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CoMP Dynamic Point Selection with Multiple CSI Processes

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This example shows how multiple Channel State Information (CSI) processes provide the network with feedback for Coordinated Multipoint (CoMP) operation. In this example User Equipment (UE) data is transmitted from one of two cooperating eNodeB as part of a Dynamic Point Selection (DPS) scheme. The transmission decision is based on Channel Quality Indicator (CQI) reports from the UE.

Introduction

Coordinated multipoint (CoMP) is a term used to describe schemes in which a group of base stations dynamically cooperate to mitigate interference, or even turn this interference into a useful signal. The group of coordinating base stations is termed the cooperating set. CoMP in LTE Release 11 is designed to be able to take advantage of low latency and high capacity backhaul between base stations within a cooperating set. Therefore data for a User Equipment (UE) may be available at one or more cooperating base stations.

There are three categories of downlink CoMP:

  • In Coordinated Scheduling and Beamforming (CS/CB), UE data is only available at a single base station within the coordinating set, therefore the PDSCH is transmitted from a single base station. Scheduling and link adaptation are coordinated using information from other base stations within the cooperating set. Other cooperating base stations can also coordinate their scheduling and beamforming decisions to mitigate interference.

  • In Dynamic Point Selection (DPS), UE data is available at multiple base stations within the coordinating set but data is only transmitted from one base station at a time. The base station transmitting to the UE, named the transmission point (TP), can be changed subframe-to-subframe, to provide the best transmission for a UE with varying channel conditions. This scenario is most likely at a cell edge, where long term channel characteristics favor the serving base station, but short term characteristics may favor other cooperating base stations.

  • In Joint Transmission (JT), UE data is transmitted from multiple base stations simultaneously. This can be coherent or non-coherent. Coherent JT jointly precodes transmissions from multiple TPs to allow the receiver to achieve coherent combining of the transmission. In non-coherent JT, each TP precodes the transmission independently, therefore only a power gain is available to the receiver.

The network uses Channel State Information (CSI), reported by the UE, or inferred from TDD uplink transmissions, to make CoMP transmission decisions. The UE feeds back multiple reports, each of which correspond to different hypotheses regarding the transmission decisions of cooperating base stations. To provide a report, a UE is configured with a CSI process. A CSI process consists of a CSI Reference Signal (CSI-RS) resource, a CSI interference Measurement resource (CSI-IM) and a reporting mechanism. For CSI reporting, the network can configure a UE with up to four CSI processes. For each CSI process the UE reports calculated CSI indicators as requested by the network:

  • Channel Quality Indicator (CQI)

  • Rank Indicator (RI)

  • Precoder Matrix Indicator (PMI)

For more information about CQI/RI/PMI reporting see the examplesReporting of Rank Indicator (RI) Conformance TestandReporting of Channel Quality Indicator (CQI) Conformance Test。

This example shows a simple DPS scenario for PDSCH transmission to a UE. The cooperating set contains two transmission points, TP1 and TP2, each of which is capable of transmitting the PDSCH to the UE. TP1 is the serving cell for the UE. The network selects the PDSCH transmission point and the modulation and coding scheme using the CQI reported by the UE. The following diagram shows the principle of DPS operation in this example. Both transmission points transmit a CSI-RS and cell-specific reference signal (CRS). The serving cell also transmits downlink control information for the UE in the PDCCH. The PDSCH transmission point can change subframe-to-subframe to take advantage of instantaneous channel conditions. In the diagram the PDSCH transmission point changes from TP1 in subframento TP2 in subframen+1。

In this example the CSI processes and transmission points are configured as required by the conformance test "CQI Reporting requirement with multiple CSI processes" in TS36.101 Section 9.3.6.1 [1]. This example differs from this conformance test by selecting one of two possible PDSCH transmission points based on the highest reported wideband CQI from either transmission point. In this conformance test the PDSCH transmission point is fixed. Additionally no CQI reporting delay is implemented.

Simulation Controls

In this example the PDSCH transmission point can be either dynamically selected or fixed to the serving cell, TP1, using the parameterdpsOperation。Use this parameter to explore the impact of DPS on throughput.

dpsOperation = true;% Enable DPS {true,false}totSubframes = 150;% Number of subframes to simulate

Transmission Point Configurations

Two transmission points are defined and configured as per TS36.101 Table 9.3.6.1-1 [1]: TP1 is a macro cell (the serving cell) and TP2 is a cooperating base station such as a remote radio head. A structure arrayenbcontains the parameters for both transmission points.

