clearclc%=====================================================% common settings%=====================================================ifftsize=256;                                  % equals to number of samples in a useful symbol.numcarr=256;                                   % Number of transmission carrierscp=64;                                         % Guard Interval(length of cyclic extension)=25% of ifftsizeguardtype=2;                                   % 1=zeroed signal; 2=cyclic extension; 3=half zero,half cyclicframeguard=ifftsize+cp;                        % Guard Time between successive frames (one symbol period)wordsize=2;SNRindex=1;numsymb=100;%===============信源==================================  N = 512*numsymb;   % bits  source = randint(1,N);  source = reshape(source,numsymb,512);%=====================================================  for SNR=0:2:20    SNR_dB(SNRindex)=SNR;    numofbiterror_idea=0;         %誤比特率初值設為0；    for kk=1:numsymb    t1 = source(kk,:);    t1 = mapping_ofdm_qpsk(t1);    st1 = ifft(t1);    st1 = [st1((length(st1)-cp+1):end) st1];    rt1= st1;    rt1= awgn(rt1,10^(SNR/10),'measured',1234,'linear');    rt1= rt1(cp+1:cp+1+255);    rt1=fft(rt1);       %變換到頻域    p1_idea=rt1;    deofdm1_idea = demapping_ofdm_qpsk(p1_idea);    for jj=1:512           %求誤比特率        if (deofdm1_idea(jj) ~= source(kk,jj))            numofbiterror_idea = numofbiterror_idea+1;        end    end    end   BER1_idea(SNRindex)=numofbiterror_idea/N;   SNRindex=SNRindex+1;  end   semilogy(SNR_dB,BER1_idea,'b-*');   xlabel('SNR')   ylabel('BER')   legend('ideal awgn')   grid on   hold off;