a2-a4-rsrq-handover-algorithm.cc

Go to the documentation of this file.

/*
 * Copyright (c) 2011 Centre Tecnologic de Telecomunicacions de Catalunya (CTTC)
 * Copyright (c) 2013 Budiarto Herman
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Original work authors (from lte-enb-rrc.cc):
 *   Nicola Baldo <nbaldo@cttc.es>
 *   Marco Miozzo <mmiozzo@cttc.es>
 *   Manuel Requena <manuel.requena@cttc.es>
 *
 * Converted to handover algorithm interface by:
 *   Budiarto Herman <budiarto.herman@magister.fi>
 */
 
#include "a2-a4-rsrq-handover-algorithm.h"
 
#include "ns3/log.h"
#include "ns3/uinteger.h"
 
#include <algorithm>
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("A2A4RsrqHandoverAlgorithm");
 
NS_OBJECT_ENSURE_REGISTERED(A2A4RsrqHandoverAlgorithm);
 
///////////////////////////////////////////
// Handover Management SAP forwarder
///////////////////////////////////////////
 
A2A4RsrqHandoverAlgorithm::A2A4RsrqHandoverAlgorithm()
    : m_servingCellThreshold(30),
      m_neighbourCellOffset(1),
      m_handoverManagementSapUser(nullptr)
{
    NS_LOG_FUNCTION(this);
    m_handoverManagementSapProvider =
        new MemberLteHandoverManagementSapProvider<A2A4RsrqHandoverAlgorithm>(this);
}
 
A2A4RsrqHandoverAlgorithm::~A2A4RsrqHandoverAlgorithm()
{
    NS_LOG_FUNCTION(this);
}
 
TypeId
A2A4RsrqHandoverAlgorithm::GetTypeId()
{
    static TypeId tid =
        TypeId("ns3::A2A4RsrqHandoverAlgorithm")
            .SetParent<LteHandoverAlgorithm>()
            .SetGroupName("Lte")
            .AddConstructor<A2A4RsrqHandoverAlgorithm>()
            .AddAttribute("ServingCellThreshold",
                          "If the RSRQ of the serving cell is worse than this "
                          "threshold, neighbour cells are consider for handover. "
                          "Expressed in quantized range of [0..34] as per Section "
                          "9.1.7 of 3GPP TS 36.133.",
                          UintegerValue(30),
                          MakeUintegerAccessor(&A2A4RsrqHandoverAlgorithm::m_servingCellThreshold),
                          MakeUintegerChecker<uint8_t>(0, 34))
            .AddAttribute("NeighbourCellOffset",
                          "Minimum offset between the serving and the best neighbour "
                          "cell to trigger the handover. Expressed in quantized "
                          "range of [0..34] as per Section 9.1.7 of 3GPP TS 36.133.",
                          UintegerValue(1),
                          MakeUintegerAccessor(&A2A4RsrqHandoverAlgorithm::m_neighbourCellOffset),
                          MakeUintegerChecker<uint8_t>());
    return tid;
}
 
void
A2A4RsrqHandoverAlgorithm::SetLteHandoverManagementSapUser(LteHandoverManagementSapUser* s)
{
    NS_LOG_FUNCTION(this << s);
    m_handoverManagementSapUser = s;
}
 
LteHandoverManagementSapProvider*
A2A4RsrqHandoverAlgorithm::GetLteHandoverManagementSapProvider()
{
    NS_LOG_FUNCTION(this);
    return m_handoverManagementSapProvider;
}
 
void
A2A4RsrqHandoverAlgorithm::DoInitialize()
{
    NS_LOG_FUNCTION(this);
 
    NS_LOG_LOGIC(this << " requesting Event A2 measurements"
                      << " (threshold=" << (uint16_t)m_servingCellThreshold << ")");
    LteRrcSap::ReportConfigEutra reportConfigA2;
    reportConfigA2.eventId = LteRrcSap::ReportConfigEutra::EVENT_A2;
    reportConfigA2.threshold1.choice = LteRrcSap::ThresholdEutra::THRESHOLD_RSRQ;
    reportConfigA2.threshold1.range = m_servingCellThreshold;
    reportConfigA2.triggerQuantity = LteRrcSap::ReportConfigEutra::RSRQ;
    reportConfigA2.reportInterval = LteRrcSap::ReportConfigEutra::MS240;
    m_a2MeasIds = m_handoverManagementSapUser->AddUeMeasReportConfigForHandover(reportConfigA2);
 
    NS_LOG_LOGIC(this << " requesting Event A4 measurements"
                      << " (threshold=0)");
    LteRrcSap::ReportConfigEutra reportConfigA4;
    reportConfigA4.eventId = LteRrcSap::ReportConfigEutra::EVENT_A4;
    reportConfigA4.threshold1.choice = LteRrcSap::ThresholdEutra::THRESHOLD_RSRQ;
    reportConfigA4.threshold1.range = 0; // intentionally very low threshold
    reportConfigA4.triggerQuantity = LteRrcSap::ReportConfigEutra::RSRQ;
    reportConfigA4.reportInterval = LteRrcSap::ReportConfigEutra::MS480;
    m_a4MeasIds = m_handoverManagementSapUser->AddUeMeasReportConfigForHandover(reportConfigA4);
 
