector<double> pds;
    auto pdit = m_propDelay.begin();
 
    for (; pdit != m_propDelay.end(); pdit++)
    {
        pds.push_back(pdit->second.GetSeconds());
    }
    while (pds.size() < m_numNodes)
    {
        pds.push_back(m_maxDelta.GetSeconds());
    }
 
    std::sort(pds.begin(), pds.end());
    // Find expected min. prop. delay for k nodes
    std::vector<double> exppdk;
    exppdk.push_back(m_maxDelta.GetSeconds());
    for (uint32_t k = 1; k <= n; k++)
    {
        uint32_t ind = CompExpMinIndex(n, k) - 1;
        exppdk.push_back(pds[ind]);
    }
    return exppdk;
}
 
double
UanMacRcGw::ComputeExpS(uint32_t a, uint32_t ld, std::vector<double> exppdk)
{
    UanHeaderCommon ch;
    uint32_t lh = ch.GetSerializedSize();
 
    uint32_t n = m_numNodes;
    double expk = n * (1 - std::exp(-((double)a) / (double)n));
    NS_LOG_DEBUG("expk = " << expk);
 
    // Compute expected data per cycle
    double expdata = 8 * ld * expk;
 
    // Compute expected time per cycle
    double alpha0 = ComputeAlpha(0, 0, n, a, exppdk[0]);
    double c0 = 8.0 * m_ctsSizeG / (m_totalRate * (1 - alpha0)) + 2 * m_maxDelta.GetSeconds() +
                (a * std::exp(1.0) + 0.5) * 2 * m_rtsSize * 8.0 / (alpha0 * m_totalRate);
    double exptime = ComputePiK(a, n, 0) * c0;
    double expp = 0;
    for (uint32_t i = 1; i <= n; i++)
    {
        expp += ComputePiK(a, n, i) * exppdk[i - 1];
    }
 
    exptime += ComputeExpBOverA(n, a, ld + lh, exppdk) + expk * 2 * m_sifs.GetSeconds() +
               m_sifs.GetSeconds() + 2 * expp;
    double s = (1.0 / m_totalRate) * expdata / exptime;
 
    return s;
}
 
double
UanMacRcGw::ComputeExpS(uint32_t a, uint32_t ld)
{
    return ComputeExpS(a, ld, GetExpPdk());
}
 
uint32_t
UanMacRcGw::CompExpMinIndex(uint32_t n, uint32_t k)
{
    double sum = 0;
    for (uint32_t i = 1; i <= n - k + 1; i++)
    {
        auto nChK = static_cast<double>(NchooseK(n, k));
        double p = (nChK > 0) ? (static_cast<double>(NchooseK(n - i, k - 1)) / nChK) : DBL_MAX;
        sum += p * i;
    }
    return (uint32_t)(sum + 0.5);
}
 
double
UanMacRcGw::ComputePiK(uint32_t a, uint32_t n, uint32_t k)
{
    auto nck = (double)NchooseK(n, k);
    return nck * std::pow((std::exp((double)a / (double)n) - 1.0), (double)k) *
           std::exp(-((double)a));
}
 
double
UanMacRcGw::ComputeExpBOverA(uint32_t n, uint32_t a, uint32_t ldlh, std::vector<double> deltaK)
{
    double sum = 0;
    uint32_t lt = 8 * (m_ctsSizeN + ldlh + m_ackSize);
    for (uint32_t k = 1; k <= n; k++)
    {
        double num = 8.0 * m_ctsSizeG + k * lt;
        double denom = (1.0 - ComputeAlpha(k, k * ldlh, n, a, deltaK[k])) * m_totalRate;
        double pik = ComputePiK(a, n, k);
        double term = pik * num / denom;
 
        sum += term;
    }
 
    return sum;
}
 
uint64_t
UanMacRcGw::NchooseK(uint32_t n, uint32_t k)
{
    if (k > n)
    {
        return 0;
    }
 
    if (k > n / 2)
    {
        k = n - k;
    }
 
    double accum = 1;
    for (uint32_t i = 1; i <= k; i++)
    {
        accum = accum * (n - k + i) / i;
    }
 
    return (uint64_t)(accum + 0.5);
}
 
uint32_t
UanMacRcGw::FindOptA()
{
    double tput = 0;
    uint32_t a = 1;
    while (true)
    {
        double newtput = ComputeExpS(a, m_frameSize);
        if (newtput < tput)
        {
            a--;
            break;
        }
        else
        {
            tput = newtput;
            a++;
        }
    }
    NS_LOG_DEBUG(Now().As(Time::S) << " GW: Found optimum a = " << a);
    return a;
}
 
int64_t
UanMacRcGw::AssignStreams(int64_t stream)
{
    NS_LOG_FUNCTION(this << stream);
    return 0;
}
 
} // namespace ns3