% Transmission point 1 cell-wide settingsenb = struct; enb.NDLRB = 50; enb.CellRefP = 2; enb.DuplexMode ='FDD'; enb.CFI = 3; enb.CyclicPrefix ='Normal'; enb.NFrame = 0; enb.NCellID = 0;% PDSCH configuration for transmission mode 10 (TM10)enb.PDSCH.TxScheme ='Port7-14'; enb.PDSCH.NLayers = 1; enb.PDSCH.RNTI = 1; enb.PDSCH.NSCID = 0; enb.PDSCH.Modulation = {'16QAM'}; enb.PDSCH.Rho = 0; enb.PDSCH.RV = 0; enb.PDSCH.NTurboDecIts = 5; enb.PDSCH.PRBSet = (0:enb.NDLRB-1).'; enb.PDSCH.NTxAnts = 4; enb.PDSCH.W = lteCSICodebook(enb.PDSCH.NLayers,enb.PDSCH.NTxAnts,0).'; enb.PDSCH.AltCodebook4Tx ='Off'; enb.PDSCH.CSI ='On';

The configuration for TP2 is based on TP1. Different cell-specific settings are configured as required.

enb = repmat(enb,2,1); enb(2).NCellID = 6; enb(2).PDSCH.NTxAnts = 2; enb(2).PDSCH.W = lteCSICodebook(enb(2).PDSCH.NLayers,enb(2).PDSCH.NTxAnts,0).';

Transmission Hypothesis, CSI Resources and CSI Processes

当两个协调传输点使用DPS, the PDSCH can be transmitted from either TP1 or TP2. When the PDSCH is transmitted by one transmission point to a UE, for example TP1, there are two transmission options for the other transmission point, TP2. The first option is to serve other UEs using the same resources thereby interfering with the PDSCH transmission from TP1. The second option is to mute transmission in these resources thereby not interfering with the PDSCH transmission from TP1. These options are grouped into transmission hypotheses. In this example four transmission hypotheses are tested by the network:

TP1 Hypothesis TP2 Hypothesis ------------------------------------------------------ Hypothesis 0: Transmitting PDSCH Muting Hypothesis 1: Muting Transmitting PDSCH Hypothesis 2: Transmitting PDSCH Interfering Hypothesis 3: Interfering Transmitting PDSCH

Although four hypotheses are tested in this example, PDSCH transmissions made to the UE are only consistent with hypotheses 2 or 3.

To provide the network with CSI for these transmission hypotheses, two CSI-RS resources and three CSI-IM resources are configured at the UE. CSI processes use these resources to report CSI for each hypothesis.

In the following sections the resources and CSI processes are configured to test these four transmission hypotheses.

CSI-RS Resources

A unique CSI-RS is transmitted by each cooperating base station. The UE is configured with two CSI-RS resources to provide channel quality estimates, one for each transmission point:

  • CSI-RS #0: Transmission from TP1

  • CSI-RS #1: Transmission from TP2

Each CSI-RS is defined by a configuration, a period and a CSI-RS scrambling identity. The number of CSI reference ports is the number of transmit antennas. For this simulation the periods of CSI-RS and CSI-IM resources must be the same. These are parameterized bySimCSIPeriod。

SimCSIPeriod = [5 1];% [Tcsi-rs Dcsi-rs]% CSI-RS资源: {CSI-RS #0, CSI-RS #1}SimCSIRS.CSIRSConfig = [0 5];% CSI-RS configurationSimCSIRS.CSIRSPeriod = {SimCSIPeriod,SimCSIPeriod};% CSI-RS periodSimCSIRS.NCSIID = [10 16];% CSI-RS scrambling identitySimCSIRS.CSIRefP = [enb(1).PDSCH.NTxAnts enb(2).PDSCH.NTxAnts];

CSI-IM Resources

Elemen CSI-IM资源描述的一组资源ts (REs) over which the average power is measured by the UE. These measurements are used to estimate the interference for CSI calculations. Three CSI-IM are required to measure interference when the TPs are transmitting:

  • CSI-IM #0: Measure background noise when both TPs are muted

  • CSI-IM #1: Measure TP2 interference

  • CSI-IM #2: Measure TP1 interference

Each CSI-IM is defined by a configuration and a period. Note the configurations differ from the CSI-RS configurations but the periods are the same.

