unison/examples/wireless/wifi-eht-network.cc

/*
 * Copyright (c) 2022
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Sebastien Deronne <sebastien.deronne@gmail.com>
 */

#include "ns3/attribute-container.h"
#include "ns3/boolean.h"
#include "ns3/command-line.h"
#include "ns3/config.h"
#include "ns3/double.h"
#include "ns3/eht-phy.h"
#include "ns3/enum.h"
#include "ns3/internet-stack-helper.h"
#include "ns3/ipv4-address-helper.h"
#include "ns3/log.h"
#include "ns3/mobility-helper.h"
#include "ns3/multi-model-spectrum-channel.h"
#include "ns3/neighbor-cache-helper.h"
#include "ns3/on-off-helper.h"
#include "ns3/packet-sink-helper.h"
#include "ns3/packet-sink.h"
#include "ns3/spectrum-wifi-helper.h"
#include "ns3/ssid.h"
#include "ns3/string.h"
#include "ns3/udp-client-server-helper.h"
#include "ns3/udp-server.h"
#include "ns3/uinteger.h"
#include "ns3/wifi-acknowledgment.h"
#include "ns3/wifi-static-setup-helper.h"

#include <algorithm>
#include <array>
#include <functional>
#include <numeric>

// This is a simple example in order to show how to configure an IEEE 802.11be Wi-Fi network.
//
// It outputs the UDP or TCP goodput for every EHT MCS value, which depends on the MCS value (0 to
// 13), the channel width (20, 40, 80, 160 or 320 MHz) and the guard interval (800ns, 1600ns or
// 3200ns). The PHY bitrate is constant over all the simulation run. The user can also specify the
// distance between the access point and the station: the larger the distance the smaller the
// goodput.
//
// The simulation assumes a configurable number of stations in an infrastructure network:
//
//  STA     AP
//    *     *
//    |     |
//   n1     n2
//
// Packets in this simulation belong to BestEffort Access Class (AC_BE).
// By selecting an acknowledgment sequence for DL MU PPDUs, it is possible to aggregate a
// Round Robin scheduler to the AP, so that DL MU PPDUs are sent by the AP via DL OFDMA.

using namespace ns3;

NS_LOG_COMPONENT_DEFINE("eht-wifi-network");

/**
 * @param udp true if UDP is used, false if TCP is used
 * @param serverApp a container of server applications
 * @param payloadSize the size in bytes of the packets
 * @return the bytes received by each server application
 */
std::vector<uint64_t>
GetRxBytes(bool udp, const ApplicationContainer& serverApp, uint32_t payloadSize)
{
    std::vector<uint64_t> rxBytes(serverApp.GetN(), 0);
    if (udp)
    {
        for (uint32_t i = 0; i < serverApp.GetN(); i++)
        {
            rxBytes[i] = payloadSize * DynamicCast<UdpServer>(serverApp.Get(i))->GetReceived();
        }
    }
    else
    {
        for (uint32_t i = 0; i < serverApp.GetN(); i++)
        {
            rxBytes[i] = DynamicCast<PacketSink>(serverApp.Get(i))->GetTotalRx();
        }
    }
    return rxBytes;
}

/**
 * Print average throughput over an intermediate time interval.
 * @param rxBytes a vector of the amount of bytes received by each server application
 * @param udp true if UDP is used, false if TCP is used
 * @param serverApp a container of server applications
 * @param payloadSize the size in bytes of the packets
 * @param tputInterval the duration of an intermediate time interval
 * @param simulationTime the simulation time in seconds
 */
void
PrintIntermediateTput(std::vector<uint64_t>& rxBytes,
                      bool udp,
                      const ApplicationContainer& serverApp,
                      uint32_t payloadSize,
                      Time tputInterval,
                      Time simulationTime)
{
    auto newRxBytes = GetRxBytes(udp, serverApp, payloadSize);
    Time now = Simulator::Now();

    std::cout << "[" << (now - tputInterval).As(Time::S) << " - " << now.As(Time::S)
              << "] Per-STA Throughput (Mbit/s):";

    for (std::size_t i = 0; i < newRxBytes.size(); i++)
    {
        std::cout << "\t\t(" << i << ") "
                  << (newRxBytes[i] - rxBytes[i]) * 8. / tputInterval.GetMicroSeconds(); // Mbit/s
    }
    std::cout << std::endl;

