%**************************************************************************

%The simulation adopted the model in paper "ML estimation of time and

%frequency offset" written by J.J van de Beek e.t.Programmed by binyue-Liu

%**************************************************************************

close all; clear all;

N=1024;                                     %length of one symbol

L=128;                                      %length of CP

SNR=15;

Symbol_num=6;

Bit_sym=4;                                  %16_QAM

s=randint(1,N*Symbol_num*Bit_sym);

s_map=qammod(2.^(Bit_sym-1:-1:0)*reshape(s,Bit_sym,N*Symbol_num),16);

%Reflecting to the 16_QAM constallation

t=ifft(reshape(s_map,N,Symbol_num))*N;        %OFDM modulation

t_add_CP=[t(N-L+1:N,:);t];                  %Addition with CP

SNR_line=10^(SNR/10);                    

transmit=reshape(t_add_CP,1,(N+L)*Symbol_num);

sigmma=(1^2+3^2)/2/SNR_line;

Noise=(randn(1,(N+L)*Symbol_num)+j*randn(1,(N+L)*Symbol_num))*sqrt(sigmma/2);

recieve=zeros(1,Symbol_num*(N+L));

erro_rate=zeros(1,10);

index=1;

for e=0.02:0.01:0.12;                     %The offset of norminal carrier frequency

    for i=1:Symbol_num;    

        k=1:N+L;

        recieve((i-1)*(N+L)+1:(N+L)*i)=transmit((i-1)*(N+L)+1:(N+L)*i).*exp(j*2*pi*e*k/N);

    end

    r=reshape(recieve+Noise,N+L,Symbol_num);

    r1=reshape(fft(r(L+1:end,:))/N,1,N*Symbol_num);

    Out_symbol=qamdemod(r1,16);

    

    Out_bit=zeros(4,N*Symbol_num);

    for i=1:N*Symbol_num;

      for k=1:Bit_sym

        Out_bit(k,i)=floor(Out_symbol(i)/(2^(Bit_sym-k)));

        if Out_bit(k,i)==1

           Out_symbol(i)=Out_symbol(i)-2^(Bit_sym-k);

        else

        end

      end

    end

    Out_bit=reshape(Out_bit,1,Bit_sym*N*Symbol_num);

erro_rate(index)=length(find(Out_bit~=s))/length(s);

index=index+1;

end

semilogy(0.02:0.01:0.12,erro_rate,'-*')

axis([0.01 0.12 10^(-5) 1])







    

    

    

    

    

    

    

    

    

    

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