NB-IoT Downlink In-Band and Guardband Waveform Generation and Analysis

prbTable = nbAllowedPRB()

operationMode = "Inband-SamePCI"; % NB-IoT operation mode
ltecfg = struct(); % LTE configuration
ltecfg.TotSubframes = 10; % Number of subframes
ltecfg.NDLRB = 25; % Number of downlink resource blocks
nbPRB = 7; % PRB in which the NB-IoT is deployed (0-based)
lteDisabled = false; % Set to true to disable the LTE component
nbPowerBoost = 6; % NB-IoT power boost in dB

% Verify that the PRB chosen for the NB-IoT operation mode in the LTE carrier is allowed.
verifyNBPRB(nbPRB,ltecfg.NDLRB,operationMode);

ngen = NBIoTDownlinkWaveformGenerator;
ngen.Config.CellRefP = 1;
ngen.Config.NNCellID = 0;
ngen.Config.NFrame = 0;
ngen.Config.TotSubframes = ltecfg.TotSubframes;
ngen.Config.OperationMode = operationMode;
ngen.Config.NPDSCH.StartSubframe = 2;
ngen.Config.NPDSCH.NRep = 1;
ngen.Config.Windowing = 3; % Set Windowing to 3, as shown in Table E.5.1-1a of TS 36.104

figure;
displayResourceGrid(ngen);

[nbWaveform,nbGrid,nbInfo] = generateWaveform(ngen);
nbInfo

nbPRB = double(nbPRB);
ltecfg.PDSCH.PRBSet = (0:ltecfg.NDLRB-1)'; % Full PRB allocation for LTE
if contains(ngen.Config.OperationMode,'Inband')
    ltecfg.PDSCH.PRBSet(nbPRB+1) = []; % Leave nbPRB empty for in-band NB-IoT
end

[~,lteGrid,lteInfo] = lteRMCDLTool(ltecfg,[1 0 0 1]);

% Create the parameter structure needed to generate the combined grid
combGridParams = struct();
combGridParams.OperationMode = ngen.Config.OperationMode;
combGridParams.NBPRB = nbPRB;
combGridParams.OFDMInfo = nbInfo;
combGridParams.LTEDisabled = lteDisabled;
[combGrid,offset] = hNBInbandGuardbandCombinedGrid(combGridParams,lteGrid,nbGrid*db2mag(nbPowerBoost));

OSR = lteInfo.SamplingRate/nbInfo.SamplingRate; % Oversampling ratio for NB-IoT
wavecfg.Windowing = ngen.Config.Windowing*OSR; % Use the same windowing as the NB-IoT waveform
txWaveform = lteOFDMModulate(wavecfg,combGrid);

txPlot = spectrumAnalyzer('SampleRate',lteInfo.SamplingRate,'Title','Transmitted Waveform Power Spectrum');
txPlot(txWaveform);

rxWaveform = txWaveform;
figure;
spectrogram(rxWaveform(:,1),ones(lteInfo.Nfft,1),0,lteInfo.Nfft,'centered',lteInfo.SamplingRate,'MinThreshold',-130);

rxWaveformB = lteFrequencyCorrect(ltecfg,rxWaveform,offset); % Received waveform with NB-IoT in baseband
combinedSpecPlotB = spectrumAnalyzer('SampleRate',lteInfo.SamplingRate,'Title','Received Waveform Power Spectrum with NB-IoT in Baseband');
combinedSpecPlotB(rxWaveformB);

rxwave = resample(rxWaveformB,1,OSR);

filteredSpecPlot = spectrumAnalyzer('SampleRate',nbInfo.SamplingRate,'Title','Original and Recovered NB-IoT Waveform Power Spectrum',...
    'ChannelNames',{'Original NB-IoT waveform','Recovered NB-IoT waveform'},'ShowLegend',true);
filteredSpecPlot([nbWaveform/OSR*db2mag(nbPowerBoost),rxwave]);

figure;
spectrogram(rxwave(:,1),ones(nbInfo.Nfft,1),0,nbInfo.Nfft,'centered',nbInfo.SamplingRate,'MinThreshold',-130);

enb = ngen.Config;
enb.NSubframe = lteInfo.NSubframe;

