CYCLIC PREFIX FOR ERROR CONTROLLING

 %%%%%%%%%% Cyclic Prefix %%%%%%%%%%

 %%%%%%%%%% SURAJ BASTOLA %%%%%%%%%%

M = 8; % for 8 BPSK

N = 64;% this means we are using 64 point FFT/IFFT

data = randi(M,1,N)-1;

subplot(411);

myplot(stem(data),'Data',3);

X = pskmod(data,M);

figure(2);

subplot(111);

myplot(plot(X,'o'),'8PSK',2);

% IFFT with real result for Baseband 

% for broad band go directly to line 17 from 10 with code x = ifft(X, N);

X1 = X;

X2 = conj(X(N:-1:2));

X1(1) = real(X(1));

X = [X1, imag(X(1)), X2];

x = ifft(X, N*2);

figure(1)

subplot(412);

myplot(plot(1:128,x),'IFFT', 1);

% add circular prefix

delay = 10;

xt = [x(2*N-delay+1:2*N),x];

subplot(413);

myplot(plot(1:(2*N+delay),xt),'CP',2);

hold on

myplot(plot(1+delay:(2*N+delay),x),'OFDM',1);

% remove Cyclic Prefix

r = xt((1+delay):(2*N+delay));

%fft

r2 = fft(r,N*2);

% undo complex number modification

r3 = r2(1:N);

r3(1) = r2(1)+1i*r2(N+1);

data2 = pskdemod(r3,M);

subplot(414);

myplot(stem(data2),'Received',4);

disp([data;data2]);