three-gpp-ntn-channel-example.cc

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/*
 * Copyright (c) 2023 SIGNET Lab, Department of Information Engineering,
 * University of Padova
 *
 * SPDX-License-Identifier: GPL-2.0-only
 */
 
/**
 * @file
 * This example is a modified version of "three-gpp-channel-example", to include
 * the 3GPP NTN channel model.
 * Specifically, most changes (which are also highlighted throughout the code)
 * impact the main method, and comprise:
 * - the configuration of ad-hoc propagation and channel condition models;
 * - the use of GeocentricConstantPositionMobilityModel for the nodes' mobility.
 * The pre-configured parameters are the one provided by 3GPP in TR 38.821,
 * more specifically scenario 10 in down-link mode.
 * Two static nodes, one on the ground and one in orbit, communicate with each other.
 * The carrier frequency is set at 20GHz with 400MHz bandwidth.
 * The result is the SNR of the signal and the path loss, saved in the ntn-snr-trace.txt file.
 */
 
#include "ns3/antenna-model.h"
#include "ns3/core-module.h"
#include "ns3/geocentric-constant-position-mobility-model.h"
#include "ns3/isotropic-antenna-model.h"
#include "ns3/mobility-model.h"
#include "ns3/node-container.h"
#include "ns3/node.h"
#include "ns3/spectrum-signal-parameters.h"
#include "ns3/three-gpp-channel-model.h"
#include "ns3/three-gpp-propagation-loss-model.h"
#include "ns3/three-gpp-spectrum-propagation-loss-model.h"
#include "ns3/uniform-planar-array.h"
 
#include <fstream>
 
NS_LOG_COMPONENT_DEFINE("NTNChannelExample");
 
using namespace ns3;
 
static Ptr<ThreeGppPropagationLossModel>
    m_propagationLossModel; //!< the PropagationLossModel object
static Ptr<ThreeGppSpectrumPropagationLossModel>
    m_spectrumLossModel;          //!< the SpectrumPropagationLossModel object
static std::ofstream resultsFile; //!< The results file
 
/**
 * @brief Create the PSD for the TX
 *
 * @param fcHz the carrier frequency in Hz
 * @param pwrDbm the transmission power in dBm
 * @param bwHz the bandwidth in Hz
 * @param rbWidthHz the Resource Block (RB) width in Hz
 *
 * @return the pointer to the PSD
 */
Ptr<SpectrumValue>
CreateTxPowerSpectralDensity(double fcHz, double pwrDbm, double bwHz, double rbWidthHz)
{
    unsigned int numRbs = std::floor(bwHz / rbWidthHz);
    double f = fcHz - (numRbs * rbWidthHz / 2.0);
    double powerTx = pwrDbm; // dBm power
 
    Bands rbs; // A vector representing each resource block
    for (uint32_t numrb = 0; numrb < numRbs; ++numrb)
    {
        BandInfo rb;
        rb.fl = f;
        f += rbWidthHz / 2;
        rb.fc = f;
        f += rbWidthHz / 2;
        rb.fh = f;
 
        rbs.push_back(rb);
    }
    Ptr<SpectrumModel> model = Create<SpectrumModel>(rbs);
    Ptr<SpectrumValue> txPsd = Create<SpectrumValue>(model);
 
    double powerTxW = std::pow(10., (powerTx - 30) / 10); // Get Tx power in Watts
    double txPowerDensity = (powerTxW / bwHz);
 
    for (auto psd = txPsd->ValuesBegin(); psd != txPsd->ValuesEnd(); ++psd)
    {
        *psd = txPowerDensity;
    }
 
    return txPsd; // [W/Hz]
}
 
/**
 * @brief Create the noise PSD for the
 *
 * @param fcHz the carrier frequency in Hz
 * @param noiseFigureDb the noise figure in dB
 * @param bwHz the bandwidth in Hz
 * @param rbWidthHz the Resource Block (RB) width in Hz
 *
 * @return the pointer to the noise PSD
 */
Ptr<SpectrumValue>
CreateNoisePowerSpectralDensity(double fcHz, double noiseFigureDb, double bwHz, double rbWidthHz)
{
    unsigned int numRbs = std::floor(bwHz / rbWidthHz);
    double f = fcHz - (numRbs * rbWidthHz / 2.0);
 