% CSI-IM resource: {CSI-IM #0, CSI-IM #1, CSI-IM #2}SimCSIIM.ZeroPowerCSIRSConfig = [2 6 1]; SimCSIIM.ZeroPowerCSIRSPeriod = {SimCSIPeriod,SimCSIPeriod,SimCSIPeriod};

CSI流程

Four processes are configured to test the four transmission hypotheses. These use the CSI-RS and CSI-IM resources described above:

TP1假说TP2假说CSI-RS CSI-IM—------------------------------------------------------------------ Process 0: Transmitting PDSCH Muting CSI-RS #0 CSI-IM #0 Process 1: Muting Transmitting PDSCH CSI-RS #1 CSI-IM #0 Process 2: Transmitting PDSCH Interfering CSI-RS #0 CSI-IM #1 Process 3: Interfering Transmitting PDSCH CSI-RS #1 CSI-IM #2

A process is defined by a CSI-RS resource, a CSI-IM resource and a reporting mode. The CSI reporting mode, PMI reporting mode and codebook subset restriction for each process are configured as per TS36.101 Table 9.3.6.1-1 [1]. The codebook subset restriction for each process restricts PMI selection to a single PMI therefore PMI and RI reporting is not required.

% {CSI Process #0, CSI Process #1, CSI Process #2, CSI Process #3}SimCSIProcess。CSIRSResource = [1 2 1 2];% CSI-RS资源s index (1 based)SimCSIProcess。CSIIMResource = [1 1 2 3];% CSI-IM resources index (1 based)SimCSIProcess。CSIMode = {'PUCCH 1-1','PUSCH 3-1','PUSCH 3-1','PUSCH 3-1'};% CSI reporting modesSimCSIProcess。PMIMode = {'Wideband','Wideband','Wideband','Wideband'};% PMI reporting modesSimCSIProcess。CodebookSubset = {'0x0000000000000001','000001','0x0000000000000001','000001'};% Codebook subset restrictions

In this simulation only two of the four hypotheses are implemented by the network; PDSCH transmission from either TP1 or TP2 with the other TP interfering. Therefore only the feedback from CSI processes 2 and 3 is used for the transmission decision.

Fading Channel and SNR Configuration

The SNR for each transmission to the UE is defined in TS36.101 Table 9.3.6.1-1 [1]. The noise power is defined usingNoc。

snrTP = [11 8];% SNR of received transmission from TP1 and TP2Noc = -98;% dBm/15kHz average power spectral density

A fading channel is configured between TP1 and the UE, and TP2 and the UE. The structure arraychcfgparameterizes the channels from TP1 and TP2.

% Channel between TP1 and UEofdmInfo = lteOFDMInfo(enb(1)); chcfg = struct; chcfg.DelayProfile ='EPA'; chcfg.NRxAnts = 2; chcfg.DopplerFreq = 5; chcfg.MIMOCorrelation ='Low'; chcfg.SamplingRate = ofdmInfo.SamplingRate; chcfg.InitPhase ='Random'; chcfg.ModelType ='GMEDS'; chcfg.NTerms = 16; chcfg.NormalizeTxAnts ='On'; chcfg.NormalizePathGains ='On'; chcfg.Seed = 1;% Channel between TP2 and UEchcfg = repmat(chcfg,2,1); chcfg(2).Seed = 2;% Calculate the size of the received waveformrxWaveformSize = [chcfg(1).SamplingRate*1e-3+15 chcfg(1).NRxAnts];

Channel Estimation Configuration

Two reference signals must be used by the UE: the CSI-RS and DM-RS. Two separate channel estimation configurations are required to estimate each reference signal. Here cubic interpolation will be used with an averaging window of 1-by-2 REs. This configures the channel estimator to use a special mode which ensures the ability to despread and orthogonalize the CSI-RS and DMRS transmissions.

