% 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,1);
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]);