    Bands rbs;              // A vector representing each resource block
    std::vector<int> rbsId; // A vector representing the resource block IDs
    for (uint32_t numrb = 0; numrb < numRbs; ++numrb)
    {
        BandInfo rb;
        rb.fl = f;
        f += rbWidthHz / 2;
        rb.fc = f;
        f += rbWidthHz / 2;
        rb.fh = f;
 
        rbs.push_back(rb);
        rbsId.push_back(numrb);
    }
    Ptr<SpectrumModel> model = Create<SpectrumModel>(rbs);
    Ptr<SpectrumValue> txPsd = Create<SpectrumValue>(model);
 
    // see "LTE - From theory to practice"
    // Section 22.4.4.2 Thermal Noise and Receiver Noise Figure
    const double ktDbmHz = -174.0;                        // dBm/Hz
    double ktWHz = std::pow(10.0, (ktDbmHz - 30) / 10.0); // W/Hz
    double noiseFigureLinear = std::pow(10.0, noiseFigureDb / 10.0);
 
    double noisePowerSpectralDensity = ktWHz * noiseFigureLinear;
 
    for (auto rbId : rbsId)
    {
        (*txPsd)[rbId] = noisePowerSpectralDensity;
    }
 
    return txPsd; // W/Hz
}
 
/**
 * @brief A structure that holds the parameters for the
 * ComputeSnr function. In this way the problem with the limited
 * number of parameters of method Schedule is avoided.
 */
struct ComputeSnrParams
{
    Ptr<MobilityModel> txMob;        //!< the tx mobility model
    Ptr<MobilityModel> rxMob;        //!< the rx mobility model
    double txPow;                    //!< the tx power in dBm
    double noiseFigure;              //!< the noise figure in dB
    Ptr<PhasedArrayModel> txAntenna; //!< the tx antenna array
    Ptr<PhasedArrayModel> rxAntenna; //!< the rx antenna array
    double frequency;                //!< the carrier frequency in Hz
    double bandwidth;                //!< the total bandwidth in Hz
    double resourceBlockBandwidth;   //!< the Resource Block bandwidth in Hz
 
    /**
     * @brief Constructor
     * @param pTxMob the tx mobility model
     * @param pRxMob the rx mobility model
     * @param pTxPow the tx power in dBm
     * @param pNoiseFigure the noise figure in dB
     * @param pTxAntenna the tx antenna array
     * @param pRxAntenna the rx antenna array
     * @param pFrequency the carrier frequency in Hz
     * @param pBandwidth the total bandwidth in Hz
     * @param pResourceBlockBandwidth the Resource Block bandwidth in Hz
     */
    ComputeSnrParams(Ptr<MobilityModel> pTxMob,
                     Ptr<MobilityModel> pRxMob,
                     double pTxPow,
                     double pNoiseFigure,
                     Ptr<PhasedArrayModel> pTxAntenna,
                     Ptr<PhasedArrayModel> pRxAntenna,
                     double pFrequency,
                     double pBandwidth,
                     double pResourceBlockBandwidth)
    {
        txMob = pTxMob;
        rxMob = pRxMob;
        txPow = pTxPow;
        noiseFigure = pNoiseFigure;
        txAntenna = pTxAntenna;
        rxAntenna = pRxAntenna;
        frequency = pFrequency;
        bandwidth = pBandwidth;
        resourceBlockBandwidth = pResourceBlockBandwidth;
    }
};
 
/**
 * Perform the beamforming using the DFT beamforming method
 * @param txMob the mobility model of the node performing the beamforming
 * @param thisAntenna the antenna object associated to txMob
 * @param rxMob the mobility model of the node towards which will point the beam
 */
static void
DoBeamforming(Ptr<MobilityModel> rxMob, Ptr<PhasedArrayModel> thisAntenna, Ptr<MobilityModel> txMob)
{
    // compute the azimuth and the elevation angles
    Angles completeAngle(txMob->GetPosition(), rxMob->GetPosition());
    double hAngleRadian = completeAngle.GetAzimuth();
    double vAngleRadian = completeAngle.GetInclination(); // the elevation angle
 
    // retrieve the number of antenna elements and resize the vector
    uint64_t totNoArrayElements = thisAntenna->GetNumElems();
    PhasedArrayModel::ComplexVector antennaWeights(totNoArrayElements);
 
    // the total power is divided equally among the antenna elements
    double power = 1.0 / sqrt(totNoArrayElements);
 