% CSI-RS estimationceccsi.FreqWindow = 1; ceccsi.TimeWindow = 2; ceccsi.InterpType ='cubic'; ceccsi.PilotAverage ='UserDefined'; ceccsi.InterpWinSize = 1; ceccsi.InterpWindow ='Causal'; ceccsi.Reference ='CSIRS';% DM-RS estimationcecdmrs = ceccsi; cecdmrs.Reference ='DMRS';

Transmission Point Parameterization for CSI Estimation and Reporting

In this section the transmission points are parameterized from the configured CSI-RS resources and CSI-IM resources for CSI-RS generation and PDSCH mapping. The appropriate parameters are set in the configuration structure arrayenb。

CSI-RS Resources

Both transmission points are parameterized with all CSI-RS configured at the UE.

% Set TP1 and TP2 CSI-RS configurationforenbIdx = 1:2 enb(enbIdx).CSIRefP = SimCSIRS.CSIRefP; enb(enbIdx).CSIRSConfig = SimCSIRS.CSIRSConfig; enb(enbIdx).CSIRSPeriod = SimCSIRS.CSIRSPeriod; enb(enbIdx).NCSIID = SimCSIRS.NCSIID;end

ZP CSI-RS Resources

Zero Power (ZP) CSI-RS resources prevent the PDSCH from being mapped to a set of REs. Therefore ZP CSI-RS are used to mute REs within each TP PDSCH transmission to allow configured CSI-IM to measure the interference for different hypotheses.

The diagram below illustrates how ZP CSI-RS are configured to allow CSI-IM resources to measure interference. CSI-IM #0 measures the noise when neither TP is transmitting in resource 2. Therefore to prevent the TPs transmitting in this resource, the ZP CSI-RS is configured in resource 2 for both TPs. This stops the PDSCH being mapped to this resource, muting the transmission. The ZP CSI-RS for each TP is also configured to map around the CSI-RS of the coordinating TP to prevent interference. CSI-IM #1 and CSI-IM #2 measure the individual interference caused by TP2 and TP1 in resources 6 and 1. Therefore the ZP CSI-RS for TP1 is configured to prevent PDSCH transmission in resource 6 to allow measurement with CSI-IM #1. The ZP CSI-RS for TP2 is configured to prevent PDSCH transmission in resource 1 to allow measurement with CSI-IM #2.

The ZP CSI-RS are configured with a 16-bit bitmap. Each bit controls whether a set of REs should be muted (1) or unmuted (0). For each transmission point, a ZP CSI-RS configuration is created from the required CSI-IM configurations and the CSI-RS configuration used by the coordinating transmission point.

% ZP CSI-RS resource for TP1zp1 ='0000000000000000';% Assume all CSI configurations unmutedzp1(SimCSIIM.ZeroPowerCSIRSConfig([1 2])+1) ='1';% Mute CSI-IM #0,1 (background & TP2 interference)zp1(SimCSIRS.CSIRSConfig(2)+1) ='1';% Mute CSI-RS #1 (TP2 transmission)% Add ZP CSI-RS resource to TP1 parametersenb(1).ZeroPowerCSIRSConfig = zp1; enb(1).ZeroPowerCSIRSPeriod = SimCSIPeriod;% ZP CSI-RS resource for TP2zp2 ='0000000000000000';% Assume all CSI configurations unmutedzp2(SimCSIIM.ZeroPowerCSIRSConfig([1 3])+1) ='1';% Mute CSI-IM #0,2 (background & TP1 interference)zp2(SimCSIRS.CSIRSConfig(1)+1) ='1';%静音CSI-RS # 0 (TP1传输)% Add ZP CSI-RS resource to TP2 parametersenb(2).ZeroPowerCSIRSConfig = zp2; enb(2).ZeroPowerCSIRSPeriod = SimCSIPeriod;

UE Parameterization for CSI Estimation and Reporting

In this example the CSI-RS, CSI-IM and CSI processes are represented at the UE as structure arrays. Each element of the structure array configures a single resource or process. This section creates these structure arrays from the configured CSI-RS resources and CSI-IM resources.