    rxBytes.swap(newRxBytes);

    if (now < (simulationTime - NanoSeconds(1)))
    {
        Simulator::Schedule(Min(tputInterval, simulationTime - now - NanoSeconds(1)),
                            &PrintIntermediateTput,
                            rxBytes,
                            udp,
                            serverApp,
                            payloadSize,
                            tputInterval,
                            simulationTime);
    }
}

int
main(int argc, char* argv[])
{
    bool udp{true};
    bool downlink{true};
    bool useRts{false};
    bool use80Plus80{false};
    uint16_t mpduBufferSize{512};
    std::string emlsrMgrTypeId{"ns3::DefaultEmlsrManager"};
    std::string emlsrLinks;
    uint16_t paddingDelayUsec{32};
    uint16_t transitionDelayUsec{128};
    Time channelSwitchDelay{"100us"};
    bool switchAuxPhy{true};
    uint16_t auxPhyChWidth{20};
    bool auxPhyTxCapable{true};
    Time simulationTime{"10s"};
    bool staticSetup{true};
    auto clientAppStartTime = Seconds(1);
    meter_u distance{1.0};
    double frequency{5};  // whether the first link operates in the 2.4, 5 or 6 GHz
    double frequency2{0}; // whether the second link operates in the 2.4, 5 or 6 GHz (0 means no
                          // second link exists)
    double frequency3{
        0}; // whether the third link operates in the 2.4, 5 or 6 GHz (0 means no third link exists)
    std::size_t nStations{1};
    std::string dlAckSeqType{"NO-OFDMA"};
    bool enableUlOfdma{false};
    bool enableBsrp{false};
    std::string mcsStr;
    std::vector<uint64_t> mcsValues;
    int channelWidth{-1};  // in MHz, -1 indicates an unset value
    int guardInterval{-1}; // in nanoseconds, -1 indicates an unset value
    uint32_t payloadSize =
        700; // must fit in the max TX duration when transmitting at MCS 0 over an RU of 26 tones
    Time tputInterval{0}; // interval for detailed throughput measurement
    double minExpectedThroughput{0.0};
    double maxExpectedThroughput{0.0};
    Time accessReqInterval{0};