    // compute the antenna weights
    const double sinVAngleRadian = sin(vAngleRadian);
    const double cosVAngleRadian = cos(vAngleRadian);
    const double sinHAngleRadian = sin(hAngleRadian);
    const double cosHAngleRadian = cos(hAngleRadian);
 
    for (uint64_t ind = 0; ind < totNoArrayElements; ind++)
    {
        Vector loc = thisAntenna->GetElementLocation(ind);
        double phase = -2 * M_PI *
                       (sinVAngleRadian * cosHAngleRadian * loc.x +
                        sinVAngleRadian * sinHAngleRadian * loc.y + cosVAngleRadian * loc.z);
        antennaWeights[ind] = exp(std::complex<double>(0, phase)) * power;
    }
 
    // store the antenna weights
    thisAntenna->SetBeamformingVector(antennaWeights);
}
 
/**
 * Compute the average SNR
 * @param params A structure that holds the parameters that are needed to perform calculations in
 * ComputeSnr
 */
static void
ComputeSnr(ComputeSnrParams& params)
{
    Ptr<SpectrumValue> txPsd = CreateTxPowerSpectralDensity(params.frequency,
                                                            params.txPow,
                                                            params.bandwidth,
                                                            params.resourceBlockBandwidth);
    Ptr<SpectrumValue> rxPsd = txPsd->Copy();
    NS_LOG_DEBUG("Average tx power " << 10 * log10(Sum(*txPsd) * params.resourceBlockBandwidth)
                                     << " dB");
 
    // create the noise PSD
    Ptr<SpectrumValue> noisePsd = CreateNoisePowerSpectralDensity(params.frequency,
                                                                  params.noiseFigure,
                                                                  params.bandwidth,
                                                                  params.resourceBlockBandwidth);
    NS_LOG_DEBUG("Average noise power "
                 << 10 * log10(Sum(*noisePsd) * params.resourceBlockBandwidth) << " dB");
 
    // apply the pathloss
    double propagationGainDb = m_propagationLossModel->CalcRxPower(0, params.txMob, params.rxMob);
    NS_LOG_DEBUG("Pathloss " << -propagationGainDb << " dB");
    double propagationGainLinear = std::pow(10.0, (propagationGainDb) / 10.0);
    *(rxPsd) *= propagationGainLinear;
 
    NS_ASSERT_MSG(params.txAntenna, "params.txAntenna is nullptr!");
    NS_ASSERT_MSG(params.rxAntenna, "params.rxAntenna is nullptr!");
 
    Ptr<SpectrumSignalParameters> rxSsp = Create<SpectrumSignalParameters>();
    rxSsp->psd = rxPsd;
    rxSsp->txAntenna =
        ConstCast<AntennaModel, const AntennaModel>(params.txAntenna->GetAntennaElement());
 
    // apply the fast fading and the beamforming gain
    rxSsp = m_spectrumLossModel->CalcRxPowerSpectralDensity(rxSsp,
                                                            params.txMob,
                                                            params.rxMob,
                                                            params.txAntenna,
                                                            params.rxAntenna);
    NS_LOG_DEBUG("Average rx power " << 10 * log10(Sum(*rxSsp->psd) * params.bandwidth) << " dB");
 
    // compute the SNR
    NS_LOG_DEBUG("Average SNR " << 10 * log10(Sum(*rxSsp->psd) / Sum(*noisePsd)) << " dB");
 
    // print the SNR and pathloss values in the output file
    resultsFile << Simulator::Now().GetSeconds() << " "
                << 10 * log10(Sum(*rxSsp->psd) / Sum(*noisePsd)) << " " << propagationGainDb
                << std::endl;
}
 
int
main(int argc, char* argv[])
{
    uint32_t simTimeMs = 1000; // simulation time in milliseconds
    uint32_t timeResMs = 10;   // time resolution in milliseconds
 
    // Start changes with respect to three-gpp-channel-example
    // SCENARIO 10 DL of TR 38.321
    // This parameters can be set accordingly to 3GPP TR 38.821 or arbitrarily modified
    std::string scenario = "NTN-Suburban"; // 3GPP propagation scenario
    // All available NTN scenarios: DenseUrban, Urban, Suburban, Rural.
 
    double frequencyHz = 20e9;    // operating frequency in Hz
    double bandwidthHz = 400e6;   // Hz
    double RbBandwidthHz = 120e3; // Hz
 