The structure arraycsirscontains the CSI-RS resource parameterization. This is based on the parameters of the serving cell but the CSI-RS parameters are configured to use the appropriate resource given in the simulation settings.

numCSIRS = numel(SimCSIRS.CSIRSConfig); csirs = repmat(enb(1),numCSIRS,1);foridx = 1:numCSIRS csirs(idx).CSIRefP = SimCSIRS.CSIRefP(idx); csirs(idx).CSIRSConfig = SimCSIRS.CSIRSConfig(idx); csirs(idx).CSIRSPeriod = SimCSIRS.CSIRSPeriod{idx}; csirs(idx).NCSIID = SimCSIRS.NCSIID(idx);end

The structure arraycsiimcontains the CSI-IM resource parameterization. This is based on the parameters of the serving cell but the CSI-IM parameters are configured to use the appropriate resource give in the simulation settings. As a CSI-IM resource is a ZP CSI-RS configuration theCSIRSPeriodparameter is set to'Off'so only ZP CSI-RS REs are used to measure interference.

numCSIIM = numel(SimCSIIM.ZeroPowerCSIRSConfig); csiim = repmat(enb(1),numCSIIM,1);foridx = 1:numCSIIM csiim(idx).ZeroPowerCSIRSConfig = SimCSIIM.ZeroPowerCSIRSConfig(idx); csiim(idx).ZeroPowerCSIRSPeriod = SimCSIIM.ZeroPowerCSIRSPeriod{idx}; csiim(idx).CSIRSPeriod ='Off';end

The structure arrayprocesscontains the CSI process parameterization. This is based on the parameters of the serving cell. The parametersCSIRSIdxandCSIIMIdxare used to index the CSI-RS and CSI-IM resources for calculating CSI. The reporting modes are configured for each process from the simulation settings. The CQI reported by the UE for each CSI process is selected using the estimated Signal to Interference plus Noise Ratio (SINR). The lowest SINRs recommended to achieve 90% throughput for each CQI index in this scenario are defined by the vectorSINRs。这个向量用于参数化医院药学部的希利ction for each CSI process.

SINRs = [1.3 1.3 2.3 3.7 5 6.8 9.2 10.9 13 14.8 17.1 18.9 21 23.9 24.3]; numCSIProcesses = numel(SimCSIProcess.CSIRSResource); process = repmat(enb(1),numCSIProcesses,1);foridx = 1:numCSIProcesses% Index CSI-RS and CSI-IM resources used by the processprocess(idx).CSIRSIdx = SimCSIProcess.CSIRSResource(idx); process(idx).CSIIMIdx = SimCSIProcess.CSIIMResource(idx);% Reporting configurationprocess(idx).PDSCH.CSIMode = SimCSIProcess.CSIMode{idx}; process(idx).PDSCH.PMIMode = SimCSIProcess.PMIMode{idx}; process(idx).PDSCH.CodebookSubset = SimCSIProcess.CodebookSubset{idx}; process(idx).PDSCH.SINRs90pc = SINRs;% CSI-RS configuration for CSI estimationprocess(idx).CSIRefP = SimCSIRS.CSIRefP(process(idx).CSIRSIdx); process(idx).CSIRSConfig = SimCSIRS.CSIRSConfig(process(idx).CSIRSIdx); process(idx).CSIRSPeriod = SimCSIRS.CSIRSPeriod(process(idx).CSIRSIdx); process(idx).NCSIID = SimCSIRS.NCSIID(process(idx).CSIRSIdx);end

Simulation Setup

The required signal power to satisfy the SNR for each TP is calculated below.

% Convert to linear and WattsnocLin = 10.^(Noc/10)*(1e-3);% linear in Watts% Take into account number of antennas and FFT (OFDM) scalingNo = sqrt(nocLin/(2*double(ofdmInfo.Nfft))); NocW = 10.^((Noc-30)/10);% convert to W/15kHz% SINR = Es/Noc TS 36.101 Sec. 8.1.1NocTot = NocW;% W/15kHzsnrLin = 10.^(snrTP/10); Es = snrLin*NocTot;% W/15kHz% Amplitude scaling factorsK = sqrt(Es);

Variables required for the simulation are initialized in this section.

% Set the random number seedrng('default');% Initialize containers which store the channel estimates interference% measurements for CSI-RS and CSI-IM resourcescsirshest = cell(numCSIRS,1); csiimnest = zeros(numCSIIM,1);% Initialize a buffer to store CQI reports for each process. Size buffer% for subband CQI reporting.numCSIReports = ceil(totSubframes/SimCSIPeriod(1)); pmiInfo = ltePMIInfo(process(1),setfield(process(1).PDSCH,'PMIMode','Subband'));%#okcqiBuffer = ones(numCSIReports,pmiInfo.NSubbands+1,numCSIProcesses);% Initialize buffers to store the CRC, BER and TP selectedcrcBuffer = cell(totSubframes,1); berBuffer = zeros(totSubframes,2); tpBuffer = zeros(totSubframes,1); csiReportIdx = 1;% Index of CSI reportlastOffset = 0;% Initialize overall frame timing offsetframeOffset = 0;% Initialize frame timing offset

Simulation Loop

The simulation is run subframe-by-subframe. For each subframe the following steps are carried out:

  • A time domain waveformrxWaveformis initialized with noise. The received waveform from TP1 and TP2 will be added to this.