    CommandLine cmd(__FILE__);
    cmd.AddValue("staticSetup",
                 "Whether devices are configured using the static setup helper",
                 staticSetup);
    cmd.AddValue(
        "frequency",
        "Whether the first link operates in the 2.4, 5 or 6 GHz band (other values gets rejected)",
        frequency);
    cmd.AddValue(
        "frequency2",
        "Whether the second link operates in the 2.4, 5 or 6 GHz band (0 means the device has one "
        "link, otherwise the band must be different than first link and third link)",
        frequency2);
    cmd.AddValue(
        "frequency3",
        "Whether the third link operates in the 2.4, 5 or 6 GHz band (0 means the device has up to "
        "two links, otherwise the band must be different than first link and second link)",
        frequency3);
    cmd.AddValue("emlsrMgrTypeId", "The ns-3 TypeId of the EMLSR manager to use", emlsrMgrTypeId);
    cmd.AddValue("emlsrLinks",
                 "The comma separated list of IDs of EMLSR links (for MLDs only)",
                 emlsrLinks);
    cmd.AddValue("emlsrPaddingDelay",
                 "The EMLSR padding delay in microseconds (0, 32, 64, 128 or 256)",
                 paddingDelayUsec);
    cmd.AddValue("emlsrTransitionDelay",
                 "The EMLSR transition delay in microseconds (0, 16, 32, 64, 128 or 256)",
                 transitionDelayUsec);
    cmd.AddValue("emlsrAuxSwitch",
                 "Whether Aux PHY should switch channel to operate on the link on which "
                 "the Main PHY was operating before moving to the link of the Aux PHY. ",
                 switchAuxPhy);
    cmd.AddValue("emlsrAuxChWidth",
                 "The maximum channel width (MHz) supported by Aux PHYs.",
                 auxPhyChWidth);
    cmd.AddValue("emlsrAuxTxCapable",
                 "Whether Aux PHYs are capable of transmitting.",
                 auxPhyTxCapable);
    cmd.AddValue("channelSwitchDelay", "The PHY channel switch delay", channelSwitchDelay);
    cmd.AddValue("distance",
                 "Distance in meters between the station and the access point",
                 distance);
    cmd.AddValue("simulationTime", "Simulation time", simulationTime);
    cmd.AddValue("udp", "UDP if set to 1, TCP otherwise", udp);
    cmd.AddValue("downlink",
                 "Generate downlink flows if set to 1, uplink flows otherwise",
                 downlink);
    cmd.AddValue("useRts", "Enable/disable RTS/CTS", useRts);
    cmd.AddValue("use80Plus80", "Enable/disable use of 80+80 MHz", use80Plus80);
    cmd.AddValue("mpduBufferSize",
                 "Size (in number of MPDUs) of the BlockAck buffer",
                 mpduBufferSize);
    cmd.AddValue("nStations", "Number of non-AP EHT stations", nStations);
    cmd.AddValue("dlAckType",
                 "Ack sequence type for DL OFDMA (NO-OFDMA, ACK-SU-FORMAT, MU-BAR, AGGR-MU-BAR)",
                 dlAckSeqType);
    cmd.AddValue("enableUlOfdma",
                 "Enable UL OFDMA (useful if DL OFDMA is enabled and TCP is used)",
                 enableUlOfdma);
    cmd.AddValue("enableBsrp",
                 "Enable BSRP (useful if DL and UL OFDMA are enabled and TCP is used)",
                 enableBsrp);
    cmd.AddValue(
        "muSchedAccessReqInterval",
        "Duration of the interval between two requests for channel access made by the MU scheduler",
        accessReqInterval);
    cmd.AddValue(
        "mcs",
        "list of comma separated MCS values to test; if unset, all MCS values (0-13) are tested",
        mcsStr);
    cmd.AddValue("channelWidth",
                 "if set, limit testing to a specific channel width expressed in MHz (20, 40, 80, "
                 "160 or 320 MHz)",
                 channelWidth);
    cmd.AddValue("guardInterval",
                 "if set, limit testing to a specific guard interval duration expressed in "
                 "nanoseconds (800, 1600 or 3200 ns)",
                 guardInterval);
    cmd.AddValue("payloadSize", "The application payload size in bytes", payloadSize);
    cmd.AddValue("tputInterval", "duration of intervals for throughput measurement", tputInterval);
    cmd.AddValue("minExpectedThroughput",
                 "if set, simulation fails if the lowest throughput is below this value",
                 minExpectedThroughput);
    cmd.AddValue("maxExpectedThroughput",
                 "if set, simulation fails if the highest throughput is above this value",
                 maxExpectedThroughput);
    cmd.Parse(argc, argv);

    if (useRts)
    {
        Config::SetDefault("ns3::WifiRemoteStationManager::RtsCtsThreshold", StringValue("0"));
        Config::SetDefault("ns3::WifiDefaultProtectionManager::EnableMuRts", BooleanValue(true));
    }

    if (dlAckSeqType == "ACK-SU-FORMAT")
    {
        Config::SetDefault("ns3::WifiDefaultAckManager::DlMuAckSequenceType",
                           EnumValue(WifiAcknowledgment::DL_MU_BAR_BA_SEQUENCE));
    }
    else if (dlAckSeqType == "MU-BAR")
    {
        Config::SetDefault("ns3::WifiDefaultAckManager::DlMuAckSequenceType",
                           EnumValue(WifiAcknowledgment::DL_MU_TF_MU_BAR));
    }
    else if (dlAckSeqType == "AGGR-MU-BAR")
    {
        Config::SetDefault("ns3::WifiDefaultAckManager::DlMuAckSequenceType",
                           EnumValue(WifiAcknowledgment::DL_MU_AGGREGATE_TF));
    }
    else if (dlAckSeqType != "NO-OFDMA")
    {
        NS_ABORT_MSG("Invalid DL ack sequence type (must be NO-OFDMA, ACK-SU-FORMAT, MU-BAR or "
                     "AGGR-MU-BAR)");
    }

    double prevThroughput[15] = {0};

    std::cout << "MCS value"
              << "\t\t"
              << "Channel width"
              << "\t\t"
              << "GI"
              << "\t\t\t"
              << "Throughput" << '\n';
    uint8_t minMcs = 0;
    uint8_t maxMcs = 13;

