OFDM

clc
clear all
close all

%INITIATION
no_of_data_bits=64;
M=4;     %NO OF SUBCARRIERS
n=256;   %NO OF BITS TO BE TRANSMITTED AT TRANSMITTER
block_size=16; %OFDM BLOCK FOR CYCLIC PREFIX
cp_len=floor(0.1*block_size);

%TRANSMITTER (TO GENERATE RANDOM DATA SOURCE)
data=randsrc(1,no_of_data_bits,0:M-1);
figure(1),
stem(data);
grid on;
xlabel('Data points');
ylabel('amplitude');
title('original data');

%PERFORM QPSK MODULATION
qpsk_modulated_data=pskmod(data,M);
figure(2),
stem(qpsk_modulated_data);
title('QPSK Modulation');

S2P=reshape(qpsk_modulated_data,no_of_data_bits/M,M);
sub_carrier1=S2P( :,1);
sub_carrier2=S2P( :,2);
sub_carrier3=S2P( :,3);
sub_carrier4=S2P( :,4);
figure(3),subplot(4,1,1),stem(sub_carrier1),title('Sub Carrier 1'),grid on;
subplot(4,1,2),stem(sub_carrier2),title('Sub Carrier 2'),grid on;
subplot(4,1,3),stem(sub_carrier3),title('Sub Carrier 3'),grid on;
subplot(4,1,4),stem(sub_carrier4),title('Sub Carrier 4'),grid on;

%IFFT OF 4 SUBCARRIERS
M=4;     %NO OF SUBCARRIERS
cp_start=block_size-cp_len;
ifft_subcarrier1 = ifft(sub_carrier1);
ifft_subcarrier2 = ifft(sub_carrier2);
ifft_subcarrier3 = ifft(sub_carrier3);
ifft_subcarrier4 = ifft(sub_carrier4);

figure(4),subplot(4,1,1),plot(real(ifft_subcarrier1),'r'),
title('IFFT ON ALL THE SUBCARRIERS')
subplot(4,1,2),plot(real(ifft_subcarrier2),'c')
subplot(4,1,3),plot(real(ifft_subcarrier3),'b')
subplot(4,1,4),plot(real(ifft_subcarrier4),'d')

%ADD CYCLIC PREFIX
for i=1:M
    ifft_subcarrier (:,i) = ifft(S2P(:,i),16);
    for j=1:cp_len
        cyclic_prefix(j,i) = ifft_subcarrier (j+cp_start,i);
end
Append_prefix(:,i) = vertcat(cyclic_prefix(:,i),ifft_subcarrier(:,i));
end
A1=Append_prefix(:,1);
A2=Append_prefix(:,2);
A3=Append_prefix(:,3);
A3=Append_prefix(:,4);

%Appends prefix to each subcarrier
A1=Append_prefix(:,1);
A2=Append_prefix(:,2);
A3=Append_prefix(:,3);
A4=Append_prefix(:,4);

figure(5),subplot(5,1,1),plot(real(A1),'r'),
title('CYCLIC PREFIX ADDED')
subplot(5,1,2),plot(real(ifft_subcarrier2),'c')
subplot(5,1,3),plot(real(ifft_subcarrier3),'b')
subplot(5,1,4),plot(real(ifft_subcarrier4),'d')

figure(6),plot(real(A2),'r'),
title('ORTHOGONALITY'),hold on
plot(real(A2),'c'),hold on
plot(real(A3),'b'),hold on
plot(real(A4),'d'),hold on
grid on;


%CONVERT SERIAL STREAM FOR TRANSMISSION
[row_Append_prefix cols_Append_prefix]=size(Append_prefix);
len_ofdm_data=row_Append_prefix*cols_Append_prefix;

ofdm_signal=reshape(Append_prefix,1,len_ofdm_data);

figure(7),
plot(real(ofdm_signal));
xlabel('TIME');
ylabel('AMPLITUDE');
title('OFDM SIGNAL');
grid on;