  • The PDSCH TP is selected using the wideband CQI reported by the UE.

  • For each TP in turn a subframe is generated containing the relevant synchronizing and reference signals and TM10 OCNG.

  • The PDSCH for the UE is generated from either TP1 or TP2 in a single subband.

  • The two subframes are OFDM modulated, passed through a fading channel, and combined.

  • The received waveform at the UE is synchronized and OFDM demodulated.

  • The configured CSI-RS and CSI-IM measurements are performed by the UE

  • A CSI report is generated using the CSI-RS and CSI-IM resources for configured CSI processes.

  • The PDSCH is demodulated.

fornsf = 0:totSubframes-1% Initialize UE receive waveform with noiserxWaveform = No*complex(randn(rxWaveformSize),randn(rxWaveformSize));% Select PDSCH TP based on the highest reported wideband CQIbufferIdx = mod(csiReportIdx-2,numCSIReports)+1;% Buffered CQI to useifdpsOperation widebandCQI = permute(cqiBuffer(:,1,:),[1 3 2]);if(widebandCQI(bufferIdx,3)>=widebandCQI(bufferIdx,4)) pdschTransmissionPoint = 1;% TP1elsepdschTransmissionPoint = 2;% TP2endelsepdschTransmissionPoint = 1;%#ok % TP1end% Generate TP1 and TP2 transmissions.% Each transmission contains cell-specific reference signal,% synchronizing signals, CSI-RS and TM10 OCNG. One transmission% contains the PDSCH for the UE.forenbIdx = 1:2% Update subframe number for each transmissionenb(enbIdx).NSubframe = nsf;% Turn off the CSI resource not transmitted by this TPtpenb = enb(enbIdx); tpenb.CSIRSPeriod{mod(enbIdx,2)+1} ='Off';% Blank subframe; CRS, PSS and SSSsf = lteResourceGrid(tpenb,tpenb.PDSCH.NTxAnts); crsInd = lteCellRSIndices(tpenb);% Cell-specific reference signalsf(crsInd) = lteCellRS(tpenb); pssInd = ltePSSIndices(tpenb);% Primary synchronizing signalsf(pssInd) = ltePSS(tpenb); sssInd = lteSSSIndices(tpenb);% Secondary synchronizing signalsf(sssInd) = lteSSS(tpenb);% CSI-RS资源csitp = tpenb; csitp.ZeroPowerCSIRSPeriod ='Off'; csiInd = lteCSIRSIndices(csitp); sf(csiInd) = lteCSIRS(csitp);% TM10 OCNG transmitted apart from subframes containing PSS/SSS/PBCHifisempty(pssInd) tpenb.PDSCH.RNTI = 0;% Add OCNG at DMRS locationsoncngInd = lteDMRSIndices(tpenb,tpenb.PDSCH); ocngSym = lteDMRS(tpenb,tpenb.PDSCH); sf(oncngInd) = ocngSym;% Add OCNG for PDSCH symbols[oncngInd,ocngInfo] = ltePDSCHIndices(tpenb,tpenb.PDSCH,tpenb.PDSCH.PRBSet); ocngSym = ltePDSCH(tpenb,tpenb.PDSCH,randi([0 1],ocngInfo.G,1)); sf(oncngInd) = ocngSym;end% PDSCH and DMRS Transmission to UE from either TP1 or TP2.% The transport block size and modulation scheme for transmission% are selected using the reported CQI for the appropriate CSI% process. The PDSCH must be mapped around the ZP CSI-RS configured% for the UE and the ZP CSI-RS of the TP. Only transmit PDSCH for% subframes not containing CSI resources or PSS/SSS as per TS36.101% Table 9.3.6.1-1.if~isempty(pssInd)||~isempty(csiInd) tbs = 0;% Transport block size is 0 as no PDSCH transmittedelseif(pdschTransmissionPoint==enbIdx) tpBuffer(nsf+1) = pdschTransmissionPoint;% Get relevant configuration for transmission point and CQI to% use.txenb = enb(enbIdx); cqi = cqiBuffer(bufferIdx,:,enbIdx+2);% Select subband for PDSCH transmission.% The PDSCH is transmitted in the highest differential CQI% subband. Subbands less than full size are excluded.partialSubband = (pmiInfo.k*pmiInfo.NSubbands>txenb.NDLRB); [~,idx] = max(cqi(2:(end-partialSubband)));% Maximum differentialsbCandidates = find(cqi(2:(end-partialSubband))==cqi(idx+1)); sb = sbCandidates(randi([1 numel(sbCandidates)],1,1)); cqi = cqi(1)+cqi(1+sb);% Calculate SB PMI from wideband and differentialtxenb.PDSCH.PRBSet = ((sb-1)*pmiInfo.k+(0:(pmiInfo.k-1))).';% PRB allocation for subband% Select MCS according to CQI using TS36.101 Table A.4-1 CSI% RMC RC.12 FDD (MCS.13), which defines the relationship% between CQI indices and MCS indicesimcsTable = [-1 0 0 1 3 5 7 10 12 14 17 19 21 22 24 25]; imcs = imcsTable(cqi+1);% Determine TBS and modulation order, fixed RI (1) and PMI (0).% Generate PDSCH for only a non-zero transport block size.