    // Satellite parameters
    double satEIRPDensity = 40;     // dBW/MHz
    double satAntennaGainDb = 58.5; // dB
 
    // UE Parameters
    double vsatAntennaGainDb = 39.7;       // dB
    double vsatAntennaNoiseFigureDb = 1.2; // dB
    // End changes with respect to three-gpp-channel-example
 
    /* Command line argument parser setup. */
    CommandLine cmd(__FILE__);
    cmd.AddValue("scenario",
                 "The 3GPP NTN scenario to use. Valid options are: "
                 "NTN-DenseUrban, NTN-Urban, NTN-Suburban, and NTN-Rural",
                 scenario);
    cmd.AddValue("frequencyHz", "The carrier frequency in Hz", frequencyHz);
    cmd.AddValue("bandwidthHz", "The bandwidth in Hz", bandwidthHz);
    cmd.AddValue("satEIRPDensity", "The satellite EIRP density in dBW/MHz", satEIRPDensity);
    cmd.AddValue("satAntennaGainDb", "The satellite antenna gain in dB", satAntennaGainDb);
    cmd.AddValue("vsatAntennaGainDb", "The UE VSAT antenna gain in dB", vsatAntennaGainDb);
    cmd.AddValue("vsatAntennaNoiseFigureDb",
                 "The UE VSAT antenna noise figure in dB",
                 vsatAntennaNoiseFigureDb);
    cmd.Parse(argc, argv);
 
    // Calculate transmission power in dBm using EIRPDensity + 10*log10(Bandwidth) - AntennaGain +
    // 30
    double txPowDbm = (satEIRPDensity + 10 * log10(bandwidthHz / 1e6) - satAntennaGainDb) + 30;
 
    NS_LOG_DEBUG("Transmitting power: " << txPowDbm << "dBm, (" << pow(10., (txPowDbm - 30) / 10)
                                        << "W)");
 
    Config::SetDefault("ns3::ThreeGppChannelModel::UpdatePeriod",
                       TimeValue(MilliSeconds(10))); // update the channel at every 10 ms
    Config::SetDefault("ns3::ThreeGppChannelConditionModel::UpdatePeriod",
                       TimeValue(MilliSeconds(0))); // do not update the channel condition
 
    RngSeedManager::SetSeed(1);
    RngSeedManager::SetRun(1);
 
    // create and configure the factories for the channel condition and propagation loss models
    ObjectFactory propagationLossModelFactory;
    ObjectFactory channelConditionModelFactory;
 
    // Start changes with respect to three-gpp-channel-example
    if (scenario == "NTN-DenseUrban")
    {
        propagationLossModelFactory.SetTypeId(
            ThreeGppNTNDenseUrbanPropagationLossModel::GetTypeId());
        channelConditionModelFactory.SetTypeId(
            ThreeGppNTNDenseUrbanChannelConditionModel::GetTypeId());
    }
    else if (scenario == "NTN-Urban")
    {
        propagationLossModelFactory.SetTypeId(ThreeGppNTNUrbanPropagationLossModel::GetTypeId());
        channelConditionModelFactory.SetTypeId(ThreeGppNTNUrbanChannelConditionModel::GetTypeId());
    }
    else if (scenario == "NTN-Suburban")
    {
        propagationLossModelFactory.SetTypeId(ThreeGppNTNSuburbanPropagationLossModel::GetTypeId());
        channelConditionModelFactory.SetTypeId(
            ThreeGppNTNSuburbanChannelConditionModel::GetTypeId());
    }
    else if (scenario == "NTN-Rural")
    {
        propagationLossModelFactory.SetTypeId(ThreeGppNTNRuralPropagationLossModel::GetTypeId());
        channelConditionModelFactory.SetTypeId(ThreeGppNTNRuralChannelConditionModel::GetTypeId());
    }
    else
    {
        NS_FATAL_ERROR("Unknown NTN scenario");
    }
    // End changes with respect to three-gpp-channel-example
 
    // create the propagation loss model
    m_propagationLossModel = propagationLossModelFactory.Create<ThreeGppPropagationLossModel>();
    m_propagationLossModel->SetAttribute("Frequency", DoubleValue(frequencyHz));
    m_propagationLossModel->SetAttribute("ShadowingEnabled", BooleanValue(true));
 