    if (mcsStr.empty())
    {
        for (uint8_t mcs = minMcs; mcs <= maxMcs; ++mcs)
        {
            mcsValues.push_back(mcs);
        }
    }
    else
    {
        AttributeContainerValue<UintegerValue, ',', std::vector> attr;
        auto checker = DynamicCast<AttributeContainerChecker>(MakeAttributeContainerChecker(attr));
        checker->SetItemChecker(MakeUintegerChecker<uint8_t>());
        attr.DeserializeFromString(mcsStr, checker);
        mcsValues = attr.Get();
        std::sort(mcsValues.begin(), mcsValues.end());
    }

    int minChannelWidth = 20;
    int maxChannelWidth =
        ((frequency != 2.4) && (frequency2 != 2.4) && (frequency3 != 2.4))
            ? (((frequency == 6) && (frequency2 == 0) && (frequency3 == 0)) ? 320 : 160)
            : 40;
    if ((channelWidth != -1) &&
        ((channelWidth < minChannelWidth) || (channelWidth > maxChannelWidth)))
    {
        NS_FATAL_ERROR("Invalid channel width: " << channelWidth << " MHz");
    }
    if (channelWidth >= minChannelWidth && channelWidth <= maxChannelWidth)
    {
        minChannelWidth = channelWidth;
        maxChannelWidth = channelWidth;
    }
    int minGi = enableUlOfdma ? 1600 : 800;
    int maxGi = 3200;
    if (guardInterval >= minGi && guardInterval <= maxGi)
    {
        minGi = guardInterval;
        maxGi = guardInterval;
    }

    for (const auto mcs : mcsValues)
    {
        uint8_t index = 0;
        double previous = 0;
        for (int width = minChannelWidth; width <= maxChannelWidth; width *= 2) // MHz
        {
            const auto is80Plus80 = (use80Plus80 && (width == 160));
            const std::string widthStr = is80Plus80 ? "80+80" : std::to_string(width);
            const auto segmentWidthStr = is80Plus80 ? "80" : widthStr;
            for (int gi = maxGi; gi >= minGi; gi /= 2) // Nanoseconds
            {
                if (!udp)
                {
                    Config::SetDefault("ns3::TcpSocket::SegmentSize", UintegerValue(payloadSize));
                }

                NodeContainer wifiStaNodes;
                wifiStaNodes.Create(nStations);
                NodeContainer wifiApNode;
                wifiApNode.Create(1);

                NetDeviceContainer apDevice;
                NetDeviceContainer staDevices;
                WifiMacHelper mac;
                WifiHelper wifi;

                wifi.SetStandard(WIFI_STANDARD_80211be);
                std::array<std::string, 3> channelStr;
                std::array<FrequencyRange, 3> freqRanges;
                uint8_t nLinks = 0;
                std::string dataModeStr = "EhtMcs" + std::to_string(mcs);
                std::string ctrlRateStr;
                uint64_t nonHtRefRateMbps = EhtPhy::GetNonHtReferenceRate(mcs) / 1e6;

                if (frequency2 == frequency || frequency3 == frequency ||
                    (frequency3 != 0 && frequency3 == frequency2))
                {
                    NS_FATAL_ERROR("Frequency values must be unique!");
                }

