Adding cyclic prefix in clipped ofdm

Question

Dipsikha Roy 2021-2-2

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/733898-adding-cyclic-prefix-in-clipped-ofdm

clc

close

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.