[itbs,modulation] = lteMCS(imcs); tbs = double(lteTBS(size(txenb.PDSCH.PRBSet,1),itbs));ifany(tbs)if~iscell(modulation) modulation = {modulation};endtxenb.PDSCH.NLayers = 1; txenb.PDSCH.Modulation = modulation; txenb.PDSCH.W = lteCSICodebook(txenb.PDSCH.NLayers,txenb.PDSCH.NTxAnts,0).';% PDSCH mapping[pdschInd,pdschInfo] = ltePDSCHIndices(txenb,txenb.PDSCH,txenb.PDSCH.PRBSet);% Generate DL-SCH datatxtrblk = arrayfun(@(x)randi([0 1],x,1),tbs,'UniformOutput',false); cw = lteDLSCH(txenb,txenb.PDSCH,pdschInfo.G,txtrblk);% Generate PDSCH symbols with cell identity of serving cell% for correct scramblingtxenb.NCellID = enb(1).NCellID; pdschSym = ltePDSCH(txenb,txenb.PDSCH,cw);% Create UE specific DMRS configuration to allow for% scrambling code to change depending on transmission pointtxenb.NCellID = enb(1).NCellID;ifpdschTransmissionPoint == 2 txenb.NCellID = enb(2).NCellID;enddmrsInd = lteDMRSIndices(txenb,txenb.PDSCH); dmrsSym = lteDMRS(txenb,txenb.PDSCH);% Map PDSCH and DMRSsf(pdschInd) = pdschSym; sf(dmrsInd) = dmrsSym;endend% OFDM modulate, pass through a fading channel, scale for SNR and% add to existing receive waveformtxWaveform = lteOFDMModulate(tpenb,sf); txWaveform = [txWaveform; zeros(15,size(txWaveform,2))];%#okchcfg(enbIdx).InitTime = nsf/1e3; rxWaveform = rxWaveform + K(enbIdx)*lteFadingChannel(chcfg(enbIdx),txWaveform);end% Receiver Synchronization and OFDM demodulation% Synchronize using the PSS/SSS of the serving cell (TP1) and OFDM% demodulateif~isempty(pssInd) frameOffset = lteDLFrameOffset(enb(1),rxWaveform);if(frameOffset > 25) frameOffset = lastOffset;endlastOffset = frameOffset;endrxWaveform = rxWaveform(1+frameOffset:end,:); rxsf = lteOFDMDemodulate(enb(1),rxWaveform);% Calculate CSI-RS Estimates% Generate channel estimates for CSI-RS resources configured at the UE.foridx = 1:numCSIRS% Calculate channel estimatecsirs(idx).NSubframe = nsf; csirshest{idx} = lteDLChannelEstimate(csirs(idx),csirs(idx).PDSCH,ceccsi,rxsf);end% Calculate interference using CSI-IM% For each CSI-IM resource calculate the energy in resource elements.% This is the noise+interference estimate.foridx = 1:numCSIIM% Calculate noise and interference estimatecsiim(idx).NSubframe = nsf; imIndices = lteCSIRSIndices(csiim(idx)); imSym = lteExtractResources(imIndices,rxsf); csiimnest(idx) = mean(abs(imSym(:)).^2);end% CSI Process Reporting% When estimated CSI resource elements are not zero calculate CSIif~isempty(csiInd)% For each CSI process calculate CSI feedbackforidx = 1:numCSIProcesses% Update subframe numberprocess(idx).NSubframe = nsf;% Extract CSI-RS estimate and CSI-IM estimate for processhest = csirshest{process(idx).CSIRSIdx}; nest = csiimnest(process(idx).CSIIMIdx);% Calculate CQI/PMI/RI, condition CQI on PMI/RI selection[ri,PMISet] = lteRISelect(process(idx),process(idx).PDSCH,hest,nest); process(idx).PDSCH.PMISet = PMISet; process(idx).PDSCH.NLayers = ri; process(idx).PDSCH.NCodewords = min(ri,2); [cqi,sinrs] = lteCQISelect(process(idx),process(idx).PDSCH,hest,nest); cqiBuffer(csiReportIdx,1:numel(cqi),idx) = cqi;end% New CSI reportcsiReportIdx = csiReportIdx+1;end% PDSCH Demodulation% If the transport block size is not 0, a PDSCH exists to decodeifany(tbs)% Estimate channel using DMRS. To use the correct scrambling% sequence for the DMRS use the configuration for the active TP.[dmrshest,dmrsnest] = lteDLChannelEstimate(txenb,txenb.PDSCH,cecdmrs,rxsf);% Extract PDSCH symbols from received grid and channel estimate[sym,symhest] = lteExtractResources(pdschInd,rxsf,dmrshest);% Scale the received symbols by the PDSCH power factor Rho and% decode the PDSCH with the CellID for the serving cellsym = sym*(10^(-txenb.PDSCH.Rho/20)); txenb.NCellID = enb(1).NCellID; [cws,recsym] = ltePDSCHDecode(txenb,txenb.PDSCH,sym,symhest,dmrsnest);% Scale cws by 1/K(1) to avoid numerical issues with DLSCH decodingcws = cellfun(@(x) x*(1/K(1)),cws,'UniformOutput',false); [trblk,crc] = lteDLSCHDecode(txenb,txenb.PDSCH,tbs,cws,[]);% Store CRC and BERcrcBuffer{nsf+1} = double(crc); berBuffer(nsf+1,:) = [sum(trblk{1}~=txtrblk{1}),numel(trblk{1})];endend