                for (auto freq : {frequency, frequency2, frequency3})
                {
                    if (nLinks > 0 && freq == 0)
                    {
                        break;
                    }
                    channelStr[nLinks] = "{0, " + segmentWidthStr + ", ";
                    if (freq == 6)
                    {
                        channelStr[nLinks] += "BAND_6GHZ, 0}";
                        freqRanges[nLinks] = WIFI_SPECTRUM_6_GHZ;
                        Config::SetDefault("ns3::LogDistancePropagationLossModel::ReferenceLoss",
                                           DoubleValue(48));
                        wifi.SetRemoteStationManager(nLinks,
                                                     "ns3::ConstantRateWifiManager",
                                                     "DataMode",
                                                     StringValue(dataModeStr),
                                                     "ControlMode",
                                                     StringValue(dataModeStr));
                    }
                    else if (freq == 5)
                    {
                        channelStr[nLinks] += "BAND_5GHZ, 0}";
                        freqRanges[nLinks] = WIFI_SPECTRUM_5_GHZ;
                        ctrlRateStr = "OfdmRate" + std::to_string(nonHtRefRateMbps) + "Mbps";
                        wifi.SetRemoteStationManager(nLinks,
                                                     "ns3::ConstantRateWifiManager",
                                                     "DataMode",
                                                     StringValue(dataModeStr),
                                                     "ControlMode",
                                                     StringValue(ctrlRateStr));
                    }
                    else if (freq == 2.4)
                    {
                        channelStr[nLinks] += "BAND_2_4GHZ, 0}";
                        freqRanges[nLinks] = WIFI_SPECTRUM_2_4_GHZ;
                        Config::SetDefault("ns3::LogDistancePropagationLossModel::ReferenceLoss",
                                           DoubleValue(40));
                        ctrlRateStr = "ErpOfdmRate" + std::to_string(nonHtRefRateMbps) + "Mbps";
                        wifi.SetRemoteStationManager(nLinks,
                                                     "ns3::ConstantRateWifiManager",
                                                     "DataMode",
                                                     StringValue(dataModeStr),
                                                     "ControlMode",
                                                     StringValue(ctrlRateStr));
                    }
                    else
                    {
                        NS_FATAL_ERROR("Wrong frequency value!");
                    }

                    if (is80Plus80)
                    {
                        channelStr[nLinks] += std::string(";") + channelStr[nLinks];
                    }

                    nLinks++;
                }

                if (nLinks > 1 && !emlsrLinks.empty())
                {
                    wifi.ConfigEhtOptions("EmlsrActivated", BooleanValue(true));
                }

                Ssid ssid = Ssid("ns3-80211be");

                SpectrumWifiPhyHelper phy(nLinks);
                phy.SetPcapDataLinkType(WifiPhyHelper::DLT_IEEE802_11_RADIO);
                phy.Set("ChannelSwitchDelay", TimeValue(channelSwitchDelay));

                mac.SetType("ns3::StaWifiMac", "Ssid", SsidValue(ssid));
                mac.SetEmlsrManager(emlsrMgrTypeId,
                                    "EmlsrLinkSet",
                                    StringValue(emlsrLinks),
                                    "EmlsrPaddingDelay",
                                    TimeValue(MicroSeconds(paddingDelayUsec)),
                                    "EmlsrTransitionDelay",
                                    TimeValue(MicroSeconds(transitionDelayUsec)),
                                    "SwitchAuxPhy",
                                    BooleanValue(switchAuxPhy),
                                    "AuxPhyTxCapable",
                                    BooleanValue(auxPhyTxCapable),
                                    "AuxPhyChannelWidth",
                                    UintegerValue(auxPhyChWidth));
                for (uint8_t linkId = 0; linkId < nLinks; linkId++)
                {
                    phy.Set(linkId, "ChannelSettings", StringValue(channelStr[linkId]));

                    auto spectrumChannel = CreateObject<MultiModelSpectrumChannel>();
                    auto lossModel = CreateObject<LogDistancePropagationLossModel>();
                    spectrumChannel->AddPropagationLossModel(lossModel);
                    phy.AddChannel(spectrumChannel, freqRanges[linkId]);
                }
                staDevices = wifi.Install(phy, mac, wifiStaNodes);

                if (dlAckSeqType != "NO-OFDMA")
                {
                    mac.SetMultiUserScheduler("ns3::RrMultiUserScheduler",
                                              "EnableUlOfdma",
                                              BooleanValue(enableUlOfdma),
                                              "EnableBsrp",
                                              BooleanValue(enableBsrp),
                                              "AccessReqInterval",
                                              TimeValue(accessReqInterval));
                }
                mac.SetType("ns3::ApWifiMac",
                            "EnableBeaconJitter",
                            BooleanValue(false),
                            "BeaconGeneration",
                            BooleanValue(!staticSetup),
                            "Ssid",
                            SsidValue(ssid));
                apDevice = wifi.Install(phy, mac, wifiApNode);

                int64_t streamNumber = 100;
                streamNumber += WifiHelper::AssignStreams(apDevice, streamNumber);
                streamNumber += WifiHelper::AssignStreams(staDevices, streamNumber);

