% Faculty of Engineering, University of Fukui. 2003/11/11 coded by Sokthai
% Chan (sokthai@msn.com) OFDM signal and its spectrum ( Guard Interval
% insertion )

clear all;

Fd=1;             % symbol rate (1Hz)
Fs=1*Fd;          % number of sample per symbol
M=4;              % kind(range) of symbol (0,1,2,3)

Ndata=1024;       % all transmitted data symbol 
Sdata=64;         % 64 data symbol per frame to ifft
Slen=128;         % 128 length symbol for IFFT 
Nsym=Ndata/Sdata; % number of frame -> Nsym frame
GIlen=144;        % symbol with GI insertion
GI=16;            % guard interval length

% vector initialization
X=zeros(Ndata,1);
Y1=zeros(Ndata,1);
Y2=zeros(Ndata,1);
Y3=zeros(Slen,1);
z0=zeros(Slen,1);
z1=zeros(Ndata/Sdata*Slen,1);
% g=zeros(GIlen,1);
z2=zeros(GIlen*Nsym,1);
z3=zeros(GIlen*Nsym,1);

% random integer generation by M kinds 
X = randint(Ndata, 1, M);

% digital symbol mapped as analog symbol
Y1 = modmap(X, Fd, Fs, 'qask', M);

% covert to complex number
Y2=amodce(Y1,1,'qam');

for j=1:Nsym;

    for i=1:Sdata;
        Y3(i+Slen/2-Sdata/2,1)=Y2(i+(j-1)*Sdata,1);
    end

    z0=ifft(Y3);
    
    for i=1:Slen;
        z1(((j-1)*Slen)+i)=z0(i,1);
    end

    %
    for i=1:Slen;
        g(i+16)=z0(i,1);
    end
    
    for i=1:GI;
        g(i)=z0(i+Slen-GI,1);    
    end

    for i=1:GIlen;
        z2(((j-1)*GIlen)+i)=g(i);
    end
    
end

% graph on time domain
figure(1);
f = linspace(-Sdata,Sdata,length(z1));
plot(f,abs(z1));
   
Y4 = fft(z1);

% if Y4 is under 0.01 Y4=0.001
for j=1:Ndata/Sdata*Slen;
if abs(Y4(j)) < 0.01
    Y4(j)=0.01;
end
end

Y4 = 10*log10(abs(Y4));

% graph on frequency domain
figure(2);
f = linspace(-Sdata,Sdata,length(Y4));
plot(f,Y4);
axis([-Slen/2 Slen/2 -20 20]);