timeOffset = lteNBDLFrameOffset(enb,rxwave); % Time delay in samples
rxwave = rxwave(1+timeOffset:end,:);

cec = struct;                        % Channel estimation config structure
cec.PilotAverage = 'UserDefined';    % Type of pilot symbol averaging
cec.FreqWindow = 13;                 % Frequency window size
cec.TimeWindow = 9;                  % Time window size
cec.InterpType = 'Cubic';            % 2D interpolation type
cec.InterpWindow = 'Centered';       % Interpolation window type
cec.InterpWinSize = 1;               % Interpolation window size
cec.Reference = 'NRS';               % Reference signal for channel estimation

[evmmeas,plots] = hNPDSCHEVM(enb,cec,rxwave,nbInfo);

function prbTable = nbAllowedPRB()
    % Generate a table showing the PRB indices allowed for NB-IoT in-band
    % and guardband operation mode for each LTE bandwidth.

    NDLRBList = [6 15 25 50 75 100];
    bwMHz = [1.4 3 5 10 15 20]; % Bandwidth in MHz
    bw = (pad(string(bwMHz),'left') + repmat(" MHz (",size(bwMHz)) + pad(string(NDLRBList),'left') + repmat(" RBs)",size(bwMHz)))';

    % In-band mode
    % The allowed PRB indices for in-band mode of NB-IoT anchor
    % carrier are derived from Table 16.8-1 of TS 36.213.
    prbIndexOdd = [-35:5:-5 5:5:35]; % DC (i.e., PRB 0) is excluded
    prbIndexEven = [-46:5:-6 5:5:45]; % DC (i.e., PRB 0) is excluded
    PRBInband = cell(length(NDLRBList),1);
    for ibw = 1:length(NDLRBList)
        if mod(NDLRBList(ibw),2) % Odd
            prbTemp = prbIndexOdd + floor(NDLRBList(ibw)/2);
        else % Even
            prbTemp = prbIndexEven + floor(NDLRBList(ibw)/2);
        end
        prbTemp(prbTemp<0 | prbTemp>=NDLRBList(ibw)) = [];
        PRBInband{ibw} = prbTemp;
    end
    PRBVariableNameInband = "Allowed PRB indices for NB-IoT in-band mode";

    % Guardband mode
    % The allowed PRB indices for NB-IoT guardband mode are derived
    % here for all channel bandwidths.
    totalGuardHz = bwMHz*1e6 - NDLRBList*12*15e3; % Total guardband in Hz
    NRBGuard = floor((totalGuardHz/2) / (12*15e3)); % Number of RBs allowed on each side of the guardband for all BWs
    PRBGuard = cellfun(@(x,y)([-x:-1, y+(0:(x-1))]),num2cell(NRBGuard(:)),num2cell(NDLRBList(:)),'UniformOutput',false); % Allowed PRB indices for guardband (0-based)
    PRBVariableNameGuard = "Allowed PRB indices for NB-IoT guardband mode";

    prbTable = table(bw,PRBInband,PRBGuard);
    prbTable.Properties.VariableNames = ["LTE Bandwidth" PRBVariableNameInband PRBVariableNameGuard];
end

function verifyNBPRB(nbPRB,NDLRB,operationMode)
    % Check whether the PRB chosen for the NB-IoT operation mode in the LTE
    % carrier is allowed.
    prbTable = nbAllowedPRB();

    r = contains(prbTable{:,1},string(NDLRB)+" RBs"); % prbTable row associated to the given bandwidth
    c = 1+contains(operationMode,'Inband')*1+contains(operationMode,'Guard')*2; % prbTable column associated to the given operation mode

    errorFlag = ismember(nbPRB,prbTable{r,c}{1}); % If true, the selected nbPRB is allowed
    tmp = extract(prbTable{r,1},digitsPattern);
    msg = "The chosen PRB index ("+string(nbPRB)+") is invalid for "+operationMode+" operation mode on a "+string(tmp(1))+...
        " MHz LTE carrier. See 'prbTable' for the allowed PRB indices for all combinations of LTE bandwidth and operation mode.";
    assert(errorFlag,msg); % Throws an error if the chosen nbPRB is invalid for the given combination of NDLRB and operation mode
end