ofdm carrier frequency offset estimation code

%Initilization %%%%%%%%%%%%%%%%%%%%

 nBitPerSym = 64;

 nSym =  10^3; 

 nFFT = 64; % fft size
 nDSC = 64; % number of data subcarriers

 samplesPerSymbol = 1;
Ts = 1e-6;    % Sample time of each symbol / bit
samplesPerFrame = nBitPerSym;

carriersQ = (1:nBitPerSym) ;

 % NORMALIZED DOPPLER SHIFT
 ep = [0 .15 .3];

 EbN0dB = [1:20]; % bit to noise ratio

% Input Data Generation

ipBit = rand(1,nBitPerSym*nSym) > 0.5; % random 1's and 0's

 oddData = ipBit(1:2:end);
 evenData = ipBit(2:2:end);
 qpskModulated = sqrt(1/2)*(1i*(2*oddData-1)+(2*evenData-1)); %QPSK Mapping

 for lll= 1:length(ep)

 for iii=EbN0dB,
k1 = 1;
for n1 = 1:nSym/2
ofdm_symbol = zeros(1,nFFT);
% Map modulated data to FFT bins in OFDM symbol
ofdm_symbol(carriersQ) = qpskModulated(k1:k1+nBitPerSym-1);

% Time Signal to transmit

tx_signal = (nFFT/sqrt(nDSC))*ifft(ofdm_symbol,nFFT);

% DOPPLER SHIFT

freqOffset = 0; phaseOffset = 0;

hPFO = comm.PhaseFrequencyOffset('FrequencyOffset', freqOffset, ... 'PhaseOffset', phaseOffset, ... 'SampleRate', samplesPerSymbol/Ts);

rx_signal1l = step(hPFO,tx_signal);

 rx_signal = rx_signal1l.';

%%========================= Carrier Recovery =================

hDelayInstFreq = dsp.Delay;

hMovAve = dsp.DigitalFilter('TransferFunction','FIR (all zeros)', ... 'Numerator', ones(1,100)/100);

hCumSum = dsp.CumulativeSum('Dimension','Channels (running sum)', ... 'FrameBasedProcessing', true);

%% Calculate the frequency shift estimate

P = 2;

currInstFreq = rx_signal.^(2*P);

prevInstFreq = step(hDelayInstFreq, currInstFreq);

freqShiftEst1 = currInstFreq .* conj(prevInstFreq);

% Average over 1 frame

freqShiftEst = mean(freqShiftEst1);

% Moving average over 100 frames

freqShiftEst = step(hMovAve, freqShiftEst);

freqShiftEst = angle(freqShiftEst) / (2*P);

% Convert digital frequency to Hertz

freqShiftEst = freqShiftEst / (2*pi*Ts);

%% Apply frequency correction

freqCorr = repmat(-freqShiftEst*Ts, samplesPerFrame, 1);

% Calculate cumulative phase shift

freqCorr = step(hCumSum, freqCorr);

% Apply frequency shift correction

rxSym = rx_signal .* exp(1i*2*pi*freqCorr);

rxSym = abs(rx_signal) .* exp(1i*freqCorr);

rxSym = rxSym.';

% FFT

 received_ofdm = (sqrt(nDSC)/nFFT)*fft(rxSym.', nFFT);

% Extract data from carriers in OFDM symbol

received_symbolsQ(k1:k1+nBitPerSym-1) = received_ofdm(carriersQ);

k1 = k1 + nBitPerSym;

end

% PERFROM DEMODULATION

yFQ=received_symbolsQ;

%--------------Demodulation-----------------------------

%Threshold Detector

TX = reshape(yFQ.',nBitPerSym*nSym/2,1).';

detected_real = real(TX)>=0;

detected_img = imag(TX)>=0;

estimatedBits=reshape([detected_img;detected_real],1,[]);

% counting the errors

nErrQ1(lll,iii) = size(find(estimatedBits - ipBit),2)/(nSym*nBitPerSym);

end end

% Plotting output data

close all;

figure

semilogy(EbN0dB, nErrQ1(1,:),'r--');

hold on

semilogy(EbN0dB, nErrQ1(2,:),'r*-');

semilogy(EbN0dB, nErrQ1(3,:),'r.-');

axis([1 20 10^-4 1])

grid on

legend('QPSK- CFO Recovery ep=0','QPSK- CFO Recovery ep= 0.15','QPSK- CFO Recovery ep=0.3');

xlabel('Eb/No, dB')

ylabel('Bit Error Rate')

title('Bit error probability curve for QPSK with Frequency estimation and recovery OFDM') =========================================================================== 0 Comments Comment on this Question

Answer 1

[Zeyad Qasem]

Hello, Did you solve this issue ?

Could you please share the solution with us

thnx