Communication Technology

  

 

 

 

OFDM Modulator

 

 

Creating OFDM Modulator

 

    hMod = comm.OFDMModulator;

    hModInfo = info(hMod);

     

    hMod

      Properties:

                   FFTLength: 64   

        NumGuardBandCarriers: [6;5]

                InsertDCNull: false

              PilotInputPort: false

          CyclicPrefixLength: 16   

                   Windowing: false

                  NumSymbols: 1    

         NumTransmitAntennas: 1    

     

    hModInfo

       DataInputSize: [53 1]

          OutputSize: [80 1]

 

FFTLength = NumGuardBandCarriers(1) + DataInputSize +  NumGuardBandCarriers(2) = 6 + 53 + 5 = 64

OutputSize = FFTLength + CyclicPrefixLength = 64 + 16 = 80

 

 

Generating OFDM Symbol Data with Default Setting

 

    hMod = comm.OFDMModulator;

    hModInfo = info(hMod);

     

    rng(0);

    dataIn = complex(randn(hModInfo.DataInputSize),randn(hModInfo.DataInputSize));

    modData = step(hMod,dataIn);

     

    subplot(2,1,1);

    stem(abs(dataIn));xlim([1 length(dataIn)]);title('Input Data');

    subplot(2,1,2);

    stem(abs(modData));xlim([1 length(modData)]); title('Output Data');

 

Generating OFDM Symbol Data with Internal Procedure

    hMod = comm.OFDMModulator;

    hModInfo = info(hMod);

     

    rng(0);

    dataIn = complex(randn(hModInfo.DataInputSize),randn(hModInfo.DataInputSize));

    dataInGuardBand = [zeros(hMod.NumGuardBandCarriers(1),1); ...

                               dataIn; ...

                               zeros(hMod.NumGuardBandCarriers(2),1)];

    dataInGuardBandIfft = ifft(dataInGuardBand);

    CP = dataInGuardBandIfft(length(dataInGuardBandIfft)-(hMod.CyclicPrefixLength)+1: ...

                                       length(dataInGuardBandIfft));

    dataInGuardBandIfftCP = [CP ; dataInGuardBandIfft];

     

    modData = step(hMod,dataIn);

     

    subplot(5,1,1);

    stem(abs(dataIn));xlim([1 length(dataIn)]);title('Input Data');

    subplot(5,1,2);

    stem(abs(dataInGuardBand));xlim([1 length(dataInGuardBand)]);title('Input Data + GuardBand');

    subplot(5,1,3);

    stem(abs(dataInGuardBandIfft ));xlim([1 length(dataInGuardBandIfft)]);title('IFFT(Input Data + GuardBand)');

    subplot(5,1,4);

    stem(abs(dataInGuardBandIfftCP ));xlim([1 length(dataInGuardBandIfftCP)]);title('CP + IFFT(Input Data + GuardBand)');

    subplot(5,1,5);

    stem(abs(modData));xlim([1 length(modData)]); title('Output Data');