Conclusion and Results

The Block Error Rate (BLER) and PDSCH throughput are displayed for the simulation duration. Two figures are also created:

The first figure plots the reported wideband CQI for each CSI process over the duration of the simulation. The reported CQI of process 0 and process 1 show the channel conditions favor TP1 during the middle of the simulation but TP2 otherwise, as the reported CQI exceeds than of TP1. The reported CQI of processes 2 and 3 show a similar pattern, but the reported CQI is lower than for processes 0 and 1. This is because these processes assume added interference from the TPs.

The second figure plots the PDSCH transmission point selected and the reported wideband CQI of the two processes used to make the transmission point decision. This figure shows TP1 was selected for PDSCH transmission during the middle of the simulation as the reported CQI favored this transmission point.

hCoMPResults(totSubframes,SimCSIPeriod,crcBuffer,berBuffer,cqiBuffer,tpBuffer);
BLER: 0.044444 (target is 0.1) Throughput: 266.875 kbps

This example showed how multiple CSI processes provide feedback for DPS CoMP operation. UE data was transmitted from one of two cooperating eNodeB, based on the wideband CQI reported by the UE. This examples simulated a cell-edge scenario where DPS provides a throughput gain for the UE. Try disabling DPS by settingdpsOperation = falseand note the decrease in throughput.

Appendix

This example uses the following helper function:

Selected Bibliography

  1. 3GPP TS 36.101 "User Equipment (UE) radio transmission and reception"

  2. 3GPP TS 36.211 "Physical channels and modulation"

  3. Erik Dahlman, 4G: LTE/LTE-Advanced for Mobile Broadband, Elsevier 2014

  4. Joydeep Acharya, Heterogeneous Networks in LTE-Advanced, Wiley 2014