    LteHandoverAlgorithm::DoInitialize();
}
 
void
A2A4RsrqHandoverAlgorithm::DoDispose()
{
    NS_LOG_FUNCTION(this);
    delete m_handoverManagementSapProvider;
}
 
void
A2A4RsrqHandoverAlgorithm::DoReportUeMeas(uint16_t rnti, LteRrcSap::MeasResults measResults)
{
    NS_LOG_FUNCTION(this << rnti << (uint16_t)measResults.measId);
 
    if (std::find(begin(m_a2MeasIds), end(m_a2MeasIds), measResults.measId) !=
        std::end(m_a2MeasIds))
    {
        NS_ASSERT_MSG(measResults.measResultPCell.rsrqResult <= m_servingCellThreshold,
                      "Invalid UE measurement report");
        EvaluateHandover(rnti, measResults.measResultPCell.rsrqResult);
    }
    else if (std::find(begin(m_a4MeasIds), end(m_a4MeasIds), measResults.measId) !=
             std::end(m_a4MeasIds))
    {
        if (measResults.haveMeasResultNeighCells && !measResults.measResultListEutra.empty())
        {
            for (auto it = measResults.measResultListEutra.begin();
                 it != measResults.measResultListEutra.end();
                 ++it)
            {
                NS_ASSERT_MSG(it->haveRsrqResult == true,
                              "RSRQ measurement is missing from cellId " << it->physCellId);
                UpdateNeighbourMeasurements(rnti, it->physCellId, it->rsrqResult);
            }
        }
        else
        {
            NS_LOG_WARN(
                this << " Event A4 received without measurement results from neighbouring cells");
        }
    }
    else
    {
        NS_LOG_WARN("Ignoring measId " << (uint16_t)measResults.measId);
    }
}
 
void
A2A4RsrqHandoverAlgorithm::EvaluateHandover(uint16_t rnti, uint8_t servingCellRsrq)
{
    NS_LOG_FUNCTION(this << rnti << (uint16_t)servingCellRsrq);
 
    auto it1 = m_neighbourCellMeasures.find(rnti);
 
    if (it1 == m_neighbourCellMeasures.end())
    {
        NS_LOG_WARN("Skipping handover evaluation for RNTI "
                    << rnti << " because neighbour cells information is not found");
    }
    else
    {
        // Find the best neighbour cell (eNB)
        NS_LOG_LOGIC("Number of neighbour cells = " << it1->second.size());
        uint16_t bestNeighbourCellId = 0;
        uint8_t bestNeighbourRsrq = 0;
        for (auto it2 = it1->second.begin(); it2 != it1->second.end(); ++it2)
        {
            if ((it2->second->m_rsrq > bestNeighbourRsrq) && IsValidNeighbour(it2->first))
            {
                bestNeighbourCellId = it2->first;
                bestNeighbourRsrq = it2->second->m_rsrq;
            }
        }
 
        // Trigger Handover, if needed
        if (bestNeighbourCellId > 0)
        {
            NS_LOG_LOGIC("Best neighbour cellId " << bestNeighbourCellId);
 
            if ((bestNeighbourRsrq - servingCellRsrq) >= m_neighbourCellOffset)
            {
                NS_LOG_LOGIC("Trigger Handover to cellId " << bestNeighbourCellId);
                NS_LOG_LOGIC("target cell RSRQ " << (uint16_t)bestNeighbourRsrq);
                NS_LOG_LOGIC("serving cell RSRQ " << (uint16_t)servingCellRsrq);
 
                // Inform eNodeB RRC about handover
                m_handoverManagementSapUser->TriggerHandover(rnti, bestNeighbourCellId);
            }
        }
    }
}
 
bool
A2A4RsrqHandoverAlgorithm::IsValidNeighbour(uint16_t cellId)
{
    NS_LOG_FUNCTION(this << cellId);
 
    /**
     * @todo In the future, this function can be expanded to validate whether the
     *       neighbour cell is a valid target cell, e.g., taking into account the
     *       NRT in ANR and whether it is a CSG cell with closed access.
     */
 
    return true;
}
 
void
A2A4RsrqHandoverAlgorithm::UpdateNeighbourMeasurements(uint16_t rnti, uint16_t cellId, uint8_t rsrq)
{
    NS_LOG_FUNCTION(this << rnti << cellId << (uint16_t)rsrq);
    auto it1 = m_neighbourCellMeasures.find(rnti);
 
    if (it1 == m_neighbourCellMeasures.end())
    {
        // insert a new UE entry
        MeasurementRow_t row;
        auto ret = m_neighbourCellMeasures.insert(std::pair<uint16_t, MeasurementRow_t>(rnti, row));
        NS_ASSERT(ret.second);
        it1 = ret.first;
    }
 
    NS_ASSERT(it1 != m_neighbourCellMeasures.end());
    Ptr<UeMeasure> neighbourCellMeasures;
    auto it2 = it1->second.find(cellId);
 
    if (it2 != it1->second.end())
    {
        neighbourCellMeasures = it2->second;
        neighbourCellMeasures->m_cellId = cellId;
        neighbourCellMeasures->m_rsrp = 0;
        neighbourCellMeasures->m_rsrq = rsrq;
    }
    else
    {
        // insert a new cell entry
        neighbourCellMeasures = Create<UeMeasure>();
        neighbourCellMeasures->m_cellId = cellId;
        neighbourCellMeasures->m_rsrp = 0;
        neighbourCellMeasures->m_rsrq = rsrq;
        it1->second[cellId] = neighbourCellMeasures;
    }
}
 
} // end of namespace ns3