                // Set guard interval and MPDU buffer size
                Config::Set(
                    "/NodeList/*/DeviceList/*/$ns3::WifiNetDevice/HeConfiguration/GuardInterval",
                    TimeValue(NanoSeconds(gi)));
                Config::Set("/NodeList/*/DeviceList/*/$ns3::WifiNetDevice/Mac/MpduBufferSize",
                            UintegerValue(mpduBufferSize));

                // mobility.
                MobilityHelper mobility;
                Ptr<ListPositionAllocator> positionAlloc = CreateObject<ListPositionAllocator>();

                positionAlloc->Add(Vector(0.0, 0.0, 0.0));
                positionAlloc->Add(Vector(distance, 0.0, 0.0));
                mobility.SetPositionAllocator(positionAlloc);

                mobility.SetMobilityModel("ns3::ConstantPositionMobilityModel");

                mobility.Install(wifiApNode);
                mobility.Install(wifiStaNodes);

                if (staticSetup)
                {
                    /* static setup of association and BA agreements */
                    auto apDev = DynamicCast<WifiNetDevice>(apDevice.Get(0));
                    NS_ASSERT(apDev);
                    WifiStaticSetupHelper::SetStaticAssociation(apDev, staDevices);
                    WifiStaticSetupHelper::SetStaticEmlsr(apDev, staDevices);
                    WifiStaticSetupHelper::SetStaticBlockAck(apDev, staDevices, {0});
                    clientAppStartTime = MilliSeconds(1);
                }

                /* Internet stack*/
                InternetStackHelper stack;
                stack.Install(wifiApNode);
                stack.Install(wifiStaNodes);
                streamNumber += stack.AssignStreams(wifiApNode, streamNumber);
                streamNumber += stack.AssignStreams(wifiStaNodes, streamNumber);

                Ipv4AddressHelper address;
                address.SetBase("192.168.1.0", "255.255.255.0");
                Ipv4InterfaceContainer staNodeInterfaces;
                Ipv4InterfaceContainer apNodeInterface;

                staNodeInterfaces = address.Assign(staDevices);
                apNodeInterface = address.Assign(apDevice);

                if (staticSetup)
                {
                    /* static setup of ARP cache */
                    NeighborCacheHelper nbCache;
                    nbCache.PopulateNeighborCache();
                }

                /* Setting applications */
                ApplicationContainer serverApp;
                auto serverNodes = downlink ? std::ref(wifiStaNodes) : std::ref(wifiApNode);
                Ipv4InterfaceContainer serverInterfaces;
                NodeContainer clientNodes;
                for (std::size_t i = 0; i < nStations; i++)
                {
                    serverInterfaces.Add(downlink ? staNodeInterfaces.Get(i)
                                                  : apNodeInterface.Get(0));
                    clientNodes.Add(downlink ? wifiApNode.Get(0) : wifiStaNodes.Get(i));
                }

                const auto maxLoad = nLinks *
                                     EhtPhy::GetDataRate(mcs,
                                                         MHz_u{static_cast<double>(width)},
                                                         NanoSeconds(gi),
                                                         1) /
                                     nStations;
                if (udp)
                {
                    // UDP flow
                    uint16_t port = 9;
                    UdpServerHelper server(port);
                    serverApp = server.Install(serverNodes.get());
                    streamNumber += server.AssignStreams(serverNodes.get(), streamNumber);

                    serverApp.Start(Seconds(0));
                    serverApp.Stop(simulationTime + clientAppStartTime);
                    const auto packetInterval = payloadSize * 8.0 / maxLoad;

                    for (std::size_t i = 0; i < nStations; i++)
                    {
                        UdpClientHelper client(serverInterfaces.GetAddress(i), port);
                        client.SetAttribute("MaxPackets", UintegerValue(4294967295U));
                        client.SetAttribute("Interval", TimeValue(Seconds(packetInterval)));
                        client.SetAttribute("PacketSize", UintegerValue(payloadSize));
                        ApplicationContainer clientApp = client.Install(clientNodes.Get(i));
                        streamNumber += client.AssignStreams(clientNodes.Get(i), streamNumber);

