Hi, I'm developing an OFDM system. In the transmitter I have taken 4 transmission symbols. Then zero padding is done according to IFFT size and to get a real signal after IFFT, I have taken the symmetry of that. The problem is I'm not receiving the same transmitted symbol stream after doing FFT at the receiver (transmission channel is not included yet). Please correct my MATLAB code. clc close all clear all n = 4; n_bits = 2^n; %Number of bits to process M = 4; %Size of the signal constellation m = log2(M); %Number of bits per symbol IFFT_size = 2^6; %Size of overall usable symbol size (without cyclic prefix) num_zeros = (IFFT_size/2)-4; %Number of zeros z_zero =[1;2;3;4;zeros(num_zeros,1)]; %Zero-Padding z_symmetry = flipud(z_zero); %Taking symmetry to get a real signal z_full = [z_zero;0;z_symmetry(1:length(z_symmetry)-1)]; subplot(2,1,1); stem(z_full); z = ifft(z_full); w = fft((z)); subplot(2,1,2); stem(w); Thank You. _____________________________ Posted through www.DSPRelated.com

# IFFT and FFT of a real signal in OFDM

Started by ●December 19, 2013

Reply by ●December 19, 20132013-12-19

>Hi, > >I'm developing an OFDM system. In the transmitter I have taken 4 >transmission symbols. Then zero padding is done according to IFFT sizeand>to get a real signal after IFFT, I have taken the symmetry of that. The >problem is I'm not receiving the same transmitted symbol stream afterdoing>FFT at the receiver (transmission channel is not included yet). Please >correct my MATLAB code. > >clc >close all >clear all > >n = 4; >n_bits = 2^n; %Number of bits to process >M = 4; %Size of the signal constellation >m = log2(M); %Number of bits per symbol >IFFT_size = 2^6; %Size of overall usable symbol size (without cyclic >prefix) > >num_zeros = (IFFT_size/2)-4; %Number of zeros > >z_zero =[1;2;3;4;zeros(num_zeros,1)]; %Zero-Padding >z_symmetry = flipud(z_zero); %Taking symmetry to get a real signal >z_full = [z_zero;0;z_symmetry(1:length(z_symmetry)-1)]; >subplot(2,1,1); >stem(z_full); > >z = ifft(z_full); >w = fft((z)); >subplot(2,1,2); >stem(w); > >Thank You. > > > > >_____________________________ >Posted through www.DSPRelated.com >change the line w = fft((z)) to w = fft(real(z)) -Doug _____________________________ Posted through www.DSPRelated.com

Reply by ●December 19, 20132013-12-19

>>Hi, >> >>I'm developing an OFDM system. In the transmitter I have taken 4 >>transmission symbols. Then zero padding is done according to IFFT size >and >>to get a real signal after IFFT, I have taken the symmetry of that. The >>problem is I'm not receiving the same transmitted symbol stream after >doing >>FFT at the receiver (transmission channel is not included yet). Please >>correct my MATLAB code. >> >>clc >>close all >>clear all >> >>n = 4; >>n_bits = 2^n; %Number of bits to process >>M = 4; %Size of the signal constellation >>m = log2(M); %Number of bits per symbol >>IFFT_size = 2^6; %Size of overall usable symbol size (without cyclic >>prefix) >> >>num_zeros = (IFFT_size/2)-4; %Number of zeros >> >>z_zero =[1;2;3;4;zeros(num_zeros,1)]; %Zero-Padding >>z_symmetry = flipud(z_zero); %Taking symmetry to get a real signal >>z_full = [z_zero;0;z_symmetry(1:length(z_symmetry)-1)]; >>subplot(2,1,1); >>stem(z_full); >> >>z = ifft(z_full); >>w = fft((z)); >>subplot(2,1,2); >>stem(w); >> >>Thank You. >> >> >> >> >>_____________________________ >>Posted through www.DSPRelated.com >> > >change the line > >w = fft((z)) > >to > >w = fft(real(z)) > >-Doug > >_____________________________ >Posted through www.DSPRelated.com >I meant stem(real(w)) _____________________________ Posted through www.DSPRelated.com