trying to reaccunting the subcarriers

Question

itsik 2011-5-18

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/7640-trying-to-reaccunting-the-subcarriers

hello y'all!!! i got this code its a ofdm signal modulate by bpsk does any ones know how do i make the subcarriers 0:52 and not -1:26,1:26 ? i tried to change only the numbers but it make nothing.. thanks alot!!! and this is the code

clear all
nFFTSize =64 ;
% for each symbol bits a1 to a52 are assigned to subcarrier 
% index [-26 to -1 1 to 26] 
subcarrierIndex = [-26:-1 1:26];
nBit = 2500; 
ip = rand(1,nBit) > 0.5; % generating 1's and 0's
nBitPerSymbol = 52;
nSymbol = ceil(nBit/nBitPerSymbol);
% BPSK modulation
% bit0 --> -1
% bit1 --> +1
ipMod = 2*ip - 1; 
ipMod = [ipMod zeros(1,nBitPerSymbol*nSymbol-nBit)];
ipMod = reshape(ipMod,nSymbol,nBitPerSymbol);
figure(1)
plot(ipMod)
st = []; % empty vector
for ii = 1:nSymbol
inputiFFT = zeros(1,nFFTSize);
% assigning bits a1 to a52 to subcarriers [-26 to -1, 1 to 26]
inputiFFT(subcarrierIndex+nFFTSize/2+1) = ipMod(ii,:);
%  shift subcarriers at indices [-26 to -1] to fft input indices [38 to 63]
inputiFFT = fftshift(inputiFFT); 
outputiFFT = ifft(inputiFFT,nFFTSize);
% adding cyclic prefix of 16 samples 
outputiFFT_with_CP = [outputiFFT(49:64) outputiFFT];
st = [st outputiFFT_with_CP]; 
end
close all
fsMHz = 20;
[Pxx,W] = pwelch(st,[],[],4096,20);    
figure(2)
plot([-2048:2047]*fsMHz/4096,10*log10(fftshift(Pxx)));
xlabel('frequency, MHz')
ylabel('power spectral density')
title('Transmit spectrum OFDM (based on 802.11a)');