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Adding cyclic prefix in clipped ofdm

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Dipsikha Roy
Dipsikha Roy on 2 Feb 2021
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M =8; %here we initialize the number of constellation point of qam
no_of_data_points = 1024;
Fm=10^6;%Max freq
data_source= abs(round(randn(1,8)));%here we take random normal function
figure(1);
x=1:M;
stem (x*(1/Fm),data_source);
grid minor;
xlabel('time(Microsecond)','Fontsize',14);
ylabel('amplitude','Fontsize',14);
title('Transmitted Data','Fontsize',14);%here we plot that transmitted data
qam_modulated_data = qammod(data_source, M);%here we perform 8bit qam on the random normal function
data = 0:M-1;
scatterplot(qam_modulated_data,1,0,'r*');
grid minor
for k=1:M
text(real(qam_modulated_data(k))-0.4,imag(qam_modulated_data(k))+0.4,num2str(data(k)));
end
axis([-4 4 -2 2])
qm = abs(qam_modulated_data);
figure(3);
stem(qm)
title('MODULATED TRANSMITTED DATA','Fontsize',14);%here we plot those constellation point
y=ifft(qam_modulated_data);
figure(4);
x=1:M;
stem(x*Fm,abs(y));
grid minor;
xlabel('freq(Mhz)');
ylabel('amplitude of ifft');
title('without hermitian ifft','Fontsize',14);
qam_modulated_data1(1:(M/2))=qam_modulated_data(1:(M/2)); %here we introduce another array named qam_modulated_data1 where first four element is first four constellation point
qam_modulated_data1(((M/2)+1):M)=qam_modulated_data(1:(M/2));% in my qam_modulated_data1 array last four point is Hermitian of first four point
figure(5);
x=1:M;
stem (x*Fm,abs(qam_modulated_data1));
grid minor;
xlabel('frequency(MHZ)','Fontsize',14);
ylabel('amplitude','Fontsize',14);
title('Hermitian symmetry','Fontsize',14);
y1=ifft(qam_modulated_data1); %here we apply fast Fourier transform on the data of qam_modulated_data1 array
figure(6);
x=1:M;
stem(x*Fm,abs(y1)); %here we plot that fft result
grid minor;
xlabel('Freq(Mhz)','Fontsize',14);
ylabel('amplitude','Fontsize',14);
title('even frequency suppressed output','Fontsize',14);
y1c=conj(y1);
real_y1=y1.*y1c ;
figure(7);
x=1:M;
stem(x*Fm,real_y1);
grid on;
xlabel('Freq(Mhz)','Fontsize',14);
ylabel('amplitude of real values of ifft','Fontsize',14);
title('real value of ifft','Fontsize',14);
z=fft(y1);
figure(8);
x=1:M;
stem(x*Fm,abs(z)); %here we plot that fft result
grid minor;
xlabel('frequency(MHZ)','Fontsize',14);
ylabel('amplitude','Fontsize',14);
title('fft output','Fontsize',14);
qam_modulated_data2(1:(M/2))=z(1:(M/2));
qam_modulated_data2(((M/2)+1):M)=qam_modulated_data(((M/2)+1):M);
figure(9);
x=1:M;
stem(x*Fm,abs(qam_modulated_data2));
xlabel('frequency(MHZ)','Fontsize',14);
ylabel('amplitude','Fontsize',14);
title('reverse Hermitian symmetry','Fontsize',14);
receieved_data=qamdemod(qam_modulated_data2,M);
figure(10)
x=1:M;
stem(x*(1/Fm),receieved_data); %here we plot that fft result
grid minor;
xlabel('time(Microsec)','Fontsize',14);
ylabel('amplitude','Fontsize',14);
title('received data','Fontsize',14);
Here I have written a piece of code to generate even freq clipped ofdm,now I want to add cp on the ifft output y1 then transmit it through AWGN channel and then at the receiver remove the cp,how to do that,I am absolutely clueless.

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