OFDMA.m

 %This program simulates OFDMA transmission in AWGN channel%
clear all
clc
close  
M = 4;                          %  QPSK signal constellation
no_of_data_points = 64;         %  have 64 data points
block_size = 8;                 %  size of each ofdm block
cp_len = ceil(0.1*block_size);  %  length of cyclic prefix
no_of_ifft_points = block_size; %  8 points for the FFT/IFFT
no_of_fft_points = block_size;
%  Generate 1 x 64 vector of data points phase representations
data_source = randsrc(1, no_of_data_points, 0:M-1);
figure(1)
stem(data_source); grid on; xlabel('Data Points'); ylabel('Transmitted Data Phase Representation')
title('Transmitted Data "O"')
%  Perform QPSK modulation
qpsk_modulated_data = pskmod(data_source, M);
scatterplot(qpsk_modulated_data);title('QPSK Modulated Transmitted Data')
%  Do IFFT on each block
%  Make the serial stream a matrix where each column represents a pre-OFDM
%  block (w/o cyclic prefixing)
%  First: Find out the number of colums that will exist after reshaping
num_cols=length(qpsk_modulated_data)/block_size;
data_matrix = reshape(qpsk_modulated_data, block_size, num_cols);
%  Second: Create empty matix to put the IFFT'd data
cp_start = block_size-cp_len;
cp_end = block_size;
%  Third: Operate columnwise & do CP
for i=1:num_cols
    ifft_data_matrix(:,i) = ifft((data_matrix(:,i)),no_of_ifft_points);
    %   Compute and append Cyclic Prefix
    for j=1:cp_len
       actual_cp(j,i) = ifft_data_matrix(j+cp_start,i);
    end
    %   Append the CP to the existing block to create the actual OFDM block
    ifft_data(:,i) = vertcat(actual_cp(:,i),ifft_data_matrix(:,i));
end
%   Convert to serial stream for transmission
[rows_ifft_data, cols_ifft_data]=size(ifft_data);
len_ofdm_data = rows_ifft_data*cols_ifft_data;
%   Actual OFDM signal to be transmitted
ofdm_signal = reshape(ifft_data, 1, len_ofdm_data);
figure(3)
plot(real(ofdm_signal)); xlabel('Time'); ylabel('Amplitude');
title('OFDMA Signal');grid on;
%   Pass the ofdm signal through the channel
recvd_signal = ofdm_signal;
%   Convert Data back to "parallel" form to perform FFT
recvd_signal_matrix = reshape(recvd_signal,rows_ifft_data, cols_ifft_data);
%   Remove CP
recvd_signal_matrix(1:cp_len,:)=[];
%   Perform FFT
for i=1:cols_ifft_data
    %   FFT
    fft_data_matrix(:,i) = fft(recvd_signal_matrix(:,i),no_of_fft_points);
end
%   Convert to serial stream
recvd_serial_data = reshape(fft_data_matrix, 1,(block_size*num_cols));
%   Demodulate the data
qpsk_demodulated_data = pskdemod(recvd_serial_data,M);
scatterplot(qpsk_modulated_data);title('QPSK Modulated Received Data')
figure(5)
stem(qpsk_demodulated_data,'rx');
grid on;xlabel('Data Points');ylabel('Received Data Phase Representation');title('Received Data "X"')