Communication Technology

OFDM DeModulator

Creating OFDM DeModulator

hMod = comm.OFDMModulator;

hModInfo = info(hMod);

 

rng(0);

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

modData = step(hMod,dataIn);

 

hDeMod = comm.OFDMDemodulator(hMod);

hDeModInfo = info(hDeMod);

 

hDeMod

Properties:                FFTLength: 64        NumGuardBandCarriers: [6;5]          RemoveDCCarrier: false          PilotOutputPort: false       CyclicPrefixLength: 16                  NumSymbols: 1           NumReceiveAntennas: 1

 

hDeModInfo

InputSize: [80 1]     DataOutputSize: [53 1]

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

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

                = InputSize - CyclicPrefixLength - (NumGuardBandCarriers(1)+NumGuardBandCarriers(2))

                = 80 - 16 - (6 + 5) = 53

Generating Demodulated OFDM Data with Default Setting

hMod = comm.OFDMModulator;

hModInfo = info(hMod);

 

rng(0);

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

modData = step(hMod,dataIn);

 

hDeMod = comm.OFDMDemodulator(hMod);

hDeModInfo = info(hDeMod);

 

deModData = step(hDeMod, modData);

 

subplot(3,1,1);

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

subplot(3,1,2);

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

subplot(3,1,3);

stem(abs(deModData));xlim([1 length(deModData)]); title('Demod Data');

Generating Demod OFDM  Data with Internal Procedure

hMod = comm.OFDMModulator;

hModInfo = info(hMod);

 

rng(0);

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

modData = step(hMod,dataIn);

 

modDataNoCP = modData(length(modData)-hMod.FFTLength+1:length(modData));

modDataNoCPfft = fftshift(fft(modDataNoCP));

modDataNoCPfftNpGB = modDataNoCPfft(hMod.NumGuardBandCarriers(1)+1 : ...

                                    length(modDataNoCPfft) - hMod.NumGuardBandCarriers(2));

 

hDeMod = comm.OFDMDemodulator(hMod);

hDeModInfo = info(hDeMod);

 

deModData = step(hDeMod, modData);

 

subplot(6,1,1);

stem(abs(dataIn));xlim([1 length(dataIn)]);

title('Input Data');

set(gca,'xtick',[1 length(dataIn)]);

subplot(6,1,2);

stem(abs(modData));xlim([1 length(modData)]);

title('Mod Data');

set(gca,'xtick',[1 length(modData)]);

subplot(6,1,3);

stem(abs(modDataNoCP));xlim([1 length(modDataNoCP)]);

title('Mod Data - CP Removed');

set(gca,'xtick',[1 length(modDataNoCP)]);

subplot(6,1,4);

stem(abs(modDataNoCPfft));xlim([1 length(modDataNoCPfft)]);

title('ShiftFft(FFT(Mod Data - CP Removed))');

set(gca,'xtick',[1 length(modDataNoCPfft)]);

subplot(6,1,5);

stem(abs(modDataNoCPfftNpGB));xlim([1 length(modDataNoCPfftNpGB)]);

title('ShiftFft(FFT(Mod Data - CP Removed)) - GuardBand Removed');

set(gca,'xtick',[1 length(modDataNoCPfftNpGB)]);

subplot(6,1,6);

stem(abs(deModData));xlim([1 length(deModData)]);

title('Demod Data');

set(gca,'xtick',[1 length(deModData)]);