                        clientApp.Start(clientAppStartTime);
                        clientApp.Stop(simulationTime + clientAppStartTime);
                    }
                }
                else
                {
                    // TCP flow
                    uint16_t port = 50000;
                    Address localAddress(InetSocketAddress(Ipv4Address::GetAny(), port));
                    PacketSinkHelper packetSinkHelper("ns3::TcpSocketFactory", localAddress);
                    serverApp = packetSinkHelper.Install(serverNodes.get());
                    streamNumber += packetSinkHelper.AssignStreams(serverNodes.get(), streamNumber);

                    serverApp.Start(Seconds(0));
                    serverApp.Stop(simulationTime + clientAppStartTime);

                    for (std::size_t i = 0; i < nStations; i++)
                    {
                        OnOffHelper onoff("ns3::TcpSocketFactory", Ipv4Address::GetAny());
                        onoff.SetAttribute("OnTime",
                                           StringValue("ns3::ConstantRandomVariable[Constant=1]"));
                        onoff.SetAttribute("OffTime",
                                           StringValue("ns3::ConstantRandomVariable[Constant=0]"));
                        onoff.SetAttribute("PacketSize", UintegerValue(payloadSize));
                        onoff.SetAttribute("DataRate", DataRateValue(maxLoad));
                        AddressValue remoteAddress(
                            InetSocketAddress(serverInterfaces.GetAddress(i), port));
                        onoff.SetAttribute("Remote", remoteAddress);
                        ApplicationContainer clientApp = onoff.Install(clientNodes.Get(i));
                        streamNumber += onoff.AssignStreams(clientNodes.Get(i), streamNumber);

                        clientApp.Start(clientAppStartTime);
                        clientApp.Stop(simulationTime + clientAppStartTime);
                    }
                }

                // cumulative number of bytes received by each server application
                std::vector<uint64_t> cumulRxBytes(nStations, 0);

                if (tputInterval.IsStrictlyPositive())
                {
                    Simulator::Schedule(clientAppStartTime + tputInterval,
                                        &PrintIntermediateTput,
                                        cumulRxBytes,
                                        udp,
                                        serverApp,
                                        payloadSize,
                                        tputInterval,
                                        simulationTime + clientAppStartTime);
                }

                Simulator::Stop(simulationTime + clientAppStartTime);
                Simulator::Run();

                // When multiple stations are used, there are chances that association requests
                // collide and hence the throughput may be lower than expected. Therefore, we relax
                // the check that the throughput cannot decrease by introducing a scaling factor (or
                // tolerance)
                auto tolerance = 0.10;
                cumulRxBytes = GetRxBytes(udp, serverApp, payloadSize);
                auto rxBytes = std::accumulate(cumulRxBytes.cbegin(), cumulRxBytes.cend(), 0.0);
                auto throughput = (rxBytes * 8) / simulationTime.GetMicroSeconds(); // Mbit/s

                Simulator::Destroy();

                std::cout << +mcs << "\t\t\t" << widthStr << " MHz\t\t"
                          << (widthStr.size() > 3 ? "" : "\t") << gi << " ns\t\t\t" << throughput
                          << " Mbit/s" << std::endl;

                // test first element
                if (mcs == minMcs && width == 20 && gi == 3200)
                {
                    if (throughput * (1 + tolerance) < minExpectedThroughput)
                    {
                        NS_LOG_ERROR("Obtained throughput " << throughput << " is not expected!");
                        exit(1);
                    }
                }
                // test last element
                if (mcs == maxMcs && width == maxChannelWidth && gi == 800)
                {
                    if (maxExpectedThroughput > 0 &&
                        throughput > maxExpectedThroughput * (1 + tolerance))
                    {
                        NS_LOG_ERROR("Obtained throughput " << throughput << " is not expected!");
                        exit(1);
                    }
                }
                // test previous throughput is smaller (for the same mcs)
                if (throughput * (1 + tolerance) > previous)
                {
                    previous = throughput;
                }
                else if (throughput > 0)
                {
                    NS_LOG_ERROR("Obtained throughput " << throughput << " is not expected!");
                    exit(1);
                }
                // test previous throughput is smaller (for the same channel width and GI)
                if (throughput * (1 + tolerance) > prevThroughput[index])
                {
                    prevThroughput[index] = throughput;
                }
                else if (throughput > 0)
                {
                    NS_LOG_ERROR("Obtained throughput " << throughput << " is not expected!");
                    exit(1);
                }
                index++;
            }
        }
    }
    return 0;
}