    // create the spectrum propagation loss model
    m_spectrumLossModel = CreateObject<ThreeGppSpectrumPropagationLossModel>();
    m_spectrumLossModel->SetChannelModelAttribute("Frequency", DoubleValue(frequencyHz));
    m_spectrumLossModel->SetChannelModelAttribute("Scenario", StringValue(scenario));
 
    // create the channel condition model and associate it with the spectrum and
    // propagation loss model
    Ptr<ChannelConditionModel> condModel =
        channelConditionModelFactory.Create<ThreeGppChannelConditionModel>();
    m_spectrumLossModel->SetChannelModelAttribute("ChannelConditionModel", PointerValue(condModel));
    m_propagationLossModel->SetChannelConditionModel(condModel);
 
    // create the tx and rx nodes
    NodeContainer nodes;
    nodes.Create(2);
 
    // Start changes with respect to three-gpp-channel-example, here a mobility model
    // tailored to NTN scenarios is used (GeocentricConstantPositionMobilityModel)
    // create the tx and rx mobility models, set the positions
    Ptr<GeocentricConstantPositionMobilityModel> txMob =
        CreateObject<GeocentricConstantPositionMobilityModel>();
    Ptr<GeocentricConstantPositionMobilityModel> rxMob =
        CreateObject<GeocentricConstantPositionMobilityModel>();
 
    txMob->SetGeographicPosition(Vector(45.40869, 11.89448, 35786000)); // GEO over Padova
    rxMob->SetGeographicPosition(Vector(45.40869, 11.89448, 14.0));     // Padova Coordinates
 
    // This is not strictly necessary, but is useful to have "sensible" values when using
    // GetPosition()
    txMob->SetCoordinateTranslationReferencePoint(
        Vector(45.40869, 11.89448, 0.0)); // Padova Coordinates without altitude
    rxMob->SetCoordinateTranslationReferencePoint(
        Vector(45.40869, 11.89448, 0.0)); // Padova Coordinates without altitude
    // End changes with respect to three-gpp-channel-example,
 
    NS_LOG_DEBUG("TX Position: " << txMob->GetPosition());
    NS_LOG_DEBUG("RX Position: " << rxMob->GetPosition());
 
    // assign the mobility models to the nodes
    nodes.Get(0)->AggregateObject(txMob);
    nodes.Get(1)->AggregateObject(rxMob);
 
    // Start changes with respect to three-gpp-channel-example,
    // Here antenna models mimic the gain achieved by the CircularApertureAntennaModel,
    // which is not used to avoid inheriting the latter's dependence on either libstdc++
    // or Boost.
    Ptr<PhasedArrayModel> txAntenna = CreateObjectWithAttributes<UniformPlanarArray>(
        "NumColumns",
        UintegerValue(1),
        "NumRows",
        UintegerValue(1),
        "AntennaElement",
        PointerValue(
            CreateObjectWithAttributes<IsotropicAntennaModel>("Gain",
                                                              DoubleValue(satAntennaGainDb))));
 
    Ptr<PhasedArrayModel> rxAntenna = CreateObjectWithAttributes<UniformPlanarArray>(
        "NumColumns",
        UintegerValue(1),
        "NumRows",
        UintegerValue(1),
        "AntennaElement",
        PointerValue(
            CreateObjectWithAttributes<IsotropicAntennaModel>("Gain",
                                                              DoubleValue(vsatAntennaGainDb))));
    // End changes with respect to three-gpp-channel-example
 
    // set the beamforming vectors
    DoBeamforming(rxMob, rxAntenna, txMob);
    DoBeamforming(txMob, txAntenna, rxMob);
 
    // Open the output results file
    resultsFile.open("ntn-snr-trace.txt", std::ios::out);
    NS_ASSERT_MSG(resultsFile.is_open(), "Results file could not be created");
 
    for (int i = 0; i < floor(simTimeMs / timeResMs); i++)
    {
        Simulator::Schedule(MilliSeconds(timeResMs * i),
                            &ComputeSnr,
                            ComputeSnrParams(txMob,
                                             rxMob,
                                             txPowDbm,
                                             vsatAntennaNoiseFigureDb,
                                             txAntenna,
                                             rxAntenna,
                                             frequencyHz,
                                             bandwidthHz,
                                             RbBandwidthHz));
    }
 
    Simulator::Run();
    Simulator::Destroy();
 
    resultsFile.close();
 
    return 0;
}